How much water does a nuclear reactor boil in an hour?

Inside the core of a typical pressurized water reactor are pencil-thin nuclear fuel rods, each about 12 feet long, which are grouped by the hundreds in bundles called fuel assemblies. Inside each fuel rod, pellets of uranium or, more commonly, uranium oxide are stacked end to end. Also inside the core are control rods, filled with pellets of substances like hafnium or cadmium or cobalt that readily capture neutrons. When the control rods are lowered into the core, they absorb neutrons, which thus cannot take part in the chain reaction and start more fission. In reverse, when the control rods are lifted out of the way, more neutrons strike 235U nuclei in nearby fuel rods, and the level of reaction intensifies. The heat of the fission reaction is removed by the water which also acts to moderate the neutron energies.