Agenda - 05-02-2002 - Agenda - Laserfiche WebLink

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Page 4 Q. If CP&L decided today to change to dry cask storage, how long would it take? A. The limiting factor would be receipt of dry casks. CP&L could probably begin loading casks in about 9 months and be finished loading casks in about 2 to 3 years. Q. I would like more details of the scientific issues of a spent fuel pool disaster. Specifically, what is the combustible material that will fuel a fire? What is the mechanism for separation of hydrogen from water leading to a potential explosion? Is there sufficient density in the fuel pools to generate a chain reaction? Has it been necessary to provide additional shielding to prevent this? A. The spent fuel fire is initiated by the zirconium metal that forms the tubes that contain the nuclear fuel. The combustion point for zirconium metal, in the presence of air, can be as low as 700F. This temperature is less than the melting point of the fuel itself. A phenomenon known as the zirconium-water reaction has been known to generate hydrogen. Following the Three Mile Island accident, large amounts of hydrogen were liberated. About 10 hours into the accident, this hydrogen suddenly burned, causing a pressure spike inside the reactor containment from 3 psig to nearly 28 psig. The spent fuel in the spent fuel pools can reach a critical mass. It is prevented from reaching a critical mass and sustaining a chain reaction through the use of boron. Boron absorbs neutrons that might otherwise interact with uranium and plutonium atoms to cause fissioning. In pressure water reactors like Harris, boron is present both in the storage racks and in the water itself. Q. If the dam holding Harris Lake were blown up, where would the water come from to cool the waste pools? A. Nuclear plants like Harris are desgned to have sufficient cooling to cool the reactor core even at the lowest lake level following a dam break. (It's part of the dam safety program.) There's not enough cooling water for all of the equipment to operate the plant at full power, but there should be enough cooling water for the equipment needed for the plant when it is shut down under that scenario. Q. How can you prevent overheating on a rod that continues to heat? How can something be considered safe it it's not tested in some way? A. The fuel rods continue to generate heat long after the reactor is shut down. When cooling water is circulated past the fuel rods, the water absorbs the heat produced by the fuel rods and carries it away. Fuel rods inside dry casks also continue to generate heat, but at a low enough level that the heat passing through the concrete walls of the cask is sufficient cooling.