Study On Hybrid Harmonics And Linearization Perturbation Method And The Benchmark Problem For Loading Pattern Search

Despite significant progress in core loading pattern search methods over years, there still remains the issue of large computing workload and the need for improving the speed of evaluating loading pattern candidates during the search process. Most recently, a fast-running loading pattern evaluation method based on low-order harmonics augmented expansion method was proposed by Lv Dong etc., preliminary results demonstrated that the proposed method has good accuracy and its speed performance is also very encouraging.In this thesis, the author first took a closer look at the method of generating perturbation base functions, since in-depth study carried by author has revealed that the original direct substitution method adopted by Lv Dong may fail to give accurate results for cases with extremely large perturbation. A more rigorous linear perturbation method was proposed to generate the perturbation base functions, and numerical results for the enumerating loading pattern evaluation problem demonstrates that the new method is more generic and accurate, and makes the harmonics expansion method more promising.The thesis also investigated the issue of how to best define the low-order matrix problem and how to derive the most accurate expansion coefficients. Various approaches like least square method and orthogonal projection method were studied, and the Galerkin orthogonal projection method was adopted in the end based on the performance comparison among different approaches. Improved source extrapolation method was proposed and applied to the solution of harmonics and low-order eigen-value problem. Depletion and pin power reconstruction modules were developed to make the method more suitable to the future practical application. The new method was finally named as Hybrid Harmonics and Linearization Perturbation method (HHLP).Finally, exploiting the excellent speed performace of HHLP, several enumerating loading pattern evaluation problems for a 2-loop PWR were studied, all the possible LPs were exclusively analyzed and acceptable LP candidates were sorted out. Some general rules relating the loading of fuel assemblies with the performance index of a core were concluded, and the data obtained will serve as a benchmark problem for LP search method qualification in the future.