APPLICATION OF HI-F COAT TO REDUCE RECONTAMINATION AT SHIMANE UNIT 1

摘要

Chemical decontamination is one of effective methods to lower the environmental dose rate in the containment vessel to reduce radiation exposure at nuclear power plants. However, it is difficult to keep a low piping dose rate for several operation cycles after chemical decontamination. So, a new method Hi-F Coat was developed to reduce recontamination after the chemical decontamination. Hi-F Coat was first applied to Shimane Unit 1 during the 27th outage in 2008. Application targets of chemical decontamination and Hi-F Coat treatment were both A and B loops of PLR piping. Average amount of formed film was about 270 (μg/cm~2 which was enough in order to reduce Co deposition based on the laboratory test results. As a result of NWC operation of 90 days and Hi-F Coat, the dose rate of PLR piping became lower at the 28th outage. It was about 0.4 mSv/h and less than half of the previous recontamination level after one cycle operation. We evaluated the contribution of NWC operation of 90 days and Hi-F Coat and concluded that the recontamination was suppressed about 1/2 to 1/3 by Hi-F Coat. Hi-F Coat film was also confirmed to be removed easier than the natural oxide one by chemical decontamination.