Regulatory oversight of nuclear safety in Finland. Annual ... - STUK

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4.1 Loviisa NPP The Loviisa power plant also intends to expand the group of people dealing with operating experience feedback. The procedures for utilising international operating experience feedback function well at the Loviisa power plant. Foreign event reports are comprehensively analysed, and the corrective actions decided on their basis are justified and traceable. Fortum itself conducts pre-screening of the reports coming from various sources, mainly via WANO and the IRS system maintained by IAEA/ NEA. The selection criterion for events to be taken to the International operating experience team is their safety significance for the Loviisa power plant. The operating experience feedback activities and the monitoring of their impact could be further enhanced and improved using a uniform operating experience feedback database covering the company’s internal and external operating experience. The fire that occurred in connection with the containment leak tightness test performed in connection with the 2011 maintenance outage of manSv 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 µSv 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1994 STUK-B 147 Ringhals 2, and the protective plastic sheet that burned, releasing a lot of corrosive chlorides, was also identified as an issue to be investigated at Loviisa. Fortum investigated the amount of plastic materials in the reactor hall in order to assess the fire load and risk. During the cleaning operations following the fire, a possible operational risk was discovered in the containment spraying system at Ringhals, caused by foreign material found in the pipelines. The foreign material possibly consisted of plugs and welding debris dating back to the modification work carried out in 1988, and it had not been detected in the periodic tests performed using air. No similar blockage of the containment spraying system has been identified as a problem at Loviisa. The IRS reports dealing with the connecting rod bearing problems of EDGs in Germany and France had significant information for Finnish plants because the Loviisa power plant has emergency diesel generators of a similar size. The investigations performed by the power company revealed Figure 8. Collective occupational doses since the start of operation of the Loviisa nuclear power plant. 1993 1994 Figure 9. Annual radiation doses to the critical groups since the start of operation of the Loviisa nuclear power plant. Over the recent years, the doses to the critical groups have remained below one percent of the set limit, 0.1 milliSv. 1995 1995 1996 1996 1997 1997 1998 1998 1999 1999 2000 2000 2001 2001 2002 2002 2003 2003 2004 2004 2005 2005 2006 2006 Loviisa 2007 Loviisa 2007 2008 2008 2009 2009 2010 2010 2011 2011 41
STUK-B 147 4.1 Loviisa NPP Table 2. Radioactive nuclides originating from the Loviisa NPP, found in the environmental samples. Types of samples containing radionuclides originating from the NPP. Figures in the table indicate the number of samples of a certain sample type in which each radionuclide was detected. Several different nuclides may be found in the same sample. Type of sample / radionuclide H-3 Mn-54 Co-58 Fe-59 Co-60 Zr-95 Ag-110m Te-123m Sb-124 Sb-125 Total Air – 1 – 1 2 – – – – – 4 Fallout – – – – 3 – 1 – – – 4 Seawater 5 – – – – – – – – – 5 Aquatic plants – 6 6 – 9 2 9 1 5 1 39 Seabed fauna (Saduria Entomon) – – – – – – 1 – – – 1 Sedimenting materials – – – – 4 – 3 – – – 7 Total 5 7 6 1 18 2 14 1 5 1 60 that bearings of the subject type, proven to be susceptible to damage, had been installed in one of the EDGs at the Loviisa power plant in the summer 2009. The bearings were changed back to the original type in January 2011. It transpired during the basic overhaul of another EDG at Loviisa in the summer 2011 that the situation in spare bearings for the EDGs is worrying and an extensive problem because the supplier does not yet have a new, approved replacement bearing, and the old type bearings are no longer available. Fortum commissioned VTT to investigate the reasons behind the bearing damage. STUK reported the bearing problems internationally. Following the results of the root cause analysis, STUK supplemented its report submitted in 2010 to the operating experience database maintained by the IAEA regarding an event at the Loviisa power plant where radioactive resin escaped into the ventilation channel from the mixing tank of a liquid waste solidification plant in trial operation. 4.1.10 Radiation safety of the plant, personnel and the environment Occupational radiation safety STUK carried out a radiation protection inspection as part of the periodic inspection programme at the Loviisa power plant, focusing on radiation measurements in particular. The scope of the inspection included the environmental radiation monitoring programme and the instruments intended for measuring radiation at the plant. Following the inspection, STUK requested a report regarding the impact of the dosimeter box and ambient conditions of the dosimeters kept in the plant surroundings on their response and wanted to know the person appointed responsible for the radia- 42 tion measurements. STUK also required the power company to include the equipment used for collecting atmospheric samples from the environment within the scope of the periodic maintenance programme and to send the testing instructions of the three new radiation measuring instruments to STUK for information. The dosimeters used for measuring the occupational radiation doses underwent annual tests. The tests comprise irradiating a sample of dosimeters at STUK’s radiation metrology laboratory and reading the doses at the power plant. The test results were acceptable, although it was found that the test results for surface doses were systematically conservative. Closer investigation revealed that the surface doses reported to the dose register in 2011 were relatively higher in relation to deep doses when compared to previous years. As a corrective action, the Loviisa power plant intends to make technical and administrative changes to the radiation dose determination algorithms in 2012. STUK carried out targeted radiation protection inspections during the annual maintenance outages. In the inspections, STUK assessed the radiation protection personnel’s operations and resources as well as the training provided for personnel. At the same time, the activities of employees in radiation work were assessed. It was concluded that radiation protection at the plant units functions well throughout. In the inspections, it was found that the cleaning methods and equipment of the power plant in work locations where employees could be exposed to significant amounts of radiation should be developed. At the same time, it was noted that the cleaning operations have too few human resources for implementing the work efficiently, avoiding radiation doses. Follow-up of this issue will continue in 2012.
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