Chapter 7: The Fires of Nuclear Fission
What is nuclear fission?
Is using nuclear energy
safe for humans and the
environment?
Is nuclear energy better
to use than electric
generated energy?
What happens to the
waste of nuclear fission?
Would you prefer to purchase electricity being generated from a
nuclear power plant or a traditional coal-burning plant?
Which would you choose and why?
What do you think of when you hear “nuclear energy”?
Is the U.S. doing everything it can to conserve energy? How does it
compare to other countries?
Name some ways that energy can be conserved.
20% of the electricity in the U.S. is produced by 103 nuelear reactors
The Nuclear Regulatory Commission (NRC) oversees and licenses
these power plants.
No new nuclear plants have been licensed since 1978, but several have
received extensions on their operating licenses.
Energy and matter are related by Einstein’s famous equation:
E = mc2
Atomic Particle Mass (g/mole or amu)
Electron
0.0005486
Proton
1.007277
Neutron
1.008665
1
1.007825
H
Binding Energy – the difference in energy between an atom’s
nucleus and the individual subatomic particles that make it up
The energy equivalent of the mass defect is the binding
energy.
What is Fission and How Does it Produce Energy?
Nuclear fission is the splitting of a
large nucleus into smaller ones with
the release of energy.
Energy is released because the sum
of the masses of these fragments
is less than the original mass.
This 'missing' mass (about 0.1
percent of the original mass) has
been converted into energy
according to Einstein's E=mc2
equation.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
This equation dates from the early years of the 20th century and is
one of the many contributions of Albert Einstein (1879–1955).
It summarizes the equivalence of energy, E, and mass, m.
The symbol c represents the speed of light, 3.0 x 10 8 m/s.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
Consider this: c2 is equal to 9.0 x 1016 m2/ s2
When mass is in kg, the energy units are kg x m2/s2,
which is equivalent to 1 Joule.
The large value of c2 means that it should be possible to
obtain a tremendous amount of energy from a small
amount of matter - whether in a power plant or in a
weapon.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
For 1.0 g of U-235:
E = (1.0 x 10-3 kg)(3 x 108 m/s)2
E = (1.0 x 10-3 kg)(9.0 x 1016 m2/s2)
E = 9.0 x 1013 kg m2/s2 = 9.0 x 1013 J
Don’t
forget to
cube or
square
where
needed
This is equivalent to
33,000 tons of TNT
7.2
TNT, or trinitrotoluene (discovered in 1863 by Alfred Nobel)
became the standard of explosive power as a result of the birth of
nuclear weapons-they needed to be compared to some substance of
known explosiveness.
CH3
NO2
O2N
TNT
NO2
The TNT molecule is
very unstable and when
explodes, 2 moles of TNT
rearrange to form 15 moles of
hot gas (3 mol N2, 7 mol CO, 5
mol H2O) plus some carbon.
About 1 g of TNT will
produce about 1 L of hot gas
– a 1000 times increase in
volume.
1 kg of U-235, where only about 0.1% mass is converted
to energy is equivalent to 33,000 tons of TNT
7.2
What is special about the mass number of U-235?
When a massive nucleus like U-235 undergoes fission, the
net yield of energy is a result of the sum of the fragments
being slightly less than the mass of the uranium nucleus.
If the mass of the fragments is equal to or greater than that
of iron (element 26) at the peak of its binding energy
curve, the nuclear particles (daughters) will be more
tightly bound than the uranium nucleus was, and that mass
decrease is converted to energy according to E = mc2.
For elements with lower mass numbers than iron,
fusion may lead to energy release
7.5
Discovery of Nuclear Fission
Nuclear reactions involve changes in the atomic nuclei (where the
protons and neutrons are). Ordinary chemical reactions involve bond
making and breaking with the valence (outermost) electrons.
