A Sandia National Laboratories building where the lab conducts performance tests on non-nuclear nuclear-weapons components opened back up for its regular work schedule Monday after closing down for a COVID-19 deep-cleaning, the labs network said.

Sandia said last week that one person in Building 720, home of the Ion Beam Laboratory, tested positive for COVID-19, the respiratory disease caused by the novel coronavirus that broke out in China last year, and that the building would close down for cleaning while the lab conducted contact tracing.

Now, “all employees who have confirmed contact with the individual who tested positive have been contacted by the Sandia Medical Clinic,” the lab wrote in a statement posted to its website.

This is the second time, at least, that Building 720 has shut down because of COVID-19. The building reopened after a previous closure and deep cleaning on April 6. Sandia can use the building’s high-energy ion beams to performance-test non-nuclear nuclear-weapons components, including by exposing them to radiation environments.

Since March 15, most Sandia employees have been working from home. A lab spokesperson said Friday that some 60% to 75% of its roughly 12,500 employees are still working remotely. As at other Department of Energy nuclear-weapon sites managed by DoE’s semiautonomous National Nuclear Security Administration (NNSA), some Sandia employees have been working on site throughout the pandemic.

The NNSA has had a spate of minor nuclear-weapon maintenance programs ongoing throughout the pandemic, and is preparing for major refurbs of the W88 submarine-launched ballistic-missile warhead and the B61 nuclear gravity bomb. Sandia, which designs non-nuclear weapons components, has a role in those programs, and all the other major refurbishments that are further back in the NNSA’s production pipe.

NNSA plans to finish the first-production unit of the refurbished warhead, W88 Alt-370, in July 2021. The first refurbed bomb, B61-12, is supposed to be done in November 2021. The first-production unit is the immediate precursor to mass production. Both refurbs are supposed to add several decades of service life to these aging weapons.

Sandia can test its own employees for COVID-19 and had processed nearly 2,000 tests as of Friday, the labs spokesperson said. As of last week, Sandia had confirmed 40 cases of COVID-19 among its workforce, including 31 in its main campus at Albuquerque, and nine in its Livermore, Calif., satellite office, located near NNSA’s Lawrence Livermore National Laboratory.