Talk:Nuclear meltdown

China syndrome

A nuclear meltdown is also colloquially known as the China syndrome after the 1979 film The China Syndrome, which told the unlikely story of molten reactor material burrowing through the earth from California to China.

Note that (1) the movie did not portray that happening, it merely had a character half-jokingly suggest the possibility; (2) it's not unlikely, but impossible for a number of reasons - including the earth's center of gravity not being located near China. Mkweise 20:25 Mar 9, 2003 (UTC)

Minor clarification: The term "china syndrom" was in common use among professionals long before the movie. The movie was considered to be a Hollwood "lets push an agenda" joke by the professionals of the nuclear industry. It liberally mixed technology/terminology/theory of several different nuclear tecnologies in a manner that can be loosely described as "typical Hollywood".67.174.53.196 03:30, 24 July 2006 (UTC)

However, I understood there to be a definite danger of the mass of reactor material melting its way down to the water table - in fact, I thought this was what a meltdown was. Is this really a danger? --Andrew 06:55, Apr 26, 2004 (UTC)

Obviously, the risk to the water table depends on how deep it is in the area around the reactor, as well as how far melted reactor fuel would go. I found a reference on the Web to data from the NRC's Reactor Safety Study (WASH-1400), that indicates that maximum penetration into the earth beneath a melting reactor would be on the order of 10-50 feet, depending on what the reactor was built on top of.

Interestingly, the report makes explicit reference to the meltdown material reaching the water table, and states that the boiling of groundwater would draw more heat from the melt, reducing the depth of penetration. "Since the ground underneath containment is well below the level of the water table, conduction heat transfer at the surface of the melt should be augmented by steam generation and convection."

I can't find any place where you can download the whole report as a PDF, but you can read excepts here: [1]

Para 3 refers to a chemical explosion when molten core and water mix - I believe the usual concern is a _steam_ explosion/Vapour explosion/fci, which is a physical phenomenon (essentially due to very rapid boiling) not chemical. In WASH-1400 this was postulated to lead to rupture of the pressure-vessel and 'alpha-mode' containment failure.

The last paragraph mentions that there have been several catastropic nuclear meltdowns on US nuclear submarines, but this is false. I will assume the article is conjecturing on the reactors of the lost submarines USS Thresher and USS Scorpion. All the radiation surveys and samples have shown that there is only a very small increase in radiation levels around the reactor compartment of the lost ships. While fuel may have melted (and this is debatable), it certainly was not a catastropic meltdown. Additionally, the words catastropic meltdown are probably too strong when discussing the various Russian submarine nuclear accidents (for example, I can find no event where lives were lost when fuel melted on a Russian submarine).--Burzum 05:15, 22 Oct 2004 (UTC)

Error on Fast breeder reactors

The article currently states "Fast breeder reactors are more susceptible to meltdown than other reactor types, due to the larger quantity of fissile material and the higher neutron flux inside the reactor core, which makes it more difficult to control the reaction. In addition, the liquid sodium coolant is highly corrosive and very difficult to manage."

This is outright wrong. Firstly, sodium is highly reactive and flamabble, but not corrosive to steel, zirconium, nor the fuel forms suggested for such a reactor (metallic U-Pu-Zr alloys or some ceramic fuel forms). In particular, sodium's extremely low reactivity with steel is generally considered a large advantage in favour of water cooled reactors. The use of liquid metal rather than pressurised water also means the reactor doesn't need to be pressurised, dramatically lowering the risk of a loss of coolant accident, and also allows it to rely on natural convection for cooling giving a high degree of passive safety. Furthermore, due to the neutronic properties of sodium sodium cooled reactors can be built with highly negative temperature coefficients, causing the chain reaction to cease well bellow temperatures that would damage the reactor.

Secondly, the larger quantity of fissile material is largely irrelevant, most reactors contain enough of it to sustain their reaction for years, and typically the limit of the reactor's energy production is down to other factors. The larger enrichment level might be an issue as it means the fuel has a higher power density, but this has less of an impact than the fuel form. Metallic fuels operate at much lower temperature than ceramic ones due to the greatly increased heat conductivity, as an example. Regardless, it is the power density and enrichment level that is relevant, not teh total quantity of fissile material.

Thirdly, whereas sodium is one of the best developed coolants for fast breeder reactors, it is far from the only one possible. Lead, Lead_Bismuth alloys, Molten salts and Helium have all been suggested (Interestingly, lead is far more corrosive than sodium, yet meltdown is less likely due to the higher boiling temperature ).

Finally, the risk of a nuclear meltdown is much more a matter of design and safety regulations than it is one of reactor type. As an example, the CANDU and RBMK reactors share some features, but because the RBMK has several serious design flaws it is generally very unstable and dangerous, meanwhile the CANDU reactors are among the safest nuclear powerplants ever built. Similarly, liquid metal cooled fast reactors are probably the least likely to undergo a loss of coolant accident ( and consequentially a meltdown ), whereas it is difficult to ensure sufficient cooling under low pressure conditions for gas cooled fast breeders. 213.55.27.154 19:46, 2 March 2007 (UTC)

Chernobyl Accident

Chernobyl wasnt a nuclear meltdown, and accidnet which was essentially impossible due to its core design. (Graphite tubes seperated all the fuel elements, meaning there was insufficent radioactive slag for a chain reaction). I have edited the topic to reflect this.

Also, while there was one partial meltdown of a reactor in a russian sub (K-219), there has not been a complete one, that I have ever noted. Once again I have edited the topic to reflect this fact.

(Comments by User:210.50.61.200)

Could you please provide a reference for these claims? In particular the claim about the Chernobyl accident could really use some support. Certainly the core material did melt, and was found in the basement, so it's not clear in what sense this should be removed from the list of meltdowns. Certainly this contradicts our article on the subject:

"[T]he fourth reactor of the Chernobyl power plant [...] suffered a catastrophic nuclear meltdown that resulted in a series of explosions and fire."

and, later,

"[T]he fuel rods began to melt [...]".

If you have references to cite, that would be great, as we could fix both articles. Until then, I'll leave this article in agreement with Chernobyl accident. --Andrew 09:24, Dec 7, 2004 (UTC)

I have done much research into the subject over the years and from my readings I have understood that the chernobyl accident happened as follows: A section of the core went critical, which caused the tubes to expand and crack. The tubes were made out of zirconium, which when exposed to oxygen forms Hydrogen. This hydrogen then exploded, rubutring all containment. Surely, fuel materials did melt, but this was a byproduct of the accident, and due to the core design, finding critical mass would have been difficult.

http://www.world-nuclear.org/info/chernobyl/inf07.htm

http://www.bellona.no/imaker?id=12663&sub=1

http://www.chernobyl.co.uk/

Pretty much, its a common mistake that Chernobyl was a meltdown, but it was really one very large steam explosion

I've read all those articles, and some of the others linked from Chernobyl accident. None of them say the core didn't melt, but none of them say it did. The following sources do claim a meltdown occurred, although I have no way to judge their reliability (although the second is a PhD thesis at MIT and the third is the Encyclopedia Britannica):

• http://academic.brooklyn.cuny.edu/physics/sobel/Nucphys/acc.html
• http://www-tech.mit.edu/V115/N0/chernobyl.00n.html
• http://www.britannica.com/ebc/article?tocId=9360495

The following source does not claim it was a meltdown, and do list several other meltdowns, suggesting rather strongly that they don't think there was a meltdown there:

• http://www.science.uwaterloo.ca/~cchieh/cact/nuctek/accident.html

Perhaps more convincingly, the following site, which appears authoritative, claims there was a meltdown.

• http://www.chernobyl.info/index.php?userhash=864065&navID=10&lID=2

Specfically, they say

"At temperatures of over 2000°C, the fuel rods melted. The graphite covering of the reactor then ignited. In the ensuing inferno, the radioactive fission products released during the core meltdown were sucked up into the atmosphere."

They also give specific references, which are unfortunately in what appears to be German.

I think I would take it as fairly well shown that the core did in fact melt. Perhaps there is some confusion with respect to definitions - the definition we use here is simply "a meltdown is an accident in which the core melts, partially or completely". This may not be quite a standard definition; perhaps it is necessary, in the usual usage, that the molten mass be critical. If so, perhaps we could find a reference for that definition and clarify this article. --Andrew 04:38, Dec 9, 2004 (UTC)

Incidentally, the following site:

• http://www.usnews.com/usnews/doubleissue/heroes/borovoi.htm

describes scientists chipping a piece off an "elephant's foot" of molten and refrozen fuel in the basement.

"[...]they found the elephant's foot was made of uranium and zirconium from the reactor fuel rods and silicon from sand packed around the reactor vessel. As the reactor core burned at thousands of degrees, molten fuel had apparently eaten through the concrete floor and oozed into the warren of rooms below, where it cooled and hardened. The uranium in this "Chernobyl lava," it turned out, was too dilute to threaten a new nuclear reaction."

and

"In May 1988, they drilled through concrete walls into the reactor pit itself–and found it empty. All of the fuel, it appeared, had either been blown out in the explosion or had oozed into the lower rooms as a dilute lava."

