UNIT 7
POWER PLANTS
Vocabulary:
 Thermal (conventional) power plants
 Nuclear power plants
 Hydroelectric schemes
Grammar:
 Translation
 Revision of verb tenses (ACTIVE and PASSIVE)
TRANSLATION
GREAT/LARGE AMOUNTS OF ELECTRICITY CANNOT BE GENERATED
UNLESS (No se pueden generar grandes cantidades de electricidad a menos que) a
coil rotates in a magnetic field and that IS DONE BY MEANS OF/WITH A TURBINE
(se hace mediante una turbina) connected to a generator. The turbine converts the
kinetic or thermal energy of a flowing fluid INTO useful rotational energy. A
generator contains the stator, WHICH IS THE MAGNET (que es el imán) and a rotor,
WHICH IS THE COIL (que es la bobina). WHEN/AS THE ROTOR TURNS (Cuando
gira el rotor) the wires cut the lines of force in the magnetic field of the stator
PRODUCING AN ALTERNATING CURRENT (produciendo una corriente alterna).
The enormous size of modern generators and the speed AT WHICH the rotor can
turn mean that electric power of very high voltage can be produced. AS MUCH AS
HALF A MILLION VOLTS (Tanto como medio millón de voltios) can be transmitted
over high voltage lines to substations IN WHICH (THE) VOLTAGE IS REDUCED BY
MEANS OF THE USE OF/USING TRANSFORMERS (en las que se reduce el voltaje
mediante el uso de transformadores).
The rotor is turned BY a turbine, a huge machine moved by water, or
STEAM/VAPOUR IN POWER PLANTS (vapor en las centrales eléctricas).
There are different types of power plants ACCORDING TO/DEPENDING
ON/ON THE BASIS OF THE SOURCE OF ENERGY (THAT/WHICH IS) USED (según la
fuente de energía que se use) to move the turbine. By far, the most important
sources of power are those/the ones produced by THE CHEMICAL ENERGY
OF/FROM FOSSIL FUELS, LIKE/SUCH AS OIL OR COAL (la energía química de los
combustibles fósiles, como el petróleo o el carbón), nuclear energy and the potential
energy of waterfalls.
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Fossil-fueled power plants contain a boiler, WORKING/WHICH WORKS LIKE
(que funciona como) a big kettle. AFTER BEING HEATED (UP) TO A CERTAIN
TEMPERATURE (Después de ser calentada hasta una determinada temperatura), the
steam is passed through small holes, increasing the speed of the water molecules.
The fast moving molecules hit the blades of the turbine and MAKE IT (THEM) TURN
(hacen que gire(n)).
act AS
behave LIKE
work LIKE
GRAMMAR: verb tenses
NUCLEAR ENERGY
Nuclear energy is the energy RELEASED (RELEASE) through the
fission or fusion of atomic nuclei. In the process KNOWN (KNOW) AS
nuclear fusion two light atoms join together UNDER conditions of extreme
HEAT and PRESSURE (at LEAST 50,000,000 degrees Celsius) until they
merge, forming a new nucleus WHOSE mass is only slightly smaller
THAN the total masses of the nuclei that FUSE/ARE FUSED (FUSE). The
opposite process is nuclear FISSION which MEANS (MEAN) “splitting
apart” or “dividing”. If either nuclear fusion or fission TAKES place quickly,
the result is a sudden release of ENERGY but so far the only one THAT
can BE SLOWED (SLOW) down and CONTROLLED (CONTROL) is
fission.
Nuclear fission is the splitting of the nucleus of an atom; however,
only a few elements are suitable FOR use IN this way, the most important
ones BEING (BE) U-235, U-233 and Pu-239. When one of THESE
elements is STRUCK (STRIKE) by a free neutron, IT BREAKS (BREAK)
down INTO two lighter nuclei, WHICH fly apart AT high speeds, colliding
WITH surrounding atoms. This kinetic energy IS CONVERTED
(CONVERT) INTO heat. AT the same time, two or three more neutrons
ARE RELEASED (RELEASE) and one of THEM enters the nucleus of a
neighbouring atom, causing fission TO OCCUR (OCCUR) again, and so
on. The reaction SPREADS (SPREAD) very quickly with more and more
energy RELEASED (RELEASE). This IS REFERRED (REFER) to as A
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“chain” reaction because the splitting of each nucleus IS LINKED (LINK) to
another and another and another.
