Showing posts with label Nuclear Power Plant. Show all posts
Showing posts with label Nuclear Power Plant. 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

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.

CANDU Reactor Power Plant

A reactor developed and designed by Canadian is called as CANDU (CANadian Deutorium Uranium ) reactor.
It uses pressurized heavy water (which has 99.8% deutorium oxide ) as moderator and primary coolant. Natural Uranium is used as fuel for this reactor.
A Canadian Deutorium Uranium Pressurized Heavy Water power plant is shown in figure.
CANDU Reactor Power Plant |
CANDU Reactor Power Plant

Natural uranium used as fuel is in the form of small cylinder palletes. These are packed in corrosion resistant Zirconium alloy tubes of 0.5 cm long and 1.3 cm in diameter to form a fuel rod.
These short rods are combined in 37 bundles of 37 rods and 12 bundles are placed end to end in each pressure tubes.
This type of arrangement helps in refuelling the reactor while in operation.
Reactor vessel is a cylinder called Calandria.It is placed horizontally . It has pressure tubes penetrating the reactor vessel. The active core is about 6 m high abd 7-8 m diameter.
In the primary circuit deutorium coolant enters the array of pressure tubes at 110 bar pressure and 260 degree Celsius temperature. It flows through the fuel element and leaves the pressure tubes at about 370 degree Celsius after absorbing the heat generated by fission of fuel material.
The coolant at 110 bar and 370 degree leaving the reactor enters the steam power plant where the generated steam is used in conventional steam power plant.
Control rods are made up of cadmium. These control rods are used to start and shut down the reactor. In addition, there are other absorbing rods which are used to control the power output during reactor operation.

Advantages of CANDU Reactor :

1. Enriched fuel is not required.
2. Cost and time of construction is less.
3. It has good neutron economy resulting into good breeding ratio.
4. Heavy water is used as moderator which has low fuel consumption.

Disadvantages of CANDU Reactor :

1. Heavy water used as moderator is costly.
2. Leakage problem may occur.
3. It has critical temperature limitations.
4. It requires has standard of design, manufacture and maintenance.
5. Size of plant is large.