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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Perhaps a longer distance robotic removal system needs to be developed. A method which can take the spent rods to a seperate building as strong as the reactor vessel building itself. but isolated from H explosions and meltdown.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
Perhaps a longer distance robotic removal system needs to be developed. A method which can take the spent rods to a seperate building as strong as the reactor vessel building itself. but isolated from H explosions and meltdown.
I think the idea is to keep it within the 'containment building'. moving it from one building to another would entail it's own set of risks/hazards.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
I think the idea is to keep it within the 'containment building'. moving it from one building to another would entail it's own set of risks/hazards.
Yes, I beleive that is the reasoning.
But isnt the presence of too much fissile material part of the problem? I geuss Im thinking that the few year old cooled off ones should be moved out as soon as levels allow it. Thus only a few of the most hot rods would be left at the reactor. Generally accepted practice is to keep the least amount of a dangerous material (poison, explosive, biologic hazard, radioactive) neccassary on scene. Storing +30 years of spent fuel on site in pools was never intended.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
Klugesmith wrote ...
If the circulation fails, the decay heat may eventually cause the water to boil. But it should take a couple of weeks to boil off the top 5 meters of water, and that should be long enough to find a way to refill the pool. (megacuries of fission product decay activity is not that many thermal kilowatts)
I hope that's the case. Let's see if the math supports that. Should be relatively simple to figure out.
We know that the pools contain an average of around 40 megacuries of Cs-137. That's a total of 3.7×10^10 decays per second multiplied by 40x10^6 curies = 1.48 × 10^18 decays per second in the fuel pool. Cesium 137 either decays via a 0.5120 MeV beta to 56Ba137m, then a 0.6617 MeV gamma to 56Ba137, or directly to 56Ba137 via a 1.174 MeV beta. In either case, that's 1.174 MeV of energy per decay, but only 0.662 MeV can be counted -- much of the beta decay energy is carried away by a neutrino which will not deposit energy in the pool. 0.662 MeV times 1.48 × 10^18 decays per second is 9.80 × 10^17 MeV/s, or 157,000 watts (J/s) of thermal energy.
Assuming we're starting with 40 C water, each liter of water should take 1.0 (specific heat of water) * 60 (delta T) * 1000 (grams of water) * 4.184 (joules per calorie) or 251,000 J to heat to 100C, and another 2,257,000 J to vaporize. In total, each liter of water will take 2,508,000 J to remove from the fuel pool. So, once the water has been heated to boiling, we're looking at a total water loss of around 0.063 liters per second. I don't know the dimensions of the fuel pools, but even if we assume a modest 10 meters by 10 meters, that's about 49.7 hours to boil off one meter of water level.
One potential problem with my calculation is that spent fuel initially contains much more active elements than Cs-137. This means I have probably dramatically underestimated the thermal output of the spent fuel. Here's an attempt to arrive at the same figure a different way:
According to , spent nuclear fuel emits 10kW per ton thermally after one year, falling to 1kW per ton after 10 years. At Fukushima, 60 percent of the total on-site fuel is in the shared pool, 6% is in dry storage, and 34% is housed with the reactors. If we assume a logical fuel rotation, the oldest fuel is in the casks, the next oldest fuel is in the shared pool, and the newest fuel is in the fuel pools next to the reactors. Reactor 1 began commercial operation on March 26, 1971, meaning it has been in operation for about 40 years. The fuel should be divided up approximately like this: first 2.4 years, dry storage; next 24 years, shared pool; most recent 13.6 years; fuel pool near the reactor. Thus the average age of fuel in the fuel pool is 6.8 years. The decay is certainly exponential, and other sources indicate that the most rapid decline in heat is from 2-4 years. So, a figure of 2.5kW per ton at 6.8 years average age is probably quite generous.
