The Sandia National Laboratories in New Mexico temporarily closed parts of the MESA complex where it produces radiation-hardened microelectronics for nuclear weapons after someone working there tested positive for COVID-19.

However, the Department of Energy-operated, nuclear weapons-engineering labs network said it planned to reopen Buildings 858N and 858EF on Thursday morning, after shutting them down for deep cleaning. Sandia is attempting contact tracing with “state and federal health officials” to determine where else on its sprawling campus, and elsewhere, the infected person might have been shortly before testing positive, according to a statement posted online Tuesday, when Sandia disclosed the labs’ latest confirmed case.

“All employees with confirmed contact with the individual who tested positive will be contacted by the Sandia Medical Clinic for further instructions within 24 hours,” Sandia wrote Tuesday.

Sandia now has 12 confirmed cases of COVID-19. The labs say they are able to test its own workforce for the viral disease, using contractor AB Healthcare Solutions of Gilbert, Ariz., to perform nasal swabs that are analyzed on-site. It was not clear whether the labs relied on this capability to confirm the positive case just announced in the vicinity of the Microsystems and Engineering Sciences Applications complex.

As of last week, the Department of Energy’s National Nuclear Security Administration (NNSA) in Washington, D.C., said it had tracked 65 confirmed cases of COVID-19 across the U.S. nuclear weapons design-and-production complex since the viral outbreak hit the United States in January. The civilian agency has not disclosed how many people wound up in mandatory two-week quarantine because of suspected contact with a co-worker who later tests positive, but quarantines at some NNSA facilities have in the past have handily outnumbered confirmed infections.