Question 1: Define a nuclear chain reaction and explain how it is sustained in a nuclear reactor.

Answer: A nuclear chain reaction is a process where the splitting of one nucleus causes further nuclei to split, releasing energy and neutrons that continue the process. It is sustained by maintaining a critical mass of fissile material where enough neutrons cause additional fissions without escaping.

Question 2: Describe the role of control rods in managing a nuclear chain reaction.

Answer: Control rods absorb excess neutrons to slow down or stop the chain reaction, thereby regulating the reactor's power output and ensuring safety.

Question 3: Explain what is meant by 'critical mass' in the context of nuclear fission.

Answer: Critical mass is the minimum amount of fissile material needed to sustain a self-perpetuating nuclear chain reaction.

Question 1: If a neutron causes 0.8 fission events on average before escaping, what is the multiplication factor (k) of the chain reaction? Use the formula: k = number of neutrons produced / neutrons absorbed.

Answer: k = 1.25

Question 2: Calculate the energy released in a fission event of Uranium-235, given that each fission releases approximately 200 MeV of energy. How much energy is released if 1 gram of Uranium-235 undergoes fission? (Atomic mass of U-235 = 235 g/mol, Avogadro's number = 6.022×10^23).

Answer: Energy per atom = (200 MeV) × (1.602×10^-13 J/MeV) = 3.204×10^-11 J. Number of atoms in 1 g of U-235 = (1 g / 235 g/mol) × 6.022×10^23 ≈ 2.56×10^21 atoms. Total energy = 2.56×10^21 × 3.204×10^-11 J ≈ 8.2×10^10 J.

Question 1: Describe a simple experimental setup to demonstrate a chain reaction process using safe, non-radioactive materials or simulations. Include variables that need to be controlled.

Answer: A safe demonstration could involve a simulation or a model showing how neutrons trigger fission in fissile material like uranium. Variables to control include neutron source intensity, material purity, and geometric arrangement to ensure consistent and safe conditions.

Question 2: Identify three safety precautions necessary when working with actual nuclear materials or reactors in a theoretical setting.

Answer: 1. Use of shielding to prevent radiation exposure. 2. Maintaining proper distance from radioactive sources. 3. Strict control and monitoring of neutron flux and fissile material quantities.

Question 1: A nuclear reactor's neutron multiplication factor (k) is measured as 1.02 during operation. Explain what this indicates about the chain reaction and what actions might be necessary.

Answer: A k value of 1.02 indicates the chain reaction is slightly supercritical, meaning it is increasing. To ensure safety and steady power output, control rods may need to be adjusted to bring k closer to 1.

Question 2: If the measured k drops below 1.0, what does this imply about the chain reaction, and what would be the consequences for the reactor's operation?

Answer: A k below 1.0 implies the chain reaction is subcritical and decreasing, which could lead to a shutdown of the reactor as it cannot sustain itself.

Question 1: Describe how nuclear chain reactions are used in nuclear power plants to generate electricity.

Answer: Nuclear power plants use controlled chain reactions in reactors where fissile material like uranium-235 undergoes fission. The energy released heats water, producing steam that drives turbines to generate electricity.

Question 2: Explain one advantage and one disadvantage of using nuclear chain reactions for energy production.

Answer: Advantage: Nuclear energy produces a large amount of electricity with low greenhouse gas emissions. Disadvantage: It produces radioactive waste that requires long-term management and poses safety risks.