主动安全性.docVIP

Passive Safety System ABSTRACT In order to improve the security of reactors, the concept of passive safety system was raised in 1980s. It pertains to the field of pressurized water reactor type and is concerned with the fluid systems which mitigate consequences of events. These systems provide emergency cooling of reactor core, reactor building heat removal and pressure reduction, and reactor building fission product control. Passive safety system just relies on natural forces, like gravity, natural circulation, compressed gas and known laws of physics. So it needn’t rotating machinery or external power. BACKGROUND Fukushima Daiichi nuclear disaster made the public draw attention to nuclear safety. Since 1952, there have been 14 nuclear accidents, including 6 accidents with local consequences (Level 4), 5 accidents with wider consequences (Level 5), 1 serious accident (Level 6) and 2 major accidents (Level 7). The reason of most nuclear reactor accidents is that operator errors or design flaws caused cooling system failure and core meltdown, such as Jaslovské Bohunice in 1977 and Three Mile Island accident in 1979. When an emergency occurs, the reactor is supposed to shut down safely to prevent radioactive leak. However, reactors continue to produce heat from radioactive decay products even after the main reaction is shut down, so it is necessary to remove this heat to avoid meltdown of the reactor core. Current nuclear safety, which is called active safety system, is based on external power to drive the cooling system. Once the external power was damaged or operated wrong, the nuclear reaction would fail to slow down, even it might accelerate. For example, in Fukushima Daiichi nuclear disaster, the tsunami broke the reactors connection to the power grid and also resulted in flooding of the rooms containing the emergency generators. Those generators ceased working and made the pumps circulating coolant water in the reactor cease to work, which caused the reactors t