environmental impacts of nuclear technologies bill menke october 19 2005
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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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Presentation Transcript
summary
Summary

1 radioactivity measurment

2 Neutron chain reactions

3 Environmental Issues

production

storage

use

disposal

slide4

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

slide5
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.
leo szilard 1898 1964
Leo Szilard, 1898-1964

1934: patents idea

of neutron chain

reaction

(British patent 440,023)

And nuclear reactor

(patent 630726)

slide23

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

slide24

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

slide25

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.

slide26

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)

slide27

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.

slide28

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.

slide29

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.

slide30

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

slide31

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.

slide32

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)

production of fissile materials
Production of fissile materials

Production of fissile materials

Mining Uranium and Concentrating the Ore

Concentrating U235

Breeding Pu239

mining uranium
Mining uranium

Key Lake mine, Saskatchewan, Canada

mining uranium36
Mining uranium

global distribution of uranium deposits

slide38

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.

slide39

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.

slide40

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

slide41
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
creating pu requires reactor
Creating Pu: requires reactor

French Super Phenix Breeder Reactor

problems
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
storage
Storage
  • Here we focus mainly
    • Storage of weapons
    • Storage of spent nuclear fuel rods
storage49
Storage

1997 Global Fissile Material Inventories (tonnes)

HEU = highly enriched uranium

slide51
A 1 GW commercial reactor contains 75 tonnes of low-enriched uranium.About 1/3 of the fuel is replaced every 18 months.

Indian Point, about 35 miles north of Manhattan

current storage at indian point
Current Storage at Indian Point

1500 tons spent fuel, stored immersed in “swimming pools” of water, where

Shrot-lived radionucleides decay away

Storage pool at a Canadian reactor

commericial reactor usage
Commericial Reactor Usage

About 20% of US

electricity generated

By nuclear plants

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