Application of linear superposition methods to within-lattice loading design optimization of light water reactor nuclear fuel assemblies
This study has developed a linear superposition model (LSM) for the speedy and accurate estimation of lattice physics parameters during within-bundle "pin-by-pin" loading optimization calculations. The LSM has been implemented into the FORMOSA-L optimization code and typical results show that the run-time requirements can be reduced by at least an order of magnitude relative to performing direct lattice-physics evaluations with the CPM-2 or CASMO-3 code. Moreover, the speedups noted include all overhead expenses associated with the direct lattice physics calculations required to construct the LSM sensitivity libraries. Additionally, it is shown that the errors generated by this technique can be kept well under control by treating material and spatial shuffles separately during optimizations. Interpolation and second-order compensation improve the error level to an acceptable level. Finally, some flexibility has been built into the FORMOSA-L code so that the LSM may be applied in conjunction with direct lattice physics evaluations for fidelity adjustments, if needed. However, the results obtained, so far, indicate that the LSM can effectively substitute for direct lattice physics evaluations throughout the entire optimization process with no noticeable loss of fidelity. The technique of parallel computing via RPC has been added to the FORMOSA-L code to speed up the LSM library creation. Synchronous and asynchronous implementations are studied and the results show that the asynchronous implementation is better.