Use of Existing Light-Water Reactors and an Accelerator-Driven System for the Transmutation of Spent Nuclear Fuel

The use of both reactors and accelerator-driven systems (ADSs) for the transmutation of spent nuclear fuel has been examined for decades. The advantage of burning the material in a reactor is that it can provide more reliable electricity generation than an ADS (which is subject to beam interruptions). The advantage of an ADS is that the material does not have to maintain constant reactivity (i.e., it can be subcritical, and the keff can decrease over a cycle) and thus, operations are inherently more 'safe' (i.e., turning off the accelerator stops the production of additional fission neutrons). Using a combination of (1) existing or new light-water reactors (LWRs) to burn at least the plutonium and (2) an ADS for the remaining material allows both advantages to be utilized and is referred to as a two-tiered approach. In addition to power production, burning a fraction of the plutonium in the LWR helps the ADS by decreasing the fission-to-capture ratio of the actinides being transmuted. At ∼0.8, this ratio causes the reactivity in the accelerator to remain fairly constant for cycles of up to 2 to 3 years. The use of three different fuels (mixed oxide, thorium/plutonium oxide, and non-fertile fuel) in a simple LWR is addressed in this paper, as is the use of several different actinide streams for the non-fertile fuel (plutonium by itself and plutonium plus minor actinides). In addition, the effect of each type of fuel/material stream on the ADS is addressed, as is the transmutation of long-lived fission products in this two-tiered environment. (authors)