Pressurized Water Reactor
Overview
The Pressurized Water Reactor (PWR) is the most common type of nuclear reactor worldwide, accounting for about 65% of all nuclear power plants. It uses ordinary water as both coolant and neutron moderator, operating under high pressure to prevent boiling in the reactor core—a design that emerged from Admiral Rickover’s nuclear navy and now powers millions of homes globally.
Basic Design
Primary Loop
- Reactor pressure vessel: Contains the nuclear fuel and control rods
- Steam generators: Heat exchangers that transfer heat to secondary loop
- Primary pumps: Circulate water through the reactor core
- Pressurizer: Maintains system pressure (~2,250 psi)
Secondary Loop
- Steam generators: Convert feedwater to steam
- Turbine-generator: Steam drives turbine to produce electricity
- Condenser: Converts steam back to water
- Feedwater pumps: Return water to steam generators
Key Features
Water Under Pressure
- Primary coolant: Pressurized to ~2,250 psi (155 bar)
- Temperature: ~300°C (572°F) without boiling
- Subcooled water: Remains liquid throughout primary loop
Two-Loop System
- Primary loop: Radioactive, contained within reactor building
- Secondary loop: Clean steam, drives turbine
- Separation barrier: Steam generators isolate radioactive primary water
Safety Systems
Engineered Safety Features
- Emergency core cooling: Multiple backup cooling systems
- Containment structure: Steel-lined concrete building
- Control rod insertion: Rapid shutdown capability
- Reactor protection system: Automatic safety responses
Passive Safety Features
- Negative temperature coefficient: Reactor power decreases as temperature rises
- Negative void coefficient: Power decreases if water turns to steam
- Delayed neutrons: Allow time for control system response
Fuel and Core Design
Fuel Assemblies
- Uranium dioxide pellets: Ceramic fuel form
- Zircaloy cladding: Corrosion-resistant fuel rods
- Control rod assemblies: Neutron-absorbing materials
- Fuel enrichment: Typically 3-5% U-235
Core Configuration
- Fuel assembly array: Usually 15×15 or 17×17 rod arrays
- Core lifetime: 18-24 month operating cycles
- Refueling: Typically 1/3 of core replaced each cycle
Advantages
Safety
- Proven technology: Decades of safe operation
- Passive safety features: Inherent physics provide safety margin
- Redundant systems: Multiple backup safety systems
Operations
- Load following: Can adjust power output for grid demand
- High availability: Typical capacity factors >90%
- Standardized design: Reduced costs and improved safety
Disadvantages
Economics
- High capital costs: Expensive to build
- Long construction times: 5-10 years typical
- Complex licensing: Extensive regulatory requirements
Technical
- Pressure vessel limitations: High pressure requires thick steel
- Steam generator maintenance: Heat exchanger tube problems
- Neutron economy: Water absorbs neutrons, reducing efficiency
Variants
Generation II
- Westinghouse PWR: Original commercial design
- Framatome PWR: French variant (N4, EPR)
- Mitsubishi PWR: Japanese variant
Generation III+
- AP1000: Westinghouse advanced design
- EPR: European Pressurized Reactor
- APR1400: Korean advanced design
Global Deployment
Major PWR Countries
- United States: 65 operating PWRs
- France: 58 PWRs (standardized program)
- China: Rapidly expanding PWR fleet
- South Korea: APR1400 technology
Relevance to Nuclear Weapons
PWR technology is relevant to weapons programs because:
- Plutonium production: Can produce weapons-grade plutonium
- Enrichment capability: Requires uranium enrichment infrastructure
- Nuclear technology: Demonstrates nuclear competence
- Dual-use concern: Peaceful nuclear technology can support weapons programs
However, commercial PWRs are not optimized for weapons material production and are subject to international safeguards and monitoring.
Sources
Authoritative Sources:
- World Nuclear Association - Nuclear reactor technology and design
- International Atomic Energy Agency (IAEA) - Nuclear power and safety standards
- Nuclear Regulatory Commission - Reactor licensing and safety
- Electric Power Research Institute (EPRI) - Nuclear technology research
- Westinghouse Electric Company - PWR technology and design