Just five reactors supply 95 percent of the world's Mo-99, and they're all past their prime. A nuclear reactor's average life span is 40 to 50 years. Chalk River is 52 years old. The Dutch reactor—which came back online in August—is 47. The other three, in France, South Africa and Belgium, are 42, 43 and 47, respectively. In 1996, Canada boldly tried to replace them all with its own two-reactor facility, called MAPLE, that would pump out enough Mo-99 to supply the whole world. Other reactor-builders, figuring they would be crushed by MAPLE's massive output, stayed out of the isotope-making business. But MAPLE engineers found a set of flaws in the reactors, and last spring, after spending $600 million—several times the project's budget—Canada officially killed it. "That was our big 'oh, sh-t' moment," says Steve Mattmuller, chief nuclear pharmacist at Kettering Medical Center in Ohio. "We were right back where we were 20 years ago, but now our reactors were 20 years older."