Recent status and some considerations on oxygenation of primary coolant at shutdown of PWR

At shutdown of PWR nuclear power plant, a oxygenation process in adopted to reduce the radioactivity level in the primary coolant. Recent status of oxygenation is surveyed to clarify the water chemistry behavior of the coolant, such as pH, DO, H2O2, and radionuclides. To propose a new oxygenation process, characteristics of the crud deposits and the coolant chemistry at the shutdown of PWR plant were discussed and analyzed in relation to the solubility of the oxides containing Co-58, Co-60 and Ni. The new oxygenation process proposed is as follows. (1) To promote the release of Co-58, Co-60 and others in the coolant, oxygenation process is operated in the range of pH value 4.5 - 5.0 by the removal of Li-7 in the coolant and at coolant temperature of 700C. Then, the aeration is operated at the early stage of the oxygenation process to produce hydrogen peroxide. (2) Co-58, Co-60 and others released in the coolant should be quickly removed by the full power operation of the clean-up demineralizer to accelerate the release of radioactivity in the coolant. (3) At the completed point of the oxygeneration, the radioactivity level in the coolant should be reduced, as low as possible, by the pH increase Li-7 addition and temperature decrease to suppress the solubility of the crud deposits. (author)