Talk:Nuclear meltdown

message: The article currently states
"Fast breeder reactors are more susceptible to meltdown than other reactor types, due to the larger quantity of fissile material and the higher neutron flux inside the reactor core, which makes it more difficult to control the reaction. In addition, the liquid sodium coolant is highly corrosive and very difficult to manage."
This is outright wrong. 
Firstly, sodium is highly reactive and flamabble, but not corrosive to steel, zirconium, nor the fuel forms suggested for such a reactor (metallic U-Pu-Zr alloys or some ceramic fuel forms). In particular, sodium's extremely low reactivity with steel is generally considered a large advantage in favour of water cooled reactors. The use of liquid metal rather than pressurised water also means the reactor doesn't need to be pressurised, dramatically lowering the risk of a loss of coolant accident, and also allows it to rely on natural convection for cooling giving a high degree of passive safety. Furthermore, due to the neutronic properties of sodium sodium cooled reactors can be built with highly negative temperature coefficients, causing the chain reaction to cease well bellow temperatures that would damage the reactor.   
Secondly, the larger quantity of fissile material is largely irrelevant, most reactors contain enough of it to sustain their reaction for years, and typically the limit of the reactor's energy production is down to other factors. The larger enrichment level might be an issue as it means the fuel has a higher power density, but this has less of an impact than the fuel form. Metallic fuels operate at much lower temperature than ceramic ones due to the greatly increased heat conductivity, as an example. Regardless, it is the power density and enrichment level that is relevant, not teh total quantity of fissile material.
Thirdly, whereas sodium is one of the best developed coolants for fast breeder reactors, it is far from the only one possible. Lead, Lead_Bismuth alloys, Molten salts and Helium have all been suggested (Interestingly, lead is far more corrosive than sodium, yet meltdown is less likely due to the higher boiling temperature ).
Finally, the risk of a nuclear meltdown is much more a matter of design and safety regulations than it is one of reactor type. As an example, the CANDU and RBMK reactors share some features, but because the RBMK has several serious design flaws it is generally very unstable and dangerous, meanwhile the CANDU reactors are among the safest nuclear powerplants ever built. Similarly, liquid metal cooled fast reactors are probably the least likely to undergo a loss of coolant accident ( and consequentially a meltdown ), whereas it is difficult to ensure sufficient cooling under low pressure conditions for gas cooled fast breeders. 213.55.27.154 19:46, 2 March 2007 (UTC)
thread_title: Error on Fast breeder reactors

message: 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)
thread_title: numerous clarifications and corrections

message: I've significantly updated the leading paragraphs and the causes section.  Additionally I am going to have to create a couple of new articles on reactor containment (which is a superset of the containment structure article), loss of pressure control accident, uncontrolled power excursion or reactivity addition accident, and reactivity_(nuclear).  Being a person who previously worked as a reactor operator, I may not always realize when certain parts are too technical, so I apologize beforehand.  If any of the correct articles exist (or if you want to create them before I do) feel free to do so.--Burzum 07:10, 9 July 2006 (UTC)
thread_title:  Burzum's Changes 

message: For the benefit of User:Power2084 who refuses to participate in a discussion:
A molten core mass may well melt or burn anything below it. However, as it does so, the mass becomes diluted and eventually non-critical. For the mass to melt down much farther than the containment structure, it would need to remain in a critical state, and to do so, it needs to remain in a compact form, kinda like it is in the reactor but without anything to hold it together in such a form. This is exceedingly unlikely; I'm not a scientist but I'm pretty sure the Second law of thermodynamics backs me up here. Saying this could happen "in theory" grossly overstates the case. We could just as well say that the sun, in theory, might not rise tomorrow.
The "China Syndrome" is a proverbial term; no one seriously believes a meltdown will burn through all the way to China, or even through a significant portion of the Earth's crust. A number of editors have called you on this, and the burden is now on you to find a legitimate scientific source for your claims. Simishag (talk) 01:20, 6 March 2008 (UTC)
replies: text: We should note that at Three Mile Island, the core did not breach the pressure vessel, and at Chernobyl the core only made it to the basement.  It is not credible that the core could melt through several miles of the earth's crust.  Paul Studier (talk) 02:53, 6 March 2008 (UTC)
thread_title: Meltdown "theories"

