Radiation Measurements to Qualify Spent Reactor Fuel for Loading into Burnup Credit Casks

Transport casks that make use of burnup credit are designed to accommodate spent-fuel assemblies with a specified combination of initial enrichment, minimum bumup, and minimum cooling time (age) to ensure acceptable nuclear criticality safety. Radiation measurements can be used to help prevent misleading of a cask by verifying that each assembly has the appropriate characteristics. Measurements of gross neutron and gamma-ray yield from spentfuel assemblies have been used successfully for many years by the International Atomic Energy Agency (IAEA) to confirm reactor records in the United States and abroad. This technique has proved to be adequate to eliminate the need for more complex active or high-resolution measurement techniques. The IAEA system (called FORK, designed at Los Alamos National Laboratory [LANL]) is being evaluated for applicability to burnup credit operations. Under a joint program involving Sandia National Laboratories (SNL), LANL, and the Electric Power Research Institute (EPRI) test measurements on spent-fuel assemblies will be performed at U.S. utility storage sites using a FORK system. The objectives of the tests are to (1) demonstrate that simple measurements can be used to confirm reactor records for spent-fuel assembly characteristics, (2) obtain calibrations of the instrument over the burnup range of interest, (3) examine the axial distribution of bumup in some assemblies, and (4) develop operational procedures with utility input.