Sunday, September 7, 2014
Pit Options Examined
According to JM:
The Plutonium Facility PF-4 at Los Alamos National Laboratory was built in 1970, to withstand a Design Basis Earthquake of a strength considered to be reasonable at that time.
Only recently, PF-4 has been structurally reinforced and is said now to be able to withstand today's much stronger DBE; i.e., with less than a 50% chance of collapse.
Fume hoods in PF-4 have been improved so as to better resist spilling their contents onto the PF-4 floor, following a DBE.
Fire suppression technology at PF-4 has been ungraded so as to better impede the spread of out-of-control fire in the facility.
JM claims that the probability of a significant medical hazard to the surrounding community, in the event of a DBE, out-of-control fire, and release of Pu laden dust and smoke into the atmosphere above PF-4, has become nil.
Although Defense Nuclear Facilities Safety Board has taken note of these LANL upgrades, it may still believe that in the event of a DBE and fire at PF-4, as much as "100,000 Ci of Pu could go up in the air." According to my very rough calculations, described in my blog (July 14, 2012, entitled "DNFSB Disagrees with NNSA Analysis",) this much radioactive material released into the air above PF-4 might require the evacuation of the entire surrounding Los Alamos community.
JM also notes, in "Manufacturing Nuke Pits," that the (unvaulted) Material At Risk allowance at PF-4 is currently 1,800 kg Plutonium Equivalents, or ~670,000 Ci (using conversion factor of 0.37 Ci/gm.) Of this allowed MAR, only 295 kgs have been allotted to pit fabrication (corresponding to 109,000 Ci,) up to 441 kg of MAR can be used for PU-238 programs, and 386 kg of MAR is still unallotted.
With unvaulted MAR capable of emitting as much as ~670,000 Ci onto the floor in PF-4, it seems plausible that ~100,000 Ci could be released as smoke and dust following a DBE, facility collapse, and out-of-control fire. This corresponds to the DNFSB's worst case scenario.
Also, with this much MAR, a criticality issue would probably intrude. Interestingly, and according to a letter dated 5 Sept., 2014 from NNSA's James J. McConnell to DNFSB's Peter S, Winokur, the criticality issue has recently been readdressed.
It is true too that the allowable MAR is just a planned for upper limit, and the actual MAR at PF-4 today may be less. It which case, NNSA's future plans for PF-4 would become a subject for public inquiry.
Finally, based on JM's statement that it takes three months to produce one pit and my own simple back-of-the-envelope estimations, I imagine that the upper limit of 295 kg of MAR allotted to pit fabrication may enable the construction of many more pits per year than LANL's publically planned for maximum of 30 ppy.