A Comparison of Neutron Energy Spectra in Low-Enriched and High-Enriched Uranium Cores

Abstract

The Pakistan Research Reactor-1 has been converted from highly enriched uranium to low-enriched fuel. The reactor power was also upgraded from 5 to 9 MW. An experimental program was undertaken to measure the neutron energy spectra in the core and the irradiation facilities of the new reactor. The objectives of these measurements were to provide useful data to the reactor users and to determine the changes in neutron energy spectrum due to the core conversion. The results were also compared to the neutron energy spectrum measurements made in the highly enriched uranium core. For energy spectrum measurements, several threshold activation detectors were irradiated in the reactor, and their measured activities were analyzed using the spectrum adjustment code SANDBP, which is a modified version of SAND-II. A sample energy spectrum for the material test reactor was used for the input to the SANDBP code, and the final spectrum was obtained by iterative adjustment. It was observed that the design of the low-enriched uranium core results in a harder energy spectrum than that resulting from highly enriched uranium core.