Question

Define fusion and give two examples of fusion processes (i.e., reactions) that may be used in power reactors of the future.

Short answer

Fusion is where light nuclei combine, releasing energy. Examples: Deuterium-Tritium fusion and the Proton-Proton chain.

Step-by-step solution

Understanding Fusion

Fusion is a nuclear reaction where two light atomic nuclei combine to form a heavier nucleus, releasing energy in the process. This is the process that powers stars, including our sun, where hydrogen nuclei fuse to form helium.

Example 1: Hydrogen Isotopes Fusion

One potential fusion reaction for power reactors is the fusion of deuterium ( D_{2} ) and tritium ( T_{3} ), both isotopes of hydrogen. This reaction can be represented as: D_{2} + T_{3} ightarrow He_{4} + n n+18Mev , releasing helium, a neutron, and substantial energy.

Example 2: Proton-Proton Chain

Another example is the proton-proton chain reaction, more common in stars but considered for future technology. It involves protons combining to eventually form helium, with intermediate steps producing isotopes and emitting energy: 4p ightarrow He_{4} + 2e^{+} + 2 u_{e} + energy .

Key concepts

Fusion Reactions

Fusion reactions are fascinating physical processes that lie at the heart of many stellar bodies in the universe. Unlike fission, which splits heavy atomic nuclei, fusion combines light atomic nuclei into a heavier nucleus. This process releases a tremendous amount of energy. This is the energy source of stars, including our own sun. During a fusion reaction, hydrogen atoms fuse together under extreme pressure and temperature conditions to form helium and release energy in the process. Through this reaction, stars like the sun generate the light and heat that sustain life on Earth.
Potentially, fusion reactions could revolutionize how we generate power on Earth. It’s a cleaner, more sustainable alternative to fossil fuels or nuclear fission. However, achieving the conditions necessary for controlled fusion reactions on Earth is extremely challenging, requiring advanced technology and an in-depth understanding of nuclear physics.

Deuterium-Tritium Reaction

One of the most promising fusion reactions for future power generation involves the isotopes of hydrogen known as deuterium and tritium. These isotopes can fuse to form helium, a neutron, and produce a significant amount of energy. The reaction can be expressed as follows:
\( D_2 + T_3 \rightarrow He_4 + n \)
The deuterium-tritium reaction is favored for research and potential use in future power reactors because it takes place at relatively lower temperatures compared to other fusion reactions. Moreover, this reaction yields a substantial energy output, around 18 MeV (mega-electronvolts), which makes it particularly attractive for power generation.
Despite these advantages, there are challenges, such as sourcing enough tritium, managing the high-energy neutrons produced, and sustaining the required plasma conditions. Scientists are actively working on developing reactors that could harness this reaction efficiently and safely for energy production.

Proton-Proton Chain

The proton-proton chain reaction is a series of nuclear reactions that occur in the cores of stars, including the sun, and is how stars primarily produce energy. In this process, protons (which are essentially hydrogen nuclei) combine through a series of reactions to ultimately form helium. Along the way, these reactions produce positrons (\(e^{+}\)), neutrinos (\(u_e\)), and other intermediates, releasing energy.
The overall process of the proton-proton chain can be summarized as:
\(4p \rightarrow He_{4} + 2e^{+} + 2u_e + \text{energy}\)
This fusion chain is less practical for immediate use in terrestrial power plants due to the extremely high temperatures required to initiate and sustain the reactions. However, understanding this process helps scientists in attempting to harness fusion energy on Earth, guiding the development of controlled fusion technologies that may be applicable centuries into the future.

Future Power Reactors

The concept of future power reactors running on fusion energy is both exciting and ambitious. These reactors, often referred to as fusion reactors, aim to harness energy similar to the sun's by utilizing fusion reactions like the deuterium-tritium reaction. The promise of fusion reactors lies in two main potentials: producing a nearly unlimited energy supply and significantly reducing radioactive waste compared to traditional nuclear fission reactors.
Key advantages include:

• High energy output with minimal carbon emissions, contributing to a sustainable energy future.
• The abundance of deuterium in water, making fuel resources more readily available globally.
• Reduced long-term radioactive waste, posing less environmental risk.

However, there are notable challenges in realizing these reactors. Containment of high-temperature plasmas, the durability of reactor materials, and economic feasibility are areas of intense research and development. International projects like ITER (International Thermonuclear Experimental Reactor) are spearheading the efforts to overcome these obstacles, striving toward a future where fusion power is a practical, reliable source of energy.