Nuclear Data for Reactor Physics: Cross sections and level densities in the actinide region

J.N Wilson,S Siem,F Gunsing,S.J Rose,A Georgen,L Bernstein,B Jurado

doi:10.1051/epjconf/20100212001

Abstract

Nuclear data in the actinide region are particularly important because they a re basis behind all sim- ulations of nuclear reactor core behaviour over both long time scales (fuel depletion and waste production) and short time scales (accident scenarios). Nuclear reaction cross sectio ns must be known as precisely as possible so that core reaction rates can be accurately calculated. Although cross se ction measurements in this region have been widely performed, for certain nuclei, particularly those with short h alf lives, direct measurements are either very diffi cult or impossible and thus reactor simulations must rely on theoretical calc ulations or extrapolations from neighbouring nuclei. The greatest uncertainty in theoretical cross section calculations comes from the lack of knowledge of level densities, for which predicted values can often be incorrect by a factor of two or more. Therefore there is a strong case for a systematic experimental study of level densities in the actinide region for the purpose of a) providing a stringent test of theoretical cross section calculations for nuclei where experimental cross section data are available and b) for providing better estimations of c ross sections for nuclei in which no cross section data are available.

Highlights

Nuclear data in the actinide region are important because they are basis behind all simulations of nuclear reactor core behaviour over both long time scales and short time scales
The greatest uncertainty in theoretical cross section calculations comes from the lack of knowledge of level densities, for which predicted values can often be incorrect by a factor of two or more
There is a strong case for a systematic experimental study of level densities in the actinide region for the purpose of a) providing a stringent test of theoretical cross section calculations for nuclei where experimental cross section data are available and b) for providing better estimations of cross sections for nuclei in which no cross section data are available

Summary

Introduction

There are currently around 400 nuclear reactors operating around the world producing some 16% of the world’s electricity. There is currently no other available technology that emits little CO2 and can be scaled up quickly and efficiently enough to attack the aforementioned problems in a significant way This expansion is already beginning, with the construction of the latest generation of nuclear power plants (generation III) under way in China, Finland, France, India and Japan. Reactor physics simulations require a value for the cross sections over large energy ranges for large numbers of nuclei, and any value for the cross section at a given energy, even a highly inaccurate value, is better than no value at all For this reason the evaluated data bases (e.g. ENDF, JEFF, JENDL) have been constructed whereby measured nuclear data, extrapolations and theoretical calculations are mixed together to provide simulations with the best available information. The goal is to understand the isotopic composition of the spent fuel with a view to either recycling the useful fissile and fer-

Nucleosynthesis in a reactor core

Important short lived nuclei

Limitations of the nuclear data

The Hauser-Feshbach statistical formalism

Findings

Program of Level Density Measurements