The NRX reactor was the main objective when Chalk River Laboratories were first built in the mid-1940s. ZEEP was built to help with the design of NRX; scientists needed a better understanding of how a reactor core worked. NRX was under construction when ZEEP was finished.
NRX was originally an abbreviation of National Research X-metal. During the second world war the allies referred to uranium as 'X-metal' for secrecy purposes. Later the name came to mean National Research eXperimental.
When it was completed in 1947 it was truly a scientific wonder of its age. At 25 million watts it was the most powerful nuclear reactor in the world, and was equipped with facilities for a host research purposes. Scientists came from everywhere to Chalk River to explore the new possibilities that were opened up by such a facility.
The NRX reactor made plutonium for export to the USA. Canada did not pursue military uses of nuclear energy itself, though it was one of only a few countries with the technology to do so at the close of the second world war.
From its earliest days NRX was put to three important uses, each grew to be a Canadian science success story. NRX was powerful enough to make radioactive isotopes, some of these have important medical applications, a field pioneered in Canada. NRX had holes that could be opened to allow beams of neutrons to 'shine' out; using beams of neutrons to explore inside solid matter also became a field of Canadian excellence recognized with a Nobel Prize. NRX also helped to develop the Canadian nuclear engineering knowledge base, which would later result in the design of CANDU nuclear power stations, an important source of electricity.
The NRX reactor had put Chalk River Labs on the scientific map. It was a best in class facility. The NRC were concerned that they must not lose that international position, so in 1949 they began to plan its successor...