UTILIZATION OF NUCLEAR ENERGY

NUCLEAR POWER PLANT

                A nuclear power plant is a type of power station that generates electricity using heat from nuclear reactions. These reactions take place within a reactor. The plant also has machines which remove heat from the reactor to operate a steam turbine and generator to make electricity. Electricity made by nuclear power plants is called nuclear power.

                Nuclear power plants are usually near water to remove the heat the reactor makes. Some nuclear power plants use cooling towers to do this. Nuclear power plants use uranium as fuel. When the reactor is on, uranium atoms inside the reactor split into two smaller atoms. When uranium atoms split, they give off a large amount of heat. This splitting of atoms is called fission.

                The most popular atoms to fission are uranium and plutonium. Those atoms are slightly radioactive. The atoms produced when fuel atoms break apart are strongly radioactive. Today, fission only happens in nuclear reactors. In nuclear reactors, fission only happens when the reactors parts are arranged properly. Nuclear power plants turn their reactors off when replacing old nuclear fuel with new fuel.

Major components of the systems are described below:-

-Nuclear reactors

 A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most common use of nuclear reactors is for the generation of electric energy and for the propulsion of ships.

Nuclear reactors usually rely on uranium to fuel the chain reaction. Uranium is a very heavy metal that is abundant on Earth and is found in sea water as well as most rocks. Naturally occurring uranium is found in two different isotopes: uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) accounting for about 0.7%. Isotopes are atoms of the same element with a different number of neutrons. Thus, U-238 has 146 neutrons and U-235 has 143 neutrons. Different isotopes have different behaviours. For instance, U-235 is fissile which means that it is easily split and gives off a lot of energy making it ideal for nuclear energy. On the other hand, U-238 does not have that property despite it being the same element. Different isotopes also have different half-lives. A half-life is the amount of time it takes for half of a sample of a radioactive element to decay. U-238 has a longer half-life than U-235, so it takes longer to decay over time. This also means that U-238 is less radioactive than U-235

The nuclear reactor is the heart of the plant. In its central part, the reactor core's heat is generated by controlled nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn powers either ship's propellers or electrical generators.

Since nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield. This containment absorbs radiation and prevents radioactive material from being released into the environment. In addition, many reactors are equipped with a dome of concrete to protect the reactor against both internal casualties and external impacts.

 

-Steam turbine

The purpose of the steam turbine is to convert the heat contained in steam into mechanical energy. The engine house with the steam turbine is usually structurally separated from the main reactor building. It is so aligned to prevent debris from the destruction of a turbine in operation from flying towards the reactor.

In the case of a pressurized water reactor, the steam turbine is separated from the nuclear system. To detect a leak in the steam generator and thus the passage of radioactive water at an early stage, an activity meter is mounted to track the outlet steam of the steam generator. In contrast, boiling water reactors pass radioactive water through the steam turbine, so the turbine is kept as part of the control area of the nuclear power plant.

-Generator

The generator converts kinetic energy supplied by the turbine into electrical energy. Low-pole AC synchronous generators of high rated power are used.

-Cooling system

A cooling system removes heat from the reactor core and transports it to another area of the plant, where the thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot coolant is used as a heat source for a boiler, and the pressurized steam from that drives one or more steam turbine driven electrical generators.

-Safety valves

In the event of an emergency, safety valves can be used to prevent pipes from bursting or the reactor from exploding. The valves are designed so that they can derive all of the supplied flow rates with little increase in pressure. In the case of the BWR, the steam is directed into the suppression chamber and condenses there. The chambers on a heat exchanger are connected to the intermediate cooling circuit.

-Feedwater pump

The water level in the steam generator and nuclear reactor is controlled using the feedwater system. The feedwater pump has the task of taking the water from the condensate system, increasing the pressure and forcing it into either the steam generators (in the case of a pressurized water reactor) or directly into the reactor (for boiling water reactors).

-Emergency power supply

Most nuclear plants require two distinct sources of offsite power feeding station service transformers that are sufficiently separated in the plant's switchyard and can receive power from multiple transmission lines. In addition in some nuclear plants the turbine generator can power the plant's house loads while the plant is online via station service transformers which tap power from the generator output bus bars before they reach the step-up transformer (these plants also have station service transformers that receive offsite power directly from the switchyard.) Even with the redundancy of two power sources total loss of offsite power is still possible. Nuclear power plants are equipped with emergency power systems to maintain safety in the event of unit shutdown and loss of offsite power. Batteries provide uninterruptible power to instrumentation, control systems, and valves. Emergency diesel generators provide direct AC power to charge the batteries and to provide power to systems requiring AC power such as motor driven pumps. The emergency diesel generators do not power all plant systems, only those required to shut the reactor down safely, remove decay heat from the reactor, provide emergency core cooling, and, in some plants, spent fuel pool cooling. The large power generation pumps such as the main feedwater, condensate, circulating water, and (in pressurized water reactors) reactor coolant pumps are not backed up by the diesels.

Advantages of nuclear power plant

i. The nuclear power plant is more economical compared with thermal in areas where coal field is far away.
ii. There is no problem of fuel transportation, storage and handling and ash handling as in thermal power plants.
iii. Man power required for the operation of nuclear power plant is less. Therefore the cost of operation is reduced.
iv. Nuclear plant occupies less space than thermal power plants, which reduces the cost of civil construction.
v. The capital cost in structural materials, piping and storage are less than thermal plants of the same capacity.

Disadvantages of nuclear power plant

i. Danger of nuclear radiation.
ii. Problem of disposing the radioactive waste materials.
iii. It has to be operated at full load throughout for a good efficiency. So part load operation becomes inefficient.
iv. Capital cost of small size plants is very high.