Nuclear Power GenerationIn The United States

103 Nuclear Power Reactors

Steam Engines

HOW A NUCLEAR REACTOR WORKS

Outline

Electric Power Generation

What About Accidents?

Safety By Design and Operation

Waste Contained in Used Fuel Assemblies, Cooling-off In Pools

Loaded into Steel Containers, Stored in Concrete Casks

Steel Containers Buried Deep Underground WHEN?/WHERE?

Three Mile Island (TMI)

March 28th 1979, Unit 2 reactor trips at 4 AM.(The movie “China Syndrome” is playing in theaters)

Pressurer relief value sticks open, lose of cooling accident (LOCA) begins.

Hampered by inadequate training and instrumentation, operators shut off emergency core cooling.

By 6:30 AM, blocking value is closed, shutting off the loss of coolant but …

The water level has fallen below the top of the reactor core. The fuel rods containing the uranium fuel pellets melt and release radioactive gas into the Containment Building.

TMI: Hydrogen “Bubble” When the fuel rods melt, hydrogen gas is generated.

A “bubble” of hydrogen gas collects in the reactor head.

Fear that the hydrogen could explode result in confusion, panic. About 150,000 people evacuate.

However, the hydrogen explosion was never possible (not enough oxygen)

Major lessons: Better operator training Better emergency planning

TMI: Consequences Public confidence is severely damaged.

Many health effects studies have been conducted. In 1996, a U.S. District Court dismisses all lawsuits finding no evidence of harm.

Improvements to operator training, instrumentation, and emergency plans are now required.

Chernobyl

Chernobyl April 1986 disaster at Chernobyl in the Ukraine was a

result of a dangerous reactor design and weak operational controls.

Weak Operational Control:

Poorly trained operators were performing a dangerous and unauthorized “test”.

Dangerous Reactor Design: A “positive” temperature coefficient of “reactivity”

resulted in a huge power surge that cause water to flash to steam, blowing the cover plate off the top of the reactor…

Broken pipes spilled water onto the hot “graphite” moderator, which bursts into flames.

Flawed Reactor Design

graphite core & unstable reactor

Environmental Pathways

82% of the iodine exposure was avoidable

Chernobyl: Consequences

Huge release of radioactive material, distributed around Europe.

World confidence is severely damaged.

Fuel RodsTypical values:

The uranium fuel is made of solid ceramic pellets.

The fuel pellets are sealed inside 13’ long zirconium alloy rods.

236 rods in each assembly

217 assemblies in the reactor core

Reactor Vessel

Typical values:

Weight: 400 tons

Thickness: 8 inches

Fuel Assemblies (Core)

PWR Containment

Initial Construction

Completed Concrete Dome

Regulatory Control

Nuclear Regulatory Commission Headquarters

Rockville, Maryland

(www.nrc.gov)