Showing posts with label Sodium Graphite reactor. Show all posts
Showing posts with label Sodium Graphite reactor. Show all posts

Types of Nuclear Reactor Power Plants

There are many concepts for the nuclear reactors, however, we will discuss few of following types of power plants that have been developed commercially.

Pressurized Water Reactor (PWR) Power Plant :

Pressurized Water Reactor uses water or heavy water as both the coolant as well as moderator. It uses enriched uranium as fuel. Water in the reactor absorbs the heat generated and converts it into steam. This steam generated is used for thermal power plant to drive its turbine and produce energy.

Boiled Water Reactor (BWR) Power Plant :

Boiled water reactor uses water as both coolant as well as moderator. It uses enriched uranium as fuel. In this reactor, water is directly converted into saturated steam. This steam is supplied to the steam turbine in conventional power plant and electrical energy is produced.

CANDU Reactor Power Plant :

CANDU stands for Canadian Deutorium Uranium reactor. It uses pressurized heavy water as moderator and primary coolant. Fuel used is natural uranium.
  For more details see - CANDU Reactor Power Plant

Gas Cooled Reactors (GCR) Power Plant :

These type of reactors uses gas as coolant and graphite as moderator. The advantage of using gas as coolant is that it is safe, easy to handle and it can be heated up to any temperature without change of phase at any pressure.
For more details see - Gas Cooled Reactor (GCR) Power Plants

Sodium Graphite Reactor (SGR) Power Plant :

This power plant uses graphite as moderator and sodium as coolant. Here, sodium is used as primary coolant and sodium potassium (NaK) is used as secondary coolant.

Fast Breeder Reactor (FBR) Power Plant :

In this reactor, moderator is not used. The primary fuel U-235 is surrounded by a blanket of fertile material. Fertile material like U-238 is kept there. Here, fast speed electrons are absorbed by U-238 which produces Pu-239.
  For more details see - Fast Breeder Reactor (FBR) Power Plant

Sodium Graphite Reactor (SGR) Power Plant

Sodium graphite reactor is a typical liquid metal reactor. The arrangement of sodium graphite reactor power plant is shown in figure.
Sodium Graphite Reactor Power Plant |
Sodium Graphite Reactor Power Plant

It uses graphite as a moderator and liquid sodium as coolant which reach a temperature of about 850 degree Celsius at a low pressure of only 7 bar.
In the primary circuit, the heat is absorbed by liquid sodium in the reactor. The sodium becomes radioactive while it passes through the core and reacts chemically with water.
Therefore, the heat absorbed by sodium is transferred to secondary coolant sodium potassium (NaK) in the primary heat exchanger which in turn transfers the heat in the secondary heat exchanger called Steam generator.
 Water leaving the generator is converted into super-heated steam up to a temperature of 540 degree Celsius. This steam is used for power generation in the steam plant circuit in the usual manner. The reactor vessel, primary circuit and the primary heat exchanger have to be shielded from radiations.
The liquid metal is required to be handled under the cover of an inert gas like helium to prevent the contact with air while charging or draining in the primary and secondary heat exchangers.

Advantages of Sodium Graphite Reactor (SGR) : 

1.High temperature of the steam can be obtained due to the use of liquid sodium as coolant.
2. Thermal efficiency is high.
3. System need not to be pressurized.
4. Cost of pressure vessel and piping system is reduced due to the use of low pressure sodium in primary circuit.

Disadvantages of Sodium Graphite Reactor :

1. Any leakage of sodium coolant is highly dangerous.
2. Sodium is highly violent with air and water.
3. Primary and secondary heat exchangers are needed to be shielded with concrete blocks against radiations.
4. Intermediate heat exchanger is required to separate radioactive sodium with water and steam.

Fast Breeder Reactors (FBR) Power Plant

When uranium U-235 is fissioned by slow neutrons it produces heat and an additional neutron. In case a fertile material like U-238 is kept in the same reactor surrounding the core of U-235, the fast moving additional neutron is absorbed by U-238 and converts it into plutonium (Pu-239), a fissile material. This man made fuel Pu-239 can be used for further fission.
Therefore, these type of reactors are important since they not only produce heat but also produce more secondary fissile fuels like plutonium more than fuel consumed in the reactor.
This is known as Breeding.
Similarly, Thorium (Th-232) can be converted into U-233 which is also a secondary fissile material.
Since, India has massive reserves of thorium and limited resources of uranium, development of these fast breed reactors are important.
As Fast breeder reactor is shown in figure below.
Fast Breeder Reactor Power plant |
Fast Breeder Reactor Power Plant
The enriched uranium U-235 or plutonium Pu-239 is kept without a moderator in the reactor core surrounded by a thick blanket of depleted U-238.
One additional neutron available from fission of U-235 is used to convert U-238 or Th-232 into U-233 as secondary fuels.
As in case of sodium graphite reactor, this reactor also uses two liquid metal coolants in which sodium is used as primary coolant and sodium potassium as secondary coolant.
In fast breeder reactors, the neutron shielding is provided by the use of boron or graphite. In order to protect against gamma radiations, a shield is provided made of lead or concrete or of other materials.

Advantages of Fast Breeder Reactor :

1. Moderator is not required.
2. Absorption of neutron is slow.
3. Secondary fissile material by breeding are obtained.
4. Small core is sufficient since it gives high power density as compared to other reactors.

Disadvantages of Fast Breeder Reactor :

1. Requires enriched uranium as fuel.
2. Neutron flux is high at the center of the core.
3. Thick shielding is necessary against radioactive radiations in primary and secondary circuits as in case of sodium graphite reactors.