Evaluation of Dual-Zone Loading over Uniform Loading for Shipping Spent Nuclear Fuel

Current fuel assembly designs can achieve burnups that exceed the design burnups for many shipping casks. A proposed solution for this situation is regionalized loading, which involves 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 each region. The analysis evaluated how regionalized loading affected spent-fuel shipments.

Fuel having a range of burnups and a shipping cask were used in the analysis. The SCALE5 control module SAS2 was used to develop the radiological source terms, and MCNP5 was used to calculate the dose rates associated with the different loading patterns. The analysis indicated that the use of dual-zone loading patterns violated the principles of as-low-as-reasonably-achievable radiation levels. However, the analysis also showed that dual-zone loading patterns reduced the dose rates associated with shipping high-burnup fuel and reduced the time required to ship the fuel. Further analyses were performed to see if a compromise existed.