Energy, Environment, and Industrial Development

1. Energy, Environment, and Industrial Development Michael B. McElroy Frederick H. Abernathy Lecture 22 May 1, 2006

2. Elements of Nuclear Physics • As seen earlier, the nucleus of an atom consists of a specified number of protons and neutrons. Collectively, we refer to the protons and neutrons as nucleons. The number of protons in the nucleus determines its electric charge (positive). The sum of the number of protons and neutrons determines its mass. • For example: 92U235 In this case, the nucleus contains 92 protons and 143 neutrons. mass number atomic number, number of protons

3. Elements of Nuclear Physics • Example of a fission process: 0n1 + 92U235 38Sr90 + 54Xe143 + 30n1 Products in this case are strontium, xenon and 2 extra neutrons. • Fission of U235 produces a variety of fission products: there are almost 50 modes of fission. The average neutron yield is about 2.5. Energy released in a fission event is about 200 million electron volts (MeV). To put this in context, energy involved in a typical chemical reaction is about a few eV  difference of more than a factor of 106 Neutron, zero charge, mass 1

4. Elements of Nuclear Physics • Energy released by fission of 1 mole of U235 (235g). Number of atoms in mole = 6.02x1023 Energy per atom = 200 MeV = 2x108 eV = (2x108)(1.602x10-19)J = 3.204x10-11 J Energy per mole = 6.02x1023 x 3.204x10-11 J = 1.93x1013J = 1.93x1013 / 4.184 cal = 4.61x1012 cal = 4.61x109 kcal 1Btu = 2.52x102 cal Energy per mole = 4.61x1012 / 2.52x102 = 1.83x1010 Btu

5. Elements of Nuclear Physics • Remember: total annual US energy use is about 100 Quad 1 Quad = 1015 Btu • US annual use: 1017 Btu • Could be supplied by 1017/1.83x1010 moles of U235 = 5.5x106 moles = 5.5x106 x 2.35 x102g = 1.3x109 g = 1.3x103 tons • By comparison, we burn more than 109 tons coal per year

6. Elements of Nuclear Physics • Natural uranium consists mainly of U235 and U238, with U238 most abundant • U235 consists of about 7x10-3 of total U (0.7%) • To obtain 1.3x103 tons of U235 we would require 1.3x103/7x10-3 tons U = 1.9x105 ton U  190,000 metric tons U  about 10,000 times less than requirement for coal

7. Contemporary Nuclear Power • Most nuclear power plants today use enriched uranium. Concentration of U235 is increased from 0.7% to between 4~5%. • Enrichment is accomplished either by centrifuge or by differential diffusion. Bombs require much more extensive enrichment – typically more than 90% • Key ingredients of the nuclear reactor in most common use: • Fuel Rods • Control Rods – used to absorb neutrons and cut off the chain reaction in event of an emergency. Metal cadmium is a useful material for the control rods • Water used as a moderator whose function is to slow neutrons so that most of neutrons react with U235 rather than U238

8. Contemporary Nuclear Power • The system of fuel rods, control rods and moderator is contained in a pressure vessel composed of thick steel. Second line of defense is a heavy concrete containment building. The Chernobyl reactor was not enclosed in a containment building. • The energy released is contained mainly in the kinetic energy of the fission fragments – about 82% of total energy released • Heat from the fuel rods is absorbed by the water in the moderator and is transformed to steam in an isolated system. The steam drives the turbines producing electricity. • After about 2 years, sufficient quantities of U235 has been converted to fission products and fission products have accumulated to the point where the fuel rods must be removed and replaced.

9. Contemporary Nuclear Power • Reactors are refueled about every 18 months in the U.S. One third of the fuel rods are replaced. The procedure takes between 2 and 3 weeks • When fuel rods are removed they contain large quantities of highly radioactive material. Major heat source. They are stored initially in a large tank of water. When they cool down, fuel cells can be removed and stored in concrete cylinders filled with metal inner liners or separate metal containers. • When removed, the fuel rods contain not only fission products but also plutonium-239 produced by capture of a fast neutron by U238.

