Study On The Response Characteristics Of Pressure Suppression Containment System

The pressure suppression containment system(PSCS)can meet the design requirements of compact structure and high inherent safety of small modular reactors(SMRs)and has been introduced into the design and construction of some small light water reactors.However,there is no experience in running BWR in our country,so the research on PSCS is lacking.In addition,the thermal stratification of pressure suppression pool(PSP)is a significant factor affecting the long-term response characteristics of containment.In previous studies,most of the experiments were done under atmospheric pressure or even sub-atmospheric pressure,which is inconsistent with the real thermal-hydraulic condition of the PSP.Based on the above research requirements,the following works are carried out and completed in this paper:(1)A small facility was built and the experimental investigation on response characteristics was carried out.The comparsion between volume expansion scheme and pressure suppression scheme was made,and the influence of parameters,including mass and energy release,gas-water volume distribution of PSP and initial water temperature,were investigated.The results show that the latter is a better one when the volume expansion scheme can not alleviate the pressure rise of containment well.With the change of the amount of steam released,the response characteristics of PSCS will show different laws.The gas-water volume distribution of PSP has a great influence on the response characteristics of PSCS,too low or too high pool water volume fraction will weaken the capacity of PSP.In other words,there exists a excellent range of gas-water distribution ratio;The increase of the initial temperature of the pool water will lead to the deterioration of the condensation capacity of the steam,which will directly weaken the ability of the PSP to suppress the pressure rise of the containment.The modeling and analysis results of the PPOOLEX MIX experiments show that MELCOR code could well reflect the response characteristic of the PSCS except for the deficiencies of the lumped model itself.(2)Thermal stratification experiments were carried out in a wide range of air space pressure of PSP(0.1～0.2 MPa)and steam mass flow rate(20～60 kg/(m~2·s)).The results show that the boundary of steam mass flow rate in chugging regime under atmospheric pressure is between 30～40 kg/(m~2·s),which is in good agreement with the condensation rigime divided by Lahey and Moody.With the increase of steam flow rate,the position at the beginning of the thermal stratification is different,including the stratification starting from the bottom of the pool and then gradually moving up near the nozzle,the stratification above the nozzle and the stratification generated from a certain position between the nozzle and the pool bottom.Compared to the atmospheric pressure condition,pool water could enter the blowdown pipe in a wider range of mass flow rate under the condition of back pressure.Furthermore,the thermal stratification of pool water is more serious and lasts longer.