A boiling water reactor produces 20-30 tons of spent fuel per year. 13.6 years of fuel, therefore, should be no more than 408 tons of spent fuel in the fuel pool. That's a total of 1,020,000 MW of thermal energy in the spent fuel pool. One could probably fudge these numbers a bit in either direction, but I doubt this is far off the mark. Going back to looking at how fast water is consumed, we're now looking at 0.407 liters per second. During the second part of this calculation, I found the typical dimensions of a fuel pool: 10-20m long by 7-14m wide, and 12-13m deep (at least 5 meters of water covering the tops of the fuel assemblies). The smallest fuel pool would lose about half a meter of water per day. The largest, about 0.125 meters per day. This is a depth loss of about 4.2% at worst, and at least ten days before the spent fuel is exposed to air.
That means that the math agrees pretty well with the posted fact sheet; presuming no damage to the fuel pool, there should not be a spent fuel fire yet. If there is damage to the fuel pool, however, all bets are off.
Please feel free to check my math and make sure I didn't make a foolish mistake.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Chris, apparently the explosions have damaged the pools and they are leaking. This is definitely the case at No. 3 reactor pool, maybe at the others as well, so they aren't just losing water due to evaporation.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
Ash Small wrote ...
Chris, apparently the explosions have damaged the pools and they are leaking. This is definitely the case at No. 3 reactor pool, maybe at the others as well, so they aren't just losing water due to evaporation.
That does seem to be the case, especially considering the attempted water drop on reactor 3, but I haven't seen any sources confirming a leak as of yet. Do you have a source confirming a leak at the number 3 pool? If so, do they know how badly it is leaking?
Mostly I was interested in fact-checking the safety sheet. It does seem to be correct in that without damage, the fuel pools should be relatively safe for a while. Whether the combined effects of the earthquake, tsunami, and hydrogen explosions have caused a leak in any of the fuel pools seems to be a matter of some speculation at the moment.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Chris Russell wrote ...
Ash Small wrote ...
Chris, apparently the explosions have damaged the pools and they are leaking. This is definitely the case at No. 3 reactor pool, maybe at the others as well, so they aren't just losing water due to evaporation.
That does seem to be the case, especially considering the attempted water drop on reactor 3, but I haven't seen any sources confirming a leak as of yet. Do you have a source confirming a leak at the number 3 pool? If so, do they know how badly it is leaking?
Mostly I was interested in fact-checking the safety sheet. It does seem to be correct in that without damage, the fuel pools should be relatively safe for a while. Whether the combined effects of the earthquake, tsunami, and hydrogen explosions have caused a leak in any of the fuel pools seems to be a matter of some speculation at the moment.
It was on the BBC news about half an hour ago. The BBC seem to be very careful not to report facts until they have been confirmed.
EDIT: This was reported by Reuters yesterday:
" The top U.S. nuclear regulator warned that one reactor's cooling pool for spent fuel rods may have run dry and another was leaking"
EDIT: The BBC says pools at 3 and 4 reactors are damaged (leaking).
EDIT: Update 13.45 GMT, According to Tepco, they were effective in cooling the fuel pool, but the radiation levels didn't decrease.
AND: Summary of Unit 3 water strategies from NHK news - First 4 buckets of water from helicopters with lead plates on the bottom to shield radiation, Second pumping from below (assume water canon) but too high radiation and water did not reach pool, Finally Japan SDF used pump trucks to spray 30 tons of water between 7:45pm and 8:09pm. Effect under evaluation.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
. Part of a Blog by a worker at Fukushima: (EDIT:it appears she works at fukushima diianni, not fukushima diachii)
'As a worker at Tepco and a member of the Fukushima No. 2 reactor team, I was dealing with the crisis at the scene until yesterday (Monday).'
'In the midst of the tsunami alarm (last Friday), at 3am in the night when we couldn't even see where we going, we carried on working to restore the reactors from where we were, right by the sea, with the realisation that this could be certain death,' .
'People have been flaming Tepco,' . 'But the staff of Tepco have refused to flee, and continue to work even at the peril of their own lives. Please stop attacking us.'
'The machine that cools the reactor is just by the ocean, and it was wrecked by the tsunami. Everyone worked desperately to try and restore it. Fighting fatigue and empty stomachs, we dragged ourselves back to work. 'There are many who haven't gotten in touch with their family members, but are facing the present situation and working hard.' ..
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Nuclear events taking place in Japan.
