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

On 27 August 2021, ASN (Autorité de Sûreté Nucléaire), the French nuclear regulator, was notified by the Cruas nuclear power plant licensee of a significant radiation protection event concerning the exceeding of an annual individual dose limit by an EDF employee.

On 24 August 2021, two operators were checking the sealing of the pneumatic valve air supplies in the reactor 2 building. This check consisted in spraying the connections between these valves and the instrument compressed air distribution system (SAR) with an aerosol to detect any leaks.

On leaving the controlled zone, the radioactivity monitor revealed contamination of one of the workers in the "shoulder—head" region. The medical service immediately took charge of the employee and located the radioactive particle causing the contamination at the nape of the neck. The particle was removed.

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

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.

Consequently, EDF conducted an evaluation of the received dose considering that the particle was present from the moment the worker entered the reactor building until the particle was removed. This evaluation gives a dose at the nape of the worker's neck exceeding the regulatory limit set for the equivalent dose to the skin. The whole body dose received by the worker, however, is well below the regulatory annual limit.

ASN conducted an on-site inspection on 31 August 2021. The inspectors verified that EDF had taken all the necessary measures to manage the event appropriately and to analyse its causes. An event analysis report setting out the corrective actions put in place to prevent its recurrence must be transmitted to ASN within two months.

Owing to the exceeding of an occupational regulatory exposure limit, this event was rated 2 on the International Nuclear and Radiological Events Scale (INES).