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Question 1. Which particle is emitted during alpha decay? A) Neutron B) Proton C) Helium‑4 nucleus D) Electron Answer: C Explanation: Alpha decay releases a helium‑4 nucleus, consisting of two protons and two neutrons. Question 2. The binding energy per nucleon is highest for which element? A) Iron‑ 56 B) Uranium‑ 235 C) Carbon‑ 12 D) Lead‑ 208 Answer: A Explanation: Iron‑56 has the maximum binding energy per nucleon, making it the most stable nucleus. Question 3. The half‑life of a radionuclide is 10 years. After 30 years, what fraction of the original activity remains? A) 1/ B) 1/ C) 1/ D) 1/ Answer: C Explanation: After three half‑lives (10 yr × 3), activity = (1/2)³ = 1/8 of the original.
Question 4. Which radiation type has the greatest penetrating power in tissue? A) Alpha particles B) Beta particles C) Gamma photons D) Neutrons Answer: C Explanation: Gamma photons are highly penetrating; alpha and beta are stopped by a few centimeters of tissue or skin. Question 5. In a reactor, the effective multiplication factor (k_eff) equal to 1.0 indicates: A) Subcritical condition B) Critical condition C) Supercritical condition D) Prompt critical condition Answer: B Explanation: k_eff = 1.0 means each fission generates exactly one subsequent fission, sustaining a steady chain reaction. Question 6. Delayed neutrons are essential because they: A) Increase the reactor power instantly B) Provide a time buffer for control‑rod actions C) Cause prompt criticality D) Reduce fuel enrichment requirements Answer: B Explanation: Delayed neutrons extend the neutron generation time, allowing operators to adjust reactivity safely.
Question 10. Which of the following is a Generation III+ reactor design feature? A) Natural‑circulation cooling B) On‑site fuel enrichment C) Passive safety systems that operate without AC power D) Graphite moderation in a light‑water environment Answer: C Explanation: Generation III+ reactors incorporate passive safety systems that rely on gravity, convection, or natural circulation. Question 11. Small Modular Reactors (SMRs) are primarily distinguished by: A) Use of heavy water as moderator B) Ability to be factory‑fabricated and transportable C) Requirement for high‑enriched uranium D) Operation at cryogenic temperatures Answer: B Explanation: SMRs are designed for modular construction, allowing factory fabrication and transport to the site. Question 12. The purpose of a containment building is to: A) Provide structural support for the turbine B) Shield the reactor from external radiation only C) Contain radioactive releases during accidents D) Store spent fuel pools Answer: C Explanation: Containment structures are robust barriers designed to prevent the release of radioactive material.
Question 13. Which of the following is a chemical shim used for reactivity control? A) Boric acid dissolved in the primary coolant B) Cadmium rods inserted into the core C) Hafnium alloy control rods D) Graphite blocks in the moderator Answer: A Explanation: Boric acid (borate) dissolved in water acts as a soluble neutron absorber, providing fine reactivity control. Question 14. The term “criticality accident” refers to: A) Loss of coolant leading to fuel overheating B) Uncontrolled chain reaction causing a rapid power surge C) Failure of the containment building D) Release of radioactive gases during a steam rupture Answer: B Explanation: A criticality accident is an uncontrolled, self‑sustaining chain reaction that can release intense radiation. Question 15. A “stop‑work” authority in a nuclear plant means: A) Only supervisors can halt operations B) Any employee can halt work if a safety concern is identified C) Work can be stopped only after a formal safety committee vote D) Only the plant manager may issue a stop order Answer: B Explanation: The stop‑work authority empowers any worker to halt activities when a safety issue is perceived.
Question 19. The inverse square law for radiation indicates that intensity decreases: A) Linearly with distance B) Proportionally to the square of the distance from the source C) Exponentially with distance D) Not at all, intensity is constant Answer: B Explanation: Radiation intensity follows a 1/r² relationship, so doubling distance reduces intensity to one‑quarter. Question 20. A half‑value layer (HVL) for a material is defined as: A) The thickness that reduces radiation intensity by 10 % B) The thickness that halves the photon energy C) The thickness that reduces radiation intensity to 50 % of its original value D) The thickness that completely stops neutrons Answer: C Explanation: HVL is the material thickness required to attenuate a photon beam to half its initial intensity. Question 21. Which waste classification requires geological repository disposal? A) Low‑level waste (LLW) B) Intermediate‑level waste (ILW) C) High‑level waste (HLW) D) Decommissioning waste Answer: C Explanation: HLW, primarily spent fuel, contains long‑lived radionuclides and is destined for deep geological storage.
