Talk:Criticality accident/Archive 1

Archive 1

Replaced the introduction:

A criticality accident is when nuclear fission is unexpectedly and accidentally triggered. The term refers to the achievement of criticality in fissile material, such as uranium, plutonium, or thorium, which releases an often fatal amount of beta radiation (neutrons).

There are a number of things wrong here. For a start, it's not just any fission reaction. It must be a chain reaction, otherwise it's neither a criticality nor likely to be dangerous. Fission is happening all the time, spontaneous fission of Pu-241 for example is the main problem in trying to make weapons from low grade plutonium. For another, thorium is neither fissile nor capable of criticality. Thirdly, I see there's already been a dispute (but no discussion here) on whether beta radiation is a problem in this context. It's not, the problem is the neutrons. They are not the same thing.

I've flagged the article as disputed because there are a number of equally suspect claims throughout the article and they'll take a while to check. Rather than stubify the whole thing, I've left this material in for the moment, but it means the article now has a good introduction followed by some very shaky stuff! Andrewa 03:48, 25 Oct 2004 (UTC)

• Your point on the chain reaction is well-taken -- I misclarified. I had thought that thorium-232 is fissile but now that I look into a bit more it seems that it is just fertile. And I seem to have gotten mixed-up about beta radiation, for some reason I think was thinking of it being neutrons but again, I see that's not the case. Ugh, I occasionally get slightly turned around on such things, it is embarassing. Nevertheless, the historical aspects ought to be just fine, for whatever that's worth; that's more my area than the physics. --Fastfission 20:32, 25 Oct 2004 (UTC)

Fair enough, on that basis I've removed the dispute notice. Andrewa 00:33, 26 Oct 2004 (UTC)

A probable error.

Harry K. Daghlian, Jr. is listed in this article as having died after a mistake in an experiment involving using two hemispheres of plutonium; on his own article, in Lists of Nuclear Accidents. and in Tungsten Carbide, he is listed as having dropped a brick of tungsten carbide onto a subcritical mass of plutonium at Los Alamos while doing research into using neutron reflectors to reduce the mass necessary to attain criticality.

As I do not yet feel myself competent to make the change personally, I simply put this forth for someone more experienced to consider.

You are right. Edit away!--Deglr6328 02:44, 16 August 2005 (UTC)

It is done. Swuboo 05:59, August 16, 2005 (UTC)

Cool. see? 'twas easy! :) --Deglr6328 06:14, 16 August 2005 (UTC)

Einstein was wrong? "Charged particles travelling faster than the speed of light

I allways heard that the speed of light was an absloute limit, however this article indicates Cherenkov radiation is produced by charged partickles traveling faster than the speed of light.

"However, this is merely a coincidence. Cherenkov radiation is produced by charged particles travelling faster than the speed of light in a medium other than a vacuum. The only charged particle radiation types produced in the process of a criticality accident (fission reactions) are alpha particles, beta particles, positrons (which all come from the radioactive decay of unstable daughter products of the fission reaction) and energetic ions"

http://en.wikipedia.org/wiki/Criticality_accident

• Take a look at the linked article on Cherenkov radiation. You can go faster than the speed of light when the light is slowed down, i.e. is in a medium. Einstein's rule about the speed of light is when it is in a vacuum. --Fastfission 18:03, 2 September 2005 (UTC)

Some rewording might make things more clear

Maybe it would be better to reword this as:

Cherenkov radiation is produced by charged particles travelling faster than the propagation speed of light in a medium (which is slower than the normal speed of light when the medium is not a vacuum).

By adding the word propagation, you're illustrating that the light isn't so much traveling through the medium, but being absorbed and re-radiated from atom to atom through the medium. And this, as far as I understand it, is what "slows" the light down.

