Chapter 15: Nuclear Power

Future Energy

• Fossil Fuels

  • Have Limited Reserves

  • Enviromental Costs

• Non-Fossil Sources Are Needed

• Nuclear Power Has Few Emissions (main waste is thermal/heat pollution)

• Enough Uranium for Years of Nuclear Power

• 32 Countries Have Nuclear Power Plants in Operation

• Nuclear Age Started after WWII

• US Gov. Led The Way

• Often believed that Nuclear Power would provide cheap electricity

  • Most people are scared of nuclear weapons

The Nuclear Age

• Beginning: Gov. researched, developed, and promoted nuclear power

• companies constructed the plants

• approx. 1000 plants expected; utilities order & paid in preparation

• Price-Anderson Act- 1957

  • Guarantees insurance for plants produced

• Nuclear Regulatory Commissions (NRC)

  • Set of laws used to help

• 1973: 53 US Plants producing Electricity

Nuclear Power Just Stopped

• After 1975; Construction Terminated

• Utilities Stopped Ordering Nuclear Plants

• Elevated Construction Costs (public opinions turned on nuclear energy

• 3 mile island (radioactive got released & Chernobyl accidents (worst nuclear disaster in Ukraine; both technical and human error)

• emergence of cheaper & more readily available energy

  • natural and gas

Current Nuclear Power in USA

• 18.6% of US power is nuclear

• <100 Nuclear Reactors (approx. 52)

• Nuclear plants only built to replace old plants (Modern Times)

World Nuclear

• 419 Nuclear Reactors Worldwide in 32 Countries

• Nuclear Currently Provided 10% World’s Electricity

  • Varies by County

    • USA = #1 Nuclear Producer

    • France - #2

    • China- Rapidly growing; projected to become #1 soon

    • countries lacking fossil fuels; eager for nuclear

How Nuclear Works

• Control Nuclear Reactions so energy is released gradually as heat

  • boil water

  • steam turns turbogenerators

• Baseload Plants- large & always on

• Changes at atomic level form new elements

• New elements created by:

  • Fission: element broken down into smaller pieces

  • Fusion: cram two elements together

• Products of Both have less mass than starting material

• mass is converted to energy

• e = mc²

Nuclear Fuel

• Nuclear Plants use Fission of Uraniaum-235

• Uranium Occurs Naturally in 2 forms (isotypes)

  • U₂₃₈: Does not Readily Undergo Fission

  • U₂₃₅: Readily Undergoes Fission

• isotopes - different numbers of neutrons, same number of protons

• Mass number is proton + neutrons

• Uranium Ore is Mined

• Milled Into Yellowcake - 80% UO₂

• Purified & Enriched - Separate U₂₃₅ from U₂₃₈

  • 3-5% U₂₃₅ Perfect Concentrations

  • Technical Difficulties Make It Difficult For Less Developed Countries

• Control Rods Absorb Extra neutrons helping control reactions

• Nuclear Reactors Have Continuous Chain Reactions Using U235

• Uranium refined to 3-5% U235

• faster neutrons absorbed by u238 convert it to Pu239

• plutonium undergoes fission & releases energy

• moderators surround the enriched uranium (slow down neutrons and capture heat)

