ORALS

Lithium hydroxide (LiOH) is added to the water coolant in Pressurized Water Nuclear Reactor (PWR) to control its pH. However, the demand and the cost of Lithium-7 has substantially increased since 2015. Thus, potassium hydroxide (KOH) has been proposed as a candidate to replace LiOH for the same purposes [1] since it is economically favorable and also has been used in Russian pressurized water reactors for more than 40 years. Nevertheless, the corrosion behavior of Ni-based Alloy 600 (an alloy used for structural components in US PWRs) in KOH water chemistry is not really known; in fact no studies were found in the literature for the corrosion behavior of Alloy 600 corroded in KOH versus LiOH solutions. Therefore, the question of its corrosion sensitivity to exposure of KOH (at various concentrations) must be answered before KOH can be used in PWRs safely. It is the focus of this work. For that matter, Alloy 600 coupons were corroded in both relatively low and high (i.e. crevice-like) KOH concentrated water chemistry. Corrosion experiments were conducted in a static autoclave in simulated PWR primary water condition (325 ℃, 2200 psi, 30 cc H2/kg of H2O at STP) for 7 days to 30 days. Transmission Electron Microscopy (TEM) of cross-sectional samples was used to characterize the oxide formation through diffraction analysis. Secondary Ion Mass Spectrometry (SIMS) was used to see the ingress of K+ in the oxide films and metal matrix for different KOH concentration. The same experiments were done with LiOH. A discussion was conducted to substantiate the effects of KOH concentration in terms of corrosion of Alloy 600 compared to LiOH exposure.

References:
[1] Fruzzetti, K., Potassium hydoxide for PWR Primary Coolant pH control: Qualification Program. 2018(Electric Power Research Insitute): p. 15.