However, it does point out that the lava was too dilute to be critical (this was one of the reasons people ran into a radioactive building to look around). So while the core melted, it seems like no liquid critical mass was formed. But has such an event ever occurred? --Andrew 04:53, Dec 9, 2004 (UTC)

Also incidentally, zirconium cannot produce hydrogen on exposure to oxygen, as it is an element. I think what you mean is that it might produce hydrogen upon exposure to steam, which is entirely plausible, and one of the suggested explanations for the second explosion. Graphite simply burns on exposure to oxygen, and this certainly occurred, so the core was definitely very hot. --Andrew 04:59, Dec 9, 2004 (UTC)

I did mean zirconium + steam = hydrogen, thanks for correcting me. While the core did melt, it was not the actual cause of the accident, and it could be argued that it didn't really add to the problems of accident. I recall reading that the primaryreason that the core did melt was that when the core was covered with lead, sand, boron and other things it caused the heat to be traped inside the core, causing it to raise to the level required for Uranium to melt. Unfortunately I can not find a source for this information. I do agree with the above statement about differnce in definitions. I believe that a 'meltdown' is when the core melting is the entire accident, primarily due to a Loss of Coolant. Therefore, I class Three Mile Island as a meltdown accidnet, while I do not believe Windscale is one, as the fuel only melted due to afire starting in the graphite moderator - despite the fact both cores did melt.

I think of it like this: If your car was stolen, you would say it was stolen. If your car was stolen, and the theif crashed the car, you would say thatt the car was stolen. Its just like this. Chernobyl was caused by a explosion and fire. In the process of the fire, the core did indeed melt...but still, Chernobyl was an explosion.

The core melted. Therefore it was a meltdown. You can't melt a nuclear pile with fire, so let's not pretend it was some kind of sub-critical meltdown. It wasn't. The core went supercritical when the rods were plunged because their tips weren't graphite as they should have been. Not that that design is at all safe in the first place. The meltdown occurred after the explosion, and it's the explosion that caused the most trouble, but it was a meltdown also. This semantic debate has no merit. The meltdown DID add to the problems of the accident; that's why the core is still there, encased in concrete. Arguably this is the only real long-term problem, as the radioactive material that was ejected by the steam rupture is long since gone. Except perhaps for some strontium. But at any rate it's spread too thin to matter. --68.253.253.62 08:07, 6 September 2005 (UTC)

No. In terms of terminology you always call an accident according to the worst effect of that excident. If a fuel tank explodes, you don't call it a fuel leak. Even though massive amounts of fuel will leak into the ground, It's still an explosion.

Same with Chernobyl. Here we had a reactor which went promt supercritical and had a reactivity excursion. This is a huge difference to only supercritical by the way. You can read why in the section about nuclear physics on the wikipedia. Since the reactor went promt supercritical parts of it nearly instantly vaporized as well as several tons of water which nearly instantly vaporized. This caused the reactor to explode. BTW, already before the reactor exploded, the reactor again became sub-critical due to doppler widening. And after the explosion, the core was most definitely VERY subcritical.

The core meltdown did not add in any meaningfull way to the severity of the accident. This wase entirely governed by the explosion. Hance Chernobyl was an explosion. Dio1982 10:08, 26 March 2007 (UTC)

Windscale

In a similar vein, I recollect that Windscale was in fact a graphite fire caused by the build-up of Wigner energy in the graphite lattice. It was not related directly to decay heating levels. It was essentially chemical, but with an 'enhanced heat of combustion' Linuxlad 09:44, 25 Mar 2005 (UTC)

In the Windscale fire, the core certainly got too hot and melted; that's what a meltdown is. But you're right that some of the heat came from Wigner energy; once the pile got hot enough, it began to burn in air as well, releasing more heat. The reactor also remained critical, releasing yet more heat. So the incident was not a loss of coolant incident; in fact the coolant was air, of which there was too much. Perhaps they couldn't turn off the air for fear of the reactor overheating due to nuclear reactions; it's hard to say. But in any case, all this is irrelevant. All a nuclear meltdown is is an incident where the core melts.

I think the reason people are uncomfortable with this definition is that we have an idea that a nuclear meltdown is somehow the worst possible kind of disaster that can happen in a nuclear power plant, with severe long-term results. That's just not the case. What happened at Chernobyl and Windscale was worse than a simple meltdown; what happened at Goania was also worse (much worse than Windscale or Three Mile Island) but it had nothing at all to due with nuclear chain reactions, let alone a meltdown. A nuclear meltdown is a specific kind of accident, with the possibility to be very bad (by melting down to the water table and causing a steam explosion, say). There's a whole spectrum of other possible accidents that have the possibility to be very bad also. Some of them have a meltdown as a probable side effect. --Andrew 19:52, Mar 25, 2005 (UTC)

I'm not too sure you've got all your detail right there (but then the event happened when I was ten, I recollect). But I don't think the pile was critical or that nuclear heating played a significant role. The Wigner energy built up to very high levels because the graphite was normally too cool for the graphite defects to anneal out. The article here is written from the aspect of loss of adequate cooling for the nuclear-decay heat level - this wasn't really that - it was enhanced chemistry.

Of course, the melting is pretty irrelevant and a result of the article having started out with a PWR bias.

I am by no means an expert, but I have done some reading on this particular issue; perhaps we should discuss it at Talk:Windscale fire? Anything we decide there can of course be used to improve this article.

I agree that the melting hardly mattered in the Windscale incident. In general, a meltdown may be only an insignificant part of a real accident, especially if th e reactor is designed to contain it (as the Chernobyl reactor was). The other things that go wrong about the same time are often much worse. But for some reason, perhaps by the China syndrome and the publicity around Three Mile Island, "nuclear meltdown" has a magical weight in people's minds that is not matched by "steam explosion" or "fire", even though those have been the real problems in the Big Accidents. --Andrew 22:17, Mar 25, 2005 (UTC)

numerous clarifications and corrections

I was in grad school when TMI-2 occurred and on the job when Chernobyl-4 burned. I'm expert on BWRs and PWRs but not the older British reactors. I've tried to clarify the difference between reactor vessel and containment structure. Also, TMI was far more of a meltdown than was originally thought - once they removed the melted fuel, they found that the melt had cracked the RV's stainless steel liner but not attacked the base metal (this was unexpected and, so far, unexplained, but meltdowns don't penetrate RVs - Chernobyl's concrete RV failed due to the explosion, not the melt). The RBMKs have since been modified and de-rated (and, hopefully very soon, closed). Simesa 01:40, 26 Jun 2005 (UTC)

WASH-1400

There are still a few LWR-isms in it from a UK perspective, but probably near enough for most readers... Note again that 'meltdown to China' is NOT the worst accident, radiologically. 'Alpha-mode' (fci-induced) or HPME-induced containment failures would be much worse.

NB the melt just wandering down to the water table would be unlikely to be that dangerous. A fairly coherent in-core melt release together with efficient generation of a missile (usually from the top head) is necessary to fail a modern 'large,dry' containment (IIRC).

Later - I have added a stub for WASH-1400, Rasmussen's original 'Reactor Safety Study' for USNRC.

Technical

I added the technical template because the article (especially the Causes section) seems to assume a high degree of familiarity with the material. Perhaps the context template would be more appropriate. Either way, it calls attention to a problem. I am fairly familiar with the basics, but I find myself stopping after every sentence and trying to backtrack and see how it fits in with what's already been said. Example: "Borated water is injected by the emergency systems and thus in the large-break accidents, control rod insertion is not needed to stop the fission reaction." What is "control rod insertion"? It is discussed in the Nuclear reactor article, but if this article is about the failure of the system, it could at least overview the measures that have to fail. Even if it's ABCs to nuclear reactor buffs, there ought to be some explanation for the unwashed masses. On the other hand, I can be lazy in my research, but I don't think excessive clarity can ever be a drawback. icydid 02:05, August 23, 2005 (UTC)

Burzum's Changes

I've significantly updated the leading paragraphs and the causes section. Additionally I am going to have to create a couple of new articles on reactor containment (which is a superset of the containment structure article), loss of pressure control accident, uncontrolled power excursion or reactivity addition accident, and reactivity_(nuclear). Being a person who previously worked as a reactor operator, I may not always realize when certain parts are too technical, so I apologize beforehand. If any of the correct articles exist (or if you want to create them before I do) feel free to do so.--Burzum 07:10, 9 July 2006 (UTC)

Header

I have removed some information that was added to the header about TMI and 'fizzles.' The term fizzle is used for the failure of a nuclear bomb, not any condition of a nuclear reactor. The correct term for an extreme uncontrolled reactivity excursion incident is prompt critical (which is discussed further in the article). Additionally, the information that TMI was only decommissioned due to a coolant leak and that the reactor vessel did not suffer damage is almost certainly false. There are several publicly available images (including this one) that show extensive damage to the core. The claim that the reactor vessel did not fail does not mean that it did not suffer extensive damage and could be reused (such as temperature gradient stresses and pressure stresses). With the fuel assemblies looking like a pile of rubble there was never any doubt that the reactor vessel interior supports for the fuel assemblies were trashed and that irreparable damage to the vessel occurred. Cheers.--Burzum 22:25, 29 November 2006 (UTC)

After the corium was removed, it was found that the stainless steel liner of the reactor vessel had cracked but that the base metal was undeformed (although this was unexpected). Large portions of TMI are extensively and irremediably contaminated due to infiltration into the concrete (which is why some or all plants now seal their concrete, as I saw at a plant I worked at). I didn't add the part about fizzles, just tried to work with it. I'll settle for saying that the TMI RV didn't fail. Simesa 00:31, 30 November 2006 (UTC)

I don't think that the statement about TMI's RV is applicable because the introductory sentence says "nuclear meltdowns are typically characterized by severe damage to the nuclear reactor in which it occurs." TMI certainly isn't an exception since the fuel elements were destroyed, the inner RV fuel element support skirt was destroyed, heat stress damage to the RV occurred, the primary coolant system was contaminated beyond any reasonable design factor, the interior of the containment structure was severely contaminated, the U-tubes in the steam generators were cracked, etc. To say that the reactor did not suffer severe damage just because the reactor vessel didn't crack in half is false. If this doesn't convince you, then realize that the standard nuclear power plant definition of core damage is damage to the core that reduces the full power rating of a reactor or releases fission products to the environment. TMI was reduced to 0% power and suffered extreme core damage. This discussion about the RV doesn't belong in the header (which is an introduction to nuclear meltdowns). Cheers.--Burzum 11:55, 30 November 2006 (UTC)

All of the above is true. However, I'm thinking from a layman reader's point of view, and for many US readers (particularly those about to live near new plants) the first thing that will pop into their heads is "Did this happen at TMI?" (I'll also agree that it was expected that the corium melt through - last I read, why it didn't was still unknown. TMI certainly had no LVHDC.)

