Talk:Nuclear chain reaction

Cyclical Link

In the section "Effective neutron multiplication factor", there is a link to "Reactivity_(nuclear)" which is the same page as "Nuclear chain reaction". 165.91.10.150 (talk) 21:55, 2 December 2012 (UTC)

Bias toward nuclear weapons technology

This article lacks any citation of formulas or numbers. Also, it is extremely bias towards nuclear weapon technology instead of taking a balanced approach by discussing nuclear power, too. I am going to go through it to attempt to provide basic formulas (cited!), add nuclear power plant concepts, and make it clearer. I welcome any feedback on my edits. MNNE 05:55, 7 November 2007 (UTC)

I have finished editing the article! We still need info on fusion, though. -- MNNE (talk) 21:17, 16 November 2007 (UTC)

As I pointed out below, fusion is not a chain reaction. Man with two legs (talk) 00:00, 17 November 2007 (UTC)

I would disagree with that statement. While I am not a fusion expert, I know that the fusion reaction is propagated by the intense kinetic energy of the products of previous fusion reactions, which is the concept of a chain reaction. To quote the fusion reaction page: "When the fusion reaction is a sustained uncontrolled chain, it can result in a thermonuclear explosion, such as that generated by a hydrogen bomb. Reactions which are not self-sustaining can still release considerable energy..." Obviously, the chain reaction is not propagated by neutrons as we typically think of fission reactions, but is it not a chain reaction? MNNE (talk) 07:06, 17 November 2007 (UTC)

You're wrong. Fusion has to be sustained externally because it cannot generate its own reactants or reaction conditions; in a fusion weapon, this is usually done using a fission device to compress the hydrogen, while in a star the vast mass creates the required heat and pressure. If you take away those conditions the reaction simply stops; it's self-limiting, not self-sustaining. Herr Gruber (talk) 13:00, 25 August 2012 (UTC)

Seems that this article is extremely biased towards nuclear fission. What about nuclear fusion? 145.97.223.187 11:36, 6 Mar 2005 (UTC)

I agree. Is there anyone out there who can add some (cited) information on fusion? MNNE 17:47, 9 November 2007 (UTC)

Fusion is not a chain reaction so it does not belong in this article. Man with two legs 11:56, 16 November 2007 (UTC)

See above comment. MNNE (talk) 07:06, 17 November 2007 (UTC)

Needs a discussion of chain-reaction timescales, to differentiate between prompt and delayed neutrons, and so between critical and prompt critical. Linuxlad 10:11, 26 Nov 2004 (UTC)

Yes yes yes! Removed text:

The rate of reactions will accelerate exponentially if left unmoderated.

which is highly misleading at least. The role of a neutron moderator is not really control, but I can see how someone might think that.

I've just added a very brief mention of prompt-criticality to critical mass. Do we need it here too? Should we perhaps have a separate article on supercriticality, with prompt critical redirecting to it? Andrewa 02:08, 29 Nov 2004 (UTC)

Eeek! The good news is there's already an article on prompt Criticality which I've now added to category:nuclear technology. The bad news is that I've also added a disputed tag to it...! And of course the capital "C" is wrong in the title. Andrewa 02:32, 29 Nov 2004 (UTC)

The part about natural chain reactions, don't the sun and other stars count?

Sustainable fusion is not a nuclear chain rection: in this case, the reactions occur randomly inside the plasma which is exposed to extreme pressure and temperature conditions. The fusion processes release energy which indirectly induces more fusion processes by heating the plasma, but this is very different from the exponential behaviour described in the article. --Philipum 08:09, 3 August 2005 (UTC)

I added a remark about fusion.--Patrick (talk) 13:23, 17 November 2007 (UTC)

Spelling

Caesium is NOT archaic - but the standard UK spelling. Linuxlad

You are Right see Caesium File:Gavel.gif

Scott 22:49, 13 September 2005 (UTC)

Exponential increase

Hi,

is it really a good idea to define a nuclear chain reaction (in the introductory sentence) as always having an increasing reaction rate? In a fission reactor at normal operation, the reaction rate is controlled to be constant (k = 1), but it is still a chain reaction. 217.190.37.72 15:16, 30 May 2006 (UTC)

effective neutron multiplication factor k

I don't get it. Could someone rewrite it? --Gbleem 03:14, 13 June 2006 (UTC)

