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Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Tue, 07-10-2025
ERF description: On 13. 1. 2025, the lcencee reported a radiation emergency when an unplanned radiation exposure of a radiation worker occurred. The worker was in the radiation room with a source of ionizing radiation - the Chisostat SO 1 irradiator, which contained a sealed radionuclide source ("URZ") Co-60 with an activity of 30TBq as of 13. 1. 2025. At the time of the preparatory work, the source was not in a shielded position. The total time the worker spent in the radiation room during 2 entries (7. 1. 2025 and 13. 1. 2025) was about 12.5 minutes.

The investigation found that the last time the irradiator was used on 18. 12. 2024, it was incorrectly turned off. The irradiator was turned off by the main circuit breaker (not via the main control console), therefore the source was not put into the shielded position. It was also found that the backup power source (UPC), which would ensure the insertion of the source even in the event of an erroneous shutdown, was not functional. Before entering the radiation room, the worker did not use a portable dose rate meter in either case to verify the radiation situation, and was not equipped with a personal electronic dosimeter that would have alerted him to a non-standard situation (increased dose rate).

No one else entered the radiationroom between 18. 12. 2024 and 13. 1. 2025.

The total effective dose received by the radiation worker for both days (7. 1. 2025 and 13. 1. 2025) was estimated at 150 mSv. The equivalent dose to the radiation worker's hand was estimated at approximately 8 Sv. Deterministic effects (radiation dermatitis) have not yet been detected (within approximately 8 months of the event).

The radiation emergency is still under investigation by SÚJB inspectors. During 06/2025, the irradiator experienced another malfunction, probably related to the age of the irradiator. Due to the suspicion of a stuck shielding block, the specialist company recommended that the irradiator be dismantled and taken out of service.
ERF rating date: 03-10-2025
ERF contact person: Bohuslav Novotny
ERF address: Reported by State Office for Nuclear Safety of Czech Republic on 07 Oct 2025. Last update on 07 Oct 2025
ERF affiliation: State Office for Nuclear Safety

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