Since neutrons are neutrally charged, they have the ability to insert themselves in a wide variety of materials, sometimes turning the material into a radioactive isotope of the original material and sometimes causing the material to change into an entirely different element.
Unlike other commercial reactor designs, this capability has been put to profitable use in CANDU¨ reactors. The program has established Canada as one of the primary sources of isotopes for medical and industrial use.
Ease of Entry
The designers and owners of light water reactors did not simply ignore a potential commercial opportunity. Instead, they understood the limitations of their plants and decided that the material that could be produced was not worth the expense of providing a material production capability.
Since the reactor core of a light water reactor is limited in size by the size of the available pressure vessel, and since the core of a commercial light water reactor is invariably a high temperature, high pressure environment, it would be a significant engineering challenge to provide a capability to insert and remove materials on a schedule amenable to isotope production.
In contrast, a large portion of the core of a CANDU is a low pressure tank full of cool (70 C) water. It is fairly simple to design pipes and other access ports that allow carefully controlled material insertion into a portion of the core with an intense neutron flux.
In several cases, existing access tubes normally used for control systems have been modified to accept a suitable material for neutron irradiation. In one specific example, several CANDUs use Cobalt adjuster rods to allow the production of the very useful Co-60 isotope.
Canada now produces approximately 85 percent of the world’s supply of Co-60 and more than 50 percent of the Co-60 medical therapy devices and medical device sterilizers. It also produces most of the world’s supply of molybdenum-99, the precursor of Technetium-99m, the isotope that is the most widely used radioactive pharmaceutical. A person who has undergone tests involving imaging scans of the brain, bone, liver, spleen or kidney probably owes some thanks to the CANDU design.
The business of providing isotopes provides a nice income kicker when combined with the usual reactor business of providing electricity. It has provided Canadians with a substantial return on their nuclear technology investments while providing physicians with previously unavailable diagnostic and treatment tools.