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