The National Nuclear Security Administration in November shot its first deep-underground test involving special nuclear materials at the Nevada National Security Site in more than a year, according to a recent report from the Defense Nuclear Facilities Safety Board.
The Los Alamos National Lab and Nevada site prime Mission Support and Test Services supervised the test, according to the defense board. It was the first experiment with special nuclear material in the site’s U1a Complex since the Ediza test of February 2019, during which conventional explosives used to compress a plutonium sample inside a metal sphere to a sub-critical mass blew out a diagnostic port on the containment vessel and leaked contamination into the test room.
This time, Los Alamos and Nevada site personnel took extra precautions, including a new o-ring arrangement for the ports, and plastic coverings for “possible contamination locations” that might wind up in an accidental blast zone, if the vessel once again failed to hold its seal, the defense board reported.
With the Ediza tests in the bag, Los Alamos was scheduled to move on to the Nightshade series of tests. There were three of these subcritical tests planned. The National Nuclear Security Administration (NNSA) delayed the tests into fiscal year 2021 because of COVID-19. The agency had planned to fire the Nightshade shots in fiscal year 2020, prior to the pandemic.
Subcritical tests produce no sustainable nuclear yield, but explosively compress plutonium almost to the point of a fission chain reaction. Observing that compression allows the NNSA’s weapons labs to determine whether plutonium is aging as expected — an important consideration when the U.S. produces no new plutonium and is still a few years away from being able to cast more than a handful of new plutonium pits annually.
