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Thorium Cycle Hype

August 1, 2011 | A version of this story appeared in Volume 89, Issue 31

I read with interest the exchanges on nuclear power in response to Rudy Baum’s editorial (C&EN, May 9, page 5). The thorium cycle in particular gets well-deserved nods as an improvement over the uranium-plutonium processes. And yet, in A. J. Shaka’s letter (C&EN, June 20, page 4) I sense a boosterism that I hoped we had outgrown:

“No long-lived waste is produced”? Importantly, no transuranium elements, but what about 233U itself (t1/2 = 162,000 years)? What about 231Pa, a fission side product that contaminates the fuel (t1/2 = 32,500 years)? Is this one of the “fission products that are hot for a few decades and then can just be thrown away ”? And is the remaining fuel of no concern when decommissioning a plant?

The fission products’ distribution of 233U resembles those of 235U and 239Pu. The familiar unfriendly faces are all there, and in similar concentrations: 90Sr, 131I, 137Cs. In an accident (which may occur in any human endeavor), we’ll face familiar concerns.

233U is about 10 times less α-radioactive than 239Pu, so lethal airborne particles of 233U start about 10 times larger than lethal airborne Pu particles. Enjoy a sigh of relief—but don’t inhale too forcefully.

233U has a larger critical mass than 239Pu and is hard to handle, so military or terrorist use is less likely but not impossible.

Thorium is cheaper, easier to extract, and more widely available than uranium, but that was never a critical consideration or we would be using thorium already. The raw fuel cost is a red herring. The core issues are safety and environmental concerns and the resulting regulatory, investment, and insurance difficulties. The thorium cycle should alleviate, but cannot eliminate, these concerns.

If nuclear energy turns out to be needed for climate catastrophe prevention, the thorium cycle looks like a good idea. But let’s not idealize it lest we blind ourselves to the problems that remain.

By Emanuel Cooper
Scarsdale, N.Y.



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