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Nuclear Slides
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Nuclear Power Plant
D. Sakthivadivel Teaching Fellow
Institute for Energy Studies Department of Mechanical Engineering
CEG, Anna University Chennai - 25
World Energy Scenario
There are 435 nuclear power reactors in 31 countries.
30 more are under construction.
They account for 16% of the worlds electricity.
They produce a total of 374,411 MW (billion watts) of electricity.
435 commercial reactors in 31 countries, producing
16% electricity
Indian Energy Scenario
History and Basics
Henri Becquerel discovered radioactivity in 1896
Becquerel named the emission of invisible radiation from uranium ore radioactivity.
Radioactive materials was the name given to materials that gave off this invisible radiation.
When he exposed a light-tight photographic plate to a radioactive mineral, then developed the plate. (A) A photographic film is exposed to an uranite
ore sample. (B) The film, developed normally after a four-day exposure to
uranite. Becquerel found an image like this one and deduced that the mineral
gave off invisible radiation that he called radioactivity.
Ernest Rutherford later discovered that there were three kinds of radioactivity.
Alpha particles () is a helium nucleus (2 protons and 2 neutrons)
A beta particle () is a high energy electron
A gamma ray () is electromagnetic radiation with a very short
wavelength.
Radiation passing through a magnetic field shows that massive, positively charged
alpha particles are deflected one way, and less massive beta particles with their
negative charge are greatly deflected in the opposite direction. Gamma rays, like
light, are not deflected.
Radioactivity is the spontaneous emission of particles or energy from an atomic
nucleus as it disintegrates.
Radioactive decay is the spontaneous disintegration of decomposition of a nucleus.
Nuclear Equations
The two subatomic particles that occur in the nucleus, the proton and the neutron,
are called nucleons.
The number of protons is the atomic number which determines the identity of the element.
The number of protons and neutrons determines the atomic mass of the element.
Different isotopes of an element have the same atomic number (same number of protons) but different atomic masses (different number of neutrons)
The three isotopes of hydrogen have the same number of protons but different
numbers of neutrons. Hydrogen-1 is the most common isotope. Hydrogen-2, with
an additional neutron, is named deuterium, and hydrogen-3 is called tritium.
Neutrons and protons are called nucleons because they are in the nucleus.
Just like any other chemical reaction, we use symbols to show a nuclear reaction
As an example, when uranium 238 emits an alpha particle, it loses 2 protons and 2 neutrons.
Nuclear reactions must balance just like any other chemical reaction, but we must also be aware of balancing protons and neutrons
The Nature of the Nucleus.
Protons and neutrons are held together by a nuclear force when they are
very close together.
The shell model of the nucleus visualizes the protons and neutrons
moving on energy levels or shells, much like the electrons move in
shells.
HeThU 42234
90
238
92
Radioactive Decay Series
Radioactive decay produces a simpler and more stable nucleus.
A radioactive decay series occurs as a nucleus disintegrates and achieves a
more stable nuclei
There are 3 naturally occurring radioactive decay series.
Thorium 232 ending in lead 208
Uranium 235 ending in lead 207
Uranium 238 ending in lead 206
Nuclear Energy
The energy that exists within the nucleus of an atom.
Nuclear Fission the release of energy from the splitting of atoms!
Nuclear Fusion the combining of two smaller atoms into one larger atom.
Bombs & power plants
Big, unstable isotopes are struck by
neutrons, which splits the isotopes
nuclei
More neutrons shoot out to strike
nearby isotopes, causing a chain
reaction.
Sun and stars, some weapons
2 small (light) isotopes are forced
together
H + H = He
Need temps > 100,000,000C
Releases more E than fission
Nuclear Fission Nuclear Fusion
Nulear Change
What is Radiation?
Radiation particles given off by unstable atoms.
3 Types:
Alpha ()
Travels few inches
Blocked by paper (skin)
Beta ()
Travels few feet
Blocked by aluminum, glass
Gamma ()
Travels far
Blocked by lead (steel & concrete).
Nuclear Chain Reactions
A chain reaction refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus.
This nucleus in turn produces neutrons, and the process repeats.
