Transcript Nuclear Energy - bba-npreiser

Nuclear Power – Is this the
answer to global warming??
Chapter 39
History of nuclear power
1938– Scientists study Uranium nucleus
1941 – Manhattan Project begins
1942 – Controlled nuclear chain reaction
1945 – U.S. uses two atomic bombs on Japan
1949 – Soviets develop atomic bomb
1952 – U.S. tests hydrogen bomb
1955 – First U.S. nuclear submarine
Advantages
• The energy in one pound of highly enriched Uranium
is comparable to that of one million gallons of
gasoline.
• One million times as much energy in one pound of
Uranium as in one pound of coal.
• Nuclear energy annually prevents
– 5.1 million tons of sulfur
– 2.4 million tons of nitrogen oxide
– 164 metric tons of carbon
• Nuclear often pitted against fossil fuels
– Some coal contains radioactivity
– Nuclear plants have released low-level radiation
Disadvantages
• One possible type of reactor disaster is known as a
meltdown. In such an accident, the fission reaction
goes out of control, leading to a possible explosion
and the emission of great amounts of radiation.
• Nuclear reactors also have waste disposal problems.
Reactors produce nuclear waste products which emit
dangerous radiation. Because they could kill people
who touch them, they cannot be thrown away like
ordinary garbage. Currently, many nuclear wastes are
stored in special cooling pools at the nuclear
reactors.
• Nuclear reactors only last for about forty to fifty
years.
States with nuclear power plant(s)
Nuclear power around the globe
•17% of world’s electricity from
nuclear power
•U.S. about 20% (2nd largest
source)
•431 nuclear plants in 31 countries
•103 of them in the U.S.
•Built none since 1970s (Wisconsin
as leader).
•U.S. firms have exported nukes.
•Push from Bush/Cheney for new
nukes.
Nuclear Energy
• The nucleus of an atom is
the source of nuclear
energy.
• When the nucleus splits
(fission), nuclear energy is
released in the form of heat
energy and light energy
• Nuclear energy can also be
released when nuclei collide
at high speeds and join
(fusion).
Nuclear Energy and the Sun
• The sun’s energy is
produced from a
nuclear fusion
reaction in which
hydrogen nuclei fuse
to form helium nuclei.
• Nuclear energy is the
most concentrated
form of energy.
Fusion – Images of Magnetic Confinement
Device
Nuclear Fission
• Nuclear power plants use
nuclear fission reactions to
produce heat which is used
to boil water. The steam
produced by boiling water
turns a turbine which
produces electricity.
• The energy from fission is
explained by Einstein’s
famous equation:
The mass of Kr and Ba plus
the three neutrons is less than
the mass of the 235U plus a
neutron. The mass that is
“lost” is converted to energy.
Nuclear Power Plant
Combustion Turbine Power Plant
Radioactive decay
• Some products produced in the fission
reaction are radioactive. Radioactive elements
decay and emit radiation.
• Radioactive decay is the process in which an
unstable atomic nucleus loses energy by
emitting radiation in the form of particles or
electromagnetic waves.
7Be
4
=> 7Li3 + 0e1
Half-life
• Each radioactive element has a unique half-life.
• The half-life is the amount of time it takes for half of the
atoms in a sample to decay.
• The half-life for a given isotope is always the same ; it
doesn't depend on how many atoms you have or on how
long they've been sitting around.
• Certain radioactive elements (such as plutonium-239) in
“spent” fuel will remain hazardous to humans and other
living beings for hundreds of thousands of years.
After one
half-life there
½ the original
amount left
After another
half-life there is
¼ of the
original amount
left
Half-lives
Medium-lived
fission products
Property: t½
Unit: (a)
155Eu
Yield
(%)
4.76 .0803
Q*
(KeV)
βγ
*
252
βγ
85Kr
10.76
.2180
687
βγ
113mCd
14.1
.0008
316
β
90Sr
28.9
4.505
2826
β
137Cs
30.23
6.337
1176
βγ
121mSn
43.9
.00005
390
βγ
151Sm
90
.5314
77
β
Elements that have a longer half-life may
not be as radioactive but the amount of
time they remain hazardous to humans
and other living beings is longer.
Generally a substance is “safe” after 10
half-lives so some radioisotopes will
remain hazardous for millions of years.
The faster a radioisotope decays,
the more radioactive it will be. The
energy and the type of the ionizing
radiation emitted by a pure
radioactive substance are important
factors in deciding how dangerous it
will be.
Long-lived
fission products
Property: t½
Unit: (Ma)
Yield
(%)
Q*
(KeV)
99Tc
.211
6.1385
126Sn
.230
.1084
79Se
.295
.0447
93Zr
1.53
5.4575
135Cs
2.3
6.9110
269 β
107Pd
6.5
1.2499
33 β
129I
15.7
.8410
βγ
*
294 β
4050
βγ
151 β
91
194
βγ
βγ
Nuclear Reactions – Fission and Fusion
Note: Short hand notation C-14, the number after the dash is the mass number
Neutron number is often not shown when writing reactions
For a correctly written nuclear reaction, the total of the
mass numbers (bottom numbers) on the left side must
equal and total mass numbers on the right side and the
sum of the atomic numbers (top numbers) on the left
side must equal the sum of the atomic numbers on the
right side.
