Combined Cycle Nuclear Power Plants

Nuclear energy produced from nuclear fuels is directly involved in power generation. Mostly, nuclear reactor is with steam power plants.

Nuclear Steam Combined Power Plant

In this combined cycle, heated helium gas is used to run the helium turbine. First, helium gas is compressed in the compressor to raise its pressure and temperature. Then it is preheated in the regenerator. This preheated helium is again heated in high temperature gas cooled reactor (HTGR).

After this, this high temperature helium gas is expanded in the turbine to produce electricity in the generator. Both the compression and expansion processes are carried out isentropically. Then the exhausted helium gas is sent to the regenerator.

Here, it is again heated. This helium gas is passed to the feed water to make steam. The feed water coming in to the feed is heated by heat released by helium gas. The steam is collected in steam boiler. Here, supplementary heat supply is given to the steam water mixture. The super heated is produced due to this supplementary heat. Then this steam is expanded in steam turbine isentropically. After expansion, the steam is condensed in steam condenser. The condensed steam will become as water now. It is passed to the feed pump to raise its pressure. Finally, it is sent to the feed water heater. Both the cycles are closed cycles.

Here, topping cycle is helium gas turbine cycle and bottoming cycle is Rankine cycle. So, the overall efficiency this combined cycle is dependent on the individual efficiency of topping and bottoming cycles. The only disadvantage is, the thermal efficiency of this cycle is less because of its high temperature gas cooled reactor.

Advantages of Nuclear Power Plants

• No atmospheric pollution by combustion products.
• Space requirement is less when compared to other conventional power plants are of equal size.
• Environmental pollution is less as compared to fossil fuel power plants.
• It is well suited to meet large power demands. They give better performance at high load factors (80 to 90%).
• Increased reliability of operation.
• Fuel transportation cost is less and large storage facilities are not needed since nuclear fuel has very high energy density.
• Nuclear power plants are not affected by adverse weather conditions.
• The expenditure on metal structure, piping, storage mechanisms are much lower for nuclear power plants than a coal burning power plants.
• Water requirement is very less.

Disadvantages of Nuclear Power Plants

• High initial cost and complexity of nuclear fuel cycle is beyond the reach of poor developing countries.
• Nuclear power plants are not well suited for varying load conditions.
• The danger of radioactivity always persists in the nuclear stations.
• Danger of nuclear explosion in the reactor due to failure of controls.
• Maintenance cost is very high.
• Disposal nuclear radioactive waste is the major problem in nuclear power plants. If they are not disposed carefully, it may have bad effect on the health of workers.
• These power plants require highly trained personnel to operate nuclear reactors.