If the process is controlled it is used for nuclear power or if uncontrolled it
is used for nuclear weapons
Controlled Nuclear Fission Reaction
Nuclear Fission from Slow Neutrons and Water
Moderator
Inside a Nuclear Reactor
Steam outlet
Fuel Rods
Control Rods
Fuel Rods
35,000 70,000 fuel rods
3% Uranium-235 pellets
In water (moderator)
Control Rods
absorb extra neutrons
Control the chain reaction
Nuclear Basics Power plants produce radioactive wastes
mostly spent fuel rods (3-4 years)
each reactor produces about 20-30 tons yearly
Currently stored in pools on site
some remain dangerous for tens of thousands of years
Half life time is a time needed for one-half of the nuclei in a radioisotope to
decay and emit their radiation to form a stable isotope
Half-time Emitted
Uranium 235 710 million yrs alpha, gamma
Plutonium 239 24,000 yrs alpha, gamma
Measurement Methods
Film badges
Workers who are exposed to radioactivity carry film badges
The film is exposed and the optical density of the film shows the
workers exposure levels during the time the film badge was worn.
Ionization counter
Measure ions that are produced by radiation
Scintillation counter
Measures the flashes of light that occur when radiation strikes a
phosphor.
Geiger counter
Measures pulses of electrons released from the ionization of gas
molecules in a metal cylinder
Each pulse of electrons is heard as a pop or click
This is a beta-gamma probe, which can measure beta and gamma
radiation in millirems per unit of time.
The working parts of a Geiger counter
Radiation Units
Curie (Ci)
Measurement of the activity of a radioactive source.
Measured as the number of nuclear disintegrations per unit of
time
A curie is 3.70 X 1010 nuclear disintegrations per second.
Rad
Measures the amount of energy released by radiation striking living tissue
Short for radiation absorbed dose
One rad releases 1 X 10-2 J/kg
Rem
Short for roentgen equivalent man
This takes into account the possible biological damage to humans of certain types of radiation.
CONTROL RODS
Control rods made of a material that absorbs neutrtons are inserted into the
bundle using a mechanism that can rise or lower the control rods.
The control rods essentially contain neutron absorbers like, boron, cadmium
or indium.
STEAM GENERATORS
Steam generators are heat exchangers used to convert water into steam from
heat produced in a nuclear reactor core.
Either ordinary water or heavy water is used as the coolant.
STEAM TURBINE
A steam turbine is a mechanical device that extracts thermal energy from
pressurized steam, and converts it into useful mechanical.
Various high-performance alloys and super alloys have been used for steam
generator tubing.
COOLANT PUMP
The coolant pump pressurizes the coolant to pressures of the order of 155bar.
The pressure of the coolant loop is maintained almost constant with the help
of the pump and a pressurizer unit.
FEED PUMP
Steam coming out of the turbine, flows through the condenser for
condensation and recirculates for the next cycle of operation.
The feed pump circulates the condensed water in the working fluid loop.
CONDENSER
Condenser is a device or unit which is used to condense vapor into liquid.
The objective of the condenser are to reduce the turbine exhaust pressure
to increase the efficiency and to recover high quality feed water in the
form of condensate & feed back it to the steam generator without any further
treatment.
COOLING TOWER
Cooling towers are heat removal devices used to transfer process waste heat to
the atmosphere.
Water circulating through the condenser is taken to the cooling tower for
cooling and reuse
Nuclear Fission We convert mass into energy by breaking large atoms (usually Uranium) into
smaller atoms. Note the increases in binding energy per nucleon.
A slow moving neutron induces
fission in Uranium 235
Fission products
The fission products shown are just examples, there are a lot of different
possibilities with varying probabilities
Expanding Chain Reaction
The fission reaction produces more neutrons which can then induce fission in
other Uranium atoms.
Linear Chain Reaction Obviously, an expanding chain reaction cannot be sustained for long (bomb). For controlled nuclear power, once we reach our desired power level we want each fission to produce exactly one additional fission
Moderator Neutrons are slowed down by having them collide with light atoms (Water in
US reactors).
