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Ex-Vessel Steam Explosion Analysis with MC3D
A steam explosion is a fast fuel-coolant interaction that might occur if an accident scenario proceeds to late-phase including core degradation and melt relocation. It is of importance in safety research of severe accidents as it could possibly cause loss of safety barriers preventing the release of fission products. The focus is on the type of steam explosion known as ex-vessel steam explosion which can occur if the reactor pressure vessel breaks and molten core material is released into the containment vessel.
A literature review of the steam explosion phenomenon is provided, followed by a description of the MC3D code, used in this report to assess the steam explosion loads in the Nordic BWR geometry and examine the sensitivity of the results for some key input parameters. The effect of an ex-vessel steam explosion is analysed via computational models. The main focus of the analysis is on the dynamic loads on the cavity wall imposed by the explosion.
Simulations were made to analyse the effect of different triggering times on a standard case with central break location. The results showed that as long as the mixture is triggerable the resulting explosion is fairly similar. Different side breaks scenarios were also tested but here the mixture did not trigger.
The sensitivity analysis was done for melt temperature, coolant subcooling, cavity water level and melt drop size. The results show that the parameter with the strongest effect is the drop size, which is largely tied to the physical properties of the melt.
Steam Explosions, MC3D, Fuel Coolant Interactions, Severe Accidents