Part of Sellafield is due to close down in response to the Covid-19 emergency.
The nuclear plant at Seascale is due to shut its Magnox plant in the coming days.
A company spokesman said: "We have a critical mission so our response must ensure the safety and security of the public, our workforce and protection of the environment at all times.
"The Government’s evolving response means we must now scale back some operations to make best use of available people. This allow us to keep a focus on delivering high hazard risk reduction activities.
"As a proactive measure, to retain the reprocessing stream in a sustainable state for the future, we are moving to a controlled shutdown of the Magnox reprocessing plant over the next few days.
"This approach will enable the best opportunity for an effective re-start when circumstances permit. With safety in mind, similar measures may be necessary elsewhere across the business."
Remote working is being organised for employees at Sellafield Ltd as a measure to prevent the spread of coronavirus.
However some workers will still be required to attend the site.
The spokesman added: "We have developed plans for wider remote working but given the number of employees we have and the range of roles we undertake, this isn’t a simple task.
"We need to be flexible and agile, so that we minimise the spread of the virus by minimising the time we spend together, while at the same time operating the business to the best extent with the people we have available at any given time."
A communication to employees said: "Given the nature of our work many of you will need to continue to attend your workplace – either because your work directly impacts nuclear safety or security, or because you provide a business continuity or support function and are unable to work remotely. Your line manager may require you to attend work for some of the time to deliver your role.
"Where possible we seek to enable employees working from home. You should determine how this arrangement will work in discussion with your line manager. You may still need to come into work on occasion to access our systems or to provide support and input in other ways to the business."
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