Nuclear Power Generation& Emergency Preparedness

Health Physics SocietyPower Reactor Section

103 Nuclear Power Reactors

Steam Engines

HOW A NUCLEAR REACTOR WORKS

Outline Electric Power Generation Why Nuclear? What About Accidents? Safety By Design and

Operation What About Drill Scenarios?

Electricity: A Vital Resource

Sources of Power

Gas17.9%

Oil2.3%

Nuclear20.4%

Hydro6.9%

Renewable2.2%

Coal50.3%

Source: EIA - Updated 11/03

(2002)

Pros & Cons

COAL

HYDRO

NATURAL GAS

SOLAR & WIND

cheap and abundant but source of greenhouse gases

clean but seasonal and no new

sources

cleaner than coal but limited supply

renewable but expensive, low energy

density, and intermittent

Why Nuclear?

NUCLEAR

high energy density

no air pollution

small, contained waste

But what about… safety, security, and waste

disposal ?

High Energy Density Each person in the United States uses either:

4 tons of coal or a few ounces of uranium

1 pellet = 150 gallons gasoline 1780 pounds coal 16,000 ft3 natural gas 2.5 tons wood

No Air Pollution

0%

10%

20%

30%

40%

50%

60%

70%

80%

76% 22% 1.4% 0.7% 0.1%Nuclear Hydro Geothermal Wind Solar

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

Loaded into Steel Containers, Stored in Concrete Casks

Steel Containers Buried Deep Underground

Waste Hazard Decreases Over Time

Nuclear Safety Record 440 civil nuclear reactors in 30 countries

sharing operating experiences (http://www.world-nuclear.org/index.htm)

Impressive safety record covering 12,000 reactor-years of operating experience

Two nuclear accidents: TMI (1979) Chernobyl (1986)

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

No one killed, no one injured. Offsite radiation is minimal, a small fraction of

natural background radiation. 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

31 workers, mostly fire fighters are killed largely due to acute radiation exposure.

Huge release of radioactive material, distributed around Europe.

World confidence is severely damaged. The Whole Health Organization has linked hundreds

of child thyroid cancers to the accident (10 deaths), but no detectable increase in other cancers.

The greatest damage was from fear (psychological), NOT radiation.

Can Chernobyl Happen Here?

Reactor Design: Apples & Oranges Positive temperature coefficients of reactivity Graphite core that catches fire and burns for days No containment building

Institutional Controls: Apples & Oranges No strict operating license No strict regulatory oversight

Lesson: Never Take Safety For Granted

Nuclear Safety

Design and Construction Operation and Training

Safety By Design: Low “Enrichment”

Fission “chain reaction”: E = m * c2

U-235 atoms fission. 5% in fuel, 95% in bombs.

Safety By Design: Fuel Rods

Typical 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

Safety By Design: Reactor Vessel

Typical values:

Weight: 400 tons

Thickness: 8 inches

Fuel Assemblies (Core)

Safety By Design: PWR Containment

Initial Construction

Completed Concrete Dome

Layers of Protection Against 9/11

Safety By Design: Reactor Control

Automatic shutdown system relies on gravity

Negative temperature & pressure coefficients of reactivity*

Controls rods maintain maximum shutdown potential

Safety By Design:Redundant Safety Systems

Reactivity Control

Core Heat Removal

“RCS” Inventory Control

“RCS” Heat Removal

Containment Isolation

Regulatory ControlNuclear Regulatory Commission Headquarters in Rockville, Maryland

(www.nrc.gov)

NRC Regulatory Functions

This IS Rocket Science

Final Safety Analysis Report (FSAR) Volume 15: Accident Analysis Design Basis Accidents (Worst Case Scenarios):

Loss of Cooling Accident (LOCA) Steam Generator Tube Rupture (SGTR)

What Can Get Released?

Noble gas fission products Chemically inert (xenon)

Volatile fission products Chemically reactive (iodine)

All other fission products Remain in solid form

Beyond “Worst Case Scenarios”

EP drills must exercise the emergency plan, requiring an unbelievable sequence of events.

Nuclear Engineering uses the science of: “Probabilistic Risk Assessment”

Probability of an typical “EP Scenario”: “1 in 10 billion”

Summary Benefits of nuclear power include no air pollution and

low volume of contained waste. We’re here today because of the lessons-learned at TMI. Because of differences in design, the Chernobyl disaster

has little relevance to the safety of U.S. nuclear power plants.

U.S. nuclear plants are safe through design, operation, and strict regulatory control.

EP Drills must use unrealistic scenarios to exercise our Emergency Plan.

Thanks…for your interest and patience !