Highest level of energy transfer occurs when the masses of the colliding particles are equal (ex: neutron and hydrogen)
Control Rods
Control rods are made of a material that absorbs excess neutrons (usually
Boron or Cadmium).
By controlling the number of neutrons, we can control the rate of fissions
Basic Ideas
The Uranium is both the fuel and the source of neutrons.
The neutrons induce the fissions
The Water acts as both the moderator and a heat transfer medium.
Control rods regulate the energy output by sucking up excess neutrons
Feasibilities
Processing of Uranium
Each ton of Uranium ore produces 3-5 lbs of Uranium compounds
Uranium ore is processed near the mine to produce yellow cake, a material rich in U3O8 (Triuranium octoxide).
Only 0.7% of U in yellow cake is 235U. Most of the rest is 238U which does not work for fission power.
World Distribution of Uranium
Enrichment To be used in reactors, fuel must be 3-5% 235U.
Yellow cake is converted into UF6 and this compound is enriched using gaseous diffusion and/or centrifuges.
There are some reactor designs that run on pure yellow cake.
A nuclear bomb requires nearly 100% pure 235U or 239Pu. The 3% found in reactor grade Uranium CANNOT create a nuclear explosion!
Fuel Pellets The enriched UF6 is converted into UO2 which is then made into fuel pellets.
The fuel pellets are collected into long tubes. (~12ft).
The fuel rods are collected into bundles (~200) rods per bundle.
~175 bundles in the core.
Cladding The material that the fuel rods are made out of is called cladding.
It must be permeable to neutrons and be able to withstand high heats.
Typically cladding is made of stainless steel or zircaloy.
Controlling the chain reaction
depends on Arrangement of the fuel/control rods
Quality of the moderator
Quality of the Uranium fuel
Neutron energy required for high probability of fission
Two common reactor types: Boiling
Water Reactor and Pressurized Water
Reactor.
BWR: P=1000 psi
T=545F
PWR P=2250 psi
T=600F
PWR is most common and is basis of
marine nuclear power.
CANDU (CANada Deuterium
Uranium) Reactor
1 Nuclear fuel rod
2 Calandria
3 Control Rods
4 Pressurizer
5 Steam generator
6 Light water condensate pump (secondary
cooling loop)
7 Heavy water pump (primary cooling loop)
8 Nuclear fuel loading machine
9 Heavy water (moderator)
10 Pressure tubes
11 Steam
12 Water condensate
13 Reactor containment building
Reactor is inside a large
containment building
Other Options
Other countries use different reactor designs.
Some use heavy water (D2O) as a moderator. Some use Graphite as a
moderator.
Some are designed to use pure yellow cake without further enrichment
Liquid metal such as sodium or gasses such as Helium are possibilities to
use for coolants
Breeder Reactors
A big problem with nuclear power is the creation of Plutonium in the
reactor core.
This is a long lived radioactive element that is difficult to store.
Q: Why not use it as a fuel too?
Basic Idea
Process that creates the Pu.
During fission use one of the extra neutrons to create a Pu atom
Somewhat difficult in that we want fast neutrons to breed the 239Pu out of the 238U, but we want slow neutrons to induce the fission of 235U.
Requires a different design of reactor.
Doubling time: Time required to produce twice as many 239Pu atoms as 235U destroyed. A good design will have a 6-10 doubling time.
There are no currently operating breeder reactors.
0
1
239
944.2
239
93
0
1
239
93min23
239
92
239
92
238
92
PuNp
NpU
UUn
days
ADVANTAGES
Nuclear power generation does emit relatively low amounts of carbon dioxide
(CO2). The emissions of green house gases and therefore the contribution of
nuclear power plants to global warming is therefore relatively little.
This technology is readily available, it does not have to be developed first.
It is possible to generate a high amount of electrical energy in one single plant
DISADVANTAGES
The problem of radioactive waste is still an unsolved one.
High risks: It is technically impossible to build a plant with 100% security.
The energy source for nuclear energy is Uranium. Uranium is a scarce
resource, its supply is estimated to last only for the next 30 to 60 years
depending on the actual demand.
Thank You
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