Corrosion products deposit on Pressurized Water Reactor (PWR) fuel rod cladding surfaces and can create a number of issues including increased cladding temperature, elevated cladding corrosion, and the precipitation of boron species within the deposits. The deposits can also release and lead to increased radiation fields on system ex-core surfaces. These effects can vary widely from plant-to-plant. The amount of the deposits, commonly known as crud, is an important factor in determining the impact, but other parameters such as crud thickness, porosity, and composition are also thought to be important.
The Electric Power Research Institute (EPRI) has sponsored a number of programs to better understand the characteristics of crud and its effects. Crud has been sampled by fuel scraping and by collecting suspended crud during operation and during fuel cleaning. The chemistry and structure of the crud was then characterized. These data were then used to create simulated crud in laboratory heated rod tests. These tests explored how the crud deposits affected heat transfer at the rod surface and the interaction between the crud and the simulated coolant.
This paper discusses the nature of PWR crud and some of the practical aspects of crud simulation. Different approaches to laboratory crud creation will be reviewed, and the success in matching plant crud characteristics will be shown, with special emphasis on the production of crud for thermal conductivity measurement.