Finite Element Modelling of CRUD Deposition in PWRs

Abstract

The research presented in this doctoral thesis is the modelling work on the Corrosion Related Unidentified Deposition (CRUD) in Pressurized Water Reactors (PWRs). It aims to develop an all-inclusive deposition model, which will reproduce the morphology of deposits found in actual plants and assist in elucidating the electrokinetic mechanism. Three models have been developed during this research, using the Finite Element Method (FEM). The first model is a pure fluid dynamics model which attempted to describe the deposition mechanism based on the fluid flow behaviour. It analysed the time-dependent deposit growth, based on the relationship between the derivative of shear rate and the streaming current which is generated from the movement of excess charge in the Electrical Double Layer (EDL) and known as the driving force of the deposition process. Some features of the deposits were predicted, matching the observation in the actual plants and experiments. However, the deposition pattern was not accurately predicted, which motivated the change of approach for the next two model. The second model is a conductivity-based model, aiming to reproduce the morphology based on the effect of the electric field. The deposition pattern has been successfully predicted, which matches that seen in plants and experimental data. Coupled anodic (deposit) and cathodic regions were found at the inlet of a pipe restriction, associated with a region of recirculating fluid flow. A subsequent anode (deposit) always forms following the recirculation zone. However, no chemical reactions were put in this model, which lead to the development of the next model. The third model is a combined electrochemistry, conductivity and fluid dynamics model. It incorporated magnetite precipitation/dissolution, three electrochemical reactions and six chemical reactions. The effect of mass transport (movement of charged species) and electric field was studied and the electrokinetic deposition pattern was well predicted. This model is a further step of the second model. It is evident that the electrokinetic mechanism is a result of both mass transport and electric field effect.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nicholas Stevens (Supervisor) & Brian Connolly (Supervisor)