Talk:Nuclear power
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Shortening the intro[edit]
Someone tagged the intro as too long. They had a point, this whole bit about FDNPP sticks out like a sore thumb. So I'm moving it here. I also don't know who wrote this paragraph that I'm removing, but for some reason they thought it should be in the introduction. Four years after the Fukushima-Daiichi accident, there have been no fatalities due to exposure to radiation, and no discernible increased incidence of radiation-related health effects are expected among exposed members of the public and their descendants.[1] The Japan Times estimated 1,600 deaths were the result of evacuation, due to physical and mental stress stemming from long stays at shelters, a lack of initial care as a result of hospitals being disabled by the tsunami, and suicides.[2]
References
- ^ International Atomic Energy Agency (2015-08-31). "The Fukushima Daiichi Accident: Report from the Director General". p. 13.
- ^ http://www.japantimes.co.jp/news/2014/02/20/national/post-quake-illnesses-kill-more-in-fukushima-than-2011-disaster#.VxRuJHBVvSF
Semi-protected edit request on 17 January 2018[edit]
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Change the last sentence of section 4.2.4 from "...R&D on disposal or radioactive waste..." to "...R&D on disposal of radioactive waste..." Brmlyklr (talk) 23:07, 17 January 2018 (UTC)
External links modified (January 2018)[edit]
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Accuracy of discussion of delayed neutrons[edit]
Seeing recent edits to this paragraph, I wonder if it needs to be edited more thoroughly to be technically accurate:
- In commercial nuclear fission reactors, the system is operated in an otherwise self-extinguishing state. The reactor specific physical phenomena, that nonetheless maintains the constant heat output, are the predictably delayed,[29] and therefore easily controlled, transformations or movements of a vital class of fission product, or reaction ember, as they decay.[30][31] Operating in this delayed critical state, with the dependence on the inherently delayed transformation or movement of fission products/embers to maintain the reactions from self-extinguishing, this physically delayed process occurs slow enough to permit human feedback on the temperature control. In a similar manner to fire dampers varying the opening to control the movement of wood embers towards new fuel, control rods are comparatively varied up or down, as the nuclear fuel burns up over time.[32][33][34][35]
Just about every sentence raises questions of accuracy. What is "otherwise self-extinguishing"? I interpret as saying "self-extinguishing taking into account only prompt neutrons." But delayed neutrons cannot be ignored, so this "self-extinguishing" characteristic is counterfactual (i.e. assumes facts known to be untrue). Calling fission products "embers" may be an evocative metaphor, but it not accurate. The reference to "movement" of fission products seems like a red herring, as they usually do not move appreciable distances. What delayed neutrons do is slow down the exponential ramp-up of a super-critical reaction to a time-scale amenable to external control. It does not necessarily mean that the reaction is "easily controlled," considering other factors that affect the stability of the reaction. One such factor is the thermal coefficient of reactivity (or in worse cases the void coefficient or reactivity). As the reaction rate increases and raises the temperature, does this accelerate (positive coefficient) or slow (negative coefficient) the rate of increase? For a thermal neutron reactor, it is usually the latter, since the fission cross section falls with increasing neutron energy. This may all be too much to put into the introductory section, but the explanation here does not seem accurate. NPguy (talk) 10:15, 6 May 2018 (UTC)
- I think the whole section should be removed. Also, a discussion about delayed neutrons other than a mention and a link is too technical for the lead of this article. --Ita140188 (talk) 13:42, 6 May 2018 (UTC)
- One of the most common questions of the common-person, is what makes a reactor different from a bomb? The lead of the article should explain this and this paragraph under review does somewhat succeed in that, followed by then moving readers into the background of the discovery of fission. Which would be greater expanded with the discovery of delayed neutrons and therefore the spark of the idea that fission could be controlled in a reactor. unfortunately the background section is very much focused on bomb work. To the detriment of an understanding on reactors being expressed.
- 78.18.52.84 (talk) 01:14, 20 July 2018 (UTC)
- It may be useful to make a distinction of the processes involved, but the discussion is very technical and needs to be summarized skillfully if it is to be included in the lead. The section that was removed was not helping in clarifying this point, on the contrary, it was extremely confusing especially for someone not familiar with the topic. I propose we try to find a better way of explaining this point here in the talk page and then in case we add it in the article. --Ita140188 (talk) 02:36, 20 July 2018 (UTC)
- The paragraph was re-inserted without much modifications by Boundarylayer in the History section. While I think the position is more appropriate than the lead, the problems with clarity and accuracy listed above remain. Please engage in discussion to see how this paragraph can be improved. Right now it is almost incomprehensible and almost completely inaccurate. --Ita140188 (talk) 09:16, 1 August 2018 (UTC)
- I also ping NPguy. --Ita140188 (talk) 09:18, 1 August 2018 (UTC)
- I made one fix, to eliminate the ember analogy, which seems more likely to confuse than to illuminate. Nothing else jumped out to me as wrong or misleading, but I'm open to further discussion. It seems like a full discussion of reactor controllability would need to include some reference to control rods (which I also deleted as part of the misleading ember analogy) and as well as other factors such as poisoning and reactivity coefficients to explain the stability of the reaction. NPguy (talk) 16:01, 2 August 2018 (UTC)
- In attempting to explain to readers what is the difference in operation of a bomb to a power reactor? One of the most common questions about nuclear reactors. It was necessary to convey the "otherwise self-extinguishing" analogy. In continuing this analogy, the image of embers is accurate, as embers being the almost last product of the combustion reaction, before ash formation, are akin to delayed neutrons. Once embers become small enough they frequently become airborne from buoyancy, self lofting reaction propagating "sparks" and with that, can transmit heat to distant locations, to continue the fire. The analogy is helpful if you know about embers and how they move, which I assumed most readers would.
