NUCLEAR POWER PLANT

                            Nuclear power plant  is a thermal plant in which the heat source is one or more nuclear reactors.The conversion to electrical energy takes place by burning coal, as in conventional thermal power plants: The heat is produced by fission in a nuclear reactor. Directly or indirectly water vapor-steam is produced. The pressurized steam is then usually fed to a multi-stage steam turbine. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser. The condenser is a heat exchanger which is connected to secondary side such as a river or a cooling tower. The water then pumped back into the nuclear reactor and the cycle begins again.Nuclear power is the use of sustained nuclear fission to generate heat and electricity.

                                     NUCLEAR POWER STATIONS WORKING

We  know that every substance is simply a collection of a large number of very minute particles known as atoms. It has been found that there are 92 different kinds of atoms present in nature.Some substances consist of only one kind of atoms. These substances are known as elements, e.g.hydrogen, carbon, oxygen, uranium. Atoms of hydrogen are very much smaller than atoms of uranium.Other substances contain two or more kinds of atoms joined together in groups, e.g. water which contains atoms of hydrogen and oxygen joined together. Some atoms of hydrogen are heavier than others. When these heavy hydrogen atoms combine with oxygen atoms, we get heavy water.For a long time, it was believed that atoms cannot be broken up into two smaller parts. In fact, the word atom means indivisible. Modern scientific discoveries have shown that an atom itself is a collection of still smaller particles. Three such particles are known namely electrons, protons, and neutrons. The structure of an atom has also been identified.The neutrons and protons are packed together in the central part of the atom called the nucleus. The electrons keep hovering around the nucleus.

Atoms of uranium are the largest and also the heaviest known to occur on earth. Being heavy they are also unstable. The nucleus of a uranium atom can easily break up into two smaller pieces. This process is called fission. The two fragments so produced fly apart with tremendous speed. As they  collide with other atoms in a lump of uranium they come to a stop. In the process they heat up the uranium lump. This is how energy is released from the atom and converted to heat. The energy produced in fission is described as atomic energy by some and nuclear energy by others. Besides uranium, the atoms of plutonium are also fissionable. But plutonium does not occur in nature.It has been found that 2 or 3 free neutrons are also released as a uranium atom  breaks up during fission. When one of these neutrons collides with another uranium nucleus that nucleus also breaks up. In this manner using one Neutron from every fission, we can cause another fission. This is known as chain reaction and produces heat at a steady rate.In contrast to fission, when a lump of coal burns, the atoms of carbon in coal combine with atoms of oxygen in the air and form carbon dioxide. Heat is released in the process and we see it as a flame. Smoke is also generated. When fission generates heat in uranium, there is no flame and no smoke.

Basically, all power stations adopt the same method to produce electricity. A turbine is caused to rotate. A generator is attached to the shaft of the turbine. As the turbine turns, electricity is produced in the generator.

In hydroelectric power stations, the turbine is turned by flowing water. In thermal power stations,steam is produced by heating water in a furnace which burns coal or oil. In nuclear power stations, the  steam is produced by the heat generated in the fission process.Control of operation of the nuclear power station involves two things. i.e. regulation of power generation to maintain it at a safe and steady level and secondly total shutdown of the reactor very quickly if needed.At MAPS, the power is kept constant by the use of what are known as adjuster rods. These are stainless steel rods.When these rods are introduced into the reactor vessel, the chain reaction slows down and heat generation drops.If the control rods are slightly pulled out of the reactor vessel, the chain reaction picks up and power level rises. To shutdown the reactor completely, the heavy water is drained out of the reactor vessel in a fraction of a second.In the absence of heavy water in the vessel, the chain reaction ceases totally.Compared to the burning of coal, the fission process is far more efficient. One gram of fissionable uranium can produce a million times more heat than one gram of coal.

                                      Nuclear Reaction

A nuclear reaction is at its most basic nothing more than a reaction process that occurs in an atomic nucleus. They typically take place when a nucleus of an atom gets smacked by either a subatomic particle (usually a “free neutron,” a short-lived neutron not bound to an existing nucleus) or another nucleus. That reaction produces atomic and subatomic products different from either of the original two particles. To make the kind of nuclear reaction we want, a fission reaction (in which the nucleus splits apart), those two original particles have to be of a certain type: One has to be a very heavy elemental isotope, typically some form of uranium or plutonium, and the other has to be a very light “free neutron.” The uranium or plutonium isotopes are referred to as “fissile,” which means we can use them to induce fission by bombarding them with free neutrons.In a fission reaction, the light particle (the free neutron) collides with the heavy particle (the uranium or plutonium isotope) which splits into two or three pieces. That fission produces a ton of energy in the form of both kinetic energy and electromagnetic radiation. Those new pieces include two new nuclei (byproducts), some photons (gamma rays), but also some more free neutrons, which is the key that makes nuclear fission a good candidate to generate energy. Those newly produced free neutrons zoom around and smack into more uranium or plutonium isotopes, which in turn produces more energy and more free neutrons, and the whole thing keeps going that way–a nuclear fission chain reaction.Nuclear fission produces insane amounts of energy, largely in the form of heat–we’re talking several million times more energy than you’d get from a similar mass of a more everyday fuel like gasoline.

