In the power plant of a nuclear submarine, the temperature of the water in the reactor is above 100 degrees C.

Question

How is this possible?

Answer 1

1. its under high pressure so the boiling point is MUCH higher than 373 K

2. if you drink that water you will take a trip to the hospital...that there is special neuclear reactor water called heavy water...not hard water or anything else...look it up

Answer 2

It is sealed.

Steam engines, coal fired electric power plants and nuclear power plants all work the same way; they boil water to make steam and the steam turns a turbine.  In a nuclear reactor the water in the reactor chamber is allowed to heat up and the nuclear reaction is the furnace that keeps it hot.  It is a very compact furnace with a long lasting and very efficient fuel, but it works the same way any steam powered generator works, just in a smaller space.

The water in a nuclear reactor that goes through the pile is kept sealed and away from the environment so it won't cause contamination.

So the next question you have is why aren't nuclear subs easily seen by their thermal bloom?  The ocean is large enough and cold enough to soak up most of the heat and a good deal of the heat from a nuclear reactor in a submarine is contained in the nuclear pile.  This is what makes nuclear subs so dangerous; their only limit to a voyage is the amount of food they can carry.  They can even make their own oxygen by breaking up the water and they can make clean drinking water out of sea water.

Answer 3

Yes

This is a concept that every baker needs to be aware of if they cook at high altitudes.  It's the basis of a pressure cooker.  It's the basis of an automobile's coolant system.

Water's boiling point is 100 degrees C at 1 atmosphere of pressure.  If you increase the pressure, you have to increase the temperature at which the water boils.  Conversely, if you lower the pressure than water will boil at a temperature of less than 100C (thus the high-altitude baking scenario I mentioned)

Boiling (evaporation) of a fluid takes place when the liquid molecules at the liquid's surface have enough momentum to overcome the intermolecular cohesive forces and escape to the atmosphere. When heat is added to the liquid the molecular momentum and the evaporation increases. A reduction of the pressure above a liquid will reduce the momentum needed for molecules to escape the liquid and increase the evaporation. Increasing the pressure above the liquid reduces the evaporation. This can be observed as lower boiling temperature for water at higher altitudes.

The pressures in the reactor vessel is kept quite high.  This keeps the high temperatures attained in the fuel cells from boiling the reactors coolant water.  The coolant then circulates to the primary side of a steam generator where the heat is transferred to the secondary side.  On the secondary side the pressure is now dictated by the temperature of the fluid (saturation temperature and pressure) and steam is produced.

In the 1800's a German Professor named Richard Mollier perfected what is still known as the Mollier Diagram, also known as the steam tables, showing the relationship between pressure, temperature, enthalpy and entropy of water in the realm of thermodynamics.