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PostPosted: May 02, 2014 8:54 am 
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There's a draft version of a major new NRC study on spent fuel pool accidents available online.

http://pbadupws.nrc.gov/docs/ML1313/ML13133A132.pdf

A lot of great stuff in there for those interested in the topic.


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PostPosted: May 02, 2014 9:19 am 
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"The purpose of this consequence study was to determine if accelerated transfer of older, colder spent fuel from the spent fuel pool at a reference plant to dry cask storage significantly reduces risks to public health and safety. The specific reference plant used for this study is a GE Type 4 BWR with a Mark I containment.

...

This study’s results are consistent with earlier research studies’ conclusions that spent fuel pools are robust structures that are likely to withstand severe earthquakes without leaking cooling water and potentially uncovering the spent fuel.

The study shows the likelihood of a radiological release from the spent fuel after the analyzed severe earthquake at the reference plant to be about one time in 10 million years or lower.

In addition, the regulatory analysis included with this study does not support accelerated spent fuel transfer to casks for the reference plant."


Last edited by MSJ on May 02, 2014 11:13 am, edited 2 times in total.

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PostPosted: May 02, 2014 9:28 am 
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MSJ wrote:
https://what-if.xkcd.com/29/

OK who wants to go swimming?


Swimming in demineralized water for long times is not advisable.

In any case that is not the topic of this thread.


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PostPosted: May 03, 2014 5:43 am 
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Molten salt reactors do not require spent fuel pools. In fact they'd use the current "spent" fuel as fuel. What I'd like to see is a paper from the NRC on the viability of MSRs to consume the current stockpile of spent fuel rods.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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PostPosted: May 03, 2014 6:05 am 
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Quote:
the regulatory analysis included with this study does not support accelerated spent fuel transfer to casks for the reference plant.


In fact, it strictly argues against it. Only old spent fuel can be transferred to dry casks. The old spent fuel does not make much heat, so it is a good heat sink. The results from the 1x8 analysis (that is, 1 fresh spent fuel assembly surrounded by 8 old ones) show that no cladding failure occurs upon a draindown accident unless the fuel is very fresh (just offloaded from the reactor). This will work with the spent fuel as little as 3 months old. This result shows that, if anything, please pack the fuel assemblies very tight, with as much old fuel around it as possible. Fresh spent fuel is a risk, but it is helped more by having cold fuel assemblies next to it rather than insulating void (though long cans of water where the open spaces are would be an even better heat sink than old spent fuel).

One of the lessons from Fukushima is that debris covering the spent fuel is a realistic event in a severe emergency (hydrogen explosion, but could also be severe storm damage or terrorist attack). Debris would be a major problem for air cooling, but not for water cooling. So if anything, use a water spray backup injection system powered by fire engines, rather than spending much more money in transferring the old fuel to dry casks at accellerated rates and hope that no debris will ever cover the spent fuel so air cooling can work. Even with no debris on top of the fuel, fresh spent fuel can't be air cooled sufficiently.

There is one major issue I do have with the study, which is again the assumption that oxygen (in air) will result in a zirconium fire. As we have seen in the video from Berkeley, this is almost certainly wrong. Superheated steam, yes, but oxygen, no.


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PostPosted: May 03, 2014 7:29 am 
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Wouldn't it be best to remove the old spent fuel so you can add more water.

Or is the fuel a better heat sink than the boiling of water of the same volume? - which seems ratehr unlikely


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PostPosted: May 03, 2014 7:56 am 
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The accident considered is a leak in the bottom of the pool. So water will drain. Fuel assemblies wont and they have high surface area to make them a decent radiator. Water in cans would be better of course.


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PostPosted: May 05, 2014 5:40 pm 
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Cyril R wrote:
One of the lessons from Fukushima is that debris covering the spent fuel is a realistic event in a severe emergency (hydrogen explosion, but could also be severe storm damage or terrorist attack). Debris would be a major problem for air cooling, but not for water cooling. So if anything, use a water spray backup injection system powered by fire engines, rather than spending much more money in transferring the old fuel to dry casks at accellerated rates and hope that no debris will ever cover the spent fuel so air cooling can work. Even with no debris on top of the fuel, fresh spent fuel can't be air cooled sufficiently.

My impression is that the spent fuel pools weren't inside a strong containment structure at Fukushima. Is this true? Is it true for most nuclear power plants? My impression is that an airplane striking the spent fuel pool at Fukushima would have smashed the spent fuel rods.
Moving spent fuel rods to dry cask storage would make this problem less likely.
(Of coarse, an airplane strike during the super bowl would be much more serious.).


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PostPosted: May 06, 2014 9:28 am 
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Lars wrote:
Cyril R wrote:
One of the lessons from Fukushima is that debris covering the spent fuel is a realistic event in a severe emergency (hydrogen explosion, but could also be severe storm damage or terrorist attack). Debris would be a major problem for air cooling, but not for water cooling. So if anything, use a water spray backup injection system powered by fire engines, rather than spending much more money in transferring the old fuel to dry casks at accellerated rates and hope that no debris will ever cover the spent fuel so air cooling can work. Even with no debris on top of the fuel, fresh spent fuel can't be air cooled sufficiently.

My impression is that the spent fuel pools weren't inside a strong containment structure at Fukushima. Is this true? Is it true for most nuclear power plants? My impression is that an airplane striking the spent fuel pool at Fukushima would have smashed the spent fuel rods.
Moving spent fuel rods to dry cask storage would make this problem less likely.
(Of coarse, an airplane strike during the super bowl would be much more serious.).


Yes, a secondary containment only. The service floor. Fairly thin steel panel structure. But, not quite feeble. Can withstand hurricanes and such. It will shred any aircraft coming through it. Then it gets sort of interesting. There is always min. 7 meters of waters on top of the spent fuel. That's a lot of shock absorber. It will completely stop a .50 cal depleted uranium round even at vertical insertion. Light aircraft debris likely won't get to the spent fuel assemblies at speed. Water is incompressible and the pool is open at the top so no shock compression. The pools and spent fuel survived a 800-1100 kg hydrogen explosion.


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PostPosted: May 06, 2014 12:14 pm 
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7 meters for a 50 cal? Overkill. IIRC, if Mythbusters is anything to go by, IIRC like 2 feet of water can stop a 50 cal. Smaller velocity bullets make it farther in water than higher velocity bullets. When faster bullets hit the water, they get shredded faster, I guess from the larger forces involved, compared to lower velocity bullets.

Side point, sorry. 8)


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PostPosted: May 06, 2014 3:30 pm 
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Joshua Maurice wrote:
7 meters for a 50 cal? Overkill. IIRC, if Mythbusters is anything to go by, IIRC like 2 feet of water can stop a 50 cal. Smaller velocity bullets make it farther in water than higher velocity bullets. When faster bullets hit the water, they get shredded faster, I guess from the larger forces involved, compared to lower velocity bullets.

Side point, sorry. 8)


About 3 feet to be safe. That's for a regular round, DU is much heavier.

For the spent fuel pool though the main thing would be the engine. The shaft is quite heavy and long, fortunately it has all those blades attached making for a high surface area.

Anyway the point is it is unlikely that any debris will damage the fuel. 7 meters of water is just too good a shock absorber. Then there are the spent fuel assembly grappling rings and top piece. These will act like a further shield to protect the fuel rods underneath.


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