Tripoli-4 Gamma-Ray Dose Calculation for Spent PWR Fuels

The gamma-ray dose calculation is essential for the radiation shielding of pressurized water reactor (PWR) spent fuels. Homogenization modeling of fuel pin lattices for typical PWR spent fuel pins is regularly applied on the radiation protection calculation of gamma-ray dose in an air medium. However, depending on the size of the homogenized lattice and the location of the detectors, under-estimation or over-estimation of the gamma-ray dose due to the homogenization modeling can be obtained with respect to the detailed heterogeneous model. In previous published results from MCNP-4A and 4C calculations on gamma-ray dose from spent PWR fuel pins, very different homogeneous to heterogeneous (Hom/Het) ratios were reported. In this study these Hom/Het ratios have been re-evaluated and benchmarked by using the TRIPOLI-4 Monte Carlo transport code. The new TRIPOLI-4 mesh tally capabilities have also been applied to calculate the radial and axial gamma-ray dose distribution. With the recently upgraded TRIPOLI-4 display tool, the dose rate maps and the isodose rate curves around a spent PWR fuel assembly have been established.