The Effect of Zinc Injection into PWR Primary Coolant on the Reduction of Radiation Buildup and the Corrosion Control Considered from the Solubilities of Spinel Oxides

Abstract

Zinc injection into PWR primary coolant in order to reduce radiation buildup has been widely studied, and the reduction effect has been experimentally confirmed. However, some items, such as the optimal concentration of zinc required to reduce radiation buildup, the corrosion control effect of zinc injection, and the influence of zinc injection on the integrity of fuel cladding, have not been clarified yet. In particular, the corrosion suppression effect of zinc remains unconfirmed. Therefore, it is necessary to measure and calculate the solubilities of zinc and nickel spinel oxides, which are formed on the surface of Ni-based alloys in PWR primary systems.
In this study, in order to assess the effectiveness of zinc injection in the reduction of radiation buildup and the corrosion control of Ni-based alloy, the potential-pH diagrams for Zn-Cr-H₂O, Ni-Cr-H₂O and Co-Cr-H₂O systems at 573K were constructed and the solubilities of Zn-Cr, Ni-Cr, and Co-Cr spinel oxides were also calculated.
It is concluded that under pH conditions for which NiCr₂O₄ is stable, zinc injection is effective in corrosion control as well as in reducing radiation buildup.