Development of Alternative Reductant Application in Pressurized Water Reactor Primary Systems

Abstract

In primary coolant of pressurized water reactors, high concentration dissolved hydrogen (DH) has been added, to prevent generation of oxidizing species through radiolysis of the coolant. Recently, number of ageing plants is increasing and utilities are concerned about primary water stress corrosion cracking (PWSCC). Some researchers consider that occurrence of PWSCC and crack propagation rate are affected by the DH concentration. The authors consider that one of possible mitigation methods toward PWSCC is use of alternative reductant in place of hydrogen. Because from the radiation chemical aspect aliphatic alcohols are typical scavengers of the oxidizing radical generated through the radiolysis of water, they are promising candidates of the alternative reductant. In the present work, possible alternatives of hydrogen were screened, and methanol was selected as the best candidate. Corrosion tests of type 304 stainless steels were carried out in high temperature water at 320°C without irradiation under two conditions: (1) DH 1.5 ppm (part per million) and (2) methanol 2.9 ppm. Electrochemical corrosion potential of the stainless steel specimens was measured during the immersion tests. After the immersion tests for 1500 h, surface morphology of the stainless steel specimens was observed by scanning probe microscope. Major component of the oxide film formed on the stainless steel specimens was analyzed by X-ray diffraction. From comparison of the test results, it is concluded that addition of 2.9 ppm methanol has almost the same effect on corrosion environment as DH 1.5 ppm addition.