Impact of Integral Burnable Absorbers on PWR Burnup Credit Criticality Safety Analyses

Conference · Thu Nov 15 04:00:00 EST 2001

OSTI ID:788579

Sanders, Charlotta E. ^[1]; Wagner, John C. ^[2]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); ORNL
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

The concept of taking credit for the reduction in reactivity of burned or spent nuclear fuel (SNF) due to fuel burnup is commonly referred to as burnup credit. The reduction in reactivity that occurs with fuel burnup is due to the net reduction of fissile nuclide concentrations and the production of actinide and fission-product neutron absorbers. The change in the inventory of these nuclides with fuel burnup, and the consequent reduction in reactivity, is dependent upon the depletion environment. Therefore, the use of burnup credit necessitates consideration of all possible fuel operating conditions, including the use of integral burnable absorbers (IBAs). The Interim Staff Guidance on burnup credit issued by the Nuclear Regulatory Commission's (NRC) Spent Fuel Project Office recommends licensees restrict the use of burnup credit to assemblies that have not used burnable absorbers (e.g., IBAs or burnable poison rods, BPRs). This restriction eliminates a large portion of the currently discharged spent fuel assemblies from cask loading, and thus severely limits the practical usefulness of burnup credit. The reason for this restriction is that the presence of burnable absorbers during depletion hardens the neutron spectrum, resulting in lower ²³⁵U depletion and higher production of fissile plutonium isotopes. Enhanced plutonium production has the effect of increasing the reactivity of the fuel at discharge and beyond. Consequently, an assembly exposed to burnable absorbers may have a slightly higher reactivity for a given burnup than an assembly that has not been exposed to burnable absorbers. This paper examines the effect of IBAs on reactivity for various designs and enrichment/poison loading combinations as a function of burnup. The effect of BPRs, which are typically removed during operation, is addressed elsewhere.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 788579
• Report Number(s): P01-111316
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
BURNABLE POISONS
BURNUP
CRITICALITY
Combustion Engineering (CE)
Integral Burnable Absorbers (IBAs)
Integral Fuel Burnable Absorber (IFBA) Rods
KENO V.a
Monte Carlo Code
NEUTRON ABSORBERS
Nuclear Criticality Safety Program (NCSP)
PLUTONIUM ISOTOPES
PWR TYPE REACTORS
Pressurized-Water Reactors (PWRs)
REACTIVITY
SAFETY
SPENT FUELS
Spent Nuclear Fuel (SNF)
U.S. Nuclear Regulatory Commission (NRC)
URANIUM 235