Question 22. The most common enrichment method for commercial uranium is: A) Gaseous diffusion B) Gas centrifuge C) Laser isotope separation D) Electromagnetic isotope separation Answer: B Explanation: Gas centrifuges spin uranium hexafluoride at high speeds to separate ^235U from ^238U efficiently. Question 23. In‑core fuel management aims to: A) Maximize the number of fuel assemblies in the core at all times B) Optimize burnup while maintaining power distribution and safety limits C) Keep fuel temperature below 50 °C at all times D) Eliminate the need for control rods Answer: B Explanation: Fuel management balances burnup, reactivity, and thermal‑hydraulic constraints to achieve efficient operation. Question 24. Spent fuel is initially stored in: A) Dry casks located on site B) Deep geological repositories C) Water‑filled spent‑fuel pools for cooling and shielding D) Open‑air concrete pads Answer: C Explanation: Pools provide cooling and radiation shielding for freshly discharged fuel before transfer to dry storage.
Explanation: Prompt criticality eliminates the time buffer of delayed neutrons, causing an uncontrolled power surge. Question 28. The most common moderator in commercial light‑water reactors is: A) Heavy water (D₂O) B) Graphite C) Light water (H₂O) D) Beryllium Answer: C Explanation: Light water slows neutrons effectively and also serves as the primary coolant. Question 29. Which of the following is NOT a deterministic (non‑stochastic) radiation effect? A) Skin erythema at high dose rates B) Increased lifetime cancer risk at low doses C) Cataract formation after high‑dose exposure D) Acute radiation syndrome Answer: B Explanation: Cancer risk at low doses is stochastic; deterministic effects have a threshold dose. Question 30. The ALARA principle stands for: A) As Low As Reasonably Achievable B) Always Limit Radiation Appropriately C) Atomic Level Absorption Radiation Assessment D) Automated Low‑dose Alert Regulation Act Answer: A Explanation: ALARA guides radiation protection programs to keep exposures as low as practical.
Question 31. In radiation shielding, which material provides the greatest attenuation per unit thickness for gamma rays? A) Water B) Concrete C) Lead D) Polyethylene Answer: C Explanation: Lead’s high density and atomic number make it highly effective for gamma attenuation. Question 32. The decay constant (λ) is related to half‑life (T½) by: A) λ = ln 2 / T½ B) λ = T½ / ln 2 C) λ = 2 × T½ D) λ = 1 / (T½)² Answer: A Explanation: λ = ln 2 / T½ defines the exponential decay rate. Question 33. Which of the following best describes a “subcritical assembly”? A) An arrangement where k_eff > 1 B) A configuration that cannot sustain a chain reaction without an external neutron source C) A reactor operating at full power D) A system where delayed neutrons dominate the reaction Answer: B Explanation: Subcritical assemblies require an external neutron source because each fission produces fewer than one subsequent fission.
Question 37. Which of the following is a key advantage of heavy‑water reactors (HWRs)? A) Ability to use natural uranium as fuel B) Higher thermal efficiency than PWRs C) No need for a containment building D) Use of liquid metal coolant Answer: A Explanation: Heavy water’s low neutron absorption allows reactors to run on unenriched natural uranium. Question 38. The “dose‑rate” is expressed in which unit? A) Becquerel (Bq) B) Gray per hour (Gy/h) C) Sievert per hour (Sv/h) D) Curie (Ci) Answer: C Explanation: Dose‑rate measures the rate of dose delivery, commonly in Sv/h or mSv/h. Question 39. In the event of a loss‑of‑coolant accident (LOCA), the most immediate safety concern is: A) Reactor core overheating leading to fuel damage B) Containment building collapse C) Loss of electrical power to the grid D) Release of gaseous iodine Answer: A Explanation: LOCA reduces coolant flow, risking fuel temperature rise and potential core melt.
Question 40. Which of the following is a typical component of a nuclear emergency response plan? A) Daily turbine efficiency reports B) Evacuation zones and shelter‑in‑place procedures C) Routine coolant chemistry monitoring D) Fuel enrichment scheduling Answer: B Explanation: Emergency plans define protective actions for the public, including evacuation and sheltering. Question 41. The “criticality safety index” (CSI) is used to: A) Predict reactor power output B) Evaluate the likelihood of an accidental criticality in handling fissile material C) Measure the effectiveness of shielding D) Determine coolant flow rates Answer: B Explanation: CSI quantifies parameters (mass, geometry, moderation) to assess criticality risk during material handling. Question 42. Which of the following best describes “burnup” in a nuclear fuel assembly? A) The total number of control rods inserted B) The amount of energy extracted per unit mass of fuel, usually expressed in GWd/tU C) The temperature of the fuel cladding D) The rate of neutron leakage from the core Answer: B Explanation: Burnup measures how much fission energy has been produced relative to the original fuel mass.
