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Chapter 13.3 Hazards and Costs of Nuclear Power Facilities

Chapter 13.3 Hazards and Costs of Nuclear Power Facilities. when uranium undergoes fission, direct products are unstable isotopes become stable by spontaneously ejecting subatomic particles (alpha and beta particles), high-energy radiation (gamma and X-rays), or both

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Chapter 13.3 Hazards and Costs of Nuclear Power Facilities

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  1. Chapter 13.3Hazards and Costs of Nuclear Power Facilities • when uranium undergoes fission, direct products are unstable isotopes • become stable by spontaneously ejecting subatomic particles (alpha and beta particles), high-energy radiation (gamma and X-rays), or both • indirect products form as materials around the reactor are converted to unstable isotopes when the absorb neutrons from fission • radioactivity is measured in curies • collectively, particles and radiation are referred to as radioactive emissions

  2. biological effects • radioactive emissions can penetrate biological tissue, resulting in radiation exposure • exposure measured as absorbed dose (J / kg) • joules = energy unit • kilogram = mass of body tissue • unit referred to as sieverts (Sv) in cases of high level radiation exposure • as radiation penetrates tissue, it displaces tissue, leaving behind ions

  3. biological effects of radiation • high dose: radiation may cause enough damage to prevent cell division • used in cancer treatment to destroy tumors • whole body exposure results in radiation sickness • low dose: may damage DNA, leading to tumors or leukemia • damage to egg or sperm cells (mutations) may lead to birth defects • effects may go unseen for 10 – 40 years after the event • exposures of 100-500 millisieverts or more results in an increased risk of developing cancer

  4. sources of radiation • normal background radiation from uranium and radon underground, as well as from cosmic radiation • deliberate exposures come from medical and dental tests (primarily X-rays) • average person in U.S. receives a dose of about 3.6 mSv per year • radiation detectors pick up more radiation from most basement floors than from measurements in and around nuclear power plants

  5. radioactive wastes • radioactive decay: process in which an unstable isotope becomes stable by releasing particles and radiation • half-life: time for half of the amount of a radioactive isotope to decay • each radioactive isotope has a characteristic half-life

  6. disposal of radioactive waste • low-level • low amount of radioactivity • remains dangerous for a short period • has short half-life (a few hundred years or less) • high-level • high amount of radioactivity • remains dangerous for a relatively long period • has long half-life (tens of thousands of years)

  7. disposal of radioactive waste • storage of low-level waste • on-site until it has decayed enough to go into regular trash or until amounts are large enough to go into hazardous waste landfill • necessary for relatively short period • usually stored in barrels or drums

  8. disposal of radioactive waste • Storage of high-level waste • on-site until it can be shipped to an isolated area • necessary for relatively long period (tens of thousands of years) • must be stored in specially shielded containers or in water pools; must be cooled before long-term storage

  9. disposal of radioactive wastes • current problem of nuclear waste disposal is two-fold: • short-term containment: allows radioactive decay of short-lived isotopes; in 10 years, fission wastes lose 97% of their radioactivity • spent fuel is first stored in deep pool-like tanks on the sites of nuclear power plants • water in tanks helps to dissipate heat and prevent escape of radiation • current U.S. pools will be full by 2015 • after a few years of decays, spent fuel may be paced in air-cooled dry casks until long-term storage is available (able to resist flood, tornadoes, etc.)

  10. disposal of radioactive wastes • current problem of nuclear waste disposal is two-fold: • long-term containment: EPA recommended a 10,000 year minimum to provide protection from long-lived isotopes; government standards require isolation for 20 half-lives

  11. military radioactive wastes • some of the worst failures in handling wastes have occurred at military facilities • wastes associated with the manufacture of nuclear weapons • U.S. • activities have been top-secret • Ex. releases of uranium dust, xenon-133, iodine-131, and tritium into environment • clean-up is now responsibility of Department of Energy • DOE has spent $50 billion and full clean-up may require $250 billion

  12. military radioactive wastes • former U.S.S.R. • worst case is complex called Chelyabinsk-65, near the Ural Mts. • nuclear wastes were discharged into the Techa River and then into Lake Karachay for at least 20 years • at least 1000 cases of leukemia have been traced to radioactive contamination from site • even today, standing on the shore of Lake Karachay for an hour can result in enough radioactive contamination to cause radiation poisoning

  13. military radioactive wastes • Megatons to Megawatts program • private U.S. company oversees the dilution of weapons-grade uranium to lower-grade power plant uranium • processed uranium sold to U.S. power plants at market price, with payments then sent to Russian government

