Pending "rigorous retraining," Los Alamos National Laboratory temporarily suspended workers who violated safety protocol for handling nuclear materials last month, the National Nuclear Security Administration said Tuesday. The agency said the incident posed no threat to workers or the public.
The U.S. Energy Department sets limits on the amount of nuclear materials that can be kept in a given area to prevent an unintentional, self-sustaining nuclear chain reaction, which can lead to an explosive release of radiation, depending on the amount and type of radioactive materials present.
A spokeswoman for the NNSA in Washington, D.C., said in an email Tuesday that the lab "did not follow its operating procedures during a movement of materials within its plutonium facility" but that the "amount of material involved was well within parameters known to be safe. At no time was there any risk of an inadvertent criticality. There was also no risk of injury or exposure to the workforce or public."
The statement partly contradicted a weekly report from the Defense Nuclear Facilities Safety Board, an independent adviser to the Energy Department, which detailed the incident in mid-August and called it a nuclear criticality safety event, meaning there was a possible threat that an unintentional nuclear chain reaction could have led to a radiation accident.
Preventing such a reaction is a main objective of safety programs at nuclear facilities, according to the International Atomic Energy Agency.
The safety board, in a Sept. 1 weekly report, said workers
at the lab's plutonium facility moved a plutonium shell into an area that already contained plutonium metal, "violating the posted limit set" and posing risks of a reaction. The materials were placed in the location Aug. 18, the safety board said, but workers
failed to notice or report the violation until Aug. 21. The New Mexican reported on the incident Saturday.
Toni Chiri, a spokeswoman for the NNSA's Los Alamos Field Office, said further investigation revealed that the event occurred Aug. 17 but was not self-reported by the lab until Aug. 22, according to the "official timeline."
The event was related to the construction of plutonium pits, the grapefruit-sized atomic cores that trigger a fission reaction inside a nuclear weapon. The hollow exterior shells that surround the pits are made in the lab's casting room, which is where the incident occurred. The NNSA has said it wants to build as many as 80 pits per year by 2030 and has tasked Los Alamos with that mission.
The unspecified number of workers
involved in the August incident were suspended to undergo retraining, the NNSA spokeswoman in Washington said, and the lab has "taken steps to help prevent a similar event in the future."
"NNSA requires its contractors to meet the highest standards of safety while working with hazardous and nuclear materials," she said, adding that there are multiple layers of "defense" to prevent accidents. "These multiple layers of defense account for the fact that people will occasionally make mistakes and that equipment will occasionally malfunction."
In 2011, a near miss occurred at the lab's plutonium facility when workers
placed plutonium rods in a row to take pictures, creating the risk of a nuclear chain reaction, according to a safety board report at the time. The error, which revealed "significant weaknesses in the criticality safety and conduct-of-operations programs," the board said, led to an exodus of skilled workers
and a shutdown of the plutonium facility in 2013.
Work slowly began to resume at the facility in late 2015, but a review of safety operations for fiscal year 2016, which covered this restart period, found 23 criticality events, making Los Alamos the only Department of Energy site to fail its nuclear criticality safety program review that year.
The lack of a skilled workforce also remained an issue within Los Alamos' safety operations, said the audit, released in February.
The safety board, in its Sept. 1 report, said, "Notably, this casting operation had recently completed a federal readiness review and is one of the few operations where the crew that underwent readiness has not experienced personnel turnover."
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