message: Article says: "Although pressurized water reactors are more susceptible to nuclear meltdown in the absence of active safety measures, this is not a universal feature of civilian nuclear reactors."  Every time I think about some worldwide disaster making it unlikely nuclear power plants would have any outside power sources for 3-6 months or more, I assume some percentage of them are going to melt down.  Given the possibility of big EMPs over the US (or else where like Iran or Pakistan or Israel), small nuclear wars, asteroid attacks, nasty viruses that kill off too many power plant engineers, etc. a) how long can the reactors described above last; b) how long can reactors that don't have these precautions last.  
I think this would be very informative for general public and media people, plus history channel and scifi writers who might look type in nuclear meltdown on google and end up here, of course!  I don't know enough about it except what I learned 30 years ago as an anti-nuke activist, which may be a bit outdated and inaccurate.  So reliable info in its own section would be great. Carol Moore 17:42, 25 August 2008 (UTC)
replies: text: From Decay heat at the moment of reactor shutdown, decay heat will be about 6.5% of the previous core power if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1% of the previous core power.  It would seem to me that a couple days of cooling would be enough, after which passive cooling would be enough to prevent disaster.  Any actual nuclear engineers here?  Paul Studier (talk) 05:25, 28 August 2008 (UTC)
replies: text: It's been awhile for me (although with the recent resurgence I'm looking to get back into the industry, at which time I'd have to stop editing Wikipedia).  In the first few seconds after the SCRAM button is pushed, 99.3% of the reaction stops - what's left comes from the 0.7% of "delayed" neutrons (the heat content of the fuel rods still has to be cooled).  You then get a logarithmic decrease in power generation over time, reaching "cold shutdown" in just hours.  A "Reactor Engineer" would have the decay heat curves you want to consult.  A new industry tool is at ; look at the very last graphic to see how heat generation occurs over time.  We should note that GE says you can walk away from an ESBWR for at least three full days without a meltdown occurring.  Simesa (talk) 09:32, 28 August 2008 (UTC)
replies: text: If the scenario is an EMP pulse that blows out electronics it's anyones guess whether "scram" functions will work properly. As for a scenario that involves the total disappearance of active management, there is a relevant, though not authoritative, discussion on an engineering forum here: "Aftermath: Population Zero" view of unattended nuke plants. In these discussions I don't see anything about the saturation of control rods and moderators, or the long term effects of corrosion on containment structures. Even a properly shut-down reactor may begin to have trouble after a few years or centuries. Aside from the reactor core, the National Geographic documentary apparently asserts that cooling ponds would boil off after a week without outside power to maintain circulation. As for the article, I'm not sure there are enough solid sources on this topic to add anything.  ·:· Will Beback  ·:· 09:57, 28 August 2008 (UTC)

text: Where this is relevant and probably sourceable is in regard to Nth-generation power designs that have walk-away capabilities, like some pebble bed designs, etc. with passive safety.  ·:· Will Beback  ·:· 10:10, 28 August 2008 (UTC)
replies: text: SCRAM occurs when a system is either grounded or at zero power, so if the system is "blown out" you'll still get a scram.  The control rods won't saturate because with the chain reaction stopped there won't be a significant number of neutrons flying around.  The actual containment structure is inside the missile shield (several feet of concrete), which shields it from the weather - in any event, with the reactor at atmospheric rather than operating pressure (15 psi vs. 1000 psi BWRs, 2000 psi PWRs) there's much less of a challenge.  I'll have to give you that the current generation of plants was not designed to be neglect-tolerant - perhaps SSTAR would be more appropriate for nations with regime instability.  Note: "walking away" for a couple of days applies only to the ESBWR, under most (but not one) cases the AP1000, and the PBMR (I haven't seen a claim for the EPR) - in the event of an unusual occurrence, the normal situation is that engineers rush TO the plant. Simesa (talk) 18:27, 28 August 2008 (UTC)
thread_title: Section on fate of reactors without outside power?

