January 13 1 Nuclear Chemistry; Use and misuse

19.2 Nuclear Chemistry

The Good, Bad and Ugly Application of Nuclear Chemistry

Dr. Fred Omega Garces General Chemistry 201 Miramar College

January 13 2 Nuclear Chemistry; Use and misuse

Energy Change in Nuclear Reactions

Einstein showed the relationship between energy and mass: E=mc2 Energy obtained from a nuclear process is much greater than a chemical

reaction; note the c2 term in Einstein’s equation.

Consider 238U g 234Th + 4He

for 1 mol of 238U, 238.0003g g 233.9942 g + 4.0015 g + E

the change in mass during reaction is:

Thorium and Helium mass - Uranium mass = change in mass

233.9942 g + 4.0015 g - 238.0003 g = -0.0046 g

237.9957 g - 238.0003 g = -0.0046 g

the process is exothermic because the system lose mass. E = Δ(mc2 ) = c2 (Δm) = (3.00•108 m)2 •(-0.0046 g)•(1 kg / 1000g)

= - 4.1•1011 kg m2 / s2 = - 4.1•1011 J

January 13 3 Nuclear Chemistry; Use and misuse

Nuclear Binding Energy Mass defect - Difference between mass of the nucleus and the

masses of the nucleons. Binding Energy - The energy required to separate a nucleus into its

nucleons. E=mc2 g E(binding energy) = m(mass defect) c2

Mass of nuclei < Σ mass nucleons Mass of helium nucleus = 4.00150 amu Mass of Σ nucleons = 4.03190 amu Mass defect = 0.03040 amu (Binding Energy)

Average binding Energy per nucleon increases to a maximum at a mass of 50 to 60 and decreases slowly thereafter. Fusion (bring nuclei together) is exothermic for low mass number and fission (splitting of nuclei) is exothermic for high mass number.

React g prod + mass defect (Fission) U g Ba + Kr + E React g prod + mass defect (fusion) H + H g He + E

January 13 4 Nuclear Chemistry; Use and misuse

Nuclear Fission Splitting of heavy nuclei is exothermic for large mass number In a nuclear Fission Process:

• Neutrons move slowly because they’re absorbed by the nucleus. • 235U nucleus split into different daughter nuclei and give off

approximately 3.5•1011 J / nucleus • Every 235U nucleus produced 2.4 neutrons. • Each neutron produced can cause fission to another 235U • Number of fissions and energy release increase rapidly. • Eventually a chain reaction forms and without control an explosion.

January 13 5 Nuclear Chemistry; Use and misuse

Chain Reaction and a nuclear bomb A chain reaction forms-

• A minimum mass of fissionable material is required for a chain reaction (neutrons escape before they cause another fission).

• With enough material present, critical mass is achieve. •Below critical mass (sub-critical mass), neutrons escape and no chain

reaction occurs. • At Critical mass, the chain reaction accelerates • Above critical mass - super-critical mass • Critical mass 235U = 1 Kg

Utilization-

• Nuclear Bombs • Nuclear Reactors

i.e.,

1n + 235 U g 140 Ba + 93 Kr + 3 1n

January 13 6 Nuclear Chemistry; Use and misuse

Manhattan Project: Revisited

The first sustained nuclear fission chain reaction occurred in the squash courts at University of Chicago.

Piles of 235U were embedded between bricks of Graphite. Graphite was used to slow the 1n so that bombardment to 235U was more effective. Fast moving 1n were ineffective in fission.

Cadmium rods were situated between 235U and graphite to absorb 1n and control the fission reaction. The Cd rods served two purpose, first by removing the rods, fission 1n were allowed to bombard 235U to cause fission. Second if the reaction was out of control then the rods would be rammed back into place and the whole assembly will also be drench with Cd solution.

On Dec. 2, 1942 the Cd rods were slowly removed and a Geiger counter showed an increase in radiation. This was continued for another 30 min. after which the rods were slowly reinserted.

The simulation was a success !! ... and the world would never be the same.

January 13 7 Nuclear Chemistry; Use and misuse

Nuclear Bomb (Fission) Blue prints to a Nuclear Bomb Little Boy and Fat Man

• Two sub-critical wedges (.6 kg) of 235U are separated by a gun barrel.

• Conventional explosives are used to bring the two sub-critical masses together to form one super-critical mass.

• The supercritical mass leads to uncontrolled nuclear fission and a violent explosion.

