Approaches for reducing carbon-14 stack emissions from Korean CANDU nuclear power plant

Relatively high carbon-14 emissions, which occurred at Wolsong Nuclear Power Plant during 1998 and 1999, made the site staff to implement several operational improvements: (1) restriction of the maximum in-service time of moderator ion exchange (IX) resin columns to 80 days, (2) discontinuation of the practice of re-using 'used' IX resin columns for removing the gadolinium nitrate at star-up, (3) reduction of the frequency and volume of the moderator cover gas purging through increased O2 additions to the cover gas. In this way, the emission rates returned to normal levels during the remainder of 1999 and 2000. To optimize the use of the moderator IX resin column, the special surveillance was carried out at Wolsong Unit 3. This showed that only the 14C stack emission data were a practical indicator for exhaustion of IX resin column. From this data, a criterion was derived: IX resin column can be put in service for 100 days unless a 14C emission rate higher than about 20 GBq·month-1 (0.4 Ci-month-1) takes place for two consecutive weeks. Finally it was suggested that using a portable 14C scrubber could benefit for reducing the 14C stack emissions, especially those due to leakage of the moderator cover gas. (author)