Chapter 13.3 Hazards and Costs of Nuclear Power Facilities

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

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

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

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

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

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)

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

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

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.)

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

Chapter 13.3 Hazards and Costs of Nuclear Power Facilities