PCCAC-2D is a two dimension computer code which has be already used in the design of AC600/1000 passive containment cooling system. PCCAC-3D is a three dimension computer code which will be finished by the end of next September. PCCAC-2D, 3D can be used to predict the pressure and temperature of mixing gas inside the containment following the accident of primary pipe rupture or main steam line rupture. The heat removal characteristics from inside containment to atmosphere through the water film on the out surface of steel shell and natural circulation flow of air can be also simulated and calculated by PCCAC-2D or PCCAC-3D.

It follows from preliminary calculation results that the maximum pressure 0.37 Mpa of mixing gas in the containment will occur in 1123S after double ended rupture accident of cold leg pipe. The maximum temperature 138°C will occur in 14S after the accident.

FIG. 13. Flowrate distribution in containment

The maximum pressure 0.34MPa of mixing gas in the containment will occur in 16.8S after double ended rupture accident of hot leg pipe. The maximum temperature 143°C will occur in

6.85 after the accident. The maximum pressure 0.387MPa of mixing gas in the containment will occur in 395.3S after main steam line rupture accident. The maximum temperature 153°C will occur in 3S after the accident.

The flow fields of coolant in the containment indicate that main flow vortex will be established at 0.9S following accident, will be in equilibrium at 5.2S and will be destroyed at

24.85 because of the end of blow down. The temperature fields of coolant in the containment show that high temperature area is in around and above the break and low temperature area is in the bottom near steel shell at the beginning of the accident. Then the temperature fields become uniform after main flow vortex equilibrium. The natural circulation mass flowrate of air in the channel between steel shell and concrete shell of containment varies with time and reaches maximum 168 kg/s at 8000S. After 72 hours, the spray water will be ended and the natural circulation mass flowrate will reach 120 kg/s. It can be noted from the preliminary analysis and calculation that AC600 passive containment cooling system is able to remove decay heat of reactor from inside to outside of containment.

3.1.

Station blackout accident calculation for AC600/1000

ERHRAC is a special computer code for AC600/1000 design. ERHRAC can be used to calculate the natural circulation flowrates of three cycles (primary coolant cycle, secondary side cycle of SG and air flow cycle). The links connecting those three cycles are the steam generator and air cooler, establishing a tandem system.

In the unlikely event of a station black out accident, the flowrate through reactor core rapidly reduces. The changeover of coolant flow in primary coolant loop from the forced circulation
to the natural circulation is initiated automatically when main pump coast down is ended. In the secondary side loop, from steam generator the steam passes on to an air cooler, in which its heat is transferred to the air and steam is condensed to water. Then condensed water returns back to the steam generator by gravity to establish a natural circulation flow cycle.

Natural circulation flow rate is: 4% rated flowrate for each primary coolant loop and 3% rated flowrate for each secondary side loop of SG respectively. Air flowrate is about 290Kg/s for each air cooler.

Tre(S)

4.