Talk:Nuclear meltdown

Windscale

In a similar vein, I recollect that Windscale was in fact a graphite fire caused by the build-up of Wigner energy in the graphite lattice. It was not related directly to decay heating levels. It was essentially chemical, but with an 'enhanced heat of combustion' Linuxlad 09:44, 25 Mar 2005 (UTC)

In the Windscale fire, the core certainly got too hot and melted; that's what a meltdown is. But you're right that some of the heat came from Wigner energy; once the pile got hot enough, it began to burn in air as well, releasing more heat. The reactor also remained critical, releasing yet more heat. So the incident was not a loss of coolant incident; in fact the coolant was air, of which there was too much. Perhaps they couldn't turn off the air for fear of the reactor overheating due to nuclear reactions; it's hard to say. But in any case, all this is irrelevant. All a nuclear meltdown is is an incident where the core melts.

I think the reason people are uncomfortable with this definition is that we have an idea that a nuclear meltdown is somehow the worst possible kind of disaster that can happen in a nuclear power plant, with severe long-term results. That's just not the case. What happened at Chernobyl and Windscale was worse than a simple meltdown; what happened at Goania was also worse (much worse than Windscale or Three Mile Island) but it had nothing at all to due with nuclear chain reactions, let alone a meltdown. A nuclear meltdown is a specific kind of accident, with the possibility to be very bad (by melting down to the water table and causing a steam explosion, say). There's a whole spectrum of other possible accidents that have the possibility to be very bad also. Some of them have a meltdown as a probable side effect. --Andrew 19:52, Mar 25, 2005 (UTC)

I'm not too sure you've got all your detail right there (but then the event happened when I was ten, I recollect). But I don't think the pile was critical or that nuclear heating played a significant role. The Wigner energy built up to very high levels because the graphite was normally too cool for the graphite defects to anneal out. The article here is written from the aspect of loss of adequate cooling for the nuclear-decay heat level - this wasn't really that - it was enhanced chemistry.

Of course, the melting is pretty irrelevant and a result of the article having started out with a PWR bias.

I am by no means an expert, but I have done some reading on this particular issue; perhaps we should discuss it at Talk:Windscale fire? Anything we decide there can of course be used to improve this article.

I agree that the melting hardly mattered in the Windscale incident. In general, a meltdown may be only an insignificant part of a real accident, especially if th e reactor is designed to contain it (as the Chernobyl reactor was). The other things that go wrong about the same time are often much worse. But for some reason, perhaps by the China syndrome and the publicity around Three Mile Island, "nuclear meltdown" has a magical weight in people's minds that is not matched by "steam explosion" or "fire", even though those have been the real problems in the Big Accidents. --Andrew 22:17, Mar 25, 2005 (UTC)

numerous clarifications and corrections

I was in grad school when TMI-2 occurred and on the job when Chernobyl-4 burned. I'm expert on BWRs and PWRs but not the older British reactors. I've tried to clarify the difference between reactor vessel and containment structure. Also, TMI was far more of a meltdown than was originally thought - once they removed the melted fuel, they found that the melt had cracked the RV's stainless steel liner but not attacked the base metal (this was unexpected and, so far, unexplained, but meltdowns don't penetrate RVs - Chernobyl's concrete RV failed due to the explosion, not the melt). The RBMKs have since been modified and de-rated (and, hopefully very soon, closed). Simesa 01:40, 26 Jun 2005 (UTC)

WASH-1400

There are still a few LWR-isms in it from a UK perspective, but probably near enough for most readers... Note again that 'meltdown to China' is NOT the worst accident, radiologically. 'Alpha-mode' (fci-induced) or HPME-induced containment failures would be much worse.

NB the melt just wandering down to the water table would be unlikely to be that dangerous. A fairly coherent in-core melt release together with efficient generation of a missile (usually from the top head) is necessary to fail a modern 'large,dry' containment (IIRC).

Later - I have added a stub for WASH-1400, Rasmussen's original 'Reactor Safety Study' for USNRC.

Technical

I added the technical template because the article (especially the Causes section) seems to assume a high degree of familiarity with the material. Perhaps the context template would be more appropriate. Either way, it calls attention to a problem. I am fairly familiar with the basics, but I find myself stopping after every sentence and trying to backtrack and see how it fits in with what's already been said. Example: "Borated water is injected by the emergency systems and thus in the large-break accidents, control rod insertion is not needed to stop the fission reaction." What is "control rod insertion"? It is discussed in the Nuclear reactor article, but if this article is about the failure of the system, it could at least overview the measures that have to fail. Even if it's ABCs to nuclear reactor buffs, there ought to be some explanation for the unwashed masses. On the other hand, I can be lazy in my research, but I don't think excessive clarity can ever be a drawback. icydid 02:05, August 23, 2005 (UTC)

Original research of core meltdown definition

Referring to edit, a unsourced catchall definition of core meltdown is stated. The definition is illogical, per definition of nuclear reactor core "the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place". If I say engine meltdown it means a damage occurred of at least some portion of the engine and not simply of what is contained in the engine. The contested definition seeks instead to extend the meaning to what ever event happens in the core. A reputable source (Encyclopædia Britannica) of English language core meltdown meaning writes of core melt and not simply of that of a single fuel element. Robertiki (talk) 11:57, 7 March 2025 (UTC)

@Robertiki:You wrote that a core meltdown is a result of an "uncontrolled chain reaction". That is not true, see Fukushima nuclear accident. I fixed that mistake. I did not change your text about a single fuel element vs. core. Please undo your revert. --TuomoS (talk) 12:54, 7 March 2025 (UTC)

Done. --Robertiki (talk) 16:18, 7 March 2025 (UTC)

We should go by what ACADEMIC sources define as a "core meltdown", not what you or I think it is (per Wikipedia's policy on WP:NOR. ---Avatar317^(talk) 01:18, 8 March 2025 (UTC)

Two questions:

1) why should academic sources have priority about an industrial and safety issue ?

2) have you links about academic sources giving a rational core meltdown definition ?

--Robertiki (talk) 12:09, 9 March 2025 (UTC)