Nuclear Energy Overview

Nuclear Energy in the US and World
Overview of Nuclear Energy in the US

  • In 2025, the USA has 94 nuclear reactors across 54 nuclear power plants.

  • These plants produced 782 billion kWh in 2024, constituting over 18.2% of the total electrical output in the country.

  • Nuclear energy stands as the largest source of greenhouse gas (GHG) emission-free electricity, accounting for 18%. Other sources include:

    • Wind: 10.3% - 10.5%

    • Solar: 6.9%

    • Hydropower: 5.5%

    • Biomass/Geothermal: ~1.5%

    • Natural Gas: 42.7%

    • Coal: 14.9%

    • Petroleum & Others: < 1%

Improvements in Plant Performance

  • Continuous enhancement in the performance of nuclear power plants is noted:

    • Capacity factors are reaching approximately 90%.

    • The earliest reactors now entering their 4th decade of operation.

    • Operating licenses for many plants are being extended from 40 years to 60 years.

    • The objective is to maintain average capacity factors at current levels.

New Licensing Process (10 CFR Part 52)

  • Key features of the new licensing process include:

    • Licensing decisions will be made before major construction begins.

    • Inspections are conducted to verify construction.

    • Pre-Construction: Early Site Permit or equivalent site information required.

    • Construction Verification: Standard Design Certification or equivalent design information.

    • Combined License Review: Involves a hearing and decision, along with verification of regulations with Inspections, Tests, Analyses, and Acceptance Criteria (ITAAC).

    • Construction Operating License is eventually issued.

Advanced New Reactor Designs

  • Five new reactor designs are being licensed, with output capacity ranging from 1,100 to 1,700 MWe. Features include:

    • Standardized designs that are easier to operate and faster to build.

    • Utilization of the latest technology featuring fewer equipment and components.

    • Integration of passive safety systems exemplified by AP1000 and ESBWR.

    • The ABWR has been operational in Japan since 1996, while US-EPR is under construction in Europe and AP1000 in China.

Future Needs in the Nuclear Sector

  • Significant investments are needed in:

    • New Generation III reactors.

    • Upgrading existing reactors.

    • Extending operating licenses from 40 to 60 years.

    • Development of Small Modular Reactors (SMRs) like mPower, NuScale, Purdue Novel Modular Reactor (NMR), Modular Helium Reactor (RS-MHR), Traveling Wave Reactor, and Westinghouse SMR.

    • Proper management of spent fuel to ensure safety and efficiency.

Nuclear Workforce Challenges

  • There is a need for substantial investments in human capital due to a shortage of skilled workers:

    • Each new reactor requires about 1,400 to 1,800 workers for construction.

    • Approximately 50% of the current workforce is 47 years or older and will be eligible to retire in the next 10 years.

    • The nuclear industry is projected to need 90,000 new workers within the next decade according to the Nuclear Regulatory Commission (NRC).

Generation of Nuclear Reactors

  • Categorization of reactors:

    • Generation I: Early reactors (1960s) with output <200 MWe, mostly shut down.

    • Generation II: Primarily light water reactors with output up to 1,000 MWe.

    • Generation III and III+: Includes Westinghouse AP1000 and Advanced Boiling Water Reactor (ABWR).

    • Generation IV: Features substantially different reactors, such as High Temperature Gas Reactor, Molten Salt-cooled Reactor, etc. Not ready for deployment until at least 2030.

    • Small Modular Reactors (SMRs) and MicroReactors.

Important Attributes for Future Reactors

  • Essential parameters for future reactors include:

    • Safety:

    • Core damage frequency: < 10E-5 - 10E-6 /RY

    • Large early release frequency: 10E-6 - 10E-7/RY

    • Economy: Cost-effective design and construction.

    • Proliferation Resistance: Minimization of risks related to the diversion of materials for weapon purposes.

    • Waste Reduction and Fuel Economy: Focus on minimizing long-lived radionuclides and incorporating effective fuel reprocessing strategies.

Generation III+ Design Objectives

  • Key aspects of Generation III+ reactor designs include:

    • Standardized designs for uniformity.

    • Simplicity and reduced plant sizes.

    • Increased plant design life, projected at 60 years.

    • Lower costs through larger plant ratings and simplifications.

    • Shortened construction schedules.

    • Incorporation of passive safety systems for enhanced safety and reliability.

    • Digital Instrumentation & Control (I&C) for accurate monitoring.

    • Improved seismic responses through advanced design.

    • Reduction of overall equipment and components for simpler operation and maintenance.

Advanced Reactor Designs Under Consideration

  • Reactor designs currently under review include:

    • GE-Hitachi ABWR – NRC Certified since 1997.

    • Westinghouse AP1000 – NRC Certified since 2005.

    • GE-Hitachi ESBWR – Current NRC Review status.

    • AREVA US-EPR – Under NRC review.

    • Mitsubishi US-APWR – Current NRC Review status.

Utilities Interest in Nuclear Plants

  • Utilities have expressed interest in building more than 28 nuclear plants, including:

    • ABWR (GE-Hitachi): Design certified, operating plants in Japan, output 1370-1460 MW.

