On Fri, 18 Mar 2011, Harry Pollard wrote: > Ray, > > If Japan loses 40,000 people from this incident, it will be the worst. > > But the chance of that is small. > > Instead, spare a tear for the thousands of Japanese already lost from the > natural events. > > The workers in the plants are suffering and will suffer, but the chance of > further serious contamination of the civilian population is not great. > Anything might still happen, but the probability is that things will be soon > under control and the main damage will be economic. I don't like the stories > of spent fuel rods in temporary water tanks losing their water, but that's a > continuing problem caused by various governments, including the US, fiddling > around unable to provide them a permanent home. At least one nuclear plant > got fed up with waiting and built above ground places (like a row of brick > garages) for spent fuel rods. But, everywhere, in the absence of a safe > place to get rid of them they sit in tanks of water. I would prefer them to > be processed (against the law) and then suitably covered in concrete be > dropped into the Pacific Trench >
You don't want to either reprocess or dispose of spent fuel rods from pressurized light water reactors (the only kind in the US). These "spent" rods of enriched uranium contain 0.9% U235. Canadian "CanDU" heavy water reactors normally use natural, unenriched uranium, which is 0.7% U235. They can run happily with the "spent" light water rods, unreprocessed, in fact with a slightly greater power output than normal. And when rods are spent after running in a CanDU, they are really spent, but they can still be processed further by running in a thorium reactor (except, as a newly conceived technology, there are no commercial thorium reactors yet in existence), which will lower the radioactivity content even further. Upon final extraction from a thorium reactor, the rods can be potted in glass and nested in gravel beds in tunnels dug deep in the geologically inert canadian shield, at depths below the water table, and sealed in. These will essentially be returned to the rock from which they were mined. The existing CanDU reactors, by the way, are very close to the current benchmark of "inherently safe", even though the design is 40 years old. The low activity level of the fuel means it can only achieve criticality in a bath of heavy water, and while it does acquire residual heat from daughter product decays continuing after shutdown stops the fission chain, the larger size of the chamber reduces the heat density. Further more, the individual rods are accessible outside the heavy water envelope, and can be extracted one at a time to further dampen reaction. The spent rods are thus not in a fixed geometry matrix (unlike the rod packs in the GE design used in Japan), and thus are initially placed for cooling storage in a lower density array, further reducing the heat load generated during their cooldown period. The Old GE design in Japan is referred to as "engineered safe", which is PR-speak for "safe as long as all the engineered safety systems are working properly". These devices should have been retired years ago. -Pete _______________________________________________ Futurework mailing list [email protected] https://lists.uwaterloo.ca/mailman/listinfo/futurework