Comments from others?

Simesa 16:56, 30 November 2006 (UTC)

I am eventually going to need to revert back so that it is obvious that a nuclear meltdown causes significant damage to the nuclear reactor, not just the reactor vessel. I still hold that your TMI addition is extraneous and should be removed, but I would like to get some consensus here to avert an edit war. I also still hold that the TMI reactor vessel was severely damaged and unusable. As a former reactor operator I can see no way that the significant rearrangement in the core would not have affected brittle fracture pressure limit (BFPL) curves, heatup or cooldown rate limits, or maximum pressure limits. The metal of any reactor vessel is carefully heat treated for a desired strength. Melting fuel elements might not crack it but they will certainly affect this heat treatment. Cheers.--Burzum 21:14, 30 November 2006 (UTC)

I'd still like a statement in the introduction saying that a complete nuclear reactor malfunction not equivalent to a Hiroshima, but to a Chernobyl. That's not clear to people coming to this page, it wasn't clear to me until a discussion with Cadmium. When people think nuclear they think "mushroom cloud" in my back yard, and I used to think that too, and it's not clear from this article at first glance. Sillybilly 01:06, 1 December 2006 (UTC)

I have adjusted the header due to your concerns. Cheers.--Burzum 03:23, 1 December 2006 (UTC)

Nuclear accident versus Reactor accident

I see we've now agreed to go with "reactor accident" after all, so there's no need to belabor the point, but it'd be good for Wikipedia to explain the reasons behind this.

The term "nuclear accident", as can be seen by the somewhat-relevant-but-largely-irrelevant nuclear accident article, is a poorly constructed term with regard to semantics/meaning. Clearly, everything made up of matter (at our level of abstraction) has a nucleus...so the term is immediately suspect and non-descript, with vague implications of high radiation issues. It's basically non-scientific media shorthand for "somethin' nuke-u-lar" that's gone wrong. You won't find it being used (intelligently) in the nuclear profession...it's just too meaningless. The most appropriate shorthand, in the case of nuclear reactors, is the term "reactor accident," with the phrase "nuclear reactor accident" being most complete. "Reactor accident" is also the phrase used by the U.S. Navy's nuclear propulsion program.

As an aside, there's no real way of solving the semantic problems with the term "nuclear accident." Even a cursory review of the "nuclear accident" article will bear this out. It's a term that is best parsed by either expanding it to include other descriptors (e.g., "nuclear weapons accident") or simply eliminating the nearly useless term "nuclear" altogether (e.g., "reactor accident").

If it's of any assistance information-wise, I've served as the Engineer Officer (Chief Engineer) of a nuclear powered attack submarine during Admiral Rickover's era. That's not a badge I wear these days – nor does it matter with respect to the objective or subjective quality of my edits – but it may help with regard to communications here. --24.28.6.209 02:06, 13 November 2007 (UTC)

I'll have to disagree with you on cutting out of the link to nuclear accident. While it is true that industry and the military use more specialized terms, many watchdog groups still use the term 'nuclear accident' and I would argue that this term is fairly well known among the public. In fact if we are discussing strict naming we have to note that the term 'nuclear meltdown,' which is the title of this article, is used nowhere in industry or the military. But since Wikipedia is an encyclopedia for the general public we should have some discussion of these sometimes ambiguous names, like nuclear meltdown and nuclear accident. Cheers.--Burzum 03:54, 13 November 2007 (UTC)

It's easy to confuse something that is "often used" with "well known." There is no knowing what "nuclear accident" means, as it is a poorly constructed term. Using it often doesn't make it any more clear with frequency of usage. Again, we need look no further than Wikipedia's own nuclear accident article, which is something of an accident itself, as it is a hodge-podge of unrelated and ill-formed ideas.

You're quite right about "nuclear meltdown" itself being a media term, rather than being one that's well informed (or informing). But the fact that "watchdog" groups use these terms doesn't make them any more literate.

My position is that we need to deal with these poor language constructs without propogating them any more than is absolutely necessary. The ultimate goal is to inform. The good news is that this is not very difficult once we examine how well we're actually communicating. --24.28.6.209 10:57, 13 November 2007 (UTC)

Meltdown "theories"

For the benefit of User:Power2084 who refuses to participate in a discussion:

A molten core mass may well melt or burn anything below it. However, as it does so, the mass becomes diluted and eventually non-critical. For the mass to melt down much farther than the containment structure, it would need to remain in a critical state, and to do so, it needs to remain in a compact form, kinda like it is in the reactor but without anything to hold it together in such a form. This is exceedingly unlikely; I'm not a scientist but I'm pretty sure the Second law of thermodynamics backs me up here. Saying this could happen "in theory" grossly overstates the case. We could just as well say that the sun, in theory, might not rise tomorrow.

The "China Syndrome" is a proverbial term; no one seriously believes a meltdown will burn through all the way to China, or even through a significant portion of the Earth's crust. A number of editors have called you on this, and the burden is now on you to find a legitimate scientific source for your claims. Simishag (talk) 01:20, 6 March 2008 (UTC)

We should note that at Three Mile Island, the core did not breach the pressure vessel, and at Chernobyl the core only made it to the basement. It is not credible that the core could melt through several miles of the earth's crust. Paul Studier (talk) 02:53, 6 March 2008 (UTC)

Section on fate of reactors without outside power?

Article says: "Although pressurized water reactors are more susceptible to nuclear meltdown in the absence of active safety measures, this is not a universal feature of civilian nuclear reactors." Every time I think about some worldwide disaster making it unlikely nuclear power plants would have any outside power sources for 3-6 months or more, I assume some percentage of them are going to melt down. Given the possibility of big EMPs over the US (or else where like Iran or Pakistan or Israel), small nuclear wars, asteroid attacks, nasty viruses that kill off too many power plant engineers, etc. a) how long can the reactors described above last; b) how long can reactors that don't have these precautions last. I think this would be very informative for general public and media people, plus history channel and scifi writers who might look type in nuclear meltdown on google and end up here, of course! I don't know enough about it except what I learned 30 years ago as an anti-nuke activist, which may be a bit outdated and inaccurate. So reliable info in its own section would be great. Carol Moore 17:42, 25 August 2008 (UTC)Carolmooredc {talk}

From Decay heat at the moment of reactor shutdown, decay heat will be about 6.5% of the previous core power if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1% of the previous core power. It would seem to me that a couple days of cooling would be enough, after which passive cooling would be enough to prevent disaster. Any actual nuclear engineers here? Paul Studier (talk) 05:25, 28 August 2008 (UTC)

It's been awhile for me (although with the recent resurgence I'm looking to get back into the industry, at which time I'd have to stop editing Wikipedia). In the first few seconds after the SCRAM button is pushed, 99.3% of the reaction stops - what's left comes from the 0.7% of "delayed" neutrons (the heat content of the fuel rods still has to be cooled). You then get a logarithmic decrease in power generation over time, reaching "cold shutdown" in just hours. A "Reactor Engineer" would have the decay heat curves you want to consult. A new industry tool is at [2]; look at the very last graphic to see how heat generation occurs over time. We should note that GE says you can walk away from an ESBWR for at least three full days without a meltdown occurring. Simesa (talk) 09:32, 28 August 2008 (UTC)

If the scenario is an EMP pulse that blows out electronics it's anyones guess whether "scram" functions will work properly. As for a scenario that involves the total disappearance of active management, there is a relevant, though not authoritative, discussion on an engineering forum here: "Aftermath: Population Zero" view of unattended nuke plants. In these discussions I don't see anything about the saturation of control rods and moderators, or the long term effects of corrosion on containment structures. Even a properly shut-down reactor may begin to have trouble after a few years or centuries. Aside from the reactor core, the National Geographic documentary apparently asserts that cooling ponds would boil off after a week without outside power to maintain circulation. As for the article, I'm not sure there are enough solid sources on this topic to add anything. ·:· Will Beback ·:· 09:57, 28 August 2008 (UTC)

Where this is relevant and probably sourceable is in regard to Nth-generation power designs that have walk-away capabilities, like some pebble bed designs, etc. with passive safety. ·:· Will Beback ·:· 10:10, 28 August 2008 (UTC)

