Science and Technology Class 05

 Science and Technology Class 05

Space Debris 

• Space Debris is orbital junk that is orbiting around the earth, at a very high speed.
• This debris can collide with space missions and damage satellites, space stations, and other space assets.
• The main sources of Debris are:
• (a) upper stages of rockets.
• (b) Discarded rocket stages.
• (c) Explosion of rockets or accidents in space.
• (d) Anti-satellite demonstrations.
• (e) Outdated satellites.
• There can be natural sources such as micro-meteorites
• Kessler Syndrome
• A scenario in which the density of low earth orbit is so high that one accident can produce debris, causing more accidents, and thus, enhancing the likelihood of more collisions.
• This debris is a danger to the existing missions, as well as creates challenges for future missions.
• Steps to be taken
• (a) Keeping track of larger Debris as part of space situational awareness.
• For example, Project Netra of ISRO.
• (b) Ban on anti-satellite demonstrations.
• (c) Separation of rocket stages at lower altitudes.
• (d) Dedicated missions to destroy existing pieces of debris.
• For example, the Remove Debris Mission led by the University of Surrey, and the Elsa-D mission by Astroscale.
• An international organization interagency space debris coordination committee aims to coordinate efforts at a global scale, to take care of space debris issues.
• ISRO is a member.

Nuclear Technology 

• Basics of Nuclear Technology
• Nuclear Technology in Energy production
• Radioactivity
• Nuclear Technology Application: Agriculture, Medicine, Space, Industry, defence.

Basic of Nuclear Technology

• Atomic number refers to the number of protons.
• Atomic mass refers to the number of protons and neutrons.
• Isotopes are a family of elements that have the same atomic number. For example, Carbon-12 and Carbon-14, protium, deuterium, and tritium (Isotopes of Hydrogen)
• Isobars are those elements that have the same atomic mass but the same atomic number.
• The protons in the nucleus are held together by a strong nuclear force.
• This force exists between the proton-proton, neutron-neutron, and proton-neutron.
• What is Nuclear technology?
• Nuclear Technology is the application of nuclear reactions. These are the reactions in which the nucleus or nuclear particles participate.
• There are nuclear reactions, which occur in nature such as nuclear fusion in stars, and the decay of radioactive substances.
• There are nuclear reactions that can be conducted in a lab setup or an industrial setup.
• These reactions have applications in energy production, agriculture, medicine, space, etc

Nuclear Technology in Energy Production 

• Energy production can occur in two ways, Nuclear Fission and Nuclear Fusion.
• Nuclear Fission
• In Nuclear fission, a heavy nucleus such as uranium-235 is bombarded with neutrons, so that a nucleus becomes unstable.
• Because of this instability, it disintegrates into lighter nuclei and produces a huge amount of energy.
• This energy can be calculated using Einstein's mass-energy equivalence equation, E= Mc^2.
• Here 'C' refers to the speed of light in a vacuum (3*10^8 m/s).
• 
• Nuclear fission reaction produces an excess of neutrons. These neutrons can continue the fission reaction.
• The reaction will grow exponentially in an uncontrolled manner.
• Such an uncontrolled chain reaction is the mechanism, behind nuclear bombs.
• If we can absorb the excess of neutrons, the reaction becomes a controlled chain reaction, and energy output can be controlled.
• This is the mechanism behind the nuclear reactor.

Nuclear Reactors and their major components 

• Nuclear reactors utilize controlled fission to produce energy.
• 
• It has the following major components:
• (a) Fissile material- Those which can undergo fission easily. 
• There are two isotopes of Uranium, U-235, and U-239. Plutonium-239 is also good fissile material.
• (b) Control Rods- These are used to absorb the excess neutrons. 
• These are made of Cadmium, Boron
• (c) Moderators- They are used to slow down the speed of neutrons and slower neutrons are better at causing fission.
• Water and heavy water are good moderators.
• (d) Coolant- It maintains the temperature of the core by transporting the heat away from the core of the reactor.
• Often, moderators and coolants are the same.
• For example, water and Heavy water are used as coolants.
• Liquid sodium is a good coolant, but not a good moderator.

Nuclear Fuel Cycle 

• 
• The Nuclear Fuel Cycle signifies all the steps involved in nuclear energy production, as well as nuclear waste management.
• It comprises two parts: The front end and the back end.
• Front-end steps are the following: Mining, Milling, Enrichment, fabrication process, and Nuclear fission at the reactor.
• Mining refers to the extraction of uranium ore from a geographical location.
• Milling refers to the removal of impurities from the uranium ore by crushing and the use of physical and chemical separation methods.
• Enrichment refers to the removal of uranium 238, from the natural uranium, using isotopic separation methods.
• It is to increase the concentration of the U-235 in the ore, to 3-5 %.
• (*Natural uranium has more than 99% of uranium 238 and less than 1 per cent of uranium-235)
• In the fabrication process, enriched uranium is converted into pellets, and embedded into a tube, which makes one fuel rod.
• Many fuel rods make one assembly and many assemblies, are used in the core of the reactor.
• Depending on the capacity, the reactor can produce energy for up to 4-7 years.
• The backend step comprises of following:
• (a) Interim storage
• Nuclear waste is dangerous. It is removed from the core and is kept in a deep pool of water, for a few years.
• (b) Spent Fuel reprocessing
• We try to recover useful material, such as fissile material from nuclear waste.
• (c) Final Disposition
• Nuclear waste is deposited in the permanent underground facility. 
• Some countries do not use spent fuel reprocessing, such a cycle is called the open nuclear fuel cycle.
• India's nuclear program is dependent upon spent fuel reprocessing, which is called a closed nuclear fuel cycle.

The topics for the next class: Nuclear Fission, Nuclear Fusion, Radioactivity