From Theory to Practice
The nuclear age began in Germany, in the 1930s in the lab of chemist
Otto Hahn.
Hahn was attempting to produce radium (In great need during the war) by
bombarding uranium atoms with neutrons. To his surprise, he ended up with
a much lighter element, barium.
That was 1938, This started the race for the power of the atom. Just
four years later Canada entered nuclear age in cooperation with the
british.
Wartime, 1942: The British wanted a safe place to conduct nuclear
experiments; Since their country feared invasion by the nazi’s or bombing
attacks, Canada provided the haven the british needed in return for a
opportunity to work in the project.
The leader of the team that crossed the atlantic to Canada was Hans von
Halban, who along with Dr. Lew Kowarski had escaped from the Institute Du
Radium in Paris one step ahead of the invading german army. They took the
world supply of 200 Kg of heavy water with them to Canada.
Having pioneered the chain reaction using uranium and heavy water, the
scientists applied their knowledge and their heavy water to the new
Canadian nuclear industry.
On September 5th, 1945 near Ottawa the team started up the first
operating nuclear reactor outside the USA. Of course, the output was
minuscule, but the significance was immense; the principal of getting
energy from splitting atoms in a controlled chain reaction (fission) was
established beyond doubt. It was now the job of the scientists and
engineers to put it to a practical use.
Nuclear Reactors
A nuclear reactor is a device which produces heat. In a nuclear power
station, the reactor performs the same function as a boiler in a
conventional coal, gas or oil-fired station. Whether from a conventional
boiler or a nuclear reactor, heat is required to turn water into steam. The
steam is used to spin large turbines which in turn drive generators that
produce electricity. A reactor creates heat by splitting uranium atoms.
This is called ‘Nuclear reaction’ or ‘Fission’.
When the nucleus of an uranium atom is stuck by a neutron travelling at
the right speed, it splits into fragments which separate rapidly and
generate heat. It also gives off a few, new neutrons. In order to sustain a
continuous nuclear reaction, the speed of these neutrons must be slowed
down, or moderated. CANDU reactors use heavy water (Deuterium Oxide is
called heavy water because it is heavier than normal water by about 10%),
Thus the reactor is named CANDU, for (CAN)ada (D)euterium (U)ranium.
During Fission (the process used in nuclear reactors) some of the atom
breaks up, and energy is released. On average, 80% of the released energy
is carried off by the fragments in the form of kinetic energy. The other
20% is collected by the heavy water in the form of heat.
The core of a CANDU reactor
The core of a reactor is contained in a large cylindrical tank called
the ‘Calandria’. The calandria contains a series of tubes that run from one
end of the calandria to the other. Inside the calandria tubes are smaller
tubes which house fuel bundles containing natural uranium in the form of
ceramic pellets.
Heavy water is also used as the reactor coolant and is pumped through
the tubes containing the fuel pellets to pick up heat generated from the
reaction. The heated, heavy water travels to heat exchangers to produce
steam from ordinary water. This cooled heavy water is recycled back to the
reactor. The steam is then piped to conventional turbines and generators
that produce electricity. In this way the nuclear reactor is separate from
the equipment used to produce electricity.
Viable solutions for Energy needs
Annually, the demand for energy in Ontario increases by 5%. In response
to this increase, Hydro companies around Canada facing similar situations
have the responsibility of meeting the increase, usually by adding to their
arsenal of generators. The question which is brought up at this point is
how to do this most effectively in terms of impact on the environment,
cost, efficiency and several other aspects. In the case of Ontario Hydro,
they have chosen to expand on the method which appears to be best: nuclear
power. (Note: All of the following data on nuclear generating stations is
based on information on Canada’s CANDU plants.)
There are four main competitors in the energy race, but only two of
them are ‘technically viable’ Those right now are Nuclear and fossil fuels.
Of the other two, Solar energy is in limited use at the moment to things
like Solar calculators, or Solar cells used to supplement energy needs in a
large building. To collect 10^14 kWh (kilo-watt hours) (Average reactor
output) per year with solar cells, they would take up 1% of the earths
total land surface, or a area comparable in size to Western Europe!
Wind energy is an unviable solution because, the wind is not a constant
energy, unlike fossil fuels or nuclear. Another problem with wind energy,
is that it would take a space as big, or bigger than Western Europe to
place all the wind collectors to generate the electricity.
The problem with fossil fuels is demonstrated below. this makes Nuclear
energy the best solution for the worlds energy needs.
Energy sources such as fossil fuels (coal, etc.), and nuclear, emits
by?products which are often harmful to much of the environment. However,
nuclear plants are considerably less harmful than coal burning plants in
this respect. 1 tonne of coal used in coal burning plant produces 2.5
tonnes of carbon dioxide (which harms the environment in more ways than
one), 45 kilograms of acid rain (coming from the plant’s SO2 and NOx
emissions) and 90 kilograms of ash. In comparison of emissions, nuclear
plants are harmful as well, but are not harmful to this degree.
