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Beginnings + 1945: ZEEP + 1947: NRX + 1957: NRU + 1994: Nobel Prize
Canada's first nuclear reactor, ZEEP was an operating reality just 13 years following the discovery of the neutron: a staggering scientific achievement. But it was just the start. The NRC's plans for Chalk River had intended ZEEP as an experiment which would be used to gather knowledge on the fission process. The ultimate goal however was a much larger research facility...
ZEEP was the simplest design of reactor that can be imagined. A large empty tank with a drain pipe at the bottom formed the basic size: a vertical cylinder about 2 m in diameter and almost 3 m high. Into this tank fuel rods were suspended, these were slugs of uranium stacked inside aluminum tubes. The final component needed was a moderator, the material that slows down the fast neutrons emitted from uranium atoms as they split.
In ZEEP, the chosen moderator was heavy water. That is water H2O, in which all the hydrogen atoms contain an extra neutron. Heavy water is in fact about 10% heavier than regular water. It is an extremely good moderator. To start the fission reaction, heavy water was pumped up into the tank through the drain pipe. A glass tube on the side of the reactor indicated the height of water inside. As the heavy water level rose, its moderating effect on the neutrons increased until a point was reached where a sustained nuclear reaction could continue. Uranium atoms split, giving out neutrons which were slowed in the heavy water and struck other uranium atoms in a self-perpetuating process. Scientists used ZEEP to understand better how reactors worked. It was a low power experiment, making less than 10 watts of heat.
ZEEP was the first reactor outside the USA to operate. It was the brainchild of physicist Lew Kowarski, an emigre to Canada from France, escaping the conflict in Europe. The reactor itself was designed and constructed by a team led by George Klein, one of Canada's great inventors. As ZEEP was being constructed and then began to operate, yielding crucial information about the nuclear fission process, alongside it, a huge building rose. It was to house the NRX reactor, the most powerful research facility of its day.
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The ZEEP reactor building circa 1945