Nuclear Energy
Chemistry in Context: Chapter 7:
Fires of Nuclear Fission
Assignment: All the problems with blue
codes or answers on Page 530
Mass and Energy
‹E
= mc2
‹ Where E = energy released, m = mass lost, and c =
3.0 x 108 m/s.
‹ Since c2 =9.0 x 1016 m2/s2 and 1 Joule is equal to 1
kg-m2/s2, a tremendous amount of energy can be
obtained from a very small amount of mass.
‹ 1 kg of U-235 with 0.1 % mass loss results in the
production of 9.0 x 1013 Joules or the energy
equivalent to 33000 tons of TNT.
‹ 1957,
the first nuclear power plant near Pittsburgh,
PA.
‹ Seabrook plant first proposed in 1972,
construction began in 1976, and operating license
granted in 1990.
‹ 1/5 your electricity is generated by nuclear power
‹ 103 nuclear plants in US; 9 nuclear plants have
closed since 1990 due to perceived risk.
Subatomic Particles
‹ Electrons
(Negatively charged particles outside
nucleus; discovered by Thomson)
‹ Nucleons held together by very strong nuclear force
– Protons (Positively charged particles inside the
nucleus; discovered by Rutherford)
– Neutrons (Neutral particles inside the nucleus;
discovered by Chadwick)
History of Nuclear Fission
Equations for Nuclear Reactions
‹
1938, Hahn and Strassmann found Ba atoms when bombarding
U with neutrons
‹ Lise Meitner and Otto Frisch hypothesized that the U atoms
were “splitting” to form atoms of lighter elements such as Ba in
a nuclear fission process.
‹ Energy given off fission is described by Einstein’s equation;
mass of products less than mass of reactants; mass loss =
energy!
‹ Neither mass nor energy is individually conserved; matter is a
concentrated form of energy.
‹ Mass
Decay Series of Radioactive Elements
Nuclear Fission vs. Fusion
Transmutation of elements occur by nuclear emission of α or β
particles that change the atomic number by –2 and +1, respectively.
number of an element is equal to the sum of
protons (p) and neutrons (n).
‹ Atomic nuclei of heavier elements or higher
atomic number tend to undergo nuclear reactions
or decay due to the high p:n ratio.
‹ Balancing equations for nuclear reactions
involves making sure that the sums of subscripts
(charges) and superscripts (mass number) on both
sides of the equation are equal.
Fission in which a large nucleus splits into smaller nuclei
and neutrons is associated with loss of nuclear mass or
release of a vast amount of energy in nuclear reactors.
‹ Fusion involves smaller nuclei combine to form larger
nuclei with a greater release of energy.
– Sun and stars rely on fusion to achieve high temperature ~
100 million degrees.
– Fusion produce ionized gas of electrons, protons and other
nuclei.
– Advantages of fusion include low cost, abundance of
deuterium, and “no” waste problems
‹
Fig reaction (i.e. exponential increase of
Chain
neutrons) can occur spontaneously if a
critical mass (~15 kg) of U-235 is available.
How does this work?
‹ Each
Figure 7.5 on Page 291
Nuclear Fuel
UO2 pellets of the size of pencil eraser
are packed into metal tubes that are
assembled into fuel assembly
‹Critical mass of U-235 needed is about 33
pounds (15 kg).
‹Plutonium or americium are used to
generate neutrons needed to initial the
fission as follows:
neutron hits a U-235 nucleus and causes
its fission or splitting into lighter nuclei along
with the production of 2-3 neutrons.
‹ The chain reaction of successive fission events
lead to loss of mass (0.1 %) which is related to
energy release (E=mc2)
‹ Note that the Kr-Ba pathway releases 3 neutrons
whereas the Rb-Cs and Xe-Sr pathways release
2 neutrons each.
UO2 Fuel Pellets and Fuel Rod Assembly
‹200
– 238Pu→234U + 4He; 4He + 9Be → 12C + 1n
Fig. 7.1 on Page 284
Fig. 7.7 on Page 293
Coal and nuclear power plants are similar except for
water being heated by energy from coal combustion
as opposed to nuclear fission.
