By John Fleck, Albuquerque Journal Staff Writer
Los Alamos National Laboratory is watching stored plutonium more closely after safety auditors found a risk that water used for cooling the material could boil away, leading to what in a worst-case scenario could be a deadly radiation accident.
If the cooling system were to fail, there would be a chance plutonium containers could burst, according to federal auditors with the Defense Nuclear Facility Safety Board. Such an accident would have the potential to release a deadly dose of radiation within the lab's main plutonium complex, according to the Safety Board, which called the problem "one of the laboratory's highest consequence accident scenarios."
The Safety Board analysis did not look at the question of whether plutonium could escape the building.
To deal with the problem, Los Alamos workers have begun checking daily to make sure the water level does not drop, according to National Nuclear Security Administration chief Tom D'Agostino.
A Los Alamos National Laboratory spokesman referred questions to the NNSA.
The lab plans to eventually reduce the risk by ensuring that all the plutonium is stored in containers that can withstand a loss of cooling without bursting, D'Agostino wrote in a letter to the Safety Board.
The problem involves 200 containers used to store plutonium-238, a type of the radioactive metal used to make long-lived power supplies for NASA deep space missions. The power supplies use heat from the plutonium's natural radioactive decay to generate electricity and warm spacecraft parts.
The natural heating, while an advantage in spaceflight, poses problems for plutonium in storage. Inside storage containers, helium builds up as the plutonium decays. Heat then raises the pressure of the helium gas, creating a risk that a container could burst, according to an April 7 letter from the Safety Board to the National Nuclear Security Administration.
The first line of defense is containers that can withstand the heat and pressure. But according to the Safety Board, 200 containers at Los Alamos either do not meet that safety standard or there is insufficient data to determine whether they are safe.
In a worst-case scenario, according to the Safety Board, a single bursting container could release a 500 rem radiation dose (the rem is the standard measure of radiation exposure). According to the U.S. Nuclear Regulatory Commission, a person exposed to a 500 rem dose "will likely die without medical treatment."
To reduce the risk, the containers are stored submerged in water, with a cooling system to ensure the water does not boil away. If the cooling system fails, the Safety Board wrote in its letter to NNSA, the water could begin boiling away within 18 hours, leaving the containers uncovered and subject to heating and eventual bursting.
Of the 200 suspect containers, a preliminary analysis suggests 160 could safely be left uncooled for 18 months, according to a report by NNSA staff to the Safety Board made public this week. An additional six containers have so little plutonium in them that they pose no risk, according to the report.
NNSA staff is still determining the risk posed by the remaining 34 containers.
In the meantime, according to D'Agostino's letter, Los Alamos has installed a camera to allow remote monitoring, and water levels are being checked daily. The tank is to be refilled as needed to ensure there is at least an inch of water above the questionable containers.
Eventually, the lab plans to repackage plutonium into safer containers, a task scheduled for completion in summer 2010, according to D'Agostino's letter.