The Z Pulsed Power Facility at the Sandia National Laboratories in Albuquerque, N.M., was back online this week after a serious accident in June knocked the facility out of commission for three weeks, a senior laboratory employee said this week.
The June 17 accident, which shook Sandia’s high-energy density physics lab longer and harder than a typical Z-machine shot, badly damaged 18 of the pulsed-power facility’s 36 generators.
There is evidence one generator fired prematurely “because a piece of debris was present on the spark gap,” Chris Bourdon, senior manager for Z Experimental Capability Management, wrote in an email. The spark gap is a space between electrically conductive surfaces that is only supposed to carry electrical current when the Z machine is ready to fire.
When the first generator fired, it set off a cascade that knocked other generators offline, putting the Z machine out of commission for almost a month.
Nobody was injured during the June 17 misfire, a Sandia spokesperson said, although one lab employee received an electrical shock a week after the accident while examining one of the failed generators. The employee “had numbness to their hand and forearm for about 2-4 hours after the shock,” but was cleared to return to work the same day, Bourdon said by email.
As for what the debris was, “it’s hard to tell,” he wrote. “The debris was completely destroyed.”
The generators, on the other hand, were not destroyed. All were repaired, and none replaced, Bourdon said.
The Z machine is one of the National Nuclear Security Administration’s (NNSA) three main high-energy density physics facilities. The others are the National Ignition Facility at the Lawrence Livermore National Laboratory in California and the the Laboratory for Laser Energetics at the University of Rochester in New York.
These facilities subject small targets made of various materials to extremes of temperature and pressure similar to the early stages of a nuclear detonation. The operations help the NNSA verify the potency and functionality of aging nuclear-weapon components and materials without resorting to nuclear-explosive tests.
June’s failed Z machine shot interrupted an experiment called Plasma Transport 19A. The multi-shot experiment will go on, Bourdon said, with the remaining shots keeping their previously assigned places in the queue of 62 Z machine firings scheduled through December.
Z-Machine returned to service Tuesday with a shot supporting a different experiment, this one called MagLIF integration 18a, Bourdon said.
The Z machine has suffered this sort of malfunction before, Bourdon said. The last time was in 2016, although June’s misfire “caused more damage than the previous event.”
The June misfire might not be the last, either. The odds of a misfire on any given shot is “estimated at 1/800 chance of occurring,” Bourdon said.
