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

Tonoike, Kotaro ; Miyoshi, Yoshinori; Uchiyama, Gunzo 

A series of critical experiments were performed using heterogeneous cores at STACY in JAEA in order to obtain systematic benchmark criticality data concerning the dissolving process in reprocessing plants. Focusing on the use of gadolinium as a soluble poison, critical mass was measured for a combination of uranium dioxide fuel rods and uranyl nitrate solution poisoned with gadolinium (Gd). The Gd concentrations were varied up to 0.1 gGd/L. The other series of experiments were also conducted, as reference cases, varying uranium concentration in the fuel solution without Gd. The results provided benchmark criticality data for validation of neutron multiplication factor calculation on heterogeneous systems such as a dissolver. Validation calculation of JACS based on the newly obtained benchmarks supports the justification of its utilization for the criticality safety analysis.