Nuclear Power – Is this the answer to global warming??

Chapter 39

History of nuclear power

1938– Scientists study Uranium nucleus1941 – Manhattan Project begins1942 – Controlled nuclear chain reaction1945 – U.S. uses two atomic bombs on Japan1949 – Soviets develop atomic bomb1952 – U.S. tests hydrogen bomb1955 – 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.

7Be4 => 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-livesMedium-lived

fission products

Property: t½

Unit: (a)Yield(%)

Q *(KeV)

βγ*

155Eu 4.76 .0803 252 βγ85Kr 10.76 .2180 687 βγ113mCd 14.1 .0008 316 β90Sr 28.9 4.505 2826 β137Cs 30.23 6.337 1176 βγ121mSn 43.9 .00005 390 βγ151Sm 90 .5314 77 β

Long-livedfission products

Property: t½

Unit: (Ma)Yield(%)

Q *(KeV)

βγ*

99Tc .211 6.1385 294 β126Sn .230 .1084 4050 βγ

79Se .295 .0447 151 β93Zr 1.53 5.4575 91 βγ

135Cs 2.3 6.9110 269 β107Pd 6.5 1.2499 33 β

129I 15.7 .8410 194 βγ

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.

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.

Nuclear Reactions – Fission and Fusion

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.

Note: Short hand notation C-14, the number after the dash is the mass number

Radioactive decay reactions

(gamma) decay 152Dy* ----> 152Dy +

Gamma is high energy electromagnetic radiation and has no mass

Both + and - decay are possible

- decay

+ decay

Antimatter• When+ 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  (m).•The mass defect can be used to calculate the binding energy for the atom with E = mc2.• 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 y? a) 0 b) 1 c) 2 d) 3 e) 4 235U + 1n → 144Ba + 89Kr + y 1n

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/

teacher/lesson3/flash/whiteboardcomplete.swf