EFFECT OF DH CONCENTRATION ON CRUD DEPOSITION ON HEATED ZIRCALOY-4 IN SIMULATED PWR PRIMARY WATER

摘要

In order to mitigate PWSCC initiation and propagation in Ni base alloys, Japanese PWR utilities desire to employ optimized dissolved hydrogen (DH) control operation in the near future. Prior to the application of the optimized DH control operation to PWR, the effect of DH concentration on the fuel crud deposition should be clarified.Crud deposition tests were carried out in boric acid (1200ppm) + lithium hydroxide (2.2ppm) + hydrogen (7 to 25cm~3-STP/kg-H_2O) solutions at 325°C under sub-cooled boiling and non-irradiated conditions. The corrosion resistance of zircaloy-4 was also investigated.From the test results, it was revealed that a crud layer composed of NiFe_2O_4 and NiO was formed on zircaloy-4 fuel cladding. NiO was easy to form in the crud layer under the 7cm~3-STP/kg-H_2O condition. The amounts of deposited crud layer, boron incorporated into the crud layer and the corrosion resistance of the zircaloy-4 cladding were not affected by DH concentration.