2.3. Analysis of Heterogeneous Fuel Geometries Heterogeneous Pu-MA-Th fuel assembly geometries offer some potential advantages over the homogeneous Pu-MA-Th fuels. Assuming that Pu and MA come as separate streams from the separation process, the relative amounts of Pu and MA in the fuel can be varied so that most of the Pu can be concentrated in one type of fuel assemblies while all of the MA can be concentrated in another type of assemblies. Therefore, for each assembly type, the fuel lattice can be optimized to a certain degree for preferential destruction of either Pu or MA. Additionally, different fuel management schemes can be applied to the fuel assemblies containing different relative amounts of Pu and MA. As a result, assembly types that required to reach higher burnup (and, therefore, higher TRU destruction efficiency) can reside in the core for larger number of cycles than other types of fuel assemblies. An assessment of these potential advantages for an equilibrium core containing heterogeneous fuel configurations were performed with the CASMO-4 computer code that allows 2D transport and burnup calculations of 2x2 segment (“colorset”) of fuel assemblies of different types. A schematic diagram of such 2x2 colorset of fuel assemblies is shown in Figure 2.3.1.
Th–Pu assembly
Th–Pu-MA assembly
Th–Pu-MA assembly
Th–Pu assembly
Figure 2.3.1. Example of CASMO 2x2 colorset layout.
The analysis of heterogeneous fuel configurations was performed through variation of fuel composition (Pu:MA:Th ratio) and variation of lattice H/HM ratio for each assembly type and the destruction efficiencies and destruction rates for Pu and MA averaged over the entire colorset
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