Talk:CANDU reactor

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requesting more references[edit]

I placed two {{cn}} after two statements I thought needed references -- namely:

  1. "At the time of its design, Canada lacked the heavy industry to cast and machine the large, heavy steel pressure vessel used in most light water reactors..."
  2. "Canada also lacked access to uranium enrichment facilities, which were then extremely expensive to construct and operate..."

WRT the second assertion -- surely this was true for every nation that developed a nuclear industry?

WRT the first assertion -- this may very well be correct. But it is not what I remember when I first read about the CANDU design.

Cheers! Geo Swan (talk) 16:19, 20 March 2010 (UTC)

I don't know about the 1st, but as to the 2nd, no, I think the other nations working on nuclear power had already developed enrichment capability as part of their nuclear weapons programs.
—WWoods (talk) 04:34, 24 March 2010 (UTC)
Both assertions are true - and in fact are still true for most of the world. Whitlock (talk) 12:33, 25 March 2010 (UTC)

Pressurized or not?[edit]

I dont know if this is really an error, but I was confused when I got to this part..

"The heavy water is unpressurized, and a cooling system is required to keep it from boiling.
At the time of its design, Canada lacked the heavy industry to cast and machine the large, heavy steel pressure vessel used in most light water reactors.[citation needed] Instead, the pressure is contained in much smaller tubes, "

It seems rather contradictory. (talk) 06:31, 17 March 2011 (UTC)

The moderator is heavy water in a large tank (calandria) at atmospheric pressure which must be kept cool by the moderator heat exchangers.

The primary fuel coolant (also heavy water) is pressurised but flows through tubes containing the fuel which run horizontally through the calandria. These tubes are a lot easier to fabricate than the thick walled pressure vessels used in Pressurised water Reactors which contain both the fuel and light water which acts as a moderator and coolant. Dabbler (talk) 14:35, 17 March 2011 (UTC)

I'm not 100% sure of your source of confusion, but maybe I can help. I'm not a nuclear engineer, but based on reading the article and looking at the colored "schematic" of the reactor, I can say this:

  • heavy water is used for two purposes in the CANDU reactor. It is used as the moderator (pink on the diagram) and it is used in the primary heat carrying loop (yellow and orange on the diagram, although the orange looks to me more like a darker yellow), carrying heat from the reactor to the steam generator.
  • the heavy water used to carry heat to the steam generator is pressurized, the heavy water uses as the moderator is not pressurized. (I don't know if the terminology "atmospheric pressure" adds to the confusion--to say something is at atmospheric pressure essentially means it is not pressurized--it is at the same pressure as the rest of the atmosphere around it--you don't need a special high strength tank (pressurized vessel) to contain it)
  • so, the pink is at atmospheric pressure, and the tank holding it (the calandria) does not have to be built to deal with pressure higher than atmospheric--it is, in the common parlance, not a pressurized vessel
  • the yellow and orange is pressurized, but note (if you can) that the orange and yellow is contained in pipes built in and through the calandria--those pipes must (and are built to) contain the pressurized moderated water

Hope that helps! Rhkramer (talk) 12:40, 17 June 2011 (UTC)

Picture of fuel bundle.[edit]

I believe that the picture of the fuel bundle with text that states '"Two CANDU fuel bundles: Each about 50 cm in length and 10 cm in diameter, and generating about 1 GWh of electricity during its time in the reactor. Photo courtesy of Atomic Energy of Canada Limited.' has a problem.

I think it should say 1 GW or 1 GWe.

1 GWh is worth about $ 80.00 ( at $ .08/KWh retail ).

Could someone who knows more check and make the change if I am correct please.