Fusion is a burning process, not a chain reaction

Chain reaction requires a critical amount of fuel to start. That is why fission reactors have to contain large amount of fuel. Fusion has no critical amount, fuel can be supplied continuously. In other words, fusion is a burning process. Indeed it is simply wrong to say that fusion is a chain reaction. —Preceding unsigned comment added by 147.231.36.239 (talk) 11:32, 26 February 2008 (UTC)

However, the general definition of a chain reaction does not include a critical mass. Chain reactions occur in sub-critical masses as well (they will simply die out over time). If a fusion reaction depends on its own products (such as energy) to continue, then it still could be considered a chain reaction. MNNE (talk) 17:33, 1 March 2008 (UTC)

No, a chain reaction has to create more reactants, otherwise it isn't a chain. Fusion happens once and does not create additional fusion fuels; the energy produced does not undergo fusion either ("energy" is not a reactant in fusion), and so could not be considered evidence of a chain reaction. Herr Gruber (talk) 14:14, 24 August 2012 (UTC)

That is one opinion, and is certainly not held by all authors. JM Valentine, Atomic Physics (1960) says (p.132) that chain reactions are frequently encountered in everyday life, that a column of tipping dominos is just one example, explicitly adding "the ignition of a match head may be considered as a chain reaction." Britannica defines a chain reaction as a "process yielding products that initiate further processes of the same kind, a self-sustaining sequence. Examples from chemistry are burning a fuel gas, the development of rancidity in fats, “knock” in internal-combustion engines" [1]. Columbia Encyclopedia states "A line of dominoes falling after the first one has been pushed is an example of a mechanical chain reaction; a pile of wood burning after it has been kindled is an example of a chemical chain reaction. In the latter case each piece of wood, as it burns, must release enough heat to raise nearby pieces to the kindling point. The wood, therefore, must be piled close enough together so that not too much heat is lost to the surrounding air. The conditions for a nuclear chain reaction can be understood by analogy." [2] (Emphasis added obviously.) So far I haven't found a source which refuses to include burning processes as chain reactions, provided the burning is of such a nature that the reaction in one part directly causes the reaction in the next adjoining part, and so on continuously. Note that this mightn't necessarily always be the way: for example, if the temperature of a long sheet of paper is raised quickly enough, it should be possible for it to all oxidise simultaneously and spontaneously, rather than being induced chain-wise. So for fusion, I think this is central to the question. Does a fusion reactor raise the temperature uniformly so that fusion spontaneously occurs in uncorrelated and distributed manner, or can the activation energy for nearly every fusion event be directly traced back to the energy liberated by a previous fusion event in a specific nearby location? I suspect the case is more the former for both early H bombs and stellar fusion. But on the other hand, supposedly Szilárd proposed fusion chain reactions before fission was even discovered. Cesiumfrog (talk) 03:28, 28 November 2012 (UTC)

So one source that's fifty years old and two which are not speaking in strictly scientific terms or about nuclear chain reactions. Colour me not impressed. But regardless, fusion requires immense pressure before it can even start, and since you can't expect a fusion reaction to build a reactor for itself you need to supply that externally. H-Bombs require compression using explosives or a fission bomb to get going, while the sun only functions because the gigantic mass of hydrogen present creates the necessary reaction conditions. If you built a magical anti-physics device which could suddenly remove the sun's mass, it would burn out almost instantly because it would no longer create sufficient pressure to make the reactions continue. Same if you built a commercial fusion reactor somehow; without the vessel, the reactions would cease almost immediately because the laws of physics want your fusion fuels to equalise pressure with their surroundings rather than sit there under the thousands of atmospheres they need to actually do anything.

