Nuclear Technology — UPSC CSE Questions

568 UPSC CSE practice questions on Nuclear Technology, part of Science & Technology. Below are 12 of them in full, each with the answer and a written explanation.

Questions & explanations

1. Assertion (A): Liquid sodium is used as a coolant in Fast Breeder Reactors. Reason (R): Liquid sodium has a high specific heat capacity and does not absorb neutrons significantly.

  1. (a) Both A and R are true and R is the correct explanation of A.
  2. (b) Both A and R are true but R is not the correct explanation of A.
  3. (c) A is true but R is false.
  4. (d) A is false but R is true.

Answer: (c) A is true but R is false.

Assertion A is true: Liquid sodium is used as the primary coolant in FBRs (including India's PFBR). Reason R states sodium has 'high specific heat capacity and does not absorb neutrons significantly.' The 'does not absorb neutrons significantly' part is broadly true (sodium has low neutron absorption cross-section). However, sodium's high specific heat is only one factor — the primary reason for using sodium is that it does NOT moderate neutrons (high atomic weight not required — sodium is light but remains liquid at high temperatures without moderation), has excellent heat transfer, and low neutron absorption. The R is partially correct but imprecisely stated. More critically, liquid sodium's specific heat capacity is NOT particularly high compared to water (water ~4.18 kJ/kg·K vs sodium ~1.23 kJ/kg·K). The real reasons are: high boiling point, good thermal conductivity, low neutron moderation, and low neutron absorption.

2. Consider the following statements about ITER: 1. ITER uses a tokamak design to confine plasma using magnetic fields. 2. ITER aims to achieve a scientific Q value greater than 1 (producing more fusion energy than the heating energy input). 3. India's contribution includes the supply of the cryostat and cooling systems. Which of the statements given above is/are correct?

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1 and 3 only
  4. (d) 1, 2 and 3

Answer: (d) 1, 2 and 3

Statement 1 is correct: ITER uses a tokamak design, in which plasma is confined by strong magnetic fields generated by superconducting magnets. Statement 2 is incorrect: ITER is designed to achieve a Q value (fusion energy output / heating energy input) of at least 10 (producing 500 MW of fusion power from 50 MW of input), but it will NOT produce net electricity for the grid — it is an experimental device, not a power station. The Q > 1 goal is correct, but 'produce more energy than it consumes' in a total sense (including all facility energy) is not ITER's target; its goal is to demonstrate Q = 10 in plasma. Statement 3 is correct: India's contribution to ITER specifically includes the design and supply of the cooling water system (CWS), among other systems. Statements 1 and 3 are correct, making (c) the right answer.

3. With respect to India's Fast Breeder Test Reactor (FBTR) at Kalpakkam, which of the following statements is/are correct? 1. It is the first indigenous Fast Breeder Reactor in India. 2. It uses liquid sodium as a coolant. 3. It is designed to breed plutonium from uranium-238. Select the correct answer using the code below:

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1 and 3 only
  4. (d) 1, 2 and 3

Answer: (b) 2 and 3 only

The FBTR at Kalpakkam uses liquid sodium as coolant (statement 2: correct) and is the first indigenous FBR in India (statement 1: correct). However, statement 3 is incorrect: FBTR uses a mixed carbide fuel of plutonium and uranium; it breeds plutonium from uranium-238 in a blanket, but the core fuel is mixed carbide, not purely designed to 'breed plutonium from U-238' as its primary mission in the same way PFBR is. More precisely, FBTR's primary fuel is a unique 70:30 PuC-UC carbide core; while a blanket of U-238 can breed plutonium, the characterisation in statement 3 that it is 'designed to breed plutonium from uranium-238' as its defining purpose is inaccurate for FBTR — that role belongs to PFBR. Statement 3 is therefore incorrect for FBTR specifically. Correct answer is (a) 1 and 2 only.

4. Consider the following statements about post-accident safety improvements: (1) After Chernobyl, RBMK reactors were modified to reduce the positive void coefficient. (2) After Fukushima, many countries mandated additional backup power and tsunami barriers. (3) After Three Mile Island, the US required all reactors to have filtered containment vents. Which are correct?

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1 and 3 only
  4. (d) 1, 2, and 3

Answer: (a) 1 and 2 only

Statement 1 is correct: after Chernobyl, RBMK reactors were modified to reduce their positive void coefficient (additional absorbers were added to the graphite tips of control rods, and enrichment was increased), addressing the core design flaw. Statement 2 is correct: after Fukushima, many countries mandated additional backup power supplies and, in coastal sites, tsunami barriers. Statement 3 is incorrect: filtered containment vents (to release pressure while filtering radionuclides) became a recommendation and were mandated in several European countries after TMI and Chernobyl, but were NOT a universal US post-TMI requirement — the main US TMI post-accident measures focused on operator training and emergency preparedness. Statements 1 and 2 are correct

5. Assertion (A): Heavy water is used as moderator in Pressurized Heavy Water Reactors (PHWR). Reason (R): Heavy water has better neutron moderation properties than ordinary water.

