Potential Crud Related Margin Gains With Chromium Coated Zirconium Cladding

Abstract

The build-up of deposits (Crud) on fuel cladding can cause several issues for PWRs. The crud becomes activated and is transported to other locations in the RCS increasing radiation fields, it can collect boron causing power shifts (CIPS, Crud Induced Power Shifts) and if thick enough localized corrosion will be increased (CILC, Crud Induced Localized Corrosion). The application of a chromium coating to zirconium alloy cladding is being pursued to improve the corrosion performance of the cladding both during normal operation and in the event of accident conditions producing high cladding temperatures. The change will also influence the crud affinity of the cladding. The deposition of corrosion products from the ex-core portions of the plant will be altered. Also, corrosion of the cladding itself contributes to the crud burden in a PWR, and this factor will undoubtedly change with the application of a chromium coating. Changes in the surface texture produced by the coating will also influence crud deposition by changing boiling nucleation and thermal hydraulic factors. This paper discusses how a change to chromium coated fuel cladding will likely affect crud deposition and will give the results of crud deposition testing of chromium coated cladding in the WALT loop.