NUCLEAR POWER PLANT

A nuclear power plant is very similar to a conventional steam power plant except  for  the  furnace.  The  nuclear  reactor  becomes  the  furnace  in  this case.

It  has been estimated that  complete  fission of 1  kg of uranium produces heat energy equivalent to 4500 tons of coal or 1700 tons of oil.

Some of the important commercial reactors commonly used for power generation are given below:

1. Boiling water reactor (BWR)

2. Pressurized water reactor (PWR)

3. Gas cooled reactor (GCR)

Boiling Water Reactor

• A simple boiling water reactor is shown in Fig. 17.2.

• Due  to  nuclear  fission  of  the  fuel  uranium,  large  amount  of  heat  is produced.

• The   nuclear   reaction   and   thereby   the   temperature   is   controlled   by moderators.

• The  coolant  used  here  is  water  which  absorbs  the  heat  produced  in  the reactor. Water evaporates and steam is generated in the reactor itself.

• In this type of power plant. there is no need for a separate boiler.

• The steam produced in the reactor is used to run the turbine coupled with a generator from which we get the electrical power.

• The steam after expansion i the turbine is condensed in the condenser. The condensate  after  getting  heated  in  several  feed  water  heaters  is  pumped again into the reactor by means of feed pump.

• In  the  reactor,  the  thermal  shielding  reduces  the  heat  loss  and  th  thick concrete shielding prevents external radiation.

• In the primary loop, the pressuriser maintains a high pressure in the water in the range of 150 bar. Due to the high pressure of water in the reactor, the water does not boil.

• The coolant  gets heated  in the reactor and the  hot water goes to the boiler and transfers the heat to the feed water in the boiler in the secondary loop.

• The  feed  water  evaporates  and  becomes  steam and  runs a  turbo  generator  from which power is obtained. Functions of various parts of the reactor are the same as those of a boiling water reactor.

Gas Cooled Reactor

• The schematic diagram of a gas cooled reactor is shown in Fig. 17.2(b).

• In this, gas CO is employed as coolant and the heat carried by the gas from the reactor is either used for steam generation in the secondary circuit like pressurized water  reactor  or  is  directly  used  as  the  working  fluid  in  a  gas  turbine  plant. Usually the gas used is CO and graphite is the moderator.

• C  O gas gets heated in the reactor and loses its heat to the superheater, evaporator and economiser tubes in the secondary loop.

• The cooled gas is recirculated again in the primary loop by means of a gas blower. The superheat ed steam is expanded in the turbine to run the generator to produce electrical power.

Advantages of a Nuclear Power Plant

1. Very large amount of heat is liberated by a very small quantity of fuel

2. Suitable for large power generation

3. Cost of fuel transportation and storage is less.

Disadvantages

1.Installation cost is very high.

2. Availability of nuclear fuel is scarce and cost is high.

3. Large number of trained and qualified personnel are required to oper ate the plant.

4. Maintenance cost is higher.

5.  We  have  the  problems  involved  in  waste  disposal  and  also  the  risk  of  radiation
hazards.