The Chalk River lab is owned by Atomic Energy of Canada (AECL) and supplies molybdenum-99, iodine-125, iodine-131 and xenon-133 to MDS Nordion for the manufacture of radiopharmaceuticals. A derivative of molybdenum-99 - technetium 99 - is used in 90 per cent of hospital radiopharmaceutical medical procedures. This amounts to over 15 million medical procedures per year.

Most of the isotopes manufactured by the plant have a shelf life of less than three days. If the strike continues over the weekend, then present stocks will become critically short and cancer and heart procedures will have be cancelled world-wide. Meanwhile MDS Nordion has spent the week trying to source fresh supplies from Belgium, South Africa and the Netherlands.

The strike - caused by a breakdown in talks between the United Steel Workers of America union and AECL - started one minute after midnight on Monday morning. Shortly afterwards the main reactor, the isotope production line and several other research projects were shut down. Last night AECL proposed independent arbitration to the union to solve the dispute.

Peter Lahaie, managing director of MDS Nordion's European subsidiary, believes that there are grounds for optimism. "There will be some shortfall next week, and we will have to ration use of molybdenum 99, but the idea is still to get the isotopes straight to the patients" he says. He hopes an agreement with the workers can be reached over the weekend.