— Ke6jjj 23:02, 11 November 2005 (UTC)

Criticality monitors

THese should be mentioned, but I have no up to date info.--Light current 23:42, 11 September 2006 (UTC)

Godiva device

The article features a pic of a 'Godiva device', but it's not mentioned anywhere in the body or the list of accidents at the bottom. I'd love to know what the story about this device was. -- MiG 23:03, 10 December 2006 (UTC)

I've just created an article on the Godiva device. -- MightyWarrior 23:51, 22 February 2007 (UTC)

SL-1?

Should the SL-1 incident be included here? That criticality accident occurred when the reactor's single control rod was withdrawn too far as the result of an improperly-conducted maintenance procedure.

Atlant 16:19, 4 May 2007 (UTC)

image used in article

Hello, I have made a comment on the critical mass page referring to this as well. The image used here is part of an experimental device used to produce pulses of neutrons-the operator failed to use the instrument correctly. Isn't this less of an accident than perhaps the Louis Slotin incident? shouldn't that be a better image to use-at one stage I thought it was????--Read-write-services 23:52, 7 October 2007 (UTC)

Cherenkov radiation overexplained outside of the scope of the article?

Somehow I feel that the article has got really deep into analyzing Cherenkov radiation in some point.

No need to such lenghthy explanation to why "Blue glow is wrongly linked to Cherenkov radiation". A simple reference and an internal link would suffice.

Maybe the explanation would fit better at Cherenkov radiation's main article. Makrisj (talk) 02:19, 24 December 2007 (UTC)

Godiva Question

I've read a bit about Lady Godiva and Godiva II, and find the pictures really interesting.

I know that Lady Godiva was damaged during the criticality event, but what actually caused the damage to the device? Did the reaction produce heat which bent the rods, or was there something else taking place?

Thanks in advance for any info.

150.134.120.220 (talk) 16:54, 26 February 2008 (UTC)

Even though most of the fission energy becomes heat, a small fraction becomes kinetic energy. Page 80 of the LA reference has the following paragraph.

“ The fission yield of 1.2 × 10^17 in the second

accident is equivalent to the energy contained in 1.7 lb of high explosive (HE), but the damage was much less than would have been caused by that quantity of HE. The above mentioned code can predict the fraction of fission energy converted to kinetic energy; in this case, only about 1.4% of the energy, equivalent to 0.024 pounds of HE, was available as kinetic energy to do damage. The damage was consistent with this figure, and it is evident that most of the fission energy was deposited as heat.

”

For example, heating of the uranium mass would cause its rapid expansion which pushes the upper and lower rods apart (with a force of a 'mere' 0.024 pounds of high explosive, or 45000 Joule). That's roughly the kinetic energy of a 200 kg motorbike at 76 kilometres per hour (47 miles per hour). -Wikianon (talk) 20:47, 26 February 2008 (UTC)

Mayak incident

This section should be rewritten, since some of the sentences are swiped from the Darwin Award site, with some of the words changed. —Preceding unsigned comment added by 168.156.70.30 (talk) 16:55, 19 May 2008 (UTC)

Problems, questions

The summary of criticality accidents from the Los Alamos report should be placed here. That report details many dozens of accidents; by contrast, this article would lead one to believe that there are relatively few. Its rather morbid, gruesome reading, but compelling.

The Los Alamos report uses a number of terms I don't understand, and would like to have defined: "prompt critical" "delayed critical", "superprompt", etc.

A recurring theme from that report is "favorable geometry" (which I do know how to define); this article should describe this, as it is an important aspect of many/most of the accidents.

Not at all clear to me why this article spends so much time discussing the "blue light"; this seems to be a minor point. linas 07:11, 22 March 2006 (UTC)

It spends so much time on the 'blue light' because people were constantly, CONSTANTLY coming along and mislabelling it as cherenkov radiation. I got tired of reverting it so I put in this exhaustive explanation which I must say seems to have worked as I have only had to revert one cherenkov edit since adding it. If the article needs more information (it does) that can simply be added. Though I do NOT think this page needs a list of crit. accidents as many (all?) can already be found on the subpages of this page and even if we did list all these types of accidents separately the list would not belong here but instead on another page. --Deglr6328 09:24, 22 March 2006 (UTC)

