Nuclear Energy

Nuclear structure is of major importance in chemistry, since nuclei remain intact in a vast majority of chemical reaction.

A few nuclei under ordinary conditions and all nuclei in a vast majority of nuclei under special conditions, undergo changes leading to what are known as Nuclear reactions. Examples of nuclear reactions are Nuclear fission and nuclear fusion.
These reactions provide us with an inexhaustible source of energy. Thus studying these reactions, and the way they provide energy is vital. We will discuss further the energy derived from nuclear reactions.

Nuclear Energy Definition

A heavy isotope of U-235 or plutonium - 239 can undergo chain reaction yielding vast amounts of energy. The Energy released during a nuclear process like nuclear fission is called as Nuclear energy.

Fission of U-235 or Pu - 239 occurs instantaneously, producing incomprehensible quantities of energy in the form of heat and radiation. If the reaction is uncontrolled, it is accompanied by explosive violence and can be used in atom bombs.

Tremendous amounts of energy are released in nuclear fission reactions. There reactions, when done at a controlled pace, can be very useful power/electricity source. Nuclear energy is also calculated as Kilo calories.

What is Nuclear Energy?

The energy produced during a fission or a fusion reaction is called the nuclear energy. It is a very useful source of energy and is trapped for many purposes.

Nuclear Fission Process

When a nucleus is bombarded with some sub-atomic particles such as α - particles, neutrons, protons etc, these particles are captured by the target nucleus, which then disintegrates. The new element formed has mass either slightly greater or slightly smaller than the parent element.

The process of splitting of a heavier nucleus (like that of U235) into a number of fragments of much smaller mass, by suitable bombardment with sub-atomic particles is called nuclear fission.

Of the three natural isotopes of uranium

nucleus undergoes nuclear fission when bombarded with slow neutrons. U²³⁶ is formed which being unstable, further breaks up in several different ways.

²³⁵₉₂U + ₀¹n → ²³⁶₉₂U → ¹⁴⁰₅₆Ba + ⁹⁴₃₆Kr + 2 ₀¹n

The tremendous amount of energy released during nuclear fission is because of the loss in mass. The sum of the masses of the fragments produced and neutrons released as a result of fission is less than the sum of the masses of target ²³⁵U and bombarding neutron. The loss in mass gets converted into energy according to Einstein equation

E = mc²

The mass loss in Uranium fission is of the order of 0.2 amu, which corresponds to 186 million electron volt (MeV) per Uranium atom fission or about 4.3 x 10⁹ k cal per mole of Uranium atoms fission. This represents tremendous amount of release of energy.

For example, we can calculate the loss of mass when types of nuclear reactions - nuclide splits up into 144Ba and 90Kr along with the release of two neutrons.

This is one of the nuclear reaction equations. Dm, the mass defect or the mass converted into energy is given by,

Dm = 236.127 - 235.846 = 0.281 amu

1 amu = 931.48 MeV

Energy released = 0.281 amu = 931.48 x 0.281

= 261.75 MeV

The neutrons emitted from the fission of first uranium atom hit other uranium nuclei and cause their fission resulting in the release of more neutrons, which further continue the fission process. In this way, a nuclear chain reaction sets up releasing tremendous amount of energy

The fission process is complicated by the fact that a given nucleus undergoing fission may split in a variety of alternative ways. Over 30 pairs are known. Following are some possible ways of fission of Uranium nucleus.

Let us consider the nuclear fission reaction of U-235 nucleus brought about by neutron capture. Although this fission process occurs in a large number of ways, in each case a large amount of energy is released and more than one neutron emitted.

For example,

²³⁵₉₂U + ₀¹n → ²³⁶₉₂U → ⁹⁰₃₇Rb + ¹⁴⁴₅₅Cs + 2 ₀¹n

Two neutrons are emitted for every neutron that initiates the fission process. The neutrons emitted during fission may be further absorbed by other U-235 nuclei thus causing further fission and emission of more neutrons. Thus, a chain reaction is initiated in this way and it releases a tremendous amount of energy.

If the amount of the parent nuclei, U-235 is small, most of the neutrons will escape from the surface and the reaction stops. Therefore, a certain mass of Uranium, called critical mass is necessary in order to start and sustain a chain reaction. The critical mass is mostly found to be between 1 to 100 kilograms.

Nuclear fusion process

Another type of nuclear reaction that generates even larger amount of energy is the fusion reaction. For example, when two deuterium nuclei are made to fuse together to form a helium nucleus:

₁²H + ₁²H → ₂⁴He

5.5 x 10⁸ K Calories per mole of Helium formed is released. Following are the examples of fusion reactions together with the energies released.