message: In reference to some of the recent discussions above, it has become obvious that the nuclear meltdown article has too narrow a focus to cover all of the issues involved with nuclear reactor accidents.  This isn't a problem with this article, but many topics involved with reactor accidents need a more thorough description (for example, coolant-cladding interactions, environmental effects, and what constitutes core damage among others).  To resolve this, I propose that we:
* create a reactor accident article to focus on the specific issues involved with reactor accidents,
* narrow the focus on the nuclear meltdown article to the public, press, and activist perception of what a meltdown entails while noting that a 'nuclear meltdown' is not a nuclear engineering term,
* discuss 'very severe' reactor accidents (the focus of the nuclear meltdown article) as well as the less severe accidents, and
* separate out the reactor accident sections from the nuclear accident and nuclear meltdown articles.
This will present a nice hierarchal order which I think will be easier to update, maintain, and expand.--Burzum (talk) 12:17, 9 September 2008 (UTC)
replies: text: I certainly agree - "nuclear meltdown" is a term that has no definition - not even found in IAEA manuals - and only has a colloquial meaning to refer to a superset of incidents known as core damage incidents that includes - but is not limited to - fuel melt incidents. I would suggest "Nuclear reactor accident" for the title of the article. Katana0182 (talk) 05:46, 22 August 2009 (UTC)
thread_title:  Reactor Accident Article 

message: In the paragraph that reads:
By design, the geometry and composition of the reactor core do not permit the extraordinary conditions necessary for explosively prompt criticality. However, conditions that can cause a meltdown can also cause a steam explosion, which can cause the core to be thrown over a wide area if the reactor is not within a containment building. All Western nuclear reactors are within containment buildings. Each containment building consists of 1.2 to 2.4 meters of steel-reinforced, pre-stressed, airtight concrete, capable of withstanding tornadoes of OF6 scale (320+ mph winds) and seismic accelerations of at least 2 m/s.
the final 2 m/s is wrong.  Either replace acceleration with speed or replace m/s with m/s^2.  —Preceding unsigned comment added by 24.78.96.84 (talk) 05:45, 28 October 2009 (UTC)
thread_title:  Wrong Units 

message: When reading through this article, I noticed that the exact phrase '1.2 to 2.4 metres (3.9 to 7.9 ft) of pre-stressed, steel-reinforced, air-tight concrete' occurs at least four times throughout this article, and a slightly different permutation of the phrase occurs in at least one other place. This doesn't serve to give any new information, it just gets repetitive and is a blatant copy/paste from somewhere else in the article, or possibly from an outside source. I suggest that the article be rewritten to remove this repetition. Arathald (talk) 06:40, 3 June 2010 (UTC)
thread_title:  Repetition of Description of Western Reactor Containment Structure 

message: this line apears way to often. could someone plaes shorten this by just saying the containment wall?
it's enugh to just once mention that this wal is pre-stressed, steel-reinforced, air-tight concrete between 1.2 to 2.4 metres (3.9 to 7.9 ft) thick.
makes the article bad to read.
greats
an anonymosus idiot  —Preceding unsigned comment added by 131.234.240.105 (talk) 23:37, 7 June 2010 (UTC)
replies: text: WP:SOFIXIT. There's nothing wrong with this article that a few hours with the editorial Weed Whacker can't fix. My goodness, whoever wrote this loves to talk and doesn't have a footnote to save his soul. First we boil this down to the nubbin, then we can build it up again if more detail is necessary.  We don't need to know that the Binford Model 6100 reactor had the frammis valve on the left side of the dingus hatch, but the later MOdel 6100a had dual redundant frammis valves and power seats. --Wtshymanski (talk) 16:02, 18 November 2010 (UTC)
thread_title:  pre-stressed, steel-reinforced, air-tight concrete between 1.2 to 2.4 metres (3.9 to 7.9 ft) thick,  

message: 5000 dead destruction of the city?
I think this is a wrape.
94.196.91.160 (talk) 18:42, 20 January 2011 (UTC)
replies: text: Obviously vandalism, I reverted it. Paul Studier (talk) 18:54, 20 January 2011 (UTC)
thread_title: First paragraph. Nuclear accident in Missouri?