How is fission controlled?
‹ Control
rods made of cadmium, silver, indium
serve as neutron absorbers to prevent
uncontrollable chain reaction of the fission
process.
‹ The fuel bundles and control rods are bathed in a
primary coolant solution of boric acid in water to
provide heat transfer and to absorb neutrons via
borons and slow down the speed of neutrons.
‹ Contains boric acid, neutron absorber
Fig. 7.6 on Page 292
Seabrook Nuclear Power Plant
Figure 7.12
Page 297
400-ton reaction vessel with 44-ft wall of 8-in carbon steel; 4.5 ft
thick inner concrete walls of containment and 15in outer wall.
Fig. 7.2
“Natural” waters does not come in
contact with nuclear materials
Figure 7.8 on Page 293
Chernobyl Nuclear Accident
Nuclear reactor
Cooling towers
Figure 7.9 on Page 295
Chernobyl Nuclear Accident -1986
‹ Cooling
water stopped as part of a “safety test”;
reactor temperature rose quickly.
‹ Due to insufficient number of graphite control
rods and steam pressure to deliver coolant, a
power surge led to the meltdown of reactor core
and burning of graphite rods.
‹ Water sprayed on rods led to the production of
hydrogen gas that exploded upon reaction with
oxygen in the air
Fig. 7.10: Chernobyl Reactor 4
In 1986, an
explosion blew off
the 4000-ton steel
plate covering the
reactor at the
Chernobyl plant and
spewed radioactive
products in the
vicinity.
What happened at Chernobyl?
Could nuclear mishaps happen here?
‹2
H2O + C → 2 H2 + CO2
‹ 2 H2 + O2 → 2 H2O + Energy
‹ Explosion spewed radioactive materials into the
atmosphere across Ukraine, Belarus, and Scandinavia
‹ Tragic outcomes include several outright deaths, deaths
of 31 firefighters due to acute radiation sickness, 190
patients with acute radiation sickness, and 200,000
“liquidators”, who buried the most hazardous waste and
constructed the “sarcophagus”.
‹ Chernobyl closed in 2000.
‹More
Radioactivity
Radioactivity: History
‹Radioactivity
is a spontaneous process of
nuclei undergoing a change in atomic
number or elemental identity by emitting
particles or rays (transmutation).
‹Nuclei continue to decay till stable nucleus
is produced (Z [atomic number] < 83).
‹Exceptions are Technetium (Z = 43) and
Promethium (Z = 61).
regulations and different plant
designs in the U. S.
‹Three Mile Island 1979 - Lost coolant,
partial meltdown.
‹Disasters result from the complex
interplay of faulty plant design, human
error, and political instability.
•
•
•
Discovered in 1896 by Antoine Henri
Becquerel who noticed the radiation of a
uranium sample on a photographic plate.
Marie Curie applied the term “Radioactivity”
and discovered 2 other radioactive elements,
Radium and Polonium.
Ernest Rutherford identified 2 types of
radiation, namely the alpha (α) and the beta (β)
particles.
Radioactive Emissions
Page 301
Gamma ray is a form of electromagnetic
radiation that is even more energetic than the
X-ray discovered by Wilhelm Roentgen
Nuclear Bomb vs. Nuclear Power
‹Rapid
and uncontrolled fission in a bomb
compared to the slow and controlled
energy release and use of control rods.
‹Bomb uses highly enriched U-235 (>90%)
relative to the 3-5% U-235.
‹Separation of U-235 and U-238 is
achieved by the diffusion of UF6 at 56 C at
Paducah, KY.
Penetration Powers of Nuclear Radiation
‹Beta
(β) particle is a form of high
speed electron with a –1 charge.
‹Alpha particle (α) is a helium
nucleus with +2 charge.
‹Gamma ray (γ) is a highly
energetic photon with no mass and
no charge.
