Mastertextformat bearbeiten,Zweite Ebene,Dritte Ebene,Vierte Ebene,Fnfte Ebene,Mastertitelformat bearbeiten,*,Laboratory for Thermal HydraulicsNuclear Energy and Safety,Workshop of the European MELCOR User Group,16 December 2008,MELCOR Application to Plant Accident Analyses at PSI,Y.Liao,S.Guentay,J.Birchley,T.Haste,Paul Scherrer Institute,Switzerland,Outline,Introduction to recent MELCOR applications at PSI,Loss of RHR accidents during mid-loop operation,LOCAs,during hot shutdown operation,LOCAs,during full power operation,Sensitivity study to the primary side nodalization,Conclusions,Introduction to recent MELCOR applications at PSI,Beznau,power plant:,Two loop Westinghouse PWR,1130MW core thermal power,Safety injection pumps:JSI 1-A,B,C,D,Loss of RHR during mid-loop operation(22h after reactor trip),Initial conditions with core power at 0.57%FP,low primary pressure,LOCAs,during hot shutdown operation(4h after reactor trip),Initial conditions with core power at 0.92%FP,intermediate primary pressure,LOCAs,during full power operation,Initial conditions with core power at 100%FP,high primary pressure,This talk focuses on effect of safety injection time,injection rate and steam generator reflux condensation on core recovery,MELCOR nodalization for 2-loop Westinghouse PWR,Loss of RHR during mid-loop operation,Objective,Determine latest injection time to recover the core without damage,Assumptions,Upper head in place and bolts,detensioned,No accumulator available,One injection pump available for recovery,with limited flow rate(3.5kg/s for base case,3.0kg/s for sensitivity study),delayed some time after core uncovery(2840s for the reference case,2640s and 3040s for sensitivity studies),Comparison of event sequences,Parameter(unit),Injection time(s),15000,15200,15400,Start of core uncovery(s),12360,12360,12360,Start of injection,t,i,(s),+2640,+2840,+3040,Level in core at t,i,(m),1.26,1.25,1.25,Max.core temperature at t,i,(K),992,1100,1185,Start of oxidation(s),+35,-165,-365,Peak core temperature(K),1185,1240,2369,Time to final quench(s),+3920,+4010,+3040*,Mass of H,2,generated(kg),2,3,20,+relative to start of core uncovery *for intact rods,-/+relative to start of injection,Comparison of core liquid levels,Comparison of maximum fuel rod temperatures,Loss of RHR during mid-loop operation,Summary,Core can be recovered with just 3.5 kg/s injected(one charging pump)before oxidation excursion,Insensitive to injection rate as low as 3.0kg/s,Injection can be delayed until core is about 50%uncovered,corresponds to max.core temperature of about 1000 K in reference case,high likelihood of oxidation excursion if injection is delayed further,Details appear in,Accident Management following Loss of Residual Heat Removal during Mid-Loop Operation in a Westinghouse Two-Loop PWR(J.Birchley,T.Haste,M.Richner,Nuclear Engineering and Design),LOCAs during shutdown operation,Objective,Examine the margin against core damage when actuation of safety injection is delayed,Large break LOCA,No accumulator available,Base case assuming 30s delay for JSI 1-D safety injection shows core recovery without core damage,Three sensitivity cases assuming 930s delay to study safety margin against safety injection availability,Case I:Full injection rate with only JSI 1-D,Case II:Full injection rate with only JSI 1-A,Case III:Full injection rates with JSI 1-A,B and D,Comparison of cladding temperatures(Effect of JSI availability and injection point),LOCAs during shutdown operation,Small break LOCA(3cm),No accumulator available,Full injection of only one pump(JSI 1-D)at 1500s after core uncovery,Secondary side at constant pressure(37bar),Cladding temperatures in central ring,LOCAs during shutdown operation,Summary,Large break LOCA,MELCOR calculations indicated that with 930s delay,one pump alone might not be sufficient,as the temperatures at the start of core refilling are already high enough for clad oxidation to start,If all three JSI pumps available after 930s delay,MELCOR shows that the injection taken may be sufficient to refill the core,Intermediate break LOCA(20cm),Recovery shown for injection of one pump alone(JSI 1-D)delayed by 930s,Small break LOCA(3cm),Recovery shown for injection of one pump alone(JSI 1-D)even actuated at 1500s after core uncovery,More details presented in,MELCOR AND SCDAP ANALYSES OF LOSS-OF-COOLANT ACCIDENTS DURING COOLDOWN IN A WESTINGHOUSE 2-LOOP PWR(,J.Birchley,T.Haste,M.Richner,NENE 2007 Conference),LOCAs during full power operation,Objective,Examine effect of SG reflux condensation on core recovery,Help the detailed analysis for the success criteria of the recirculation safety injection system once the injection rate is limited by sump clogging,Assumptions,SGs,depressurized at 50K/h,AFW available,Accumulators available,Before switching to sump recirculation,Full injection rates available for safety injection pumps JSI 1-A,B,D,When switching to sump recirculation,One recirculation injection pump available,Actuated when co