Nucular Reactors: Classification and Technology Oliver Gothe Nucular Physics Laboratory

Nucular Reactors: Classification and Technology Oliver Gothe Nucular Physics Laboratory Professor Ralf Gothe May 12, 2008

Three main reaction types: Radioactive Decay Atomic Batteries Radioisotope thermoelectric generators passive Nuclear Fusion Not suitable for power production yet Nuclear Fission Used in most reactors including all commercial ones Reaction Types

Conventional thermal power plants All have a fuel source to provide heat Gas, coal, or oil Nuclear fission Uranium-235 or plutonium-239 Produce steam Drive a turbine that generates electricity (86%) Enriched uranium is uranium in which the percent composition of uranium-235 has been increased from that of uranium found in nature Reactors - Introduction

Electric Generator Obtains power from passive radioactive decays Utilized in satellites and space probes Seebeck effect Junction of two dissimilar metals at different temperatures create a current Fuel Long half life, low shielding... Plutonium 238 most common Radioactive Decay (passive) - RTG

Advantages: Relatively constant power production Useful for long time missions Solar Panels not applicable Disadvantages: Decays over time May require shielding Radioactive waste Advantages and Disadvantages

Experimental Technology Not yet in use Generally utilizes Hydrogen as fuel Contained with Magnetic fields Farnsworth-Hirsch Fusor Not viable for power creation Neutron Generator Nuclear Fusion

First Reactor: Chicago Pile-1 Enrico Fermi in 1942 Inspired by the discovery that Uranium fissions after being bombarded with neutrons Fission process creates new neutrons Creates chain reaction that needs to be moderated Unmoderated reaction used for bombs Nuclear Fission Reactors - Overview

Nuclear Fission - Process • Fission is initialized in the reaction chamber • Creates Chain reaction

Nuclear Fission - Process • Fission is initialized in the reaction chamber • Creates Chain reaction • Moderators are used to control the amount of neutrons in the reactor chamber

Nuclear Fission - Process • Fission is initialized in the reaction chamber • Creates Chain reaction • Moderators are used to control the amount of neutrons in the reactor chamber • Heat released from fission is processed via heat exchangers or directly via steam turbines

Nuclear Fission - Process • Turbines create electricity and the coolant is recycled through the reactor • The environmental problems with nuclear reactors is the heat that is released into the environment from the condensors.

Two Types Thermal vs. Fast Neutron speeds Thermal Reactors (most common)‏ Classified by Moderator Material Absorption cross-section much smaller than fission cross-section Natural Uranium Fast Reactors No moderator Requires Enriched Uranium Nuclear Fission – Reactor Classification

Fuel must be enriched Produces fast neutrons Can be used for transmutation Fuel Production Breeder Reactors Fast Breeder Reactors Fast Neutron Reactor

Graphite moderate reactors Graphite has high neutron absorption cross section Water moderated reactors Heavy water moderated reactors can be fueled with unenriched uranium Light Water moderated reactors Negative feedback stabilizes reaction (neutron absorption) Light element moderated reactors are moderated by a light elements such as Li or Be Organically moderated reactors Use biphenyl and terphenyl as moderator and coolant Nuclear Fission - Moderators

Pressurized Water Cooling specialized pressure vessel A pressurizer is partially filled with water steam bubble is maintained above it by heating the water with submerged heaters Avoid film boiling Nuclear Fission Reactors - Coolant

Boiling water reactor Simplification of designs for civilian purposes Heat is generated directly in the reaction chamber Chamber is still pressurized and boils at about 285 degrees Celsius Nuclear Fission Reactors - Coolant

In pool type reactors the reactor core and control roads are immersed into a pool Water is simultaneously: Cooling agent Moderator Shielding Used for: Neutron generation Training Not for generating electricity Pool Type Reactors

Liquid metal cooled nuclear reactor primary coolant is a liquid metal Used in nuclear submarine use extensively studied for power generation applications Fast Breeder Reactors Lead Sodium Bismuth Mercury Liquid Metal Cooled Reactors

Gas Cooled Reactors • Gas cooled reactors • Use inert gases such as Helium or Carbon dioxide to cool • Some heat the gas enough to run turbines • Older models run through heat exchangers to generate steam • Can be refuelled while online • Higher thermal efficiency than BWRs • Uses fuel less efficiently though 1. Charge tubes 2. Control rods 3. Graphite moderator 4. Fuel assemblies 5. Concrete pressure vessel and radiation shielding 6. Gas circulator 7. Water 8. Water circulator 9. Heat exchanger 10. Steam

Molten salt reactors cooled by circulating a molten salt mixture of fluoride salts, such as LiF and BeF2 Uranium is often dissolved in the matrix Maintenance issues Corrosion Can use spent fuel Immature Technology Molten Salt Reactors

Generations of Nuclear Reactors • Generation I reactors • Developed in 1950-60s • used natural uranium fuel • graphite as moderator • Generation II reactors • use enriched uranium fuel • mostly cooled and moderated by water • Generation III • advanced reactors • developments of the second generation with enhanced safety. • Generation IV • drawing board • burn the long-lived actinides now forming part of spent fuel

Pressurized Water Reactors high pressure liquid majority of current reactors considered the safest and most reliable Examples – Pressurized Water Reactor Diablo Canyon

Boiling Water Reactors (BWR)‏ Cooled and moderated by water Lower pressure Water boils in reactor Simpler Potentially more stable Substantial percentage of modern reactors Examples – Boiling Water Reactor Laguna Verde nuclear power plant

Pressurized Heavy Water Reactor (PHWR)‏ Heavy water cooled and moderated Hundreds of pressure tubes Fueled with natural uranium Thermal neutron reactor design Can be refueled without shutdown Examples – Pressurized Heavy Water Reactor CANDU at Qinshan

High Power Channel Reactor (RBMK)‏ Produces plutonium as well as power Graphite moderator Too large to have containment buildings Chernobyl accident RBMK reactors are considered the most dangerous reactor designs in use Examples – High Power Channel Reactor The Ignalina Nuclear Power Plant

Advanced Gas Cooled Reactor (AGCR)‏ Graphite moderated CO2 cooled High thermal efficiency compared with PWRs Thermal neutron reactor design Examples – Advanced Gas Cooled Reactor Torness nuclear power station

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Nucular Reactors: Classification and Technology Oliver Gothe Nucular Physics Laboratory