Evaluation of Significance of Zr Bound in ZrH_x for its Possible Inclusion in the WIMSD-5 Cross Section Library

摘要

The principal objective of this study was to evaluate the significance of a separate data for Zirconium bound in Zirconium hydride rather than as a free atom and its possible inclusion in the WIMSD library. A TRIGA research reactor benchmark input specified for WIMSD-5 was prepared. The calculations have been performed by the WIMSD-5B code and the ANL version of WIMSD code. In the ANL version, two sets of data for Hydrogen were available: for Hydrogen bound in water and Hydrogen bound in Zirconium hydride. For Zirconium, the available data were for Zirconium natural and Zirconium bound in Zirconium hydride prepared without taking into account the P_1 correction. A separate data for Zirconium bound for Zirconium hydride with P_1 correction was prepared for the WIMSD-5B code at INST, AERE, Savar. The cross section data for all the elements of the benchmark input have been processed by NJOY94.10+ based on ENDF/B-VI library and incorporated in the 69-group WIMS library. All the calculations have been carried out applying 69 energy groups in the main transport routine with subsequent condensation to 7 group. Four cases namely (i) diffusion, (ii) B_1 with P_1 thermal scattering matrices for H and O in water only, (iii) as above but with a P_1 matrix also for H bound in ZrHx, (iv) as above but with a P_1 matrix also for Zr bound in ZrHx were studied. It is seen that the differences in cross sections are negligible although the overall effect in K-eff is up to 700 pcm in the case of ANL, and in our case, the effect is even stronger. The possible cause of this inconsistency could be the absence of P_1 matrices for all the principal materials for the benchmark input in the WIMSD library. The author of the WIMS recommends the usage of P_1 matrices only if they are available for all principal isotopes of a material. No material is treated separately on the level of leakage calculations and the contribution from the first order is weighted over spectra in materials, their volume and number densities.