The mysterious cesium casks

[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]

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?

0.662 Mev gamma

[thenuttyneutron]

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?

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]

0.662 Mev gamma

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.

[Marlin]

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.

Early morning "fuzzy math" is cured by a couple of cups of coffee.   four if hangover is involved.

[macgator]

If we assume the total source term of 271,000 Ci is evenly distributed among the 3 casks then we have ~ 90,000 Ci each multiplied by 0.38 Rem/hr/Ci at 1 meter = 34,200 R/hr at 1 meter. Tenth value for Pb is 0.9 inch so if there is 1.8 inches of Pb and we ignore buildup, we get 342 R/hr at 1 meter, 2.7 inches = 34 R/hr, not as hard to handle as you might think.

[roadhp]

If we assume the total source term of 271,000 Ci is evenly distributed among the 3 casks then we have ~ 90,000 Ci each multiplied by 0.38 Rem/hr/Ci at 1 meter = 34,200 R/hr at 1 meter. Tenth value for Pb is 0.9 inch so if there is 1.8 inches of Pb and we ignore buildup, we get 342 R/hr at 1 meter, 2.7 inches = 34 R/hr, not as hard to handle as you might think.

That's 566 mrem each minute at 1 meter.  Assuming it is a point source from a good distance, that would equal 342 mr/hr at 10 meters, and 3.4 mr/hr at 100 meters.  Handling it would be dose intensive, especially if you didn't know it was there in 2005 when it was discovered.  And that is just for 1 cask.

[Rennhack]

0.662 Mev gamma

85% of the time.

[Marlin]

85% of the time.

and 0.284 Mev  at 0.00058% 

[macgator]

Roadhp, my intent was to assist you in the proper estimation of the dose rate for these casks, I wasn't trying to minimize the extent of the hazard. The internet is an excellent reference for isotopic decay modes and energies as well as dose rate to Curie conversions.
Your attempt at a calculation shows that you care about your craft and I hope you continue to have a questioning attitude and progress in your field by becoming NRRPT and/or CHP qualified.
Good luck to you!

[roadhp]

Roadhp, my intent was to assist you in the proper estimation of the dose rate for these casks, I wasn't trying to minimize the extent of the hazard. The internet is an excellent reference for isotopic decay modes and energies as well as dose rate to Curie conversions.
Your attempt at a calculation shows that you care about your craft and I hope you continue to have a questioning attitude and progress in your field by becoming NRRPT and/or CHP qualified.
Good luck to you!

I am NRRPT although not current.  The point I was trying to make in the first place is that something like that with those dose rates would not be an easy thing to miss, and I believe the initial reporting of the curie content is possibly flawed.  I was not trying to do an analysis of the casks as I nor you have the proper information about them to perform such an analysis, and anyway, analysis and calculation are only so good, and an accurate meter in the hands of a professional tells the real story.

[thenuttyneutron]

Bill Nye the science guy explains what Cs 137 is and what it is used for.

I remember seeing this on tv a while back.

[MGH]

271,000 curies of cesium-137
In what appears to be a damaged, rusted cylindrical (drum-like) cask
Laying on it's side...outside
And they don't know where it came from?

Methinks Mr. Munger (author) is telling stories...also called journalism

There's probably a grain of truth about three casks that have Cesium-137 in them and the origin may be questionable (or something they were not authorized to talk about), but much of the story is obviously embellished.

Stranger things have been true, but the specifics surrounding this story is highly suspect.