3/11/2016
Clicker Question
What drives the world wide price of Uranium?
A) Very limited world supply B) Fluctuating projected demand
C) Control of supply by one country D) Mining operations in Colorado
Reading Assignment
Read about Nuclear Energy, All of Chapter 7.
Uranium Dinnerware?
Homework Assignment
No Homework due next week…
Exam #2 next week Wednesday, March 16, 2016
(details given last lecture)
Years ago, ceramic plate manufacturers thought it was a good idea
to add Uranium Oxide to the ceramic glaze that
covered their dinner plates.
-- My office hours are Monday 1-2 pm,
Tuesday 11 am –12 pm
Also available by appointment – just email me.
Colorado Uranium
Uranium mining and milling became a large industry (1950’s) on
the Colorado Plateau. The Grand Junction Operations Office of the
United States Atomic Energy Commission was headquarters for
the enterprise, and bought all the uranium produced.
Grand Junction also was home base for as many as 35 mining
companies, including area offices of major mining corporations.
It did make a bright orange attractive color, but it also made them
radioactive.
Published on Sunday, July 6, 2003 by
the New York Times
What I Didn't Find in Africa by Joseph
C. Wilson 4th
“Given the structure of the consortiums that operated the mines, it would be
exceedingly difficult for Niger to transfer uranium to Iraq. Niger's uranium
business consists of two mines, Somair and Cominak, which are run by French,
Spanish, Japanese, German and Nigerian interests. If the government wanted to
remove uranium from a mine, it would have to notify the consortium, which in
turn is strictly monitored by the International Atomic Energy Agency. Moreover,
because the two mines are closely regulated, quasi-governmental entities,
selling uranium would require the approval of the minister of mines, the prime
minister and probably the president. In short, there's simply too much oversight
over too small an industry for a sale to have transpired.”
Remember though this is just the Uranium ore.
The job of isotope separation is a big challenge.
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In the “Gulf War I” in the early 1990’s the Iraqi government was
developing a full facility for uranium enrichment.
They were attempting to use electrostatic separation, which is a
very large scale operation.
Claims were made that they were restarting this program prior to
the “Gulf War II”. It turned out not to be true.
Enriching Uranium
Recall that natural Uranium is mostly
U(238) which does not easily fission.
Thus, to use in power plants it must
be enriched in U(235) up to 3% and
higher for weapons.
Gaseous diffusion
– Uranium gas pumped through porous membranes
– Isotopes have different speeds at the same kinetic energy
Enriching Uranium
Electrostatic Separation
- utilizes very small difference in mass to electric charge ratio
- large scale operation, original method at Oak Ridge during WWII
Centrifuge method
- Also depends on difference in mass
- Lighter mass moves to smaller radius
Zippe design
90,000 rpm
Efficiency ~ (rpm)2
• Requires thousands of stages of separation
Requires very large electric power input
Aluminum Tubing Is an Indicator of an Iraqi Gas Centrifuge
Program: But Is the Tubing Specifically for Centrifuges?
Nuclear reactors use controlled fissions (steady reaction, not a
“runaway” growth). These fissions generate heat and can be
coupled to a heat engine (stream turbine for example).
1954: First reactor online in USSR.
1957: First online in the United States
There are over 400 around the world today.
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1979: Three Mile Island nuclear accident (more on this later)
1986: Chernobyl nuclear accident (more on this later too)
Some nuclear reactions occur spontaneously
(not induced).
What kinds of reactions produce radiation?
What does it mean for a material to be radioactive?
2011: Fukushima nuclear accident …
“Beta” (b) Radiation.
Any nucleus that is “unstable” will decay.
Such a nucleus is generically referred to as radioactive.
The “Beta” particle is actually just an electron.
“Alpha” (a) Radiation

Cs82 137
56 Ba81  b  
137
55
Nuclei can spontaneously decay by Alpha (a) Radiation.
An “alpha” particle is a helium nucleus (2 protons + 2 neutrons).
4
Pu145235
92 U143 2 He2
239
94
One neutron in the Cs nucleus turns into a proton and an electron
and another particle called a “neutrino”.
“Beta” radiation is more penetrating that “alphas”, and typical safe
shielding is 1-2 cm of plexiglass or very heavy clothing.
“Alpha” particles are readily absorbed by
materials, including one layer of dead skin
or one inch of air or a sheet of paper. Not
much risk, unless it is ingested.
“Gamma” (g) Radiation
“Gamma” (photons or g) radiation. This can be very penetrating
(for example X-rays). Induced fission reactions also production g
radiation. Can only shield with very thick lead (lots of material).
Some unstable nuclei decay quickly and others very slowly. We often
characterize their level of “radioactivity” by how much time it takes
for half of a set of nuclei to decay (half-life).

Cs82 137
56 Ba81  b  
137
55
Cs Half-life = 30 years.
