Talk:Spent fuel pool

Cherenkov radiation

Sorry, just a simple question: on most images showing such spent fuel pools the water in the tub has this strange glooming blueish color? What causes this color? Is that because of radiation coming from the fuels or is that external light? Thanks, "No more Fukushima!"

Cherenkov radiation 129.67.86.189 (talk) 19:21, 15 March 2011 (UTC)

Cherenkov radiation is very unlikely (you can observe only close to the source of the beta radiation (=the rods)). It's just the effect of normal lamps and the water, just like the water seems blue at the beach of an island if it's clear enough. The water in a nuclear facility is kept very clear to reduce corrosion to a minimum. --137.226.40.42 (talk) 17:55, 17 March 2011 (UTC)

The blue effect is, in fact, often Cherenkov radiation. See reference [1]. --70.112.150.168 (talk) 20:22, 19 March 2011 (UTC)

Yes, in that picture it's mostly Chrenkov radiation, but in the pictures in the article here it's clearly lamps illuminating the pool. If there is Cherenkov radiation, then it's not visibale as the lamps are much brighter. --91.61.102.207 (talk) 23:25, 20 March 2011 (UTC)

On the left there appears to be a lamp, but the other rods look like cherenkov welling up from below. But if it is in dispute, it should stay removed. 129.67.86.189 (talk) 19:23, 2 April 2011 (UTC)

Dry pool and critical reaction

"increased risk of re-criticality should the pool be drained" Can this be correct? If the pool is drained the spent fuel would heat up, but how could it go critical without a moderator?? --128.214.182.110 (talk) 11:32, 17 March 2011 (UTC)

I also think this would be impossible. Going to remove the statement for now. I am not a scientist so I would like to see it re-added if true, but my reading is that the lack of water moderating the speed of prompt neutrons makes criticality in a fuel pool LESS likely when drained, not more.131.107.0.81 (talk) 19:31, 18 March 2011 (UTC)

Difficult...not impossible . There's also a reason that they're adding boron to reactors in Japan that already have their control rods fully inserted: adding shutdown margin, but also the remote threat of becoming prompt critical (also see public literature for this term). Moderated neutrons have a much higher probability of capture and subsequent fission, but some percentage of fast neutrons can cause fission. Closer geometries => higher probabilities of absorption. --70.112.150.168 (talk) 20:15, 19 March 2011 (UTC)

You can have many fast neutron triggered fissioning, but still not having a *sustained* reaction which is criticality. The only effect of the spurious fissioning is some more heating, but no criticality.--Robertiki (talk) 19:22, 25 September 2013 (UTC)

This wasn't about whether criticality is possible in a spent fuel pool. You can do that by crushing/compacting it. This is about whether draining it increases the chance of criticality. I'm arguining the act of draining the pool cannot possibly increase your risk of criticality. Zirconium fire and irradiation of the surroundings, absolutely, but creating a criticality by draining a spent fuel pool makes no sense.131.107.0.81 (talk) 23:18, 23 March 2011 (UTC)

I agree. My education is Electronic Engineering, however I have some expertise here. Low enriched Uranium requires a moderator to produce a chain reaction. The reason is that it can only sustain a slow (thermal) neutron reaction. There is simply not enough fissionable material (Uranium-235 and Plutonium isotopes) to sustain a fast neutron reaction.

Tyrerj (talk) 11:07, 7 May 2012 (UTC)

The reason I provided a citation (see link in my earlier comment) is that re-criticality can indeed happen if the spent fuel actually melts down and the geometry gets a lot tighter. The spent fuel still generates heat, and -- in the case of most-recently used fuel -- quite a bit of heat. This is why Unit #4's spent fuel pool is the most problematic at Fukushima Daiichi. Criticality does not require water -- it requires neutrons in sufficient density and energy levels for a given fuel density. Moderated (thermal) neutrons certainly have a higher probability of capture, but 'fast fission' happens. Again...see the link for specifics. --70.112.150.168 (talk) 22:42, 25 March 2011 (UTC)

More clarity here for those who are not specialists in nuclear matters when it comes to such basic things as criticality. As this article on the Tokaimura nuclear accident mentions, the minimum critical mass for 18.8% uranium fuel is about 46 kg...and that's with ZERO water being involved. --70.112.150.168 (talk) 22:41, 31 March 2011 (UTC)

Another example of "dry" criticality to help educate readers here: the plutonium half-spheres accident at Los Alamos that claimed Louis Slotkin's life. --70.112.150.168 (talk) 23:09, 31 March 2011 (UTC)

Criticality in a spent fuel pool is not possible, so I corrected the paragraph here, adding of course a source (I have a master in nuclear engineering, but I have anyway to respect the common rules). The fact is that there is not an enrichment level high enough to self-sustain the chain reaction, out of the accurate disposal of the spent fuel; and when the rods get dry, there is also no moderator for that reaction (water).

