Experimental Study Of Loop Heat Pipe Passive Containment Cooling System

After the Fukushima nuclear accident,the safety of nuclear power plants has attracted much attention.The importance of the containment vessel which the last barrier to nuclear power plants has been deeply recognized once again.In this context,in order to extract the heat effectively from the containment under accident conditions,and to cool and depressurize the containment vessel,A new passive containment cooling systems(PCCS)based on separate heat pipes was introduced.The natural circulation system based on separated heat pipe can provide passive cooling for the two-double concrete containment vessel.As a closed loop type heat pipe,it is.generally composed of evaporator,condenser,steam and liquid pipeline.Its working principle is:when the evaporator is subjected to thermal load,the working substance evaporates in the evaporator,The generated steam flows from the evaporator into the steam pipeline,and then into the condenser to condense into liquid and undercool.After cooling,the backflow liquid enters the evaporator through the liquid pipeline to resupply.In this way,the natural circulation is formed only by the density difference between the up-leg and the down-leg,without the external power.In this paper,the research of separated heat pipe PCCS based on natural cycle is summarized firstly.The research results of domestic and foreign researchers on liquid-filling rate of separated heat pipe and flow and heat transfer characteristics in evaporation section are introduced.Then the flow and heat transfer mechanism of the passive containment cooling system with separate heat pipes is analyzed.The flow resistance,liquid filling rate,system thermal resistance,heat transfer coefficient of each part and heat transfer limit of the loop heat pipe are analyzed and calculated.At the same time,the model experiment system of PCCS is established,and the steady-state and transient operation characteristics of the system are studied through experiments.According to the experimental data,the circulating flow rate of the heat pipe in the loop under different temperature of the containment,different liquid filling rate of the loop and different vacuum degree of the loop were obtained.And the heat exchange amount and heat transfer coefficient under each state were analyzed and calculated.The influence of temperature,filling rate and vacuum degree on heat exchange and heat transfer coefficient of the containment vessel was analyzed,and the optimal filling rate of the heat pipe in the loop was obtained.At the same time,the dynamic performance of the system was studied by means of heating power and liquid filling rate.The change rule of temperature pressure,circulation flow rate,heat exchange and heat transfer coefficient with time before stabilization are obtained:With the increase of heating power,the time for the temperature and pressure to reach stability decreases,and the oscillation amplitude of circulation flow,heat exchange and heat transfer coefficient before stabilization becomes more severe.With the increase of liquid filling rate,the initial temperature pressure,circulation flow and heat exchange will decrease,and increase correspondingly after stabilization.