In 1938, Otto Hahn and Fritz Strassmann, two German chemists, were
attempting to make heavier-than-uranium elements by bombarding
uranium (the heaviest naturally-occurring element) with neutrons.
Instead of the heavier elements they hoped to synthesize, they discovered
barium-139, a lighter element.
Hahn and Strassmann sent a copy of their results to Lise Meitner, a
colleague of theirs, now living in Sweden. Meitner published a paper
with her nephew, Otto Frisch, in which they explained that barium and
other light elements were formed by the cleavage of the uranium nucleus,
a process they named nuclear fission.
Nuclear Fission – the splitting of a large atomic nucleus into smaller ones
with the release of energy
Chain Reaction – a self-sustaining fission reaction; sufficient fissionable
atomic nuclei are necessary for this condition to be reached
Critical Mass – the amount of fissionable material required to sustain a
chain reaction; the critical mass of U-235 is about 15 kg or 33 lb.
A Chain Reaction with U-235
Visit Figures Alive! For more information on
nuclear fission and chain reactions!
7.5
Schematic of a
Nuclear Reactor
A nuclear
reactor is a
device in which
nuclear chain
reactions are
initiated,
controlled, and
sustained at a
steady rate (as
opposed to a
nuclear explosion,
where the chain
reaction occurs in
a split second).
7.3
Primary Coolant – a liquid that comes into direct contact with the nuclear
reactor to carry away heat (e.g. aqueous solution of H3BO3)
Moderator – substance that slows the speed of the neutrons and makes
them more effective at causing fission
Secondary Coolant – water in the steam generators that never comes in
direct contact with the reactor
Basics of a Nuclear Reactor
Actual size of
fuel pellet
An awesome
source of
electrical
energy— but
what to do with
the spent nuclear
fuel?
Reactor core
Cooling tower
7.3
Two cooling towers at the Byron
nuclear plant in Illinois
This image shows a fuel
assembly submerged in
an active reactor core
7.6
Still, the only person to
win two unshared
Nobel Prizes was
Linus Pauling, the
American chemist who
won for his chemistry
work and also a Nobel
Peace Prize for his
objection to nuclear
testing.
Marie Sklodowska Curie won two Nobel Prizes—one
in chemistry, the other in physics—for her research on
radioactive elements.
7.5
Discovery of Radioactivity
In 1896, Henri Becquerel left a sample of
K2UO2(SO4)2 on top of a sealed photographic
plate in a drawer. After several days, he
discovered the plate was fully exposed as if it
had been exposed to light. He realized that the
uranium salt must be emitting some type of
radiation.
Pierre and Marie Curie investigated further to
show that the uranium and not the potassium or
sulfur was the source of the radiation. All
uranium-containing compounds behaved the
same way.
The Curies and Henri Becquerel shared the 1903
Nobel Prize in Physics for the discovery of
radioactivity.
Neutron/Proton Ratio for Isotopes
Types of Radioactivity
Ernest Rutherford discovered alpha and beta
radiation, and gamma radiation was later
discovered.
Alpha particles – Helium nuclei (He2+) are
bundles of two protons and two neutrons. By
losing two protons, alpha emitters decrease their
atomic number by two. This is nature’s method
of reducing an isotope atomic number.
Beta particles – Electrons that increase the
atomic number by one. Beta emitters have too
high of a neutron/proton ratio and loss of a beta
particle improves this ratio.
Gamma rays – This type of radioactivity does
not consist of matter at all. It is simply
electromagnetic radiation of a very high
frequency. Gamma rays are usually emitted
along with alpha or beta particles.
All radioactive isotopes undergo a radioactive
decay (or a series of radioactive decays) until
they form a stable isotope.
Each radioisotope has its own unique half-life
(the amount of time it takes for half of the
radioisotope to undergo its radioactive decay
reaction). This half-life is a physical
characteristic of the particular isotope and
cannot be changed.
Radioactivity
Include alpha, beta, and gamma rays.