Thank you,

Rob Walker. RS Walker (talk) 17:30, 31 March 2011 (UTC)

1 GWh(e) is correct:
nominal CANDU burnup = 7500 MWd/Te
1 CANDU bundle = 20 kg U (roughly)
therefore, 1 CANDU bundle's energy output = 7500 * 20/1000 = 150 MWd = 3.6 GWh ~ 1 GWh(e)
Also, at $ 0.08/kWh 1 GWh(e) would be $80,000, not $80
Whitlock (talk) 05:59, 1 April 2011 (UTC)

Thank you for clearing that up. It makes sense now.RS Walker (talk) 19:31, 1 April 2011 (UTC) — Preceding unsigned comment added by RS Walker (talkcontribs) 19:29, 1 April 2011 (UTC)

"Relieved"? Should be some other word: "believed", "discovered"[edit]

In this sentence: "The deal for the reactor had not been opened to competition, and it was later relieved that a $20 million payment had been made to an "agent" to sell the system. Construction started in 1977 and commercial operation began in April 1983."

"relieved" is not the appropriate word. Even if there is a meaning of relieved that applies here, I have not found it, so it must be a rather obscure meaning. Better would be a word like "believed" or "discovered". As I don't know which is the case, I'm thinking of waiting until someone else comes forward who knows the facts.

Quite possibly, next time I think of it, I'll come back and, if no one has resolved the problem, I'll choose a new word, possibly at random lacking knowledge. ;-) Or maybe I'll try to indicate ambiguity today, with something like "[ believed | discovered (uncertain of the facts) ]"

Hmm, maybe that is better, unless it prompts someone to delete the sentence. Rhkramer (talk) 12:19, 17 June 2011 (UTC)

I think it should have been "revealed" and I have altered it to suit and put the comment into hiding! Dabbler (talk) 13:47, 17 June 2011 (UTC)
To no end, as it turns out. Our local CANDU apologist has removed the entire statement as being "off topic". I believe a separate section on this might be in order. Maury Markowitz (talk) 11:14, 20 June 2011 (UTC)

POV Section Tag[edit]

I have tagged this section because it uses a mixture of cost bases and it is not clear which cost estimates are used to calculate the cost overruns, early initial ones or final detailed once once the project scope was finalised? It quotes costs/kWhj without stating the base year and compares with other values and draws conclusions without allowing for inflation etc. It also compares the performance of a couple of restarted elderly units with the anticipated performance of proposed refurbished of much younger ones despite the vastly different scope of work involved. I also suggest that the Clean Air Alliance as an advocacy group is an inherently biassed source. Dabbler (talk) 17:49, 27 June 2011 (UTC)

Please tag the pecific sentences you believe are POV, with notes here on each one as to why you believe them to be POV. Many of the generalized complaints you note here are fully referenced in the article, so I want to make sure there's an actual problem to fix.
The CAA's numbers are fully referenced and are all taken from OPG, OPA, and the COP. One might suggest these sources are "inherently biassed" as well, but not in the way that is being implied here. Maury Markowitz (talk) 11:28, 28 June 2011 (UTC)

Economic performance[edit]

I think the economic performance section should be updated to include information on some of the non-Ontario units. This link from the Canadian Nuclear Association include some information on the capacity factors. It might also be good to include reference to the capacity factors or cost of competing designs to give context? — Preceding unsigned comment added by Hologram0110 (talkcontribs) 04:07, 8 December 2011 (UTC)

Design: Is This Information Necessary or Relevant?[edit]

"A CANDU power plant generates power in the same fashion as a fossil fuel power station; heat is generated by "burning" fuel, and that heat is used to drive a steam turbine, normally located in a separate "power hall". A typical coal-fired plant burns coal and air and produces mostly carbon dioxide and fly ash, the CANDU burns nuclear fuel in-situ; when the fuel is "burned up" it is removed from the reactor and stored." That entire bit there can be replaced by a single sentence including a hyperlink: "CANDU power plants generate power through the same basic design principle at the heart of all nuclear power plants." This intro is misleading and out of place in an article about a highly specific proprietary power plant design. It would be appropriate in a general article on nuclear power generation. (talk) 08:55, 23 January 2012 (UTC)

