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03-16-2011 , 04:13 PM

#1126

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Just found this study from 1987 discussing the consequences of a severe accident in a spent fuel pool resulting in the complete draining of the pool.

http://www.osti.gov/bridge/product.b...sti_id=6135335

03-16-2011 , 04:22 PM

#1127

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Quote:

5.4 EVALUATION OF FUEL CLADDING FAILURE
The SFUEL computer code developed at Sandia National Laboratories (SNL) by Benjamin et al.,3 analyzes the behavior of spent fuel assemblies after an accident has drained the pool. The analyses predict that self-sustaining oxidation of the Zircaloy cladding (i.e., a cladding fire) would occur for a wide range of decay heat levels and storage geometries. Several limitations in the SFUEL analyses had been recognized in Reference 3 and have been addressed in a modified version of the code, SFUEL1W.1*

The BNL evaluations of SFUEL1W have led to the conclusions that the modified code gives a reasonable estimate of the potential for propagation of a cladding fire from high power to low power spent fuel while the fuel is intact. The code therefore provides a valuable tool for assessing the likelihood of a cladding fire for a variety of intact spent fuel configurations in the event that the pool is drained.

Well that is not good.

03-16-2011 , 04:34 PM

#1128

SenorKeeed

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Join Date: Jul 2006 Posts: 37,478

Quote:

Calculations with SFUEL indicated that, for some storage configurations and decay times, the Zircaloy cladding could reach temperatures at which the exothermic oxidation would become self-sustaining with resultant destruction of the cladding and fission product release. The possibility of propagation to adjacent assemblies (i.e., the cladding would catch fire and burn at a hot enough temperature to heat neighboring fuel assemblies to the ignition point) was also identified. Under certain conditions, the entire inventory of stored fuel could become involved. Cladding fires of this type could occur at temperatures well below the melting point of the U02 fuel. The cladding ignition point is about 900 C compared to the fuel melting point of 2880 C.

03-16-2011 , 04:35 PM

#1129

will1530

self-banned

Join Date: May 2009 Posts: 5,773

Quote:

Originally Posted by Chips Ahoy

OK, so assume the pool is dry and full of new fuel. Also assume it's going to stay dry and nature will run its course unmitigated. What will happen? What will it mean for controlling the other reactors?

Thanks for your expertise.

Well, first water is a reasonably good shield against gamma radiation. The fact that water is always supposed to be their means that it will be taken into account when calculating shielding requirements for a vessel like this.

The 1/10th thickness of water for gamma's is about 24". This means that for every 24" of water between you and the gamma source your dose rate will decrease by 90%. So it works kinda like this.

24" of water -> dose rate is reduced by 90%
48" of water -> dose rate is reduced by 99%
72" of water -> dose rate is reduced by 99.9%

A complete loss of water means there will be an insta spike of radiation in the area. Possibly up to acutely dangerous levels (this depends on several factors).

As MJ said above, the next risk is a cladding fire. Like all metal fires a zirconium fire will burn rediculously hot (5000F is not unheard of). Also, once it starts it's very hard to put out. spraying water on a metal fire is kinda like spraying everclear on a house fire.

03-16-2011 , 04:43 PM

#1130

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Will, if the pool is dry it has to be the result of a leak, right? Is there any way the fuel could boil off a thousand tons of water in five days?

If the pool draining is the result of a leak it is extraordinarily serious because even if more water is added it will presumably continue to leak out.

03-16-2011 , 04:43 PM

#1131

NameOnTheCake

Carpal \'Tunnel

Join Date: Jul 2004 Posts: 19,597

so the fire would just burn unchecked indefinitely? how large of an area would have to be evacuated, in your opinion?

03-16-2011 , 04:48 PM

#1132

foldpre

grinder

Join Date: Dec 2009 Posts: 531

wtf man, we should be sending them this...

not "cooling fluid" (water)

03-16-2011 , 04:50 PM

#1133

DVaut1

Carpal \'Tunnel

Join Date: Nov 2004 Posts: 30,005

Sounds like we should be sending them boats and planes so they can leave.

03-16-2011 , 04:53 PM

#1134

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Quote:

Originally Posted by mjkidd

Apparently this is not true...from the 1987 report

Quote:

In the event that normal circulation of the cooling water is disrupted, e.g., due to station blackout, pump failure, pipe rupture, etc., the water temperature of the pool would steadily increase until bulk boiling occurred. (Note: In a situation where the stored inventory was small, an equilibrium temperature, below the boiling point, would be reached at which surface evaporation balanced the decay heat load).

Thermal-hydraulic analyses of the consequences of partial or complete loss of pool cooling capability are a routine part of the safety analysis reports required for licensing and amendments thereto. Generally, these analyses consider several scenarios ranging from typical to extremely conservative conditions. A sampling of conservative results for several plants is given in Table 2.3. The data clearly demonstrate that the time interval from loss of circulation until exposure of fuel to air is quite long. Even in the most pessimistic case cited in Table 2.3 (Docket No. 50-247), the water level in the pool would drop only about 6 inches per hour. Thus, there is considerable time available to restore normal cooling or to implement one of several alternative backup options for cooling.

