Check this picture out. It is a crane lifting a 40 meter wide, 4.5 cm thick dome for the top of a nuclear reactor containment building under construction in China. The containment building is extraordinarily massive, the dome alone weighs 655 tonnes (1.4 million pounds).
Believe it on not, the containment building’s purpose is to capture a steam explosion.
Water boils at 100°C at one atmosphere of pressure, but the boiling temperature goes up at higher pressures. For example, the water in your car radiator will go to higher than 100°C without boiling because the radiator is pressurized to about 2 atmospheres when the car is warmed up. What happens if the pressure is suddenly released by a puncture or someone foolishly removing the radiator cap? See the video below for a steam explosion…
Carnot engine efficiency increases with increasing temperature, so there is a great advantage to running a nuclear reactor (or any heat engine) at high temperatures, which requires very high pressures to keep the reactor’s water from completely boiling. Conventional boiling water reactors and pressurized water reactors operate at around 70 atmospheres and 160 atmospheres to achieve temperatures of 285°C and 315°C respectively. If water escapes from the reactor for any reason it will instantly expand to about 1600 times its liquid volume as it explodes into steam. The containment building is supposed to capture that exploding steam. It is so massive because it must restrain the steam under great pressure without exploding itself.
But this type of massive containment building would not be necessary for a Liquid fluoride Thorium Reactor (LFTR)! This type of reactor concept does not use water to transfer heat away from solid pieces of fissioning metals. Instead, thorium is dissolved in liquid fluoride salts, where it is converted to uranium233, which fissions and generates heat. One of the beauties of the LFTR is that the liquid fluoride salts can go to incredible temperatures before they boil – temperatures vastly exceeding the operating temperature of the reactor. Consequently, the reactor operates at atmospheric pressure – no high pressure needed. In the event of a liquid leak there would be no explosive effect like the water instantly boiling into steam in a conventional reactor.
The LFTR would operate at around 700°C, reaching a much higher carnot efficiency than boiling water reactors or pressurized water reactors. Yet the fluid medium of the LFTR would not boil until reaching the extraordinary temperature of about 1400°C.