Primary Ionization Density Produced by Charged Fragments in the Working Volume of the Fission Chambers

The question of the spatial distribution of ion pairs created by 235U fission fragments in the active volume of the fission chamber has been studied. The formulas of the spatial distribution of ion pairs in cylindrical fission chambers are proposed, which allows you to evaluate correctly the density of ion pairs in any point in the sensitive volume of the fission chamber

Nuclear Data Sensitivity Study for the EBR-II Fast Reactor Benchmark Using SCALE with ENDF/B-VII.1 and ENDF/B-VIII.0

The EBR-II benchmark, which was recently included in the International Handbook of Evaluated Reactor Physics Benchmark Experiments, served as a basis for assessing the performance of the SCALE code system for fast reactor analyses. A reference SCALE model was developed based on the benchmark specifications. Great agreement was observed between the eigenvalue calculated with this SCALE model and the benchmark eigenvalue. To identify potential gaps and uncertainties of nuclear data for the simulation of various quantities of interest in fast spectrum systems, sensitivity and uncertainty analyses were performed for the eigenvalue, reactivity effects, and the radial power profile of EBR-II using the two most recent ENDF/B nuclear data library releases. While the nominal results are consistent between the calculations with the different libraries, the uncertainties due to nuclear data vary significantly. The major driver of observed uncertainties is the uncertainty of the 235U (n,γ) reaction. Since the uncertainty of this reaction is significantly reduced in the ENDF/B-VIII.0 library compared to ENDF/B-VII.1, the obtained output uncertainties tend to be smaller in ENDF/B-VIII.0 calculations, although the decrease is partially compensated by increased uncertainties in 235U fission and ν¯.

ENERGY PARTITION IN 235U FISSION REACTION INDUCED BY THERMAL NEUTRON

The partition of the total excitation energy between the fission fragments for the n th +235 U and n(En = 5.55 MeV)+235 U fission reactions are analyzed with the experimental data available. Our results show that the total excitation energy is not shared by the fragments in proportion of their masses but support the so-called energy sorting-mechanism. The temperature of the heavy fragment is generally lower than that of the light one when the shell effect does not play a strong role. As soon as the mass of heavy fragment closes to 132, its temperature becomes higher than the complementary light one because of strong shell effect. Our results also show that the heavy fragments gain more energy than the complementary light ones when the incident neutron energy increases.