CANDU Reactors with Thorium Fuel Cycles

CANDU technology provides unequalled flexibility for the use of different fuel cycles. Its inherent high neutron economy, fuel channel design, on power refuelling capability and simple fuel bundle design allow for the optimisation of an assortment of different nuclear fuel-cycles. The suitability of CANDU technology for alternative fuel cycles, such as thorium and MOX, was first recognized during the conception of this unique technology. To this end Atomic Energy of Canada Ltd. (AECL) has carried out theoretical and experimental investigations of thorium and other fuel cycles over the years in order to develop the expertise necessary to exploit them should market conditions and availability change. However, because of the relative abundance and low cost of uranium, to date, there has not been a financial incentive to accelerate development of such fuel cycles. Today, approximately half a century after the first deployment of atomic energy for peaceful purposes, a number of factors have converged and added momentum to the possible exploitation of alternative fuel cycles involving thorium. For the first time in decades the price of uranium has increased substantially, having more than tripled over the last three years [3]. Although the impact of this increase on the cost of running nuclear plants is not substantial, neither is it insignificant. Uranium resources are not distributed throughout the world ubiquitously. Countries like India, China and Turkey, which currently have expanding economies, and a corresponding need for more electricity, do not have abundant uranium resources. However, they have a great abundance of Thorium and have a natural desire for self-reliance in energy supply. Only a few percent of the material in nuclear fuel is actually converted into energy, with the used fuel containing over 95% of the original energy content. This has long been recognized but, again, with the relative worldwide abundance of uranium there has not been financial incentive to exploit this potentially valuable resource. However, there is interest in reducing the volume of hazardous material in spent fuel, such as Plutonium, to make it easier to dispose of. These various economic and political drivers; the increasing cost of uranium, the abundance of thorium in countries with expanding economies and the desire to reduce the amount of long lived radioactive material in used fuel, have converged and motivated us to investigate a fuel cycle that combines Thorium with Plutonium. This paper will show that using fuel based on these fissile and fertile elements can be economical and can greatly extend the useful life of nuclear fission technology for production of electricity. We also examine the practical aspects of conversion of a CANDU reactor from operation with a 235U fuel cycle to one operating with a Pu-Th fuel cycle. Necessary design changes can be implemented during a refurbishment outage or built into the design of a new plant, to make a mid-life conversion even easier.

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