Ten workers at the Dounreay nuclear plant are suspected to have been exposed to low-level radioactivity.
The staff were decommissioning a laboratory at the time
Routine monitoring has shown that only half the group received a dose which is considered serious enough for further investigation.
Tests have been completed on two, whose intake has been calculated to be less than four per cent of the annual limit for radiation workers.
They were decommissioning a laboratory when they were contaminated.
The former experimental reactor site in Caithness is being taken out of service and is due to be handed over to the Nuclear Decommissioning Authority next April.