Calls Grow for Spent Nuclear Fuel to Be Stored More Securely
With more scrutiny on spent fuel pools in the United States, some are pointing to dry casks as a storage option.
Michele Kearney's Nuclear Wire - Major Energy and Environmental News and Commentary affecting the Nuclear Industry. Nuclear Activities
Wednesday, July 6, 2011
Calls Grow for Spent Nuclear Fuel to Be Stored More Securely
With more scrutiny on spent fuel pools in the United States, some are pointing to dry casks as a storage option.
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Ok. Here is my letter to the editor. We'll see if it is worthy of publication.
ReplyDeleteTo the Editor:
In the July 5 article “A Safer Nuclear Crypt”, Matt Wald presents the option of storing nuclear waste in dry cask storage casks. The article does a good job at presenting benefits and potential problems with following this path. Without going further into this topic, I just want to point out, how even good reports seem to perpetuate statements that are not true. These are myths that repeated over and over in the media and are taken as truth because they are heard so often.
Here is the myth in Matt Wald’s article: “Spent fuel must be isolated from the environment for hundreds of thousands of years before it loses its potency”. This is not true. According to the World Nuclear Association, most of the radioactivity from high-level waste will have decayed after 1000 years. This is still a long time, but in terms of geological time scales it is “blink of an eye”. This is an important consideration if geological disposal is eventually implemented.
The longer time comes from misapplication of a rule of thumb that it takes 10 half lives for a nuclide to essentially disappear. This leads to the false reasoning that one needs to multiply the half life to Plutonium 239 (24,200 years) by 10 for spent fuel to lose its potency. By the same false reasoning one could argue that one needs to wait 7 billion years for U-235 to lose its potency or 44 billion years for U-238 to lose its potency. To keep these times in perspective, the age of the earth is 4.5 billion years. Mankind has existed for only a few hundred thousand years.
Neither U-235 nor U-238 are potent to begin with, (one can stand next to an un-irradiated fuel assembly without getting significant radiation exposure) so there is no need to wait for these nuclides to disappear at all. It is not important to wait for nuclides to disappear, but rather to wait until the radioactivity decays to a level that we are normally exposed to. This is the basis for the shorter time that spent fuel must be isolated from the environment.
Ulrich Decher PhD Nuclear Engineering