ACCELERATOR-DRIVEN SUBCRITICAL FISSION TO DESTROY TRANSURANICS AND CLOSE THE NUCLEAR FUEL CYCLE* S. Assadi, C. Collins, J. Comeaux, K. Damborsky, J. Kellams, F. Lu, P. McIntyre # , K. Melconian, N. Pogue, M. Salanne, A. Sattarov, E. Sooby, and P. Tsvetkov, Texas A&M University, College Station, TX 77845 USA Abstract A design for accelerator-driven subcritical fission in a molten salt core (ADAM) has been made for the purpose of destroying the transuranic elements in used nuclear fuel as fast as they are made in a conventional nuclear power plant. The oxide fuel is extracted from the used fuel assemblies into molten chloride salt using pyropro- cessing, and the transuranic, uranium, and fission product salts are separated into three batches using electro- separation. The transuranic salt is then transferred to a subcritical core, with neutron gain 0.97. The core is driv- en by 800 MeV proton beams from a 12 mA CW strong- focusing cyclotron. The transuranics are destroyed and the fission heat is used to produce electric power. Simu- lations of many potential failure modes have been per- formed; the core cannot reach criticality in any failure- mode scenario considered. It operates as an energy am- plifier with an energy gain ~5.5. INTRODUCTION Today nuclear power plants generate 20% of the elec- tric power in the United States [1]. Until recently nuclear power comprised 20% of the grid in Germany and 30% in Japan, but Germany has moved to end their nuclear power production and Japan has idled their reactor fleet. Those decisions reflect a growing public concern about the safe- ty of nuclear power. The meltdowns at Three Mile Island [2], Chernobyl [3], and Fukushima [4] underscore that this abundant source of energy can also produce extreme hazards. The most enduring hazard of nuclear power is the large quantity of hazardous radioisotopes in used nuclear fuel (UNF). The most dangerous among those are transuran- ics (TRU, elements beyond uranium in the periodic table). The transuranics contained in the ~70,000 tons of UNF in the US have a radiotoxicity >10 13 Sv and half-lives of 10 5 -10 6 years. The present accumulation of UNF also still contains about 1/3 of the entire US reserves of urani- um. Long-term storage would pose the risk unto the gen- erations of future release of immense radiotoxicity, and would sequester a major portion of available uranium resources. ADAM has been designed to offer an alterna- tive: to destroy the transuranics, to recover the uranium for future use, and to produce 10x more energy than was produced in the first use of the fuel. ADAM OVERVIEW ADS Core Neutronics The individual ADS core must be sized to optimize the normalized burn rate ; i.e. to minimize the TRU in- ventory required to sustain core operation. Figure 3 shows the energy dependence for neutron capture on 238 Uwhich breeds TRU) and for n-induced fission of the dominant TRU isotopes. The fission cross sections for most TRU isotopes are significant only for ultra-fast neu- trons (>1 MeV). Optimization of fast spectrum for the ADAM core places strong constraints upon the core size and geometry and upon the fuel salt composition. The optimized core is shown in Figure 1, and its neutronics properties are summarized in Table 1. In its spectrum 20% of the neutrons have >1 MeV energy. It operates with a neutron gain k eff = 0.97, produces 280 MW th , and requires a 10 MW proton driver. The optimized burn rate is  T / T = 5.6% / year , corresponding to a destruction time of 18 years.  T / T Figure 1: ADS molten salt core assembly. Fuel salt pumps Primary heat exchanger Beam windows Core Pb reflector ____________________________________________ * Work supported by State of Texas and the Mitchell Foundation. # mcintyre@physics.tamu.edu MOZAB1 Proceedings of PAC2013, Pasadena, CA USA ISBN 978-3-95450-138-0 62 Copyright c  2013 CC-BY-3.0 and by the respective authors 09 Industrial Accelerators and Applications U04 - Transmutation and Energy Production