External contamination of a worker leading to exceeding of the annual statutory dose limit for the equivalent dose to the skin

On 6 June 2024, in the reactor 4 building, which was in a maintenance and refuelling outage, a worker was fitting heat insulation.

During the reactor building exit check, contamination was detected on the worker’s foot. The agent was immediately taken care of by the medical service,which removed the radioactive particle causing the contamination.

For workers likely to be exposed to ionising radiation in the course of their professional activity, the annual statutory dose limits for twelve consecutive months are 20 millisieverts for the whole body and 500 millisieverts for a skin surface area of 1 cm².

The dose received by the worker was estimated, notably by the licensee and the occupational health service, on the basis of worst-case hypotheses in terms of exposure duration. It is potentially greater than the statutory annual limit for the skin.

Despite the investigations carried out along the route followed by the worker, the areas or points of contamination that could have caused this contamination could not be determined.

ASN carried out a reactive inspection on 20 June 2024, which showed that the steps taken with regard to the employee were appropriate but that the origin of this contamination remained unknown. Therefore, as a precaution, the decision was to assume that the employee could have been contaminated as soon as he entered the reactor building. In this case, the dose likely to have been received by the employee is higher than the statutory annual limit on the skin.

Owing to the statutory annual exposure limit for a worker having being exceeded, this event was rated level 2 on the International Nuclear Event Scale (INES).