7.5
Three Types of Radioactivity
Neutron Source
Alpha Emitter
238
94 Pu
Gamma Emitter
4
2 He
234
92 U
+
9
4
Be
12
6
+
4
2 He
C
+
1
n
0
+
0γ
0
Control Rods
Typically made of cadium; the control rods are interspersed with the
fuel rods and can be raised and lowered into the fuel rod bundle.
112
48 Cd
+
1n
0
113
48 Cd
Uranium consists of approximately 99.3% of
U-238 and 0.7% U-235. U-238 does not
undergo fission, but U-235 does.
1n
0
+
[ 236
92 U]
235
92 U
141
56 Ba
+
92
36 Kr
+
3 10 n
U-238 absorbs neutrons. For this reason, unenriched uranium cannot
sustain a chain reaction.
1n
0
+
238
92 U
239
92 U
(half-life = 23.5 min)
239
92 U
239
93 Np
+
0e
–1
239
93 Np
239
94 Pu
+
0e
–1
(half-life = 2.35 days)
(half-life = 24,400 yr)
U-238 Radioactive Decay Series
Radioactive isotopes
undergo decay until
they reach a stable
species.
All isotopes of all
elements with atomic
number 84 (Po) and
higher are radioactive.
7.5
Halflives for the U235 Decay Series
Half-life: the time required for the level of radioactivity to fall to
one-half of its value.
7.8
Half-life: the time required for the level of radioactivity to fall to
one-half of its value.
7.8
Writing Nuclear Equations
14
6C
14
6C
210
84
210
84
Po
is a beta emitter.
14
7N
+
0
–1
e
Po is an alpha emitter.
206
82
Pb +
4
2 He
Writing Nuclear Equations
Fission of
235
92 U
+
Fission of
235
92 U
1n
0
235
92 U
with a fast-moving neutron produces144
55 Cs and
two neutrons
144
55 Cs
+
90
37 Rb
+
2 10 n
with a fast-moving neutron produces139
52 Te , an
isotope with a mass number of 94 and some
number of neutrons
235
92 U
+
1n
0
139
52 Te
+
94
40 Zr
+
3 10 n
A nuclear power plant cannot undergo a
nuclear explosion because it uses uranium ore
that contains only 4-5% U-235. Nuclear
weapons use fuel that is typically 80-90% U235.
Gaseous Diffusion – a process in which a gas is
forced through a series of permeable
membranes; lighter mass materials of the same
type move through the membranes more quickly
UF6 is a solid that vaporizes at 56°C. A 235UF6
molecule moves about 0.4% faster than 238UF6.
Diffusion through a very long series of
permeable membranes results in separation of
the isotopes.
Depleted uranium is almost entirely U-238 since
it has been depleted of most of the small amount
of U-235 it once had.
Nuclear fuel can be diverted to make nuclear
weapons.
1n
0
+
238
92 U
239
93 Np
239
92 U
+
0
–1
e
(half-life = 2.35 days)
239
93 Np
239
94 Pu
+
0e
–1
(half-life = 24,400 yr)
Spent nuclear fuel (SNF) is the radioactive
material remaining in fuel rods after they have
been used to generate power in a nuclear reactor.
Pu-239, like U-235, is a fissionable radioisotope.
During WWII, a breeder reactor was built on the Columbia River in
Hanford, Washington. It was designed to convert U-238 to Pu-239 by
neutron capture. The plutonium was then chemically separated from the
uranium.
Plutonium was used in the first atom bomb exploded in New Mexico in
July, 1945 as a proof of concept.
The bomb dropped on Nagasaki a few weeks later was also fueled by
plutonium.
Pu-239 reacts easily with oxygen to form PuO2, one of the most toxic
compounds known. It is a powdery substance which is easily inhaled. It
causes lung cancer in minute quantities and accumulates in the liver and
bones where its radioactivity does serious damage.