4
β = -1oe α = 2He
Nuclear Fuel for Weapons
Processing of U-235 is too complex and costly for use in
nuclear weapons.
‹ Pu-239, which can be extracted from spent nuclear fuel
with U-238, is a more likely fissionable material in bombs.
‹ Nuclear reaction in breeder reactor is:
– 1n + 238U → 239Pu + 2 0e (Hanford, WA)
‹ PuO2 is easily inhaled, causing lung cancer and damage to
bone and liver via its solubility in blood; Nagasaki bomb is
based on Pu-239.
‹
Measurement of radioactivity
‹Rate
of emission of decay particles in
counts per minute (cpm) can be
measured by a Geiger counter.
‹1 Curie = 3.7 x 1010 disintegrations/sec
– Disintegrations refer to α, β, or γ emission
– Typically measured as mCi, µCi, and pCi
Table 7.2 Page 284
Radiation Doses and Health
Alpha, beta, gamma, neutrons, x-rays are ionizing radiation
that can damage living cells (white blood cells or bone
marrow) or induce DNA transformation or cancer.
‹ One RAD is the absorption of 0.01 Joule of radiant energy per
kg of tissue.
‹ Physiological damage is measured by rem or Roentgen
equivalent applied to mammals.
– REM = n x (Number of Rads) where n = 10 for α and neutrons
and n = 1 for β, γ, and X-rays.
‹ 1 Sv (sievert) = 100 rem; 1 µSv = 1 x 10-6 Sv = 0.10 mrem
‹
Radioactive Decay
‹ Nuclide
refers to a nucleus with a unique atomic
number and mass number
‹ Radionuclide decays spontaneously as follows: A
→B+b
– where A is a parent nuclide, B is a daughter
nuclide, and “b” is the emitted radiation.
‹ The
rate of decay is given by the half-life or the
time required for the level of radioactivity to fall
to ½ of its initial value.
Figure 7.15, 7.16, &7.17 Page 303
Applications of Radionuclides
Smoke detectors - Americium-241 as an α emitter
Food irradiation to kill harmful microbes
‹ Medical diagnosis and cancer treatment
– I-131 used to treat thyroid cancer and hyperthyroidism
– 85Sr, 99Tc, 197Hg, and 123I are used for diagnosis
‹ Research: Studies chemical reaction pathways and
distribution of pollutants using radioactive labels
‹ Dating of archaeological objects by C-14
– 1 C-14 radionuclide for every 1012 C-12 atoms; C-14
concentration decreases by ½ every 5730 years.
‹
‹
Table 7.4 Page 305
High-Level Nuclear Waste (HLW)
‹HLW
or mixed waste is hazardous due its
radioactivity and toxicity; it consists of
radioactive materials from the reprocessing
of spent nuclear fuel.
‹The harmful characteristics of HLW depend
on the fission products, their half-lives, the
type of radiation, and accumulation in the
food chain
Spent fuel rods containing U-238, I-131, Cs-137, and Sr-90
are kept under onsite pools of water with neutron absorbers.
Figure 7.20
Page 310
←Active management
Fig. 7.24
Figure 7.18 on Page 293
Burial of low-level nuclear wastes
Figure 7.22
Page 312
Special glasses or
ceramics are used
to enclose high
level nuclear
wastes and then
packed into metal
canister for burial
in repository (e.g.
vitrification of Pu239)
Underground Disposal of Nuclear Waste
Fig. 7.23
Ideal
repository
will be at
least 1000 ft
underground
and 1000 ft
above water
table; the
host rock
formation
should
ideally be
salt, basalt,
tuff, and
granite.
Figure 7.17 on
Page 291
Table 7.7 Page 318
Coal-fired power
plants release more
radioactivity than
nuclear plants due to
the vast amounts of
coal consumed that
contain both thorium
and uranium.
Usage of Nuclear Power in Various Countries
The extent of
usage of nuclear
power is
dependent upon
the people’s
perception of
nuclear risk and
the existing
resources for
energy
production
Figure 7.25
Page 317