The Los Alamos National Laboratory has traced an unprecedented radioactive leak during an explosive plutonium test in 2019 to a breached diagnostic port in the steel container that housed the subcritical experiment, a lab spokesperson said this week.
“A diagnostic port was momentarily displaced due to the dynamic pressure exerted on the confinement vessel during experiment execution,” the lab spokesperson wrote in a Thursday email to Nuclear Security & Deterrence Monitor.
That is the official conclusion of an unreleased causal analysis the nuclear weapons laboratory completed on Dec. 24, the spokesperson said. The lab detonated the underground subcritical test, called Ediza, on Feb. 13 at the Nevada National Security Site’s U1a complex. The independent federal Defense Nuclear Facilities Safety Board disclosed the leak in a subsequent report.
The defense board said that immediately after the experiment, which was performed in isolation from the rest of U1a in a zero room, Honeywell-led site contractor Mission Support and Test Services “identified cracks in [the Ediza vessel’s] fastener washers but found no evidence that the cover plates on the vessel were fractured.”
It took about a month to decontaminate the zero room. No personnel were exposed to contamination from the leak, the lab said. The Ediza vessel has since been entombed at the test site.
Data from the Ediza test was usable, despite the leak, Los Alamos told NS&D Monitor after the mishap. The lab sidestepped questions this week about whether Lot 1 steel confinement vessels, one of which was used for Ediza, are fit for future explosive tests.
“There are no plans to use other Lot 1 confinement vessels for subcritical experiments,” the lab spokesperson wrote Thursday.
Subcritical experiments explosively compress plutonium, yielding data the National Nuclear Security Administration can use to determine how much destructive power the fissile material — which powers every U.S. nuclear weapon — has retained as it ages. Subcritical experiments do not create a nuclear yield: a norm for the U.S. since it ceased full-up underground explosive tests in the 1990s.
Editor’s note: the story was updated to show the test happened in 2019.
