Testing practice and operating experience of off-gas cleaning systems gained during the first years of operation at Finnish PWR nuclear power stations

Imatran Voima Oy (IVO) is a Finnish power company in possession of two 440 MWe PWR nuclear power stations at Loviisa. The reactor primary and auxiliary systems were delivered mainly from the Soviet Union. The off-gas system consists of ambient temperature charcoal beds and iodine filters. Active gases from degasifier and tanks connected with the primary circuit pass before delay through the hydrogen recombiner. Regeneration gases from a desiccant dryer are led through iodine filters. Gases from other active tanks pass through a scrubber and an iodine filter. According to the Finnish regulations, the off-gas iodine filters must have a decontamination factor of minimum 99 percent for methyliodide. The iodine filters are to be tested after 3000 h of operation. Because of unsatisfactory test results, the filtration material of the iodine filters have been changed twice. The problems involved in these cases were moisture or chemical penetration to the filter. (author)