MAPLE Reactors

To secure the long-term supply of medical isotopes with the NRU reactor reaching the end of its life, two new 10 MW pool-type research reactors of the MAPLE design (Multipurpose Applied Physics Lattice Experiment) were commissioned in 1996. While the MAPLE design is capable of fuel and materials testing and neutron experimentation and medical isotope production, these two MAPLE reactors (which became known as MMIR-1 and MMIR-2) were designed solely for the production of medical isotopes.

In 1996, MDS Nordion, a global radiopharmaceutical supplier based in Ottawa, Ontario entered into an agreement with Atomic Energy of Canada Limited (AECL, now Canadian Nuclear Laboratories) to build two MAPLE reactors and a processing facility to extract the isotopes. The reactors were to be built by AECL on behalf of MDS Nordion at the Chalk River Laboratories.

MMIR-1 was declared “critical” (began a self-sustaining chain reaction) at 2:53 a.m. on Saturday, February 19, 2000 at Chalk River Laboratories, becoming the world’s first reactor of the new millennium. MMIR-2 achieved first criticality at 2:08 p.m. on October 9, 2003.

While commissioning exercises successfully took the MMIR-2 core to high power (8 MW) and tested many of the crucial safety systems, several first-of-a-kind technical issues delayed the commissioning process, to the point where AECL and the Government of Canada decided, in May 2008, to discontinue the project. The reasons cited were the costs, the time frame and risks of continuing with the project.

MDS Nordion, Canadian Nuclear Laboratories, and the Government of Canada are investigating a new strategy for guaranteeing a stable long-term supply of medical radioisotopes. Meanwhile medical isotope production continues in the NRU reactor at Chalk River Laboratories.


Tammemagi, Hans, and Jackson, David (2002). Unlocking the Atom: The Canadian Book on Nuclear Technology. McMaster University Press.
Canadian Nuclear FAQ, Section H: Research Reactors,
World Nuclear Association, Outline History of Nuclear Energy,
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