If this reaction IS UNCONTROLLED (UNCONTROL), the result is
an atomic explosion like THE ONE CAUSED (CAUSE) by the atomic
bombs of Hiroshima and Nagasaki. However, the reaction can BE
SLOWED (SLOW) down and that is WHAT happens in a nuclear reactor
or pile. Here the highly fissile material IS SURROUNDED (SURROUND)
BY a substance that is non-fissile, FOR instance, graphite. This material
IS CALLED (CALL) A moderator. The neutrons LOSE (LOSE) some of
THEIR energy through COLLIDING with the atoms of the moderator and
no expansion IS PRODUCED (PRODUCE). The moderator has a second
function: by SLOWING (SLOW) down the speed of the free neutrons, IT
makes it more likely that one neutron will collide WITH the nucleus of a
neighbouring atom to continue the chain REACTION
The major advantage of nuclear energy is that it DOES NOT
DEPEND (NOT DEPEND) ON any local factors. A nuclear reactor,
UNLIKE conventional power plants, DOES not have TO BE BUILT
(BUILD) near a fossil-fuel source, nor does it depend ON a large flow of
water WHICH may BE REDUCED (REDUCE) during some seasons of the
year.
GRAMMAR REVISION
THE NUCLEAR REACTOR
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The nuclear reactor is the place IN which a fission ................. reaction
TAKES place. It contains sufficient fissionable material distributed in THE form
of rods to produce the appropriate result. The reactor consists OF a fuel, a
moderator and A cooling system. An instrument releases a free neutron
WHICH strikes the nucleus of an atom of U-235. The nucleus breaks releasing
other free neutrons which collide WITH other nuclei and split, and so on.
However, if no explosion occurs, IT is because the pile IS moderated
BY a non-fissionable material such AS graphite or heavy water. This absorbs
most OF the free neutrons and prevents them FROM splitting too MANY
nuclei too quickly. The process releases great AMOUNTS of energy in the
form of heat. This heat is then used to boil water and the steam produced can
be USED to generate electric power.
As the fuel becomes extremely radioactive during .....ITS...... (SU) use
inside the reactor, when ....IT............ is taken out of the vessels, ..IT..... is
stored in the fuel pools, where it is cooled for a period of time, in general more
.....THAN............... a year, before sending ....IT........... to the processing plant.
LISTENING
COMPARISON OF NUCLEAR ENERGY WITH CONVENTIONAL METHODS
What do you want to know about energy generation?
We’ve heard so much these days about different fuels and processes.
We’ve been told that nuclear power is more efficient than conventional fossil
fuels and we know that fossil fuels are limited. How can we compare the
efficiency of the different fuels and processes?
-Well, first of all, what types of fuel do you know? Conventional fossil
fuels, i.e., oil, coal and gas, and nuclear fuels, i.e., uranium and plutonium.
-Right, and what processes do you use? Well, I know there different
nuclear reactors and different conventional processes.
-Well let’s imagine a bucket of fuel? What exactly do you mean? How much
does a bucket hold?
-Say a bucket holds 10 kg How long does a bucket last?
That depends on the type of fuel and the type of process. Let’s look at the
2 million Kw power station. How many megawatts does this make?
2 million kw make 2,000 megawatts
-So which fuel produces the most energy? That’s nuclear fuel
-Which process does this use? It uses the most efficient nuclear process,
which converts all the matter in this fuel into energy.
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-So, how long will it last? You will be surprised when I tell you that it may
last 8 ½ years. In fact, you will be very surprised if you compare it with the
hydrogen fusion reactor.
- How long does a bucket of fuel last if you use that process? Only two
weeks
- Only two weeks, there is certainly an incredible difference
- The next process is a fast reactor. After just a week. And now we come
on to natural uranium. And when will that fuel stop producing energy?
After three days. Now let’s look at conventional fossil fuels, shall we?
