 Complete the following phrase:  The density of thermal energy contained in the core of a light water reactor PWR or BWR of typically 1 GWe 1 000 MW electrical corresponding to 3 000 MW thermal is in the range of 10 to 100 MW of thermal energy per cubic meter of cooling water depending on the location considered in the system the core itself 30 m3, the reactor pressure vessel 50 m3, or the whole primary circuit 300 m3. This represents a considerable density of energy which requires under all circumstances a continuous water flow at high velocity in order to be able to remove the heat from the core, even after an emergency shutdown of the reactor. The incapacity to cool the cores of three boiling water reactors BWR at 