Distribution of Characteristics of LWR Spent Fuel

The Materials Characterization Center (MCC) at Battelle Pacific Northwest Laboratory (PNL) has the responsibility to select appropriate spent fuel Approved Testing Materials (ATMs) and to characterize, via hot-cell studies, certain detailed properties of the discharged fuel. The purpose of this report isto develop a collective description of the entire spent fuel inventory in terms of various fuel properties relevant to ATMs using information available from the Characteristics Data Base (CDB), which is sponsored by the U.S. Department of Energy’s (DOE’S) Office of Civilian Radioactive Waste Management.

A number of light-water reactor (LWR) characteristics were analyzed including assembly class representation, fuel burnup, enrichment, fuel fabrication data, defective fuel quantities, and, at PNL‘s specific request, linear heat generation rate (LHGR) and the utilization of burnable poisons. A quantitative relationship was developed between burnup and enrichment for BWRs and PWRs. The relationship shows that the existing BWR ATM is near the center of the burnup-enrichment distribution, while the four PWR ATMs bracket the center of the burnup range but are on the low side of the enrichment range. Fuel fabrication data are based on vendor specifications for new fuel. Defective fuel distributions were analyzed in terms of assembly class and vendor design. LHGR values wefe calculated from utility data on burnup and effective full-power days; these calculations incorporate some unavoidable assumptions which may compromise the value of the results. Only a limited amount of data are available on burnable poisons at this time.

Based on this distribution study, suggestions for additional ATMs are made. These are based on the class and design concepts and include BWR/2,3 barrier fuel, and the WE 17 x 17 class with integral burnable poison. Both should be at relatively high burnups.