Reply #8: atm = atmospheres of pressure. [View All]

[Statistical]

Water boils at 100 deg (technically 99.7) Celsius @ 1 atmosphere of pressure (sea level normal air pressure). You can't specify the boiling pont of a fluid without also specifying the pressure. For common usage most humans live at around 1 atm of pressure thus you can assume water boils at 100 deg.

However the core of a reactor is pressurized. The pressure inside a BWR is 75 atmospheres (75x sea level air pressure or 1100 psi). As pressure rises so does the boiling point of a fluid. At 75 atm water boils at 280 deg not 100 deg Celsius.

A side note this is why water doesn't boil in a PWR (pressurized water reactor) despite the core having the same thermal output as a BWR. The water is pressurized to 150 atmospheres of pressure putting the boiling point of water to over 350 degrees.