Analysis of sulfate ion content increase in the primary circuit of VVER

Regarding the abnormal increase of sulfate ion content in the spent fuel pool during the refueling period, all the adding reagents which may produce sulfate ion in the primary circuit and spent fuel pool were investigated, and such adding reagents as feedwater, boric acid, KOH solution are excluded as the main sources of sulfate ion generation. It was found out that the oxidizing substance generated under the conditions of radiation and enriched oxygen in the spent fuel pool and sulfonic group of cation resin was oxidized and decomposed into sulfate ion when resin bed purified the spent fuel pool through the analysis of changing trend for sulfate ion content in the spent fuel pool during the refueling period. Based on the research results, the run mode of resin bed was optimized and the abnormal increase of sulfate ion content in the primary circuit commonly existing in VVER was controlled effectively. (authors)