Nuclear Weapons
The isotopes U-235 and
U-238 behave essentially
the same in all chemical
reactions, so the separation
of these two isotopes is
extremely difficult and relies
on advanced technology that
is not readily available.
Building and deploying a nuclear weapon is a very
difficult operation to carry out.
7.10
The Three Mile Island Accident
The accident began about 4 a.m. on March 28,
1979 in the non-nuclear portion of the plant,
when the main feedwater pumps stopped
running due to either a mechanical or electrical
failure.
Pressure in the nuclear portion of the plant
increased and a relief valve opened. The valve
should have closed when pressure decreased by
a certain amount, but did not. Cooling water
poured out of the stuck-open valve and the
reactor core overheated.
Nuclear operators had no instrument to show the
level of coolant in the reactor core (a design
flaw) and no signal that the relief valve was
open. As alarms rang and warning lights
flashed, they did not realize the plant was
experiencing a loss-of-coolant accident.
Conditions worsened when they reduced the
flow of coolant through the core (human error).
Some of the fuel rods ruptured and the fuel
pellets spilled out and melted. When federal and
state authorities were notified, they took steps to
gain control of the reactor by ensuring adequate
cooling.
It is estimated that 2 million people received an
average dose of one millirem. The average
person receives 100-125 millirems per year from
natural sources.
Monitoring of thousands of samples of air,
water, milk, soil and foodstuffs in the years
following the accident indicates that most of the
radiation was contained and the actual release of
radioactive materials had negligible effects on
the physical health of individuals or the
environment.
July, 1 982:
Und er water cam er a survey s the i nside o f t he re ac tor vessel for the
first t im e, re vealing t hat t he ext ent of t he core m eltdown was far
greater t ha n ex pe cte d.
Current Status
The reactor is permanently shut down and
defueled, with the reactor coolant system
drained, the radioactive water decontaminated
and evaporated, radioactive waste shipped offsite to an appropriate disposal facility, and
reactor fuel and core debris shipped off-site to a
Dept. of Energy facility.
Impact of the Accident
The U.S. Nuclear Regulatory Commission’s
(NRC) oversight of its licensees has increased
since the Three Mile Island incident.
Plant design and equipment requirements were
upgraded and strengthened.
Operator training was revamped since human
performance was identified as a critical part of
plant safety. Drills and response plans are now
tested several times a year by licensees.
Two NRC inspectors live nearby and work
exclusively at each plant to provide daily
surveillance of licensee adherence to NRC
regulations.
Chernobyl – Causes of the Accident
Lack of a “Safety Culture”
Violation of Procedures:
1) Only 6-8 control rods (normally a
minimum of 30 are required) were used by
the end of a test to see if the turbines could
produce sufficient energy to keep the
coolant pumps running until an emergency
diesel generator was activated
2) The reactor’s emergency cooling system
was disabled
Design Fault in the RBMK Reactor
In this type of reactor, the neutrons released by
the fission of U-235 nuclei are slowed down
(moderated) by graphite and water so as to
maintain a chain reaction.
Nuclear experts have criticized this type of
reactor primarily because it lacks a containment
structure and requires large quantities of
combustible graphite within its core.
The RMBK reactor type suffers from instability
at low power and may experience a rapid,
uncontrollable power increase. The cause of this
instability is:
1) Water is a better coolant than steam
2) The water acts as a moderator and neutron
absorber (slowing down the reaction)
while steam is much less effective.
Excess steam pockets in the RBMK design lead
to increased power generation. The additional
heat produces more steam and means less
neutron absorption, which causes the problem to
escalate.
Timeline
On April 25, 1986, Chernobyl reactor #4 is
powered down to 1600 MW (about half power)
in preparation for the test. At 2 p.m., an
electricity grid controller requested that
Chernobyl stay online till 11:10 p.m. The test
was therefore delayed, but the emergency core
cooling system was not switched back on.
