Save Our Environment, Stop Nuclear Energy Usage
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Transcript of Save Our Environment, Stop Nuclear Energy Usage
Nuclear Energy: Not a solution for energy crisis
Dr. Manabendra Nath Bera
1) Nuclear Physics: Radioactivity1) Nuclear Physics: Radioactivity
2) Nuclear Power Plants2) Nuclear Power Plants
3) Nuclear Fuel3) Nuclear Fuel
4) Nuclear Waste4) Nuclear Waste
5) Nuclear Safety5) Nuclear Safety
6) Conclusion6) Conclusion
Agenda
Nuclear Physics: Radioactivity
Nuclear Fission
The reaction:
¿235¿¿U ¿ ¿
235U + n
141Ba + 92Kr +3 n + Energy
144Cs + 90Rb +2n + Energy
Measuring Radioactivity
• Half-Life– The time for a radioactive source to lose 50% of its
radioactivity– For each half-life time period, radioactivity drops by
50%• 1/2; 1/4; 1/8; 1/16; 1/32; 1/64; 1/128; 1/256; …• A half-life of 1 year means that radioactivity drops to <1%
of its original intensity in seven years
• Intensity vs. half-life– Intense radiation has a short half life, so decays more
rapidly
Types of Radiation
http://www.uic.com.au/wast.htm
Health Effects of Radiation
• Radiation changes living cells– body repairs low dose rate damage– body cannot repair large acute doses– Cancer
• Degree of effect depends on dose intensity, length of exposure, and type of cell exposed
Nuclear Power Plants
Nuclear Heat
Heat
Steam produced
Steam
Turbine
Generator
Electricity
Nuclear Fuel
Creating Uranium Fuel
• 50,000 tonnes of ore from mine • 200 tonnes of uranium oxide concentrate (U3O8)
– Milling process at mine• 25 tonnes of enriched uranium oxide
– uranium oxide is converted into a gas, uranium hexafluoride (UF6),
– Every tonne of uranium hexafluoride separated into about 130 kg of enriched UF6 (about 3.5% U-235) and 870 kg of 'depleted' UF6 (mostly U-238).
– The enriched UF6 is finally converted into uranium dioxide (UO2) powder
– Pressed into fuel pellets which are encased in zirconium alloy tubes to form fuel rods.
Creating Uranium Fuel
Green house gases during these process
What Is the Nuclear Fuel Cycle?
• Mine the uranium
• Process the uranium to make the fuel
• Use it in the reactor
• Safely store the radioactive waste
• Decommission the reactor
Nuclear Waste
Spent Fuel rods
• After about 3-4 years of use, the Fuel rods become spent-level of fission drops beneath a certain level
• Rods are taken out of reactor stored nearby in water filled pools or dry casks
• Stored until they cool down enough to be shipped for permanent storage or to be recycled
• These storage facilities are next to the reactor plants, vulnerable to terrorist attack or accidents
Waste Burial
• Immobilize waste in an insoluble matrix– E.g. borosilicate glass, Synroc (or leave them as uranium oxide
fuel pellets - a ceramic)
• Seal inside a corrosion-resistant container– Usualy stainless steel
• Locate deep underground in stable rock• Site the repository in a remote location. • Most radioactivity decays within 10,000 years
– Remaining radioactivity similar to that of the naturally-occurring uranium ore, though more concentrated
http://www.uic.com.au/wast.htm
http://www.uic.com.au/opinion6.html
After 3 or 4 Years in a Reactor, Spent Fuel Rods Are Removed and Stored in Water
Dealing with Radioactive Wastes Produced by Nuclear Power Is a Difficult Problem
• High-level radioactive wastes – Must be stored safely for 1,000–24,000 years
• Where to store it– Deep burial: safest and cheapest option– Transportation concerns– Would any method of burial last long enough?– There is still no facility
Cooled in a spent fuel pool: 10 to 20 years
Onsite temporary dry storage: Until permanent site becomes available
Case Study: Experts Disagree about What to Do with Radioactive Wastes in the U.S.
• 1985: plans in the U.S. to build a repository for high-level radioactive wastes in the Yucca Mountain desert region (Nevada)
• Problems– Cost: $58–100 billion– Large number of shipments to the site: protection from
attack?– Rock fractures– Earthquake zone– Decrease national security
Nuclear Safety
List of dangers connected to NPPs
Release of radioactive element into environmentRadioactive isotope pollutionWater temperature increaseThe threat of nuclear accidentThreat of nuclear terrorismTransportation of the waste can be risky
During the operation of nuclear power plants, radioactive
waste is produced, which in turn can be used for the
production of nuclear weapons.
Worst Commercial Nuclear Power Plant Accident in the U.S.
