Experimental research on the gravity-driven boron injection system for a 200 MW nuclear heating reactor

The gravity-driven boron injection system (GDBIS), designed by the Institute of Nuclear Energy Technology (INET) of the Tsinghua University, PR China, is a new type of passive system to be applied in the 200 MW nuclear heating reactor (NHR-200), also designed by INET. The function of this system is to shut down the reactor in an emergency, in case con- trol rods do not operate properly. A borate water tank is located 10 m above the top of the pressure vessel. When the pressure of the reactor and the boron tank balances, the borate water will be driven by gravity to ¯ow into the reactor, and thus shut down the reactor. The thermal hydraulic performances of the system for cold (room temperature nitrogen) and hot (mixture of hot steam and nitrogen) operating conditions, especially the response time of pressure and water injection, have been researched under di€erent initial conditions. Firstly, several factors, e.g. ori®ce on steam lines, and the volume ratio of the gas±steam spaces of the reactor and the boron tank, have e€ects on the pressure and water injection response time and other thermal hydraulic performance of the system. Secondly, the steam and liquid commu- nication modes, namely the acting time and sequence of the action of valves connecting steam and liquid lines, have great in¯uences on the performance of the system. Thirdly, the limited pressure balance time (about 1.0 s) can be achieved under the cold condition. This investiga- tion shows that GDBIS can be properly used in the 200 MW nuclear heating reactor