Impact of ²³⁵U Resonance Parameter Evaluation in the Reactivity Prediction

Resonance parameter evaluation of the ²³⁵U cross sections using the Reich-Moore formalism was done with the computer code SAMMY from 0 to 2.25 keV to address issues with capture cross-section and standard fission cross-section values. The evaluation includes recent capture and fission cross-section measurements as well as high-resolution data used in previous ²³⁵U evaluation. Moreover the new ²³⁵U resonance parameter evaluation has been used in the calculation of a new benchmark experiment performed at the IPEN/MB-01 research reactor. The experiment, named the inversion point of the isothermal reactivity coefficient, is used to test temperature effects at low temperature. The results demonstrate that the new ²³⁵U evaluation has greatly improved the prediction of reactivity temperature coefficient in contrast to previous evaluations. This paper is outlined in two parts, namely the first part deals with the description of the ²³⁵U resonance analysis and evaluation up to 2.25 keV, and the second part presents the results of the isothermal reactivity coefficient calculations performed on the IPEN/MB-01 reactor.