Effects of Organic Impurities on BWR Water Chemistry, (2)

In order to keep ⁶⁰Co radioactivity low without incurring serious disadvantages regarding integrity of fuel cladding and reliability of structural materials, it is desirable to relate cooling water (especially ⁶⁰Co behavior), structural materials and fuel cladding quantitatively. Organic impurities, such as fragments of cation resin, are fed into the reactor where they decompose, increasing conductivity of the reactor water and decreasing pH, which, in turn, increase ⁶⁰Co radioactivity in the reactor water and then, shutdown dose rate. The relationships between ⁶⁰Co radioactivity in the reactor water and pH have been analyzed by using water chemistry experience at operating BWR plants as well as laboratory data of resin decomposition in the water at elevated temperature, and analytical formulas to explain the shutdown dose rate increase caused by organic impurities intrusion were proposed. Effects of organic impurities on the shutdown dose rate can be moderated preventively by application of weak alkali control.