Measurements of the modified conversion ratio by γ-ray spectrometry : Comparison with Monte Carlo calculations using the JEF2.2 and JEFF3.1 data librairies

P. Leconte (1, 2) , J. P. Hudelot (1, 2) , Muriel Antony (1, 2) , A. Lyoussi (1, 2)

1 LP2E - Laboratoire des Programmes Expérimentaux et d'Essais en Sûreté
2 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

This paper aims at validating the new JEFF3.1 evaluation of the 238U (n,γ) cross section whose precision is important in many scopes of the nuclear reactor physics. It describes measurements of the Modified Conversion Ratio (MCR), defined as the ratio of the 238U radiative capture rate to the total fission rate. The study focuses on different UO2 fuels, enriched from 0.25% to 5% in 235U. The experiments consist in irradiating fuel samples in the MINERVE low power facility, in a typical UO2-PWR neutron spectrum. After irradiation, the fuel samples are analyzed with a specific γ-ray spectrometry technique in order to measure the related integral reaction rates. At first in this paper, the principle of the experiment and the theoretical approach of the problem, including post-treatment and variance propagation, are presented. Then, the experimental MCRs are compared with calcultional results obtained from the reference Monte Carlo MCNP4C2 code using the JEF2.2 and JEFF3.1 data libraries. Finally, the improvements in the calculated integral radiative capture rate of 238U are discussed.

Domaines: Physique Nucléaire Théorique [nucl-th]

P. Leconte, J. P. Hudelot, Muriel Antony, A. Lyoussi. Measurements of the modified conversion ratio by γ-ray spectrometry : Comparison with Monte Carlo calculations using the JEF2.2 and JEFF3.1 data librairies. 1st International Conference on Physics and Technology of Reactors and Applications (PHYTRA - 2007), Mar 2007, Marrakech, Morocco. ⟨cea-01104114⟩