The Department of Energy’s nuclear-weapon sites are modifying confinement vessels for planned underground subcritical plutonium experiments, after one such vessel blew a leak last year.
A confinement vessel is designed to contain an explosive compression of plutonium metal, which is rigged to bring the material to the brink of a fission chain reaction. Observing that process helps DOE’s National Nuclear Security Administration (NNSA) gauge how well plutonium retains its destructive power as it ages.
The confinement vessel used in the February 2019 “Ediza” subcritical test, however, sprang a leak on one diagnostic port. That ejected radioactive material into the zero room at the deep-underground U1a Complex at the Nevada National Security Site, forcing personnel to spend about a month cleaning up.
Now, other vessels have been reinforced to prevent another messy subcritical shot, a spokesperson for the Los Alamos National Laboratory said Tuesday. Los Alamos and the rival Lawrence Livermore National Laboratory in California each use the vessels at Nevada for their own subcritical tests.
“The vessel confinement system has been enhanced,” the spokesperson wrote in an email.
These improvements include “adding additional o-rings to radiographic ports and covers, adding material to radiographic covers to increase strength and stiffness, and improving the bolt surface finish for all radiographic ports,” according to a recent report from the Defense Nuclear Facilities Safety Board (DNFSB).
The NNSA sites identified confinement vessel issues before the Ediza test, the board said.
In late 2018, the DNFSB warned there were “several quality assurance concerns with the confinement vessel to be used for the next experiment at the U1a Complex.”
“In particular, the vessel did not meet requirements that were intended to minimize and/or prevent the risk of brittle fracture and identify any surface defects,” the board wrote.
Despite the leaky Ediza vessel, and the monthlong cleanup, Los Alamos has said no one, other than the on-site cleanup crew, ever came anywhere near the radioactive material ejected by the experiment.
Between the zero room and the underground complex that houses it, “the containment system worked as designed, assuring adequate protection of employees, the public and the environment,” the Los Alamos spokesperson said.
Ediza was an experiment by Lawrence Livermore, and Los Alamos is next on the subcritical testing schedule. The New Mexico lab plans to fire the first of three planned Nightshade tests some time in 2020. Los Alamos has repeatedly declined to share the scheduled shot dates.