At 11:10 p.m. power reduction resumed in order
to reach the designated range of 700-1000 MW.
Due to operator error, the power fell to about 30
MW at 12:28 a.m. on April 26.
The reactor control engineer tries to raise the
power by removing control rods and at 1:00 a.m.
power had stabilized at about 200 MW.
Although far below the desired range, Chernobyl
engineers decide to continue with the
experiment.
The water level in the steam drums drops below
emergency levels. At 1:19 a.m., engineers
override an emergency signal and keep the
reactor running. Water in the cooling circuit
nears the boiling point.
In order to keep power at 200 MW, all 12
automatic control rods and some manual control
rods are withdrawn from the core.
Computer printouts at 1:22 a.m. indicate an
immediate shutdown of the reactor is required,
but the experiment begins at 200 MW. The
generator and turbines are shut down. Steam
quantities begin to increase spontaneously and
uncontrollably. Water flow through the core
declines as the water temperature increases.
A steep rise in power occurs and a full
emergency shutdown is ordered. Control rods
do not fully descend into the core due to damage
or malfunction. Power reaches 530 MW in 3
seconds and continues to increase exponentially.
Fuel rods rupture and fuel particles react with
water creating a large steam explosion. The
graphite ignited and in the ensuing inferno, the
radioactive fission products and burning graphite
were sucked up and released into the air. A
second explosion shortly thereafter adds to the
destruction. Fires start in over 30 places.
In the first ten hours after the explosion,
firefighters pumped cooling water into the
reactor core. 31 members of this group died of
radiation sickness shortly afterwards. After this
attempt was abandoned, military helicopters
dropped 2400 tons of lead and 1800 tons of sand
in an attempt to smother the fire. This made
matters worse as heat accumulated under the
dumped materials and more radiation was
released.
In the final phase of firefighting, the reactor core
was cooled with liquid nitrogen. Not until May
6 were the fire and radioactive emissions under
control.
Of the 800,000 firefighters and soldiers
(liquidators) involved in the clean-up operations
until 1989, a total of 25,000 have died according
to government agencies. Estimates provided by
the liquidator associations are far in excess of
official figures. Today, the surviving liquidators
are still suffering from the damage to their
health.
36 hours after the explosion, the 45,000
inhabitants of Pripyat, 4 km away, were
permanently evacuated by bus. Within 10 days,
130,000 people who lived within 30 km, were
also evacuated.
Within seven months, the ruined reactor building
was enclosed in a reinforced concrete casing. A
second shelter is scheduled to be completed by
2011 and is intended to safely confine
radioactive material for at least 100 years.
After prolonged international negotiations, the
entire Chernobyl complex was closed in Dec.
2000.
Types of Radiation Released
More than 40 different radionuclides escaped
into the atmosphere in the first ten days
following the accident. Most significant are
iodine (I-131, half-life = 8 days), cesium (Cs137, half-life = 30 years), strontium (Sr-90, halflife = 29 years) and plutonium (Pu-241, half-life
= 24,400 years) and its decay products.
Variable weather conditions in the days
following the accident, spread the radiation in a
very uneven pattern. Severely contaminated
“hot spots” often lie close to only mildly
contaminated areas.
These radionuclides can enter the food chain
through livestock and crops, wind erosion, forest
fires, and transport by rivers.
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Environmental Damage
There are 600 to 800 unsecured burial pits of
radioactive debris in the 30 km zone around
Chernobyl. These dumps were never precisely
mapped and still pose a threat to groundwater.
Contamination via river water in Ukraine is still
a major problem. Measurements in Belarus and
Ukraine show that radiation has concentrated in
the sediments at the bottom of water bodies,
particularly standing waters such as lakes or
ponds. Some people continue to fish these
waters and receive contamination via the food
chain.
The severe radioactive contamination of
mushrooms, berries, game and fish, as well as of
grass and hay used as feed for dairy cattle, are
the main pathways whereby food is
contaminated.
