Pressurized Heavy Water Reactor (PHWR)
India currently operates 24 reactors with a total capacity of 8,180 MWe. Eight additional units, of which RAPP-7 is one, are under construction, adding 6,800 MWe. Plans for 10 more reactors are in the pre-project phase to be progressively completed by 2031-32.
PHWR
This is a nuclear reactor that utilizes heavy water as the moderator and coolant. Natural uranium serves as the fuel. This has high pressure in order to liquefy the heavy water for an enhanced heat transfer and efficiency. Heavy water is a form of water whose hydrogen atoms are all deuterium and not the common hydrogen-1 isotope that makes up most of the hydrogen in normal water.
Key Features
- Fuel: Natural uranium is typically used, eliminating the need for enriched uranium.
- Coolant/Moderator: Heavy water serves dual functions, slowing neutrons and transferring heat.
- PHWRs use pressure tubes, which enable the reactor to operate at high pressures while keeping the coolant and moderator separated. This distinguishes it from Light Water Reactors.
Working Principle
- Fission Reaction: Neutrons generated from uranium fuel are slowed by the heavy water, allowing them to sustain a chain reaction.
- Heat Generation: Fission produces heat, which is absorbed by the pressurized heavy water circulating through the reactor core.
- Heat Transfer: This heat is transferred to a secondary system, where ordinary water is heated to produce steam, which then drives turbines for electricity generation.
Advantages of PHWR
- PHWRs can use natural uranium, reducing the need for fuel enrichment facilities.
- Unlike other reactors, PHWRs can be refueled without shutting down.
- PHWRs have the potential to use different types of fuel, including mixed oxide (MOX) fuel and thorium, which is abundant in India.
Disadvantages
- Heavy water is expensive to produce and maintain due to its isotopic composition.
- The use of pressure tubes adds complexity to the reactor’s design and increases maintenance needs.
Global Usage
PHWRs are predominantly used in Canada (CANDU reactors) and India.
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