Nuclear data uncertainty propagation: Perturbation vs. Monte Carlo

Two methods of nuclear data uncertainty propagation are compared, using the same nuclear data uncertainties and criticality-safety benchmarks. The first method, based on perturbation theory uses covariance files, covariance processing and the perturbation card of MCNP. The second method makes use of a large number of MCNP calculations, all alike, but using different random nuclear data libraries, consistent with the covariance files of the first method. The consistency of the nuclear data used by both methods is checked and results for 33 criticality-safety benchmarks are presented. Relatively good agreements are found, but depending on the benchmark cases, differences due to the elastic cross-section, ν-bar, angular and energy distributions are observed.     

车载放射性废物体在线监测结果的不确定度评定

基于BECK公式建立了车载放射性废物体在线监测模型,其复杂的测量公式使得公式的求导、各影响因素之间的相关系数难以采用解析计算方法实现,导致利用不确定度传播定律进行不确定度评定存在困难。应用蒙特卡罗不确定度合成方法评价了车载放射性废物体在线监测结果的不确定度,解决了就地γ能谱测量中的不确定度评定问题。其评定流程是首先采用A、B类不确定度评定方法评价各测量参数的不确定度,然后使用蒙特卡罗不确定度合成方法对不确定度分项进行合成。结果表明,241Am测量结果的不确定度<40%(1σ),137Cs、60Co和152Eu测量结果不确定度<34%(1σ)。     

超级蒙特卡罗核计算仿真软件系统SuperMC

蒙特卡罗方法对于复杂核系统的模拟具有明显优势,然而在实际工程应用中存在巨大的挑战,如复杂结构与材料分布精准建模难度大、计算收敛速度慢、海量数据难以及时有效分析等。超级蒙特卡罗核计算仿真软件系统SuperMC设计为支持以辐射输运为核心,包含燃耗、辐射源项/剂量/生物危害、材料活化与嬗变等的综合中子学计算,支持热工水力学、结构力学、化学、生物学等多物理耦合模拟。SuperMC目前已发展了精准建模、高效计算、四维可视化等关键技术,通过2 000余个国际基准模型及实验的验证与确认,在反应堆工程等方面获得广泛应用,本文对其发展概况进行介绍。     

Benchmarking of JEFF-3.2, FENDL-3.0 and TENDL-2014 evaluated data for tungsten with 14.8 MeV neutrons

Integral experiments on tungsten slab samples were carried out on the D-T neutron source facility at China Institute of Atomic Energy.Leakage neutron spectra from the irradiated tungsten target were measured by the time-of-flight technique.Accuracy of the nuclear data for tungsten was examined by comparing the measured neutron spectra with the leakage neutron spectra simulated using the MCNP-4C code with evaluated nuclear data of the JEFF-3.2,FENDL-3.0 and TENDL-2014 libraries.The results show that the calculations with JEFF-3.2 agree well with the measurements in the whole energy range and all angles,whereas the spectra calculated with FENDL-3.0 and TENDL-2014 have some discrepancies with the experimental data.     

Benchmarking of JEFF-3.2, FENDL-3.0 and TENDL-2014 evaluated data for tungsten with 14.8 MeV neutrons

Integral experiments on tungsten slab samples were carried out on the D-T neutron source facility at China Institute of Atomic Energy.Leakage neutron spectra from the irradiated tungsten target were measured by the time-of-flight technique.Accuracy of the nuclear data for tungsten was examined by comparing the measured neutron spectra with the leakage neutron spectra simulated using the MCNP-4C code with evaluated nuclear data of the JEFF-3.2,FENDL-3.0 and TENDL-2014 libraries.The results show that the calculations with JEFF-3.2 agree well with the measurements in the whole energy range and all angles,whereas the spectra calculated with FENDL-3.0 and TENDL-2014 have some discrepancies with the experimental data.     

Optimization of moderator assembly for neutron flux measurement: experimental and theoretical approaches

A moderator of paraffin wax assembly has been demonstrated where its thickness can be optimized to thermalize fast neutrons. The assembly is used for measuring fast neutron flux of a neutron probe at different neutron energies, using BF03(U10and 200) and3He(U0.500)neutron detectors. The paraffin wax thickness was optimized at 6 cm for the neutron probe which contains an Am–Be neutron source. The experimental data are compared with Monte Carlo simulation results using MCNP5 version 1.4. Neutron flux comparison and neutron activation techniques are used for measuring neutron flux of the neutron probe to validate the optimum paraffin moderator thickness in the assembly. The neutron fluxes are measured at(1.17 ± 0.09) 9 105 and(1.19 ± 0.1) 9 105n/s, being in agreement with the simulated values. The moderator assembly can easily be utilized for essential requirements of neutron flux measurements.     

The range of penetration and the backscattering coefficient by using both the analytic and the stochastic theoretical ways of electron slowing down in solid targets: Comparative study

The aim of this paper is to determine the best theoretical way (stochastic or analytic) to use in the study of the range of penetration and the backscattering coefficient of electron impinging in solid target, by adopting the same input in the form of collision cross-sections. For this purpose, differential elastic cross sections has been calculated by using our semi-empirical model [A. Bentabet, Z. Chaoui, A. Aydin, A. Azbouche, Vacuum 85 (2010) 156]; and that of inelastic cross sections has been calculated by using Gryzinski’s excitation function. Moreover, in stochastic case, the obtained quantities are calculated by using both Monte Carlo schemes based on continuous slowing down approximation (CSDA) and on individual electron scattering events methods.