Belarus
The official Chernobyl Committee in Minsk
estimates the total damage to Belarus at USD
235 billion. The nuclear disaster effectively
deprived the country of 22 percent of its
agricultural land and 21% of its forests.
Ukraine
By 2015, Ukrainian experts estimate the disaster
will have cost the country USD 201 billion.
40% of Ukraine’s forested area is contaminated.
Russia
Russian costs were about USD 3.8 billion
between 1992 and 1998. 2 million people still
live in the contaminated westernmost area.
Chernobyl: Social and Environmental Consequences
Over 1,000 injuries and thirty-one deaths of firefighters and others who
reported to scene of accident.
150,000 people evacuated from their Ukraine homes.
Radioactive cloud released over a large part of Europe. Health threatening
levels of radioactive materials were found in at least twenty nations, and as
far away as 2,000 km from Chernobyl. Estimated 250 million people were
exposed to unhealthy amounts of radiation.
Estimates of future cancers from the accident range anywhere from 7,500 to
1 million.
Radioactive particles in the environment and in the food chain.
Large amount of uncertainty and fear in the population.
7.6
Chernobyl: Political Consequences
Distrust of government.
Soviet Union cover up: Sweden and Poland were the first
nations to bring attention to the accident.
Other nations attempted to downplay the health effects of the
accident in their own nations.
Public opposition to building
additional nuclear power plants
increased significantly worldwide.
7.6
Nuclear Energy
Pros
Cons
No greenhouse
gas emissions
Nuclear fission
generates a
number of
radioactive
isotopes, some
of which have
long halflives
No air
pollutants (e.g.
sulfur or nitrogen
oxides, mercury
emissions)
Uranium ore,
although not
limitless, is
relatively
abundant
Remote
possibility o f
a nuclear
accident
If there are approximately 50 years of easy-to-extract oil and
petroleum available and 75 years of domestically produced
natural gas, it can be safely predicted that the prices of these
nonrenewable fuels will drift upward as the supplies decrease
and energy demand increases.
For the future, what energy sources should the US invest in?
Nuclear energy?
Expensive-to-extract oil?
Renewables such as wind, solar or ethanol?
Measures of radioactivity:
1 Curie = 1 Ci = 3.7 x 1010 decays/second =
number of radioactive decays from one gram of
radium
1 rad (radiation absorbed dose) = 0.01 joule of
radiant energy absorbed per kg of tissue
The rem is a measure of radioactivity adjusted
for the type of radiation and the rate at which it
is delivered.
# of rems = Q x (# of rads)
The sievert (Sv) is an international unit and
equals 100 rems.
rad = “radiation absorbed dose” – absorption of 0.01 J of
radiant energy/kg tissue
rem = “roentgen equivalent man” = Q x (number of rads)
where Q is a relative biological effectiveness factor
1 Sv = 100 rem
7.7
Hazards of Radioactivity
Rapidly dividing cells are particularly
suspectible to damage from radioactivity. In
adults, rapidly dividing cells are found in the
bone marrow, skin, hair follicles, and the lining
of the stomach and intestines.
Radiation sickness is the illness produced by
exposure to large amounts of radiation. The
immune system is suppressed and anemia results
from loss of red blood cell production.
Disposal of Nuclear Waste
High-Level radioactive waste (HLW) – the
mixture of radioactive material from spent
nuclear fuel (SNF) or from the reprocessing of
SNF; because of the very long half-lives of some
of the radioisotopes, it must be permanently
isolated
HLW also contains heavy metals, which are
toxic. It poses a hazard both chemically and
because of the high levels of radioactivity.
HLW comes from both military facilities and
commercial nuclear plants. Most of this waste is
stored under water in pools at the site where it
was generated.
7.9
Since 1977 there has been a moratorium on
spent fuel reprocessing in which plutonium and
uranium are separated from the other fission
byproducts and used to generate additional
energy.
