Critical heat flux impact due to cladding surface condition

Abstract

This paper demonstrates how the cladding surface condition can impact fuel rod heat transfer and CHF performance at Pressurized Water Reactor (PWR) type conditions. The cladding surface that is investigated here is a surface with a crud deposit similar to ones observed in a PWR reactor. Tests are performed in the Westinghouse WALT (Westinghouse Advanced Loop Tester) loop test facility where a single ZIRLO® clad electrically heated rod with approximately one-foot length is tested at PWR thermal hydraulic conditions and chemistry. Tests are performed for a normal clean rod surface, an oxide surface and with CRUD deposits to investigate the impact on fuel rod heat transfer and CHF performance. The CRUD deposit is characterized for thickness, chimney size and porosity. Test results are presented for the different cladding surface conditions along with comparisons to evaluations performed in the literature for different surfaces at pool boiling conditions. Future testing is planned for testing rods with different hydrophilic cladding surface conditions with and without CRUD deposits. This future work will also help design an optimum surface for heat transfer and CHF improvement for accident tolerant fuel.