  14. high-level nuclear waste disposal • most countries (including U.S.) have decided that geologic burial is best ultimate fate for nuclear waste, but no nation has carried out the plan • basic problem is that no rock formation can be guaranteed to remain stable and dry for tens of thousands of years • no spot without evidence of volcanic activity, earthquake, or groundwater leaching in the past 10,000 years

  15. Yucca Mt. nuclear waste disposal • Nuclear Waste Policy Act of 1982 required the U.S. government to begin receiving nuclear waste from commercial power plants by 1998 • Yucca Mountain, NV site selected in 1987 • studies have indicated that storerooms 1000 feet above current groundwater levels will be safe for at least 10,000 years

  16. Yucca Mt. nuclear waste disposal • 2004 court ruling said that time period was inadequate and caused EPA to extend the protection standard to 1 million years (and raised allowable dose maximum past 10,000 years to 3.5 mSv/year) • in 2002, President Bush signed a resolution (passed by Congress) voiding a veto by Nevada’s governor that had attempted to block further development at the site • Yucca Mt. could begin receiving waste from storage facilities around the country by 2018

  17. nuclear power accidents • Three Mile Island (PA, 1979) • partial meltdown due to series of human and equipment failures resulting from flawed design • operators of the plant have paid $30 million to settle claims from the accident, although the company has never admitted that radiation-caused illnesses occurred

  18. nuclear power accidents • Chernobyl (U.S.S.R., 1986) • disabling plant safety systems for test of standby diesel generators eventually led to: • a steam explosion that blew the top off the reactor • core meltdown • release of 50 tons of dust and debris bearing 100-200 million curies of radioactivity • plume rained radioactive particles over thousands of square miles • 400x the radiation fallout associated with bombs dropped on Hiroshima and Nagasaki

  19. consequences of Chernobyl • 135,000 people were evacuated and relocated • reactor eventually was sealed with concrete and steel • barbed-wire fence now surrounds a 1000 square mile exclusion zone around the reactor site • 2 engineers were directly killed by the explosion, along with 28 people brought in to contain the reactor after the explosion • U.N. report offers assessment of impact: • long-term confinement, and $800 million project undertaken by 28 governments, is set to conclude in 2010 • over 4000 cases of thyroid cancer, mainly from children drinking milk containing radioactive iodine • several thousand additional deaths due to cancer are expected (difficult to track)

  20. new generations of reactors • Generation I: earliest, developed in 1950s and 1960s, few still in operation • Generation II: majority of today’s reactors, utilize many different designs • Generation III: newer designs with passive safety features, usually simpler and smaller power plants • advanced boiling-water reactors (ABWR) • two separate passive safety features cause water to drain by gravity into the reactor • design of choice in east Asia

  21. new generations of reactors • Generation IV: now being designed, will likely be built in the next 20 years • pebble-bed modular reactor (PBMR) • will feed spherical carbon-coated uranium fuel pebbles gradually through the reactor • new designs are cheap to build, inherently safe, and inexpensive to operate

  22. worries about terrorism • 3 main threats: • jetliner could fly into control building, triggering a LOCA • strike force could overcome plant defenses and bring on a core meltdown by manipulating the controls • Both of the above scenarios would result in few, if any, immediate civilian casualties, but effects of radiation (cancer, etc.) would be emerge over the course of many years • “dirty bombs” containing spent fuel rods could spread radioactivity over a large area • response: • security around plants increased • pools of spent fuels are most vulnerable locations

  23. economics • economic reasons slowed the development of nuclear power plants beginning in the 1970s • projected future energy demands were overly ambitious • increased safety standards caused cost to increase 5x • public protests delayed construction • the lifespan of plants has been much shorter than expected • embrittlement and corrosion • potential for Climate change has given nuclear power new hope, despite expense

  24. advanced reactors • breeder (fast-neutron) reactors • U-238 absorbs extra neutrons from fission reaction at high speed • U-238 is converted to plutonium (Pu-239), which can be purified and used as fuel • advantages: • extract more energy from recycled nuclear fuel; produce much less high-level waste than conventional nuclear power plants • disadvantages: • Meltdown would be far more serious due to long half-life of Pu; fuel can be purified into nuclear weapons far more easily; more expensive to build and operate

  25. advanced reactors • fusion reactors • solar energy is the result of the fusion of hydrogen nuclei to form larger atoms, such as helium • process is duplicated in hydrogen bombs • in ideal world, hydrogen (for which there’s an inexhaustible supply in water) is converted to nonpolluting inert gas, helium • however, isotopes of hydrogen, deuterium (H-2) and tritium (H-3) are used in d-t reaction • currently, conducting fusion requires more energy than it produces • main problems are producing enough heat to cause H atoms to fuse, then extracting heat for useful energy

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