The Effects of Zinc injection from HFT at TOMARI Unit 3

摘要

Zinc injection for dose rate reduction has been applied since Hot Function Test (HFT) at TOMARI Unit 3 (3-Loop PWR, 912 MWe) for the first time in the world. We previously reported that the stable oxide films were formed on the inner surface of the primary materials with zinc injection, based on the results of Steam Generator (SG) insert plate analysis after HFT. We also previously reported that the dose rates of the main components and piping such as SG, Main Coolant Piping (MCP) and the inner surface of Reactor Vessel (RV) were about 50% less than the values of the reference plant (3-Loop PWR plant in Japan). It is considered that the corrosion of the materials and the radioactive Co uptake into the inner oxide layer were suppressed by zinc injection. (These were reported at AWC 2009 in Nagoya, 2013 in Taiwan, NPC 2010 in Quebec and 2012 in Paris.) The material of SG tube is 690TT at TOMARI Unit 3. Generally it is observed that the dose rates are the highest on the 1st or 2nd re-fuelling outage (RFO) at the plants with 690TT SG tube. Therefore the dose rates on the 2nd RFO at TOMARI Unit 3 were compared with the values of the reference plant. As the results, the dose rates of the main components and piping were successfully accomplished about 60 to 80% less than the reference plant. The dose rates are expected to decrease more in the future by the corrosion suppression effect and decreasing of the Ni release rate from 690TT with zinc injection. In this report, the dose rates of the main components and piping, experiences of water chemistry and the effect of dose rate reduction with zinc injection on the 2nd RFO at TOMARI Unit 3 are presented.