After the Fukushima Daichi nuclear power plant accident in 2011, there has been an increase on the safety of nuclear reactors and power plants. And the concept of passive safety began to be more and more widely accepted, in other words, passive cooling systems are more potential to enhance plant safety through system reliability and eliminate cost associated with the installation, maintenance and operation of the active cooling system that constitutes numerous electric pumps with independent and dedicated power supplies. For instance, in the new generation nuclear reaction, AP1000, passive cooling technologies are widely adopted and the inherent safety features improves dramatically [1, 2].However, the cooling of Spent Fuel Pool (SFP) has not been taken into full consideration.
The most recent development of heat pipes has been the application within the nuclear sector. Hybrid heat pipes are used to cool down nuclear reactors and increase the control of the system (Fig. 1). As pointed earlier, the concept of a hybrid heat pipe, that is, the combination of the heat pipe and neutron absorber was proposed to enhance the safety of advanced nuclear power plants. With the unique features of heat pipe and control rod, the hybrid heat pipe can remove decay heat directly from the core as it is inserted into the reactor pressure vessel with the same drive mechanism of a control rod. Furthermore, the actual shut down system in nuclear reactors is composed of a neutron absorber (or rod assembly).
The function of the rod assembly is to control the nuclear reaction in the reactor core. Raising and lowering the control rods allow operators to control the rate of the nuclear reaction. For emergency cases, the control rod will be lowered by gravity to stop the nuclear reaction and shutdown the reactor. However, this system is limited as far as the Three Miles Island and the Fukushima Daichi nuclear power plant accidents are concerned. Truly, the active cooling system failed to remove the heat decay of the water contained in the reactor, which led to a fusion or melt down of the core, even after the depressurisation of the pressure vessel. In the nuclear reactors, Heat pipe serves as a shutdown device. Investigations of heat pipe technology has been reviewed in .The hybrid heat pipe is used for two main purposes. The first is to shut down the reactor in case of accident, and the second is to remove the heat decay generated during the reaction from the core after the shutdown. A passive device that combines the functions of the current control rod assembly and the passive cooling systems could avoid such accidents in the future.
Writer: Emmanuel Osei Tutu (Harbin Engineering University)
Editor: Zhang Chao& Priscilla Oforiwaa
Designers: Zhang Chao& Zhang Jing
Translation : Zhang Chao