In November 2010 several persons were exposed to radiation during repair of an X-ray machine at Boliden Mineral AB. The event was immediately investigated on site by a team from the Swedish Radiation Safety Authority. Based on new dose estimations and on the criteria of defence in depth, the Authority has now made a final classification of the event as INES Level 2.
The X-ray machine is used for metal analysis of ore in Boliden Mineral AB's mining process at the Aitik mine in Gällivare. On Monday 29 November, the X-ray equipment was malfunctioning and troubleshooting and repair work started, and was conducted for a period of three days. The work was performed in a way where an unintentional exposure situation occurred. Seventeen persons were either directly involved in the repair work or visited the area where the X-ray equipment was present. Some of them were reported to have experienced nausea, eye irritation, headaches, dizziness and fatigue. All seventeen persons were considered potentially exposed to X-rays and underwent a medical examination. Blood samples from eight persons were sent for analysis of chromosome aberrations to be used for biological dosimetry.
On Thursday, 2 December 2010, the Swedish Radiation Safety Authority received information from Boliden Mineral AB stating that personnel might have been exposed to X-rays while repairing an X-ray machine. The Authority investigated the event and the investigation showed that four persons may have received radiation doses exceeding annual dose limits for employees under the Authority's regulations. The investigation showed that the event was a result of several interacting factors, including unclear allocation of responsibility, deficiencies in terms of skills and training, unclear information and inadequate routines. No deterministic effects have been reported from the event. None of the persons carried a dosimeter during their work, for which reason the doses were assessed based on air kerma measurements and the estimated time spent in the radiation field.
The persons were mainly exposed to scattered X-rays of maximum energy 7 keV. Two persons received an effective dose of 1 â€“ 8 mSv. Both the equivalent dose to the lens of the eye and the equivalent dose to the skin were for one of the persons estimated to be in the range 80 â€“ 500 mSv. For the other person, the corresponding eye and skin doses were estimated to be in the range 250 â€“ 1000 mSv. The annual dose limits for occupational exposures are 50 mSv for effective dose, 150 mSv for the equivalent dose to the eye lens, and 500 mSv for the equivalent dose to the skin.
The Authority is very concerned about this event and several actions were taken and restrictions made to ensure short-term safety. Since no safety provisions were remaining during the maintenance work, it was only fortunate that additional persons were not exposed to much higher doses. The Authority has now filed charges against Boliden Mineral for non-compliance with the Radiation Protection Act and the Authority's regulations. An extensive programme for following up and inspecting the company's activities will be carried out over the next two years.