Sellafield Police have reassured the public there is "no risk" to them or the nuclear plant after an incident last week which saw a man flee from the site.
The Civil Nuclear Constabulary said police officers on routine patrol outside Sellafield on Friday had approached a man who was walking near the site.
The man ran off when he was approached by CNC officers.
A spokesman for the Civil Nuclear Constabulary said: "The officers were concerned for the man’s welfare and consequently CNC police officers, along with colleagues from Cumbria Constabulary conducted a search to try and locate the individual.
"The search around the local area proved negative and the man is believed to have left the area.
"We would like to reassure the public that there is no evidence to suggest there is a risk either to the public or the Sellafield site."
The matter was referred on to Cumbria Constabulary who investigated whether any immigration offences had been committed.
The Civil Nuclear Constabulary said they understood that Cumbria Police are "no longer investigating the matter".
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 The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.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