Measurement of doppler effect up to 2000degC at FCA. 4. Investigation on calculation model for the Doppler effect measurement with a heated foil using MVP code

A collision probability code with ultra-fine group structure, PEACO-X, is used to consider precisely the resonance interaction effect between 238U in the foil and resonance nuclides in surrounding regions. The PEACO-X code calculates collision probabilities for one dimensional geometries such as cylinder, sphere and slab. To obtain an appropriate spherical cell model for the PEACO-X calculation in the analysis of the activation Doppler effect, the following items were investigated by the Monte Carlo calculation: 1) Evaluation of the heterogeneity effect of a fuel cell on the Doppler effect calculation. 2) Selection of a spherical cell model for a disk-shaped foil. In the evaluation of the heterogeneity effect, the calculated results of the activation Doppler effect were compared between the heterogeneous and homogeneous cell models. By this comparison, it was found that homogenizing the fuel cell decreased the contribution to the 238U capture reaction rate in the energy region less than 2 keV. The heterogeneity effect on the activation Doppler effect, however, was negligible small. In the selection of the spherical cell model for the disk-shaped foil, parametric survey was carried out being concentrated on the background cross section of 238U in the foil, which is based on the Wigner rational approximation. The energy breakdown of the 238U capture reaction rate in the disk-shaped foil was compared with those in the spherical models with various values of the background cross sections. From these comparisons, the spherical model was selected in which the background cross section for 238U is equal to that of the disk-shaped foil. (J.P.N.)