Postclosure Performance Assessment of a Hypothetical Canadian Deep Geological Repository for Thorium-Containing Advanced Heavy Water Reactor Fuels

Abstract

Lattice physics depletion calculations were performed to obtain postburnup fuel compositions for several candidate advanced heavy water reactor fuels. These fuel compositions were used as input for a deep geological repository (DGR) modeling tool for hydrogeology simulations to simulate the transport of radionuclides to the surface, to find the radionuclides that reach the surface path through the biosphere, and to estimate the hypothetical dose rate to humans located above the DGR.

Three primary factors were found to contribute to surface dose rate: burnup, composition of the primary waste matrix, and percentage of thorium in the fuel. Higher burnup and thorium percentage contribute to increased surface dose rates through increased ¹²⁹I production, while a primarily uranium waste matrix increases surface dose rate through faster dissolution leading to increased radionuclide release rate from the fuel. For all the hypothetical fuels investigated, the estimated dose rates are well within the Nuclear Waste Management Organization’s hypothetical DGR’s acceptance criterion of 0.3 mSv/year.

Keywords:

• Heavy water
• thorium
• deep geological repository

Acknowledgments

This study was funded by Atomic Energy of Canada Limited under the auspices of the Federal Nuclear Science and Technology Program.