SCRAM occurs when a system is either grounded or at zero power, so if the system is "blown out" you'll still get a scram. The control rods won't saturate because with the chain reaction stopped there won't be a significant number of neutrons flying around. The actual containment structure is inside the missile shield (several feet of concrete), which shields it from the weather - in any event, with the reactor at atmospheric rather than operating pressure (15 psi vs. 1000 psi BWRs, 2000 psi PWRs) there's much less of a challenge. I'll have to give you that the current generation of plants was not designed to be neglect-tolerant - perhaps SSTAR would be more appropriate for nations with regime instability. Note: "walking away" for a couple of days applies only to the ESBWR, under most (but not one) cases the AP1000, and the PBMR (I haven't seen a claim for the EPR) - in the event of an unusual occurrence, the normal situation is that engineers rush TO the plant. Simesa (talk) 18:27, 28 August 2008 (UTC)

Article title: "meltdown" vs. "core failure"

Due to a reecnt edit,[3] I'm wondering whether the article has the best title. A "meltdown" is a specific mode of failure, and the zirconium-steam reaction is another. A more generic title might be something like "Nuclear reactor core failure". Any thoughts? ·:· Will Beback ·:· 01:08, 28 August 2008 (UTC)

It seems to me that this article covers more than just meltdown. However, Nuclear reactor core failure sounds too dry and technical. Maybe just Nuclear reactor failure.? Paul Studier (talk) 05:20, 28 August 2008 (UTC)

It's a tricky situation. There are even more failure modes than this for a nuclear power plant, some involving the core, others not so much. Take for instance Chernobyl. That was an uncontained power excursion, resulting in a failure of the reactor vessel due to excessive steam pressure, followed by the zirconium-steam reaction and subsequent hydrogen-air explosion. But how the heck do we put that in an article?! It's a compund failure. "Meltdown" is the one mode "everyone" knows about so if they go looking for nuclear reactor failure modes, this is the place they are likely to be finding first.

All in all I think perhaps this article should be made one in a series of articles that fall under the a category of "Nuclear power plant failure modes" or "Nuclear power incidents" or something like that. This requires plenty of work so quite frankly I don't expect this to happen any time soon. --J-Star (talk) 08:43, 28 August 2008 (UTC)

All the nuclear reactor core demages which occur were done by the (cladding) metal-steam reaction. The term meltdown therefore incorrect. The partial melting of the ceramic fuel is done by the hot reaction product of Hydrogen gas and carried with it zirconia (which will solidify as a refractory, ceramic mass). It is true for the tests of severe fuel demages as well.

the relocation of the lava in Chernobyl-4 was done during solidification of the precipitating from gaseous phase zirconia and mixed in ground and melted on the surface fuel pellets. Astolmar (talk) 09:47, 28 August 2008 (UTC)

"The high-temperature oxidation reaction began at the 2.4- to 3.04-m elevation and formed a localized burn front that moved quickly downward as far as the 1.2-m elevation and then steadily upward. The burn front reached the top end caps (3.80m) and ceased 15 min before the end of the test. The oxidation reaction consumed 75% of the total Zircaloy or almost 100% of the Zircaloy in the path of the burn front. The remaining 25% of the Zircaloywas always below or near the bundle water level. The amount of hydrogen generated was 300±30 g, close to the total conversion of the 1.26-g/s makeup coolant flow within the 45-min high-temperature period. The hydrogen flow fluctuated during the 45-min high-temperature period in response to similar fluctuations (10% to 20% relative)in the bundle coolant flow. The peak hydrogen flow was 190 mg/s, which corresponded to an oxidation power of 28 kW." http://www.osti.gov/energycitations/product.biblio.jsp?query_id=2&page=0&osti_id=10188341

FULL-LENGTH HIGH-TEMPERATURE SEVERE FUEL DAMAGE TEST #5 D. D. Lanning et al.

The above clearly states that the Zircaloy burned with a rate the coolant flow allowed. Astolmar (talk) 10:18, 28 August 2008 (UTC)

Astolmar, I have placed a comment on this on your talk page. Linuxlad (talk) 18:18, 29 August 2008 (UTC)

• • Regarding modes of failure, Astolmar appears to be asserting that actual metling of fuel rods never occurs, and that all fule rod failures are really zirconium-steam reactions. I just happened to be reading about the Santa Susana Field Laboratory, and the accidents at its sodium-cooled reactor. That article asserts that fuel rods melted, and obviously the accidents did not involve steam. While the zirconium-steam reaction may be a significant mode of failure for water-cooled reactors, this article isn't limited to those reactors. Perhaps the Z-S matter can be handled in a section of its own? ·:· Will Beback ·:· 21:09, 4 September 2008 (UTC)

The term "core meltdown" was designed to indicate a specific failure of nuclear power plant reactors -- with ceramic fuel and with water as coolant -- which turns out never happens, and at the mean time nobody describes the real process which is a sudden fiery reaction of cladding metal with the steam. It is time to make justice and replace the immaginary process with the real one. Astolmar (talk) 09:09, 8 September 2008 (UTC)

Ah! I'm beginning to see why we are having such problemss! 'Nuclear meltdown' to me is NOT limited to LWRs - it certainly includes 'whole core accidents' due to transient overpower (so that's SL1 and SPERT) - it includes (re)melt due to high decay levels; it also includes single channel events in channelised designs, driven by power-coolant mismatch. Bob aka Linuxlad (talk) 10:14, 8 September 2008 (UTC)

So, can we weed out the incorrect term of "core meltdown" (stating it clearly) and describe the real problematic processes as they play in real accidents? BTW sl1 I found a reference to coolant-core chemical reaction (most likely triggered by overpower accident and agree, decay heat may cause the cladding-coolant reaction first (or only, as in the Paks 2 refueling pool) and after the cladding consumed and there is no cooling could cause local meltingAstolmar (talk) 14:43, 8 September 2008 (UTC)

I've discussed this before in these comments, but a nuclear meltdown is a term used by the public to describe certain types of severe reactor accidents--it is not an engineering term. But since is is a well known term that is cited by media organizations, activist groups, and politicians, it is certainly notable and deserves particular attention. Strictly speaking, this article is about a small subset of possible reactor accidents. The Wikipedia tree is far from complete, but I would envision that this article (meltdown) should be linked from a more general article (reactor accidents) which would itself be linked from the most general article (nuclear accidents). It may also be possible to construct a reactor accident article and simply include the meltdown information in one section if it doesn't grow too long. I would recommend creating the reactor accident article, clarifying the nuclear accident article and moving the reactor accident parts, and linking this article until it could be merged into a subsection (if possible).

By the way, I must also note that I would outright reject using the term "core failure" since it is too close to the term "core damage" that has a specific nuclear engineering meaning. Cheers.--Burzum (talk) 03:22, 9 September 2008 (UTC)

I would suggest to address the damages caused by this "core meltdown" term to the power industry and to the environment as well. Nuclear reactor core damage resulting from accidents would deserv a detailed review and the most important it should make justice about the cladding-coolant interaction. Astolmar (talk) 10:01, 9 September 2008 (UTC)

It sounds like the answer is to add more content, not to change what's already here. Astolmar, et al., how about writing an article under an appropriate title, like "Nuclear fuel cladding failure" or "Zirconium-steam reaction"? ·:· Will Beback ·:· 11:05, 9 September 2008 (UTC)

zirconium-steam

• copied from User talk:Astolmar.

I feel that your latest additions to this article have too much written down the possibility of fuel melt in favour of only the steam-Zircally reaction. My understanding was that a full core melt was still possible and was indeed observed at TMI. Admittedly the physics isn't just a urania melt, since I think there's a U3Ox/ZrOy eutectic which forms and melts out first. But I've been out of this field for nearly a dozen years... Bob aka Linuxlad (talk) 18:28, 27 August 2008 (UTC)

A full meltdown is not possibble and was not observed any meltdown at all. What was observed the end state of an intense zirconium fire in the steam. It carried away a mixture of washed away fuel both at the Chernobyl 4 and TMI 2 accidents which was deposited on the lower elevations forming a (ZR,U)O₂ (relocated core at TMI-2) lava flows at Chernobyl-4.

I'm aware of the misdirecting the investigation toward the so called eutectic - also the limiting the coolant influx in the subsequent investigations and tests; the introduction of the nonsense of steam explosion. I could not idetified the interested in these misrepresentations parties... Aladar Astolmar (talk) 14:25, 2 September 2008 (UTC)

Reference? Bob aka Linuxlad (talk) 17:30, 2 September 2008 (UTC)

I came here to aske the same thing - could you please provide references for your changes to Nuclear meltdown? ·:· Will Beback ·:· 20:11, 2 September 2008 (UTC)

There is one from a list of several, but I insert this here to see (if you follow the link) the difference between the authors description and what is cited as a summary...

"The high-temperature oxidation reaction began at the 2.4- to 3.04-m elevation and formed a localized burn front that moved quickly downward as far as the 1.2-m elevation and then steadily upward. The burn front reached the top end caps (3.80m) and ceased 15 min before the end of the test. The oxidation reaction consumed 75% of the total Zircaloy or almost 100% of the Zircaloy in the path of the burn front. The remaining 25% of the Zircaloywas always below or near the bundle water level. The amount of hydrogen generated was 300±30 g, close to the total conversion of the 1.26-g/s makeup coolant flow within the 45-min high-temperature period. The hydrogen flow fluctuated during the 45-min high-temperature period in response to similar fluctuations (10% to 20% relative)in the bundle coolant flow. The peak hydrogen flow was 190 mg/s, which corresponded to an oxidation power of 28 kW." http://www.osti.gov/energycitations/product.biblio.jsp?query_id=2&page=0&osti_id=10188341 Astolmar (talk) 11:33, 3 September 2008 (UTC)

but this 1993 reference is essentiallly fresh fuel in a low neutron flux. There's essentially no decay heat or nuclear heating. It's hardly surprising the only energy source is from the clad oxidation. Now, what on your understanding happens to a rubble-ised bed of irradiated fuel pellets???

