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Environmental Impacts of Nuclear Technologies Bill Menke, October 19, 2005

Environmental Impacts of Nuclear Technologies Bill Menke, October 19, 2005. Summary. 1 radioactivity measurment 2 Neutron chain reactions 3 Environmental Issues production storage use disposal. measurement.

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Environmental Impacts of Nuclear Technologies Bill Menke, October 19, 2005

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  1. Environmental Impacts ofNuclear TechnologiesBill Menke, October 19, 2005

  2. Summary 1 radioactivity measurment 2 Neutron chain reactions 3 Environmental Issues production storage use disposal

  3. measurement

  4. Radiation: energy-carrying particles (including light) spontaneously emitted by a radioactive atom

  5. Measuring Radiation • Assessing the radioactivity of a chunk of material. Activity: Count the number of disintegrations per second. • Becquerel (Bq): Activity expressed in disintegrations per second. • Curie (Ci): (An old unit) Activity expressed in equivalent grams of Radium. 1 Becquerel = 2.7 x 10-11 Curies. • Assessing the amount of energy absorbed by a chunk of material. • will depend upon both the number of particles and the energy carried by the particles emitted by the disintegrating atoms. • Grays (Gy), Absorption of 1 joule (J) of radiation by 1 kg of material (for example, a human body). • Rad (an old unit) 1 Gy = 100 rads • Assessing the ability of radiation to damage living tissue. Must account for the fact that not all types of radiation are equally damaging. • X-rays and beta particles more penetrating and more damaging than alphas or neutrons. • Sievert (Sv) = Grays of X-rays and beta rays + 0.10 Grays of neutrons + 0.05 Grays of alpha partcles. • Rem: (an old unit), 1 Sv = 100 rems.

  6. Radioactivity of some natural and other materials

  7. Neutron chain reactions

  8. fission of atomic nucleusby neutron bombardment

  9. one neutron in, three neutrons outpotential for usingthose neutronsto induce more fissions

  10. Leo Szilard, 1898-1964 1934: patents idea of neutron chain reaction (British patent 440,023) And nuclear reactor (patent 630726)

  11. More and more neutronscause more and more fissions

  12. I generated these images withthe appletlectureonline.cl.msu.edu/~mmp/applist/chain/chain.htmtry it out!

  13. Technical Issue 1 What isotopes of what elements exhibit induced fission and release more neutrons? Only a few: U235 + n = Ba129 + Kr93 + 3n + g Note g = gamma rays As well as Pu239, U233 and Th232 but only U235 and Pu239 commonly used

  14. Technical Issue 2 Where do you get U235 and Pu239? U235 occurs naturally, and is concentrated into ores by geological processes. But it must be separated from the much more abundant U238 by a process called gaseous diffusion separation). Pu239 does not occur naturally, but can be Manufactured by bombarding U238 with neutrons in a breeder reactor.

  15. Technical Issue 3 Where do you get that first neutron? Two sources: natural, spontaneous decay releases it (bad in a bomb!) you make it in yet another nuclear reaction (eg Po210 emits a which bombards Be to release n)

  16. Technical Issue 4 Are the output neutron going the right speed to interact with more nuclei? Perhaps not. You might have to slow them down by having them interact with a moderator. Deuterium, hydrogen, boron and graphite are all good moderators.

  17. Technical Issue 5 What if too many neutrons escape from the surface of the fissionable material? The chain-reaction ceases. This always happens if the piece of material is too small, below its critical mass. To prevent this, you can: Surround the material with a reflector (e.g. Be) Compress the material, to make it very dense.

  18. Technical Issue 6 What if you want to control the rate of fission (e.g. reactor, not a bomb)? You must absorb just enough neutrons so that the rate of fission is constant. These are the control rods in a reactor.

  19. Technical Issue 7 What are the properties of the fission product, e.g. the Ba and Kr in U235 + n = Ba129 + Kr93 + 3n + g These are very radioactive, and their safe disposal presents a serious problem

  20. Technical Issue 8 How do you get energy – kinetic energy and g - out of the chain reaction. You let them interact with things and generate heat. Bomb: Heat builds up and everything vaporizes in an explosion. Reactor: remove heat steadily using cooling system.

  21. Technical Issue 9 What happens when the neutrons interact with non-fissionable materials. They can be absorbed, causing these materials to transmute into other isotopes, some of which are radioactive. E.g. cobalt, a trace element in steel: Co59 + n = Co60 Co60 = Ni60 + b + g (half life of CO60 is 5.27 years)

  22. Environmental Issues Associated with Nuclear Fission Production Storage Use Disposal

  23. Production of fissile materials Production of fissile materials Mining Uranium and Concentrating the Ore Concentrating U235 Breeding Pu239

  24. Mining uranium Key Lake mine, Saskatchewan, Canada

  25. Mining uranium global distribution of uranium deposits

  26. What’s in the Ore ? Ore can be up to 25% uranium oxide. The other 75%, in the form of ground up rock (tailings), needs to be disposed of. Uranium is only mildly radioactive. But the ore contains significant Radon (a gas) and radium (a solid) that are more radioactive.

  27. Among uranium miners hired after 1950, whose all-cause Standardized mortality ratios was 1.5, 28 percent would experience premature death from lung diseases or injury in a lifetime of uranium mining. On average, each miner lost 1.5 yr of potential life due to mining-related lung cancer, or almost 3 months of life for each year employed in uranium mining.

  28. This wall of uranium tailings, visible behind the trees, is radioactive waste from the Stanrock mill near Elliot Lake, Ontario.

  29. In 1975, St. Mary's School in Port Hope, Ontario, Canada was evacuated because of high radon levels in the cafeteria. It was soon learned that large volumes of radioactive wastes from uranium refining operations had been used as construction material in the school and all over town. Hundreds of buildings were found to be contaminated

  30. Enriching uranium(separating the U235 from the U238)

  31. Process: UF6 gas passed througha cascade of centrifuges

  32. Creating Pu: requires reactor French Super Phenix Breeder Reactor

  33. then chemical separation of Pu from reactor fuel Sellafield Plant (UK)

  34. Legacy problems – lots of leftoversfrom Manhattan Project and other military weapons projects

  35. Problems • Safely shipping of highly-radioactive spent reactor fuel to reprocessing plant • Accidental release of radioactive materials during chemical processing • Disposal of unwanted, but very radioactive by-products

  36. Storage • Here we focus mainly • Storage of weapons • Storage of spent nuclear fuel rods

  37. Storage 1997 Global Fissile Material Inventories (tonnes) HEU = highly enriched uranium

  38. Military stockpiles of Pu by country(tonnes)

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