Thermal and radiolytic stabilities of tetra-ammine platinum(Ⅱ) complex in aqueous phase - Comparison with hexa-hydroxo platinum(Ⅳ) complex

摘要

Plant aging is a current key issue of LWR plants in Japan. Among the various items IASCC and IGSCC of structural materials are one of the most concerned problems. Water chemistry technology is able to contribute to solving this problem through the control of environmental factor that is one of the requirements for SCC to occur. HWC is now widely used in many BWR plants in U.S. and Sweden as such a measure for IGSCC of stainless steel, but has not been adopted in Japanese BWR for a long time, because of its deleterious effects on turbine radiation field and activity transport. Recently, however, the situation has been changing owing to the increase in the operational years of significant number of Japanese nuclear power plants. Thus, some of the aging BWRs have adopted HWC recently, but the injection level of hydrogen is kept rather low in these plants because radiation field rises significantly around the turbines as already mentioned. Noble metal chemical addition (NMCA) is now drawing an increasing attention as a booster to make HWC more effective, and very recently the first test of the noble metal injection was carried out in one of Japanese BWRs. As described in the other paper (ref.1) several laboratory experiments have been carried out to check the effectiveness of deposited noble metals for reducing ECP of stainless steel coupons and to measure the distribution of noble metals on the surface of the coupons by surface analyses, but chemical behavior of noble metals in the coolant systems is still not understood well and remains to be studied. In the practice of NMCA a mixture of Na_2Pt(OH)_6 and K_3[Rh(NO_2)_6] is widely used. Pt is considered to be the most important ingredient and its basic data are more available than Rh. Thus, Pt is picked up as a target in this study and the thermal and radiolytic stabilities of Pt(NH_3)_4(OH)_2 are studied in comparison with those of Na_2Pt(OH)_6. The radiolytic effect on noble metal species is considered to be important since the noble metal species are added to coolant at temperature of 100～150°C immediately after the shut down of the reactor under the condition that radiation still remains in the reactor core.