Inter-code comparison exercise for criticality excursion analysis. Benchmarks phase 1: pulse mode experiments with uranyl nitrate solution using the Tracy and Silene experimental facilities

The NEA Working Party on Nuclear Criticality Safety established an Expert Group on Criticality Excursion Analysis in 2001 to explore the performance of various transient codes to evaluate criticality accidents in a fissile solution. Inter-code comparison exercises among four transient codes (AGNES, CRITEX, INCTAC and TRACE) have been carried out with typical transient experiments using uranyl nitrate fuel solution. Two sets of benchmarks were carried out based on experimental programmes performed in the Tracy reactor in Japan, and the Silene reactor in France. Tracy and Silene have the same geometrical features: an annular cylinder with a central void tube for a transient rod and similar operational modes for reactivity insertion. The experiments selected are representative benchmarks for low- and high-enriched uranyl nitrate solution, about 10 wt% for Tracy and 93 wt% for the Silene core. This report provides an analysis of the benchmark results obtained with four different codes. It will be of particular interest to criticality safety practitioners developing transient codes, notably since little experimental data is available and the existing transient codes are presently unavailable to the public. (authors)