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Sources of Radiation

Nuclear Power Reactors

Day 4 – Lecture 3

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Objective

To discuss about Nuclear Power Reactors including their Types and Basic Elements

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Contents

Types of Nuclear Reactors• PWRs• BWRs• CANDU• Advanced Nuclear Reactors

Components of a Nuclear Power Plant

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The Beginning

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Fossil vs Nuclear

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Nuclear Reactors

Types of Nuclear Reactors:

Light Water Reactors (LWR) Heavy Water Reactors (HWR) High-Temperature Gas-Cooled Reactors Fast Neutron Fast Breeder

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Primordial Nuclides

Nuclide Half-life Natural Activity

235U 7.04 x 108 yr 0.711% of all natural uranium

238U 4.47 x 109 yr 99.275% of all natural U; 0.5 to4.7 ppm total U in common rocks

232Th 1.41 x 1010 yr 1.6 to 20 ppm in common rocks

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Fission

1n + 235U fission products

available for more fission

Slow Neutron Interactions

the mean number of neutrons released per fission for U-235 is 2.5). This leads to a self-sustaining chain reaction or “critical mass.”

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Boiling Water (BWR)Nuclear Reactors

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Pressurized Water (PWR)Nuclear Reactors

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The next five slides display the main components of a Nuclear Power Plant:

Control Building Containment Building Turbine Building Fuel Building Diesel Generator Building Auxiliary Building

Components of a Nuclear Plant

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Control Building

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Containment Building

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Turbine Building

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Fuel Building

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Diesel Generator andAuxiliary Buildings

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Protective Barriers

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Steam Generator

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Nuclear Reactors

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Advanced Reactors

The first advanced reactors now operating in Japan

Nine new nuclear reactor designs either approved or at advanced stages of planning

Incorporate safety improvements and are simpler to operate, inspect, maintain and repair

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The new generation of reactors have:

a standardised design to expedite licensing, reduce capital cost and reduce construction time

higher availability and longer operating life, will be economically competitive in a range of sizes, further reduce the possibility of core melt accidents

higher burn‑up to reduce fuel use and the amount of waste

Advanced Reactors

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More 'passive' safety features which rely on gravity, natural convection to avoid accidents

Two broad categories:

Evolutionary - basically new models of existing, proven designs

Developmental - depart more significantly from today¹s plants and require more testing and verification before large‑scale deployment

Advanced Reactors

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CANDU Reactors

CANDU stands for "Canada Deuterium Uranium“

It is a pressurized‑heavy‑water, natural‑uranium power reactor designed first in the late 1950s by a consortium of Canadian government and private industry

All power reactors in Canada are CANDU type

The CANDU designer is AECL (Atomic Energy of Canada Limited), a federal crown corporation

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CANDU Reactors

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CANDU Reactors

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High TemperatureGas Cooled Reactors

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High TemperatureGas Cooled Reactors

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Pebble Bed Reactor

In the 1950s, Dr Rudolf Schulten ( 'father' of the pebble bed reactor) had an idea. The idea was to compact silicon carbide coated uranium granules into hard billiard-ball-like

graphite spheres to be used as fuel for a new high-temperature, helium-cooled type of reactor. The idea took root, and in due course, the AVR, a 15 MW (megawatt) demonstration pebble bed reactor, was built in Germany. It operated successfully for 21 years.

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Pebble Bed Reactor

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Pebble Bed Reactor

Potential Problems (according to some groups)

It has no containment building

It uses flammable graphite as a moderator

It produces more high level nuclear wastes than current nuclear reactor designs

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Pebble Bed Reactor

Potential Problems (according to some groups)

It relies heavily on nearly perfect fuel pebbles

It relies heavily upon fuel handling as the pebbles are cycled through the reactor

There's already been an accident at a pebble bed reactor in Germany due to fuel handling problems

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Where to Get More Information

Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)

More information at: http://www.pbmr.co.za/index.htm