Nuclear Energy and Heat Exchangers

Nuclear energy produces about 19% of total electrical output in the U.S. with no carbon dioxide emissions.

So how does nuclear energy work?

The Science

The process of nuclear energy relies on heat exchangers.

A heat exchanger is a metal object that keeps things separated and ONLY exchanges the heat between them. A frying pan is an example of a heat exchanger.

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Most heat exchangers in industry are “shell and tube” exchangers.

Here’s a picture of a shell and tube exchanger. In the heat exchanger, hot water runs straight through the inner tubes. Cold water flows around the tubes in the shell. By exchanging heat through the tubes, the hot water heats up the cold water (and can convert it into steam).

The Process

Ok, so how does nuclear work?

In a nuclear reactor, a nuclear core heats up a bath of water. This hot water is then moved into the tubes of a heat exchanger.

In that heat exchanger, a SEPARATE stream of cold water flows through the shell and is boiled into steam.

The steam then leaves the heat exchanger and turns a turbine generator to produce power.

It's key to note that the water from the nuclear bath never touches the water that is boiled into steam. The heat is simply exchanged through the metal exchanger. The nuclear bath itself is contained in its own reinforced containment building.

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Ok, all of that makes sense. So what are those big stacks we always see on the news?

Because the nuclear core is constantly generating heat, heat needs to be removed from the system in order for the whole process to work.

The "stacks" that you see on the news are called "natural draft cooling towers" and they remove heat by cooling and condensing the steam from the generator back into water.

The cooling tower is its own separate loop which does not touch the steam from the generator. Instead, the cooling tower:

1) Takes in cold water (from a lake or ocean)
2) Uses the cold water to cool down the generator steam in a second heat exchanger
3) Exhausts the remaining steam out the top

The Pain Points

The effectiveness of a heat exchanger is determined by how well it transfers heat.

Over time, both the shell and tube sides of a heat exchanger get covered in deposits (mineral deposits, sludge, dirt, etc). These deposits limit the amount of heat transferred.

For example, imagine trying to cook on a frying pan covered in layer of ceramic. The heat won’t transfer very well.

Here’s a picture of limescale deposits inside a pipe.

The accumulation of these deposits is called “fouling” and companies spend millions every year cleaning these deposits off the insides of a heat exchanger.

The Solution

Heat exchangers can be a tricky subject. Cleaning exchangers too frequently creates unnecessary operating expense. But, on the other hand, a fouled heat exchanger can limit the amount of steam generated (and power produced).

By closely monitoring the temperatures of the water coming in and out of a heat exchanger, software can notify companies when they need to clean their exchangers.

Heat exchangers are used in every single building, manufacturing plant, and industrial process. If you’re interested in learning more about nuclear energy or heat exchange processes, please reach out.