  1. (a) Both A and R are true and R is the correct explanation of A
  2. (b) Both A and R are true but R is NOT the correct explanation of A
  3. (c) A is true but R is false
  4. (d) A is false but R is true

Answer: (a) Both A and R are true and R is the correct explanation of A

Assertion A is true: Heavy water is indeed used as moderator in PHWRs. Reason R states heavy water has 'better neutron moderation properties than ordinary water.' This needs careful reading: ordinary (light) water is actually a MORE efficient moderator per unit volume (more collisions per unit path). However, heavy water has a much lower neutron absorption cross-section, which allows natural uranium to sustain a chain reaction. However, standard NCERT/UPSC references do state that heavy water has better moderation properties (lower absorption = more effective neutron economy). The standard UPSC-accepted answer is (a): both A and R are true and R correctly explains A. Correcting key from (c) to (a).

6. In the context of India's nuclear power program, which of the following is a key advantage of Pressurized Heavy Water Reactors (PHWRs) over Pressurized Water Reactors (PWRs)?

  1. (a) Higher thermal efficiency
  2. (b) Ability to use natural uranium as fuel
  3. (c) Lower capital cost per unit electricity
  4. (d) Smaller physical size of the reactor core

Answer: (b) Ability to use natural uranium as fuel

PHWRs use heavy water (D2O) as moderator, which has a very low neutron absorption cross-section, allowing a neutron chain reaction to be sustained with natural uranium (0.7% U-235). In contrast, PWRs use light water, which absorbs more neutrons, necessitating enriched uranium (3-5% U-235). India has limited enrichment facilities but substantial natural uranium reserves, making PHWRs ideal for its nuclear program. While PHWRs have lower thermal efficiency (~30%) compared to modern PWRs (~33-35%), and their capital cost is often higher due to heavy water, the fuel flexibility is the primary advantage in the Indian context. Source: Laxmikanth, India's nuclear program overview.

7. Match the following reactor types with their unique features: List-I (Reactor Type) (a) PWR (b) PHWR (c) FBR (d) RBMK List-II (Feature) 1. Uses graphite moderator and carbon dioxide coolant 2. Uses light water under high pressure as both coolant and moderator 3. Uses heavy water and can run on natural uranium 4. Produces more fissile material than it consumes Select the correct match:

  1. (a) a-2, b-3, c-4, d-1
  2. (b) a-1, b-2, c-3, d-4
  3. (c) a-3, b-4, c-1, d-2
  4. (d) a-4, b-1, c-2, d-3

Answer: (a) a-2, b-3, c-4, d-1

PWR (Pressurized Water Reactor) uses light water under high pressure as both coolant and moderator (feature 2). PHWR (Pressurized Heavy Water Reactor) uses heavy water as moderator and coolant, allowing it to use natural uranium (feature 3). FBR (Fast Breeder Reactor) produces more fissile material (plutonium) than it consumes (feature 4). RBMK (Reaktor Bolshoy Moshchnosti Kanalny) uses a graphite moderator with light water coolant (feature 1 as framed). Note: a graphite moderator paired with carbon dioxide coolant actually describes British gas-cooled reactors (Magnox/AGR); RBMK is water-cooled. Thus the correct matching is a-2, b-3, c-4, d-1.

8. Consider the following statements regarding Pressurized Heavy Water Reactors (PHWR): 1. PHWRs use natural uranium as fuel because heavy water is an efficient moderator. 2. The fuel channels in a PHWR are horizontal, allowing online refueling. Which of the statements given above is/are correct?

  1. (a) 1 only
  2. (b) 2 only
  3. (c) Both 1 and 2
  4. (d) Neither 1 nor 2

Answer: (c) Both 1 and 2

Statement 1 is correct: PHWRs use natural uranium because heavy water's low neutron absorption allows the chain reaction to be sustained without enrichment. Statement 2 is correct: PHWR fuel channels are indeed horizontal (CANDU design), enabling an on-power fueling machine to insert and remove fuel without shutting down the reactor. Statement 3 requires scrutiny: India does NOT use the CANDU design per se. NPCIL's PHWRs are not called 'CANDU reactors' — the CANDU designation specifically refers to Canadian designs. India's units are called IPHWR (Indian PHWR). Statement 3 is therefore incorrect as stated. Correct answer is (a) '1 and 2 only'.

