Radiation exposure incident at Olkiluoto 3 during repair of hoist equipment in June
Four persons were exposed short-term to high radiation dose rates during repair work carried out on hoist equipment at the Olkiluoto 3 plant unit in June 2024. The exposure incident occurred during the lifting of a dummy fuel element. The incident did not cause any personal injuries.
The test weight used for the auxiliary hoist was a dummy fuel element which does not contain fuel. In this case, however, the dummy element contained a control rod that had been used in the reactor and was radioactive.
The lifting operation was discontinued immediately due to alarms issued by radiation monitors and the dummy element was lowered back underwater. The maximum personal dose caused by the incident was 40 µSv *) which did not cause any personal injuries.
The identified causes of the incident include unclear responsibilities, shortcomings of administrative procedures and guidelines as well as deficiencies in communication. Also, there were no engineering barriers in place designed to prevent the incident by stopping the lifting of the dummy element above the surface of water.
TVO launched actions immediately after the event to prevent the recurrence of a similar event. From now on, in all work that involves the handling of dummy elements, similar administrative requirements are to be applied in work management as in actual fuel handling work. In addition, the handling and markings of dummy elements will be made clearer and the presence of radiation protection personnel is required in every lifting operation above the water surface.
TVO has on 6 September 2024 submitted a special report addressing the matter to the Radiation and Nuclear Safety Authority of Finland (STUK) for approval. TVO has evaluated the classification of the event to be rated to level 1**) on the international INES scale. STUK will determine the final INES classification during the processing of the special report. Although the evaluated basic classification of the event is 0, TVO has upgraded it to 1 due to the identified deficiencies in the management of a radioactive component.
*) 1 mSv is 1000 µSv. The annual dose limit of a radiation worker specified by STUK is 20 mSv during one year. 40 µSv equals the radiation dose obtained during air travel of about 8 hours.
**) The degree of severity of events occurring at a nuclear power plant is classified on the international INES scale. The INES scale has seven categories of severity. Category 4–7 events are classified as accidents, category 1–3 events as incidents or anomalies with a negative effect on safety, and category 0 events as deviations with no significance for safety.
For further information, please contact:
Johanna Aho, Head of Communications, Tel. +358 (0)40 729 0822