Measurement of leakage neutron spectra for Tungsten with D-T neutrons and validation of evaluated nuclear data

Validation of Neutron Evaluated Data Based on The Experimental Reactivity Worth of Tungsten Target in CiADS

Measurement of a cylindrical tungsten target reactivity worth has been performed on the light water zero-power reactor of VENUS-II at China Institute of Atomic Energy (CIAE) in order to verify the neutron evaluated data related to the engineering design of Chinese initiative Accelerator Driven Systems (CiADS). The reactivity worth of the tungsten target was measured and processed as -1.234±0.114mk by a period method. The experimental result was compared with the simulation ones calculated by MCNP with five different libraries, i.e., ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0, CENDL-3.1 and JEFF-3.2. By comparing the results of experiment and simulation, the simulated results from ENDF/B-VII.0, JENDL-4.0 and JEFF-3.2 are higher than the experimental result, however that from CENDL-3.1 is lower. The result from ENDF/B-VII.1 library shows better agreement with the experiment one and the relative deviation is less than 2%. Through the analysis of the differences of the results, non-tungsten elements cross sections in the ENDF/B-VII.1 mainly affect the tungsten radiation capture and elastic scattering reaction rates in the energy range of 10-9-10-7 MeV, which results in a better simulated tungsten target reactivity worth value. Therefore, it is recommended that the tungsten target reactivity worth should be calculated with the ENDF/B-VII.1.

Measurement of leakage neutron spectra with D-T neutrons and evaluated nuclear data

Benchmarking of evaluated neutron nuclear data libraries was performed for ∼14.8 MeV neutrons on the several targets, such as gallium, graphite, silicon carbide, uranium and tungsten samples. The experiments were performed at China Institute of Atomic Energy (CIAE). The neutron leakage spectra from the samples were measured at 60◦ and 120◦ by a TOF technique with a BC501A scintillation detector. The measured spectra are rather well reproduced by MCNP-4C simulations with the CENDL3.1, JENDL-4.0 and the new release ENDF/B-VIII.0, JEFF-3.3 evaluated nuclear data libraries and so on. There have some difference between experiments and simulations for the elastic and inelastic contributions in the partial energy range. And the discrepancies of the neutron leakage spectra in the MCNP simulations originate simply from the differences in the spectra distributions of the neutron reaction channels in the evaluated nuclear data libraries.

Measurements and analysis of leakage neutron spectra from multiple-slab sample assemblies comprising W,U,C, and CH2 with D-T neutron irradiation

The accelerator driven subcritical system (ADS) is regarded as a safe and clean nuclear power system, which can be used for the transmutation of nuclear waste and the breeding of nuclear fuel. In this study, in order to validate nuclear data and the neutron transportation performance of the materials related to ADS, we measured the leakage neutron spectra from multiple-slab sample assemblies using 14.8 MeV D-T neutrons. Two types of assemblies comprising A-1 (W+U+C+CH₂) and A-2 (U+C+CH₂) were both built up gradually starting with the first wall. The measured spectra were compared with those calculated using the Monte Carlo code neutron transport coed (MCNP)-4C. A comparison of the results showed that the experimental leakage neutron spectra for both A-1 or A-2 were reproduced well by the three evaluated nuclear data libraries with discrepancies of less than 15% (A-1) and 12% (A-2), except when below 3 MeV. For 2-cm and 5-cm uranium samples, the CENDL-3.1 calculations exhibited large discrepancies in the energy range of 2-8 MeV and above 13 MeV. Thus, the CENDL-3.1 library for uranium should be reevaluated, especially around this energy range. It was significant that the leakage neuron spectra changed clearly when the latest material layer was added during the building of assemblies A-1 and A-2.