                              Construction

The main components of a nuclear reactor are: Closed containment structure, reactor, control rods, coolant, turbine, pump, and steam generator.

                             control rods

Control rods made of graphite have an extremely important role to play in maintaining the normal operation of the nuclear plant. The primary neutron on reaction with Uranium-235 atom releases 3 more neutrons into the system. If these 3 neutrons are left free, they react with 3 more U-235 atoms and release 9 more neutrons and the process continues. So if this process is not stopped, the reaction will proceed on to become what one calls a Chain reaction. The control rods absorb the 2 excess neutrons resulting from this process and permit only one to pass through. Hence, the nuclear reaction is kept under control.

                            coolant

A cooling system removes heat from the reactor core and transports it to another area of the plant.The coolant also has an important role to play.A lot of heat is produced from the nuclear reaction causing the reactor to heat up excessively. The coolant helps to extract this heat and maintains the temperature within an optimal range, making the operation of the reactor smoother. The coolant usually used is water, but in some cases carbondioxide gas or a liquid metal like sodium may also be used.

                            Turbine

The heat produced from the fission reaction is used to heat the water into steam. The steam is then passed through a steam turbine, rotating it and hence leading to production of electricity.The object 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.

                          Generator

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

nuclear reactor

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 electrical energy.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 .Since nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield.The nuclear reactor is housed in a concrete structure which serves two purposes. Firstly, it prevents the nuclear reactor from damage due to external forces. Secondly, it prevents the radioactive emissions from the nuclear reactor from escaping into the atmosphere.

                           Advantages

• Almost 0 emissions (very low greenhouse gas emissions).

• They can be sited almost anywhere unlike oil which is mostly imported.

• The plants almost never experience problems if not from human error, which almost never happens anyway because the plant only needs like 10 people to operate it.

• A small amount of matter creates a large amount of energy.

• A lot of energy is generated from a single power plant.

• Current nuclear waste in the US is over 90% Uranium. If reprocessing were made legal again in the US we would have enough nuclear material to last hundreds of years.

• A truckload of Uranium is equivalent in energy to 10,000+ truckloads of coal. (Assuming the Uranium is fully utilized.)

• A nuclear aircraft carrier can circle the globe continuously for 30 years on its original fuel while a diesel fueled carrier has a range of only about 3000 miles before having to refuel.

• Modern reactors have two to ten times more efficiency than the old generation reactors currently in use around the US.

• New reactor types have been designed to make it physically impossible to melt down. As the core gets hotter the reaction gets slower, hence a run-away reaction leading to a melt-down is not possible.

• Theoretical reactors (traveling wave) are proposed to completely eliminate any long-lived nuclear waste created from the process.

• Breeder reactors create more usable fuel than they use.

• Theoretical Thorium reactors have many of the benefits of Uranium reactors while removing much of the risk for proliferation as it is impossible to get weapons-grade nuclear materials from Thorium.

                        Disadvantages

• Nuclear plants are more expensive to build and maintain.

• Proliferation concerns – breeder reactors yield products that could potentially be stolen and turned into an atomic weapon.

• Waste products are dangerous and need to be carefully stored for long periods of time. The spent fuel is highly radioactive and has to be carefully stored for many years or decades after use. This adds to the costs. There is presently no adequate safe long-term storage for radioactive and chemical waste produced from early reactors, such as those in Hanford, Washington, some of which will need to be safely sealed and stored for thousands of years.

• Early nuclear research and experimentation has created massive contamination problems that are still uncontained. Recently, for instance, underground contamination emanating from the Hanford Nuclear Reservation in Washington State in the U.S. was discovered and threatens to contaminate the Columbia River (the largest river in North America west of the continental divide).

• A lot of waste from early reactors was stored in containers meant for only a few decades, but is well past expiration and, resultingly, leaks are furthering contamination.

• Nuclear power plants can be dangerous to its surroundings and employees. It would cost a lot to clean in case of spillages.

• There exist safety concerns if the plant is not operated correctly or conditions arise that were unforeseen when the plant was developed, as happened at the Fukushima plant in Japan; the core melted down following an earthquake and tsunami the plant was not designed to handle despite the world’s strongest earthquake codes.

• Many plants, including in the U.S., were designed with the assumption that “rare” events never actually occur, such as strong earthquakes on the east coast (the New Madrid quakes of the 1800s were much stronger than any east coast earthquake codes for nuclear reactors; a repeat of the New Madrid quakes would exceed the designed earthquake resiliency for nuclear reactors over a huge area due to how wide-spread rare but dangerous eastern North American earthquake effects spread), Atlantic tsunami (such as the 1755 Lisbon quake event, which sent significant tsunami that caused damage from Europe to the Caribbean) and strong hurricanes which could affect areas such as New York that are unaccustomed to them (rare, but possibly more likely with global warming)

• Mishaps at nuclear plants can render hundreds of square miles of land uninhabitable and unsuitable for any use for years, decades or longer, and kill off entire river systems