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.

Effects of Zinc Addition on the Corrosion Behavior of Pre-Filmed Alloy 690 in Borated and Lithiated Water at 330 °C

“…As seen in Figure 5 and Figure 6 , the chromite inner oxide layers were changed to zinc-incorporated chromite layers when the pre-filmed coupons were subsequently exposed to 60 ppb zinc water. Zinc chromite has been reported to have a wider stable region in the potential-pH diagram [ 13 , 17 , 56 , 63 ] and a lower solubility under simulated PWR primary water conditions compared to non-zinc spinels [ 19 , 56 , 63 ]. Furthermore, point defect densities in the oxides of 316 stainless steel formed in simulated PWR primary water were decreased by zinc addition [ 9 ].…”

Thermodynamic Analysis and Crystallographic Properties of MFe2O4, MCr2O4 and MAl2O4 (M = Fe, Ni, Zn) Formed on Structural Materials in Pressurized Water Reactor Primary Circuit under Zinc and Zinc-aluminum Water Chemistry

“…The solubility of FeCr 2 O 4 , NiCr 2 O 4 , and ZnCr 2 O 4 , formed in the inner layer oxide, are calculated using the method from K. Miyajima et al [ 2 ]. Electrochemical process of spinel oxide M in aqueous systems can be expressed by Reaction (17), and the dissolution of solid M to produce ions in solution N can be written by general Reaction (18): …”

“…The hydrogen partial pressure ( ) in Equation (19) is necessary to calculate the solubility of oxides, so the difference between various studies were compared in Figure 6 c. The hydrogen partial pressure of 0.252 atm was used in the calculation of K. Miyajima’s research [ 2 ]. Due to the higher value than this article, the solubility of ZnCr 2 O 4 was relatively high, shown with short dots.…”

“…The main materials in PWR primary system ( Figure 1 ) are composed of 25% zirconium alloys as fuel cladding, 65% Ni-based alloys as steam generator (SG) tubes, 5% stainless steels (SS) as SG, and some carbon steels (CS). At the same time, stainless steels are also the main materials of piping in PWR primary circuit [ 1 , 2 ].…”

“…The data presented in this study are openly available in [ResearchGate] at [10.5573/ieek.5013.50.1.034], reference number [ 2 ]; in [Elsevier] at [10.1016/j.corrsci.2011.06.011] [10.1016/S0016-7037(96)00339-0] [10.1016/S0010-938X(96)00067-4], reference number [ 11 , 25 , 27 ]; in [Springer] at [10.1023/A:1021866025627] [10.1007/BF00645517], reference number [ 28 , 29 ].…”