A Brief History of SLOWPOKE-Toronto

Summary of Dr. John Hilborn's opening presentation at the Seminar to Celebrate the 25th Anniversary of SLOWPOKE-Toronto, 1996 June 5

The idea of building a safe research nuclear reactor with a tiny core is credited to George A. Jarvis and Carroll B. Mills of the Los Alamos Scientific Laboratory of the University of California, Los Alamos, New Mexico. They published a report on March 22, 1967 entitled "Critical Mass Reduction", the abstract of which reads "A new low value for the critical mass of 235U in a critical reactor assembly has been determined. This value is 250 grams of 235U in a polyethylene core surrounded by a thick beryllium reflector."

This report led John W. Hilborn and Robert B. Lyon of the Atomic Energy of Canada Limited (AECL), Whiteshell Nuclear Research Establishment, to make in September, 1967 a "Preliminary Proposal for a Low Cost Neutron Source" of 100 watt power output.

This proposal soon flourished and by May, 1970 a prototype, 5 kilowatt power (equivalent to three electric kettles), pool-type, nuclear reactor (named SLOWPOKE) was built and successfully operated at the Chalk River Nuclear Laboratories of AECL.

With the help of Robert E. Jervis, the prototype SLOWPOKE reactor was moved to the University of Toronto, and this machine began working on June 5, 1971.

In the same year, in Ottawa, AECL's Commercial Products Division (now Nordion International Inc.) started up their prototype commercial unit, called SLOWPOKE-2. It featured more fuel in the core, so that it could operate longer, and more irradiation sites, so that much more work could be done simultaneously.

By February, 1973, the SLOWPOKE-1 reactor at the University of Toronto was uprated to 20 kilowatts power (four times more powerful than before) and was also licensed for remotely attended operation (no staff in the reactor room - a boon when there is often just one operator).

In September of 1974, the ownership of the reactor was transferred from AECL to the University of Toronto.

The SLOWPOKE-1 reactor was replaced by a commercial SLOWPOKE-2 version in 1976.

In 1988, to compensate for fuel burn-up in the core, an extra ring of beryllium metal (the "Big Shim") was added to the core in the hope of extending the life of the core of SLOWPOKE-Toronto for another ten years.

On June 5, 1996, the 25th anniversary of SLOWPOKE on campus was celebrated with an afternoon seminar, at which occasion the three original builders of SLOWPOKE-1 at Toronto (John Hilborn, Ron Kay and Peter Stevens-Guille) were present.

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