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The mysterious cesium casks

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Marlin:
Ever since the shocking discovery of three old casks of cesium-137 in an Oak Ridge scrapyard, there has been a bit of a hush-hush regarding their whereabouts and the ultimate disposition of the radioactive material (reported to be the optimum material for so-called dirty bombs). And the secretive treatment continues now, with the Department of Energy acknowledging that the casks -- retrieved from a scrapyard west of K-25 in October 2005 -- are still in Oak Ridge, reportedly housed in a safe and secure storage facility at Oak Ridge National Laboratory.

DOE spokesman Mike Koentop confirmed that the casks are still at ORNL. At some (unspecified) point, the agency plans to dispose of the radioactive material, he said. About the only thing that's changed since I last reported on the cache of cesium is that it's now under the custodianship of UCOR, which replaced Bechtel Jacobs as the agency's Oak Ridge cleanup contractor in 2011.
 
The original source of the cesium and how it got to the Oak Ridge scrapyard are apparently not known, and the actual quantity of the radioactive material has been debated and disputed.

At the time of the event, the Tennessee's Department of Environment and Conservation was told that the casks contained 271,000 curies of cesium-137. That's a lot of hot stuff. Others suggested that number was way too high. John Owsley, TDEC's environmental oversight chief in Oak Ridge, said the original curie estimate was based on non-destructive assays of the casks.

In response to questions, TDEC spokeswoman Meg Lockhart said today that the state inspects the casks on an annual basis. "They are in safe and compliant storage," she said via email.

Lockhart said there has been no additional characterization of the casks since the initial testing.

"DOE Environmental Management's plans for the casks call for characterization and disposal," she said. "The disposal location will depend on the final characterization."
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http://blogs.knoxnews.com/munger/2013/03/the-mysterious-cesium-casks.html

roadhp:
Couple of nuked out calculations...if we assume it has been there for over 30 years, or 1 half-life, then the original weight would have been around 6 kg of Cs-137, and the original dose using the 6CEN rule would have been around 3.82 million Rem/hr. using the energy of 1.176 Mev.  Me thinks their estimate is off.  Even if it had that much Curie content when it was buried, 271,000 Ci, don't believe any cask could shield that much radiation to effectively be handled.  Obviously not a CHP, but can anyone tell me how much heat that would give off?

Marlin:

--- Quote from: roadhp on Mar 30, 2013, 05:56 ---Couple of nuked out calculations...if we assume it has been there for over 30 years, or 1 half-life, then the original weight would have been around 6 kg of Cs-137, and the original dose using the 6CEN rule would have been around 3.82 million Rem/hr. using the energy of 1.176 Mev.  Me thinks their estimate is off.  Even if it had that much Curie content when it was buried, 271,000 Ci, don't believe any cask could shield that much radiation to effectively be handled.  Obviously not a CHP, but can anyone tell me how much heat that would give off?

--- End quote ---

0.662 Mev gamma

thenuttyneutron:

--- Quote from: roadhp on Mar 30, 2013, 05:56 ---Couple of nuked out calculations...if we assume it has been there for over 30 years, or 1 half-life, then the original weight would have been around 6 kg of Cs-137, and the original dose using the 6CEN rule would have been around 3.82 million Rem/hr. using the energy of 1.176 Mev.  Me thinks their estimate is off.  Even if it had that much Curie content when it was buried, 271,000 Ci, don't believe any cask could shield that much radiation to effectively be handled.  Obviously not a CHP, but can anyone tell me how much heat that would give off?

--- End quote ---

There is probably a lot of self shielding going on.  I do not know when the 271,000 Ci was obtained but my calculations show that the material was producing about 1,900 watts if there were 271,000 of Cs 137.  If the shielding is good enough and all that energy is converted into heat before anything can get out, that cask would be pretty warm to the touch.  30 years later, divide it by 2.

I used the generic 1.176 MeV per Bq because the meta-stable state is so short lived.  I am not sure what the dimensions of the cask are and how much leakage you would get so it is hard to say how much of it is actually made into heat vs how much gets out.

roadhp:

--- Quote from: Marlin on Mar 30, 2013, 07:36 ---0.662 Mev gamma

--- End quote ---

My bad.  Just woke up on night shift and relying on internet instead of knowledge till I woke up.  Still pretty hefty, though.  Don't know what the shielding factor for Cesium is for it's own gamma's, but looking at the dimensions of the cask shown, it doesn't have much external shielding factor, probably less than a type "B" cask would have.

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