The spectral indices of the IPEN/MB-01 reactor: measurements and calculation

Abstract

This experimental work aims to obtain the spectral indices 28p, 25δ , C*, C8/F and (C8/F)epith of the core of the 1PEN/MB-01 nuclear reactor. The measurements were performed with high precision at the asymptotic central core region. Specifically for 28p and 25δ, this work adopts a novice approach based on the direct gamma spectrometry of the irradiated fuel rods and the traditional one based on uranium foils. The total and epithermal reaction rates were obtained from the direct gamma spectrometry of an irradiated fuel element at the maximum neutron flux position. The gamma spectrometry was performed by a fuel rod scanning equipment with a collimator of 1 cm opening size. Correction factors for the cadmium perturbations were obtained both experimentally and from a calculational approach carried out by MCNP-4B. Furthermore, this work also introduces a new spectral index namely (C8/F)epith for verifying the adequacy of the nuclear data at the epithermal neutron energy region. The analyses reveal that the correction factors are very sensitive to the nuclear data library used by MCNP-4B; namely ENDF/B-V and ENDF/B-VI.5 libraries. The best results are obtained when the correction factors and the spectral indices are calculated with ENDF/B-VI.5.