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Jaro:
You're right on two fronts: 1) we did not
assume rebar. Steel poses more effective resistance than
concrete. We could take rebar into account. At PFS, the dry storage
casks are constructed of steel shells and concrete. We and PFS took that
into account by energy loss through each of the steel, concrete, steel
shells. But remember again that some reactor containments are only 2'
thick. Because of that, within a few days of the WTC attack, we asked the
NRC to monitor their web site, an action they took over 4 weeks
later.
2) The issue of the speed that a 767
(not a 757, which has a lighter engine and less fuel) could strike a low profile
target is a matter of probabilities. We did not investigate this
matter. Here is what the news media said:
Wash Post, CBS.com: 460 mph,
Pentagon
MSNBC: 600 mph, WTC; 450 mph, Pentagon
Wash Post: 400 - 550 mph into all
targets
Wash Post: 345 mph, Pentagon
Since video clips on the second WTC attack exist,
at least for that crash, where the plane banked, one could precisely determine
that speed.
Another issue involves flight path. Some
reactors, such as those next to the ocean, are on a clear flight
path and many reactors are as tall as the Pentagon. On the
other hand, some reactors lie in valleys next to curving rivers.
Striking such reactors at cruising speed would have a low
probability.
Thanks for your email and for maintaining a
professional dialogue on this important issue.
Marvin Resnikoff
----- Original Message -----
Sent: Tuesday, November 06, 2001 5:05
PM
Subject: RE: jet engine penetration
depth
Marvin,
According to the
reference document,
Davis,
P. R., D. L. Strenge, and J. Mishima, 1998, Final Accident Analysis for
Continued Storage, Revision 0, Jason Technologies Corporation, Las Vegas,
Nevada. [244118],
page 7 paragraph one
states :
Table 2 indicates
that the maximum thickness of concrete penetrated by a jet engine (2.80 ft.)
under the assumed conditions is considerably less than the thickness of the
concrete storage modules (3.33 ft.). Thus, unless the concrete in the
storage modules becomes degraded, aircraft penetration would not be
expected.
....where the "assumed conditions" were 500 fps
impact velocity and a Boeing 757 with Rolls Royce engines.
Note also, that the
"concrete" assumed in this document is just that -- there is no steel rebar,
as one would find in a reactor containment dome wall (or the impact target in
the 1988 Sandia F-4 Phantom impact test, where penetration depth was
trivial).
I also think that
your assumed speed of 500mph is way too high -- while its certainly
possible to hit the end of an airport runway accurately at ~100mph, trying to
steer an airliner into a relatively small building at FIVE TIMES that speed
would be virtually impossible. The WTC attacks occurred at a little over
300mph, and you could see that the terrorist pilot had his hands full trying
not to miss -- the plane banked quite sharply just prior to impact ( BTW, the
ref. doc. speed of 500 fps is about 550 kph, or 340 mph).
Jaro
Jaroslav Franta:
Thanks for pointing us in the direction of the
Sandia full-scale tests of an F-4 Phantom jet. This paper is important
to our work in analyzing the impact of a jet engine on a nuclear fuel dry
storage cask. We've now evaluated the Sandia paper presented at a
symposium, rather than the abstract.
Sandia states, "The primary purpose of the test
was to determine the impact force versus time due to the impact of a complete
F-4 Phantom onto a massive, essentially rigid reinforced concrete
target." You were correct to state that the F-4 Phantom had intact
engines. The penetration depth by the fuselage was 2 cm, as you stated;
the penetration depth of the engines was 6 cm.
However, the massive concrete block, weighing
almost 25 times the weight of the F-4 Phantom, absorbed almost all the
impact. The 469 tonne block was floated on an air cushion and moved 1.83
m until it hit the backup structure and rebounded.
Our calculations for concrete penetration do not
assume the structure moves. As must be clear to you, one cannot infer
from the Sandia test that a 767 engine moving 500 mph will penetrate 6 cm of
concrete. If the building or storage cask were stationary,
the penetration depth of the 767 jet engine is closer to 4 feet, and
several U.S. reactors have a thinner concrete containment. Our method of
calculating the penetration depth is identical to the method used by NRC staff
and DOE contractors.
Marvin Resnikoff
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