Interpretation of Fission Product Oscillations in the MINERVE Reactor, from Thermal to Epithermal Spectra

To take into account the reactivity loss in spent fuels, an experimental program was set up in 1993 at CEA-Cadarache, France, oscillating separated fission products (FPs) in the MINERVE reactor. Reactivity worth measurements of small samples allow the extraction of information about nuclear data of the studied isotopes. A fully validated calculation scheme has been implemented to interpret pile-oscillation measurements. Therefore, calculation over experiment ratios can be accurately transposed to trends in the integral capture cross section of the FPs. With the European JEFF3.1.1 library, results show a discrepancy below 3% for several nuclides: ¹⁵⁵Gd, ^{149, 152}Sm, ¹⁴³Nd, and ⁹⁵Mo, but improvements may be needed for some others: ¹³³Cs, ¹⁰³Rh, ⁹⁹Ru, and ¹⁵³Eu. Based on the Integral Data Assimilation technique, we propose new thermal cross-section values, (348 ± 14) b and (42 478 ± 1793) b, for two of the most absorbing nuclides, ¹⁴³Nd and ¹⁴⁹Sm, respectively.