• Three Mile Island– March 29, 1979– Near Harrisburg, PA, U.S.– Nuclear reactor lost its coolant– Led to a partial uncovering and melting of the
radioactive core – Unknown amounts of radioactivity escaped– People fled the area– Increased public concerns for safety
• Led to improved safety regulations in the U.S.
Cleanup lasted 14 years; cost $975 million51 US nuclear reactor orders canceled 1980-84.
• April 26, 1986
• Pripyat, Ukraine
• Catastrophic steam explosion -Destroyed reactor
-Plume of radioactive fallout spread far• USSR, eastern Europe, Scandinavia,
UK, eastern US
• Belarus, Ukraine, and Russia hit hardest
-56 direct deaths; ~4,000 long-term deaths
-350,000 people evacuated and resettled
http://en.wikipedia.org/wiki/Chernobyl_accident
Worst Nuclear Power Plant Accident in the World
What happened?
-Reactor No.4 was undergoing a test of the backup power supply in case of a power loss.
-The experiment involved shutting down the coolant pumps, which caused the coolant to rapidly heat up and boil.
-All control rods were ordered to be inserted. As the rods were inserted, they became deformed and stuck. The reaction could not be stopped.
-The rods melted and the steam pressure caused an explosion, which blew a hole in the roof. A fire also resulted from the explosion.
-To save money, the reactor was constructed with only partial containment, which allowed the radiation to escape. 13%-30% of the material escaped.
Evacuation-Following the accident hundreds of thousands of people had to be evacuated and between 1990 and 1995 an additional 210,000 people were resettled.
People evacuated:-May 2-3 (1 week later) 10 km area (45,000 people)
-May 4 30 km area (116,000
people)
http://library.thinkquest.org/3426/data/emergency/evacuation.html
-50,000 people from Pripyat, Ukraine were evacuated 2 days after the accident.
Effects of Radiation
Belarusian doctors identify the following effects from the Chernobyl disaster on the health of their people:
100% increase in the incidence of cancer and leukemia 250% increase in congenital birth deformities “Chernobyl AIDS”--the term doctors are using to describe illnesses
associated with the damage done to the immune system
Initial response• These were firemen who helped put out the fires and helped clean
up the radiation• Most did not realize the dangers of radiation.• Many later died from radiation, because they didn’t wear
protection.• An estimated 8,000-20,000 to date have died (20% from suicide)
Approximately 300,000 to 600,000 people were involved in the cleanup of the 30 km evacuation zone around the plant in the years following the meltdown.
Effects of Radiation
Victims
Victims
Fukushima
Cause and Effects
Can Nuclear Power Reduce Dependence on Imported Oil, Reduce Global Warming?
• Nuclear power plants: no CO2 emission
• Nuclear fuel cycle: emits CO2
• Opposing views on nuclear power and global warming– Nuclear power advocates– 2003 study by MIT researchers– 2007: Oxford Research Group
Conclusion: NPPs as an alternative source of energy
Fig. 15-21, p. 391
TRADE-OFFSConventional Nuclear Fuel Cycle
Large fuel supply Cannot compete economically without huge government subsidies
Advantages Disadvantages
Low net energy yieldHigh environmental impact (with major accidents)Emits 1/6 as much CO2 as
coal
Environmental costs not included in market price
Risk of catastrophic accidents
No widely acceptable solution for long-term storage of radioactive wastes
Moderate land use
Spreads knowledge and technology for building nuclear weapons
Subject to terrorist attacks and Earth quake
Fig. 15-22, p. 392
TRADE-OFFS
Coal vs. Nuclear
Coal NuclearAmple supply Ample supply of
uraniumHigh net energy yield
Low net energy yield
Very high air pollution
Low air pollution
High CO2 emissions Low CO2 emissions
Much lower land disruption from surface mining
High land disruption from surface mining
High land use Moderate land use
Low cost (with huge subsidies)
High cost (even with huge subsidies)
Thank you
Extra
Reactor Safety DesignContainment Vessel1.5-inch thick steel
Shield Building Wall3 foot thick reinforced concrete
Dry Well Wall5 foot thick reinforced concrete
Bio Shield4 foot thick leaded concrete with1.5-inch thick steel lining inside and out
Reactor Vessel4 to 8 inches thick steel
Reactor Fuel
Weir Wall1.5 foot thick concrete
Controlling Chain Reaction
Control rods
Fuel Assemblies
Withdraw control rods,reaction increases
Insert control rods,reaction decreases
Boiling Water Reactor
Human casualties
• 56 people lost their lives as a direct result of radiation poisoning or fire.
• Thyroid cancer from drinking milk 10-12 thousand.
Can Nuclear Power Reduces Dependence on Imported Oil, Reduce Global Warming?
• Nuclear power plants: no CO2 emission
• Nuclear fuel cycle: emits CO2
• Opposing views on nuclear power and global warming– Nuclear power advocates– 2003 study by MIT researchers– 2007: Oxford Research Group