Improvement of single-phase subchannel analysis code ASFRE-III. Modification and verification of porous blockage model

The purpose of the study is to offer an analytical tool for investigations of local subassembly accidents which have been recognized as a key issue of the safety assessment of liquid metal cooled fast breeder reactors due to the dense structure of the fuel grid and the high power density. The porous blockage model, which was implemented in the single-phase subchannel analysis code ASFRE-III last year, was upgraded for the accuracy improvement. Correlation equations on pressure loss, heat conduction and heat transfer based on the packed bed theory was newly applied to the model in order to more precisely evaluate thermal hydraulic phenomena in the porous blockage regions. The model verification analysis was carried out on the basis of the data of porous blockage simulation test Scarlet-2 performed in France. In the analysis, it was confirmed that this model could reproduce coolant temperature distribution in the blockage region and could predict the peak temperature with high accuracy. The detailed model validation will be carried out by using the water/sodium out-of-pile tests which have scheduled to be conducted at PNC in the near future. (author)