By 2010, the US will have more than 100,000
tons of HLW.
99.9% of radioactivity dissipates after ten halflives. For fission byproducts such as Sr-90 and
Cs-137, this would mean storing the waste for
300 years. For Pu-239 (half-life = 24,400 yr),
the waste needs to be sequestered from the
environment for a much longer time period.
Congress has approved the Yucca Mountain site
in Nevada as the nation’s first high-level nuclear
waste repository. If completed, it would have a
capacity to hold 78,000 tons of HLW.
Proposed High Level Nuclear
Waste Storage in Yucca
Mountain, Nevada
7.9
A worker in one of the Yucca mountain tunnels
7.9
Energy Secretary Steven Chu stated at a Senate
hearing in March 2009 that the Yucca Mountain
site is no longer viewed as an option to store
reactor waste. The Obama Administration
proposed to eliminate almost all funding in the
FY2009 budget while it devised a new strategy
for nuclear waste disposal. In July 2009, the
House of Representatives voted 388 to 30 not to
defund the Yucca Mountain repository in the
FY2010 budget.
This project is widely opposed in Nevada and is
a hotly debated topic. Polls indicate that most
Nevadans are against the repository. There is
also general resentment felt by many Nevada
residents over the fact that 87% of the land in
Nevada is federal property. Although about 15%
of their electricity comes from the Palo Verde
nuclear station in Arizona, many Nevadans feel
it is unfair for their state to have to store nuclear
waste when there are no nuclear power plants in
Nevada.
The nuclear waste is planned to be shipped to
the site by rail and/or truck in robust containers
approved by the Nuclear Regulatory
Commission. The transport of spent fuel in
Europe and Asia is routine with few safety or
security issues. Globally, over 70,000 MTU
(metric tons of uranium) of spent fuel have
already been transported by train, truck, and
ship. In addition, the Nevada Test Site which
encompasses Yucca Mountain, is the location
where over 900 nuclear weapons have been
detonated and continues to serve as primary
location for any future nuclear weapons tests if
needed. The likelihood that this land area would
be used for any other purpose is remote.
Is the Nevadans’ opposition merely a knee-jerk
NIMBY (not in my backyard) reaction or is it
unfair to force them to accept the nuclear waste
repository in their state?
What about concerns about transporting HLW
from the sites where it is generated to Yucca
Mountain?
Low-level radioactive waste (LLW) – waste
contaminated with smaller quantities of
radioactive material than HLW; excludes spent
nuclear fuel.
It consists of a variety of materials:
Lab clothing, gloves and instruments from
hospitals and research facilities that use
radioisotopes
Waste from facilities that manufacture enriched
uranium fuel pellets
Waste from mining operations
LLW comes military sites, commercial power
plants and medical facilities.
Currently it is placed in sealed containers and
buried in trenches at three LLW disposal sites
(Barnwell, SC; Clive, UT; Richland, WA).
Costs of HLW waste disposal
Cleanup of the Department of Energy’s Hanford
Site in southeastern Washington is estimated at
$90 billion. This is the most complex cleanup
project for DOE, which is responsible for
cleaning up some 100 other contaminated
weapons sites.
The cleanup plan calls for the production
reactors to be dismantled and their highly
radioactive cores to be encased in concrete cubes
designed to last 75 years while radiation levels
drop and scientists figure out a solution for their
ultimate disposal.
The Hanford Reservation – The Nation’s
Most Contaminated Nuclear Site
53 million gal of high-level radioactive and
chemical waste liquids and sludge are stored in
177 underground tanks. Some tanks have leaked
and there is a plume of contaminated
groundwater stretching from the tanks towards
the Columbia River. There is no technological
solution for this problem at the present time.
Current plans are to vitrify this tank waste into
glass logs, which could create 39,000 tons
(13,000 canisters) of high-level radioactive
waste and 600,000 of low-activity radioactive
and chemical waste. The vitrification facility is
currently under construction.