I tend to favor such introductory material be placed in-situ, it saves considerable click-itis. If we do as you suggest, then the reader would have to click out to some other article, locate the description in question, read it, and then page back. I think a single para as it is helps rather than hinders. Maury Markowitz (talk) 19:38, 5 March 2012 (UTC)

Safety coverage inadequate[edit]

The article lists safety features but does not actually discuss operational safety. This is like the Ford Explorer article mentioning that it has brakes and safety belts without mentioning that it's vulnerable to high speed tire blowout and subsequent rollover if the driver responds incorrectly (For the record, the Explorer article does cover this concern.) The article mentions that CANDU has a smaller positive void co-efficient than RBMK reactors, which gives operators more time to react to problems. However, what needs to be addressed is the effect of the CANDU positive void co-efficient in the event of a Three Mile Island type incident (ie, one in which coolant voids develop without the operators noticing) or Chernobyl type incident (ie, safety systems are disabled by accident or on purpose)

Similarly, the article mentions that CANDU plants continue to put out 7% of maximum power after shutdown and so have several cooling systems. What needs to be addressed is the ability of CANDU plants to deal with a Fukishima type incident (ie, the reactor is successfully shutdown but all power to run cooling systems is lost.)

I'm digging out some references that address this, but in the meantime invite anyone with the knowledge or references to weigh in on these points. — Preceding unsigned comment added by (talk) 05:42, 29 March 2012 (UTC)

Fukushima response is not part of the original CANDU design since by definition it is a "Beyond design basis" event. Each utility has to assess its own response to the events that they consider appropriate. OPG did not consider 9.5 earthquakes and 30 metre tsunamis on Lake Ontario because they are physically not crediblem they did consider tornados etc. They have decided to buy diesel pumps and generators and hoses to maintain cooling in the evnt of a complete loss of the electrical grid and internal power supplies which was the worst beyond design event that was credible.
I am not saying that this should not be addressed just that each plant will have its own problems and solutions. Dabbler (talk) 11:42, 29 March 2012 (UTC)
Excellent point Dabbler, I think I was probably not clear enough. The aspect of Fukishima I'm looking at here is not specifically the mechanism that takes cooling offline, but how (or if) CANDU can handle an extended station blackout (ie, neither internal nor external power available to run the cooling systems). Obviously Ontario isn't given to large earthquakes and tsunami, however events beyond design basis do occur - in fact it's safe to say that no nuclear accident is a design basis event, since the plants are designed not have those accidents. CANDU certainly faces the possibility of a station blackout even in Ontario. For example the Quebec ice-storm had some areas with neither power nor road access for over a week. This would strain the fuel reserves of the backup generators. Loss of station power could also occur via a maintenance problem (eg, contaminated generator fuel or a faulty valve that dumped it all), or via a Stuxnet-type computer virus, - or most likely through a series of individually trivial events that no-one could have predicted would line up to disaster, as at Three Mile Island. I don't want to get too deep into this - it's not for Wiki to get into exploring various hypothetical disaster scenarios. However we definitely need to give at least as much coverage to safety in nuclear power plants as we do to safety in the Ford Explorer. The current safety section doesn't address operational safety, it just lists safety systems, and there are some very pertinent reference-supported facts we should get in there. Is it possible for a CANDU reactor to melt down, even after it's been shut down, as Fukishima did? Is loss of all internal and external power enough to cause this? If so, how long after power fails will the meltdown start? There's sixty years of research on CANDU out there, surely there's data on this somewhere. (talk) 22:03, 30 March 2012 (UTC)
The post-Fukushima assessment for OPG did focus on the possibility of an extended grid blackout and that was the reason for the purchase of the pumps and generators. The assumption is that diesel fuel could still be trucked in as a priority in any provincial emergency.
CANDUs have the demonstrated capability for cooling of the shutdown heat from the non-critical core by natural circulation without any pump circulation, i.e. the layout of the heat transport pipework will maintain a slow flow of hot water from the core through the steam generators where the core water can be cooled if the SGs are kept topped up with feedwater (from the emergency pumps and generators if required).
Unlike the PWR, a CANDU has a large cool tank of moderator water surrounding the core which would also buy some time to hook up the emergency pumps. Here is a Toronto Star story which describes most of what I have mentioned. Dabbler (talk) 22:55, 30 March 2012 (UTC)
Read the article, thanks Dabbler. Evidently the core shuts down automatically and quite reliably if the external power fails, but will melt down if cooling fails, just as at Fukishima. However it won't happen right away if the pumps fail, since there is passive convection in the core and the presence of cool moderator, etc. What I need to find is how long is the delay before meltdown(minutes? years?). The article also mentions the possibility of a hydrogen explosion if the zirconium fuel tubes overheat. I didn't know that part! Still unaddressed is the question of primary coolant loss (eg, pipe fracture or mis-set valve) as happened at Three Mile Island. Will this result in immediate meltdown, or will there still be a delay? Another unanswered question is whether the fuel pools will boil dry or not (also a Fukishima problem), and of course I'm still looking in the positive void co-efficient. It might be worth adding a separate risks/vulnerabilities section on top of a proper operational safety section. (talk) 13:14, 1 April 2012 (UTC)

