Analysis of PWR ex-vessel steam explosion for axial and side melt release

In the paper the PWR ex-vessel steam explosion study, which was carried out with the MC3D code in conditions of the SERENA reactor exercise, is presented and discussed. The axial melt release case was simulated in 2-D and the side release case in 3-D. In reactor calculations the largest uncertainties in the prediction of the steam explosion strength may be expected due to the large uncertainties related to the jet breakup. Therefore the premixing simulations were performed with both available jet breakup models, i.e. a global and a local one, to get some insight in these uncertainties. For each premixing simulation an explosion simulation was performed, triggering the explosion around the time of the melt bottom contact. It turned out that despite the different jet breakup in both considered approaches, the calculated pressure loads are in the same range due to compensating effects. However, there were significant differences in the pressure loads between the axial and side release cases. With the side release the explosion occurs near the cavity wall and so the pressure loads on the wall are much higher. The 3-D modelling approach enables the study of realistic scenarios, thus for reliable reactor simulations it is important that the fuel coolant interaction codes have adequate 3-D modelling capabilities.