Abstract
Shielding experiments are relevant to validate elastic and inelastic scattering cross sections in the fast energy range. In this paper, we are focusing on the possibility to use the pulsed white neutron time-of-flight facility GELINA to perform this kind of measurement. Several issues need to be addressed: neutron source intensity, room return effect, distance of the materials to be irradiated from the source, and the sensitivity of various reaction rate distributions through the material to different input cross sections. MCNP6 and TRIPOLI4 calculations of the outgoing neutron spectrum are compared, based on electron/positron/gamma/neutron simulations. A first guess of an integral transmission experiment through a 238 U slab is considered. It shows that a 10 cm thickness of uranium is sufficient to reach a high sensitivity to the 238 U inelastic scattering cross section in the [2-5 MeV] energy range, with small contributions from elastic and fission cross sections. This experiment would contribute to reduce the uncertainty on this nuclear data, which has a significant impact on the power distribution in large commercial reactors. Other materials that would be relevant for the ASTRID 4th generation prototype reactor are also tested, showing that a sufficient sensitivity to nuclear data would be obtained by using a 50 to 100cm thick slab of side 60x60cm. This study concludes on the feasibility and interest of such experiments in the target hall of the GELINA facility.
Highlights
Shielding experiments concern the measurement of neutron and gamma flux attenuation through large thicknesses of material, using either point-like sources (252Cf for instance) or neutron beams from test reactors
We have investigated the possibility of using large blocks of these materials within the target hall of GELINA, in order to make integral transmission measurements as well
Preliminary calculations were performed to assess the feasibility of shielding experiments in the target hall of the GELINA facility
Summary
Shielding experiments concern the measurement of neutron and gamma flux attenuation through large thicknesses of material, using either point-like sources (252Cf for instance) or neutron beams from test reactors. Most of these experiments were initially driven by the need to validate calculation codes related to radiation protection. UOx cores (and its swing between the center and the periphery) is 5-6% (1σ) This is why CEA and IRMM have considered the possibility to perform new shielding experiments to meet the target accuracies which are required for reactor physics studies (typically less than 5% at 1σ). Some quantitative results are presented for the measurement of other materials of interest for the ASTRID 4th generation prototype reactor: iron, sodium and magnesium oxide
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