I think I've got at least a preliminary answer. Even without power, the primary coolant loop will convect enough heat to the secondary loop indefinitely, but loss of primary coolant (eg through valve mis-set or pipe rupture) or secondary cooling (by any mechanism) will stop that process and cause a meltdown. Heating up the moderator and shield water will postpone this for several hours, and gravity fed tanks to cool the steam generators will postpone it somewhat longer. It would be nice to put some numbers on these, but as a first-guess, a CANDU has perhaps half a day between a station blackout event and a meltdown. Anyone have any numerical data? (talk) 13:54, 1 April 2012 (UTC)
These specific questions on detailed performance in specific scenario types will have different answers for different plants. Pickering 'A' is not Pickering 'B' is not Qinshan is not a (theoretical) new build today. For the older plants in particular the information may not be available if it wasn't a design-basis accident at the time. Hearings/submissions from/to the CNRC post-Fukishima may shed some light on existing plants if anyone has the time and expertise (I don't). On PVR specifically there is a lot of older post-Chernobyl coverage on CANteach. Don't know if anyone has an answer on cooling pond boil-off but the residual decay of the fuel is much lower v. BWR so I don't know. I believe the risk of hydrogen explosion is siginficantly reduced by the use of hydrogen recombiners in even the older plants (retrofit) - can anyone confirm this? — Preceding unsigned comment added by (talk) 04:36, 15 August 2012 (UTC)

NPOV and missing reference[edit]

"mainly from external factors" This claim requires a reference.

It is followed by a claim concerning success in China with no reference to an reputable auditor or international organization but instead public relations material from "Canteach", a PDF file at

I am not an opponent of nuclear power, but this is SNC-Lavalin who is the owner now and an experienced wikipedia editor needs to look at reference 10 and what it means in this context that the prior claim has no reference.

Canadians long tolerated Atomic Energy of Canada exaggerations, but since the Libya-Mexico affair, I believe that fewer Canadians have illusions about the lack of scruples of SNC-Lavalin.

In the past I worked on the world's "best selling" audit software (post-Enron) and I now have some considerable skepticism even of claims by big name auditors (that OEM firm is owned by the owners of Reuters, so we all have a lesson there in having doubts about "references" when these big corporations "speak for themselves", let alone "report" on economic results in China.)

Here is a University of Toronto publication relating to transparency and governance where CANDU is concerned: byDuane Bratt, IPAC Series in Public Management and Governance, University of Toronto Press, Scholarly Publishing Div., 2006, 336 Pages.

The Calgary Herald blog site says of Duane Bratt: " Duane Bratt is Chair and Professor in the Department of Policy Studies at Mount Royal University (Calgary, Alberta). He was educated at the Universities of Windsor (BA 1991, MA 1992) and Alberta (Ph.D 1996). He teaches in the area of international relations and Canadian public policy, with specialty in the sub-field of Canadian foreign policy. His primary research interest is in the area of Canadian nuclear policy "

The book is suggested reading in the Bennett Lewis article.

