Technology development and material challenges for core catcher design of Indian nuclear power reactors

In the entire history of commercial nuclear power operation, three major accidents leading to melting of reactor core have taken place so far, i.e. at TMI (1979), Chernobyl (1986) and recent Fukushima (2011). These accidents have reinforced the necessity to further improve safety in the nuclear power plant designs. New reactor designs have incorporated measures for managing severe accident and existing reactors are being retrofitted with several new measures. In a severe accident, large number of fuel rods may melt and form a molten mass. In vessel type reactors, this mass is relocated at the lower head of the vessel. If the vessel fails, the melt is ejected into the containment cavity on the base material. The melt starts attacking the concrete base which is termed as the molten coolant-concrete interaction (MCCI). The heat transfer from the hot melt to the concrete causes ablation of the concrete. This has manifold impacts as the chemical reactions add a lot of heat into the system and generate a lot of non-condensable gases because of concrete decomposition (i.e. CO, CO₂, H₂ and water vapor) and pose a threat because of containment pressurization. The hydrogen generated has a potential danger of explosion. Besides, if basemat melt-through occurs, there is a potential danger of ground and water contamination by radiological waste. This talk shall discuss the critical issues for technology development and material chemistry issues for core catcher design of Indian nuclear power reactors