Nuclear Power Generation& Emergency PreparednessHealth Physics SocietyPower Reactor Section
103 Nuclear Power Reactors
HOW A NUCLEAR REACTOR WORKS
OutlineElectric Power Generation
What About Accidents?
Safety By Design and Operation
What About Drill Scenarios?
Electricity: A Vital Resource
Sources of PowerSource: EIA - Updated 11/03(2002)
Pros & ConsCOAL
SOLAR & WINDcheap and abundantbut source of greenhouse gases
cleanbut seasonal and no new sources
cleaner than coalbut limited supply
renewablebut expensive, low energy density, and intermittent
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
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 Record440 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:
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 BubbleWhen 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)
Better operator training Better emergency planning
TMI: ConsequencesNo 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.
ChernobylApril 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: Consequences31 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
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 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
Safety By Design: Reactor VesselTypical values:
Weight: 400 tons
Thickness: 8 inchesFuel Assemblies (Core)
Safety By Design: PWR ContainmentInitial 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
Core Heat Removal
RCS Inventory Control
RCS Heat Removal
Regulatory ControlNuclear Regulatory Commission Headquarters in Rockville, Maryland(www.nrc.gov)
NRC Regulatory Functions
This IS Rocket ScienceFinal 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 ScenariosEP 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
SummaryBenefits of nuclear power include no air pollution and low volume of contained waste.
Were 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.
Thanksfor your interest and patience !
The United States has 103 nuclear power reactors in 31 states.
Nuclear energy is the second largest source providing electricity for one of every five homes and business in the country and in California.
Some states clearly are more dependent on nuclear energy than others. Vermont gets 76 percent of its electricity from nuclear reactors New Hampshire and South Carolina well over 50 percent.
About 90% of all electric power is generated by boiling water. The only with nuclear power is the heat source. The fact is more than 50% of our electric power in the United States comes from burning coal. Nuclear power is the second largest source, contributing about 20%. Natural gas and hydro take care of most of the rest.
Coal can meet our future energy needs but global warming is the big question mark.
Realistically, no new sources of hydro power can be expected.
Natural gas is cleaner than coal, producing only the greenhouse gases, there is not enough supply.
Solar and wind are renewable but they are expensive and intermittent. Unfortunately, they are not suited to produce the bulk of our energy needs.
Solar and wind are low density sources. To supply a major with solar power, youd need an area about twice the size an the city.
In contrast, nuclear is high density. San Onofre supplies 2.3 million homes.
Ignoring the occasional shutdown, San Onofre runs pretty much 24 hours a day, 7 days a week, 365 days a year at 100% power. Supplying enough power for over 2 million homes in Southern California. After running for about 2 years, the plant shuts down with the tank still full.
Think about it this way, the average person in the U.S. uses roughly 4-tons of coal or or a few ounces of uranium each year.
More than two-thirds of our electricity is created by burning fossil fuels. The rest of Americas electricity is emission-freeand three-fourths of that comes from nuclear power plants.
Nuclear plants do emit trivial amounts of radioactivityand so do other large industrial facilities including coal plants. But these levels do not harm public health or the environment.
By replacing electricity generation from other fuels, nuclear energy reduces the volume of air emissions that cause smog and acid rain. They also reduce greenhouse gas emissionsthe most important of which is carbon dioxide.
Clean Air Energy. Of all energy sources, nuclear energy has perhaps the smallest impact on the environment, compared to the amount of