njnir.com Pressurized Heavy Water Reactors (PHWRs) use heavy water (deuterium oxide) as both coolant and moderator, enabling better neutron economy and allowing the use of natural uranium as fuel. Pressurized Light Water Reactors (PWRs) utilize ordinary light water for cooling and moderation, requiring enriched uranium to sustain the chain reaction efficiently. PHWRs offer advantages in fuel flexibility and neutron efficiency, while PWRs benefit from simpler design and widespread commercial use.
Table of Comparison
| Feature | Pressurized Heavy Water Reactor (PHWR) | Pressurized Light Water Reactor (PWR) |
|---|---|---|
| Moderator | Heavy Water (D2O) | Light Water (H2O) |
| Coolant | Heavy Water (D2O) | Light Water (H2O) |
| Fuel Type | Natural Uranium or Slightly Enriched Uranium | Enriched Uranium (3-5%) |
| Operating Pressure | ~10 MPa | 15.5 MPa |
| Thermal Efficiency | ~30-32% | ~33-37% |
| Neutron Economy | High (due to heavy water use) | Lower (due to light water absorption) |
| Fuel Cycle | Can utilize natural uranium and thorium | Requires enriched uranium, limited thorium use |
| Refueling | Online refueling possible | Typically offline refueling |
| Common Countries | India, Canada | USA, France, Japan |
| Safety Features | Lower pressure vessel design, inherent safety features | Robust reactor vessel, multiple safety systems |
Introduction to Nuclear Reactor Types
Pressurized Heavy Water Reactors (PHWRs) use heavy water (D2O) as both coolant and moderator, enabling the use of natural uranium as fuel without enrichment. Pressurized Light Water Reactors (PWRs) employ ordinary light water as coolant and moderator, requiring enriched uranium fuel to sustain the fission process. PHWRs offer advantages in fuel flexibility and neutron economy, while PWRs dominate the global nuclear power market due to their well-established technology and higher operating pressures.
Basic Principles of Pressurized Heavy Water Reactors (PHWR)
Pressurized Heavy Water Reactors (PHWR) use heavy water (D2O) as both coolant and moderator, enabling natural uranium fuel without enrichment. The high neutron economy of PHWRs allows efficient fuel utilization and on-line refueling, enhancing operational flexibility. Pressurized Light Water Reactors (PWR), by contrast, use light water as coolant and moderator, requiring enriched uranium fuel due to higher neutron absorption.
Fundamentals of Pressurized Light Water Reactors (PWR)
Pressurized Light Water Reactors (PWRs) use ordinary water as both coolant and neutron moderator, maintaining high pressure to prevent boiling within the reactor core, which enhances heat transfer efficiency and reactor stability. The fundamental design includes a primary coolant loop that circulates pressurized water through the reactor core and a secondary loop where steam is generated to drive turbines, ensuring separation of radioactive water from the turbine system. PWRs commonly utilize enriched uranium fuel, rely on zirconium alloy cladding, and achieve controlled fission through boron and control rod insertion, making them the most widely deployed reactor type globally due to their mature technology and safety features.
Fuel Types and Fuel Cycle Differences
Pressurized Heavy Water Reactors (PHWRs) primarily use natural uranium as fuel, leveraging heavy water (deuterium oxide) as both coolant and moderator, which enables efficient neutron economy and prolonged fuel cycles. Pressurized Light Water Reactors (PWRs) utilize enriched uranium fuel, typically 3-5% U-235, requiring a more intensive fuel enrichment process and shorter fuel cycles compared to PHWRs. The ability of PHWRs to use natural uranium reduces fuel fabrication costs and supports on-line refueling, contrasting with PWRs' need for periodic shut-downs for fuel replacement.
Moderator and Coolant: Heavy Water vs. Light Water
Pressurized Heavy Water Reactors (PHWRs) utilize heavy water (D2O) as both moderator and coolant, enhancing neutron economy due to heavy water's low neutron absorption properties, which allows the reactor to use natural uranium fuel. In contrast, Pressurized Light Water Reactors (PWRs) use ordinary light water (H2O) as the moderator and coolant, which absorbs more neutrons, necessitating enriched uranium fuel to sustain the chain reaction. The choice of heavy water in PHWRs improves fuel efficiency and neutron moderation, while light water in PWRs offers simpler reactor design and widespread fuel availability.
Reactor Design and Core Configuration
Pressurized Heavy Water Reactors (PHWRs) utilize heavy water (D2O) as both a moderator and coolant, allowing the use of natural uranium fuel, resulting in a unique core design with vertical pressure tubes and a distributed modular configuration. Pressurized Light Water Reactors (PWRs) use light water as both moderator and coolant, requiring enriched uranium fuel, with a reactor vessel containing a monolithic core composed of fuel assemblies arranged in a compact grid pattern. The heavy water moderator in PHWRs enables on-line refueling and flexible fuel management, whereas PWR cores are designed for batch refueling cycles with more extensive control rod insertion for reactivity control.
