Simplified model for highest cladding temperature evaluation in wire-wrapped fuel rod bundle under natural circulation decay heat removal

Doda, Norihiro  ; Ohshima, Hiroyuki; Kamide, Hideki ; Watanabe, Osamu*

We have developed a simplified model for Highest Cladding Temperature Evaluation in Wire-wrapped Fuel Rod Bundle under Natural Circulation Decay Heat Removal. We have demonstrated the case of 271-pin fuel assembly in the external power loss event with the simplified model, and the results were in good agreement with the results by using the subchannel analysis code. Some uncertainties in the fuel assembly, e.g. the variations of fuel pin power and fuel pin position, were considered by setting boundary conditions. The computational cost of the simplified model was about one-thousandth compared with the subchannel analysis model. The simplified model can be applied without unrealistic computational cost to the statistical evaluation of safety criterion under natural circulation decay heat removal, which requires a large number of transient analyses.