U₂₃₆

• Some atoms of U₂₃₆ undergo radioactive decay & release neutrons

• Neutrons hit nucleus of another

• produces highly unstable₂₃₅ atom

• U236 undergoes fission into fission products

• more neutrons given off relaxing energy

• chain reactions occur with neutrons hitting other atoms

Atomic Bombs

• when u235 is highly enriched fission triggers a self-amplifying reactions

• nuclear weapons have small amount of pure U235 or other material

• the whole mass undergoes fission in a fraction of a second

• releasing all the energy in a single large explosion

• Nuclear Power Plants ARE different

  • they want slow, steady releases on power

• Nuclear Power Plants are Safer

Nuclear Reactors

• Light-Water Reactors (LWRS) - Use a Near Pure Water Moderator

• Enriched U arranged in a geometric pattern surrounded by moderator

• Fuel Rods: Uranium Dioxide Pellets Loaded into Long Metal Tubes

  • Placed close together to form a reactor core

  • core kept inside a reactor vessel with both moderator & coolant

• control rods of neutrons absorbing material inserted between fuel rods

• control rods absorb neutrons & slow down chain reactions

• chain reaction started & controlled by withdrawing & inserting control rods

Nuclear Power Plant

• Boiling Water Reactors

• Pressurized water reactors: 65% of nuclear reactors in US

  • moderator @ high pressure, gets hot but doesn’t boil, separate pool of water is pumped via tubing

• Both types have serious problems if any cooling water is lost

• LOCA: Loss of Coolant Accident; Does not stop radioactive decay

• meltdown: enough hear released to melt materials at core

• backup cooling systems & concrete containment building

Hazards of Nuclear Power

• Fissions create new, lighter atoms

• radioisotopes: unstable direct products of fission

  • become stable by ejecting neutrons

  • high energy radiations: gamma & x-ray

• curie- measurement of radioactivity

• radioactive emissions: particles + radiation

Radioactive Wastes

• Direct: Radioisotopes that result from splitting

• Indirect Products of Fission: Become Radioactive by Absorbing Neutrons

• Radioactive Wastes: Direct & Indirect Products of Fission

• High-Level Wastes - Direct Products of Fission are highly radioactive

• Low-Level Wastes: Indirect Products are Less Radioactive

Radioactive Emissions

• Can penetrate biological tissues

• results in radioactive exposure

  • something inside the body changes due to radiation

• absorbed dose in Sieverts (Sv) (j/kg)

• Rem (an old term): 0.01 Sv

• Ionizing Radiation: Displaces electrons from tissues

  • Leaves Behind Charged Particles: Ions

  • Breaks Chemical Bonds

  • Changes Molecular Structures

  • Radiation is not seen or felt unless dose is high

Radiation

• High doses: can prevent cell division

• radiation sickness at >1 Sv

  • prevents replacement or repair of blood, skin, or other tissues

• Low doses can damage dna

  • can form malignant tumors or leukemia

  • can cause birth defects

  • effects may go unseen for 10-40 years

  • weakened immune system, mental retardation, cataracts, & more

• National Research Council found no safe level of radiation

• 100-500 mSv increase risk of developing cancer

• health effects are related to level of exposure

• federal standards set 1.7 mSv/yr maximum permitted exposure

• we get radiation from many sources, not just nuclear power

  • average US Person’s Exposure = 3.6 mSv/Yr

• Nuclear power accounts for <1% of Natural Background Radiation

Radioactive Wastes

• radioactive decay: harmless as long as it is kept away from life

• half life

• reprocessing- recovering & recycling for nuclear fuel or bombs

• 1 nuclear power plant produces 20 tons of spent fuel/ year

• worldwide 71,780 tons in 40 years

• even low-level wastes may take decades to return to safe levels

Disposal Of Radioactive Waste

• never been a solid plan for waste disposal

• assumed geological burial

• short term containment

• need one for long term containment

  • at first 10,000years, but now one million

short term storage

• spent fuel stored in deep swimming pool like tanks

  • dissipates heat and prevents radiation escape

  • nearly completely filled by 2015

• after a few years air-cooled try casks hold spent fuel

  • 72 facilities in US

  • hold until long term storage become available

high level nuclear waste disposal

• geological burial is the safest option

• few nates have actually buried wastes

  • many have no identified suitable burial sites (Finland & Sweden)

• Selected sites have questionable safety

• NIMBY Syndrome: Not In My Backyard

• Many state laws prohibit nuclear waste disposal

Locating Waste Storage Sites

• Nuclear Waste Policy 1982

  • federal government accepts nuclear waste from commercial plants

  • starting by 1988

• Congress selects Yucca Mountain, Nevada in 1987

• 1989 Nevada Prohibited Nuclear Waste Storaage

• federal government overrode the prohibition

• 2008 the DOE submitted a license application

  • NRC recommended approval (international)