The potential for Xrays to be a cause for the blue glow was primarily reasoned from nuclear weapon configurations which rely on Xray emmissions to compress a second stage explosive. It has been mentioned here http://en.wikipedia.org/wiki/Radiation_implosion

That's what the link says, but it may be wrong. From X-ray: "The two types of radiation are now usually defined by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.". Strongly referenced. --Old Moonraker (talk) 10:51, 15 May 2009 (UTC)

Motion Pictures and Television

In Fat Man and Little Boy, the character seems to take much longer than 2 hours to die. It seems to be a matter of some days, if not weeks. 114.30.101.58 (talk) 12:58, 3 October 2010 (UTC)

Agreed. At one hour the doctor is picked up in the jeep, and Merriman does not even have symptoms of a burn. By the time he gets to the hospital, they find a room for him and he is seen by the specialist it appears he is still symptom free as he is smoking and yelling in fear not pain. Then we see days pass as the film shows his condition worsen while the work on the bomb continues. I've removed that portion about the film relating to time. --DizFreak ^{talk Contributions} 22:01, 17 November 2010 (UTC)

Blue glow section

I think the notes about Cherenkov radiation might need to be corrected. While it is true that the blue flash seen in a criticality accident is not caused by Cherenkov radiation in the air, and it is also true that the gamma radiation causes ionization of the air which by coincidence also causes a blue glow--I have read descriptions of criticality accidents (and also Apollo astronauts exposed to cosmic rays) that indicates that the blue flash is caused by Cherenkov radiation occurring within the vitreous humor inside the human eye. This isn't my field so I can't speak from experience, but would energetic gamma rays generate a shower of the kind of charged particles which would be able to generate Cherenkov radiation in the vitreous humor? I know, no original research, find a source. Anyway, this would explain why in criticality accidents a blue flash is often seen by people even when their backs are to the accident or those that are in an adjacent rooms. I'll try to find a source but someone with more authority than me might be able to dig something up on google and add to the article more quickly than I can or will.--LookoutforChris (talk) 05:45, 9 June 2010 (UTC)

The blue flash being due to Cherenkov radiation is mentioned in the primary source for this article. "They immediately noticed a flash (due to Cherenkov radiation), and simultaneously, fissile solution was violently ejected, reaching the ceiling about 5 m above." McLaughlin et al. p 26 I guess the guys at Los Alamos National Laboratory don't know what they are talking about. Could someone clean up this bit of misinformation? I don't have time for an edit war right now. 24.72.137.140 (talk) 08:29, 17 March 2011 (UTC)

what is the energy needed to create cherenkov Light in the Eye? as long as there are no reliable sources for one of these phenomena, say only that blue light is seen. — Preceding unsigned comment added by 213.196.231.213 (talk) 03:48, 7 July 2011 (UTC)

Cherenkov radiation energies

The article states that energy needed for Cherenkov radiation in air is 20.3 MeV, and 14B electrons have only 20.6MeV. Surely that would produce the glow? Should not the needed energy in air be 20.3 GeV or something like that? -- Edheldil 9:52, 15 September 2011 (UTC) — Preceding unsigned comment added by 217.31.207.1 (talk)

I spotted that as well and came here to make the same point. But you beat me to it. 109.156.49.202 (talk) 15:01, 3 November 2011 (UTC)

Problem with Heat

This article questions the heat felt by people with a criticality accident occurs. If a nuclear reaction is taking place then of course heat will be produced. Heat is generated in a nuclear bomb and from the sun etc. I don't understand why the article suggestions that it is in the minds of the people witnessing the event. 124.254.78.121 (talk) 05:23, 30 May 2012 (UTC)

But this is no bomb. Heat from stopped fission fragments should have been mostly trapped in the core, which didn't even melt. A few cm of air around the core should have trapped fission fragments from the surface. Do you think people that far away would have felt heat from a ball of metal that size, even if it were glowing red-hot? Probably not-- there's just not enough radiating surface area. And a "wave" of such heat is doubly unlikely. Once red hot, that much metal would takes some time to cool to less than that. Normal thermal cooling events for masses like this (6.2 kg of metal, with a very small surface area) don't happen on that time scale, by natural convection cooling, or by radiative cooling. The physics is just wrong.

