Analysis of Safety Margins in an Initial Stage during the KALIMER Station Blackout

The main effort in the present study contributes to investigating the safety margins by analyzing the KALIMER station blackout accident. Natural circulation becomes the main heat transfer mechanism. The flow depends mostly on pump's halving time, friction factor for the wire-wrapped rod bundles in the core, and heat transfer coefficient. Therefore, physical models concerned with heat transfer in both pipe internals (IHX/DHX tube sides) and tube bundles (core, IHX/DHX shell sides), including the core wire-wrapped rod bundles, are also to be assessed in the study. In results, the heat transfer coefficient currently featured in SSC-K for an IHX rod bundle has been found acceptable. The heat transfer coefficient used for the core rod bundle, however, has not shown suitability and thus an alternative one has been proposed. Meanwhile, the friction factor model in SSC-K has not shown a prominent discrepancy in prediction trend but it has not been backed by an enough theoretical basis so that it has been replaced by the Cheng and Todreas model. An assessment matrix has been made to analyze systematically the effects of those parameters affecting on the conservatism of the safety analysis, and the matrix is constituted with the average value and the upper/lower limits in the correlation's applicable ranges. The preliminary calculation has shown negligible effect on the fuel temperature, while the pump halving time and the friction factor for the wire-wrapped rod bundle in the core have affected on the analysis results