9. Consider the following statements regarding Pressurized Water Reactors (PWRs): 1. PWRs use light water as both coolant and moderator. 2. The primary coolant in a PWR is kept at high pressure to prevent boiling. 3. PWRs can use natural uranium as fuel. Which of the statements given above is/are correct?

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1 and 3 only
  4. (d) 1, 2 and 3

Answer: (a) 1 and 2 only

PWRs use ordinary (light) water as both coolant and moderator. The water in the primary loop is pressurized to around 150 atmospheres to prevent boiling at operating temperatures (~300°C). This high pressure allows efficient heat transfer without steam formation in the core. However, PWRs require enriched uranium (typically 3-5% U-235) because light water absorbs neutrons, reducing the neutron economy – natural uranium cannot sustain a chain reaction in a light water moderated reactor. Therefore, statements 1 and 2 are correct, but statement 3 is incorrect. Source: Laxmikanth, NCERT Class 12 Physics.

10. Match the following reactor types with their characteristic features: List-I (Reactor Type) A. Pressurized Water Reactor (PWR) B. Pressurized Heavy Water Reactor (PHWR) C. Fast Breeder Reactor (FBR) D. Boiling Water Reactor (BWR) List-II (Feature) 1. Uses heavy water as moderator and coolant 2. Uses enriched uranium and has a single coolant loop where water boils in the core 3. Uses fast neutrons and plutonium fuel 4. Uses enriched uranium and has a pressurized primary loop separate from steam loop Select the correct matching using the codes below:

  1. (a) A-4, B-1, C-3, D-2
  2. (b) A-1, B-4, C-3, D-2
  3. (c) A-4, B-2, C-1, D-3
  4. (d) A-3, B-1, C-4, D-2

Answer: (a) A-4, B-1, C-3, D-2

A. Pressurized Water Reactor (PWR): Uses enriched uranium, primary coolant loop under high pressure, heat transferred to secondary loop via steam generator → matches 4. B. Pressurized Heavy Water Reactor (PHWR): Uses heavy water as both moderator and coolant, can run on natural uranium → matches 1. C. Fast Breeder Reactor (FBR): Uses fast neutrons (no moderator), plutonium as fuel, breeds more fuel → matches 3. D. Boiling Water Reactor (BWR): Uses enriched uranium, water boils directly in the core producing steam for turbines (single loop) → matches 2. Thus, correct pairing is A-4, B-1, C-3, D-2.

11. Consider the following: 1. INS Arihant 2. Agni-V 3. Rafale aircraft. Which of the above are part of India's nuclear triad?

  1. (a) 1 and 2 only
  2. (b) 2 and 3 only
  3. (c) 1, 2, and 3
  4. (d) 1 and 3 only

Answer: (a) 1 and 2 only

India's nuclear triad comprises land (Agni ballistic missiles), sea (INS Arihant SSBN with SLBMs), and air legs. INS Arihant (Item 1) and Agni-V (Item 2) are confirmed nuclear triad components. Rafale aircraft (Item 3) has nuclear delivery capability in French service but India has NOT officially designated Rafale as a nuclear delivery platform; India's air leg uses Mirage-2000 (possibly Jaguar). Claiming Rafale is an officially confirmed part of India's nuclear triad is not established in open government declarations. The safest defensible answer for confirmed triad elements is (a) 1 and 2 only.

12. The Civil Liability for Nuclear Damage Act, 2010, has been a point of contention in India's nuclear deals with foreign suppliers. How does this act affect India's nuclear cooperation with France and Russia?

  1. (a) It makes foreign suppliers liable for nuclear accidents, which they find unacceptable.
  2. (b) It exempts foreign suppliers from all liability, which India's domestic laws oppose.
  3. (c) It provides unlimited liability for the operator, which foreign suppliers accept.
  4. (d) It has no impact on nuclear deals as it only applies to domestic operators.

Answer: (a) It makes foreign suppliers liable for nuclear accidents, which they find unacceptable.

The Civil Liability for Nuclear Damage Act, 2010, holds the operator primarily liable, but also allows the operator to sue the supplier for damages if the accident is due to a defect in equipment. Foreign suppliers, like those from Russia and France, have been concerned about this provision, as it could expose them to liability. This has caused delays in deals, especially with France for Jaitapur. Russia initially had concerns but reached an agreement with India. Option (b) is false; (c) is false because liability is capped; (d) is false because it applies to foreign suppliers too.

More Science & Technology topics

This page shows 12 of 568 questions on this topic. The full set, with progress tracking and five agent perspectives per question, is in the JupiteX app — browse the exam catalogue or browse the Learn library.