Analyses of neutronic characteristics of STACY heterogeneous cores composed of 6wt%-enriched uranyl nitrate solution containing gadolinium and 1.5cm-lattice-pitch fuel pins

Izawa, Kazuhiko ; Aoyama, Yasuo; Sono, Hiroki ; Ogawa, Kazuhiko ; Yanagisawa, Hiroshi 

A series of critical experiments is conducted in FY 2006 using a heterogeneous core of the Static Experiment Critical Facility (STACY) in the Japan Atomic Energy Agency (JAEA). In the experiment, the core is composed of uranyl nitrate solution (U enrichment 6wt%) containing soluble poison (gadolinium) and 333 pins of uranium dioxide (U enrichment 5wt%) loaded at a latticepitch of 1.5cm. Prior to the experiment, the following neutronic characteristics were analyzed to assess safety of the core and operation parametor limits: criticality, reactivity and reactor shutdown margins. In the analyses, a Monte Carlo code, MVP, and a neutronics code system, SRAC, were used with an evaluated nuclear data library, JENDL-3.3. From these analyses, it was confirmed that the reactor shutdown margins would comply with the safety criteria under all conditions of the fuel used in the experiments. Simplified formulas for criticality and reactivity were also evaluated based on the analyzed values which are utilized to confirm the operation parameter limits during operations of the core.