message: although there have been so few meltdowns in the history of nuclear power that there is not a large pool of statistical information from which to draw a credible conclusion as to what "often" happens in such circumstances
An N of about 10 (counting the list in the very next section of the article) isn't great for drawing scientific conclusions, but it's better than nothing for this purpose.  "Often" is not a statistical indicator, though, so this current wording is a bit contentious.  It sounds as if the author wants a bigger data set (no thanks!) or has an ideological axe to grind about the safety of nuclear power.  If the author wants to go there, they should take that small N and divide it out over the years.  Things have been very safe for a couple decades, but starting the count in 1945 we're still averaging some level (if you believe in "partials") of meltdown on the planet about every 7.5 years.  Not exactly a puppies-and-rainbows situation.  97.81.81.105 (talk) 17:34, 13 March 2011 (UTC)
thread_title:  Statistical Sample 

message: Maybe its obvious but i find hardly any information on this and i would
expect that a meltdown article should answer it:
If a reactor core melts, can it become critical again? On one hand, for example
in Boiling water reactors, in the molten core we are missing a moderator, so
electrons won't be slowed and we would expect a lower neutron multiplication
factor, on the other hand if the rods melt we are loosing the space
in between them too, which increases the density and this should increase the
neutron multiplication factor.
So does the neutron multiplication factor increases or decrease if a core melts
and as a result of this can the core become critical again?  —Preceding unsigned comment added by 77.11.139.103 (talk) 10:35, 19 March 2011 (UTC)
thread_title:  Recriticality 

message: Fukushima seems strangly absent given that TEPCO (and even one sentence in the article) mentions the high probability of a complete meltdown in units 1-3. TEPCO is estimating based on water loss that there are holes not only in the RPV but also the drywell containment, TEPCO believes only water injection prevented worse containment failure. At least in unit2, there are indications of continued criticality, and detection of iodine in spent fuel pools which should not be there if fission has stopped. I have heard that compared to Chernobyl where most fissile material blew away, the tons of fuel rod material are still in one place and need to be cooled indefinitely without a way to isolate radioactive cooling water. What would happen if cooling efforts were to stop, or if earthquake causes building to collapse? Redhanker (talk) 21:58, 28 May 2011 (UTC)
replies: text: It's covered briefly at the end. Nuclear_meltdown#Japan. It's covered more extensively at Fukushima Daiichi nuclear disaster, in various sections. Unfortunately, much of what is known, even from official sources, is just speculation. It may take a several years before all the facts are known.   Will Beback  talk   22:20, 28 May 2011 (UTC)
thread_title:  Fukushima 

message: Appearantly, there are few robots that have been developed especially for use in areas with nuclear radiation. This one : http://spectrum.ieee.org/automaton/robotics/industrial-robots/giant-robotic-jumping-spider-giant-robotic-jumping-spider seems to be one of those robots, they're disposable.
91.182.72.118 (talk) 12:43, 22 January 2012 (UTC)
thread_title: Monitoring robots

message: Perhaps a nit but the sentences:
:"A meltdown is considered very serious because of the potential, however remote, that radioactive materials with long half-lives could breach all containment and escape (or be released) into the environment, resulting in radioactive contamination and fallout, and leading to radiation poisoning of people and animals nearby. The amount of radioactivity released into the environment due to a core melt is measured in becquerels or curies."
are odd in the following:
It's the short half-life materials (like iodine-131, half-life of 8 days) and the medium half-life materials (like cesium 137, or potassium 40, both at about 30 years) that are the most dangerous; while they decay fast, they are also the highest in radiation intensity, mole for mole. The long half-life materials, like the remaining uranium fuel, will be around a long time, but have much lower intensity. This is true even when factoring in the biological activity of the materials; in fact, uranium is more a problem for its chemical properties than for its nuclear.
As for the last sentence, it is an irrelevance; the subject of the article is meltdown, not actually release.  Stating the units of measurement doesn't seem appropriate to me.
I propose to drop the phrase about half-lives and the entire last sentence. SkoreKeep (talk) 16:20, 20 October 2012 (UTC)
replies: text: I agree; that was a good change. Especially to get rid of the non sequitur "is measured in" stuff that doesn't belong there. L8R! — UncleBubba ( T @ C ) 05:22, 21 October 2012 (UTC)
thread_title: "Long half lives" nitpick

message: I check pages listed in :Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of :Nuclear meltdown's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.
Reference named "google1":
From Uranium hydride: 
From Corium (nuclear reactor): 
I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT⚡ 05:27, 1 September 2013 (UTC)
thread_title:  Orphaned references in [[:Nuclear meltdown]] 

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thread_title:  Blacklisted Links Found on the Main Page 

message: The text uses both. --User:Haraldmmueller 16:43, 2 February 2017 (UTC)
thread_title:  molten or melted?