The HSE said the contractors are unlikely to suffer long-term effects
Sellafield has pleaded guilty to health and safety breaches after two contractors were exposed to radiation.
The workers were refurbishing a floor at the site's plutonium finishing and storage plant in July 2007 when they were exposed to airborne contamination.
Sellafield Ltd admitted failing to discharge its duty under the Health and Safety Act 1974 at Whitehaven Magistrates' Court on Friday.
The case was sent to Carlisle Crown Court for sentencing on 21 August.
The Health and Safety Executive had previously said the contractors had not shown any illness arising out of the incident and that the likelihood of adverse long-term effects from the level of dose received was low.