One harmful by-product which is virtually unique to nuclear plants is
‘spent nuclear fuel’ coming from the fission reaction. Much of the waste
from nuclear plants is radioactive. Coal plants produce radioactive waste
as well, but the amount is so small that it is not insignificant. While
coal burning plants produce 450 grams of radioactive residue per 90
kilograms, 9 kilograms of radioactive residue are produced from 90
kilograms of ‘spent nuclear fuel’. From this it is possible to see that
nuclear plants produce 20 times as much radioactive waste as coal plants
do.
Radioactive waste is widely considered to be nuclear plants’ biggest
problem, currently. More specifically, the problem of storage and handling
of it has not yet been permanently taken care of. Meanwhile, temporary
storage sites carry the radioactive waste until a later time when permanent
locations might be found. Research is still being done on what methods
should be used to store the waste over long periods of time.
It is feared that the idea of keeping it inside containers buried
beneath the ground will be faulty since the containers may break with time
or when occasional earthquakes hit. Radioactive waste does, however, become
stable after several hundreds of years.
One solution for the disposal of nuclear plant waste draws a large
amount of criticism. Tritium produced in the fission reactions in Canadian
plants is sold to the United States for use in their nuclear weapons. Many
people object to this as they do not wish to support the use of nuclear
weapons.
Nuclear energy is extremely efficient when compared with coal burning
plants. 1 tonne of coal produces the same amount of energy as 50 grams of
nuclear fuel. Since mining is often a very disruptive process to the
environment around the mining operation, this relatively small amount of
fuel needed is better for the preservation of some land.
Public Concerns
The public and the workers who operate nuclear plants have concerns
about the amount of radiation which they are receiving. Radiation is
measured in millirem. Any dose of radiation is considered safe if it is
under 3500 millirem. Operators of the plants usually only receive 700
millirem per year, as long as there are no problems. This dose is 20% of
the 3500 millirem limit. Office staff on the site receive less than 20
millirem per year (which is equal to the amount of radiation received by a
person living 4 months in Denver). Should a person live at the fence of a
station, the dose would be equal to that of a round trip (flight) between
Toronto and Vancouver: 5 millirem. Residents living closest to nuclear
stations only receive 3 millirem per year, however. Also the amount of
radiation coming directly from fission of 1 Lb of Uranium 238 is the same
as the combustion of 6000 barrels of oil, or 1000 tons of oil. When
presented with these facts, I am in support of nuclear power. Overall the
effects to the environment are less, and if the spent nuclear fuel is taken
care of appropriately, I only see benefits for the world with nuclear
power.
In the case of the Chernobyl meltdown in April 1986, one of the
generation site’s 4 units failed, which was because of poor design. The
remaining 3 units should be out of service soon, however, another 9 units
of the same design are still in operation. A similar accident is not
likely to happen in a CANDU plant because of the many fail safe devices.
Nuclear Energy and It’s Costs
Large generators such as nuclear and fossil fuel plants often cost
several billions of dollars. In terms of cost, nuclear stations cost
considerably more than fossil fuel stations to begin with. The Darlington
nuclear generating station (with 4 units) is currently having construction
completed. When it was first planned, Darlington was to cost $2.5 billion.
After 7 revisions of this price, it is 5 times higher at $12.63 billion. In
contrast, a fossil fuel plant would cost approximately $7 billion.
However, in operation, nuclear stations do not cost as much as fossil
fuel ones do. On April 7th, 1990, the distribution of energy sources, and
their prices went as follows:
Kilowatt hours
of electricity SourceCost ($)
—————————————————————-
157 561 000Nuclear1 016 268
102 399 000Fossil fuel3 870 272
113 630 000Water 153 400
37 856 000Purchased979 296
411 446 000Total$6 019 296
—————————————————————-
(1 kilowatt = 1000 watts. 1 kilowatt hour = 1 kilowatt per hour of use.)
Clearly, although nuclear generation was used on this day more than
fossil fuel generators, the operation of the fossil fuel ones was more
expensive.
The difference between the initial costs of nuclear ($12.63 billion)
and fossil ($7 billion) stations is $5.63 billion. However, since nuclear
plants cost considerably less in operation ($0.79 billion yearly), this
difference is paid for after several years of use. At $0.79 billion being
saved annually, the difference of $5.63 billion is met in roughly 7.1 years
of operation. As nuclear plants normally last for approximately 40 years,
at the end of this time one nuclear plant will have saved $31.6 billion
dollars for energy consumers. In terms of cost, nuclear power is less
expensive than other sources which can equal its amount of energy output
(water, for instance, cannot). Nuclear Plants do not create a lot of jobs
directly but because of money big industries may be able to save because of
nuclear energy more money can be put into hiring.
Summary
Of the energy sources that can currently be used on a large scale, none
are harmless to the environment and none are extremely inexpensive.
Nuclear energy is far from a perfect source, but no source of this size is.
While people wait for advancements in energy technology (such as cold
fusion or efficient solar and wind generation), with all aspects
considered, nuclear plants can supply the public with energy in the best
possible way.
Bibliography
Atomic energy council of Canada.
“Nuclear facts” Toronto: AEC, 1989.
“Understanding Nuclear power” Toronto: AEC, 1989.
“What is Radiation?” Toronto: AEC, 1988.
“CANDU Operations” Toronto: AEC, 1988.
“A Journalists guide to nuclear power” Toronto:
Ontario Hydro, 1988.
