Active Electrochemical Measurements

Non-active electrochemistry data for AGR cladding has been generated and modelling evaluation was carried out by NPL, using the newly measured data to guide inputs, to predict susceptibility of the fuel cladding to SCC in caustic conditions. Following these initial experiments, additional non-active testing has been carried out and subsequent further modelling tasks and development have been recommended.

NPL will carry out the following Tasks:

• Investigation of the sensitivity of the modelling results (tip acidification and tip chloride accumulation) to the transfer coefficient related to the cathodic reaction.
• Investigation of the sensitivity of the modelling results (tip acidification and tip chloride accumulation) to the passive current density.
• Modify previous COMSOL simulation model of crack electrochemistry for advanced gas-cooled reactor stainless steel cladding in pond storage to include the presence of boric acid.
• Modify the model to account for the dependency of the crack-tip current density on the local electrode potential.
• Assess numerical convergence issues related to the very sharp change in electrode kinetics between the crack walls and crack-tip and endeavour to resolve.
• NPL report containing the modifications to the previous model and example of results.
• Modify COMSOL model