More media coverage of the EPRI report......
Jaro
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Terror Threat Triggers Nuclear Plant Studies
MICHAEL A. DORNHEIM/LOS ANGELES
AVIATION WEEK & SPACE TECHNOLOGY/ JANUARY 13, 2003 p.417
A 450,000-lb. Boeing . 767-400 flown by a suicide pilot wouldn't be able to penetrate containment vessels at nuclear power plants, according to a recent nuclear power industry study.
Nevertheless, the Nuclear Energy Institute's December report bas raised some skeptical eyebrows. Why is it that the 757-200 that hit the Pentagon on Sept. 11, 2001, weighing less than 255,000 lb., penetrated three of the concrete building's five rings, yet the NEI study says the heavier aircraft at the same speed won't breach a 3.5-ft.-thick reinforced concrete containment dome? An NEI official explained the differences, but the details are not being released. (The study is at www.nei.org.) The Nuclear Regulatory Commission (NRC) is conducting a separate study on the same subject but hasn't decided whether the results will be publicized.
"[Nuclear power plants] are probably our best defended targets," said John Hamre, president and CEO of the Center for Strategic and International Studies. However, "when confronted by an aviation attack, there is some concern."
There are 103 nuclear plants in the U.S., and the NEI report states that it analyzed models that represented all types of radiation containment vessels, using conservative assumptions about vessel strength and targeting accuracy. The researchers assumed an impact speed of 350 mph. (304 kt.) because this was approximately the speed of the Pentagon aircraft, and because an aircraft becomes too difficult to aim precisely at high speed.
Because the 140-ft. containment dome is a small target, parts of the 170-ft.-wingspan 767-400 will miss it. Engines are about 50 ft. apart on the wing so both can hit the structure but they won't both strike a perpendicular blow. Engine weight is 9,500 lb. each - 90% of U.S. engines weigh this or less, according to the study. But the Boeing 777's huge turbofans weigh more than 16,000 lb. apiece and were not in the study. The effect of landing gear was considered, said Stephen D. Floyd, NEI senior director for regulatory reform.
About two-thirds of the plants are pressurized-water reactors (PWRs), which have the hallmark external containment dome. The structure is concrete, typically 3.5-4.5 ft. thick reinforced with 2.25-in.-dia steel bars on 12-15-in. centers. Overall dimensions are about 140 ft. high and 140 ft. in diameter. Boiling-water reactors (BWRs) usually have the containment vessel inside a building, making it hard to target. The vessel is about one-third the diameter of a PWR dome, and has a steel lining dad in at least 4 ft. of reinforced concrete.
Plant licensing by the NRC considers aircraft impact, but only in a probabilistic sense. Because most plants are not near a major airport, the chance of a large airliner hitting them was considered to be negligible and they did not have to evaluate such a strike. The idea of an intentional attack was not considered; instead, the design was driven by factors like earthquakes, hurricanes and internal overpressure.
THE REPORT STATES that while there was crushing and spalling of the concrete containment domes and vessels, they were not breached. For comparison, at least five walls of the Pentagon were breached by the 757. Each ring has its own pair of walls, each of which has about 12 in. of concrete reinforced with two layers of 1- in. steel bars, plus about 12 in. of bricks and mortar. That totals to 5 ft. of lightly reinforced concrete plus 5 ft. of weaker masonry. The key is that the walls are broken every few Feet by columns of windows, making the structure weaker than the solid containment dome with 2.25-in. steel bars, Floyd said.
[[...plus the NPP dome's wall is convex, not flat - a far stronger geometry, a fact that was already well known by arch builders in Roman times ! -- Jaro]]
The study used force versus time curves based upon aircraft impact tests done by Sandia National Laboratory in the late 1980s and early 1990s. Force spikes occur as the nose, nose landing gear, engines, main landing gear and tail hit, Floyd said. Other structures evaluated in the report include:
· Used fuel storage pools. Used fuel contains dangerous materials created by nuclear fission, and is radioactive and still producing heat. It must be cooled in the water pool for five years or more. The pools are at least 40 ft. deep and typically have a 40 X 60-ft. planform. At PWRs the pools are commonly in an auxiliary building, but some are directly outside and some are at least partly above ground level. When inside a building, sometimes a pool wall is also the exterior wall of the building. At BWRs they are usually within the reactor building, but outside the containment vessel. For the BWR case, the study looked at an elevated pool with an exterior wall. Pool walls are usually 4.5- 6.5-ft.-thick concrete reinforced with 1.25- in. steel bars, and have a stainless steel liner.
Similar to the containment vessels, researchers predicted a 767-400 strike would "cause crushing and cracking of the concrete wall, but the liner remains intact to prevent leakage.
· Used fuel dry storage. Eighteen plants have cylinders to store used fuel after it has lost enough energy for natural convection cooling to be adequate. There are three types ranging from 15-18 ft. long and 4-8 ft. in diameter. Some are surrounded by reinforced concrete that is 2 ft. thick in one case and have 0.5-2-in.- thick stainless steel liners. Another type has 10-15-in.-thick stainless steel walls. The study showed none of the container types would be breached.
· Used fuel transportation containers. These are 17 ft. long and 8 ft. in diameter and go on rail cars. The container weighs 250,000 lb., and the rail car and container skid weighs another 66,000 lb. The study assumed a direct engine hit and found that the 350-mph, impact would not penetrate the container.
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