Development of dispersant technology in primary systems of light water reactors. Radiolysis of polyacrylic acid under PWR primary condition and dissolution experiments of metal oxides

In order to develop a new technology of dispersant addition into primary coolant of nuclear power reactors and to achieve sufficient reduction of the radiation exposure, radiolysis of poly acrylic acid (PAA) solution was investigated under the PWR primary condition. PAA solution was irradiated by gamma-rays at 320degC up to 10 kGy and 100 kGy. After irradiation, TOC concentration and molecular weight significantly decreased. Carbon dioxide and acetate were detected as radiolytic products with relatively low yields. Radiation chemical simulation at 300degC demonstrated that PAA is consumed at around 5 kGy. It is considered that scission of PAA radicals is predominant up to several kGy where as disproportionation seem major reaction of PAA radicals at higher absorbed dose. Screening experiments were carried out to select promising chemical agent under the condition of BWR coolant. Immersion tests of iron oxide at 180degC in the presence of various chemical agent showed that Fe concentration was highest in the presence of PAA (weight-average molecular weight = 16,000). It was concluded that the PAA is the most promising chemical agent to remove corrosion products in BWR coolant systems. (author)