Prof.Dr. Böck Technical University Vienna Atominstitut Stadionallee 2 A-1020 Vienna, Austria ph: ++43-1-58801 141368 boeck@ati.ac.at Module 01 Basics of Nuclear Fission 1.3.2016
Structure of an Atom
Fission Process
Fission Chain Reaction
Difference between Fusion and Fission Maximum binding energy at A~60 leads to two possibilities to obtain energy: Fusion Fission
Fission If a fissionable material like U-235 or Pu-239 reacts with a thermal (slow) neutron, it disintegrates in 2 nuclei (fission products) and 2-3 neutrons which keep the reaction running In case of fission ~1MeV of energy per nucleon is set free U-235 (235 nucleons) produces more than 200 MeV per fission
Fusion Fusion of deuterium with tritium creates helium-4, frees a neutron, and releases 17.59 MeV of energy. The binding energy of the helium-4 nucleus appears as the kinetic energy of the products, in agreement with E = Δmc 2, where Δm is the change in rest mass of particles.
Working Desk of Otto Hahn 1938 December: Otto Hahn, Fritz Strassmann and Lise Meitner discover nuclear fission by irradiating uranium with neutrons
Isotopic Pathways to Fission
Fission Products Distribution Fission is asymmetric E.g. U-235 + n -> La-147 + Br-87 + 2n For U-235 maxima at A = 95 and A = 134 In the nuclide chart one can find the cumulative chain yield (%) for thermal neutron fission of U-235:
Fission Products The thermal fission of 235 U leads usually to two fission products with different mass (asymmetric fission). The fission yield has two maxima at mass number A between: 89 A 1 101 and 133 A 2 144 The fission yield in these maxima is between 5% and 7% The fission fragment yields for 233 U and 239 Pu are similar to 235 U, but not identical
Table (Chart) of the Nuclides
Energy Output of Nuclear Fission Each typical fission event releases about two hundred million ev (200 MeV) of energy. Most chemical oxidation reactions (such as burning coal or TNT) release at most a few ev per event Nuclear fuel contains at least ten million times more usable energy per unit mass than does chemical fuel. The energy of nuclear fission is released as kinetic energy of the fission fragments, and as electromagnetic radiation in the form of gamma rays In a nuclear reactor, the energy is converted into heat (by hot fuel elements), this heat is carried away by a (primary) cooling medium usually light water (sometimes heavy water, CO2, Helium or liquid sodium), the hot primary cooling medium transfers it s energy to another (secondary) water steam circuit which then drives a turbine generator, it is therefoe a three step process
Energy Output of a Fission Reaction 1 fission = 200 MeV 1 fission = 3.2 10e-11 Joule (1 ev = 1.6 10-19 Joule) 1 g U-235 = 6 10e+23 /235 fissions 1 g U-235 = (6 10e+23 /235) 3.2 10e-11 Joule 1 g U-235 = 8.2 10e+10 Joule 1 Joule = 1 Ws = 1.1 10e-11 MWd 8.2 10e+10 Joule ~ 1 MWd 1g U-235 ~ 1 MWdth
To Create a Chain Reaction As target a minimum mass (=critical mass) of 235 U nuclei is needed After each fission process the produced fast neutrons need to be slowed down (thermalize) by collisions with light nuclei (moderator) A moderator such as hydrogen or carbon is used to slow down the fast neutrons from fission so that they can cause a new fission reaction. Commonly used moderators in fission reactors are light and heavy water and graphite
Critical Mass A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (e.g. the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature and its surroundings. A nuclear chain reaction is self-sustaining, when there is no increase or decrease in power. In this case the effective neutron multiplication factor k=1 (number of neutrons in generation n to number of neutrons in generation n-1) k= n/n-1 k can be <1,=1,>1
Chain Reactions Top: A sphere of fissile material is too small to allow the chain reaction to become self-sustaining as neutrons generated by fissions can too easily escape. Middle: By increasing the mass of the sphere to a critical mass, the reaction can become self-sustaining. Bottom: Surrounding the original sphere with a neutron reflector increases the efficiency of the reactions and also allows the reaction to become self-sustaining.
Critical mass of a bare sphere The shape with minimal critical mass and the smallest physical dimensions is a sphere. Some bare-sphere critical masses at normal density are: NUCLIDE CRITICA L MASS SPHERE DIAMETE R 233 U 15 kg 11 cm 235 U 52 kg 17 cm 239 Pu 10 kg 9.9 cm The critical mass for lower-grade uranium depends strongly on the grade: with 20% U-235, it is over 400 kg; with 15% U-235, it is over 600 kg.