In a fire, heat energy liberated by combustion does create further fires, therefore in a general sense it can be called a reactant (heat + flammable thing = fire). Fusion might produce heat, but it does not produce pressure, and it needs both otherwise you can have as much fusion fuel as you like and it'll just sit there judging you. Herr Gruber (talk) 11:52, 12 December 2012 (UTC)

Semyonov

Why was Semyonov not mentioned in this article? He was the one who developed the theory of nuclear chain reaction fully. I added passage on his work.99.231.50.118 (talk) 04:33, 31 October 2008 (UTC)Pavel Golikov.

stability

This article doesn't really explain, how is criticality maintained exactly without risking an exponential run-away? Cesiumfrog (talk) 02:35, 25 March 2011 (UTC)

topic intrusion

Every section seems to be plagued by some mention of why a nuclear reactor will not explode. I suggest either a section be created on this, or that these statements be deleted. I'm not saying these statements are wrong but they seem random and sometimes irrelevant. Here is an just such an example: "Furthermore, all power plants licensed in the United States require a negative void coefficient of reactivity, which completely eliminates the possibility of the accident that occurred at Chernobyl (which was due to a positive void coefficient)".-if you go back and see what the original section was about you'll see how these sort of statements seem a little out-of-place. Themanofthewiki (talk) 17:40, 7 August 2011 (UTC)

I agree that they are out of place. Also wrong. A negative void coefficient mostly refers to whether or not the moderator is water or graphite, so that bubbles make it a worse moderator, or not. In Chernobyl, what made coolant voids BETTER moderators (as rods were being inserted) was that control rods actually had graphite tips so that they increased moderation in the leading-rod area during a (slow) SCRAM while the tip was in the "wrong" place for a moment. In retrospect, a bad idea, but not an essential feature of a graphite reactor. A carbon-moderated reactor could be built to rapid SCAM and with no graphite in the control rods (indeed they could be tipped with a neutron poison, in order to avoid the Chernobyl effect).

A negative void coefficient, of course, also doesn't guarantee no explosion, since explosions can happen by other mechanisms. An explosion can happen after the reactor has already been shut down (scrammed). The explosian even at Chernobyl was a steam explosion from a power excursion from this carbon tip, slightly before SCRAM. During the Fukushima Daiichi nuclear disaster it was a hydrogen bubble caused by overheating from decay heat due to loss of coolant flow (due to loss of power for the pumps), long after the reactors had been SCRAMed. But still devastating, as fuel rod material was still exposed to the atmosphere. SBHarris 18:03, 7 August 2011 (UTC)

I feel the definition is incomplete.

I feel this definition is incomplete: "A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating series of these reactions. "

It should state that this must happen with low enough variance for the chain reaction not to stop: the average is not necessarily enough. I don't know what the precise physical requirements are, however.

This is a nuanced critique that would mainly concern a VERY short period of time during which the (above, imprecise) definition for a chain reaction could be met and unmet several times, before finally it is met with 'n' high enough that the average is never wiped out by the variance, and it does not stop.

Given the nature of the article, I feel the definition should be precise. --80.99.254.208 (talk) 18:39, 14 May 2012 (UTC)

If you know avogadros number (and typical rates of spontaneous decay in a realistic lump of fuel) then I think the onus is on you to first demonstrate that the variance is ever actually relevant. Have you tried calculating how short that time period of concern is yet? Do you have a fuel in mind for which the variance really would be significant? (If so then maybe that could be interesting to eventually note+explain+cite in the article somewhere, but the lead should still stick to the simplified core idea IMO.) Cesiumfrog (talk) 23:08, 14 May 2012 (UTC)

In my opinion, it doesn't matter if it's ever actually relevant. It's that the definition of a 'chain reactin' should never be met and then unmet and then met again - however briefly - before a chain reaction actually occurs. Otherwise, what good is a definition? --80.99.254.208 (talk) 08:34, 15 May 2012 (UTC)

Uncontrollable

"The article says a few neutrons (the exact number depends on uncontrollable and unmeasurable factors." What are these factors? Is there a citation? TheDrD1ng3r (talk) 01:43, 23 June 2021 (UTC)

Enriched by laser

"A laser is then used to enrich the hexafluoride compound." What is this supposed to mean? The gas is enriched my the centrifuge. I don't think it involves a laser TheDrD1ng3r (talk) 01:51, 23 June 2021 (UTC)

External Links are Broken or Non-functioning

The External Links don't appear to link to what they represent. Suggest complete removal

• Nuclear Chain Reaction Animation
• Annotated bibliography on nuclear chain reactions from the Alsos Digital Library
• Stochastic Java simulation of nuclear chain reaction Archived 2011-06-11 at the Wayback Machine by Wolfgang Bauer

MoonProjections (talk) 17:26, 11 September 2023 (UTC)