Module 01
Basics of Nuclear Fission
1.3.2015
Prof.Dr. Böck
Vienna University of Technology
Atominstitute
Stadionallee 2
A-1020 Vienna, Austria
ph: ++43-1-58801 141368
[email protected]
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:
Fission
Fusion
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 = Δmc2,
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
E.g. U-235 + n -> La-147 + Br-87 + 2n
Fission is asymmetric
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:
Table (Chart) of the Nuclides
Energy Output of Nuclear Fission
• Each typical fission event releases about two hundred
million eV (200 MeV) of energy.
• By contrast, 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 to heat as the
particles and gamma rays produced during the fission
process collide with the atoms of the fuel, this heta is
carried away by a cooling medium usually light water,
sometimes heavy water, CO2, Helium or liquid sodium
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
Fission Products
• The thermal fission of 235U leads usually to two fission
products with different mass (asymmetric fission).
• The fission yield has two maxima at mass number A
between: 89 ≤ A1 ≤ 101 and 133 ≤ A2 ≤ 144
• The fission yield in these maxima is between 5% and 7%
• The fission fragment yields for 233U and 239Pu are similar to
235U, but not identical
To Create a Chain Reaction
• As target a minimum mass (=critical
mass) of 235U 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 nneutrons 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 selfsustaining.
Bottom: Surrounding the original
sphere with a neutron reflector
increases the efficiency of the
reactions and also allows the
reaction to become selfsustaining.
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
233U
15 kg
11 cm
235U
52 kg
17 cm
239Pu
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
well 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 MWe, 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
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•
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•
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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