Development of numerical estimation method for thermal hydraulics in reactor vessel of sodium-cooled fast reactor under decay heat removal system operation conditions; Investigation of thermal hydraulic modeling in gap between fuel subassemblies

Tanaka, Masaaki  ; Kikuchi, Norihiro  ; Hamase, Erina ; Murakami, Satoshi*; Fujisaki, Tatsuya*; Imai, Yasutomo*

For safety enhancement of sodium-cooled fast reactor, decay heat removal system (DHRS) by using the natural circulation without depending on the pump as the mechanical equipment is recognized as one of the most effective method. The numerical estimation method which can predict thermal hydraulic phenomena in the reactor vessel during DHRS operation is necessarily required. In this study, appropriate modeling to predict the inter wrapper flow which is caused in the gap between fuel subassemblies is preliminary investigated. The validation of the numerical results is carried out in comparison with the measured temperature data in the scaled sodium test facility named PLANDTL-1. Through the simulation, potential applicability of the gap model using the correlation equations to simulate the thermal hydraulics behavior of the inter-wrapper flow in the core is indicated.