“Neutron” (n) Radiation
“Neutron” radiation. Effects depend a lot on the kinetic energy of
the neutrons. Again, induced fission reactions are a good example.
If you start with 1000 kg of Cs,
In 30 years, you are down to 1/2
In 60 years, you are down to 1/4
In 90 years, you are down to 1/8
etc.
Thus, over time the material is
becoming less radioactive.
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Clicker Question
I have a radioactive block of material. I
measure the radiation and find that it is
a factor of 100 above safe limits. If it
has a half-life of 50 years, how long
should I store the material until it is
safe?
A) No need to store it at all
B) 50 years
C) 200 years
D) 350 years
E) Needs to be stored forever
1 half-life (1/2)
(50%)
2 half-lives (1/4)
(25%)
3 half-lives (1/8)
(12.5%)
4 half-lives (1/16)
(6.2%)
5 half-lives (1/32) (3.1%)
6 half-lives (1/64) (1.6%)
7 half-lives (1/128) (0.8%)
 7 x 50 years = 350 years
Radio-Carbon Dating
C(12) is normal stable carbon.
C(14) is produced in the atmosphere by energetic
cosmic rays from the sun. It is unstable and has a
half-life of 5730 years. Cosmic rays are steady
enough that there is a balance in the atmosphere
of newly produced C(14) and decays.
Living organisms in equilibrium with the
atmosphere have the same % of C(14) as the
atmosphere.
However, once the organism dies, it stops getting
new C(14) from the atmosphere and so the
fraction of C(14) compared to C(12) gets smaller
with time after death. That is how you can
carbon date organic materials that are up to tens
of thousands of years old.
Pu(239) has a half-life of 24,000 years. If you make it in a reactor,
and then want the level of radioactivity to drop by a factor of
1/1000 ~ 1/ (210) to be safe for people, you have to wait 10 halflives or 240,000 years. Hence the problem of radioactive waste
disposal – it stays “hot” or dangerous for a long, long time.
Rocky Flats workers in Building 707 plutonium storage area.
How to Measure Radiation?
rem = measure of a certain quantity of radiation
with a scaling factor for how damaging that type
of radiation is to biological tissue.
Radiation can modify chemical bonds, damage
cells, DNA, etc. Note that we have always been
exposed to radiation and have evolved to handle “background
radiation levels”.
Note that all life on earth has evolved in a radioactive world. It may
even play a key role in evolution.
Your lifetime chance of getting cancer is 30% !
It is increased by about 0.04% for every rem of additional exposure.
Note that this number is a very crude estimate and there may be
different threshold effects.
22 extra milli-rem (22/1000 rem) per year in Boulder due to
elevation. So over 50 years an extra 1000 mrem = 1 rem, and thus a
possible 0.04% increase in cancer risk (?)
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Nuclear Reactors
The fissioning of U(235) is used to produce heat
(instead of burning coal).
Turbine/heat engine part is then similar to a
conventional power plant.
Key elements:
Fuel Rods  contain enriched (~ 3% Uranium(235))
Moderators  some material to slow down the extra neutrons so
they do not escape.
Control Rods  they absorb neutrons when inserted to “shut
down” the reaction.
Enriched Uranium Reactor
“Moderators”
Total mass of fuel: 200,000 kg
Graphite – problem is that it burns if it gets very hot (used at
Chernobyl).
Heavy water (D20) – very effective, but expensive. Canada used
this “CANDU”
Control
Rods
Regular water (H20) – United States mostly uses this.
Moderator
Water,
graphite, …
Beryllium – effective, but a toxic metal
3% 235
Fuel rod
Paraffin (Wax) – also has problem of burning and melting.
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Clicker Question
After the control rods are inserted into the reactor and it is shut
down a great deal of energy continues to be released into the
core—this energy is primarily a result of
A. the large heat capacity of the core
B. fission product radioactivity
C. steam returning from the turbines
D. control rods heating up from neutron absorption
E. not sure/something else
B, fission products are still there and still radioactive, and produce
heat. The short lives ones decay away quickly, so the core cools
down a LOT very quickly. After a short time, it's not hot enough to
run a turbine any more. But it's hot enough to be a safety and
storage concern. Even after many years, the waste products are still
kept in casks underwater to keep them cool. It takes decades to
cool down enough to handle/move to more permanent storage.
Evolution of the Fuel Rod
• Uranium starts out enriched (~ 3% U235)
• Over time Uranium 235 depleted, eventually
decreases to < 1% or less after 3 years
– Converted to lots of stuff – not destroyed
• Neutron “poisoning”
• Uranium 238 does not
fission but is converted
to Plutonium
– 0.5% after 3 years:
• 200,000 kg of U238
creates 1000 kg of Pu
– 90+% Uranium 238
unmodified
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