Impact of experimental effects on a resolved resonance evaluation for practical applications.

Nuclear data evaluations available in existing nuclear data libraries are derived based on differential measurements that includes experimental effects such as target temperature, time-of-flight resolution, data normalization, self-shielding, multiple scattering, etc. Measurements are often made at temperatures corresponding to room temperature, 293.6 K, to avoid complexity in the experimental setup and costs of carrying out measurements for temperatures other than room temperature. This paper investigates the impact of experimental effects on the evaluation of a set of resonance parameters that fit the experimental differential data and its use in integral benchmark calculations. Given the importance of the temperature in integral benchmark results, the impact of the Doppler effect will be examined. Very seldom are experimental differential data available for temperatures below or above room temperature. Nuclear data measurements and evaluation needs are driven by reactor applications; consequently, the majority of data evaluations in nuclear data libraries are for temperatures above room temperature. Recently there has been a demand for nuclear data for low temperatures, below room temperatures, for criticality safety applications. Currently, calculations in response to low-temperature needs are based on extrapolating the existing data from the nuclear data libraries to temperatures below 293.6 K. For temperatures above 293.6 K, common practice is to process the data library to temperatures different from the temperature it was evaluated and use them in practical applications. Although this is an acceptable practice, care should be taken to understand whether the validity of the nuclear data can be extended to low and high temperatures. Issues in connection with temperature effects for low and high temperature nuclear data and their impact on practical applications are addressed in the paper. Given that experimental data for low- and high-temperatures are scarce, the results of the presented approach are based on data simulations. Simulated data for 235U in the resonance region, in particular the resolved resonance region, were used as part of the studies and demonstration. Furthermore, temperature effects were also investigated for thermal neutron scattering data, S (α , β) , for light water. However, the thermal scattering data are not based on simulation, but are the result of measurements carried out at the Spallation Neutron Source. A continuous-energy nuclear data library was used in Monte Carlo calculations to assess the impact in integral benchmark results. [ABSTRACT FROM AUTHOR]