Bob aka Linuxlad (talk) 12:07, 3 September 2008 (UTC)

What did happen to the worked over by the intense fiery reaction of zirconium-steam? Don't forget that this reaction starts at 800 C or so and the decay heat corresponding equilibrium temperature inside the fuel pellets is around 2500 C (way under the melting of ceramic fuel). You can look at Youtube under the tmi and indeed the cited article also shows a less intense but worked over rubble bed. Nothing happens. Stays as it was produced in the churning over by the fire, brocken pieces of fuel pellets. Lose debris field over the hard layer in the TMI-2 reactor. The Hydrogen gas - and most preferably the reflood with water - will keep it cool. Correction: did keep them cool in the TMI-2 accident, INEL SFD ST and the above Canadian full length test. In Chernobyl-4 not much left in a describable volume, it was mixed with all kind of material thrown at it. However the fiery process generated worked over fuel was well identifiable in the lava flows (encased in the zirconia. Hm, where could that come from?!) Astolmar (talk) 12:30, 3 September 2008 (UTC)

I have not yet found a reference or video which says that there was NO urania-melting at TMI - perhaps you can help here.

Even if TMI was mainly rubble-ised that does not gainsay the possibility of large scale melting in large PWRs, which has been used as a limiting case for safety calculations for many years.

Whole-core melt probably happened at SL1 and SPERT IIRC.

Single-channel melt has probably happened at one early UK reactor and in Enrico Fermi.

Single Channel events with fuel melt are the limiting events in many channelised designs.

the Article IS about nuclear melt - unless you argue this is synonomous with the empty set, what do you suggest we change it to!

Bob aka Linuxlad (talk) 14:33, 3 September 2008 (UTC)

I'm puzzled where did you get your convictions about "Whole-core melt probably happened at SL1 and SPERT"? Astolmar (talk) 09:13, 8 September 2008 (UTC)

• It's best to conduct discussions about articles on the article talk pages, so that other concerned editors can participate and so that it all stays together. I'm going to copy this text and request that everyone continue the discussion at talk:Nuclear meltdown#zirconium-steam.
• Done. ·:· Will Beback ·:· 02:15, 4 September 2008 (UTC)

http://www.osti.gov/energycitations/product.biblio.jsp?query_id=1&page=0&osti_id=285489 TMI-2 core bore acquisition summary report EGG-TMI--7385-Rev.1 “As part of the Three Mile Island Unit 2 (TMI-2) Vessel Investigation Project, funded by the Organization for Economic Cooperation and Development, physical, metallurgical, and radiochemical examinations were performed on samples of previously molten material that had relocated to the lower plenum of the TMI-2 reactor during the accident of 28 March 1979. This report presents the results of those examinations and some limited analysis of these results as required for the interpretation of the data. Principal conclusions of the examinations are that the bulk lower head debris is homogeneous and composed primarily of (U,Zr)O2. This molten material reached temperatures greater than 2,600°C and probably reached the lower head as a liquid or slurry at temperatures below the peak temperature. A debris bed was formed, which was composed of particulate debris above a monolithic melt that solidified on the lower head.”

http://www.osti.gov/energycitations/product.biblio.jsp?query_id=1&page=0&osti_id=10140801 Examination of relocated fuel debris adjacent to the lower head of the TMI-2 reactor vessel NUREG/CR—6195 Astolmar (talk) 09:46, 4 September 2008 (UTC)

Reactor Accident Article

In reference to some of the recent discussions above, it has become obvious that the nuclear meltdown article has too narrow a focus to cover all of the issues involved with nuclear reactor accidents. This isn't a problem with this article, but many topics involved with reactor accidents need a more thorough description (for example, coolant-cladding interactions, environmental effects, and what constitutes core damage among others). To resolve this, I propose that we:

• create a reactor accident article to focus on the specific issues involved with reactor accidents,
• narrow the focus on the nuclear meltdown article to the public, press, and activist perception of what a meltdown entails while noting that a 'nuclear meltdown' is not a nuclear engineering term,
• discuss 'very severe' reactor accidents (the focus of the nuclear meltdown article) as well as the less severe accidents, and
• separate out the reactor accident sections from the nuclear accident and nuclear meltdown articles.

This will present a nice hierarchal order which I think will be easier to update, maintain, and expand.--Burzum (talk) 12:17, 9 September 2008 (UTC)

I certainly agree - "nuclear meltdown" is a term that has no definition - not even found in IAEA manuals - and only has a colloquial meaning to refer to a superset of incidents known as core damage incidents that includes - but is not limited to - fuel melt incidents. I would suggest "Nuclear reactor accident" for the title of the article. Katana0182 (talk) 05:46, 22 August 2009 (UTC)

Western vs. Soviet

The article makes comparison between 'western style' reactors vs. 'soviet style'. Is it justifyed other than for propaganda purposes? Should not it compare actual reactor's designs? The article also says that safety was neglected by Soviet designers which is doubtful as any Soviet reactor (including RBMK) has numerous safety systems. It also says that emergency systems in Soviet reactors required operator's actions while the Western reactors equipped with automatic emergency systems, which also is not the case: any Soviet reactor had automatic safety system.--MathFacts (talk) 18:43, 20 August 2009 (UTC)

My friend, apparently you are a tad bit mistaken. The RBMK, in particular, was a disaster waiting to happen prior to Chernobyl, still is a danger, and I say this as an extremely strong supporter of nuclear power. The sources that I've used are the Ignalina NPP Sourcebook, as well as various publications from credible sources that verify that RBMKs are especially dangerous for the reasons that I've described - and even older VVERs (the VVER-440 V230) - are very dangerous.

Safety was neglected by Soviet designers in the RBMK - at least compared to Western designs.

• As for the claim that the ECCS did not automatically initiate on the RBMK, I'll take a look at my sources again. But I was under the impression that there were few if any automatic systems - per se - mainly they were driven by a human-in-the-loop modality for operations - the computer presents reactor state to the operator, the operator decides what operations to perform, and the operator operates the necessary systems, altering the reactor state.
• If emergency cooling was automatically initiated, this would be a good thing. But in the Chernobyl incident, it probably wouldn't have helped. And how robust was that ECCS? Was there only one train of ECCS systems? Or two duplicate ECCS systems, in case one fails? (Western reactors have up to 4 ECCS trains, each of which is capable of handling the maximum feasible accident.)
• The very design of the reactor - light water cooled, graphite moderated - practically screams POSITIVE VOID COEFFICIENT... and very few mitigation systems. If the coolant boils and the reactor thus loses cooling - the reaction SPEEDS UP - drastically!
• Control rods that took 15 seconds to insert? Seems a bit neglectful to me, as Western control rods insert within 1-5 seconds, and fast insertion is what allows the control rods to quickly slow the reactor down. Control rods inserted rapidly also don't get stuck because the fuel is overheating.
• Control rods tipped with graphite. As we all know, graphite is a neutron moderator. Neutron moderators have no business being in control rods. When the control rod at Chernobyl got stuck because of the expanded fuel due to heat, the moderator amplified the nuclear reaction.
• My favorite is the neutronics computer in the RBMK that took 15 minutes to recompute the core's safety AFTER fixed control rod withdrawals were made? This is like lighting a fuse to an explosive, not knowing how long the fuse was for, and relying on a fuse computer that takes 15 minutes to recompute the length of the fuse to see if there's going to be an explosion. Unfortunately, if the explosion takes place 5 minutes after the fuse is lit, then that computer isn't going to be helpful, now is it?
• Where's the containment dome over the RBMK? You build a naturally dangerous reactor but then you don't at least cover it up with some solid steel and prestressed concrete? What if it were to ...explode? Might it eject a large quantity of fission products over the area?

The VVER-440 V230 lacks an emergency core cooling system - it lacks a containment building - and then the inside of the reactor pressure vessel is made of rustable steel. The reactor is of the pressurized water type, so, well, if steel is exposed to water, then it does something called "rust". The last time there was a serious RPV rust incident in the United States (Davis Besse back in 2002) the reactor was shut for several years for repairs. In the VVER, serious rust incidents sound like they happen every day. (And where's that containment building!)

I will return tomorrow and provide citations to back up these assertions.

> As for the claim that the ECCS did not automatically initiate on the RBMK, I'll take a look at my sources again. But I was under the impression that there were few if any automatic systems - per se - mainly they were driven by a human-in-the-loop modality for operations - the computer presents reactor state to the operator, the operator decides what operations to perform, and the operator operates the necessary systems, altering the reactor state.

Completely not true. There were several automatic systems ranging from automatic shutdown to automatic core cooling. The official standard was that there should be several automatic shutdown systems and even if the most powerful of them disabled or failed, others should be able to quickly shutdown the reactor. There was also automatic reactivity control system.

> The very design of the reactor - light water cooled, graphite moderated - practically screams POSITIVE VOID COEFFICIENT... and very few mitigation systems. If the coolant boils and the reactor thus loses cooling - the reaction SPEEDS UP - drastically!

