Comparisons of Theoretical and Experimental Neutron Spectra, ¹¹⁵In(n,n′) and Fission Rates, in the Centre of Threee Spherical Natural Uranium and Iron Shell Configurations, Located at BR1

Abstract

Three spherical configurations of iron and uranium shells have been studied. The configurations were a 1-cm thick natural uranium shell, a 1-cm thick natural uranium shell with an inner 7-cm thick iron shell and a 1-cm thick natural uranium shell with an inner iron shell of 14-cm thickness. For the measurements, the shells were located at the centre of a hollow cavity, 100-cm in diameter, in the vertical graphite thermal column of the BR1 reactor.

The central neutron spectra were calculated by means of the DTF-IV code, using the 208-group KEDAK-3 library, and by means of the ANISN code, using the 171- group VITAMIN-C library. Central neutron spectra, measured by the proton-recoil and ⁶Li(n,α)t spectrometry techniques, are compared to the theory between ~ 100 keV and 5 MeV.

Mean fission cross-sections of ²⁴⁰Pu, ²³⁷Np, ²³⁴U, ²³⁵U, ²³⁶U and ²³⁸U were deduced from the calculations. Their ratios with respect to ²³⁸U are compared to measurements made with NBS dual fission chambers.