- If you can think of a better analogy, so high-school level students can grasp the difference of reaction-propagation, between a bomb and power reactor, then by all means, take a stab at it.
- Either way, considering the importance of this question, the article definitely need to describe the discovery of delayed neutrons and the developing understanding, by Fermi and others, of how these specific neutrons could be used to build a controllable reactor.
- Alongside the discovery of delayed neutrons needing to be discussed, to really do it right, an internal reactor animation, progressed by time-slices, that includes the delayed neutron generation, is really the kind of thing we need. Having checking wikicommons I unfortunately do not see anything suitable. NPguy, do you perhaps know of any animations that could be used?
- Boundarylayer (talk) 17:40, 2 August 2018 (UTC)
- I agree the analogy was misleading and essentially incorrect. I still think the paragraph lacks clarity, with excessively long and seemingly broken sentences. For example, what does "otherwise self-extinguishing" mean exactly? The whole paragraph should be rewritten. --Ita140188 (talk) 05:49, 8 August 2018 (UTC)
- I think this section in Nuclear reactor physics#Delayed neutrons and controllability is clearer and more accurate, we could just use a summarized version of this:
Fission reactions and subsequent neutron escape happen very quickly; this is important for nuclear weapons, where the objective is to make a nuclear core release as much energy as possible before it physically explodes. Most neutrons emitted by fission events are prompt: they are emitted effectively instantaneously. Once emitted, the average neutron lifetime () in a typical core is on the order of a millisecond, so if the exponential factor is as small as 0.01, then in one second the reactor power will vary by a factor of (1 + 0.01)1000, or more than ten thousand. Nuclear weapons are engineered to maximize the power growth rate, with lifetimes well under a millisecond and exponential factors close to 2; but such rapid variation would render it practically impossible to control the reaction rates in a nuclear reactor.
Fortunately, the effective neutron lifetime is much longer than the average lifetime of a single neutron in the core. About 0.65% of the neutrons produced by 235U fission, and about 0.20% of the neutrons produced by 239Pu fission, are not produced immediately, but rather are emitted from an excited nucleus after a further decay step. In this step, further radioactive decay of some of the fission products (almost always negative beta decay), is followed by immediate neutron emission from the excited daughter product, with an average life time of the beta decay (and thus the neutron emission) of about 15 seconds. These so-called delayed neutrons increase the effective average lifetime of neutrons in the core, to nearly 0.1 seconds, so that a core with of 0.01 would increase in one second by only a factor of (1 + 0.01)10, or about 1.1: a 10% increase. This is a controllable rate of change.
Most nuclear reactors are hence operated in a prompt subcritical, delayed critical condition: the prompt neutrons alone are not sufficient to sustain a chain reaction, but the delayed neutrons make up the small difference required to keep the reaction going. This has effects on how reactors are controlled: when a small amount of control rod is slid into or out of the reactor core, the power level changes at first very rapidly due to prompt subcritical multiplication and then more gradually, following the exponential growth or decay curve of the delayed critical reaction. Furthermore, increases in reactor power can be performed at any desired rate simply by pulling out a sufficient length of control rod. However, without addition of a neutron poison or active neutron-absorber, decreases in fission rate are limited in speed, because even if the reactor is taken deeply subcritical to stop prompt fission neutron production, delayed neutrons are produced after ordinary beta decay of fission products already in place, and this decay-production of neutrons cannot be changed.
I think that delayed neutrons don't belong to the History section. I moved them to the Nuclear power plants section and added a short description of the chain reaction. --TuomoS (talk) 14:57, 18 November 2018 (UTC)
Reference 154 link is broken[edit]
Here is the correct link:
http://www.oecd-nea.org/news/2012/2012-05.html
Bclamore (talk) 15:00, 7 October 2018 (UTC)
- 154 was the redbook itself. that link is to a press release but it also supports the content so is fine. Jytdog (talk) 15:13, 7 October 2018 (UTC)
Correction: "laureate" instead of "laurette"[edit]
In the "History > First nuclear reactor" section, Glenn Seaborg is a Nobel "laureate", not "lorette".
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