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Understanding Neutron Transport and Reactor Types

May 9, 2025

Lecture on Neutron Transport and Reactor Types

Introduction

  • MIT OpenCourseWare provides educational resources for free.
  • Focus of the lecture:
    • Context for learning about neutrons.
    • Explore different types of reactors.
    • Understanding neutron transport and diffusion equations.

Changes in Curriculum

  • Shift to context-first, theory-second approach.
  • Importance of understanding applications before diving into theory.

Neutron Basics

  • Neutrons interact with fissile isotopes like uranium and plutonium.
  • Neutron reactions produce more neutrons.
  • Introduction of variables and nomenclature:
    • ν (nu): Average number of neutrons per fission reaction.

Neutron Reaction Dynamics

  • Fission produces 2-3 neutrons.
  • Fission products undergo various decay processes (neutron emission, beta decay, etc.).
  • Importance of understanding the fission timeline:
    • Neutron absorption, compound nucleus formation, fission product decay.

Nuclear Data and Cross-Sections

  • ν-bar: Total neutron production, often treated as a constant in thermal reactors.
  • Fission cross-section: Probability of fission as a function of incoming neutron energy.
  • Neutron interactions include scattering (elastic and inelastic) and absorption.

Reactor Types

Light Water Reactors (LWR)

  • Use of water as coolant and moderator.
  • Types include Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR).

Gas Cooled Reactors

  • Use CO2 or helium as coolant; graphite as moderator.
  • Examples: Advanced Gas Reactors (AGR) and Pebble Bed Modular Reactors (PBMR).
  • Pros and cons regarding efficiency and material challenges.

Heavy Water Reactors

  • CANDU: Uses natural uranium, heavy water as the moderator.
  • High cost due to D2O but allows for natural uranium use.

Graphite Moderated Reactors

  • RBMK type: Known for Chernobyl disaster.
  • Issues with positive feedback coefficients.

Fast Reactors

  • Use liquid metals (like sodium or lead-bismuth) as coolant.
  • Fast reactors rely on fast neutron reactions.
  • Significant in countries like Russia.

Molten Salt Reactors

  • Use molten salt as coolant and fuel.
  • Integral safety features due to solidification upon cooling.

Reactor Physics and Neutron Balance

  • Neutron population tracking involves position, energy, angle, and time.
  • Simplifying neutron transport equation is crucial for practical applications.
  • Importance of knowing cross-sections for various neutron interactions.

Conclusion

  • Overview of different reactor types sets stage for deeper understanding of neutron transport and reactor physics.
  • Future topics include solving neutron transport equations and understanding historical nuclear events (like Chernobyl).

This lecture provided a detailed introduction to neutron interactions and various reactor types, vital for understanding nuclear engineering and reactor design.

Full transcript