The radionuclide characteristics of light-water-reactor (LWR) spent fuel play key roles in the design
and licensing activities for radioactive waste transportation systems, interim storage facilities, and the final
repository site. Several areas of analysis require detailed information concerning the time-dependent behavior
of radioactive nuclides including (1) neutron/gamma-ray sources for shielding studies, (2) fissile/absorber
concentrations for criticality safety determinations, (3) residual decay heat predictions for thermal

In the past, criticality analysis of pressurized water reactor (PWR) fuel stored in racks and casks has assumed that the fuel is fresh with the maximum allowable initial enrichment. If credit is allowed for fuel burnup in the design of casks that are used in the transport of spent light water reactor fuel to a repository, the increase in payload can lead to a significant reduction in the cost of transport and a potential reduction in the risk to the public. A portion of the work has been performed at Oak Ridge National Laboratory (ORNL) in support of the U.S.

In 1999, the United States Nuclear Regulatory Commission (U.S. NRC) initiated a research program
to support the development of technical bases and guidance that would facilitate the implementation of burnup
credit into licensing activities for transport and dry cask storage. This paper reviews the following major areas of
investigation: (1) specification of axial burnup profiles, (2) assumption on cooling time, (3) allowance for
assemblies with fixed and removable neutron absorbers, (4) the need for a burnup margin for fuel with initial