• Choices and NO choices
• What is the present state of nuclear power generation?
• Radioactivity basics
• Nuclear reactors and waste nuclear fuel
• Waste Classification and Disposal
• Proposed waste facilities
• Issues, choices?, answers?

• Wolfson (1993) Nuclear Choices: A Citizen's Guide to Nuclear Technology; MIT Press
• Rhodes (1995) Dark Sun: The Making of the Hydrogen Bomb; Simon and Schuster
• Rhodes (1986) The Making of the Atomic Bomb; Simon and Schuster
• O'Neill (1994) The Firecracker Boys; St. Martin's Press
  

• Nuclear Waste Project Office
• http:11/5/96/www.state.nv.us/nucwaste/
• Office of Civilian Radioactive Waste Mgmt.
• http:11/5/96/www.ymp.gov/

• Are you in favor of nuclear power generation?
• Should we continue nuclear weapons production for ìdeterranceî against foreign attack?
• Would you like a nuclear power or waste site near where you live?
• Do you use energy from commercial power production?
• Can we avoid dealing with nuclear wastes by continuing our current approach?
• Are you a NIMBY?

• Nuclear power generation accounts for 22% of US electrical energy production
• In other countries (France, 73%, Belgium 59%, Sweeden, 52% ....)
• 26 countries use nuclear power generation
• Estimated 110 reactors will be in operation by 2,000
• Last reactor ordered in 1978 (as of 1993)
• 64 reactors will be over 20 years old by 2,000

An added Concern

All existing nuclear power generating plants can be used to generate fissionable material that can be used for nuclear weapons

C. Sagan

• Nuclear species are characterized by their number of neutrons (N0) and protons (P+)
• All nuclear species with the same number of protons are called ELEMENTS
• Elements with variable mass (N+P), but constant number of Protons, are called ISOTOPES of an element
• Use a sub/super script notation

²³⁵U stands for Uranium-235 (an element with 92 protons and how many neutrons??)

Radioactive Decay

Numerous natural and man made isotopes of some elements are naturally unstable and spontaneously decay with the release of energy.

• [a] Alpha Particles (2N+2P; a Helium nucleus)
• Heavy, easily absorbed
• [b] Beta Particles (N->P+ + e-)
• Penetrative
• [g] Gamma rays -
• Very short wavelength, very energetic
  

Half Life = Time for 1/2 of the radioactive substance to decay to its daughter product.

• After 1 half life 50% of radioactivity is gone
• After 2 half lives 75% decayed (25% left)
• After 3 half lives 87.5% decayed
• About 7 half lives needed to reduce radioactivity to below 1% of its initial level
  

Some Naturally Radioactive Isotopes

• ¹⁴C...........................5,730 yr
• ²³⁵U.........................70.4 million years
• ⁴⁰K .........................1.25 billion years
• ²³²Th ......................1.40 billion years
• ²³⁸U ........................4.47 billion years

Radioactive Isotopes from Nuclear Reactors

• ²³⁹Pu ..(Plutonium).....t = 24,000 years
• ³H (Tritium)................t = 12.3 years
• ¹³¹I ..(Iodine).............t = 8 days
• ⁹⁰Sr ..(Strontium).......t = 29 yrs
• ¹³⁷Cs ..(Cesium) ........t = 30 yrs

• Heavy elements have natural instability and spontaneously decays to other isotopes of other elements (Uranium, Radium, ...)
• Natural Uranium composed of two isotopes: ²³⁸U and ²³⁵U in ratio of 137:1 [MORE 238U]
• Only ²³⁵U can fission efficiently and only if present in high enough concentration to have critical mass

Natural Uranium must be enriched in ²³⁵U before it can be used in a reactor (or a bomb)

Chain Reaction

Neutron --> ²³⁵U atom -->

fission products plus neutrons

Power Generation from Nuclear Material (fission reactions)

• A TYPICAL FISSION REACTION
• 1 neutron -> ²³⁵U ==> ¹⁰²Molybdenum + ¹³¹Tin + 3 neutrons + energy

• ¹³¹Tin ->b-decay steps to ¹³¹Iodine (8 day half life)

Breeder Reactions

• Need 30 lbs. of pure ²³⁵U for critical mass

²³⁵Uranium can ABSORB neutrons and produce ìtransuranicî elements, especially Plutonium a highly radioactive and fissionable substance.

• n + ²³⁸U -> ²³⁹U -> ²³⁹Np + e- (t = 24 min.)
• ²³⁹Np -> ²³⁹Pu + e- (t = 24,000 yr)
• Need 5 lbs. of ²³⁹Pu for critical mass

Moderate a Nuclear Reaction

• ²³⁵U fission produces ìfast neutronsî
• Moderators (carbon, heavy water) slow neutrons and increase chance of neutron absorption by the next ²³⁵U atom.
• Criticality is the point where the same number of neutrons are generated as are absorbed by the Uranium (steady state)
• Control rods absorb neutrons and are designed to keep reactors at steady state.

Nuclear Reactors Produce:

• Enriched Uranium (in ²³⁵U) decays by fission into two isotopes of different masses
• One group has mass range of 85-105
• Other group has mass range of 130-145
• Most of these fission products are radioactive and decay into a wide range of other isotopes

• FUEL ROD ELEMENTS typically last 3 years before being ìspentî
• Highly radioactive AND hot.
• Must be stored approx. 10 years in a water pool to cool enough to transport

RADIOACTIVE WASTE DISPOSAL
Three Kinds

• High Level Radioactive Waste
• Transuranic Radioactive Waste
• Low Level Radioactive Waste
  

High Level Waste

• Spent reactor fuel rods
• Spent fuel and process wastes from nuclear weapons production facilities

Transuranic Waste

• Largely from nuclear weapons production facilities
• Radioactive elements heavier than uranium (Plutonium)

Low Level Waste

• Radioactive waste with short half lives (weeks to 100 years)
• Waste with 500 or longer year half life, but below levels of activity for high level wastes
• Materials that have been in contact with low radioactivity materials
• Contaminated clothing, containers, low level solids, hypodermic needles, animal carcasses, tools, rags, paper, test tubes, ...

The Problem

• Spent nuclear fuel rods are filthy with fission products and transuranics (239Pu)
• Options for storage are limited
• Storage times needed are >> 20,000 years to reduce radioactivity to accaptable levels
• Earthís climate shifts within the past 10,000 years have been large.
• Climate prediction for the next 20,000 years not possible with todayís state of knowledge (Natural variation + Greenhouse warming) = ???
  

The Solutions?

• 1- Rockets to space
• 2- Deep well injection
• 3- Oceanic Sediments
• 4- Shallow sub-surface sites
• 5- Reprocess it
• 6- Burn It

Site Selection

• Stable for > 10,000 years
• Potentially recoverable wastes
• Major stability concerns
• Above the water table (and future water tables)
• Safe from earthquake damage
• Safe from volcanic eruptions
• Away from major population centers
• Low risk from foreign terrorism clandestine bomb production

Current Hot Sites

• Low Level Waste
• (WARD VALLEY, CA)
• Transuranic Waste
• (WIPP SITE, NM)
• High Level Waste
• (YUCCA MT., NV)

Other Criteria/Concerns

• Safe transportation from Reactors to waste site(s)
• Containment of waste in case of transportation accident
• Migration of nuclides following containment vessel degradation
• PUBLIC PERCEPTIONS and Vulnerability to unsubstantiated claims.

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