Storage of nuclear waste
Thousands of canisters of spent
nuclear fuel rods submerged in water
Encapsulating reprocessed
HLW in glass canisters
(vitrification).
There is 2100 tons of spent nuclear fuel in aging,
broken canisters in pools near the Columbia
river. This material is being cleaned,
repackaged, and loaded into special steel baskets
by remotely-controlled equipment that works
underwater. The baskets are loaded into 14-ft
tubular canisters, the water drained and replaced
with pressurized helium, and the canisters
trucked to a storage building on the central
plateau.
About 85% of the site will be cleaned the
radioactive and chemically hazardous soil, tank
waste, spent nuclear fuel, surplus plutonium, and
other dangerous material will be concentrated
and isolated from human contact on the central
plateau disposal area.
The Canister Storage Building holds three
underground vaults of SNF and vitrified waste
Nuclear Power Globally
Currently 441 nuclear reactors operate in 31
countries, producing 363 billion W of electricity.
Another 30 reactors are under construction and
an additional 100+ are in the planning stage.
New generations of nuclear reactors are
designed to have “passive” safety systems that
do not require human intervention in the case of
an accident.
Some new designs feature a closed fuel cycle.
Deleted uranium is used as a fuel source and
after bombardment with neutrons, Pu-239 (a
fissionable radioisotope) is produced. The
heavy nuclides – such as neptunium, areicium,
plutonium and curium – are removed from the
spent fuel and returned to the reactor.
Nuclear Reactors by Continent
Nuclear Energy in France
(http://www.world-nuclear.org)
* France derives over 75% of its
electricity from nuclear energy. This is
due to a long-standing policy based on
energy security.
* France is the world's largest net
exporter of electricity due to its v ery low
cost of generation, and gains over EUR 3
billion per year from this.
* France has been very active in
developing nuclear technology. R eactors
and fuel products and services are a
major export.
The present situation is due to the French
government deciding in 1974, just after
the first oil shock, to expand rapidly the
country's nuclear power capacity. This
decision was taken in the context of
France having substantial heavy
engineering expertise, but few
indigenous energy resources. Nuclear
energy, with the fuel cost being a
relatively small part of the overall cost,
made good sense in minimizing imports
and achieving greater energy security.
As a result of the 1974 decision, France
now claims a substantial level of energy
independence and almost the lowest cost
electricity in Europe. It also has an
extremely low level of CO2 emissions
per capita from electricity generation,
since over 90% of its electricity is
nuclear or hydro.
Highly radioactive materials, such as spent
fuel rods, are stored in The Hague (a
reprocessing facility) and at the Marcoule
nuclear facility, on the Rhone River near the
southern city of Orange.
Waste disposal is being pursued under
France's 1991 Waste Management Act
(updated 2006) which established ANDRA
as the national radioactive waste
management agency. Research is being
undertaken on partitioning and
transmutation, and long-term surface storage
of wastes following conditioning. Wastes
disposed of are to be retrievable.
After strong support in the National
Assembly and Senate, the Nuclear Materials
and Waste Management Program Act was
passed in June 2006 to apply for 15 y ears.
This formally declares deep geological
disposal as the preferred solution for highlevel and long-lived radioactive wastes, and
sets 2015 as the target date for licensing a
repository and 2025 for op ening it. It also
affirms the principle of reprocessing used
fuel and using recycled plutonium and
uranium "in order to reduce the quantity and
toxicity" of final wastes, and calls for
construction of a prototype fourthgeneration reactor by 2020 to test
transmutation of long-lived actinides. The
cost of the repository is expected to be
around EUR 15 billion: 40% construction,
40% operation for 100 years, and 20%
ancillary (taxes and insurance).
Risks and Benefits of Nuclear Power
How would you compare its safety with
coal power generation?
7.11