10. Contemporary Nuclear Power • Pu239 can also serve as a fissionable fuel, like U235. But it is also the ingredient for nuclear bombs. Normally when the fuel rods have been in the reactor for as much as 18 months, the fuel rods contain a mix of Pu isotopes. Not very useful for potential bomb makers. • But, if the fuel rods are withdrawn much earlier, the Pu may be much higher in Pu239. Proliferation risk. • A large reactor produces about 1.5 tonnes of fission products a year.

11. The Nuclear Waste Problem • Many of the radioactive products decay rapidly. But some are long lived and can pose a problem for hundreds or even thousands of years • Current US strategy is to store wastes on site. Eventually, wastes should be transferred to a permanent geological reservoir. • Problems with identifying a suitable long-term depository • Is reprocessing a solution? • Economic issues. Arguments for temporary storage. • Is the breeder reaction the solution? • Story of the Integrated Fast Reactor (IFR).

12. The Story of Chernobyl • Used a pipe of graphite to slow neutrons. Pipes inside carried the fuel rods, control rods, and cooling water. No concrete containment building. • April 25, 1986. Power level surges. Reaction vessel burst. Hot steam + graphite + (combustible) zirconium metal in fuel rods reacted to produce an intense fire • Fire plume lifted to high altitude spreading radioactive debris over large area • Remains of reactor later enclosed in a layer of thick concrete, entombing radioactive waste level inside • Plant reached 150 times normal power before high pressure steam caused the disaster.

13. The Story of Chernobyl • Immediate deaths small – 31. Twenty square miles permanently uninhabitable. The number dying of wider spread fall-out is difficult to estimate. • Conservatives would argue that the Chernobyl accident was no more serious than the Bhopal chemical plant or the Texas City explosion of a shipload of ammonium nitrate.

14. The Story of Three Mile Island • Accident took place on 28 March 1979. Location near Harrisburg, Pa. • Minor malfunction led to series of errors, shutting down for a while main and emergency cooling systems • Heat melted part of core creating free hydrogen. • Reactor vessel was not breached. Containment vessel survived intact. • Minimal radiation released. Death toll: zero, although some radioactive gases were vented to the outside.

15. Historical Milestones • October 12, 1939, President Roosevelt authorized government funding of atomic (nuclear) research responding to letter from Albert Einstein • February 1940, Uranium Committee granted Enrico Fermi and Leo Szilard contract to build a reactor at Columbia University • Arthur Compton, Nobel prize winner and Dean of Physical Sciences at University of Chicago, established laboratory to promote nuclear research. Samuel K. Allison selected to direct project • Graphite/uranium pile built under west stands of Stagy Field Stadium at University of Chicago.

16. Historical Milestones • First self-sustained reactor began 9.45am, Dec. 2, 1942, under direction of Fermi. George Weil pulled the last control Rod. Experiment ended, 3.45pm • August 1, 1946. President Truman signed the Atomic Energy Act. Federal Government gives long-term responsibility for nation’s nuclear laboratories. • Professor Abernathy invented the nuclear fly-wheel

17. Historical Milestones • Atomic Energy Commission (AEC) established a nuclear test side in Arco, Idaho, on April 4, 1949, became location for development of a number of experimental reactors including naval submarine reactor, Argonne fast-breeder reactor, and others • April 1986. Argonne engineers demonstrated passive cooling capability of integral nuclear power plant EBR-11 (Experimental Breeder Reactor) • Research on EBR-11 led to development of the integral fast reactor (IFR) • Spent fuel recycled in situ • IFR can “burn” plutonium from nuclear weapons and actinides (including plutonium) from commercial light water reactors • 1994. President Clinton and Congress terminate funding for advanced reactor technology at Argonne National Laboratory. EBR-11 placed in a radiologically and industrially safe condition.