Pressurized Heavy Water Reactors

Pressurized Heavy Water Reactors

News: Recently, India's first indigenously developed 700 MW nuclear power reactor at the Kakrapar Atomic Power Project (KAPP) in Gujarat started commercial operations.

Background:
• The Nuclear Power Corporation of India Limited (NPCIL) is building two 700 MW pressurised heavy water reactors (PHWRs) at Kakrapar.
• The government has sanctioned building of 10 indigenously developed PHWRs in fleet mode at four locations -- Gorakhpur in Haryana, Chutka in Madhya Pradesh, Mahi Banswara in Rajasthan and Kaiga in Karnataka.

What are PHWRs?
• A PHWR is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium.
• The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature without forming steam bubbles, exactly as for a pressurized water reactor.

Why PHWR?
• It uses heavy/hard water as compared to softwater (H2O).
• The advantage of using heavy water is that it has a low absorption of neutrons, which means that more neutrons can cause further nuclear fission in the fuel and sustain a chain reaction. It also ensures that there is an element of safety.
• Fuel flexibility – It uses Natural Uranium U-238. There is no need of enrichment and therefore no headache of international sanctions as well.
• Stable power supply - They can adjust the amount of electricity they produce based on needs of power grid. This helps in keeping the power supply stable, so we don’t have sudden changes in electricity availability.
• Produces useful things – Beyond electricity it also helps in making medical isotopes.

What is difference between PHWR’s and Pressurized water reactors (PWRs)?