Abstract
Cross section measurements in the fast energy region are being demanded as one of the key ingredients for modelling Generation-IV nuclear power plants. However, in facilities where there are no time-of-flight possibilities or it is not convenient to use them, using the 235U(n,f) cross section as a benchmark would require a careful knowledge of the room scatter in the experimental area. In this paper we present measurements of two threshold reactions, 238U(n,f) and 237Np(n,f), that could become a standard between their fission threshold and 2.5 MeV, if the discrepancies shown in the evaluations and in some experimental data can be solved. The preliminary results are in agreement with the present ENDF/B-VII.1 evaluation.
Highlights
The need for better cross section values to improve accuracy when modelling Gen-IV nuclear power plants has been highlighted recently by a sensitivity analysis [1]
In this paper we present measurements of two threshold reactions, 238U(n,f) and 237Np(n,f), that could become a standard between their fission threshold and 2.5 MeV, if the discrepancies shown in the evaluations and in some experimental data can be solved
The preliminary results are in agreement with the present ENDF/B-VII.1 evaluation
Summary
The need for better cross section values to improve accuracy when modelling Gen-IV nuclear power plants has been highlighted recently by a sensitivity analysis [1]. Experiments on fission cross sections are generally performed relative to 235U(n,f). Major concerns have been raised recently about the neutron-induced fission cross sections of 238U and 237Np. For the first isotope, 238U, even though considered a secondary standard above 2 MeV the related uncertainties are not negligible and different libraries (i.e. ENDF/B-VII. and JEFF-3.2) show discrepancies of up to 7% in the 1.5 MeV < En < 3 MeV range. In the case of 237Np recent experiments [2] measured the cross section to be up to 5% higher in the fast energy region. A study of the 238U(n,f) and 237Np(n,f) cross sections was performed at the Van de Graaff accelerator of the UK National Physical Laboratory (NPL) in collaboration with the Joint Research Centre under the EC-FP7 CHANDA project.
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