• India’s third home-built 700 MWe nuclear power reactor has achieved criticality and is expected to start commercial electricity generation soon, Nuclear Power Corporation of India Limited (NPCIL) said.

• The nuclear power reactor that achieved criticality on September 19 is the first of a new series of Pressurised Heavy Water Reactors (PHWRs) to be built at Rajasthan Atomic Power Project in Rawatbhata.

• Earlier, two 700 MWe PHWRs started commercial operation at Kakrapar Atomic Power Station (KAPS) in Gujarat.

• The NCPIL said RAPP-7 was the third in the series of 16 indigenous PHWRs of 700 MWe each being set up in the country. 

• These reactors are part of India’s ongoing nuclear power expansion efforts. 

• Prior to RAPP-7, the first two reactors in this series to become critical were Units 3 and 4 of the Kakrapar Atomic Power Station in Gujarat, which achieved criticality in 2020 and 2023, respectively.

What do you mean by criticality?

• Criticality is the normal operating condition of a reactor, in which nuclear fuel sustains a fission chain reaction. A reactor achieves criticality (and is said to be critical) when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions. It means the plant is now set to generate power.

Rajasthan Atomic Power Plant (RAPP):

• The agreement for India’s first nuclear power plant, Rajasthan Atomic Power Plant Unit-1 (RAPP-1), was signed in 1963, followed by the agreement for RAPP-2 in 1966. 

• Located in Rajasthan, these reactors were developed with specific safeguards in place to ensure that they could not be used for military purposes. RAPP-1 officially began operations in 1972, marking a significant milestone in India’s nuclear energy program.

• The RAPP 7 & 8 project is being set up in Rawatbhata, where six units with a total capacity of 1,180 MWe are already in operation.

• NPCIL currently operates 24 reactors with a total capacity of 8,180 MWe and has eight units (including RAPP-7) with a capacity of 6,800 MWe under construction.

• In addition, 10 more reactors with a total capacity of 7,000 MWe are in pre-project phase and are expected to be completed progressively by 2031-32.

Pressurised Heavy Water Reactor (PHWR) Structure:

• Pressurised Heavy Water Reactors (PHWRs) offer several advantages, including the ability to use natural uranium as fuel, which eliminates the need for complex and expensive fuel enrichment facilities. 

• Countries with an abundance of heavy water can benefit from PHWRs due to their relatively low uranium requirements, both for the initial reactor core and for subsequent refueling. 

• Additionally, PHWRs produce more fissile plutonium compared to reactors like Light Water Reactors (LWRs), which can be advantageous in certain nuclear fuel cycles.

• A PHWR is a horizontal pressure tube reactor that uses natural uranium dioxide as fuel. 

• Heavy water (deuterium oxide) serves as both the moderator and the coolant, maintained at low pressure and temperature. The reactor operates by transferring heat from the fuel to the heavy water coolant. 

• This heat is then transferred to a secondary loop using light water, which is used to produce steam that drives the turbine.

• To optimise the power output of the reactor, several design features are employed, such as improving the fuel’s linear heat rating and using flux flattening techniques to achieve a more even distribution of power across the reactor core. 

• Additional heat extraction is made possible by allowing the coolant to boil near the channel exit, increasing the efficiency of heat transfer.

• Overall, the same reactor design and primary coolant loop are capable of generating thermal energy equivalent to 700 MW of electrical power (MWe), making PHWRs a reliable and efficient choice for nuclear energy generation.

List of operational nuclear power sites in India:

1) Kakrapar Atomic Power Station 

Commissioned: 1993 

Location: Gujarat 

Operator: NPCIL 

2) Madras Atomic Power Station (Kalpakkam) 

Commissioned: 1984 

Location: Tamil Nadu 

Operator: NPCIL 

3) Narora Atomic Power Station 

Commissioned: 1991 

Location: Uttar Pradesh 

Operator: NPCIL 

4) Kaiga Nuclear Power Plant 

Commissioned: 2000 

Location: Karnataka 

Operator: NPCIL 

5) Rajasthan Atomic Power Station 

Commissioned: 1973 

Location: Rajasthan 

Operator: NPCIL 

6) Tarapur Atomic Power Station 

Commissioned: 1969 

Location: Maharashtra 

Operator: NPCIL 

7) Kudankulam Nuclear Power Plant 

Commissioned: 2013 

Location: Tamil Nadu 

Operator: NPCIL.

(The author is a trainer for Civil Services aspirants.)