Radioactive decay reactions
Both b+ and bdecay are
possible
b- decay
b+ decay
g (gamma) decay
152Dy*
----> 152Dy + g
Gamma is high energy electromagnetic radiation and has no mass
Antimatter
• When b+ decay occurs a positron or ‘anti-electron’ is
produced:
• An anti-electron would has the same mass as the electron,
but opposite electric charge and magnetic moment
• In the 1950's, physicists at the Lawrence Radiation Laboratory
used an accelerator to produce the anti-proton, that is a
particle with the same mass and spin as the proton, but with
negative charge and opposite magnetic moment to that of the
proton.
• When anti-electrons and anti-protons come together you get
anti-matter.
• A positron and its antimatter particle (an electron) annihilate
each other when they meet: they disappear and their kinetic
plus rest-mass energy is converted into energy (E = mc2) in the
form of gamma rays.
Mass defect and Binding energy
• The strong nuclear force binds the nucleus together with a
certain amount of energy. A small amount of the matter pulled into
the nucleus of an atom is converted into a tremendous amount of
energy, the binding energy, which holds the nucleus together.
• The difference between the mass of the atom and the sum of the
masses of its parts is called the mass defect (Dm).
•The mass defect can be used to calculate the binding energy for
the atom with E = Dmc2.
• When a nuclear reaction occurs some of the binding energy is
liberated.
• For the following reaction, 6Li + 2H → 2 4He, the energy
released can be calculated by adding the total mass on the left
side and subtracting the total mass on the right side. The “missing
mass” is converted to energy. E = (missing mass)c2
Total rest mass on left side = 6.015 + 2.014 = 8.029 u
Total rest mass on right side = 2 × 4.0026 = 8.0052 u
Missing rest mass = 8.029 - 8.0052 = 0.0238 atomic mass units.
Binding Energy Calculation
Questions – Nuclear Physics
• Which of the following particles is most massive? (A) A proton (B) A
neutron (C) An electron (D) A beta particle (E) An alpha particle
•
In the above nuclear reaction, what particle is represented by X? (A) A
proton (B) An electron (C) An alpha particle (D) A gamma ray (E) A beta
particle
• Which graph below plots the activity of a radioactive substance as a
function of time?
• Which graph below shows the half-life of a radioactive substance as a
function of time?
• Of the following, the particle whose mass is closest to that of the mass
of the electron is the a) proton b) positron c) neutron d) neutrino
More Nuclear Questions
• When a beta particle is emitted from the nucleus of an atom, the effect is
to a) decrease the atomic number by 1, b) decrease the mass number by 1
c) increase the atomic number by 1 d) increase the mass number by 1
• Gamma rays consist of a) helium nuclei b) hydrogen nuclei c) neutrons d)
radiation similar to X-rays
• It is characteristic of alpha particles emitted from radioactive nuclei that
they a) are sometimes negatively charged b) usually consist of electrons c)
are helium nuclei d) are hydrogen nuclei
• In the nuclear reaction 2H + 3H → 4He + 1n + Q, Q represents the energy
released. This reaction is an example of a) fission b) fusion c) ionization d)
alpha decay
• If the masses of the nuclei in the above reaction are 2.01472, 3.01697,
4.00391 and 1.00897. The value of Q in atomic mass units is closest to a)
5.03169 b) 5.01288 c) 0.01881 d) 5.01288 e) 2.01472
• In the nuclear reaction shown below, what is the value of the coefficient
235U + 1n → 144Ba + 89Kr + y 1n
y? a) 0 b) 1 c) 2 d) 3 e) 4
Nuclear fuel cycle
•
•
•
•
•
•
Uranium mining and milling
Conversion and enrichment
Fuel rod fabrication
POWER REACTOR
Reprocessing, or
Radioactive waste disposal
– Low-level in commercial facilities
– High level at plants or underground repository
Uranium enrichment
• U-235
– Fissionable at 3%
– Weapons grade at 90%
• U-238
– More stable
• Plutonium-239
– Created from U-238; highly radioactive
Nuclear Reactor Process
• 3% enriched Uranium pellets formed into
rods, which are formed into bundles
• Bundles submerged in water coolant inside
pressure vessel, with control rods.
• Bundles must be SUPERCRITICAL; will overheat
and melt if no control rods. Reaction converts
water to steam, which powers steam turbine
Early knowledge of Risks
• 1964 Atomic Energy Commission report
on possible reactor accident
– 45,000 dead
– 100,000 injured
– $17 billion in damages
– Area the size of Pennsylvania contaminated
Sources
• Conceptual Physics by Paul Hewitt
• www.physicsclassroom.com
• http://observe.phy.sfasu.edu/courses/phy101
/lectures101/
• http://www.acoustics.salford.ac.uk/schools/te
acher/lesson3/flash/whiteboardcomplete.swf