Studies On The Explosion And Its Preventive Measures Inside Containment During Severe Accidents

During severe accidents in Nuclear Power Plants (NPPs), the possible explosion risk inside the containment is mainly hydrogen explosion and steam explosion. Hydrogen explosions and steam explosion threatens the integrity of the containment, affects the validity of the accident treatment measures. In domestic and international nuclear safety regulations,there are related requirements on preventing hydrogen explosion and steam explosion. The mechanism, process and preventive measures of hydrogen explosion and steam explosion are studied in this paper. These studies have important implications for how the design of NPPs to meet the nuclear safety regulations, to ensure NPP safety and to practically eliminate a large-scale release of radioactivity.This paper summarizes the status of hydrogen explosion research in China and abroad;studies and analyzes the source of hydrogen, hydrogen concentration distribution, the judge criterion of hydrogen detonation transition and the hydrogen control methods; studies and summarizes hydrogen explosion prevention measures design in AP1000, EPR and the domestic Generation 3 nuclear power units HPR1000. The main source of hydrogen is from Zirconium-Water Interaction inside PRV and MCCI outside PRV. By means of setting passive hydrogen recombiners or igniters at the places with high hydrogen concentration to eliminate hydrogen and taking the measure to continuous monitor the containment hydrogen concentration, so hydrogen concentration can be reduced and the risk of a hydrogen explosion can be eliminated effectively.This paper investigates the research status of the steam explosion, analyzes the mechanism of steam explosion,studies the mainstream analysis software MC3D and uses MC3D to calculate and analyze typical ex-vessel steam explosion, lastly sums up the design of steam explosion preventive measures. Steam explosion mechanism is very complicated, the main factors include environmental pressure, melt properties and components. MC3D calculations show that steam explosion basically did not produce additional pressure in reactor pit side wall, the pressure generated at the pit center instantly peaked at 500MPa,impulse also exceeded 120kPa.s,which threatens reactor cavity structure. NPPs are designed to take measures to prevent core melt directly dropping into the water of reactor pit in order to avoid steam explosion, and the steam explosion consequences are mitigated from the reactor cavity structure design.