Scenario Analysis of PT‑HWR Used Fuel Management for Once-Through Thorium Fuel Cycles

Dan Wojtaszek

Canadian Nuclear Laboratories

Thorium-based fuel cycles offer many potential benefits, including greater long-term energy sustainability, and improved waste management characteristics, along with comparable economics relative to uranium-based fuels. Analytical studies of thorium-based fuel cycle deployment strategies can help determine the optimal approaches for a given thorium fuel cycle, and guide fuel cycle technology research and development.

The purpose of this study was to analyze the potential impacts on the management of used nuclear fuel (UNF) associated with deploying thorium-based fuels in Pressure Tube Heavy Water Reactors (PT‑HWRs) in a once through fuel cycle. The fuels that were analyzed are:

· a reference low-burnup (~7.2 MWd/kg) natural uranium (NU) fuel,

· an intermediate-burnup (~19.1 MWd/kg) fuel composed of 1.2 wt.% 235U/U slightly enriched uranium (SEU) combined with small amounts of thorium (95 wt.% SEU, 5 wt.% Th).

· a high-burnup (~40.6 MWd/kg) fuel composed of 5.0 wt.% 235U/U low enriched uranium (LEU) mixed with thorium (~48 wt.% LEU, ~52 wt.% Th).

The scenario involves the deployment of these fuels in a fleet of PT‑HWRs, with a total installed capacity equal to that of all PT‑HWRs in Canada in 2014 (~13,512 MWe (net)), for a period of 60 years. All UNF is to be ultimately placed in a deep geological repository (DGR) that is similar to the Canadian DGR concept for all PT‑HWR UNF in Canada. Any UNF that has been removed from wet storage was temporarily placed in dry storage until it could be sent to the DGR.

The UNF management metrics that were analyzed include:

· the number of MACSTOR dry storage fuel baskets required to store UNF that has been removed from wet storage, but cannot be immediately loaded into the DGR; and

· the number of Canadian DGR used fuel containers (UFCs) loaded with UNF.

These metrics reflect the cost and footprint of the respective UNF management facilities. In this analysis the total amount of UNF that can be placed in either a dry storage fuel basket or a DGR UFC cannot exceed a given number of fuel bundles and a maximum total decay power.

The results of this analysis show that the NU fuel required the fewest dry storage baskets due to its low decay power relative to the other fuels. The intermediate -burnup SEU+Th fuel required the fewest number of DGR UFCs. The high-burnup LEU+Th fuel also required fewer DGR UFCs than the NU fuel.