Talk:Fast-neutron reactor

Seemingly Conflicting Statements
In Control Section we have "fast-neutron reactors are controlled by keeping the criticality of the reactor reliant on delayed neutrons..." In Disadvantages Section we have "As delayed neutrons play virtually no role in fast reactors, other..."

These two statements seem to be a contraction. Neither statement has references, and I'm not an expert so can'd understand if they are in deed both true and could be better worded/expanded or if one statement is factually wrong. I *suspect* the second statement is wrong, my understanding is prompt neutron criticality is the domain of nuclear weapons, not reactors; but I'd like an expert to help. — Preceding unsigned comment added by 86.139.243.225 (talk) 13:05, 19 July 2023 (UTC)

Uranium and natural uranium
natural uranium is a curious (proto)link. I guess it should be uranium. Laurel Bush 14:41, 19 September 2005 (UTC).

Removed text
(Monju is)  the only FBR power station still operating in 2004

Not true... Phénix still produces power, and Monju is currently offline (but expected to return). And it's of doubtful interest anyway... China and India are both committed to comissioning FBRs, so there will be three nations running full-scale FBR power stations... all in Asia. Korea is also spending considerable amounts of money on design, they may not build one as their PWRs and CANDUs are seen as better export prospects for the moment, but they will be in there bidding for anyone else who wants to build a full scale prototype (the USA is my guess...). Andrewa 17:42, 29 December 2005 (UTC)

Other articles
I'm not quite sure what to do about the overlap between this article and the separate articles at LMFBR and FBR.

Probably LMFBR should simply redirect to FBR. The only FBRs so far built or proposed are LMFBRs, and there's reason to think that this will always be the case.


 * Wrong! My goof. There's a generation IV reactor proposal that's fast and gas-cooled. Andrewa 16:02, 3 February 2006 (UTC)

On the other hand, there are reactors such as EBR-II that aren't normally called FBRs although they do meet some definitions. So FBR or LMFBR could be seen as the power reactor class, while Fast (neutron) reactor is more general. Lead-cooled submarine powerplants aren't (LM)FBRs either in this sense, any more than Chernobyl #4 was a BWR just because it was cooled by boiling water.

In any case there's lots of cleaning up to do! Andrewa 18:24, 29 December 2005 (UTC)

I have redirected LMFBR to fast breeder, as a start. On reflection there was nothing to merge.

We now have two articles, fast breeder and fast neutron reactor, which is probably right, but both need work, and fast breeder should probably be moved to fast breeder reactor, not the other way around as now. Andrewa 19:59, 3 February 2006 (UTC)

moving its USP to the top of the article
Logically, I don't see that "Because absorption in the moderator is a major loss of neutrons in a thermal reactor, a fast reactor has an inherently superior neutron economy; that is, there are excess neutrons not required to sustain the chain reaction. These neutrons can be used to produce extra fuel, as in the fast breeder reactor, or to transmute long-halflife waste to less troublesome isotopes (see Phénix) or some can be used for each purpose." actually belonged under "nuclear fuel", and coming to this article whcih is the only one of the group witht ehexplanation of the rasion d'etre or USP of the machine, I think that needs to go near the top, in the first glance. It doesn't seem to make it overlong, and the picture balances the composition nicely on this screen at least. Midgley 22:00, 14 March 2006 (UTC)

comma missing?
"After the initial fuel charge such a reactor can be refueled by reprocessing adding natural or even depleted uranium with no further enrichment required. This is the concept of the fast breeder reactor or FBR." I can't correct this sentence because I'm not sure what it is saying.--Gbleem 01:59, 4 June 2006 (UTC)
 * It does seem a little obscure. On consideration it is accurate - you can refuel a fast breeder by taking the used fuel rod and reprocessing the contents - removing fission poisons leaving Uranium, and Plutonium, and put that back in a new fuel rod.  All you need to add to the cycle is U238 - hence natural or even depleted U.  The fact that you also take out the rods in the breeder blanket, and they hve Pu in them is separate - one assumes that gets burned in other, perhaps thermal, power plants.  I'm not sure that the reference to reprocessing hasn't crept in where it might be better applied to all forms of reactor though, and that it doesn't really depend upon or improve the concepts of the fast reactor.   I'm not an engineer or nuclear phsyicist though.  Midgley 20:58, 4 June 2006 (UTC)

