Measurement and Analysis of Fission Rates in a Spherical Mockup of Uranium and Polyethylene

TL;DR

This study measures and analyzes fission rate distributions in a spherical uranium-polyethylene mockup using micro fission chambers and compares experimental data with MCNP5 simulations, revealing generally good agreement within 10%.

Contribution

It introduces a method to determine individual uranium isotope fission rates using two types of micro fission chambers and isotope contribution correction, validated by experimental and simulation comparison.

Findings

Fission rates of 238U and 235U agree with measurements within 10% in most regions.

Discrepancies occur near polyethylene regions and outer surfaces.

Simulation results are less accurate without considering fission chamber effects.

Abstract

Measurements of the reaction rate distribution were carried out using two kinds of Plate Micro Fission Chamber(PMFC). The first is a depleted uranium chamber and the second an enriched uranium chamber. The material in the depleted uranium chamber is strictly the same as the material in the uranium assembly. With the equation solution to conduct the isotope contribution correction, the fission rate of 238U and 235U were obtained from the fission rate of depleted uranium and enriched uranium. And then, the fission count of 238U and 235U in an individual uranium shell was obtained. In this work, MCNP5 and continuous energy cross sections ENDF/BV.0 were used for the analysis of fission rate distribution and fission count. The calculated results were compared with the experimental ones. The calculation of fission rate of DU and EU were found to agree with the measured ones within 10% except at the positions in polyethylene region and the two positions near the outer surface. Beacause the fission chamber was not considered in the calculation of the fission counts of 238U and 235U, the calculated results did not agree well with the experimental ones.