For the unknown users above: your arguments have no value. Uranium is enriched up to 3-4% to enter NPPs, and it gets out with 1-1.5% enrichment level, making it almost impossible to re-ignite a self-sustainable chain reaction even with a moderator. Slotkin was dealing with a plutonium war-head, meaning an almost 100% enrichment, and so this event cannot be accounted for.

Filippo83 (talk) 23:03, 14 April 2011 (UTC)

I did not see a statement in the very technical and badly translated article you cited saying criticality in a spent fuel pool is impossible. It seems to be about how to manage things to avoid criticality. Therefore, I reverted your edits until they can be sourced to material which supports the assertion that TEPCO was wrong and it cannot happen. Jonathanwallace (talk) 05:28, 15 April 2011 (UTC)

First of all, the source is inside my statement, and inside nuclear physics: so low enriched uranium cannot turn critical, unless we have proper conditions, like a neutron source and heavy water (D2O) as moderator. More, I saw no source of Tepco saying it may get critical, nor IAEA or NISA, only media sources. You could anyway tell me it is very rare but not impossible (even if it is almost sciencefiction for that kind of nuclear fuel): "a chance" does not disagree with "very rare". Anyway, if the rods went uncovered, we would have no moderator, no water, no heavy water, no graphite, nothing else that would allow a chain reaction to happen and self-sustain: this is basic nuclear physics since Fermi's time. It is a so rare event that few ones, among technical sources, have even thought to explain it for very low enriched fuel, like the spent one coming from BWRs/LWRs. I have then to reverse the questions:

• find me the Tepco source, not a media communicate, who tells that spent fuel rods may get critical;
• find me any technical source which states that this is possible under the conditions we have there (enrichment <2%, possibly no water/other moderator).

Then I give you some other and simpler source:

• here, from which I quote: A second hazard of spent fuel, in addition to high radiation levels, is the extremely remote possibility of an accidental “criticality,” or self-sustained fissioning and splitting of the atoms of uranium and plutonium.

Your statement that my source was very technical has no sense: we are discussing about technical things, and we have to look for technical sources rather than media ones. The source states that calculations are made, for the spent fuel disposal, in the safest way; and you can easily find it in other articles from all the world, e.g. here; e.g. calculations are made considering "fresh fuel", with higher enrichment levels than the spent one. There is no reason why Fukushima-I spent fuel pool at reactor 4 should work in a different way. I am then going to reverse your roll-back, just considering to delete the impossible word, but keeping the very rare ones: is this acceptable? -- Filippo83 (talk) 09:42, 15 April 2011 (UTC)

I have changed the paragraph, making it the same of the Fukushima-I accidents article, which underwent other contributions by Wikipedia community (not mine only). -- Filippo83 (talk) 09:54, 15 April 2011 (UTC)

I made some changes to your edits for neutrality and encyclopedic style while preserving their major arguments. I have an issue saying in Wikipedia's voice that it is nearly impossible, when there does not seem to be consensus on this Talk page that this is true. So I made it according to experts. If I find other sources disagreeing, I will propose adding them as well. Also, though you do not seem to be arguing to delete the Tepco statement, the media reports are considered reliable sources and there is no Wikipedia policy which dictates that we ignore such newspaper reports in favor of a Tepco press release or document. Jonathanwallace (talk) 12:19, 15 April 2011 (UTC)

The fact is that, in the last weeks, we eared about many statements made by supposed Tepco "employees", without seeing a single company communicate, nor supported by IAEA or NISA statements; anyway, as you have seen, I insisted on this point just here in the Talk, without modidyfing once more the main article without an explicit consensus about (if I did it once more, I was wrong). I find acceptable your changes. I apologize if I was rude, when discussing the issue. -- Filippo83 (talk) 12:38, 15 April 2011 (UTC)

Thanks, but you weren't rude, and I am glad we have reached agreement. Jonathanwallace (talk) 12:41, 15 April 2011 (UTC)