How long do you think a bucket of oil will last? One hour?
-Well, nearly. In fact it will last 1/18th of a second. And the same goes with
coal. So which country today produces most electricity using nuclear energy?
-Well, In Europe, France, and then West Germany.
WRITING
Write a brief essay comparing the different types of power plants as
well as the processes taking place in them. Refer to Unit 3 to review
vocabulary and structures for comparing and contrasting in English.
Use sequence markers on page 129 and the following expressions,
UNDERLINING them
(200 words)
SPITE
INSTEAD
WHEREAS
DUE
IN ORDER
ALTHOUGH
ALLOW(+VB)
PREVENT(+VB)
THUS
BESIDES
TO RESULT
VIDEO: CHERNOBYL- 5 YEARS LATER
The giant …………………………… coffin containing the remains of
………………………… at Chernobyl, what the Soviets call “the sarcophagus” is slowly
crumbling, emitting ………………………….. than the Soviets have admitted. Readings
we took five days ago show that the ……………………… up to
…………………………………. It means that a human being would receive a dose of
radiation ………………………….. the safety limit for an entire year……………….. The
fact that the reactor is giving off significant ………………………… and that the area is
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………………………………..
means
that
……………………………………………………… so quickly and so poorly that it is
crumbling under its own weight. Soviet scientists say that a second containment
structure must be built before …………………………………. open and collapses
completely. You can see ……………………………….. the sarcophagus.
…………………………………………………. Soviet scientists are not sure how to
dispose of the …………………………………………….. that will remain dangerous for
centuries. ………………………………………….. It can all happen again here, just
…………………………………………
from
the
ruined
reactor……………………………………………….. They get a radiation check as they
arrive. Reactor number 3 uses ……………………………………. that exploded.
Nuclear physicists say that it is unstable and dangerously designed. It is also obsolete.
……………………………………………….. All the switching and signals are set up by
hand. The supervisor of this shift is a hero of Chernobyl. Alexander R. risked his life to
shut down station number 3 ……………………………………….. The radiation seems
to be taking its toll on B’s health.
The giant STEEL AND CONCRETE coffin containing the
remains of NUCLEAR POWER STATION N 4 at Chernobyl, what
Soviets call "the sarcophagus" is slowly crumbling, emitting MUCH
HIGHER LEVELS OF RADIATION than the Soviets have admitted.
Readings we took five days ago show RADIATION LEVELS up to 375
TIMES HIGHER THAN BEFORE THE ACCIDENT. It means that a
human being would receive a dose of radiation GREATER THAN the
safety limit for an entire year IN LESS THAN 14 HOURS. The fact that
the reactor is giving off significant AMOUNTS OF RADIATION and
that the area is CONTAMINATED FOR MILES AROUND means that
CHERNOBYL IS STILL UNSAFE. 5 YEARS AGO THE SARCOPHAGUS
WAS BUILT so quickly and so poorly that it is crumbling under its
own weight. Soviet scientists say that a second containment
structure must be built before THE FIRST ONE CRACKS open and
collapses completely. You can see HOW SERIOUS IT IS FROM
INSIDE the sarcophagus. SUNLIGHT FROM THE OUTSIDE FILTERS
THROUGH THE CRACKS IS THE ROOF. Soviet scientists are not sure
how to dispose of the 135 TONS OF NUCLEAR FUEL that will remain
dangerous for centuries. AND REACTOR N 4 IS NOT THE ONLY
DANGER. It could all happen again here, just A FEW HUNDRED FEET
from the ruined reactor WHERE WORKERS STILL OPERATE
NUCLEAR POWER STATION N 3. They get a radiation check as they
arrive. Reactor number 3 uses THE SAME TECHNOLOGY AND
POWER SYSTEM AS THE REACTOR that exploded. Nuclear
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physicists say that it is unstable and dangerously designed. It is also
obsolete. THE CONTROL ROOM HAS NO COMPUTERS. All the
switching and signals are set up by hand. The supervisor of this shift
is a hero of Chernobyl. Alexander R. risked his life to shut down
station number 3 WHILE N 4 WAS DISINTEGRATING NEXT DOOR.
The radiation seems to be taking its toll on B's health.
