Talk:Nuclear reactor physics

New page from nuclear fission
I just entered all of this material into nuclear fission as part of an overhaul of that article, then realized that there was enough material here to (A) bloat that article and (B) form a nicely-sized overview of reactor physics. While most of this material is covered in some measure in other articles such as nuclear reactor, uranium, plutonium, critical mass, delayed neutron, chernobyl accident, and oklo, there was and remains a need to see it all grouped into a single accessible place as an overview of reactor physics. So, er, here it is. zowie 21:33, 17 November 2005 (UTC)

element style
Isn't it wikipedia style to write U-235, rather than 235U? It makes for more intuitive linking, since the article is at Uranium-235. Night Gyr 22:02, 19 April 2006 (UTC)

Wow! No response for over a year. 235U is the nomenclature that nuclear physicists normally use. U-235 has the same meaning, but isn't as good when it comes to writing nuclear reaction equations such as: 235U + 1n -> (236U)* -> FF's + n's + energy What is Wikipedia style? User: TodKarlson 6/11/07


 * I don't know of a Wikipedia style for this, and it's probably not worth either of our time searching for one. I'd say the best solution is to use your best judgment.  In my edits, I've used the Uranium-235 style because it's quicker to type, but I would definitely use the superscripts in anything that is borderline an equation. -Theanphibian (talk • contribs) 04:50, 13 June 2007 (UTC)


 * I've used both, as both are used in the real world and readers should be exposed to both. Beware of ambiguity, I-129 is a freeway, and U-234 is a submarine. --JWB 07:14, 13 June 2007 (UTC)


 * That's pretty cool; I never heard about the U-234 before, and I agree with the previous point that people should be aware of all the various nomenclature that one might come across. I've also seen "92U235" used because on a computer it's difficult to precede the "U" with BOTH "92" and "235", the way you would if you were hand-writing a nuclear reaction equation.  While I was in the Navy we also used "U235".

heat-production decay curve
The 9.0 earthquake in Japan has just occurred. 3 nuclear reactors are having cooling problems, even though their control rods have presumably been used to bring the fission reaction to a complete halt. We are now hoping the heating rate diminishes before the temperature reaches a point that would cause meltdown. I'd like to understand what a disaster-mode cooling system should be designed to handle. The public should understand too, for nuclear policy decisions. So, can anybody contribute an estimated plot of typical heat-output decay curve after a scram from nominal 100% power? and explain which isotope's half-life sets the rate of the relevant parts of the power decay which we are waiting for now (2 days after scram) ? I realize that there is some delayed neutron emission, and multiplication of it, and heat from radioactively decaying products of prior fission. But I don't see how delayed neutrons can explain days of after-run heating. I also realize these reactors in Japan are Plutonium-based, not U-235-based. There may be different after-run explanations for each type. jimswen (talk) 09:43, 14 March 2011 (UTC)


 * I notice no more discussion on this one. As well as I know, and confirmed by an expert, there was plenty of time to bring in a diesel generator from somewhere else, to run the pumps, yet this wasn't done.  Gah4 (talk) 22:57, 10 November 2016 (UTC)
 * Otherwise, for the actual question, many fission products are radioactive with different half lives. I don't know of a table specific for what you ask, though. The fission product yields, what fraction goes to what nuclide, are pretty well known. Gah4 (talk) 22:57, 10 November 2016 (UTC)


 * There is a graph in decay heat. Gah4 (talk) 23:37, 10 November 2016 (UTC)

Assessment comment - July 2008
Substituted at 01:35, 30 April 2016 (UTC)

Likely or not?
This is because 235U is much more likely to undergo fission when struck by one of these thermal neutrons than by a freshly produced neutron from fission. While U-235 does have a larger fission cross section, as well as I know the branching ratio after absorbing the neutron is about the same. It is mostly the absorption of fast neutrons by U238 that is reduced with a moderator. Gah4 (talk) 20:05, 3 October 2016 (UTC)

Axial flux difference - where
Is this article (or maybe PWR) the best place to cover 'axial flux difference' - a factor in core design and operation ? - Rod57 (talk) 13:30, 30 May 2019 (UTC)


 * Might be worth trying out a section here, and move it to PWR if it fits better there. This article started out more about the basic physics and axial flux variation "smells" more like an engineering thing -- but the line is blurry and it could well fit here.  Zowie (talk) 19:53, 30 May 2019 (UTC)


 * Also, there isn't much about mean free path, which would also seem important, and I suspect goes along with flux differences. Also, that might make it more physics and less engineering. Gah4 (talk) 19:57, 30 May 2019 (UTC)