Chapter 4 - History
Natural nuclear reactors predated the man-made variety by about two billion
years. At that time, nuclear chain reactions generating considerable heat
occurred in several rich uranium deposits at Oklo,
Gabon, West
Africa. This prehistoric event, which has been deduced from
chemical analysis of the remaining uranium, illustrates some of the basic
principles of radioactivity and fission. Since uranium-235 is radioactive, with
a half-life of 0.7 billion years, natural uranium then would have contained
over five per cent uranium-235, a sufficiently high fissile concentration to
sustain a chain reaction with ordinary (light) water as moderator. The nuclear
reaction presumably started when groundwater seeped into the deposits. When the
chain reaction and the associated heat built up to a sufficient level to boil
the water and expel it, the resulting lack of a moderator would have caused the
reaction to shut down automatically. This cycle must have repeated itself many
times, like a gigantic coffee pot percolating away over hundreds of thousands
of years. Analysis shows that the plutonium produced in these natural reactors
remained trapped in the uranium deposits until it had decayed away by its own
radioactivity with a half-life of 24,000 years.
Before these natural reactors were discovered scientists demonstrated
man-made ones. In 1939 the first report of fission (of uranium) was reported.
The significance of this for the release of large amounts of energy was
immediately realized. In World War II (1939-45) the initial application that
was envisaged was an explosive of unprecedented power, and both Allied and Axis
powers mobilized their scientists and engineers to that end. In the U.S.
this effort bore fruit in December of 1942 with Enrico Fermi initiating the
world's first nuclear chain reaction in a rudimentary nuclear reactor.
Canada had
been involved in two developments that led up this discovery. Around the
beginning of the century Nobel Laureate Ernest Rutherford, later Lord
Rutherford, had made several pioneering advances in the physics of
radioactivity while professor at McGill
University in Montreal.
After he left Canada
some of the research stemming from his work continued in Canadian laboratories,
including those of the National Research Council (NRC) in Ottawa.
There in 1940 George Laurence started experiments with uranium and a graphite
moderator aimed at producing a chain reaction. Had his materials been purer, he
might have achieved this before Fermi.
In 1933 Gilbert Labine had brought into production Canada's
first radium mine at Port Radium on Great Bear Lake, North-West
Territories. The radium was wanted
for medical treatments. Uranium, always found in association with its
radioactive decay product, radium, was then considered a waste product. With
the wartime need for uranium, the Port Radium mine of Eldorado Gold Mines
Limited was reopened in 1942 to produce uranium. Canada
subsequently became the world's foremost producer of uranium.
In 1943, as part of the Allied war effort, a joint Canadian-U.K. team, with
important French participation, was established at Montreal
to pursue the concept of nuclear reactors using heavy water. In the same year
heavy water was first produced in Canada at the synthetic-ammonia fertilizer
plant of the Consolidated Mining and Smelting Corporation at Trail, British
Columbia, using a Norwegian process. In 1944, C.J. Mackenzie, who was then in
charge of the Canadian program, wrote with great foresight to C.D. Howe, who
was the minister responsible for it:
"In my opinion Canada has a unique opportunity to
become involved in a project which is not only of the greatest immediate
military importance but which may revolutionize the future world in the same
degree as did the invention of the steam engine and the discovery of
electricity."
Thus, even while the outcome of the war was still in the balance, the
peaceful applications of nuclear energy (then termed "atomic energy")
were seen to be the long-term objective.
The wartime assignment to develop heavy-water reactors did not determine the
future design of CANDU reactors, but it did give Canada
a head start in the technology and in the research reactors that were built as
a result, facilities that allowed Canada
to become pre-eminent in some areas of nuclear research and development. The
next important factor was the Canadian government's post-war decision not to
develop nuclear weapons, and the derivative policy not to develop
nuclear-propulsion units for military purposes. In the U.S.
the nuclear-weapons program continued at high priority, while in the U.K.
and France
programs to develop their own independent nuclear weapons were initiated. In
those two countries, graphite-moderated, gas-cooled reactors were used to
produce the plutonium for the nuclear weapons (Chapter
12) ; it was the design needing least development.