Question 46. In radiation biology, the “linear‑no‑threshold (LNT) model” assumes: A) No health effects below a certain dose B) Cancer risk increases linearly with dose, with no safe threshold C) Effects are only deterministic above 100 mSv D) Low doses are harmless due to adaptive response Answer: B Explanation: LNT posits that any amount of ionizing radiation carries some risk of stochastic effects. Question 47. Which of the following actions is part of a post‑job review in nuclear operations? A) Immediate shutdown of the reactor B) Documentation of deviations, lessons learned, and corrective actions C) Calibration of all radiation detectors D) Replacement of all fuel assemblies Answer: B Explanation: Post‑job reviews capture performance data, identify improvements, and close out safety concerns. Question 48. The “photon attenuation coefficient” depends on: A) Only the photon energy B) Only the thickness of the material C) Both photon energy and material atomic number/density D) Neither; it is a constant for all materials Answer: C Explanation: Attenuation varies with photon energy and the material’s composition and density.
Question 49. Which of the following is a primary source of heat in a nuclear fission reactor? A) Chemical combustion of fuel B) Kinetic energy of fission fragments deposited in fuel C) Friction between coolant pumps D) Solar radiation absorbed by the reactor vessel Answer: B Explanation: The kinetic energy of fission fragments is converted to heat as they slow down in the fuel. Question 50. The “neutron flux” is measured in: A) Becquerels (Bq) B) Neutrons per square centimeter per second (n·cm⁻²·s⁻¹) C) Grays (Gy) D) Coulombs (C) Answer: B Explanation: Neutron flux quantifies the number of neutrons passing through a unit area per unit time. Question 51. In a nuclear plant, the “feedwater pump” serves to: A) Circulate primary coolant through the reactor core B) Supply water to the steam generator where it is turned into steam C) Remove spent fuel from the pool D) Control the reactivity of the core Answer: B Explanation: Feedwater pumps deliver water to the secondary side of the steam generator for steam production.
Explanation: Fast reactors avoid moderation, using liquid metal (e.g., sodium) to transfer heat while preserving fast neutrons. Question 55. The “dose equivalent” takes into account: A) Only the absorbed energy in tissue B) Radiation type weighting factor and tissue sensitivity C) The decay constant of the source D) The distance from the source only Answer: B Explanation: Dose equivalent = absorbed dose × radiation weighting factor × tissue weighting factor. Question 56. In the context of nuclear licensing, “30‑day reporting” refers to: A) Submitting daily operational logs for 30 days after startup B) Reporting any safety‑significant event within 30 days to the regulator C) Providing quarterly financial statements for 30 days before the audit D) Updating the public about radiation levels every 30 days Answer: B Explanation: Regulators require that significant safety events be reported within a set timeframe, often 30 days. Question 57. Which of the following is an example of a “low‑level waste” (LLW)? A) Spent nuclear fuel assemblies B) Contaminated protective clothing and tools C) Reactor pressure vessel steel D) High‑activity liquid waste from reprocessing Answer: B
Explanation: LLW includes items with relatively low radioactivity, such as contaminated garments. Question 58. The “reactor protection system” (RPS) primarily monitors: A) Weather conditions at the plant site B) Parameters such as neutron flux, coolant temperature, and pressure to initiate automatic shutdowns C) Employee attendance records D) Fuel enrichment levels during operation Answer: B Explanation: RPS continuously checks critical safety parameters and trips the reactor if limits are exceeded. Question 59. Which of the following best defines “critical mass”? A) The mass of fuel required to achieve k_eff = 0. B) The minimum amount of fissile material needed to sustain a chain reaction under specified conditions C) The total mass of all fuel in a reactor core D) The mass of coolant needed to remove heat from the core Answer: B Explanation: Critical mass is the smallest quantity of fissile material that can maintain a self‑sustaining neutron chain reaction. Question 60. During a “fuel handling outage,” which activity is performed? A) Refueling the reactor core with fresh assemblies and removing spent ones B) Painting the containment building exterior C) Upgrading the turbine blades with new alloys
