Lab questioned on plutonium safety

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By Roger Snodgrass

Los Alamos National Laboratory is adopting extra safety measures for added assurance against an almost inconceivable accident related to a highly radioactive isotope stored in the Plutonium Facility.


The problem has been addressed, according to the National Nuclear Security Administration. A letter by NNSA Administrator Thomas D’Agostino stated that several precautionary steps are underway and that his organization and LANL intend to accomplish one or another possible upgrade by June 2010.


“The unmitigated consequences of an over-pressurization event involving even a single container of HS-Pu (heat source plutonium) amount to nearly 500 rem; the consequences of multiple failures are much higher,” wrote Defense Nuclear Safety Board Chairman A.J. Eggenberger to Energy Secretary Chu early last month.


By comparison exposures from the “Fat Man” plutonium bomb dropped on Nagasaki August 9, 1945, is generally measured in hundreds of rem.


The average exposure of the general U.S. population from natural background radiation is a little more than one-third rem per year, according to the National Council on Radiation Protection and Measurements.


Eggenberg’s warning refers to approximately 200 “non-safety class” containers that currently store plutonium-238 for use in thermal powered spacecraft systems. To compensate for the substandard containers, they are submerged in a vault water bath.


The water cooling is necessary because the decaying plutonium generates intense heat, which could cause excess pressure to build in the containers.


But, according to a March 27 site report by a local representative of the Defense Nuclear Facility Safety Board, managers of the Plutonium Facility discovered several more potential hazards, prompting them to devise additional safeguards.


At the time the vaults were inspected on a monthly basis to make sure there was enough water in the vault water bath, but after concerns raised by the DNFSB, it was discovered that “the existing minimum water level checked by the surveillance was too low” to keep all the non-safety class containers fully covered as required.


Also, LANL’s calculations revealed that “credible system upsets” could cause the water in the vault to boil away within 18 hours, which could easily go unnoticed in the meantime.


Ten days later, DNFSB Chairman A.J. Eggenberger wrote to Energy Secretary Chu calling attention to the “unresolved issues,” “the indeterminate and degraded state” and “a state that is unacceptable to the Board.”


In reply, D’Agostino, transmitting a report this week requested by Eggenberger. He stated that a camera would be installed in the next few weeks to provide daily monitoring of the water level and that LANL had been directed to identify actions to be taken in the event of the failure of the vault water baths.


The associated reported, forwarded April 23 from the Los Alamos Site Office, provided more details. About 160 containers, identified as “Russian Product Containers,” were identified as the weak link, according to the report, but would have adequate margins for another 18 months even if exposed to the air.


The LASO report also updated calculations on how long it would take to boil the bath water (33 hours) and to boil off enough water to uncover the containers (52 hours).


Interim safety measures were installed while the problem was studied, but that caused all operations involving the moving of containers to be suspended. More water was added to the vaults and greater care was taken in the stacking of the containers.


The LASO report concluded that “a daily check of the water baths would be sufficient to detect and correct a problem with the vault water baths.”


While the amount of plutonium-238 in storage at Los Alamos is classified, the inventory is apparently a large portion of the relatively small amount of the isotope in existence.


A relatively large stockpile existed at the time the nuclear weapons production facilities were shut down in 1988. A draft report by the National Research Council released earlier this year said that the fuel supply could be exhausted before the stockpile could be replenished.


LANL referred questions about the matter to NNSA headquarters in Washington. A spokesperson provided a link to D’Agostino’s letter and enclosure.


In an April 30 article about lengthy delays in finalizing a contract for the plutonium 238 program at LANL the Monitor noted Eggenberger’s concerns about the safety issue and included a strong warning from his letter of April 7 to Chu.


“Many of the highest consequence accidents at LANL involve the processing, handling and storage of plutonium-238 enriched heat source plutonium,” Eggenberger wrote.