Effect of design improvements in heavy water management systems to reduce heavy water losses and tritium releases at Wolsong 2,3 and 4

Design improvements are being incorporated into the heavy water management systems at Wolsong 2,3 and 4 to reduce the load on the vapour recovery driers and upgraders and the heavy water losses via the stack. There will also be improvements to monitor heavy water and tritium releases. This paper describes the improvements, gives background on heavy water balance mechanism, the historical trends for heavy water recovery/losses and estimated dose to the member of the public critical group resulting from the airborne and waterborne releases. The measured tritium activity levels in the heat transport system (HTS) and moderator system at Wolsong 1 are given. Using these activity levels and heavy water loss data, tritium losses from the dried and ventilated areas are estimated. A qualitative assessment of expected heavy water and tritium releases has been performed for Wolsong 2, 3 and 4. CANDU 6 plants continue to perform well in that heavy water losses are small and tritium releases are well below the design/operating targets. Tritium is retained so effectively that only small quantities are released, consequently it makes only a small contribution to the dose to the member of the public. With the design improvements in the heavy water management systems, it is expected that tritium releases to the environment and resulting public dose will be even lower for Wolsong Nuclear Power Plant. (author). 1 ref., 4 figs, 4 tabs