Experimental study on the effect of different start-up modes on the separated heat pipe for passive spent fuel pool cooling

As a kind of passive heat transfer equipment, the separated heat pipe (SHP) is highly applicable for passive cooling of spent fuel pool (SFP) in nuclear plant accident, with small temperature difference and large decay heat load. However, the start-up modes of SHP haven’t received enough attention, choosing the most suitable start-up mode is very important for SHP. In this work, three start-up modes were experimentally investigated and compared: (1) daily standby, (2) filling, and (3) control by valve. The results showed that the daily standby start-up mode has a longer start-up time compared to other modes. Under the filling start-up mode, the start-up time is only 100 s, and it can provide additional cooling capacity in the early stage of operation. The SHP has excellent self-adaptive capability when the decay heat load changes. Temperature oscillation occurs under all conditions, the presence of geyser boiling appears under filling start-up mode and the filling ratio of 50 %, and the occurrence mechanism is expounded. These results provide reference significance to guide the start-up mode choice of SHP.