Yes, but positive void coefficient may be considered the flaw of the particular design. It happened only in certain mods of operation (i.e. at low power capacity), it was unknown before the Chernobyl and it was fixed after redesigning the other RBMK-type rectors (i.e. using more enriched Uran etc).

> Control rods that took 15 seconds to insert? Seems a bit neglectful to me, as Western control rods insert within 1-5 seconds, and fast insertion is what allows the control rods to quickly slow the reactor down. Control rods inserted rapidly also don't get stuck because the fuel is overheating.

In the Chernobyl case the fuel overheated not because the control rods moved too slowly, but because of the shutdown system failure: instead of shutting down the reactor, it sped it up. Before the insertion, the reactor had about 500 MW power capacity - a half of its nominal.

> Control rods tipped with graphite. As we all know, graphite is a neutron moderator. Neutron moderators have no business being in control rods. When the control rod at Chernobyl got stuck because of the expanded fuel due to heat, the moderator amplified the nuclear reaction.

Yes. Is this because the reactor was made by Soviet untermenshen? By the way the graphite tips are always in the reactor. When the rods inserted, the graphite moves from the middle of the core to the bottom. Usually the neutron field is greather in the middle that's why moving graphite tips to the bottom slows the reaction. But in the case the reactor is xenon-poishioned, the field is greather in the bottom and in the top, but weaker in the middle. That's why in the Chernobyl case moving the tips from middle to the bottom sped up the reaction.

> My favorite is the neutronics computer in the RBMK that took 15 minutes to recompute the core's safety AFTER fixed control rod withdrawals were made? This is like lighting a fuse to an explosive, not knowing how long the fuse was for, and relying on a fuse computer that takes 15 minutes to recompute the length of the fuse to see if there's going to be an explosion.

First time hear about this. Operators in fact did not rely on computer in controlling the reactor.

Bottom line: please compare the reactor's designs using reliable sources, not Soviet barbarism vs. Western culture etc.

--MathFacts (talk) 09:39, 21 August 2009 (UTC)
This is one of the references I worked off of. I'll be back for more.
http://www.insc.anl.gov/neisb/neisb4/NEISB_1.1.html
I'm not talking about just Chernobyl either. I'm talking about the entire design - comparing the generally standard safety features on Western LWRs with the generally standard safety features on the Soviet reactors. This has nothing to do with Soviet "barbarism" or nationalism, it has everything to do with what the Soviets designed, and what the West designed in designing their reactors. If the US built a RBMK and put graphite tips on its control rods, or built the reactor without a containment building, I would be making the same criticism that I did but about the US. Designs are designs, the only thing that matters is the merits of them, not which nation made them. For example, the Soviet Union pointed out during the early Cold War that the US had a severe problem with racism. Should I, as an American, claim that the US' once severe problem with racism was an illusion created by Soviet propagandists motivated by anti-Americanism rather than a reality in daily life at least in certain parts of the country? ? No, I shouldn't. Instead I should fix the problem. Western reactors are designed differently - for example, with containment buildings. I know that these days new Russian reactors are pretty much just as safe as new Western reactors. But the point is, that previous designs weren't as safe as Western reactors, and, in fact, had markedly questionable designs. Katana0182 (talk) 14:46, 21 August 2009 (UTC)

First of all, do you expect neutrality from US government source? It's natural that they praise their own reactors. Besides this, your source says that Soviet reactors employ the same principles of 'safety in depth' as Westen ones with one exception - the containment building not implemented. This is quite different from what you wrote in this article. Note also that the confinement was not implemented in RBMK due to its large dimentions, and VVER has the confinement. It should be noted that anyway confinement may help only in the case of a small pipe rapture during a short time and in the Chernobyl case it would not help at all.--MathFacts (talk) 17:02, 21 August 2009 (UTC)

I understand your argument. However, I have found the source where I worked from: MIT OpenCourseWare Nuclear Power Plant Dynamics and Control
Pages 2-3 have an interesting summary regarding "over-moderation", the key design flaw in the RBMK design. Pages 8-9, regarding both design and operation flaws in the RBMK, and the causes of the Chernobyl accident, in particular. It's worth a look. The person who wrote this, John Bernard, is a professor at MIT (which is the best science/engineering university in the US, along with Caltech). It's hosted on a Chinese website.

From the publication, page 9, "Causes of the Chernobyl Accident" (emphasis in original):

1. Flawed Design
   1. Positive power coefficient
   2. Lack of containment
   3. Little or no use of automatic systems to prevent incorrect operator actions such as withdrawing the (...control rods...) too far.
   4. Slow response of shutdown system
   5. Possibility of excessive withdrawal of the control blades
2. Flawed Procedures
   1. Conducting a research test on a commercial reactor
   2. Lack of procedure for the test
   3. Reactor was kept operating while test was performed
3. Flawed Training
   1. Emphasis on keeping reactor in operation rather than safety
   2. Lack of understanding of reactor physics.
4. Flawed Operations
   1. Operators bypassed systems that interfered with their test. 10 major errors.

On the previous page, page 8. "Chernobyl Design Features" emphasis in original:
"Several design features of the Chernobyl Reactor stand out as being distinct from reactors of U.S., Japanese, Canadian, or European design. These are:"

• Core size - the huge size of the core makes it difficult to control. Each subregion of the core can be a critical reactor functioning independently of the rest of the core
• Positive power coefficient - graphite fully moderates neutrons; as power increases, moderation increases. Hence a positive feedback loop around neutronic and thermal power develops, that can destabilize the reactor, and this effect is only present at power levels of 20% or less. This was the fundamental cause of the Chernobyl accident.
• Containment system - the Chernobyl reactor had a containment around its primary piping and steam producing components. The core itself was NOT (emphasis in original) within a containment.
• Graphite temperature - The graphite temperature is maintained several hundred ^oC higher than recommended by Western authorities.
• Shutdown system - It takes 20 seconds to shutdown a Chernobyl-type reactor under emergency conditions. Contrast this with a fraction of a second for U.S. reactors.
  

Katana0182 (talk) 23:19, 21 August 2009 (UTC)

What is it? Theses of a conference? Here [4] I found neither author nor year information. Only a scan of a list seemingly by typewriter. The theses look completely ignorant. For example:

• Another factor was that the reactor was deliberately operated in such a way as to render the temperature coefficient positive

Yes, the reactor crew were probably suicide bombers ;-) Dyatlov, the chief of the shift at Chernobyl at the time of catastrophe, says the Nuclear Safety Division of their plant measured the thermal coefficient and reported it to be negative. He says their mistake was that they measured it at full capacity while at lower capacity modes it becomes positive. Nobody knew about that.

• Little or no use of automatic systems to prevent incorrect operator actions such as withdrawing the (...control rods...) too far.

The rods were not withdrawn 'too far'. Their positions were as usual, but is is true that too many rods were withdrawn.

• Slow response of shutdown system

Dyatlov says they pressed shutdown system to routinely switch off the reactor, not bcause of emergency.

• Conducting a research test on a commercial reactor

They did not conduct a research test.

• Lack of procedure for the test

Complete bullshit. They had a programme. Dyatlov was sentenced for that they implemented the programme incorrectly (i.e. at lower power capacity regime than was planned).

• Emphasis on keeping reactor in operation rather than safety

Again complete bullshit. What does the author mean by this? The very test they performed was done for improvement of safety in an emergency situation. Anyway, there is no reason why these flaws should be attributed to the whole Soviet system or Russian menthality rather than local circumstances. The section compares reactor designs, not training or industrial culture advantages that the West has over the East.--MathFacts (talk) 00:16, 22 August 2009 (UTC)

This is from a graduate level class on nuclear reactor control engineering, specifically this course at MIT: http://ocw.mit.edu/OcwWeb/Nuclear-Engineering/22-921January--IAP--2006/CourseHome/index.htm The PDF is in the reading materials. They're the lecture notes of the professor of the class, in essence. But enough - why don't you go ahead and rewrite the Soviet section of the article to explain the Russian/former Soviet approach to prevention, suppression, and mitigation of core damage incidents in the major Russian and former Soviet reactor types. I'm out of my depth here, so, please, go ahead. Katana0182 (talk) 05:39, 22 August 2009 (UTC)

Bias

This article is clearly biased toward the nuclear industry. I'm not a physicist, but even examining the italics used in the article, it is apparent of the slant. This article must be edited to reflect a neutral point of view. The tone of the article is reassuring (that is, it is worded in a way that suggests readers need not be afraid of nuclear power). That is not appropriate for an encyclopedia article. —Preceding unsigned comment added by 69.22.251.105 (talk) 23:39, 1 September 2009 (UTC)

If you can show a credible, unbiased source that opposes what is written in the article so far (and no, anti-nuclear NGO's do not count unless they in turn reference someone/something credible) then I suggest you bring that into the discussion. But just saying something along the lines of "In my admittedly uninformed opinion, I don't think the article is alarmist enough" will not bring about any edits at all. --J-Star (talk) 00:47, 2 September 2009 (UTC)

Asking us to be alarmist when there really is no cause for alarm - just a complex system to be understood - isn't fair. I'd advise you to get in there and start to digest the science and engineering going into reactor design - there's a lot of stuff out there on the Internet that can help you learn more. The best solution to fear is understanding what you're afraid of, and learning whether or not that fear is reasonable. If that fear is reasonable, then you can keep it and say justly that it moves you to action. If it isn't, then perhaps you can re-evaluate whether it's necessary or not. I'd encourage you to do so. Perhaps you've made some mistaken assumptions. Perhaps I have.

