| Summary: | The neutron and photon shielding is an important part of the reactor design for safety of people and facilities. CENDL-3.2 is the latest Chinese evaluated nuclear data library released by China Nuclear Data Center (CNDC) in 2020. Many nuclides were improved with new evaluation techniques and experimental data. Thanks to the high calculation efficiency, broadgroup shielding libraries are widely used in shielding calculation. To carry on the research on reactor shielding calculation, the codes NECPAtlas and NECPShield were applied to develop the broadgroup shielding library NECLCP29 based on CENDL32. Generating a broadgroup shielding library needs three stages. Firstly, NECLCP199, a finegroup library with 199 neutron groups and 42 photon groups, was produced using NECPAtlas and NECPShield. When producing the finegroup library, the neutron weight function consists of a 1/E spectrum, a fission spectrum and a thermal Maxwellian spectrum. The photon weight function consists of a 1/E spectrum at the middle energies. At the high and low energy, the spectrum goes down. Secondly, a typical 1D PWR model used in producing BUGLE libraries was calculated using NECLCP199 to obtain the finegroup flux distribution in the model. Before calculating the model, the nuclides were selfshielded using several different models, including a PWR pin cell model for the core, an ironwater model for the down comer, a concrete model for the concrete, a carbon steel model for the pressure vessel and a stainlesssteel model for the baffle and barrel. Lastly, the finegroup fluxes in core, down comer, pressured vessel and concrete were chosen to collapse finegroup cross sections of selfshielded nuclides to generate a broadgroup library. Moreover, the finegroup flux in concrete was applied to collapse the finegroup infinite diluted cross sections of all nuclides from NECLCP199. The energy group structure has an important influence on the accuracy and efficiency for shielding calculation. To obtain an improved broadgroup structure for better accuracy and efficiency, particle swarm optimization (PSO) was used. The research on application of PSO in optimizing the energy group structure for shielding calculation was performed, including the combination of PSO process and the generation of the broadgroup library, the mapping of PSO variables and the construction of fitness function. A 29group structure was optimized using PSO. NECLCP29 with the optimized 29group structure was generated. To validate NECLCP29 broadgroup shielding library, some benchmarks in SINBAD, the international shielding benchmark library, were calculated, including Iron88, ASPISNG, and HBR2. The calculated results were compared with the measured results. Moreover, the results of BUGLEB7 and BUGLE96 which are famous international broadgroup shielding libraries were also used for comparison. The numerical results show that the calculated values using NECLCP29 agree well with the measured values. Compared with BUGLEB7 and BUGLE96 whose numbers of neutron groups are all 47, the calculation accuracy of NECL-CP29 is better. Especially in calculating the reaction rate of 197Au(n,γ) in Iron88 benchmark, the results given by NECLCP29 are much closer to the measured values than BUGLEB7. Thanks to the optimized energy group structure with less neutron energy group number, the computational efficiency is obviously improved.
|
|---|