That paragraph is bad at the moment, needs rewriting. Midgley (talk) 10:59, 23 April 2008 (UTC) "Nuclear fuel

In practice sustaining a fission chain reaction with fast neutrons means using relatively highly enriched uranium or plutonium. The reason for this is that fissile reactions are favored at thermal energies, since the ratio between the Pu239 fission cross-section U238 absorbtion cross-section is ~100 in a thermal spectrum and 8 in a fast spectrum. Therefore it is impossible to build a fast reactor using only natural uranium fuel. However, it is possible to build a fast reactor that will breed fuel by producing more fissile material than it consumes. After the initial fuel charge such a reactor can be refueled by reprocessing. Fission products can be replaced by adding natural or even depleted uranium with no further enrichment required. This is the concept of the fast breeder reactor or FBR."

External link to non-free article
The external link to the Scientific American "article" does not actually take one to the full article, but only a teaser for the full article, which must be purchased. As such, does not such and external link constitute a form of marketing? I am not going to say whether this is right or wrong, but would simply like to call the matter into question.-- * daniel * 03:55, 6 February 2007 (UTC)


 * Half of the articles that I write refer to JSTOR articles -- which are not free either (unless you or your institution already subscribe to the service). The same would probably go about older New York Times articles or many other publications; or for that matter most printed books (where not only do you have to pay the money, but also to shlep to a bookstore to get it... So while it may be desirable to mark the resources that require payment as such, it would seem excessive to ban them altogether Vmenkov 06:03, 6 February 2007 (UTC)

Doppler Broadening
The Integral_Fast_Reactor is described as passively safe, mainly due to doppler broadening in its fuel in the event of a Loss_of_coolant_accident. This assertion would appear to be at odds with "However, they cannot rely on Doppler broadening (which affects thermal neutrons) or on negative void coefficient (there is no moderator, so there is no reactivity reduction from moderator boiling)." - 218.185.10.137 (talk) 05:08, 6 November 2008 (UTC)

Poor sentence in intro
"The reason for this is that the ratio between the fission cross-section and the absorption cross-section in plutonium and minor actinides are higher in a fast spectrum." This and the previous clause might be run together into "fast neutron reactors are probably better for burning radioactive waste as the fast neutrons are more likely to split actinide or transplutonian nuclei". I'd make an edit, but I think precision is demanded and there may be a nuclear physicist to hand to proof read it? Midgley (talk) 15:43, 9 November 2008 (UTC)


 * This is a technical article, and it's important that it be technically accurate and use standard terminology. The text you are proposing to change is:

"Fast neutrons also have an advantage in the transmutation of nuclear waste. The reason for this is that the ratio between the fission cross-section and the absorption cross-section in plutonium and minor actinides are higher in a fast spectrum." I don't think your sentence captures this, and "transplutonian" is not the right term. A better version might be: "Fast neutrons also have an advantage in reducing nuclear waste through transmutation, particularly of fissionable isotopes. Fast neutrons are more likely to cause fission than to be absorbed and create long-lived transuranic wastes."NPguy (talk) 18:20, 9 November 2008 (UTC)


 * Better. Can we improve it a touch more?  "Fast neutrons are better at reducing nuclear waste by transmutation particularly of fissionable isotopes. Fast neutrons are more likely to cause fission than to be absorbed creating long-lived transuranic wastes." Even?  I have a preference for reduced word count.  I feel a lack of explanation in the last sentence, of why fission is better.  Fission into stable or fast decaying fragments?  Midgley (talk) 19:37, 25 November 2008 (UTC)


