Nuclear Fission and Chain Reaction - UNSOLVED PRACTICE SET
Chapter: Nuclei | Topic: Nuclear Fission and Chain Reaction
NUCLEAR FISSION AND CHAIN REACTION - UNSOLVED PRACTICE SET
Topic: Nuclear Fission and Chain Reaction
Multiple Choice Questions
Q1. Nuclear fission is the process in which:
- Two light nuclei combine to form a heavier nucleus
- A heavy nucleus splits into two lighter nuclei of comparable masses
- A nucleus emits an alpha particle
- A nucleus emits a beta particle
Q2. A typical fission of uranium-235 releases approximately:
- 1 eV of energy
- 1 keV of energy
- 200 MeV of energy
- 1 GeV of energy
Q3. In a nuclear chain reaction, each fission event produces:
- No neutrons
- One neutron
- On average, 2-3 neutrons
- Hundreds of neutrons
Q4. For a self-sustaining chain reaction, the multiplication factor k must be:
- k < 1
- k = 1
- k > 1
- k = 0
Q5. The critical mass is:
- The minimum mass of fissile material required to sustain a chain reaction
- The maximum mass that can undergo fission
- The mass of one uranium atom
- The mass of the fission products
Q6. Natural uranium contains:
- Only U-235
- Only U-238
- About 0.7% U-235 and 99.3% U-238
- Equal amounts of U-235 and U-238
Short Answer Questions
Q7. What is nuclear fission? Write the nuclear equation for the fission of U-235 by a thermal neutron.
Q8. What is a chain reaction? What conditions are necessary for a self-sustaining chain reaction?
Q9. Why is U-235 more easily fissioned than U-238 by thermal neutrons?
Q10. What is the role of moderators in a nuclear reactor? Name two commonly used moderators.
Q11. Explain the difference between controlled and uncontrolled chain reactions. Give one example of each.
Q12. What is the function of control rods in a nuclear reactor? Name the material commonly used for control rods.
Long Answer Questions
Q13. Explain the process of nuclear fission with a suitable example. Discuss how energy is released during fission and why the fission fragments are radioactive.
Q14. Describe the mechanism of a chain reaction. Explain the conditions for a self-sustaining chain reaction and define the multiplication factor.
Q15. Compare controlled and uncontrolled chain reactions. Explain how a nuclear reactor controls the chain reaction while an atomic bomb allows it to proceed uncontrolled.
Numerical & Application-based Problems
Q16. In the fission of U-235, the fission fragments are Ba-141 and Kr-92, with three neutrons released.
(a) Write the balanced nuclear equation for this fission reaction.
(b) Calculate the energy released per fission given the masses: U-235 = 235.0439 u, n = 1.0087 u, Ba-141 = 140.9144 u, Kr-92 = 91.9262 u.
(c) Calculate the energy released when 1 kg of U-235 undergoes complete fission.
(d) How many fissions per second are required to produce a power of 1 MW?
Q17. A nuclear reactor uses U-235 as fuel and produces a power of 1000 MW.
(a) Calculate the number of fissions per second required.
(b) Calculate the mass of U-235 consumed per day.
(c) If the reactor has an efficiency of 30%, calculate the thermal power produced.
Q18. In your school's science exhibition, a student presents a project on nuclear energy in India.
(a) She explains that India's nuclear reactors use enriched uranium. Calculate how much U-235 is present in 100 kg of natural uranium (0.7% enrichment) and in 100 kg of reactor-grade uranium (3% enrichment).
(b) The student discusses the Kakrapar Atomic Power Station which uses pressurized heavy water reactors (PHWR). Explain why heavy water (D₂O) is used as a moderator instead of ordinary water, and what advantage this gives India (which has abundant thorium but limited uranium).
(c) She calculates that a typical nuclear power plant produces about 20 tonnes of spent fuel per year. If the spent fuel contains 1% plutonium-239 by mass, calculate the mass of Pu-239 produced annually and explain why this is significant for India's three-stage nuclear program.
(d) A classmate argues that nuclear power is too dangerous because of the risk of explosions like atomic bombs. Explain the fundamental differences between a nuclear reactor and an atomic bomb that make a reactor explosion impossible, using the concepts of critical mass and controlled chain reaction.
(e) India's target is to achieve 20 GW of nuclear power capacity. If each reactor produces 1000 MW, calculate how many reactors are needed. If each reactor consumes 200 tonnes of natural uranium annually, calculate India's total uranium requirement for this program.