The NRX pile at Chalk River

NOV 01, 1951

The following pages contain a description of Canada’s high flux nuclear reactor, the heavy water and uranium NRX pile.

W. B. Lewis

The NRX pile at Chalk River is distinguished among the known experimental reactors by its high neutron flux, which at its maximum is ${6×10}^{12} neutrons / {cm}^{2} / \sec .$ It ranks among the high power experimental reactors and normally operates above its designed power rating of 10 Megawatts (10,000 kilowatts). The neutron flux is about 10 to 20 times that of a graphite reactor of comparable power and this is due to the smaller physical size of the NRX reactor made possible by the use of heavy water as the moderator to slow down the neutrons. It should be noted that the rating is attained using only natural uranium metal, and enrichment of the fissionable U‐235 isotope is not necessary. On the other hand, because of the small size of the reactor and the low total amount of uranium used, enrichment by plutonium or U‐235 yields a quick return of available neutrons.

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More about the authors

W. B. Lewis, Canadian Research Council's Atomic Energy Project, Chalk River, Ontario.