1939 Lise Meitner Born 7.11.1878 in Vienna 1906 PhD at the University of Vienna Since 1907 cooperation with O.Hahn in Berlin 1922 Professor at the University of Berlin 1933 lost her job 1938 emigration to Sweden Employed at the Nobel Institut in Stockholm until her retirement in 1960 Died 27.10.1968 in Cambridge/England
1939 Albert Einstein Albert Einstein urged fellow scientist Leo Szilard to write President Franklin D. Roosevelt to warn that the U.S. must not fall behind Germany in atomic bomb research
July 1, 1946
WW II and the militarization of nuclear energy On 2 December 1942 Fermi initiated the atomic age with the first self-sustaining chain reaction, after which he became known as "father of the atomic bomb" The US military build reactors to produce Pu-239 Oak Ridge Tennessee Hanford, Washington Manhattan Project at Los Alamos, New Mexico First fission bomb detonated in New Mexico, June 1, 1945 Hiroshima bomb (U-235), August 6, 1945 Nagasaki bomb (Pu-239), August 9, 1945 Peaceful uses proposed in 1945 atomic power and radioactive by-products for scientific, medical and industrial purposes
1942 December 2: Chicago Pile (CP) 1 A team led by Enrico Fermi achieves the first controlled, self-sustaining nuclear chain reaction at the University of Chicago.
CP 1 Pile
1945 July 16: Trinity Test Trinity Site, Alamogordo Test Range Jornada del Muerto desert Yield: 19-21 Kilotons Detonation time: 5:29:45 a.m. (Mountain War Time) Pu-implosion bomb
The two paths of nuclear energy
The two paths of nuclear energy 1949 1964 Other states develop atomic bombs: USSR (1949), UK (1952), France (1960), China (1964) 1953 US Navy tests nuclear power for propulsion 1954 Nuclear energy was seen as a virtually limitless source of cheap electrical power Too cheap to meter 1956 UK power reactors operate at Calder Hall 1957 Shippingport, Pennsylvania - first commercial nuclear electric generating station (PWR) in the US 1957 International Atomic Energy Agency established Atoms for Peace 1964 France builds a prototype reactor at Chinon 1966 Criticality achieved for the Douglas Point reactor in Canada 1950s and 1960s: Nuclear research facilities established around the world Non-power applications developed for cancer treatment, isotope production, industrial uses and consumer products
First nuclear electric generating station Shippingport, Pennsylvania The Shippingport Atomic Power Station, about 40 km from Pittsburgh. The British Magnox reactor at Calder Hall was connected to the grid on 27 August 1956 before Shippingport, but it also produced plutonium for military uses The Shippingport reactor went online December 2, 1957, and was in operation until October, 1982. It was an experimental, light water moderated, thermal breeder reactor and is notable for its ability to transmute (inexpensive) Thorium 232 to Uranium 233 The reactor was capable of an output of 60 MWe. The reactor was designed with two uses in mind: for powering aircraft carriers, and serving as a prototype for commercial electrical power generation. In 1977, it was converted to a Pressurized Light-Water Breeder Reactor (PLWBR).
EBR 1 :First Reactor Generating Electricity At that time little was known how to build reactors to produce useable quantities of electricity. Because of the post-war shortage of available uranium, the Atomic Energy Commission wanted to test whether a reactor could "breed" more fuel than it consumed while still serving as a source of power. This objective led to many "firsts" in the development of the EBR-I. Built in Arco/Idaho
EBR 1: First Reactor Generating Electricity Construction started 1949, December 20, 1951 EBR-1: First atomic reactor in the world to generate usable amounts of electricity (four light bulbs) located 18 miles southeast of Arco, Idaho, it used Pu as fuel and liquid sodium as coolant
First Reactors in USSR and UK USSR: First NPP 1954 in Obninsk, 5 MW, 110 km SW of Moskawa UK: 1955 Calder Hall UK, 2 blocks each 50 MW e, in Sellafield North Cumbria, 2004 shut down
December 8, 1953: Atoms for Peace" President Eisenhower addressed the United Nations General Assembly with his now famous speech. He urged that nuclear nations begin making joint contributions of nuclear material to an International Atomic Energy Agency (IAEA) to be established under the United Nations.
Foundation of the International Atomic Energy Agency (IAEA) October 1956: The IAEA formally was established to prevent the proliferation of nuclear weapons and promote the broadest use of nuclear electric power.
Comprehensive Test Ban Treaty Organisation (CTBTO) Vienna
References www.iaea.org www.ctbto.org www.world-nuclear.org www.nuclearweaponarchive.org www.nuclearfiles.org Richard Rhodes The Making of the Atomic Bomb Simon&Schuster Paperbacks ISBN 0-684-81378-5 John Cornwell Hitler s Scientists ISBN-0-670-89362-5 Silke Fengler: Kernforschung in Österreich 1900 1978 ISBN 978-3-205-78743-3 See video The Physics of Nuclear Fission at http://www.youtube.com/watch?v=n7c14uikuv8