Fusion reactions	Mass loss (amu)	Energy released (K cal per mole He)
12H + 12H → 24He	0.026	5.5 x 108
12H + 13H → 24He + 01n	0.012	4.10 x 108
411H → 24He + 210e	0.029	6.2 x 108

So, a nuclear fusion is a type of nuclear reaction where energy is released when two smaller nuclei combine to form a heavier nuclei.

To bring about such fusion reactions, the reactants have to be initially at very high temperatures of order of 10⁷ to 10⁸ degree Celsius. The energy released by the sun results from a series of nuclear fusion reactions. The overall reaction consists of the fusion of four hydrogen nuclei to form helium nucleus.

Nuclear Energy Process

The principle underlying nuclear reactions like nuclear fission has been employed in harnessing vast amounts of energy in nuclear reactors. In these reactors, the fission reaction is made to occur at a controlled rate.

Essentially, a reactor consists of lumps of U-235 separated from each other by blocks of graphite or heavy water, D₂O, which by slowing the neutrons, help in controlling the chain reaction.

The large amount of energy in the form of heat, which is released during the reactions is converted into electrical energy. Many such nuclear power plants are set up all across the world.

Benefits of Nuclear Energy

 

There are a lot of benefits of nuclear energy. Some of them are

• Light-water nuclear power plants: There are many commercial power plants, called light water power plants, where U-235 nuclei fuel rods are submerged in water, and undergo fission reactions. These light water reactors produce a large amount of electricity and are used world wide.
• Nuclear energy is also used in the production of atom bombs and hydrogen bombs.
• Fusion reaction. occurring in the sun is also a major source of energy, called as solar energy.
• Fusion is supposed to be a source of energy in 21st century. A fusion reactor can supply and operate much better than a fission reactor for generating electricity and the raw material needed, the deuterium is also easily available.

Disadvantages of Nuclear Energy

There are many disadvantages of nuclear reactions, like its effect on the environment. For example,

1. The fusion bomb produces high temperature required fro nuclear fusion and triggers the Hydrogen bomb. The explosion of such a bomb is more powerful than that of a fission bomb or the atomic bomb. If they are used in a warfare, it may mean the end of civilization on earth.
2. Disposal of nuclear reactor waste poses another hazard. The waste produced from such reactors contain Ba-139 and Kr- 92, which are itself radioactive. They emit radiations for several hundred years.

Nuclear Energy Facts

1. Radioisotopes as such are used for many purposes. So is the nuclear fission and fusion reactions which produce nuclear energy.
2. It is possible to control fission reaction of U-235 so that energy is released slowly at a usable rate.
3. Controlled fission is carried out in a specially designed plant called a nuclear power reactor. A nuclear reactor can continue to function and supply power for generations.
4. It is believed that fusion process can also be controlled like that of fission, can produce a lot of energy

Nuclear Chemistry

Nuclear chemistry is a branch of chemistry in which the nuclear chemists frequently cover several areas such as organic, analytical, inorganic and physical chemistry. Nuclear analytical techniques are an important part of the arsenal of the modern analytical chemist.

The study of the actinides and trans-actinide elements has involved the joint efforts of nuclear and inorganic chemists in extending knowledge of the periodic table. Nuclear chemistry is concerned with the changes happening in the nucleus of the atom.

The emission of radiations from a radioactive material comes from the fact that a radioactive isotope is unstable and it converts to a stable isotope by emitting radiations like α, ß positron and Gamma -rays, etc. 

What is Nuclear Chemistry?

1. A nuclear reaction is different from a chemical reaction.
2. In a chemical reaction, atoms of the reactants combine by a rearrangement of extra nuclear electrons but the nuclei of the atoms remain unchanged.
3. In a nuclear reaction, however, it is the nucleus of the atom which is involved.
4. The number of protons or neutrons in the nucleus changes to form a new element itself.

"A study of the nuclear changes in atoms is termed as Nuclear chemistry".So, nuclear chemistry is the study of phenomenon involving nuclear reactions, like radioactivity. Nuclear chemistry also deals with the energy released from nuclear reactions, and its usage.

History of Nuclear Chemistry

The history of Nuclear chemistry dates back to 1895, with the discovery of X- rays by William Roentgen. In early 1896, Henri Becquerel was carrying out a series of experiments on fluorescence. He had used photographic film between two pieces of paper.

