Benchmark Critical Experiments and FP Worth Evaluation for a Heterogeneous System of Uranium Fuel Rods and Uranium Solution Poisoned with Pseudo-Fission-Product Elements

Abstract

A series of critical experiments were performed using heterogeneous cores at the Static Experiment Critical Facility (STACY) of Japan Atomic Energy Agency (JAEA) in order to obtain systematic benchmark data concerning the dissolving process in a reprocessing plant. Focusing on the introduction of the burn-up credit, critical mass measurement was conducted for a combination of uranium dioxide fuel rods (5 wt% 235 U) and uranyl nitrate solution (6 wt% 235 U) poisoned with pseudo-fission-product (FP) elements-samarium, cesium, rhodium, and europium. Fuel rods were arrayed at a 1.5-cm lattice interval in the poisoned fuel solution in a 60-cm-diameter cylindrical tank. The uranium concentration of the solution was roughly kept at about 320 gU/L, and the FP element concentrations were adjusted to be equivalent to that in a burn-up of about 30 GWd/t. The result provides basic experimental data for validation of computational methods to evaluate the reactivity effect of each FP element, as well as benchmark criticality data for validation of neutron multiplication factor calculation for heterogeneous systems of spent fuel. In this report, the details of the experiments and benchmark models will be presented as well as the procedure and the result of separate reactivity worth evaluation for each FP element. The experimental results and the computational evaluation results will also be compared.

Benchmark Critical Experiments of a Heterogeneous System of Uranium Fuel Rods and Uranium Solution Poisoned with Gadolinium, and Application of Their Results to JACS Validation

“…5,6) In addition, there was the third series of experiments using four fission-product (FP) elements, 12) which was already reported with the detailed descriptions of structures such as the core tank, grid plates, fuel rods, and so forth. 13) They were, except for the fuel solutions, all common to the reference and the Gd experiments. It should be noted that detailed information relating to such common parts may not be provided in this report to avoid showing too many tables, but necessary citations will be given instead.…”

“…16) An R-Z two-dimensional model was employed to approximate the experimental system, whose detail was provided in Ref. 13). Although the analysis was done for all measurement cases, Tables 3 and 4 summarize the analysis results of typical cases in the reference and the Gd experiments, respectively.…”

Benchmark Critical Experiments of a Heterogeneous System of Uranium Fuel Rods and Uranium Solution Poisoned with Gadolinium, and Application of Their Results to JACS Validation

“…The heterogeneous core consisted of the UO 2 fuel rods arrayed in a square lattice and the fuel solution, whose geometry was the same as that of the FP experiments reported in Ref. 13).…”

“…Tables 6 and 7 provide the atom densities of other structures including fuel rods, which are common to all cases, whose detailed derivation was reported in Ref. 13).…”

“…16) An R-Z two-dimensional model was employed to approximate the experimental system, whose detail was provided in Ref. 13). Although the analysis was done for all measurement cases, Tables 3 and 4 summarize the analysis results of typical cases in the reference and the Gd experiments, respectively.…”