One great way to get a better understanding of operational transients, derangements, and limiting faults in LWRs is to use any of the LWR simulation software out there. For example, somebody wrote a program called BWR which simulates BWR operations and transients at a reasonable technical level, and has a heck of a manual that simply breaks down all of the concepts of the BWR for you. Also, there are some great software packages like PCTRAN (very capable demo versions with no 30 day time limit) that allow you to simulate pretty much any operational transient in any Western nuclear reactor, somewhat graphically. Perhaps best likened to a highly technical flight simulation, but still fun, if you're that type of person. These can help you to gain an understanding of how nuclear reactors are designed, and form a reasonable technical basis for understanding how they work and why they work, and what happens if and when they don't work.

I'm perfectly willing to criticize where criticism is due. For example, the byzantine/cascading failure part of the article was written by me, as this at least was a threat to reactors prior to operators really going beyond the book and developing true professional understanding of reactor operations through INPO and the enhancement of telemetry and control pathways within the reactor building. If you look above this entry, I had a discussion at a reasonable technical level with someone who thought former Soviet reactors were safe. He had one opinion, I had another (that at least the RBMK was an accident waiting to happen, especially prior to the Chernobyl incident - where the accident stopped waiting to happen and actually HAPPENED - though the post-Chernobyl modifications have made the type safer, but not - by any stretch of the word - 'safe'), we both agreed to disagree, and I took out the questioned assertions.

If you want us to be afraid of nuclear power, you have to provide some reasonable basis for us to base our fear on, rather than a Jane Fonda movie, a black and white picture of Three Mile Island, and The Bomb. I'd encourage you to come back with that evidence on a reasonable technical level and provide it so that we can discuss this further. Katana0182 (talk) 04:59, 3 September 2009 (UTC)

I agree that the article is biased but that's not my main concern. The prose, writing style and flow are lousy. Vast portions of the article are unsourced. The overall level of detail is way too much for this article. The lead is far too long and gets into way too much detail about East vs West, this type of reactor vs that, etc. It's sufficient to say in the lead that a meltdown is a serious problem, which is what I attempted to do by removing those tags. Your rewrite is an obvious attempt to obfuscate this. Simishag (talk) 22:36, 4 September 2009 (UTC)

How serious? Why is it serious? Serious to whom? "Serious" is what we call "weasel words", or what I might call "value laden language"; it doesn't convey anything except inspire fear, uncertainty, and doubt, unfortunately. For example, would you call a 'meltdown' in a MSR a serious event? (No, it's a necessary occurrence - as MSR stands for Molten Salt Reactor - it's designed to operate when the salt is molten.) Would you call the use of coal in the United States, for example, a serious event? No, you would call it routine and normal, a phenomenon that's gone on for several hundred years. Unfortunately, that routine event causes 24,000 routine deaths and 40,000 routine heart attacks per year, due to air pollution. Serious is in the eye of the beholder.

Introducing facts that show how serious an "serious event" is not obsfucation. It is improving Wikipedia. Peace out.Katana0182 (talk) 00:39, 5 September 2009 (UTC)

To avoid the appearance of impropriety, I've reverted the page prior to my edits of last night. However, I would like the quantification of very serious to be worked on. Thanks. Katana0182 (talk) 02:11, 5 September 2009 (UTC)

The quantification is expressed in the first sentence of the article: "from Level 4 to Level 7 of the INES". Those 4 levels are defined as "accident" levels and include terms like "major", "serious" and "consequences". The use of "very serious" later in the paragraph is used to explain why it is serious, not to sway people into thinking it is serious. The term "meltdown" may be slang but it certainly has a long history in the industry and literature. It refers specifically to the deformation (melting) of solid fuel elements. No one says that a PWR or BWR uses "molten ice". All the facts do not need to go into the lead. There is plenty of room in this article for a discussion of historical trends of reactor operation, safety and accidents without overwhelming the reader with tangential information. Simishag (talk) 06:01, 5 September 2009 (UTC)

Ok, I'm sorry, I should have assumed good faith when you edited that. It's wrong that I didn't. Apologies - this is a controversial and complex topic, and someone actually here to improve the article in general would be good. I was thinking you were someone drawn here by the controversy trying to support one point of view or another. Once again, I apologize. Katana0182 (talk) 08:21, 5 September 2009 (UTC)

Pardon the lack of Wiki etiquette, but may I suggest an editor consider the NPOV implications of this passage in the opening paragraph: "Then Commissioner (and now Chairman) of the USNRC Gregory Jackzo, well known for his anti-nuclear regulatory stance, was forced to admit in a 2006 speech that "(the alpha-mode failure) is not physically reasonable and therefore does not require concern on the part of a regulator"[2]." I would suggest an editor examine the entire speech the quote is taken from and determine if the quote is taken out of context or properly introduced. —Preceding unsigned comment added by 148.184.174.62 (talk) 19:47, 14 September 2009 (UTC)

In light of reflection, I'm going to temporarily remove the Jackzo quote to ensure that the topic is presented in a neutral fashion. Katana0182 (talk) 05:15, 25 September 2009 (UTC)

Another example of this in the opening:

Due to the high level of safety of Western reactors, both partial meltdowns, though dramatic incidents, did not lead to any deaths or serious injuries. In fact, no deaths or serious injuries have ever been caused by radiation in or by a Western civil nuclear power plant.

216.188.252.240 (talk) 11:38, 26 October 2010 (UTC)

Wrong Units

In the paragraph that reads:

By design, the geometry and composition of the reactor core do not permit the extraordinary conditions necessary for explosively prompt criticality. However, conditions that can cause a meltdown can also cause a steam explosion, which can cause the core to be thrown over a wide area if the reactor is not within a containment building. All Western nuclear reactors are within containment buildings. Each containment building consists of 1.2 to 2.4 meters of steel-reinforced, pre-stressed, airtight concrete, capable of withstanding tornadoes of OF6 scale (320+ mph winds) and seismic accelerations of at least 2 m/s.

the final 2 m/s is wrong. Either replace acceleration with speed or replace m/s with m/s^2. —Preceding unsigned comment added by 24.78.96.84 (talk) 05:45, 28 October 2009 (UTC)

Repetition of Description of Western Reactor Containment Structure

When reading through this article, I noticed that the exact phrase '1.2 to 2.4 metres (3.9 to 7.9 ft) of pre-stressed, steel-reinforced, air-tight concrete' occurs at least four times throughout this article, and a slightly different permutation of the phrase occurs in at least one other place. This doesn't serve to give any new information, it just gets repetitive and is a blatant copy/paste from somewhere else in the article, or possibly from an outside source. I suggest that the article be rewritten to remove this repetition. Arathald (talk) 06:40, 3 June 2010 (UTC)

pre-stressed, steel-reinforced, air-tight concrete between 1.2 to 2.4 metres (3.9 to 7.9 ft) thick,

this line apears way to often. could someone plaes shorten this by just saying the containment wall?

it's enugh to just once mention that this wal is pre-stressed, steel-reinforced, air-tight concrete between 1.2 to 2.4 metres (3.9 to 7.9 ft) thick.

makes the article bad to read.

greats an anonymosus idiot —Preceding unsigned comment added by 131.234.240.105 (talk) 23:37, 7 June 2010 (UTC)

WP:SOFIXIT. There's nothing wrong with this article that a few hours with the editorial Weed Whacker can't fix. My goodness, whoever wrote this loves to talk and doesn't have a footnote to save his soul. First we boil this down to the nubbin, then we can build it up again if more detail is necessary. We don't need to know that the Binford Model 6100 reactor had the frammis valve on the left side of the dingus hatch, but the later MOdel 6100a had dual redundant frammis valves and power seats. --Wtshymanski (talk) 16:02, 18 November 2010 (UTC)

First paragraph. Nuclear accident in Missouri?

5000 dead destruction of the city?

I think this is a wrape. 94.196.91.160 (talk) 18:42, 20 January 2011 (UTC)

Obviously vandalism, I reverted it. Paul Studier (talk) 18:54, 20 January 2011 (UTC)

Japanese nuclear reactor meltdown

The Japanese nuclear reactor that was recently hit by a tsunami is beginning to melt down. Crazymonkey1123 (Jacob) ^(Shout!) 21:50, 11 March 2011 (UTC)

Citation? --Wtshymanski (talk) 22:03, 11 March 2011 (UTC)

Well, nobody is saying it has melted down, but this story says that the Fukushima plant is shut down along with 5 other reactors, and appears to be in distress. The LA Times Web site doesn't say if it's Fukushima I Nuclear Power Plant or Fukushima II Nuclear Power Plant, but says it's 40 years old, which would make it F 1. --Wtshymanski (talk) 22:13, 11 March 2011 (UTC) --Wtshymanski (talk) 22:13, 11 March 2011 (UTC)

Watch CNN. The reactor is emitting 1000 times more radiation than normal. It is melting down. RUN!!! Crazymonkey1123 (Jacob) ^(Shout!) 22:45, 11 March 2011 (UTC)

It's not melting down. Fires have started because, well, it was hit with a bloody tsunami. But those are gas pipelines and open fuel sources. The reactor itself is untouched. The "radiation" is from ventilation shafts being closed/flooded and the "1000X", even if it were true, is 1000 times the pitiful almost non-existent amount of radiation released to the outside. Which is still less than an X-Ray and, if true, won't reach anywhere to the surrounding areas.

