Accelerator transmutation of waste blanket considerations

Accelerator transmutation of waste (ATW) is one approach for reducing the amount of actinides and long-lived fission products that eventually will be sent to a repository. The ATW accelerator generates high-energy protons, which strike a target and produce spallation neutrons. The spallation neutrons transmute waste in a region that surrounds the spallation target. It is desirable for the waste transmutation region (WTR) to have significant neutron multiplication (a factor of 10 or higher) to keep the required accelerator size reasonable. The WTR is subcritical and is thus not required to generate a self-sustaining fission reaction in the waste. The elimination of this requirement allows the ATW system to be optimized for reducing the hazard from nuclear waste without the concerns associated with safely maintaining criticality. Subcritical operation allows waste compositions with positive prompt reactivity feedback coefficients to be considered, allows waste forms optimized for processing to be considered, and allows additional design flexibility. The WTR will be designed so that criticality cannot be achieved during any credible accident scenario. The primary advantage of the ATW approach is thus the design and operational flexibility gained from subcritical operation. The primary disadvantage of the ATW approach is the expense and complexity of integrating a large proton accelerator with a spallation target and the WTR