Efficiency and Thermal Performance Comparison
Pressurized Heavy Water Reactors (PHWRs) utilize heavy water (D2O) as both moderator and coolant, enabling the use of natural uranium fuel and achieving thermal efficiencies typically around 30-32%. Pressurized Light Water Reactors (PWRs) use ordinary light water for moderation and cooling, requiring enriched uranium but delivering comparable thermal efficiency in the range of 33-37%. The higher neutron economy in PHWRs allows better fuel utilization, while PWRs benefit from higher operating pressures and temperatures, enhancing thermal performance despite the need for enriched fuel.
Safety Features and Operational Risks
Pressurized Heavy Water Reactors (PHWRs) use heavy water (deuterium oxide) as both coolant and moderator, enhancing neutron economy and allowing use of natural uranium fuel, which reduces reactivity risks and improves safety margins under normal operations. Pressurized Light Water Reactors (PWRs) utilize ordinary light water as coolant and moderator, requiring enriched uranium fuel, with robust containment structures and multiple redundant safety systems to mitigate loss-of-coolant accidents and control reactivity excursions. Operational risks in PHWRs include potential heavy water leaks and radiological hazards, whereas PWRs face challenges like pressurizer malfunctions and core damage risks, addressed through advanced instrumentation and emergency core cooling systems (ECCS).
Economic Considerations and Deployment
Pressurized Heavy Water Reactors (PHWRs) typically offer lower fuel costs due to their ability to use natural uranium, reducing enrichment expenses compared to Pressurized Light Water Reactors (PWRs) which require enriched uranium fuel. PHWRs have higher initial capital investment attributable to complex heavy water production and handling but benefit from flexible fuel usage and longer fuel cycles, enhancing overall economic efficiency in the long term. Deployment of PHWRs is more common in countries with indigenous uranium resources and heavy water expertise, while PWRs dominate global markets owing to standardized designs and established supply chains ensuring faster construction timelines and operational scalability.
Environmental Impact and Waste Management
Pressurized Heavy Water Reactors (PHWRs) utilize heavy water as a moderator, resulting in higher neutron economy and the ability to use natural uranium fuel, which reduces mining impacts and uranium enrichment emissions compared to Pressurized Light Water Reactors (PLWRs). Waste management in PHWRs typically produces spent fuel with higher fissile content, allowing for better recycling potential but requiring specialized reprocessing techniques to handle tritium contamination from heavy water. PLWRs generate spent fuel with lower fissile content but more uniform waste streams, often facilitating established storage and disposal methods, though their reliance on enriched uranium entails higher upstream environmental impacts.
Moderator (D₂O vs H₂O)
Pressurized Heavy Water Reactors (PHWR) use heavy water (D2O) as a neutron moderator and coolant, enabling them to utilize natural uranium fuel efficiently, while Pressurized Light Water Reactors (PWR) use ordinary water (H2O) as both moderator and coolant, requiring enriched uranium fuel due to higher neutron absorption.
Coolant type
Pressurized Heavy Water Reactors (PHWRs) use heavy water (D2O) as coolant, providing superior neutron moderation and allowing use of natural uranium fuel, while Pressurized Light Water Reactors (PWRs) utilize ordinary light water (H2O) as coolant, necessitating enriched uranium fuel due to lower neutron moderation.
Fuel enrichment (natural uranium vs enriched uranium)
Pressurized heavy water reactors use natural uranium as fuel, whereas pressurized light water reactors require enriched uranium to achieve criticality.
Neutron economy
Pressurized heavy water reactors (PHWRs) exhibit superior neutron economy compared to pressurized light water reactors (PWRs) due to heavy water's lower neutron absorption cross-section, enabling more efficient fuel utilization and the use of natural uranium fuel.
Online refueling capability
Pressurized heavy water reactors (PHWRs) enable efficient online refueling due to their heavy water moderator and natural uranium fuel, contrasting with pressurized light water reactors (PWRs) that require shutdown for refueling because of their light water moderator and enriched uranium fuel design.
Calandria vessel
The Calandria vessel in a Pressurized Heavy Water Reactor (PHWR) is a key component containing heavy water moderator at low pressure, differing from the Pressurized Light Water Reactor (PWR) where the reactor core is submerged in high-pressure light water without a separate Calandria vessel.
Reactivity control mechanisms
Pressurized Heavy Water Reactors (PHWRs) utilize heavy water both as a moderator and coolant, enabling effective reactivity control through adjuster rods and liquid zone controllers, whereas Pressurized Light Water Reactors (PWRs) primarily rely on chemical shim (boric acid concentration) and control rods for precise reactivity management.
Pressure tube reactor
Pressure tube reactors, a type of pressurized heavy water reactor, use heavy water as both coolant and moderator and feature pressure tubes to contain the fuel, unlike pressurized light water reactors which use light water as coolant and moderator and have a large pressure vessel.
Tritium production
Pressurized Heavy Water Reactors (PHWRs) produce significantly higher levels of tritium due to neutron absorption in heavy water (D2O), whereas Pressurized Light Water Reactors (PWRs) generate lower tritium quantities because of light water (H2O) coolant and moderator characteristics.
CANDU reactor design
The CANDU reactor, a pressurized heavy water reactor (PHWR), uses heavy water as both coolant and moderator, enabling on-line refueling and use of natural uranium fuel, unlike pressurized light water reactors (PWRs) that require enriched uranium and use light water for both functions.
pressurized heavy water reactor vs pressurized light water reactor Infographic