More likely that the people actually felt some nerve firing from the blast of neutrons hitting them and ionizing things in the skin, and reported it as "heat" (or "temperature increase"). SBHarris 21:58, 30 May 2012 (UTC)

"Chernobyl liquidators" remark lacks context

This sentence--which concludes the penultimate paragraph of the "blue glow" subsection--cannot possibly be understood based only on the portion of the article preceding it:

It would be also interesting to remark that the ozone smell was said to be a sign of high radioactivity field through Chernobyl liquidators.

No previous mention of ozone nor Chernobyl. Is the phrase "Chernobyl liquidators" familiar to most readers? If not, then its first appearance ought to link to the relevant article.drone5 (talk) 07:22, 14 April 2011 (UTC)

See Liquidator (Chernobyl). --beefyt (talk) 04:35, 25 March 2013 (UTC)

Explosion error – Fukushima and Chernobyl

From Chernobyl entry: A second, more powerful explosion occurred about two or three seconds after the first; evidence indicates that the second explosion resulted from a nuclear excursion.[21]

From this entry: In the history of atomic power development, fewer than a dozen criticality accidents have occurred in collections of fissile materials outside nuclear reactors, but most of these have resulted in death, by radiation exposure, of the nearest person(s) to the event. However, none have resulted in explosions.

Somebody is wrong about criticality (nuclear excursions) causing explosions. —Preceding unsigned comment added by 71.184.150.132 (talk) 04:55, 16 March 2011 (UTC)

I invented a neologism "moderated nuclear explosion" some three years ago, describing these events and WP:SYNTHesized an article to include stuff like uranium hydride bomb. The article was promptly deleted as WP:OR. (The deleted article can be found here: User:Petri Krohn/moderated.)

Looking at the pictures of Fukushima Dai-ichi reactor number 4 today, it seems that what happened at Chernobyl has happened again – if in a smaller scale. There is no question, that an explosion occurred. The mechanism cannot be explained as a steam explosion, as it implies no criticality. A criticality accident – by definiton – implies no explosion. -- Petri Krohn (talk) 21:46, 16 March 2011 (UTC)

The most massive criticality excursion accident, Chernobyl, isn't present in this article!--62.202.134.232 (talk) 12:59, 8 November 2013 (UTC)

Light current and removal of images and information

Hi, regarding your recent removal of informaion on the article I'd like if you could clarify your reasoning for doing so. Firstly, the statement which you removed regarding the Slotin incident:"Immediately realizing what had happened he quickly disassembled the device, likely saving the lives of seven fellow scientists nearby." is not some random speculation. The other scientists recieved very severe doses of radiation due to this criticality (see the slotin article) and if it had not been stopped they would have unquestionably received lethal doses within mere seconds.

Second, the removal of the image of an external beam of high energy charged particles from a cyclotron is a completely plausable model for what an air glow of a criticality accident looks like. It is not likely at all that an actual image of a criticality accident will ever be taken and this is the closest we will probably ever have to knowing what one looks like. The mechanism for the production of ionized air in a criticality accident (mostly via the photoelectric effect and compton scattering due to high energy x-rays and gamma rays is indescernable from the ionization of air in the image produced by irradiation of high energy charged particle radiation. There is no good reason to remove either of these things from the article. --Deglr6328 01:19, 12 September 2006 (UTC)

"Immediately realizing what had happened he quickly disassembled the device, likely saving the lives of seven fellow scientists nearby." is not some random speculation.

THis implies some knowledge by our editors. We do'nt have that knowledge. Im happy for the quote to stay, but not this speculation by some anon editor.

