Abstract
New standard (n,f) cross sections other than 235U are important to study the relevant cross sections for Generation-IV power plants. A specific need for such standards is for performing new experiments with quasimonoenergetic neutron beams, such as those produced by Van de Graaf accelerators. Neutrons down-scattered to low energies in the experimental environment, so called room-return, become relevant for this type of measurements. Hence, a standard (n,f) cross section with a fission threshold is of great interest, in order to suppress the contribution from room-return background. For this reason we have performed two experiments at the VDG of the National Physical Laboratory to measure absolutely the (n,f) cross sections of 235U, 238U and 237Np in the fast neutron energy region. Our preliminary results are in agreement with the most up-to-date evaluations.
Highlights
Modelling of Generation-IV nuclear power plants requires highly accurate values of cross sections in the fast energy region
Cross section measurements are usually performed relative to the primary standard 235U(n,f), but in environments where the thermal and epi-thermal neutron background is non-negligible, such as the target hall of a Van de Graaff accelerator, other isotopes with a fission threshold should be preferred
The JEFF 3.2 evaluation showed discrepancies up to 7% in the range 1.5 MeV < En < 5 MeV with respect to ENDF/B-VIII.0, the new JEFF 3.3 evaluation is in agreement with ENDF/B-VIII.0. 237Np(n,f) would be more suitable as a standard because of its lower fission threshold (En = 0.5 MeV) and its higher cross section above En = 1.0 MeV, but some discrepancies between measurements have been found in the last years [1]
Summary
Modelling of Generation-IV nuclear power plants requires highly accurate values of cross sections in the fast energy region. To address these issues, two experimental campaigns have been performed at the Van de Graaff accelerator of the National Physical Laboratory (NPL,UK) under the European CHANDA project. This paper presents a follow-up on the experiment reported on [2]
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