• Yamagata

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In Janick Magne’s Oct. 7 letter “Risks of spent nuclear fuel rods,” Magne asserts that the zircaloy that covers nuclear fuel rods is a highly flammable material that cannot be extinguished by water.

The U.S. Department of Energy has a handbook on the subject, freely available on the Internet, “Primer on Spontaneous Heating and Pyrophoricity.” Pyrophoricity is a technical term for spontaneous combustion. The book states that large pieces of zirconium (which makes up more than 95 percent of zircaloy by weight) can withstand extremely high temperatures without igniting. In contrast, very fine zirconium dust, of the order of 3 millionths of a meter in size, can spontaneously combust at room temperature. These fine particles of zircaloy cannot be extinguished by water, but the larger pieces, like those covering nuclear fuel rods, can be extinguished with water when ignited.

Of course, the situation is more complex than that — the rods are also heated by the decay heat of the nuclear fuel for one thing — but incorrect statements that zircaloy is “highly flammable” do not help advance the discussion on the hazards associated with spent fuel pools.

The opinions expressed in this letter to the editor are the writer’s own and do not necessarily reflect the policies of The Japan Times.

e. watters

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