Also the cyclotron pic doesnt actually have anything to do with the page does it (apart from the color being similar to something else.) Again this is speculation about what a criticality might look like and is therefore not fact. It is misleading to include it.--Light current 01:21, 12 September 2006 (UTC)

What if we remove the word "seven"? I think we can say with a fully reasonable degree of certainty that if Slotin received 2100 REM in a criticality of duration of certainly less than ~2s and two other scientists in the room also suffered the effects of severe radiation exposure (Dr. Graves received something like 350-400 REM) then it is obvious and sane to conclude at least a few other men present at the experiment were mere seconds away from getting lethal doses and the quick action of Slotin probably saved them. I'm not trying to deify him or something, the way he did the experiment was reckless and stupid but his quick action did save lives. --Deglr6328 01:31, 12 September 2006 (UTC)

Surely this says it all and presumably is veriable:

Said Robin Connor, a professor of physics at the University of Manitoba, "Slotin's personal sacrifice undoubtedly saved those who were in the room with him. For himself, there was no hope of recovery, something he must have known at once." We need speculate no more 8-)--Light current 01:46, 12 September 2006 (UTC)

ok that's fine with me. now about the cyclotron image.

I am still unclear on what you mean when you say: "Also the cyclotron pic doesnt actually have anything to do with the page does it (apart from the color being similar to something else.)". The image has direct application to the article I would argue. Nothing is being presented by the inclusion of the image which is misleading (I have always taken extreme caution to ensure my edits do not mislead).

Let us consider the effect of ionization of the air. The consituents of air are more or less the same no matter where you are on the planet and were undoubtedly typical at the site of all criticality accidents that I can recall reading about. It is the particular elemental composition of the air of course, which gives rise to the specific and uniqe emission spectrum of an excited mixture of said gasses. In this case, of mostly nitrogen and oxygen, it is blue (sparks, corona discharge, external cyclotron beam). All criticality accident witnesses who see the airglow event report a blue haze or glow. This is air ionization produced by high energy radiation. Here, we have an image of air ionization produced by irradiation from high energy radiation. They are the same phenomenon. Save for the bragg peak effect exhibited with the cyclotron, the diffuse transparent blue glow is what those people who have seen an accident saw. I think it is a very interesting and valuable part of the aricle, it gives insight where no other substitute can. --Deglr6328 01:48, 12 September 2006 (UTC)

I think we need other comments about the applicability of this picture.--Light current 03:37, 12 September 2006 (UTC)

Ok. list at rfc maybe.--Deglr6328 11:38, 12 September 2006 (UTC)

Yes, if you would do the honours! 8-)--Light current 11:41, 12 September 2006 (UTC)

k. done.--Deglr6328 18:48, 13 September 2006 (UTC)

Thx--Light current 19:17, 13 September 2006 (UTC)

hmmm no one seems to care.--Deglr6328 06:17, 16 September 2006 (UTC)

Well I dont really want to get into an argument over it, so well just leave it for now pending any comments. OK? BTW, thanks for being so cooperative and pleasant to deal with. I wish all my edit conflicts were as easy to deal with!--Light current 16:37, 16 September 2006 (UTC)

Ok, I've just seen the RfC. In my view, the photo is fine provided that a source can be found for the statement that: "Due to the very similar mechanism of production, the blue glow is thought to resemble the "blue flash" seen by Harry Daghlian and other witnesses of criticality accidents." If a source can't be found, it's original research. Best wishes, Jakew 18:42, 1 October 2006 (UTC)

As it turns out, Slotin's quick action my have been for naught. I've read that the heating of the core probably dislodged the beryllium shell before Slotin could have reacted by simple expansion. However, it is also noted that within a few more seconds, after a bit of cooling, the halves would have come back together, causing another neutron drenching. The man did his level best, and there's no point in dissing him over his reactions. SkoreKeep (talk) 01:12, 13 January 2014 (UTC)

Backing up my statement above, Raemer Schreiber, one of the physicists in the room, is quoted as stating that later analysis showed that the reflector moved out of position due to heating of the core. Having been personally involved in the accident itself and in the investigation that lead to the safety measures that he implemented, one would presume that he knows as much as can be known about the accident. See Demon Core for the argument there and the exact reference.

