Topical Report on Actinide-Only Burnup Credit for PWR Spent Nuclear Fuel Packages (Rev. 1)

Technical Report · Tue Apr 01 04:00:00 EST 1997

DOI:https://doi.org/10.2172/884970· OSTI ID:884970

A methodology for performing and applying nuclear criticality safety calculations, for PWR spent nuclear fuel (SNF) packages with actinide-only burnup credit, is described. The changes in the U-234, U-235, U-236, U-238, Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, and Am-241 concentration with burnup are used in burnup credit criticality analyses. No credit for fission product neutron absorbers is taken. The methodology consists of five major steps. (1) Validate a computer code system to calculate isotopic concentrations of SNF created during burnup in the reactor core and subsequent decay. A set of chemical assay benchmarks is presented for this purpose as well as a method for assessing the calculational bias and uncertainty, and conservative correction factors for each isotope. (2) Validate a computer code system to predict the subcritical multiplication factor, k_eff, of a spent nuclear fuel package. Fifty-seven UO₂, UO₂/Gd₂O₃, and UO₂/PuO₂ critical experiments have been selected to cover anticipated conditions of SNF. The method uses an upper safety limit on k_eff (which can be a function of the trending parameters) such that the biased k_eff, when increased for the uncertainty is less than 0.95. (3) Establish bounding conditions for the isotopic concentration and criticality calculations. Three bounding axial profiles have been established to assure the ''end effect'' is accounted for conservatively. (4) Use the validated codes and bounding conditions to generate package loading criteria (burnup credit loading curves). Burnup credit loading curves show the minimum burnup required for a given initial enrichment. The utility burnup record is compared to this requirement after the utility accounts for the uncertainty in its record. Separate curves may be generated for each assembly design, various minimum cooling times and burnable absorber histories. (5) Verify that SNF assemblies meet the package loading criteria and confirm proper assembly selection prior to loading. A measurement of the average assembly burnup is required and that measurement must be within 10% of the utility burnup record for the assembly to be accepted. The measurement device must be accurate to within 10%. Each step is described in detail for use with any computer code system and is then demonstrated with the SCALE 4.2 computer code package using 27BURNUPLIB cross sections.

• Research Organization: Yucca Mountain Project, Las Vegas, NV (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); USDOE Office of Civilian Radioactive Waste Management (RW)
• DOE Contract Number: AC08-91RW00134
• OSTI ID: 884970
• Report Number(s): DOE/RW--0472(Rev.1); MOV.19970416.0125, DC#47704
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
BENCHMARKS
BURNUP
Burnup
COMPUTER CODES
COOLING TIME
CRITICALITY
CROSS SECTIONS
Computer Code System
DECAY
DESIGN
FISSION PRODUCTS
MULTIPLICATION FACTORS
NEUTRON ABSORBERS
NUCLEAR FUELS
Nuclear Criticality Safety Program (NCSP)
REACTOR CORES
SAFETY
SPENT FUELS