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
Radiation: energy-carrying
particles (including light)
spontaneously emitted by a
radioactive atom
Measuring Radiation
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Assessing the radioactivity of a chunk of material. Activity: Count the number of
disintegrations per second.
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Assessing the amount of energy absorbed by a chunk of material.
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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.
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.
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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.
System International (SI) Units for Radiation
Quantity
Unit Name
(Symbol)
Activity
Becqueral (Bq)
Disintegrations
Curie (Ci)
/sec
1 Bq = 2.7 x
10-11 Ci
Absorbed Dose
Gray (Gy)
Joule/kilogram
rad
1 Gy = 100
rads
Dose Equivalent
Sievert (Sv)
Joule/kilogram
rem
1 Sv = 100
rems
Definition
Former
Unit
Conversion
Factor
Radioactivity of some natural and other materials
1 adult human (100 Bq/kg)
7000 Bq
1 kg of coffee
1000 Bq
1 kg superphosphate fertiliser
5000 Bq
The air in a 100 sq metre Australian home (radon)
3000 Bq
The air in many 100 sq metre European homes (radon)
30 000 Bq
1 household smoke detector (with americium)
30 000 Bq
Radioisotope for medical diagnosis
70 million Bq
Radioisotope source for medical therapy
100 000 000 million Bq
1 kg 50-year old vitrified high-level nuclear waste
10 000 000 million Bq
1 luminous Exit sign (1970s)
1 000 000 million Bq
1 kg uranium
25 million Bq
1 kg uranium ore (Canadian, 15%)
25 million Bq
1 kg uranium ore (Australian, 0.3%)
500 000 Bq
1 kg low level radioactive waste
1 million Bq
1 kg of coal ash
2000 Bq
1 kg of granite
1000 Bq
10,000 mSv (10 sieverts) as a short-term and whole-body dose would cause
immediate illness, such as nausea and decreased white blood cell count,
and subsequent death within a few weeks.
Between 2 and 10 sieverts in a short-term dose would cause severe
radiation sickness with increasing likelihood that this would be fatal.
1,000 mSv (1 sievert) in a short term dose is about the threshold for causing
immediate radiation sickness in a person of average physical attributes, but
would be unlikely to cause death. Above 1000 mSv, severity of illness
increases with dose.
If doses greater than 1000 mSv occur over a long period they are less likely
to have early health effects but they create a definite risk that cancer will
develop many years later.
Above about 100 mSv, the probability of cancer (rather than the severity of
illness) increases with dose. The estimated risk of fatal cancer is 5 of every
100 persons exposed to a dose of 1000 mSv (ie. if the normal incidence of
fatal cancer were 25%, this dose would increase it to 30%).
50 mSv is, conservatively, the lowest dose at which there is any evidence of
cancer being caused in adults. It is also the highest dose which is allowed
by regulation in any one year of occupational exposure. Dose rates greater
than 50 mSv/yr arise from natural background levels in several parts of the
world but do not cause any discernible harm to local populations.
20 mSv/yr averaged over 5 years is the limit for radiological personnel such as
employees in the nuclear industry, uranium or mineral sands miners and
hospital workers (who are all closely monitored).
10 mSv/yr is the maximum actual dose rate received by any Australian
uranium miner.
3-5 mSv/yr is the typical dose rate (above background) received by uranium
miners in Australia and Canada.
3 mSv/yr (approx) is the typical background radiation from natural sources in
North America, including an average of almost 2 mSv/yr from radon in air.
2 mSv/yr (approx) is the typical background radiation from natural sources,
including an average of 0.7 mSv/yr from radon in air. This is close to the
minimum dose received by all humans anywhere on Earth.
0.3-0.6 mSv/yr is a typical range of dose rates from artificial sources of
radiation, mostly medical.
0.05 mSv/yr, a very small fraction of natural background radiation, is the
design target for maximum radiation at the perimeter fence of a nuclear
electricity generating station. In practice the actual dose is less.
Neutron chain reactions
fission of atomic nucleus
by neutron bombardment
one neutron in, three neutrons out
potential for using
those neutrons
to induce more fissions
Leo Szilard, 1898-1964
1934: patents idea
of neutron chain
reaction
(British patent 440,023)
And nuclear reactor
(patent 630726)
More and more neutrons
cause more and more fissions
I generated these images with
the applet
lectureonline.cl.msu.edu/~mmp/applist/chain/chain.htm
try it out!
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
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.
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)
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.
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.
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.
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
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.
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)
Environmental Issues Associated
with Nuclear Fission
Production
Storage
Use
Disposal
Production of fissile materials
Production of fissile materials
Mining Uranium and Concentrating the Ore
Concentrating U235
Breeding Pu239
Mining uranium
Key Lake mine, Saskatchewan, Canada
Mining uranium
global distribution of uranium deposits
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.
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
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
Enriching uranium
(separating the U235 from the U238)
Process: UF6 gas passed through
a cascade of centrifuges
Creating Pu: requires reactor
French Super Phenix Breeder Reactor
then chemical separation of Pu
from reactor fuel
Sellafield Plant (UK)
Legacy problems – lots of leftovers
from Manhattan Project and other
military weapons projects
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
• Here we focus mainly
– Storage of weapons
– Storage of spent nuclear fuel rods
Storage
1997 Global Fissile Material Inventories (tonnes)
HEU (weapongrade uranium
equivalent) **
Military
Plutonium
1,700
250
Civil
20
1,100
Total
1,720
1,350
HEU = highly enriched uranium
Military stockpiles of Pu by country
(tonnes)
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
1500 tons spent fuel, stored immersed in “swimming
pools” of water, where
Shrot-lived radionucleides decay away
Storage pool at a Canadian reactor
Some fuel moved to casts
Commericial Reactor Usage
About 20%
of US
electricity
generated
By nuclear
plants