The main problem in the first two test series in PACTEL was the rapid condensation in the CMT, which temporarily stopped the ECC water injection. The condensation took place when the saturated water layer in the CMT broke down, and the steam got into contact with cold ECC water. This happened when water flowed to the CMT after the level in the tank has already dropped. In the tests the water level in the CMT started to drop almost immediately after the opening of the break and the period of single phase natural circulation through the cold leg pressure balancing line to the CMT was very short. Due to this the saturated water layer in the CMT separating cold water from steam remained thin. For the third series, a flow distributor called sparger has been added to the CMT. The purpose of the sparger is to diminish possibilities of rapid condensation in the CMT. Further, the experiment procedure included filling of the PBL with hot water before the break opening. The CMT and the IL was full of cold water. All the earlier experiments begun with cold water in the CMT, PBL and IL. The main objective of the third series was to investigate the influences of break size and the removal of the pressurizer PBL on the CMT behaviour in cold leg SBLOCA’s. The tests run with four different break sizes (from I to 5 mm) including reproducibility studies. Like in the earlier tests the main objective of the tests was to simulate the PSIS behaviour and not to try to simulate any proposed ALWR reactor concept in particular.

The main results of the third series can be summarised as the following:

• the recirculation phase was much longer than in the earlier experiments with two PBL’s and without PBL heating,

• the recirculation phase was longer; and the resulting hot liquid layer, thicker in the experiments with smaller break size;

• the analyses of the test data supported using the McAdams correlation for calculating the heat transfer from the hot liquid layer to the CMT wall, as the Westinghouse suggested [11]. The use of the Nusselt film condensation correlation for the condensation in the CMT walls seems correct, although the correlation gave high values for the heat transfer coefficient;

• the oscillation phase between the injection and recirculation phases was longer in the experiments with small break size; and

• local wall heat flux to the CMT wall was higher in the experiments with larger break size.

In all experiments the CMT ran as planned. There were no problems with rapid condensation in the CMT, such as was seen in the earlier passive safety injection experiments in PACTEL. The main reason was the new CMT arrangement, with a flow distributor (sparger) installed to the CMT. The sparger spread incoming flow to the CMT horizontally, and the breakdown of the saturated water layer due to incoming water was not possible. The hot liquid layer between the steam and cold water in the CMT remained stable, even in the experiments where the hot liquid layer was less than 5 cm thick.