An analysis of dual zone loading for shipping spent nuclear fuel

Abstract

The burnups current fuet assembly designs can achieve exceeds the fuel assembly burnups the current fleet of shipping casks can ship. One method of handling this situation which has been proposed is regionalized loadiug. This coucept iuvolves administratively separating the fuel basket of a shipping cask into two or more regions and loading fuel with different burnup, cooling times and enrichments into these regons. To evaluate how regionalized loading patterns might affect shipping spent nuclear fuel in comparison to uniform loading, a test case study was performed using fuel assemblies discharged from an actual nuclear plant and a shipping cask licensed by the NRC. Using the same fuel assemblies and shipping cask, results were obtained assuming a uniform loading pattern and compared to the results obtained assuming a dual zone loading pattern. Source terms for the analysis were generated using SAS2 and the dose levels were calculated using MCNP5. The analysis showed that the dual zone loading reduced the amount of time required to ship the given quantity of fuel by roughly thirty percent compared to the uniform loading. The average dose rate to the transportation workers and the public due to the implementation of dual zone loading increased. Implications of these increases are discussed.