Basic Terms (not asked directly in exam but its good to have some level of basic understanding about these )
- It is the fundamental constituent of matter.
- It is made up of three tiny subatomic particles: protons, neutrons, and electrons.
- The protons(positively charged) and the neutrons(no charge) make up the center of the atom called the nucleus and the electrons(negatively charged) fly around above the nucleus in a small cloud.
- Atoms of the same element that have a different number of neutrons
- Unstable nuclei give off radiation so as to become stable. Isotopes of such atoms are called radioactive isotopes
3. Radioactive Decay
- It is the process by which an unstable nucleus emits elementary particles(alpha, beta, gamma rays) in the form of radiation.
- The instability is caused by either an excess of protons or an excess of neutrons. As the atom attempts to become stable, it releases energy and matter in the form of radiation
- Half-life refers to the time for half the radioactive nuclei in any atom to undergo radioactive decay.
4. Types of Nuclear Reactions
4a. Nuclear Fission:
- A heavy nucleus splits into 2 smaller nuclei.
- How does it happen? The stability of the nucleus is maintained by the balance between the repulsive forces of the protons and the nuclear attractive/binding force. During fission, the repulsive forces become dominant over the binding force in the unstable nucleus.
4b. Nuclear Fusion
- Two light nuclei combine to form a single heavier nucleus
- The sum of the masses of the product nuclei is less than the sum of the masses of the initial fusing nuclei. Therefore, a large amount of energy is released
Types of Nuclear Materials
5. Uranium Enrichment
- Natural uranium consists of nearly 99% U-238 and only around 0.7% of U-235
- U-235 is a fissile material that can sustain a chain reaction in a nuclear reactor.
Therefore, we need more U-235
- Enrichment process increases the proportion of U-235 through the process of isotope separation(U-238 is separated from U-235). Isotope separation is possible due to the mass difference between U-238 and U-235
- For nuclear weapons, enrichment is required upto 90% or more which is known as Highly Enriched Uranium/weapons-grade uranium
- For nuclear reactors, enrichment is required upto 3-4% which is known as Low Enriched Uranium/reactor-grade uranium
6. Methods of Uranium Enrichment
a) Gaseous Diffusion
- Pump UF6 through pipelines
- Force the gas through a porous filter or membrane
- Repeat the diffusion process until enough U-235 is collected
- Once the gas is enriched, UF6 is condensed into a liquid and stored in containers, where it cools and solidifies into fuel pellets
b) Gas Centrifuge Process
- Assemble a number of high speed rotating cylinders
- Pipe the UF6 gas into the centrifuge
- As the centrifuge rotates, the centrifugal force sends the heavier U-238 to the cylinder wall and lighter U-235 to the centre
- Extract the separated gases and reprocess the gases in separate centrifuges
c) Aerodynamic Separation Process
- Build a series of stationary narrow cylinders
- A mixture of gaseous UF6 and helium(H2) is compressed and directed along a curved wall at high velocity
- The heavier U-238 molecules move out to the wall relative to the U-235 molecules
- At the end of the deflection, the gas jet is split by a knife edge into a light fraction and a heavy fraction
d) Liquid Thermal Diffusion Process
- Liquify UF6 gas under pressure
- Construct a pair of concentric pipes
- Surround the pipes with a jacket of liquid water. This will cool the outer pipe
- Pump UF6 between the pipes
- Heat the inner pipe with steam. This will create a convection current in the UF6 that will push heavier U-238 isotope towards the colder outer pipe and draw the lighter U-235 isotope towards the hotter inner pipe
e) Electromagnetic Isotope Separation
- Ionize the UF6 gas i.e. give the atoms of UF6 an electric charge
- Pass the gas through a strong magnetic field
- The U-238 atoms are less deflected relative to the U-235 atoms.
- This results in two streams that could be collected by different receivers
f) Molecular Laser Isotope Separation
- UF6 gas is excited by an infrared laser system that selectively excites only those UF6 molecules that contain U-235. The other UF6 molecules that contain U-238 are untouched
- In the second stage, photons from a second laser system dissociate excited UF6 molecules to form Uranium Pentafluoride(UF5) that contain U-235 and free fluorine atoms
6. Components of Nuclear Reactor
Critical Mass: The smallest amount of fissile material needed to sustain a nuclear chain reaction.Criticality: It refers to the balance of neutrons in the system
- Sub-critical: The number of neutrons produced as a result of the fission reaction is less than the number of neutrons lost in the reaction
- Supercritical: The number of neutrons produced is greater than the number of neutrons lost
- Critical: The number of neutrons produced is equal to the number of neutrons lost. A balance is maintained.
7. Applications of Nuclear technology
- Radioactive Dating: The technique of comparing the abundance ratio of a radioactive isotope to a reference isotope to determine the age of a material
- Nuclear Medicine: Radiation is used to provide information about the functioning of a person’s specific organs or to treat diseases
- Nuclear Agriculture: Radiation is used for crop improvement food preservation by irradiation, to develop new plant types etc.
- Gamma Ray Techniques: Scattering of gamma rays can be used to determine the concentration of an element in minerals such as ash content in coal
- Water Management: Activities such as artificial recharge of groundwater system, flow measurements in rivers etc. can be undertaken