Superconducting RF (SRF) linear proton accelerators have been demonstrated by the ORNL Spallation Neutron Source (SNS) to have the power, reliability, and efficiency to drive subcritical small modular reactors (SMRs) based on the ORNL Molten-Salt (MS) Reactor Experiment (MSRE). The Mu*STAR subcritical SMR design integrates the SRF accelerator and MS reactor by using a spallation target inside the graphite-moderated reactor that produces neutrons that initiate fission chains where the heat generated is proportional to the proton beam power. The MS fuel is a lithium fluoride-based eutectic mixture of fissile or fertile fluoride materials with a melting point near 500 C. Mu*STAR can consume natural or depleted uranium, thorium, surplus weapons materials, or spent/used nuclear fuel (SNF/UNF) from Light Water Reactors (LWRs) without redesign, Once the fuel has been converted to fluoride and added to the eutectic, no further preparations are needed for Mu*STAR operation. The design is weapons proliferation resistant in that uranium enrichment and chemical reprocessing are not required. During operation, volatile fission product isotopes are continuously removed, as was done in the MSRE. Nonvolatile fission products remain in the reactor where many are beneficially transmuted to reduce the SNF radiotoxicity lifetime while the accelerator power is gradually increased over decades to overcome neutron absorption by the accumulated fission products. Simulations show that the 5% burnup of the LWR fuel can be extended to 40% using Mu*STAR before the accelerator requires 15% of the generated electrical output. We describe an experiment proposed to demonstrate high burnup and radiotoxicity lifetime reduction of SNF that will enable its onsite burial to close the nuclear fuel cycle.
Year
2020
Abstract