APPLICATION OF GLOBAL SENSITIVITY ANALYSIS APPROACH TO EXERCISE 1-2 OF THE OECD LWR UAM BENCHMARK

摘要

This paper is three fold. In the first part, continuous energy Monte Carlo calculations are performed as reference solutions to the test problems of Exercise 2 of Phase 1 (1-2), "Lattice Physics", of the OECD LWR UAM Benchmark. Using an automated tool for the generation of temperature-dependent continuous-energy cross section libraries, developed at the Pennsylvania State University (PSU), reference solutions are obtained using the different available Nuclear Data Libraries (NDL). These reference solutions provide the required data to the participants of the OECD UAM Benchmark.The second part of this paper focuses on the comparison between a new thermal scattering cross section library and the MCNP5 built-in thermal libraries. This gives the possibility of performing MCNP5 criticality calculations at the correct moderator temperature and improving the accuracy of the calculation.In the final part of the paper, global sensitivity analysis is applied to the modeling of nuclear reactor calculations for better model understanding. Specifically, it is investigated how much criticality conditions are affected by uncertainties in various inputs, including nuclear cross-sections, at different energies, from several isotopes in the fuel, the absorber and the moderator. The sensitivity analysis uses the Sobol' and Jansen formulas, which allow us to estimate, for each uncertain input, its main effect, its total effect (i.e. the overall effect, which includes all the interactions, at any order, with all the other uncertain inputs), and all two-way interactions among all possible pairs of uncertain inputs. The sensitivity analysis consists of a number of model simulations, which are performed using MCNP5.