Question 1

Indian PHWRs like RAPP-7 rely on heavily enriched uranium imported from other nations.

Accepted Answer

PHWRs use unenriched, natural uranium (containing only about 0.7 percent U-235). The design compensates for this low fissile content by using heavy water, which captures very few neutrons.

Question 2

The 'fleet mode' refers to mobile or floating nuclear reactors built in the ocean.

Accepted Answer

In nuclear policy, 'fleet mode' means building a batch of identical land-based reactors (like the ten 700 MW PHWRs approved in 2017) simultaneously using standard designs and bulk component procurement.

Question 3

Consider the following statements regarding India's nuclear power programme:
1. The 700 MW Pressurized Heavy Water Reactors (PHWRs) sanctioned under 'fleet mode' use ordinary water as a coolant and heavy water as a moderator.
2. Under Stage II of India's Three-Stage Nuclear Programme, Fast Breeder Reactors (FBRs) use Plutonium-239 to breed Thorium-232 into Uranium-233.
3. The Atomic Energy Regulatory Board (AERB) derives its regulatory powers from the Atomic Energy Act, 1962.
How many of the above statements are correct?

Accepted Answer

(b) Only two — Statement 1 is incorrect: PHWRs use heavy water (Deuterium Oxide) as BOTH the primary coolant and the neutron moderator. Statement 2 is correct: Stage II uses FBRs to process Pu-239 (derived from Stage I) to breed Thorium into U-233. Statement 3 is correct: The AERB is the independent regulatory body established under the Atomic Energy Act, 1962.

Question 4

Match the Nuclear Power Project (List I) with its specific attribute or State (List II):
List I:
A. Rawatbhata (RAPP)
B. Kakrapar (KAPS)
C. Gorakhpur (GHAVP)
D. Kudankulam (KKNPP)

List II:
1. Site of India's first operational indigenous 700 MW PHWRs (Units 3 & 4)
2. Operates Russian-assisted VVER Light Water Reactors
3. Site of the recently synchronized Unit-7 700 MW PHWR
4. Fleet mode PHWRs currently under construction in Haryana

Accepted Answer

(a) A-3, B-1, C-4, D-2 — Rawatbhata (RAPP) in Rajasthan is the site for the newly synchronized Unit-7 (A-3). Kakrapar (KAPS) in Gujarat hosts Units 3 & 4, the very first 700 MW PHWRs (B-1). Gorakhpur (GHAVP) is in Haryana where fleet mode reactors are being built (C-4). Kudankulam operates imported Russian VVER reactors, which are LWRs (D-2).

Question 5

Assertion (A): The indigenous 700 MW PHWRs are capable of sustaining a nuclear chain reaction using natural, unenriched uranium.
Reason (R): Heavy water (Deuterium Oxide) used in PHWRs has a very low neutron absorption cross-section, allowing fast neutrons to be thermalized without being lost from the reaction cycle.
Select the correct answer:

Accepted Answer

(a) Both A and R are true and R is the correct explanation of A. — Natural uranium contains only about 0.7% of the fissile isotope U-235. To sustain a chain reaction with such a low concentration, you cannot afford to lose neutrons to the moderator. Ordinary water absorbs too many neutrons, requiring enriched uranium. Heavy water, however, rarely absorbs neutrons, making it the perfect moderator to slow down fast neutrons and sustain the reaction in natural uranium (Assertion A is true, Reason R is true, and R explains A).

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