    • AP1000 (Toshiba-Westinghouse): Final design approved; however, engineering is incomplete, output includes 1117 MW.

    • EPR (AREVA): The most costly design with a large output of 1600 MW; design certification submitted in 2005 but engineering is incomplete.

    • ESBWR (GE-Hitachi): Large design of 1550 MW, with sources documenting various construction and design statuses.

Advanced Passive Designs

  • Advanced designs such as AP1000 and ESBWR utilize:

    • Natural forces to enhance safety.

    • Improved automatic safety features that drastically minimize equipment needs.

    • Smaller plant sizes leading to reduced construction time.

Benefits of Advanced Reactor Designs

  • Standardization leads to lower operational complexities, allowing for faster and more economical construction, operation, and maintenance. Benefits also include:

    • Simplicity and enhanced safety through the latest technology leading to lesser equipment and components.

    • Larger scale output varying from 1100 to 1700 MWe.

    • Operational experience from existing plants globally.

Reactor Technologies

  • Different types of reactor technologies:

    • Fast reactors: Utilize fast neutrons to cause fission reactions.

    • Thermal reactors: Utilize thermal (slow) neutrons.

Average Neutron Energy in Reactor Core

  • The average energy of neutrons and the corresponding materials are:

    • Light materials (H2O, D2O, Carbon): Thermal or slow neutrons.

    • Heavier materials (Na, Pb): Fast or high energy neutrons.

    • Gases (e.g., helium, CO2): Fast neutrons.

    • Gas cooled graphite-moderated: Thermal neutrons.

    • Supercritical water: Intermediate energy neutrons.

Fission and Fission Neutrons

Fission Cross Section

  • Average number of neutrons emitted per fission reaction by thermal and fast neutrons:

    • For U-233: Thermal neutrons - 531 barns (2.49 neutrons), Fast neutrons - 2.58 neutrons.

    • For U-235: Thermal neutrons - 582 barns (2.42 neutrons), Fast neutrons - 2.51 neutrons.

    • For U-238/Pu-239: Thermal neutrons - 743 barns (2.93 neutrons), Fast neutrons - 3.04 neutrons.

Pressurized Water Reactor (PWR)

Characteristics of Evolutionary Light-Water Reactors

  • Notable representatives such as ABWR and AP1000 showcase:

    • Design certification and demonstrated construction.

    • Output ranges from 1370–1460 MW up to large designs of 1600 MW (EPR AREVA).

    • Approvals and status of engineering need to be acknowledged for a precise overview.

Types of Safety

  • Safety classifications observed in nuclear systems are:

    • Active Safety: Example includes fire departments.

    • Passive Safety: Example includes sprinkler systems.

    • Inherent Safety: Example includes concrete buildings, providing safety through material and design choices.

Under Accident Conditions (TMI Example)

  • In the event of an accident, water is added to the light-water reactor core to provide cooling, essential in mitigating risk.

Key Advanced Reactor Technologies: ABWR & ESBWR

  • ABWR: Serves as foundational technology with immediate availability for generation needs of around 1500 MW.

  • ESBWR: Next evolution employing new features that enhance security, safety, and operational flexibility while promoting economic advantages through no active recirculation pumps.

Construction and Design Elements

  • The design comprises components like:

    • Steam generators, reactor vessels, coolant pumps, which work together to facilitate operations in thermal reactors.

Severe Accident Mitigation Strategies

In-Vessel Retention

  • The AP1000 is designed to retain core debris within the reactor vessel during a core melt scenario, utilizing natural circulation for cooling flow driven by in-containment water sources.

  • Boiler design includes:

    • Automatic depressurization capabilities and structural design to ensure core integrity and safety standards compliance.

Fuel Safety and Material Considerations

  • Safety basis for fuel in extreme temperatures is achieved through:

    • Composition choice ensuring integrity independent of active systems.

    • Use of TRISO fuel particles designed for high-performance features in reactor operations.

Spent Fuel Management

Spent Fuel Reprocessing and Disposal

  • Challenges of Spent Fuel Management:

    • Spent fuel management remains a critical challenge for nuclear power, often termed the Achilles’s heel of the power sector.

    • Advancements in reactor designs aim to improve fuel utilization efficiency over existing Generation II reactors.

  • Key strategies include:

    • Reprocessing spent fuel for reuse in advanced reactors to minimize waste.

    • Addressing proliferation concerns during the transport of spent fuel to processing facilities.

Yucca Mountain Nuclear Waste Repository

  • As part of the Nuclear Waste Policy Act amendments of 1987, the Yucca Mountain site was designated as a repository for spent nuclear fuel and other high-level radioactive waste in the United States.

Dry Cask Storage Details

  • The storage of spent nuclear fuel in steel-concrete casks exhibits varying capacities across different nations:

    • France (La Hague): 1700 tonnes per year, UK (Sellafield - THORP): 400 tonnes, and others adding to a total civil capacity of approximately 5550 tonnes.

Repository Disposal Methods

  • The process involves:

    • Bundling irradiated fuel rods into containers.

    • Vitrification of fission products, which involves mixing with molten glass encased in metal cylinders for geological disposal.