VIDEO: THE NUCLEAR REACTOR
This is a pellet of simulated URANIUM the exact SIZE that is USED in the
fuel rods. This TINY pellet CONTAINS more ENERGY than 6 car loads of coal.
We have 20 MILLION of these pellets INSIDE the reactor vessel. We call it the
CORE. Around the core, of course, there is WATER. WATER is used as a
COOLANT. Now, inside the fuel is another set of rods called the CONTROL
RODS. These rods actually control the NUCLEAR REACTION. What happens is
this: when the core is put on line, that is when it is ACTIVATED, the control rods
are lifted out; with them gone, the NUCLEAR FUEL sets up a CHAIN REACTION
that PRODUCES a tremendous AMOUNT of HEAT, that BOILS the WATER, that
turns to STEAM, that TURNS the TURBINE, that turns the GENERATOR, that
PRODUCES ELECTRICITY. That´s it.
EXTRA READING: Nuclear Structure and Nuclear Physics
Whenever we produce energy, or transmit it from one place to another, or utilize
it to run our machines or light our homes, we are actually exploiting a variety of
processes that occur on the microscopic level of atoms and atomic nuclei. For
example, the burning of fossil fuels like coal involves the rearrangement of atoms from
one molecular form (e.g., carbon and oxygen) to another (e.g., carbon dioxide), which
results in a release of energy. Note that in this sense, the burning of coal should
actually be interpreted as a form of "atomic energy" since it involves reactions among
atoms. In a similar manner, the "burning" of nuclear fuels such as uranium involves
reactions among atomic nuclei in which the constituents of uranium nuclei (protons
and neutrons) rearrange themselves to form new types of nuclei (i.e., when a uranium
nucleus "fissions" into two nuclei) and release "nuclear energy."
Since the amount of energy released by a macroscopic chunk of material will
depend on how many atoms in the material are undergoing reactions, it is important to
learn how to estimate the number of atoms in the material, or more commonly, the
number of atoms per unit volume of material-the atomic number density. This can be
easily calculated if we know the mass density (g/cm 3) and atomic weight of the
material (in grams) of 6.02x 10 atoms (Avogadro's_number). For example, uranium
has an atomic weight of 238.0. Hence, 6.02 x 10Z3 atoms of uranium would weight
238g. As yet another example, helium in gaseous form has a density of 0.00018 cm 3.
Since its atomic weight is 4.003, we find that the atomic number density of helium gas
is 2.7 X 1019.
Let us consider in more detail the atomic nucleus itself. We noted earlier that
the atomic nucleus is composed of two types of subnuclear particles, the proton and
the neutron
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Although in general the number of neutrons in a nucleus is comparable to the
number of protons, one commonly finds that each element (that is, each Z) actually
appears in several nuclide forms which differ in their neutron number and hence in
their mass number A. Nuclides with the same Z but different A are referred to as
isotopes. For example, the isotopes of hydrogen are 11H, ziH, and 1/3H while heavy
elements such as uranium may exhibit a number of isotopic forms, e.g., 233U, 234U,
236U, and 238U. Naturally occurring elements are actually a composition of several
isotopes.
The phenomenon of nuclear stability or instability is easy to understand when it
is recalled that the protons in the nucleus are all positively charged and will strongly
repel one another. Hence these electrical forces of repulsion must be counteracted by
another type of attractive force, a nuclear force, if the nucleus is to bind together. The
relative balance between the electrical repulsion of the protons forcing the nucleons
apart and the nuclear forces pulling the nucleons together determine the stability of
the nucleus.
In a crude sense, the neutrons act as the "glue" which causes these nuclear
forces to work and bind the nucleons together. On the other hand, a nucleus with too
many neutrons cannot stick together either. As the Chart of the Nuclides indicates,
roughly the same number of neutrons and protons are needed for light nuclei, while for
heavier nuclei a few more neutrons are needed (about half again as many neutrons
as protons for the heaviest .nuclides, such as U-238).
