nuclear-news

Pros and cons of moving nuclear wastes from pools to casks

Haste vs. Procrastination on Nuclear Waste, NYT By MATTHEW L. WALD  7 July 11 “…….safety concerns arise in moving the fuel to casks, too. The details, pro and con, get interesting.

When the fuel is first taken out of the reactor, it is generating a lot of heat. That’s because when the uranium is split in the nuclear reactor, it leaves behind fragments that are unstable and that seek to return to stability by giving off a subatomic particle –- an alpha or beta particle –- or an energy photon, called a gamma ray. Each time such a fragment gives off such an increment of radiation, it is generating heat. But as weeks pass, the most unstable elements cease those emissions, and heat production is reduced.

When the fuel is old enough and cool enough that it cannot heat up a sealed canister to more than 752 degrees Fahrenheit, it can be loaded into a dry cask. The fuel is sealed inside a metal capsule, and air circulating on the outside of the capsule carries off the heat, with no fans or pumps.

Generally, industry thinking has been that the fuel has to sit in the pool for at least five years before it can go into a dry cask. Thus at any reactor that is operating, a lot of fuel will remain in the pool even if operators make maximum use of the casks.

Last month, however, Holtec International, a major cask manufacturer, announced that it would apply for permission to load three-year-old fuel into casks. The company has been working with metals that conduct heat better, so that even if there is a lot of young fuel inside the capsule, the heat will radiate away without causing temperatures to rise too high inside, it says…..

Managing the fuel in casks does have a silver lining, from the perspective of long-term disposal. Eventually, as heat production declines, the radiation doses that workers are exposed to in shipping the fuel to a burial will be smaller. And at the burial site, heat production may be the factor that decides how close together the waste can be packed, and how big a repository is needed…….

July 8, 2011 - Posted by Christina Macpherson | technology, USA, wastes