Plutonium disposition by gas dynamic trap
A subcritical fission blanket driven by a Gas Dynamic Trap-Neutron Source (GDT-NS) has the ability to eliminate significant quantities of the weapons-grade plutonium that the US has held in surplus since the end of the cold war. The GDT is a variant of the traditional mirror fusion reactor and shares with it an ability to produce focused neutron emissions. Recent results have confirmed plasma stability at high β and with these results GDT models have been extrapolated. It is now thought that this device could produce sufficient neutrons for industrial scale transmutation. To assist in the blanket design and optimization, the Fusion Actinide Burner (FAB) toolkit was developed to assist in blanket development acting as an interface with the Monte Carlo n-Particle code (MCNP6). This toolkit consists of simplified and detailed blanket models, iterative problem solving, data visualization, and a fuel cycle / burnup capability integrated with the ORIGEN isotope generation and depletion code. The toolkit was benchmarked successfully to a series of mirror fusion-fission hybrid designs. Early blanket development for the Gas Dynamic Trap - Plutonium Burner (GDT-PB) heavily referenced work done under the Accelerator Transmutation of Waste program led at Los Alamos in the late 1990s. Due to the compact design of the GDT-NS, the accelerator driven designs are more applicable than the larger tokamak-driven hybrid designs which have received more recent study. The focus moved towards optimizing the blanket to be couple with the GDT-NS. Compared to early ATW based studies, the coupling was improved by 40%. Combined with other improvements, the beginning of cycle power level was doubled compared to the previous GDT state-of-the-art designs. Much of these gains can be attributed by lengthening the blanket to better match the neutron source and improved coupling by using a helium cooled beryllium buffer. The simplified blanket models used in the earlier parametric studies were replaced with discretely defined fuel assemblies; a design nicknamed Goldilox. A partial blanket fuel reloading scheme was then developed to improve overall performance. After the blanket and reloading processes were optimized, the plutonium disposition metrics of dose rate and isotopic degradation were applied. A minimum-dose assembly was found to have a dose rate exceeding 7.7 sieverts per hour one meter from the assembly thirty years after operation, well in excess of the 1.0 mandated minimum. Applying the isotopic degradation requirements, a batch average 240Pu/239Pu ratio of 0.13 with a minimum ratio of > 0.10, an average of 2.0 metric tons of plutonium could be eliminated for each year of operation. This is more than sufficient to meet US commitments under the Plutonium Management and Disposition Agreement.
Bean, Purdue University.
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