Definition of the term Criticality

Presently there is a disambiguation page for Criticality but no dedicated page providing a succinct definition. I was looking for an explanation of the milestone in the construction and operation of a nuclear power plant, where they say "achieved criticality on day/month/year". Thoughts anyone?--Graham Proud (talk) 16:23, 23 January 2014 (UTC)

For example, the Reactor Details page from the International Atomic Energy Agency lists the First Criticality Date for Hanbit-1 in Korea as 31 January 1986.--Graham Proud (talk) 06:12, 24 January 2014 (UTC)

Hi, Graham, I got your message. I only had to take Physics 201 for bio majors, and my interest is mainly curiosity, so I don't feel qualified to make informed statements about definitions. As a matter of form, a short definition under the dark "nuclear" subheader would be fine. If you want a better opinion than mine you might ask at the science ref desk for a good source to provide or base a definition on. μηδείς (talk) 01:04, 17 February 2014 (UTC)

Thanks...I am happy to take on the task, so I have made the link on the disambiguation page point to a non-existent page, and will gather some notes when I have time. In the meantime, I wanted to record here that not even the IAEA have a good definition: their Safety Glossary says criticality is "The state of a nuclear chain reacting medium when the chain reaction is just self-sustaining (or critical), i.e. when the reactivity is zero. Often used, slightly more loosely, to refer to states in which the reactivity is greater than zero." I am after the second part of that, as it applies to operating reactors, that is, up and running.--Graham Proud (talk) 08:06, 17 February 2014 (UTC)

Actually, that is a relatively succinct definition. Admittedly, it assumes a level of background knowledge which the layman does not necessarily have. On the other hand, it is intended for an audience that has a considerable background in nuclear physics.

The term criticality comes from a concept named at some point – I would have to look up when to get a ballpark as to when – during the early research into nuclear physics. That concept is that at some point you get enough radioactive material together in one place and the reaction is self sustaining. The amount of material that is needed for the reaction to be self sustaining is called the critical mass. I have always viewed it as being called this because when you do reach that point you have a problem that is critical (i.e. you better know what you are doing, or you will ruin your whole day). I was going to write more, but in a talk page message I can not equal the information available on various pages. For more information, I suggest you see: Critical mass, Nuclear chain reaction, Nuclear weapon design, and History of nuclear weapons. There are certainly other references, but those should be a good start. Makyen (talk) 08:54, 17 February 2014 (UTC)

Thanks people, I am on to it now!--Graham Proud (talk) 09:10, 17 February 2014 (UTC)

nonsense cleanup needed

The article currently has this text:

Nuclear reactors operate at exact criticality. When at least one dollar of reactivity is added above the exact critical point (the point where neutrons produced is balanced by neutrons lost per generation) then the chain reaction does not rely on delayed neutrons, and the rate of change of neutron population increases exponentially as the time constant is the prompt neutron lifetime.

The "dollar" in the paragraph above shows there's some creeping nonsense in the article, can a subject expert please read it and eliminate this and less obvious cases? BACbKA (talk) 10:43, 17 June 2013 (UTC)

The term "dollar" as a fraction of reactivity scaled in terms of delayed neutron input, is due to Louis Slotin. [1] [2]. A cent is a 1/100 of a dollar. Delayed critical reactors operate in the "cent" region from 1 cent to 99 cents. When a nuclear reactor exceeds 100 cents = a dollar it is no longer dependent on delayed neutrons, and then its power doubling time is only controlled by the half life of neutrons in the reactor, which is milliseconds or less, so there is no longer any hope of controlling it in real time, and that is what makes for a prompt critical reactor vs. a delayed critical one. Controllable nuclear reactors operate at some fraction or percent of a reactivity dollar (or, if you will, in some price in cents). Probably this term needs its own wikipage, but you can see nuclear reactor control and control physics pages. SBHarris 03:20, 18 June 2013 (UTC)

It has it's own page now. SkoreKeep (talk) 19:44, 4 August 2014 (UTC)