03-16-2011 , 04:54 PM

#1135

Chips Ahoy

help me help you

Join Date: Apr 2007 Posts: 28,869

I'm still unclear on what the consequences of a cladding fire are -- how much radiation can it make? Can it start a reaction?

It is odd how the core has the 5 level redundancy and the spent fuel pool seems to have none.

03-16-2011 , 05:03 PM

#1136

will1530

self-banned

Join Date: May 2009 Posts: 5,773

Quote:

Originally Posted by Chips Ahoy

It's bad, and I'm saying this in the context of everything else is going on. It's hard to quantify what will/could be released into the atmosphere, it depends how much fuel is actually in the pool.

Last edited by will1530; 03-16-2011 at 05:09 PM.

03-16-2011 , 05:06 PM

#1137

gumpzilla

Carpal \'Tunnel

Join Date: Feb 2005 Posts: 13,973

Quote:

Originally Posted by Chips Ahoy

It is odd how the core has the 5 level redundancy and the spent fuel pool seems to have none.

Agreed. I can definitely see how the danger associated with the spent fuel in a non-critical setup is reduced, but this does seem like a glaring oversight. I imagine things will be different in the future.

03-16-2011 , 05:13 PM

#1138

SenorKeeed

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Join Date: Jul 2006 Posts: 37,478

Quote:

The critical conditions (i.e., the decay heat level which is sufficient to cause a clad fire) for clad fire initiation as determined by SFUEL calculations are summarized in Table 3.1. Note that for the old style cylindrical fuel racks with a large inlet orifice (3 inch diameter) the natural convection cooling in air is predicted to be adequate to prevent self-sustaining oxidation (cladding "fires") after 10 days of decay for BWR assemblies and 50 days for PWR assemblies. However for the new high density fuel racks, natural convective flows are so restricted that even after cooling for a year there is potential for self-sustaining oxidation. As pointed out by Benjamin et al.l there are a number of modifications to the fuel rack design which would enhance convective cooling and reduce the potential for cladding fires. However, the limited flow area of the high density designs make it difficult to ensure adequate cooling by natural convection of air.

There is reportedly a lot of fuel in the #4 reactor so it seems quite possible they are using the high density racks. And there is an entire core's worth in the pool that has been out of the reactor less than a year...

03-16-2011 , 05:14 PM

#1139

will1530

self-banned

Join Date: May 2009 Posts: 5,773

Quote:

Originally Posted by will1530

It's bad, and I'm saying this in the context of everything else is going on. It's hard to quantify what will/could be released into the atmosphere, it depends how much fuel is actually in the pool.

Well, this is an exaggeration considering everything else going on is a massive tsunami with widespread devistation.

If you look at the situation in each of the reactors, this is worst right now. It also makes controlling the situation in the rest of the reactors more difficult due to the radiation levels it would cause.

03-16-2011 , 05:15 PM

#1140

JMa

veteran

Join Date: Mar 2005 Posts: 3,328

How come most (all?) nuclear power plants are on the east coast of Honshu? It seems like the west coast of the island would be calmer because it's a bay there.

03-16-2011 , 05:16 PM

#1141

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Prevailing winds blow east maybe?

03-16-2011 , 06:07 PM

#1142

checkmate36

Pooh-Bah

Join Date: May 2004 Posts: 5,114

So is this now as bad as Chernobyl?

03-16-2011 , 06:08 PM

#1143

ddunc33

grinder

Join Date: Jul 2008 Posts: 499

Ok, we have reached worst case scenario if the fuel pool is dry.

03-16-2011 , 06:08 PM

#1144

SenorKeeed

mew mew mew

Join Date: Jul 2006 Posts: 37,478

Quote:

Originally Posted by will1530

It's bad, and I'm saying this in the context of everything else is going on. It's hard to quantify what will/could be released into the atmosphere, it depends how much fuel is actually in the pool.

Looking at the BNL report on spent fuel fires, it says that for a cladding fire affecting the "Last fuel discharge 90 days after discharge" will release between 1.1 and 2.3 million man-rem in a 50 mile radius of the the plant.

They predict release of 1.4 million curies of Kr 85, 1.4 million of Nb 95, 1.1 million of Sb 125, 7.5 million of Cs 134, 20 million of Cs 137, 19 million of Cs 137, and negligible amounts of other elements. So release of about 50 million curies. Chernobyl released something like 52 million curies.

03-16-2011 , 06:09 PM

#1145

O.A.F.K.1.1

Ted Patrick

Join Date: Dec 2007 Posts: 27,951

03-16-2011 , 06:14 PM

#1146

checkmate36

Pooh-Bah

Join Date: May 2004 Posts: 5,114

Not sure exactly what all this is but it can't be good and no way to sugar coat anything.

Top US nuke official says stay 50km away.

03-16-2011 , 06:20 PM

#1147

pvn

Guest

Posts: n/a

Quote:

Originally Posted by O.A.F.K.1.1

too soon?

03-16-2011 , 06:24 PM

#1148

ddunc33

grinder

Join Date: Jul 2008 Posts: 499

Time for a major re-evaluation of "whats the worst that could happen" at our nuclear facilities. I can't imagine anybody saw the possibility of all of this.