Note: This story was updated at 11:45 a.m.

On Monday, the Y-12 National Security Complex began limited operations and transitioning to mission-critical operations. The change is in response to the COVID-19 pandemic. For now, all non-essential personnel will leave the 811-acre nuclear weapons production plant in Oak Ridge, and employees who can telework will continue to do so.

“Since mid-March, Y-12 has been in a preventive phase of its pandemic plan,” the site in a a response to questions on Wednesday. The response was provided by spokesperson Kathryn King of Consolidated Nuclear Security, a federal contractor that manages and operates Y-12 and another nuclear weapons production plant, the Pantex Plant northeast of Amarillo, Texas.

“With additional cases now confirmed at Y-12 and the growing number of cases in East Tennessee, the plant is transitioning to a ‘containment’ phase that ensures mission-critical operations while further protecting the Y-12 workforce and the community,” the response said. “In the containment phases, all non-essential plant personnel will leave the site until further notice. Employees who are able to telework will continue to do so.”

CNS said all Y-12 processes, systems, and facilities will be maintained in safe and secure configurations. Key mission activities related to stockpile stewardship and modernization, and key infrastructure and reestablishment of production capabilities, will continue.