Coolants in a nuclear reactor are very essential when it comes to heat transfer. Nuclear power plants mainly depend on the heat produced during fission to produce electricity.
If you have no idea how nuclear power plants produce electricity check the article below.
You might like this: Nuclear Power Plant: Introduction, Components And Working Principle
The heat that is produced in the reactor core is transferred to the turbine through the coolant.
So, coolant is a very special element when it comes to nuclear power plants.
The coolants exist in different forms, they can be in liquid, liquid metals or gas.
The type of coolant used in the nuclear reactor depends on the type of reactor used.
Without going too deep let me share with you some of the coolants used to transfer heat during nuclear fission.
Types of coolants used in transferring heat in a nuclear power plant.
These are some of the common coolants used in transferring the heat produced in the reactor core.
- Water (light or heavy water).
- Carbon dioxide, hydrogen and helium.
- Sodium and an alloy of sodium and potassium
1. Water (light and heavy water).
If water is used as a coolant, it’s converted to steam in the nuclear reactor and sent to the turbine directly.
This makes the process of heat transfer efficient as it prevents energy losses through the tubes or pipes used to transfer it to the turbine.
Water is the first coolant people think of since it’s available in high quantity and it’s cheap.
Also, handling water is pretty easier compared to other coolants.
Some measures should be taken into consideration if water is used as a coolant.
The water should be free from any contamination since if it’s impure it will become radioactive as it transfers heat from the reactor core.
Handling radioactive water will be a huge problem.
When one chooses water as the main coolant then they should be ready with the other cost that comes with maintaining the efficient heat transfer from the nuclear reactor.
Water has a low boiling point (2120F), which means the water will boil when in the nuclear reactor and this will lead to insufficient heat transfer.
So, for the water to have maximum heat transfer it has to be put under pressure and this will be an additional cost.
Increasing the pressure of water will keep it in its liquid state and this will lead to efficient energy transfer.
This means a pump will have to be put into consideration, pipes with high standards to handle the coolant and a means of powering the pump.
2. Carbon dioxide, hydrogen and helium.
Air is also used as a coolant in some reactors. A fast breeder is one of the reactors that use carbon dioxide as a coolant.
The advantage of using air as a coolant is that you won’t have the problem of managing it since you will just directly send it to the atmosphere after diluting it in case it has traces of radioactivity.
The disadvantage of using air as a coolant is that you will need pipes that can handle that air without causing leakages since it’s very easy for the energy in the air to escape to the air easily.
Also, the pipes should be strong enough to handle the air pressure.
3. Sodium and an alloy of sodium-potassium.
Some reactors use sodium and its alloy as the coolant. The sodium graphite reactor uses sodium as its main coolant.
Using sodium as a coolant has certain advantages compared to the use of water or air.
The fact that sodium is a liquid metal facilitates the high transfer of heat, though it has its disadvantages.
For now, let me share with you the advantage of using sodium as a coolant.
Advantages of using sodium as a coolant in a nuclear reactor;
- It has a low absorption cross-section area thus increasing the amount of energy it absorbs from the reactor core.
- Sodium has a good heat transfer since it’s a liquid metal, it can transfer a sufficient amount of energy at high temperatures and low pressure.
- Sodium does not react with any of the parts used in the primary circuit thus increasing the longevity of the primary circuit that transfers the heat energy.
The liquid metal coolants are very effective when it comes to transferring energy, but they also have their disadvantages.
You have to understand that liquid metals are not pure since they contain other dissolved minerals.
This makes the liquid metals radioactive as they transfer the heat from the nuclear reactor core hence handling it becomes difficult.
Since the liquid metal used to transfer heat energy from the reactor core becomes radioactive another means of transferring the heat to the required point will be needed.
There will be an introduction of a heat exchanger that will transfer the heat from the primary coolant to the secondary coolant.
It will be the work of the secondary coolant to transfer the heat from the primary coolant to the feed water where the heat will be used to convert water into steam.
So, do you now notice that there will be an additional cost of a heat exchanger?
Anyway, it is worth the cost since the heat transfer will be to the maximum.
Coolant cycle system.
Several ways can be used to move the coolant around the reactor to the feed water.
Coolant takes up heat from the reactor core to the feed water in the following ways;
- Direct cycle system.
- Single circuit system.
- Double circuit system.
1. Direct cycle system.
This system uses water as a coolant since the water will get converted into steam within the reactor core and it will be transferred directly to the steam turbine.
It is direct since the coolant is directly taken to the turbine without passing through any other point.
The main advantage direct system is that it needs a minimum space for it to operate.
The will also be a reduced cost of handling waste and the cost of purchasing more pipes will be reduced.
The boiling water reactor uses a direct cycle system.
2. Single circuit system.
In this system, the coolant transfers the heat from the reactor core and takes it to feed water in the steam generator.
The single circuit system is used in a pressurized reactor.
3. Double circuit system.
The double circuit system uses two coolants, we have the primary coolant that takes the heat away from the reactor core and another secondary coolant that transfers the heat to the feed water.
The sodium graphite reactor uses this system of coolant movement.
There will be an introduction of a heat exchanger in the system to transfer the heat from the primary coolant to the secondary coolant.
After the coolant transfers the heat to the secondary coolant through the heat exchanger it goes back to the react to absorb more heat energy and the process repeats itself.
The type of circuit system used mainly depends on the type of reactor used and the needs of that reactor.
Properties of coolants.
For a coolant to be selected to be used in a heat transfer some properties should be considered.
Not any liquid or gas can be used as a coolant.
There are the properties of coolants;
- Coolants should have high boiling and low melting point since they are exposed to higher temperatures changes in their phases will affect the heat transfer process.
- Coolants should not facilitate corrosion of any parts of the reactor or the primary circuits.
- Coolants should have a higher heat coefficient to maximize the amount of heat they transfer from the reactor core.
- Coolants should not absorb any radioactivity from the reactor core as they transfer heat from it.
If a liquid or air meets the above properties it can be used as a coolant.
Thanks for reading the article, if you have any questions about nuclear reactor coolants just leave your comment.
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