Application effect of region temperature coefficients and improvement of heat transfer analysis model in HTGR

Takamatsu, Kuniyoshi  ; Nakagawa, Shigeaki  ; Takeda, Tetsuaki

The HTTR, which has thermal output of 30 MW, coolant inlet temperature of 395 C and coolant outlet temperature of 850 C/950 C, is a first high temperature gas-cooled reactor (HTGR) in Japan. The HTGR has a high inherent safety potential to accident. Safety demonstration tests using the HTTR are underway in order to demonstrate such excellent inherent safety features of HTGRs. The coolant flow reduction test demonstrates that rapid decrease of reactor power during tripping of the gas circulators is restrained by only the negative reactivity feedback effect without operation of the reactor power control system, and the temperature transient of the reactor is slow. A one-point core dynamics approximation with one fuel channel model could not simulate accurately the reactor power behavior. On the other hand, an original new method using a connection between some fuel channel models and whole core component model is adopted for calculating heat transfer in the core.