Modern day reactors can't physically meltdown anymore. In fact you can't even force them to meltdown, the safety systems are physical and not electronically enacted. In modern nuclear power plants it is quite literally impossible to cause a meltdown unless you forcibly remove the core of the plant from the building. Take your typical American ignorance elsewhere. 203.59.21.45 (talk) 03:00, 12 March 2011 (UTC) Sutter Cane

It's not melting down. Modern Nuclear reactors cannot melt down, it is physically impossible. Stop editing that into the article. --46.64.3.199 (talk) 09:46, 12 March 2011 (UTC)

Why can't it melt down? Once the cooling systems have failed, as is currently the case at Fukushima, the uranium will overheat and melt. Or am I missing something? Ok, the statement of an official meltdown, as was previously stated in a respected german magazine, has now apparently been retracted. MrOceanFrog (talk) 12:01, 12 March 2011 (UTC)

Oh. Didn't I tell all of you that the reactor was gonna melt down. Crazymonkey1123 (Jacob) ^(Shout!) 21:34, 12 March 2011 (UTC)

To 203.59.21.45: it isn't a "modern day reactor". It was built and designed in the 1960s, and opened in 1971. It's among the oldest nuclear reactors in operation. It's certainly possible for the fuel to melt. However, like with Three Mile Island, that does not necessarily mean there would be a large release of radiation. In any case, speculation is pointless. Let's just stick with what is reported by reliable sources.   Will Beback  talk  22:12, 12 March 2011 (UTC)

I think the following section can have the word speculative removed now.

Another speculative scenario sees a buildup of hydrogen within the containment. If hydrogen were allowed to build up within the containment, it could lead to a deflagration event. The numerous catalytic hydrogen recombiners located within the reactor core and containment will prevent this from occurring; —Preceding unsigned comment added by 110.32.8.12 (talk) 03:56, 13 March 2011 (UTC)

I am considering adding a mention of the Japanese plant to the list of meltdowns, but there's been some edit-warring on this issue, so I felt like I should propose it here. First, I emphatically think that the Fukushima Daiichi plant should not be listed without qualification; it is far from established that there has been a meltdown. I read the statement that they are "assuming the possibility of a meltdown" as much more of a "we are behaving as if there may have been a meltdown" (in a better-safe-than-sorry way) than a "we think there's been a meltdown." However, at the same time, it definitely seems to me like an omission to not talk about it at all; it's likely that people are coming to this page as a result of the news stories out of Japan (just look at the edit history: ~40 edits in the last 12 hours, as opposed to 50 between Oct 19 and Mar 11), and it seems like we should at least acknowledge that what's going on carries a strong possibility of a meltdown.

I therefore propose adding the following to the list of meltdowns: "In the aftermath of the 2011 Sendai earthquake and tsunami, the Japanese Fukushima Daiichi nuclear plant has been under threat of a meltdown. While there have been no confirmations either way, Japan's Chief Cabinet Secretary has said that they are taking actions based on the assumption that a partial meltdown has occurred." and I'll stick in a citation.

I'll also stick in a current event tag like can be found on the page for the plant itself. Any objections? EvanED (talk) 05:21, 13 March 2011 (UTC)

That seems like a reasonable compromise. Please take responsibility for keeping the text up to date. Presumably it will become obsolete one way or another very quickly.   Will Beback  talk  12:51, 13 March 2011 (UTC)

NHK World (English) said "Japan's first melt-down has occurred" Print it. —Preceding unsigned comment added by 128.32.166.163 (talk) 01:28, 13 March 2011 (UTC)

Well when cesium and iodine are found in the air then the rods were exposed and a partial meltdown had to occur. Everyone knows that. A partial meltdown is a meltdown. You cannot be partially pregnant either. LOL —Preceding unsigned comment added by 128.32.166.163 (talk) 01:15, 13 March 2011 (UTC)

It is being reported as a meltdown:

http://e.nikkei.com/e/fr/tnks/Nni20110312D12JFF03.htm — Preceding unsigned comment added by ROTORHEAD77 (talk • contribs) 19:57, 12 March 2011 (UTC)

Wikipedia is not intended to give partial and not proofable informations. And above all is not intended to be a gossip-breaking news broadcast channel. So I propose to completely remove for now referers to Japan's events, in order to not fall into POV or excess of RB. There will be time to write about it..if needed. 78.15.0.229 (talk) 12:00, 14 March 2011 (UTC)

Partial meltdown

Many news pieces are using the term "partial meltdown" without defining what they mean by partial meltdown. Came here to see if I could find out what that means, since I thought meldown is meltdown. That there is no "partial" about the phenomena.

Anyhow, perhaps the issue could be addressed?

--sparkit^TALK 15:49, 13 March 2011 (UTC)

Even the Wikipedia article is using the term. 2011 Sendai earthquake and tsunami

--sparkit^TALK 16:27, 13 March 2011 (UTC)

It seems "partial meltdown" is a weasel term used by politicians. Should the 2011 Japan event be listed in the "Meltdowns that have occurred" section? 71.79.30.110 (talk) 16:58, 13 March 2011 (UTC)

The focus - always - needs to be on communicating meaningful information. "Meltdown" is something of a made-up word somewhat designed for emotional effect rather than informational effect, so arriving on a complete consensus on what it means may be challenging. Having said that, the term has been around in reference to nuclear reactors since 1956. What it can/should be taken to mean (IMHO) is that the reactor core has...melted...down: as in pooled at the bottom of the reactor vessel. Localized core melts are not meltdowns. Claiming otherwise is like saying that an ice cube that has melted only somewhat has "melted down." It's the overreaching of the term that meets with natural and appropriate resistance, as it's clearly just being used in a case like that for anti-nuclear harangue rather than communicating reality. "Partial core melt" is a term that the NY Times has used, and that's both technically accurate and informative. --70.112.150.168 (talk) 17:10, 13 March 2011 (UTC)

Interesting is that the Three_Mile_Island_accident is described as a partial meltdown, yet it links to this page and is also in the list of "Meltdowns that have occurred." It can't be both ways. Three Mile Island should be removed, or the current event should be added. It seems clear that events described as partial meltdowns are indeed meltdowns. 71.79.30.110 (talk) 18:30, 13 March 2011 (UTC)

The NYT use of the term "partial core melt" was also in reference to TMI, and is technically the most accurate description. Chernobyl? Now *that* was a meltdown. There's no need for personal judgements on this...either the core has "melted down"...or it has partially melted. This is pretty straightforward unless one is pushing an agenda, as it just isn't that difficult to sort out. --70.112.150.168 (talk) 18:41, 13 March 2011 (UTC)

P.S. What would fix all the multiple labeling problems would be to revisit the name of the article itself, which - to comply with general nomenclature - would be most accurately retitled "Nuclear Reactor Accident" (alternative, also technically correct: "Reactor Accident") with "Meltdown" being a subsection of the article. --70.112.150.168 (talk) 18:58, 13 March 2011 (UTC)

FWIW... From the Nuclear Regulatory Commission "Core melt accident = An event or sequence of events that result in the melting of part of the fuel in the reactor core." (http://www.nrc.gov/reading-rm/basic-ref/glossary/core-melt-accident.html). "Meltdown" isn't on their glossary list. (http://www.nrc.gov/reading-rm/basic-ref/glossary.html) --sparkit^TALK 20:49, 13 March 2011 (UTC)

Nevermind. The lead talks about the fact that the regulatory agencies haven't defined the term

Maybe this article needs to renamed "Core melt accident," that would clear up some confusion since it would cover both full and partial meltdown. "Nuclear meltdown" would redirect to it and discussion of the common term "meltdown" could be added. --sparkit^TALK 21:02, 13 March 2011 (UTC)

The goalpost is moving I see on Wikipedia's Meltdown page. Of course the Pro-nuke Lobby is in here redefining a meltdown. Boys and girls if TMI is a meltdown then so are these in Japan -- there are multiple underway now. There is no way to release Cesium or Iodine radioactivity unless the nuclear core was exposed and began to disintegrate. So lets all be adults here and call a spade a spade. No sense in trying to cover up fissile material releases. You do not want to be distorting the truth. 4 nukes are loose right now anyway. So it will just be flat our embarrassing to watch any more posturing. This is an encyclopedia and not a propaganda post. Go to the Nuclear Lobbyist website to redefine a meltdown. Thanks for understanding that the public wants accurate information on Wikipedia. —Preceding unsigned comment added by 75.52.242.209 (talk) 21:57, 13 March 2011 (UTC)

Statistical Sample

although there have been so few meltdowns in the history of nuclear power that there is not a large pool of statistical information from which to draw a credible conclusion as to what "often" happens in such circumstances

An N of about 10 (counting the list in the very next section of the article) isn't great for drawing scientific conclusions, but it's better than nothing for this purpose. "Often" is not a statistical indicator, though, so this current wording is a bit contentious. It sounds as if the author wants a bigger data set (no thanks!) or has an ideological axe to grind about the safety of nuclear power. If the author wants to go there, they should take that small N and divide it out over the years. Things have been very safe for a couple decades, but starting the count in 1945 we're still averaging some level (if you believe in "partials") of meltdown on the planet about every 7.5 years. Not exactly a puppies-and-rainbows situation. 97.81.81.105 (talk) 17:34, 13 March 2011 (UTC)