 * Yes, fission converts long-lived transuranic waste into short-lived fission products. You probably need to say better than what - i.e. better than thermal neutrons.  Another way of stating the difference is that the fast reactors can treat transuranics as fuel rather than waste, thereby allowing the complete removal of transuranics from the waste stream.  You still get some absorption and some fission, but rather than building up isotopes that do not fission with thermal neutrons, you achieve an isotopic steady state. NPguy (talk) 03:46, 26 November 2008 (UTC)

Fast-neutron reactor, or Fast neutron reactor?
This article switches back and forth between "fast neutron reactor" and "fast-neutron reactor". Which should we standardize on? -- Dan Griscom (talk) 11:46, 9 June 2013 (UTC)

What's a spectrum?
There is something missing in wikipedia: The definition of a (neutron) spectrum. Typically when people outside of wikipedia talk about fast vs. slow with regards to reactors, they use the terms "fast spectrum" and "thermal spectrum". However, wikipedia avoids using the term "spectrum". Now there might be valid reasons that the term "spectrum" should not be used in scientific literature, however when I try to look up terms from the "real" world it would be helpful to find an explanation here.

If there is somebody here who could define "fast spectrum", "thermal spectrum" or "(neutron) spectrum", this would be greatly appreciated – I am not qualified to do that, I fear. Tony Mach (talk) 09:50, 8 December 2013 (UTC)


 * Fast/thermal neutron spectrum refers to the types of energies that neutrons have. 'Thermal' neutrons are in thermal equilibrium with the reactor (~eV energy) and 'fast' neutrons are those which have recently been released from fission evenets (~MeV). If you were to plot out the number of neutrons at different energies, you would find that in some reactors (thermal) more neutrons are around eV energies while in others (fast) many more neutrons have energies around the MeV region. This is a consequence of the reactor's physical ability to slow down (moderate) neutrons. While this is standard language in the nuclear community, I agree that it should not be assumed and that there should be an introduction which explains the difference. --Mikeflem (talk) 11:31, 30 March 2014 (UTC)

Nice article upgrade!
Oh, say now, I like this Maury fella. This article has been terri-bad for a while now, and I've been meaning to tinker on it, and lo and behold, he pops in and starts with the stuff I planned to add.

Is he me?! :)

I see there's a need for some sources now, I'll see about scaring up a few, this new addition is a good workup of the basics as-is. I was planning to add a section detailing why a fast reactor is so different from a thermal reactor. The delayed neutron fraction is lower, cross sections are lower, moderation is to be avoided, LOTS more isotopes are viable fuel, that sort of thing. Plus, try and bring out how these knock-on effects make fast reactors such totally different beasts.

(sigh) I wish I had more time. now I got even more stuff I wanna do on here.

Morg00 (talk) 05:44, 10 April 2015 (UTC)

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Inaccuracies in this article
This article makes several inaccurate claims. .

The article claims that the compact size of fast reactors leads to their common use in ships and submarines. Current submarines and ships using reactors use water cooled reactors. Non-deuterated water moderates and absorbs too many neutrons to work for fast reactors. . The article further lists fast reactors with none being shipboard. . The article lists under 'never operated' Monju, which the article notes it restarted. If it restarted, it operated at least twice. . I think there were other problems and will edit this entry as I find them.

2600:8807:8787:7700:E82B:D56:283C:58CA (talk) 06:14, 30 November 2016 (UTC) BGriffin

FNRs can reduce the total radiotoxicity of nuclear waste, and its lifetime.
This is a drastic oversimplification to the point of being false. --JWB (talk) 10:03, 21 January 2019 (UTC)


 * The sentence has a reputable source. Can you explain why you think it is a "drastic oversimplification to the point of being false"? --Ita140188 (talk) 12:04, 21 January 2019 (UTC)


