The army will arrive in Sellafield this afternoon to provide extra protection now the national terror threat level has been raised to critical.
Officers from the Civil Nuclear Constabulary (CNC) are being deployed elsewhere in the country, as part of a government-led operation, following Monday's attack in Manchester.
Soldiers have been drafted in to the nuclear plant in order to "maintain the site's security levels."
They will work alongside civilian guards in the same was as CNC and will not mean any changes to the usual access arrangements and levels of security checks for workers.
It's part of Operation Temperer, which kicked in when Prime Minister Theresa May raised the threat level to critical last night.
The operation will put thousands of soldiers on the street.
A memo, sent to staff, said: "This is a scenario which Sellafield Ltd, CNC and the MoD has planned for and exercised in the past.
"It is not due to an escalation of the perceived threat to the site, it is a resourcing solution as protection levels are escalated in civilian areas across the country."
Armed troops are being deployed to guard "key locations" across the UK, after the prime minister raised the threat level to 'critical', putting Operation Temperer into action.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here