Multiphysics Modeling and Simulation of Porous CRUD Depostis in PWRs

The buildup of corrosion deposits known as CRUD (an acronym for Chalk River Unidentified Deposits) on reactor core fuel rods represents a major problem in the operation of light water reactors LWRs. In particular, the porous nature of CRUD in pressurized water reactors (PWRs) allows for boron, present in the coolant to control the power, to "hide out" in CRUD's pores and change the power shape of the core. In addition, CRUD can often impede heat transfer from the fuel cladding rods, resulting in CRUD-induced localized corrosion (CILC). Finally, the composition of CRUD is mainly iron and nickel oxides, which become more radioactive after sitting in the core. The dissolution of CRUD upon reactor shutdown means this radioactivity is released into the coolant, adding radiation dose to workers on the plant.

This project aims to create a mesoscale, multiphysics model of CRUD's effects on fuel performance. The code, developed as part of CASL, incorporates information from the atomistic scale, feeding the effects of CRUD on the plant to higher level, engineering scale codes. Our CRUD code is written in MOOSE, a massively parallel multiscale simulation environment. We determine the temperature increase, fluid flow, boiling rate, and boron concentration within the CRUD as functions of reactor operating parameters, with the goal of predicting the effects of CRUD formation in an operating PWR.