Wednesday, January 20, 2010

Canada's Cobalt Connundrum

It appears that other nuclear reactors are getting into the Cobalt production game. But I'm not sure how much to trust the details of this news report. They are wrong about a number of details quite frankly. Canada's Chalk River reactor does not (to my knowledge) produce 80% of the world's supply of Cobalt-60. It, together with the three other major isotope production reactors does produce 85% percent of the world's Cobalt-60.

The first thing to understand about Cobalt-60 production is that there are not the same problems as with Molybdenum-99 production. Cobalt-60 can be easily stockpiled and stored so that during outages there are no medical crises, because its half-life is about 5 years. That means that its radioactivity only decreases by about 50% after 5 years.

Molybdenum-99 has a half-life of 3 days. That means that after a week its radioactivity is 25% of what it initially was. After a month, it is down to about 0.1%.

So Molybdenum-99 has to be produced and shipped on an almost daily basis in order to ensure a constant supply. Whereas Cobalt-60 can be shipped far, far less often and still maintain an adequate supply.

Cobalt-60 is produced by neutron absorption of Cobalt-59 (see figure below). This can be done a number of ways, the manner I'm most familiar with is how Gentilly-2, Pickering B, Bruce B and Qinshan 1 and 2 do it, where they replace stainless steel adjuster rods with Cobalt-59 rods. This allows the absorber rods to both help control the reactor and produce a useful (and valuable) by-product.

Does it really matter then that an American reactor is getting into the game? Not really, Canada's CANDU reactors will always easily be able to convert to produce Cobalt-60, but for PWRs there has to be a significant modification done that will always cause some pause for concern. Perhaps if that modification can be done cheap enough it will threaten the CANDU dominance of the field.

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