The IPAC site on GRC is

For a glimpse of the challenge of NPOV for Canadian commentators on this subject, I suggest the OCI website where it may not be obvious to a visitor that this is the Organization of CANDU Industry suppliers (the "C" is not for Canada) as they prefer to only use the moniker OCI on their web pages and even their "ABOUT OCI" page does not state the origin of the acronym.

Governance at CANDU: the players include an SNC-L internal auditor (Senior V-P, F and A)
  former Vice President, Finance and Administration at SNC-Lavalin Inc.
  former Director of Finance, Middle East Oil and Gas at SNC-Lavalin Inc.
  former Internal Auditor at SNC-Lavalin Inc.

G. Robert Shiplett 01:18, 30 March 2012 (UTC)

It strikes me that there's two different items here - one is about a specific reference / potential weasel wording, and CANteach can't be considered neutral but it looks like the link is dead anyway. Not sure I follow what's wrong with the reference on political interference but the wording you highlighted of "mainly from external factors" does seem to have a ring of opinion to it. Respectfully, the rest of this section seems unfocused in its criticism which makes it hard to respond to; however, the original/first point seems clear and fair enough. (talk) 04:56, 15 August 2012 (UTC)


this article needs to be cleand up. so many typos and run ons etc. I kept rereading it. does anyone agree?Longinus876 (talk) 17:45, 13 August 2012 (UTC)

Basic design and operation section[edit]

I removed the following paragraph from the Basic design and operation section:

"A CANDU power plant generates power in the same fashion as a fossil-fuel power station: heat is generated by "burning" fuel, and that heat is used to drive a steam turbine, normally located in a separate "power hall". Whereas a typical coal-fired plant burns coal and air and produces mostly carbon dioxide and fly ash, the CANDU consumes nuclear fuel in-situ; when the fuel is "burned up" it is removed from the reactor and stored as high level radioactive waste."

There are a couple of issues here...

For one, nothing here is specific to a CANDU reactor - as opposed to any old solid uranium-fueled, once-through cycle reactor. People reading this article will want to know specifics about *this* reactor type - what makes it unique - e.g. it can run on un-enriched uranium, uses heavy water, etc.

There's also something of a POV issue here and heavy use of non-sequitors. Yes, nuclear reactors use heat to make steam to turn turbines - the same as any thermal power plant - be it fossil or biomass or solar-thermal. Why is this being featured in the intro to the design section for the *CANDU* article?

It seems there's an agenda to pain nuclear (including CANDU) with the same brush as fossil fuels. There are some (at least superficial) similarities - both involve fuel being consumed and some amount of waste products. There are also some big differences though - e.g. nuclear using about a million times less fuel for the same amount of energy. In any event though - not a debate to be sorted out in this section of this article. -Helvetica (talk) 11:36, 27 December 2014 (UTC)

Number of CANDU's[edit]

I'm confused. The article says there are 29 reactors but then lists them by country and there are 31 reactors on the list. Can someone explain or correct this? — Preceding unsigned comment added by (talk) 13:38, 5 August 2015 (UTC)

Nuclear nonproliferation[edit]

The CANDU_reactor#Nuclear_nonproliferation section of the article makes the unsourced claim that,

"There is a common misconception that plutonium for India's first nuclear detonation, Operation Smiling Buddha in 1974, was produced in a CIRUS design. In fact, it was produced in the safeguarded indigenously built PHWR reactor."

This is contradicted by sourced claims on the articles Heavy_water_reactor#Nuclear_proliferation and CIRUS_reactor. I'd suggest that it be removed and replaced with a statement congruent with the other articles and their sources. If there is legitimate controversy as to whether CANDU/CIRUS reactors were used to make the weapons material, then a reference for that should be cited. (talk) 02:43, 31 August 2015 (UTC)

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