World War II left Europe desperately short of all
forms of energy. The U.K.,
before the discovery of North Sea oil and natural gas,
was critically dependent on dwindling coal resources, not only as a fuel in its
own right, but also for electricity and coal-gas. Coal shortages, exacerbated
by strikes at the mines and in the distribution systems, were causing cuts in
all three fuels, and three-day weeks for industry. Under these circumstances,
nuclear energy was seen as a boon that had arrived at just the right time to be
exploited as quickly as possible. To do so, the plutonium-producing design was
modified to allow the heat produced to generate electricity. France
followed a similar path to develop it own design of gas-graphite power
reactors.
The U.S.
suffered no such energy shortages. Instead, the imperative there was to exploit
nuclear energy for submarines with greatly extended range and quiet engines.
For this application, a small reactor core is essential and the gas-graphite
design is too large. Thus the light-water reactor (LWR) was developed, with its
enriched uranium fuel cooled by ordinary water, all in a relatively compact,
but still large, pressure vessel. This design was feasible for the U.S.
with its war-time uranium-enriching technology and an industry capable of
manufacturing the pressure vessels.
In the fifties and sixties, the U.S. Atomic Energy Commission investigated
the potential of a wide variety of power-reactor designs, carrying several to
the prototype stage. However, when it was time to offer reactors in the
marketplace, both domestically and for export, it was the multinational
corporations such as Westinghouse and General Electric that decided the reactor
type. Westinghouse, which had developed the LWR for the U.S. Navy, chose to
stick with that type for civilian applications: General Electric, which had
developed an unsuccessful, liquid-metal-cooled type for the Navy, marketed
boiling-water reactors, a variant on the LWR in which the coolant boils in the
core. Both the U.K.
and France
developed and built gas-graphite reactors for civilian applications, but
subsequently turned to the LWRs that were dominating the international market.
The way in which reactor types were developed in the three countries was an
example of "industrial inertia". Once a technology is established in
industry, it is easier to expand and extend that technology than to introduce a
new one: there is a huge financial investment, facilities exist, expertise and
experience have been gained, and there is a natural tendency to stick with the
familiar and not to strike out into the unknown. This is not necessarily bad.
The nuclear industry's customers - electrical utilities - are conservative, and
rightly so, since they have an obligation to provide a reliable service.
In Canada
there was no urgency to develop nuclear energy for either military or civilian
applications. Ontario was running
out of its traditional source of electricity, hydroelectric sites, but it could
import plentiful coal from the U.S..
Consequently, nuclear energy was viewed as desirable, to reduce dependence on a
foreign energy source, but only if it were economically competitive. The
Canadian pioneers faced a tougher challenge than their colleagues elsewhere.
How the challenge was addressed, resulting in a technically sophisticated
industry for Canada,
is described in "Canada
Enters the Nuclear Age" (McGill-Queen's University Press, 1997), written
by sixteen of us who participated in the development.
In parallel with the development of the CANDU reactor system, the Canadian
nuclear industry was producing radioisotopes for medical and industrial
applications, mostly in the NRX and NRU research reactors at Chalk
River. The first radioisotopes were
marketed in 1949. In 1951 the world's first cobalt radiotherapy units for the
treatment of cancer, using radioactive cobalt produced in the NRX reactor, were
developed by Harold Johns and others. These units were installed in the Victoria
Hospital in London,
Ontario and in the University
Hospital in Saskatoon,
Saskatchewan. Since then Canada
has manufactured more than half the world's cobalt-therapy units, exporting
them to more than 80 countries: more than half a million patients are treated
each year. Canadian manufactured irradiators using radioactive cobalt are also
widely used for sterilizing medical supplies and for food preservation.
In recent years, radioisotopes for medical diagnosis
and imaging have gained increased importance. Canada
supplies much of the isotopes needed for the 50,000 diagnostic procedures using
radioisotopes that are performed each day worldwide. These include determining
the severity of heart disease and the spread of cancer, as well as diagnosing
brain disorders. Radioisotopes are also applied extensively in industry, for
instance to control manufacturing processes and in geological exploration.
Abbreviations
Technical
Terms