By MATTHEW L. WALD WASHINGTON —
The Tennessee Valley Authority said Thursday it was considering millions of dollars of improvements to protect its six nuclear reactors from earthquakes and floods.
It is the first American reactor operator to announce safety changes that it is weighing since an earthquake and tsunami set off a nuclear crisis at the Fukushima Daiichi plant in Japan last month. Other operators have said publicly that they might have to make changes, but they have avoided saying what those were.
The T.V.A. issued a fact sheet saying that it was considering reducing the amount of fuel in its spent fuel pools by transferring older fuel to passively cooled “dry casks” and adding additional backup diesel generators.
It also listed three changes that are less commonly discussed: improving electrical switchyards to make them more resistant to earthquakes, adding small generators to recharge cellphone batteries and keep the lights on, and reinforcing the pipes that provide cooling water to spent fuel pools.
Of the six reactors operated by the T.V.A., three are boiling water reactors that resemble the Fukushima reactors. The authority said that none of its reactors are in areas where an earthquake risk is high. But it said it was looking at “potential vulnerabilities from a chain of events, such as damage from a tornado or earthquake combined with flooding from a dam failure.”
Nuclear critics have argued that all plants should be required to undertake such analyses of simultaneous events, although the Nuclear Regulatory Commission has generally rejected such hazards as too unlikely for such studies to be mandated. The commission’s staff recently began a 90-day review of how prepared American reactors are for severe accidents, but the first progress report on that effort is not expected until early next month.
The spent fuel storage problem has been debated for years. After the attacks of Sept. 11, 2001, Congress asked the National Academy of Sciences to look into the problem, and in 2005 the academy reported that the pools might in fact be vulnerable to terrorism. It said the Nuclear Regulatory Commission should evaluate whether some of the fuel should be moved to dry casks.
Lately some members of Congress have suggested more use of dry casks.
When spent fuel is removed from a reactor, it continues to generate heat and must be kept submerged for about five years. But after that it can be sealed inside a steel can that is filled with inert gas to prevent rust; the can is then loaded into a small concrete silo with air vents. Air circulating around the can keeps the fuel well below the melting point.
American reactor operators have so far resorted to that technique only when their pools have reached capacity. The pools were designed in an era when nuclear engineers thought the fuel would be hauled away from reactors after a few years for recycling or burial and are therefore quite small; most reactors have installed new equipment in their pools to be able to squeeze in more than was originally intended. But some engineers say that this raises the risk that if the pool were emptied, the fuel could heat to the point that the metal it contains is ignited.
Thinning out the pools by removing old fuel would still leave the hottest materials in place but would reduce the chance of fire.
Robert Alvarez, a former Energy Department official, calculated recently that removing the backlog of fuel older than five years from the spent fuel pools of all 104 operating reactors would cost $3.5 billion to $7 billion and take several years to accomplish.