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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1 radioactivity measurment
2 Neutron chain reactions
3 Environmental Issues
Radiation: energy-carrying particles (including light) spontaneously emitted by a radioactive atom
Measuring Radiation spontaneously emitted by a
Radioactivity of some natural and other materials spontaneously emitted by a
1934: patents idea
of neutron chain
(British patent 440,023)
And nuclear reactor
Technical Issue 1 spontaneously emitted by a
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
Technical Issue 2 spontaneously emitted by a
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.
Technical Issue 3 spontaneously emitted by a
Where do you get that first neutron?
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)
Technical Issue 4 spontaneously emitted by a
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.
Technical Issue 5 spontaneously emitted by a
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.
Technical Issue 6 spontaneously emitted by a
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.
Technical Issue 7 spontaneously emitted by a
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
Technical Issue 8 spontaneously emitted by a
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.
Technical Issue 9 spontaneously emitted by a
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)
Production of fissile materials
Mining Uranium and Concentrating the Ore
Key Lake mine, Saskatchewan, Canada
global distribution of uranium deposits
What’s in the Ore ? spontaneously emitted by a
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.
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.
This wall of uranium tailings, visible behind the trees, is 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. radioactive waste from the Stanrock mill near Elliot Lake, Ontario.
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
French Super Phenix Breeder Reactor
Sellafield Plant (UK)
1997 Global Fissile Material Inventories (tonnes)
HEU = highly enriched uranium
Indian Point, about 35 miles north of Manhattan
1500 tons spent fuel, stored immersed in “swimming pools” of water, where
Shrot-lived radionucleides decay away
Storage pool at a Canadian reactor
About 20% of US
By nuclear plants