Storage methods and heat generation

"storage methods in the United States require fuel to be stored such that in the event of a catastrophic loss of coolant the steady state temperature of the fuel assemblies in air does not exceed the cladding melt temperature." This is preposterous, which is probably why there's no citation to it. Federal regulations (10 CFR 50.46) specify that the emergency core cooling system should keep the cladding at no more than 2200 ºF. This has nothing to do with storage. How hot an uncooled fuel rod assembly can get is subject to the laws of physics, not NRC rulemaking. 68.173.53.167 (talk) 02:19, 18 March 2011 (UTC)

Agreed, removing this unless someone feels it should be re-added. The temperature of a fuel rod stored in air is a purely physical calculation, I see no mention of any system built to provide air-cooling of spent fuel rods should they be exposed, and HIGHLY skeptical that cooling by convection alone (as in a loss of coolant or loss of power accident) is even possible.131.107.0.81 (talk) 19:31, 18 March 2011 (UTC)

Adding reference on air cooling of spent fuel assemblies. According to the referenced Sandia Labs study (quoted between pages 19-20) Even using the international "wide spacing" used in non-us reactor SFP's, convective cooling begins to be possible ONLY after 5 days of reactor shutdown. In a dense-packed pool such as found at US reactors, convective cooling would not work for any fuel with less than 1 year of time underwater in the cooling pool, out of the reactor. Based on these reports I re-assert that convective cooling in a spent fuel pool as an emergency plan is NOT possible. Alvarez, et al. 2003. "Reducing the Hazards from Stored Spent Power Reactor Fuel in the United States" http://www.irss-usa.org/pages/documents/11_1Alvarez.pdf 131.107.0.81 (talk) 20:11, 18 March 2011 (UTC)

The article lacks information as to how long spent fuel assemblies must remain in a cooling pool until the heat that radioactive decay is producing has decreased to the point that they can be moved to dry storage and/or are stable without the water in the pool. Stable meaning that the zirconium cladding will not melt or burn. The article implies that this could be 10 years but I have read that SFAs can be moved to dry storage after only one year. Tyrerj (talk) 11:19, 7 May 2012 (UTC)

References

Combustibility of fuel?

As a non-expert attempting to add reliably sourced information on risks, could someone help with an unsourced assertion I have temporarily removed from the article: "Combustion of the nuclear fuel is not possible with American or Canadian electrical power reactor fuel rods since these consist of very stable uranium dioxide pellets. Burning of the cladding is possible should the fuel rods be left exposed and without coolant." Is this correct? If yes and someone can provide a reliable source I will put it back in. By the way, I assume what this means is that a fire or explosion may still spread radiation without causing criticality. Thanks. Jonathanwallace (talk) 16:40, 5 April 2011 (UTC)

It was obfuscating the facts and contained some red herrings, so you did the right thing in removing it. Parsing the individual statements:

• Uranium dioxide (and plutonium dioxide, for that matter) is technically a ceramic compound, and in a fashion is already "burned" as it is oxidized. So this is true regarding non-combustibility, but that doesn't mean that it can't melt at sufficiently high temperatures, 'pool' and possibly lead to a critical reaction via some measure of probability/quantitative statistics...a situation of much greater concern than simply 'burning.' So while fires don't cause criticality, there is some possiblity -- remote, mind you -- of criticality via melting and overall geometry tightening. See UO2 link and earlier discussion's citation on the possibility of spent fuel pool criticality.

• Burning (oxidizing) the zirconium cladding is almost certainly what led to the generation of hydrogen that caused the fires/blast(?) at Fukushima Daiichi Unit 4's spent fuel pool. This oxidation, by the way, can come from the zirconium getting hot/reactive enough to rip the oxygen atom away from the hydrogen atoms in water (H2O). See zirconium cladding link for more info on its reactions with water at high temperatures. --70.112.150.168 (talk) 04:53, 6 April 2011 (UTC)

Thanks! Jonathanwallace (talk) 10:15, 6 April 2011 (UTC)

Risks

Link #18 cites a Time.com article but has no link to the primary source. After a cursory search I was unable to find the Brookhaven 1997 report on used fuel risks. This section makes a very bold claim and it should cite a primary source, the existing source does not link to the report either. I question the reliability of that citation. — Preceding unsigned comment added by 65.246.166.58 (talk) 16:46, 5 June 2012 (UTC)

I found a source () here which seems to invalidate the original source material that Time was attempting to cite. It specifically explains that the information on calamities was likely an overstatement. Remove this line? ChunyangD (talk) 03:30, 23 January 2013 (UTC)

References

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