New experimental results for the inversion point of the isothermal reactivity coefficient of the IPEN/MB-01 reactor

New experiments for the inversion point of the isothermal reactivity coefficient of the IPEN/MB-01 research reactor facility have been successfully conducted. The experiments considered the removal of 12 central fuel rods. These positions of the core were filled either by stainless steel rods or by water. The purpose of the experiments was to give more physical insight of the reactivity coefficient behavior of the IPEN/MB-01 reactor. Particularly, it was shown that in these conditions, when compared to the previous work, the inversion point moves to higher temperatures which are in a very much agreement to the model proposed in the previous work. TORT, a SN 3-D transport code, is employed for the analysis of this set of new experiments. The analyses were performed in a companion NJOY, AMPX-II and TORT systems considering the data libraries ENDF/B-VI.8, ENDF/B-VII.0 and a third case which considers all nuclides from ENDF/B-VI.8 but 235U which was taken from the work of Haicheng-Wu. The theoretical analysis reveals that the best result for the calculated and experimental comparison was found when the 235U data which was taken from the work of Haicheng-Wu. However, all libraries considered in this work meets the desired accuracy (−1.0 pcm/°C) for the determination of this integral parameter for thermal reactors fuelled with slightly enriched uranium.