• Obama stopped yucca program for health and safety concerns

• a blue ribbon commission (a thinking team to make decisions) explored other options

Recommendations

• new approach to future facilities involving states & communities

• new federal corporation to plan and manage facility

  • independent of NRC (national)

• new, permanent facility must be prompt developed

• 1 or more centrally located interim storage facilities needed

• 2014- NRC reported yucca mt. met all criteria - can be pursued

Waste Repository Site In USA

• the waste isolation pilot program WIPP- Calsbad, NM

• stores defense related wastes in salt caves

• carlsbad community needed money

• 2 accidents in 2014 showed for safety measures

• megatons to megawatts program

  • converts Russian weapon to power plants fuel

Public Trusts

• Three-mile island in Pennsylvania (American; no deaths)

• Chernobyl Ukraine (worst in the world

• Fukushima Daiichi (tsunami hit)

• Human error & Natural Disasters: Loss of Public Trust In Nuclear

• Technology has Improved & More Backup Systems

Nuclear Safety

• Had Upgraded Safety Standards

• Eliminating All Risks Possible

• Active Safety Features

  • Requires active input; button, lever

• Passive Safety Features

  • Relies on natural processes like gravity

• Generation 1 & 2 are Active

• Generation 3 Reactors are Passive

  • Generation 4 on its way

• Simpler Power Plants

• Advanced Boiling Water Reactors ABWRs (too expensive)

• Economic Simplified Boiling Water Reactor (cheaper, more efficient, safer)

Generation 4 Plants

• Currently IN progress; will be out in next 20 years

• Pebble bed modular reactors PBMR (instead of rods, pebbles)

• cooled with fluidized helium- also spin turbines (moving away from water)

• small, cheap reactors built in a factory & shipped to plant location

• designed to restore public trust

Terrorism

• after 9/11; NRC increased security

• jetliner cannot penetrate thick walls of containment center

• spent fuel pools are the most vulnerable to attack

  • such more nuclear waste, we dont know what to do

How long will nuclear power last?

• nuclear plants have shorter lives than expected

• embrittlement: neutrons cause metals to become brittle

• corrosion: corrosive chemicals in hot pressurized water

• nuclear power now viewed more favorably

• good safety track record in US

• global warming imperative

Breeder Reactors

• Uranium is NOT highly abundant

• fast-neutron reactors: breeder reactors

  • turn nonfissionable U238 into Pu 239

  • increases nuclear fuel reserves more than 100x

• Safety & security concerns are greater

• more fuel produced & less waste

Fusion Reactors

• hydrogen nuclei fuse to form helium

• controlled fusion could power turbogenerators just like fission

• fusion can use water fuel

• D-t Reaction: H from Deuterium & Tritium

  • Deuterium: Naturally Occurring, Nonradioactive Extracted from Seawater

• Needs Effective & Costly Designs to Prevent Tritium Leaks

• Consumes energy

  • high temperature & pressure needed

• Extracting heat is also challenging due to great energy released

• Recent Experiments Showed fusion producing more money than spent

  • upscaling to commercial use not yet achieve

The Future

• Nuclear Power Faces Challenges

  • Expensive

  • Faces Opposition

  • Depends on Government Subsidies

• Many Nations are going Forward with More Plants

• Fukushima Disaster will slow but not stop nuclear energy

Can Nuclear Meet US Energy Needs?

• Nuclear Only Provided Electricity

• US Also Needs Energy for Transportation

• Coal & Natural Gas are cheaper but Emit C0_2'

• Still Controversial: 64% of Americans Oppose Nuclear Energy

• Regulation must be steamlined without sacrificing safety

• we must address the waste problem

• can be part of the solution, but not whole energy solution