Module 97. Nuclear Chemistry & Energy

Nuclear chemistry is the branch of chemistry concerned with the study of changes in atomic nuclei and the reactions that result from such transformations. It explores phenomena such as radioactivity, nuclear fission, and fusion, as well as the applications of nuclear processes in energy production, medicine, and industry. Nuclear energy, derived from the conversion of mass into energy according to Einstein’s equation E=mc2E = mc^2E=mc2, plays a significant role in meeting global power demands and advancing scientific understanding of atomic structure.

Historical Background

The study of nuclear chemistry originated in the late nineteenth and early twentieth centuries with the discovery of radioactivity by Henri Becquerel in 1896. This was followed by pioneering research by Marie and Pierre Curie, who isolated radioactive elements such as polonium and radium, providing foundational insights into nuclear transformations.
In 1911, Ernest Rutherford proposed the nuclear model of the atom, identifying the nucleus as a dense central core surrounded by electrons. Later, his experiments led to the discovery of the proton, and James Chadwick’s discovery of the neutron in 1932 completed the basic picture of atomic structure.
The field advanced rapidly with the discovery of nuclear fission by Otto Hahn, Fritz Strassmann, and Lise Meitner in 1938, where a uranium nucleus split into smaller fragments releasing vast amounts of energy. This discovery laid the foundation for both nuclear power generation and nuclear weapons.

Fundamentals of Nuclear Chemistry

At the heart of nuclear chemistry lies the atomic nucleus, which consists of protons and neutrons bound by the strong nuclear force. Nuclear reactions involve changes within this nucleus, resulting in new elements or isotopes.
Key concepts include:

• Isotopes: Atoms of the same element with different numbers of neutrons. For example, carbon exists as 12C^{12}C12C, 13C^{13}C13C, and radioactive 14C^{14}C14C.
• Radioactivity: The spontaneous decay of unstable nuclei into more stable forms, accompanied by the emission of radiation.
• Half-life: The time required for half of a radioactive substance to decay. It is characteristic of each isotope.
• Binding energy: The energy that holds the nucleus together, accounting for the mass defect between the total mass of nucleons and the actual nuclear mass.

Types of Nuclear Radiation

Radioactive decay occurs through different modes, depending on the nature of the unstable nucleus. The main types include:

• Alpha (α) decay: Emission of a helium nucleus (4He2+^{4}He^{2+}4He2+), reducing both atomic and mass numbers.
• Beta (β) decay: Conversion of a neutron to a proton (or vice versa), with emission of an electron (β−β^-β−) or positron (β+β^+β+).
• Gamma (γ) radiation: Emission of high-energy electromagnetic waves from excited nuclei without altering atomic composition.
• Neutron emission: Release of neutrons from unstable isotopes, often occurring in heavy elements.

These radiations vary in penetrating power and ionising ability, with alpha being least penetrating but most ionising, while gamma rays penetrate deeply with minimal ionisation.

Nuclear Reactions and Energy Release

Nuclear reactions differ fundamentally from chemical reactions as they involve changes in the nucleus rather than in electron configurations. The two principal types are nuclear fission and nuclear fusion.

• Nuclear Fission: Fission involves splitting a heavy nucleus (such as uranium-235 or plutonium-239) into two lighter nuclei, releasing a large amount of energy and additional neutrons. These neutrons can trigger further fissions, creating a chain reaction. Controlled fission forms the basis of nuclear power plants, while uncontrolled reactions occur in nuclear explosions.

  235U+n→141Ba+92Kr+3n+energy^{235}U + n \rightarrow ^{141}Ba + ^{92}Kr + 3n + \text{energy}235U+n→141Ba+92Kr+3n+energy

• Nuclear Fusion: Fusion occurs when two light nuclei combine to form a heavier nucleus, releasing energy due to the conversion of mass into energy. This is the process that powers the Sun and other stars.

  2H+3H→4He+n+energy^{2}H + ^{3}H \rightarrow ^{4}He + n + \text{energy}2H+3H→4He+n+energy
  Fusion offers enormous potential as a clean and virtually limitless energy source but remains technologically challenging due to the extreme temperatures and pressures required.

Applications of Nuclear Chemistry

Nuclear chemistry has wide-ranging applications in various fields:

• Energy Production: The most prominent use of nuclear reactions is in power generation. Nuclear reactors employ controlled fission to produce heat, which is then converted into electricity. Common reactor types include Pressurised Water Reactors (PWR), Boiling Water Reactors (BWR), and Fast Breeder Reactors (FBR).
• Medicine: Radioisotopes such as iodine-131 and technetium-99m are used for diagnostics and treatment. Radiotherapy employs controlled doses of radiation to destroy cancerous cells.
• Agriculture: Radiation is used for food preservation, mutation breeding, and pest control.
• Industry: Radioisotopes assist in thickness measurement, leak detection, and material analysis.
• Archaeology and Environmental Science: Carbon-14 dating helps determine the age of ancient artefacts, while isotopic tracers monitor pollution and environmental processes.

Nuclear Energy and Its Production

Nuclear energy is generated through controlled fission reactions in nuclear power plants. The key components of a nuclear reactor include:

• Fuel rods containing uranium or plutonium.
• Moderators (e.g., water or graphite) that slow down neutrons.
• Control rods made of boron or cadmium to regulate the reaction rate.
• Coolants to transfer heat away from the reactor core.
• Containment structures ensuring radiation safety.

The energy produced converts water into steam, which drives turbines connected to electric generators. Nuclear energy is considered a low-carbon source, as it produces negligible greenhouse gas emissions during operation.

Advantages and Disadvantages of Nuclear Energy

Advantages:

• High energy density compared with fossil fuels.
• Reliable and continuous power generation.
• Reduces dependency on coal and oil, aiding climate change mitigation.
• Supports medical and industrial applications of radioisotopes.

Disadvantages:

• Radioactive waste disposal remains a major environmental concern.
• Risk of nuclear accidents, as evidenced by Chernobyl (1986) and Fukushima (2011).
• High construction and decommissioning costs.
• Potential for misuse in nuclear weapons development.

Nuclear Waste and Safety Measures

Nuclear waste is categorised as low-level, intermediate-level, or high-level, depending on its radioactivity. High-level waste, such as spent fuel, requires secure long-term storage, often through deep geological repositories.
Safety measures include:

• Multiple containment barriers.
• Automated shutdown systems.
• Strict international regulations under the International Atomic Energy Agency (IAEA).
• Continuous environmental monitoring to prevent radiation leaks.

Advancements in reprocessing technologies and fast breeder reactors aim to minimise waste by recycling fissile materials.

Future of Nuclear Chemistry and Energy

The future of nuclear chemistry lies in developing sustainable and safer technologies. Research focuses on nuclear fusion reactors, such as the ITER project, which aim to replicate stellar fusion under controlled conditions. Small modular reactors (SMRs) offer decentralised, flexible power generation with enhanced safety features.
Additionally, innovations in radioisotope production, targeted radiotherapy, and nuclear imaging are expanding the medical and scientific potential of nuclear chemistry.