Simulation of the PACTEL non-condensable experiments with APROS 5.04

This paper presents the comparison between the measured and calculated (APROS code version 5.04) results of the PACTEL experiment NCg-3. The experiment was carried out in natural circulation with only one loop in operation and at ∼50% of the primary mass inventory. In the experiment NCg-3, compressed helium was used to simulate non-condensable gas. Non-condensable gas was injected in the vertical part of the hot leg below the steam generator. APROS predicts qualitative trends of the test correctly, but some quantitative disagreements were observed. In the simulated experiment NCg-3, the primary pressure increases after the injection of helium, but not as much as in the test. Passive zones in the steam generator tubes seem to be smaller than in the test, indicating that heat transfer is too effective compared to the experimental results. In the APROS calculation model it is assumed, that steam and noncondensable gas form a homogeneous mixture in the calculation node. APROS does not take into consideration the differences in the mole weights of the different substances. That increases non-condensable gas flow down wards from the steam generators cold collector. Helium does not accumulate in the steam generator as much as expected. (orig.)