Models!
A great deal of work goes into the prevention of a serious core event. If such an event were to occur, three different physical processes are expected to increase the time between the start of the accident and the time when a large release of radioactivity could occur:
- The time required for the water to boil away (coolant, moderator).
- The time required for the fuel to melt.
- The time required for the molten fuel to breach the primary pressure boundary.
Models, do your job!