A SCOPING STUDY OF ADVANCED THORIUM FUEL CYCLES FOR CANDU REACTORS

Abstract

<p>A study was conducted to scope the relative merits of various thorium fuel cycles in CANDU reactors. It was determined that, due to the very large reprocessing demands of the self-sustaining equilibrium thorium fuel cycle, an additional fissile driver fuel is required for a practical thorium fuel cycle. The driver fuels considered were PWR- and CANDU- derived plutonium, PWR-derived MOX fuel, and low-enriched uranium. The addition a RU-fuelled CANDU reactor with possible americium, curium, and lanthanides recycling was also considered. The fuel cycles were evaluated for natural uranium consumption and reprocessing demands as well as spent fuel characteristics such as: thermal and gamma power, radioactivity, and ingestion and inhalation hazards.</p> <p>The two-dimensional multigroup code, WIMS-AECL, was used to calculate the burnup and some controllability properties of the CANDU reactors. ORIGEN, a depletion and decay module, was used to evaluate the spent fuel characteristics and the systems code, DESAE, was used to simulate the introduction of the thorium fuel cycle to a growing global reactor park.</p> <p>It was determined that ²³³U production in the thorium fuels is optimized at lower exit burnups. Therefore, less external fissile driver material is required for the operation of the thorium reactors and natural uranium savings of the overall fuel cycle are increased. Furthermore, it was determined that driving the thorium fuel cycle with low-enriched uranium is the most efficient way to minimize natural uranium consumption. Assuming that a 40 MWd/kg exit burnup was achieved in the CANDU reactors, the fuel cycle yielded an 82% savings of natural uranium, compared to a scenario in which all power came from PWRs, while a 20 MWd/kg exit burnup increased the savings to 94%. The savings ranged over those exit burnups from 55%-69% for the variant with PWR-derived plutonium, 60%-73% for PWR-derived MOX fuel, and 78%-87% for CANDU-derived plutonium. The thermal power, radioactivity, and health hazards of the spent fuel were the highest for the case with MOX fuel driver but americium recycling proved effective for decreasing the long term dangers. In a global reactor park, the introduction of the thorium fuel cycle was hampered by the availability of fissile resources and, for a PWR-derived driver, natural uranium consumption was only reduced by 22% over 100 years relative to the PWR only scenario.</p>