 * There should be some caveat about this claim. It represents the ideal case of near-perfect recovery of transuranics from the waste stream.  Unfortunately, the cited source (which appears to be the primary basis for the entire section) is essentially an advocacy piece that assumes a best case scenario.  It's reasonable to include this ideal case, but it should be identified as such.  This issue was discussed in some technical detail as part of the Global Nuclear Energy Partnership (GNEP) draft Programmatic Environmental Impact Statement (PEIS) in 2008.  The summary includes important caveats, e.g. on p. S-27
 * {{blockquote|text=Removal of uranium and transuranic elements via recycling could reduce the time period for which the radiotoxicity of the waste exceeds that of uranium ore from between approximately 85,000 and 525,000 years to perhaps less than 1,000 years, depending on the amount of uranium and transuranic loss from all processes that eventually becomes part of the wastes destined for disposal. (emphasis added} }}
 * The fast neutron reactor alternatives included in the PEIS assumed a very high efficiency of recovery of uranium and transuranics from waste. Because spent fuel must be recycled multiple times to achieve the stated efficiency in uranium utilization and waste reduction, any significant loss of transuranics to waste would be cumulative and would greatly reduce those benefits.
 * Another nitpick: the source does not use the term "radiotoxicity," so it's probably best to phrase in terms of reducing the quantity of long-lived radioactive waste. NPguy (talk) 16:26, 21 January 2019 (UTC)

Is Aristos Power real?
Look at the page aristos.power.com. There are only few diagrams and nothing else. What more is there about Aristos Power? A Facebook account? If there is nothing more than than a www page, some diagrams and a Facebook account, then Aristos Power looks like a scam. That is my opinion. ⸻Nikolas Ojala (talk) 11:50, 17 November 2019 (UTC)

I wouldn't consider it a scam, just a delusional startup effort. Suggest to remove such speculative designs.165.225.88.140 (talk) 12:22, 3 January 2020 (UTC)

rewrite to wiki standards
Which alterations are suggested ? Perhaps the discussion of the practical designs, the molten sodium and molten lead // molten lead/bismuth eutectic, have no place here? Is is strange to suggest a rewrite and then not suggest alterations?Fsikkema (talk) 21:51, 30 December 2021 (UTC)
 * Easy to place a template saying that the article is wrong. The article should start with explaining the difference between a slow and a fast reactor, and between reactions with and without a moderator. Thus explain why fast-neutron reactors have been developed. --Wickey (talk) 13:58, 1 January 2022 (UTC)

Thank you. That is precisely what I have been trying to do. Any suggestion on how to improve is welcome.I am going to remove the header, as this is what the article says.Fsikkema (talk) 22:37, 2 January 2022 (UTC)


 * The section on fission processes is off-topic. This article should focus specifically on fast-neutron reactors, not on explaining the concept of (for example) moderators. For that, we already have specific articles that cover the topic extensively and readers can follow the link and check them if they don't know what a moderator is or how it works. In this article, a short paragraph summarizing these points should be enough, with appropriate links to the relevant articles. --Ita140188 (talk) 09:01, 2 January 2022 (UTC)

I don't agree, the differences between fast neutron and moderated neutron reactors is quite difficult to underpin without explaining also the effects of moderation. The whole rationale for development of these reactors is precisely the absence of a moderator. That being said, maybe it could be shorter.Fsikkema (talk) 22:37, 2 January 2022 (UTC)
 * Fully agree with Fsikkema. The current text is a relict from the past. --Wickey (talk) 09:59, 3 January 2022 (UTC)

reactor control and picture upload
Could someone input some text about reactivity control in a fast reactor? As there are no delayed neutrons, the response of the control rods alone is insufficient. Is control then attained solely by 1. Doppler broadening and 2. thermal expansion of the core ? Could someone also please insert, under fuel utlization, the file fast vs thermal" that I uploaded? no idea how to do this. thanks Fsikkema (talk) 22:34, 17 January 2022 (UTC)

Molten salt as coolant?
Hasn't molten salt been suggested as coolant for fast reactors? 150.227.15.253 (talk) 17:16, 16 February 2022 (UTC)