This report proposes and documents a computational benchmark problem for the estimation of the additional reactivity margin available in spent nuclear fuel (SNF) from fission products and minor actinides in a burnupcredit storage/transport environment, relative to SNF compositions containing only the major actinides. The benchmark problemlconfiguration is a generic burnup credit cask designed to hold 32 pressurized water reactor (PWR) assemblies.

Reactor physics computer programs are important tools that will be-used to estimate mixed oxide
fuel (MOX) physics performance in support of weapons grade plutonium disposition in U.S. and
Russian Federation reactors. Many of the computer programs used today have not undergone
calculational comparisons to measured data obtained during reactor operation. Pin power, the
buildup of transuranics, and depletion of gadolinium measurements were conducted (under Electric
Power Research Institute sponsorship) on uranium and MOX pins irradiated in the Quad Cities-l

Every year, more than 300 million packages of hazardous material are shipped in the
United States (U.S.). Most of the hazardous material shipped – about 97 percent – is
flammable, explosive, corrosive or poisonous. About 1 percent – three million packages –
of the hazardous materials shipped annually contains radioactive material, most of them
from medical and industrial applications. [DOT 1998b]
Spent nuclear fuel comprises a very small fraction of the hazardous materials packages

This report has been prepared to qualitatively assess the amount of burnup credit (reactivity margin) provided by ISG-8 compared to that provided by the burnup credit methodology developed and currently applied in France. For the purposes of this study, the methods proposed in the DOE Topical Report have been applied to the ISG-8 framework since this methodology (or one similar to it) is likely to form the basis of initial cask licensing applications employing limited burnup credit in the United States.

The U.S. Nuclear Regulatory Commission's guidance on burnup credit for pressurized-water-reactor (PWR) spent nuclear fuel (SNF) recommends that analyses be based on a cooling time of five years. This recommendation eliminates assemblies with shorter cooling times from cask loading and limits the allowable credit for reactivity reduction associated with cooling time. This report examines reactivity behavior as a function of cooling time to assess the possibility of expanding the current cooling time recommendation for SNF storage and transportation.

Taking credit for the reduced reactivity of spent nuclear fuel (SNF) in criticality analyses is referred to as burnup credit (BUC). Criticality safety evaluations require validation of the computational methods with critical experiments that are as similar as possible to the safety analysis models, and for which the keff values are known. This poses a challenge for validation of BUC criticality analyses, as critical experiments with actinide and fission product (FP)

The work reported here is an investigation of the sensitivity of component temperatures in a specific storage system, including fuel cladding temperatures, in response to modeling assumptions that differ from design-basis, including age-related changes that could degrade the thermal behavior of the system. Preliminary evaluations of representative horizontal and vertical storage systems at design basis conditions provides general insight into the expected behavior of storage systems over extended periods of time.

The U.S. Department of Energy’s (DOE) Office of Civilian Radioactive Waste Management (OCRWM) is responsible, under the Nuclear Waste Policy Act of 1982, for the transportation of spent nuclear fuel and high-level radioactive waste from point of origin to destination at a federal storage or disposal facility. Section 180(c), written into the Nuclear Waste Policy Act Amendments of 1987, requires OCRWM to prepare public safety officials along the routes for these shipments.