Water chemistry and oxidation in the primary circuit (WATCHEM): WATCHEM summary report: Development and verification of in situ techniques to study oxidation and water chemistry effects in the primary circuit

The focus in the WATCHEM project has been in development of in situ methods (a) to study oxidation of fuel cladding alloys and (b) to study optimisation of passivation (i.e. Hot Conditioning) of PWR reactor circuit surfaces prior to first fuel loading. The Controlled Distance Electrochemistry (CDE) method has been shown to be reliable and to give consistent and repeatable results both in BWR and in PWR conditions. Comparisons of the effects of elevated Li+ (PWR) and K+ (WWER) concentrations on fuel cladding oxidation were performed as part of this project. In studying the sensitivity limits of the CDE method the effects of F- concentration in the beginning of cycle conditions of WWER on Zr-1Nb alloy oxidation were found to be negligible at levels below 100 ppb. Based on a literature study the optimal water chemistry conditions in PWRs for Inconel 600 and 690 materials are 0.5-1 ppm Li+ and 25-30 ccH2/kgH2O. There is a considerable uncertainty in determining the effect of boric acid and the minimum required hot conditioning time. Two new methods were developed in co-operation with Bhabha Atomic Research Centre (BARC), India, to study the optimisation of the hot conditioning procedure and verified for carbon steel under PHWR water chemistry conditions. Preliminary studies with Inconel 690 under PWR conditions are underway.