One frequently encounters nuclides which, although unstable, will hang together
long enough to be of some importance. Eventually, these unstable nuclei will turn into
another type of nuclide by shedding a few excess neutrons and protons, converting a
neutron into a proton (and kicking out an electron),or just disintegrating into smaller
nuclei. Such unstable nuclei are referred to as radioactive, their disintegration as
radioactive decay, and the pieces they throw off during the decay as radiation.
Radioactive nuclei may decay very rapidly (millionths of a second after they are
formed) or may hang around for quite a while before decaying. For example, U-238 is
radioactive, but it takes roughly 4 billion years for a U-238 nucleus to disintegrate-so
we need not wait around.
Even stable nuclei can be induced into transmuting or changing into different
nuclides by bombarding them with nuclear particles. Such nuclear reactions are in fact
very similar to the chemical reactions that occur between atoms and molecules-with
one very important difference. Whereas the average energy release in a reaction
between atoms is typically of the order of an electron volt, the average energy
involved in nuclear reactions is more than a million times larger-on the order of
millions of electron volts or MeV. This is a consequence of the enormous strength of
the nuclear isotopes which determine the strength with which nucleons are bound
together in an atomic nucleus.
For example, consider those hydrogen isotopes with Z = 1. In nature, we find
both hydrogen H and deuterium 2D as stable nuclides. A third isotope, tritium 31T
does not occur in nature, but it can be made by adding a neutron to deuterium.
However, tritium has the wrong ratio of neutrons to protons (N/Z = 2) and is unstable.
After a period of about 12 years, it will decay by converting one of its neutrons into a
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proton and an electron, thereby becoming a helium isotope He.
Although the energy which binds each nucleon into a nucleus is roughly
comparable (about_8 MeV) from nuclide to nuclide, there is a very important trend
which can be seen by plotting the average binding energy per nucleon versus the
mass number A. It is apparent that the nucleons are more tightly bound together in
nuclides of intermediate mass number. But this suggests something rather interesting:
if we could somehow convert light nuclei or very heavy nuclei into nuclei of
intermediate mass number, we would make available as excess energy the difference
between the binding energies of the nuclei.
To be more specific, suppose we could combine or "fuse" together two light
nuclei to make a heavier nucleus. Then the average binding energy per nucleon would
increase, which would imply a net energy release. An important example of such a
nuclear fusion reaction involves fusing two isotopes of hydrogen,1 D (deuterium) and
T (tritium), together to make helium 4He and a neutron. This fusion reaction releases
roughly 17 MeV of energy. Such reactions are of considerable interest in achieving net
energy production. Unfortunately, this fusion reaction is a bit difficult to stimulate since
the light nuclei are positively charged and will strongly repel one another. To get them
to fuse, we must somehow slam them together hard enough to overcome the electrical
repulsion.
An alternative scheme to produce nuclear energy is to try to split up or "fission"
very heavy nuclei into two lighter nuclei, each with larger binding energy per nucleon.
Then we could achieve a net energy production by means of such nuclear fission
reactions. But how do we split up a heavy nucleus? From our previous discussion of
fusion reactions, it is apparent that we cannot just slam two heavy nuclei together and
hope that they will break apart since their charge would strongly repel one another. An
alternative idea is to slam a neutral particle (which will not be repelled by the nuclear
charge) into a big "overweight" nucleus and hope that this splits it. An ideal candidate
for the incident particle is the neutron. Indeed, experiments have shown that certain
nuclei have an enormous appetite for neutrons, but after devouring them, suffer from a
case of violent indigestion which causes them to fission. As an example of such a
reaction, one can bombard the uranium isotope U-235 with neutrons to induce fission
into two fission product nuclei, several neutrons and other assorted radiation, and
roughly 200 MeV worth of energy. The fission product nuclei emerge with most of this
energy in the form of kinetic energy of motion, and this kinetic energy is rapidly
converted into heat as the fission products collide with neighboring nuclei. But just as
significantly, the fission reaction kicks loose a few neutrons which can then go on to
induce still more fission reactions. In this way, one can use neutrons to propagate a
"chain" of fission reactions. This, of course, is the scheme utilized in the nuclear
reactors that power large electrical generating plants.
Source: Nuclear Power J.J. Duderstadt, Marcel Dekker Inc., New York, 1979
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