Preliminary Study on Effect of the Crud Deposits during LBLOCA Condition

The severe crud deposits on fuel rod could result in the increment of the fuel temperature during the operation of nuclear power plants. The crud inhibits heat transfer, causing the cladding temperature to increase due to the low thermal conductivity. In the event of LBLOCA at the NPP operated with heavy crud layers, the peak cladding temperature (PCT) will be higher than it would be if the cladding were clean. Therefore, NRC has been reviewing a petition for rule making to set the limit of crud and/or oxide thickness. Also, it requires that LOCA analysis be calculated by factoring the role of crud. Since the crud deposits caused the stored energy in the fuel to increase, it could influence the following requirement: The Initial Stored Energy in the Fuel in Appendix K to Part 50. ECCS Evaluation Models, to require that the steady-state temperature distribution and stored energy in the fuel at the onset of a postulated LOCA. Also, safety review guidelines in NUREG-0800