When he developed the photographic film, he found that it had the same appearance as if it had been exposed to light. And after this, by accident, he developed the photographic plates, which was kept in the same drawer as Uranium. To his surprise, the plate had been blackened. He thought that it was a new type of fluorescence. But, actually, he had come across a phenomenon of radioactivity. So, accidentally, radioactivity was discovered by Henri Becquerel.

The name radioactivity, was coined some time later by Marie Curie. She won the Nobel prize for her discovery in 1903 with Henri Becquerel and Pierre Curie. Thereby evolved the branch of chemistry called Nuclear chemistry.

The discovery of radioactivity also brought into account many other processes, such as fission and fusion, which again were used as a source of energy in many reactors. And also, with the discovery of radioactivity and other phenomenon related to radioactive elements, many new elements were brought into light.

Nuclear Symbol Chemistry

There are various types of radiations involved in Nuclear chemistry. They have their own representations. Let us look into these radiations and their symbols.

Types of radiations and nuclear symbols

The radioactive radiations are of three types. They were sorted out by Rutherford in 1902, by passing them between two oppositely charged plates. The ones bending towards negative plate carried positive charge and were named as alpha rays. Those bending towards the positive plate and carrying negative charge were called as beta rays. The third type of radiation, being uncharged, passed straight through the electric field and were named gamma rays.

Symbols of these rays

1. Alpha rays

Represented as α. These are positively charged rays. Since the alpha rays have a mass of 4 amu and charge _2, they are actually helium nuclei. So, they are also represented as

⁴ ₂He or ⁴ ₂ α

2. Beta Rays

Negatively charged rays. They are represented as: β. Since they have a mass similar to electron, they are also represented as e-. They have a unit negative charge.

⁰_-1e or ⁰_-1 β

3. Gamma rays

These rays are neutral, with no charge. They are simply represented by the symbol : γ

Radioactivity

• A number of elements such as Uranium, and radium are unstable.
• Their atomic nucleus breaks on its own accord to form a smaller atomic nucleus of another element.
• The protons and neutrons, in the unstable nucleus, regroup to give the new nucleus.
• This causes the release of excess particles and energy from original nucleus, which we know as radiation.
• The elements whose atomic nucleus emits radiation are said to be radioactive.

Radioactive decay can be defined as: " The spontaneous breaking down of the unstable atoms is termed radioactive disintegration or radioactive decay."

" The disintegration or decay of unstable atoms accompanied by emission of radiation is called radioactivity".The radioactive radiations can be detected and measured by a number of methods. Some important methods are:

• Cloud chamber method
• Geiger-Muller counter
• Ionization chamber method
• Scintillation counter method

Three types of radioactive decay occurs

1. Alpha decay.
2. beta decay.
3. Gamma decay.

Nuclear Waste Facts

The major concern, on using the nuclear materials for any purpose, is their disposal. It is a known fact that the nuclear reactions, or rather the radioactivity, does not stop anytime. It is a spontaneous process, therefore, continues even after the material has been discarded. Thus, the disposal of the nuclear waste has to be done with utmost care.

The products of fission, like Ba-139 and Kr-92 are themselves radioactive. They emit dangerous radiations for several hundred years. The waste is usually packed in concrete barrels which are buried deep in the earth or dumped in sea. But the fear is that any leakage and corrosion of the storage vessels may eventually contaminate the water supplies.

Uses of Nuclear Chemistry

Nuclear chemistry finds its use in many fields. Though there are disadvantages in the form of atom bombs, nuclear reactivity for war fare, etc, they find many useful applications too. Some of them are

1. Light -water nuclear power plant

• Most commercial power plants today are light-water reactors. U-235 is used as a fuel here.
• The Uranium -235 rods are submerged into it.
• A lot of energy is produced from the reaction in the nuclear reactor.
• A reactor, once started, can supply power for many generations.
• About 15% of consumable electricity in U.S.A is provided by Light-water reactors.

2. Breeder reactor

This is again another reactor which taps energy from nuclear reactions. Here too, U-235 is used for the production of electricity.

3. Radioactive dating

• This is a very important use of radioactivity.
• The age of an old piece of wood can be determined using radioactive dating technique.
• A plant, while alive, takes up both normal carbon, C-12 and radioactive carbon, C-14.
• When the plant dies, uptake of carbon from atmosphere stops.
• Though, the C-12 does not show any change, the decay of C-14 starts with the release of Beta radiation.
• This helps in detecting of the age of a wood piece.

4. Medicine Many radionuclide are used in medicine to detect cancerous cells, any other defect in organs, etc. These radioactive elements are combined with other compounds, or elements and administered orally. And, after some time, the path traveled by these radio isotopes are detected using a detector. The complete length traveled by it can be seen and the problems can be easily detected.