TRIGA SPENT-FUEL STORAGE CRITICALITY ANALYSIS

A criticality safety analysis of a pool-type storage for spent TRIGA M ark II reactor fuel is presented. Two independent computer codes are a pplied: the MCNP Monte Carlo code and the WIMS lattice cell code. Two types of fuel elements are considered: standard fuel elements with 12 wt% uranium concentration and FLIP fuel elements. A parametric study o f spent-fuel storage lattice pitch, fuel element burnup, and water den sity is presented. Normal conditions and postulated accident condition s are analysed. A strong dependence of the multiplication factor on th e distance between the fuel elements and on the effective water densit y is observed. A multiplication factor <1 may be expected for an infin ite array of fuel rods at center-to-center distances >6.5 cm, regardle ss of the fuel element type and burnup. At shorter distances, the subc riticality can be ensured only by adding absorbers to the array of fue l rods even if the fuel rods were burned to similar to 20% burnup. The results of both codes agree well for normal conditions. The results s how that WIMS may be used as a complement to the Monte Carlo code in s ome parts of the criticality analysis.