Wow! thanks a lot for the clarification. And it's actually explained in another place --- I guess I shouldn't have read just the few paragraphs I was interested in, but the whole article in the first place. Sorry for the bother. BACbKA (talk) 06:02, 18 June 2013 (UTC)

Total number of fatalities

I wonder if it would be worth clarifying in the 2nd paragraph that the known fatalities are from accidents that occurred in countries that have made their nuclear history public. No accidents covered by the source (1. McLaughlin, Los Alamos) occurred in Iran, Israel, North Korea, or Pakistan, which is probably not to say there have been no accidents there. Also, if 14 is truly the total number of (known) fatalities, I'm not sure this is clear from the source given (1. McLaughlin). On page 2, McLaughlin gives 9 as the total number of fatalities from process accidents. (I edited the paragraph for clarity only and did not change the numbers.) DesertRat262 (talk) 04:42, 20 October 2014 (UTC)

(less than 1 m)

"Although process accidents occurring outside of reactors are characterized by a large release of radiation, the release is localized and has caused fatal radiation exposure only to persons very near to the event (less than 1 m), resulting in 14 fatalities. No criticality accidents have resulted in nuclear explosions.[1]"

Is that "less than 1 meter" or "less than 1 mile" ? 2601:645:4100:BED2:BC37:B9E2:D06A:F3C0 (talk) 07:34, 21 August 2015 (UTC)

1 meter, obviously. If everyone within 1 mile of a criticality accident died there would have been hundreds, if not thousands, of fatalities, including everybody who worked at Los Alamos. Being 1 mile away from something can hardly be described as being 'very near'. nagualdesign 11:30, 21 August 2015 (UTC)

I would modify that to "several meters". When Chernobyl exploded, four engineers looked down into the wreckage from a platform somewhat above the reactor floor, past the displaced reactor lid and subsequently died of ARS, thought to be caused by gamma damage to their heads. See Deaths due to the Chernobyl accident, names Kudryatsev, Proskuryakov, Perevozchenko and Sitnikov. At the distance of a mile, the radiation is reduced by the shielding effect of air by a factor of 1000, and additionally by the square-cubed law. SkoreKeep (talk) 18:10, 21 August 2015 (UTC)

No, when Chernobyl exploded, the spilled "stuff" are highly radioactive, being inside of a reactor and all. Although this material is highly radioactive, the material themselves is not at critical state. Imagine that the liquidators (or so they are called) being in a food irradiation plant, and die from ARS. — Preceding unsigned comment added by 192.12.184.7 (talk) 23:00, 8 April 2016 (UTC)

Ah, OK. The sentence is restricted to "process accidents", those outside power plants, and from the source, those specifically in the US atomic bomb program. Stand corrected about the meter. SkoreKeep (talk) 18:16, 21 August 2015 (UTC)

Edit the table

Can someone edit the table to update the recorded criticality accidents per LA-13638? Currently, it is grossly incorrect. — Preceding unsigned comment added by 192.12.184.7 (talk) 22:44, 20 June 2016 (UTC)

HTRE-3

Is there a reason that the HTRE-3 excursion is excluded from both this list and the articles Nuclear-powered aircraft and Aircraft Nuclear Propulsion? — Preceding unsigned comment added by 75.85.96.25 (talk) 22:39, 25 June 2016 (UTC)

References

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External links modified

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I have just modified 4 external links on Criticality accident. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Corrected formatting/usage for http://english.kyodonews.jp/news/2011/03/80539.html
• Added archive https://web.archive.org/web/20080609054436/http://www.csirc.net/library/la_13638.shtml to http://www.csirc.net/library/la_13638.shtml
• Corrected formatting/usage for http://www.lanl.gov/worldview/news/releases/archive/00-099.shtml
• Corrected formatting/usage for http://www.cddc.vt.edu/host/atomic/accident/critical.html

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

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Cheers.—InternetArchiveBot (Report bug) 16:38, 14 August 2017 (UTC)