January 13 8 Nuclear Chemistry; Use and misuse

The Dawn of Nuclear Destruction - The Bad Hiroshima Aug 6, 1945- Little Boy Nagasaki Aug 9, 1945 - Fat man

Equivalent to 40,000-lb. TNT 200,000 Victims

http://www.dannen.com/hiroshima_links.html

January 13 9 Nuclear Chemistry; Use and misuse http://www.csi.ad.jp/ABOMB/index.html

A-Bomb WWW Museum

January 13 10 Nuclear Chemistry; Use and misuse

Nuclear Reactors The Virtual Nuclear Tourist !!! Nuclear Power Plants Around the World

Safety has been an important consideration from the very beginning of the development of nuclear reactors. On December 2, 1942, when the first atomic reactor was brought to criticality, Enrico Fermi had already made safety an important part of the experiment. In addition to a shutoff rod, other emergency procedures for shutting down the pile were prepared in advance. Fermi also considered the safety aspects of reactor operation. Shortly before the reactor was expected to reach criticality, Fermi noted the mounting tension of the crew. To make sure that the operation was carried out in a calm and considered manner, he directed that the experiment be shut down and that all adjourn for lunch. With such leadership in safety at the very beginning, it is no wonder that the operation of reactors to date has such an impressive track record. The series of WWW pages given here are intended to present a chronology of nuclear safety research and development. Above is a clickable map of a timeline beginning with Fermi's Chicago Pile experiment until today and "beyond." Much of the context does not have the glamour of high profile nuclear industry stories such as the accidents at Three Mile Island and Chernobyl. Instead, the history gives insight into the culture of the scientists, engineers, and technocrats faced with the challenges of a totally new and powerful technology. In the early years, these pioneers wandered into a brave new world of first-of-a-kind research and development. Today, nuclear industry participants must deal with the ramifications of the discussions and actions made by those pioneers. A synopsis of this chronology might suggest that the first ten years of nuclear power development were devoted to demonstrating that power reactors could be designed, built, and operated; the second ten years were devoted to showing that power reactors might be operated economically; the third decade saw the rise of a viable commercial industry, the fourth decade, punctuated by the accident at Three Mile Island, was a mix of rapid commercial growth coupled with increasing government regulation, the fifth decade, despite the Chernobyl accident, was highlighted by a reaffirmation by the nuclear industry to providing a safe source of electrical generation and serious public skepticism. The nuclear industry is now well into the sixth decade of nuclear power, public skepticism is still a major factor guiding the future of nuclear power both in the United States and internationally. For the industry to survive, nuclear advocates will have to be devoted to restoring the publics faith in the integrity of the industry and be willing to participate in a healthy debate of the issues. Meanwhile, industry technologist are continuing their devotion to operating reactors economically, advancing improvements, and development new system designs. Reactor safety has played a significant role in these developments and will continue to do so.

January 13 11 Nuclear Chemistry; Use and misuse

Nuclear Reactors Fission as a Power source- • Using sub-critical mass of 235U (enriched with 97% 238U) • Pellets in the form of 235UO2 are incased in Zr stainless steel rod • Control rods are composed of Cd or B which absorb 1n • Moderators are inserted to slow down the 1n • Heat produced in the reactor core heats a fluid • The hot fluid goes to a steam generator in which a Turbine generates

electricity.

January 13 12 Nuclear Chemistry; Use and misuse

The Good Gets Ugly Nuclear Waste and Disaster

January 13 13 Nuclear Chemistry; Use and misuse

Nuclear Fusion Light Nuclei can fuse (come together) to form heavy nuclei • Reaction occurring in the Sun is fusion • Fusion is not radioactive. • Raw resource is hydrogen (available from seawater). • High energy is needed to bring nuclei together. • Temperatures in the order of 400 million Kelvin for the following rxn. 2H + 3H g 4He + 1n • Temperature can be achieve in a nuclear bomb or a tokamak container. Tokamak is a magnetic bottle of strong magnetic field to contain plasma. • To date, only temperatures of 3 million K have been achieved.

January 13 14 Nuclear Chemistry; Use and misuse

Fusion Containment Fusion process requires a suitable core that can withstand temperatures of millions of Kelvin.

Tokamak is a donut-shaped container with a helical magnetic field that confines the plasma and keep the plasma in magnetic elevation

Nuclear Fusion: 4 1H g 4 He + oe+ + 2 oe - oe+ + 2 oe - g 4 γ

January 13 15 Nuclear Chemistry; Use and misuse

Medical Application

Radiation can be used as a diagnostic tool to non-invasively probe the body

January 13 16 Nuclear Chemistry; Use and misuse

Risk and Benefits A graph of the sources of the average annual exposure of the US population to high-energy radiation.

January 13 17 Nuclear Chemistry; Use and misuse

Biological Effects of Radiation

• Penetrating power of radiation is a function of mass.

• γ -radiation penetrates further than β-radiation which penetrates further than α-radiation.

• Radiation absorbed by tissue causes excitation (non-ionizing radiation) or ionization (ionizing radiation).

• Ionizing radiation is much more harmful than non-ionizing radiation

• Most radiation result in radical formation.

• Free radicals undergoes a chain reaction to form other radicals.

January 13 18 Nuclear Chemistry; Use and misuse

Summary •The mass of nucleus is less than the sum of its nucleon masses.

This is the mass defect.

•The energy equivalent to the mass defect is the binding energy.

•Heavier nuclides can split and lighter nuclides can fuse to become more stable.

•In nuclear fission, a neutron causes a nucleus to split, releasing neutrons that split other nuclei resulting in a chain reaction.

•A nuclear power plant controls the rate of the chain reaction. The heat generated heats a liquid which yields superheated steam which turns the turbine generator.

•A nuclear fusion requires extremely high temperatures to be practical. To date we cannot contain material at elevated temperature.