Impact induced response spectrum for the safety evaluation of the high flux isotope reactor Page: 4 of 13
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IMPACT INDUCED RESPONSE SPECTRUM FOR THE SAFETY
EVALUATION OF THE HIGH FLUX ISOTOPE REACTOR'
S. J. Chang
Research Reactors Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831-6399 USAABSTRACT
The dynamic impact to the nearby HFIR reactor vessel
caused by heavy load drop is analyzed. The impact
calculation is carried out by applying the ABAQUS
computer code. An impact-induced response spectrum is
constructed in order to evaluate whether the HFIR vessel
and the shutdown mechanism may be disabled. For the
frequency range less than 10 Hz, the maximum spectral
velocity of impact is approximately equal to that of the
HFIR seismic design-basis spectrum. For the frequency
range greater than 10 Hz, the impact-induced response
spectrum is shown to cause no effect to the control rod and
the shutdown mechanism. An earlier seismic safety
assessment for the HFIR control and shutdown mechanism
was made by EQE. Based on EQE modal solution that is
combined with the impact-induced spectrum, it is concluded
that the impact will not cause any damage to the shutdown
mechanism, even while the reactor is in operation. The
present method suggests a general approach for evaluating
the impact induced damage to the reactor by applying the
existing finite element modal solution that has been carried
out for the seismic evaluation of the reactor.
1. INTRODUCTION
The purpose of this calculation is to evaluate the
consequences of a heavy drop load near the reactor and to
estimate whether the impact caused by the drop may have
the magnitude that is capable of damaging the HFIR reactor
vessel and the reactor shutdown mechanism.
Based on work performed at Oak Ridge National Laboratory,
managed by Lockheed Martin Energy Research Corp.. for the U.S.
Department of Energy under contract DE-AC05-960R22464.
Accordingly, the U.S. government retains a nonexclusive. royal-free
license to publish or reproduce the published form of this contribution.
or allow others to do so. for U.S. government purposes.It is shown that none of these components will be
damaged and the reactor can be shut down even after the
heavy load is dropped to the concrete floor. This means that
the heavy load can be lifted while the reactor is under
operation. The total weight of the cask, including its
contents, is approximately 25,000 lb from a height of 20 ft.
The pool slab on which the HFIR vessel stands and the
surrounding concrete structure that receives the falling cask
are approximately represented by a two-dimensional plane
strain finite element model. The HFIR and its internal
components are assumed to be one rigid body and their
masses are assumed to be concentrated at four mass points
along the axis of the vessel.
The cask that falls onto the bottom concrete slab of the
HFIR pool is assumed to be rigid. Dynamic stress is
generated and propagates through the concrete slab and the
concrete walls to reach the reactor vessel and its internals.
The ABAQUS computer code is applied to obtain the
dynamic response and the time-dependent solution of this
approximate model.
To evaluate the effect of the impact to the shutdown
mechanism, an innovative approach to the problem is used.
An earlier EQE finite element solution has shown that the
shutdown mechanism will not be damaged by the HFIR
design-basis seismic response spectrum. The present
method of approach is to obtain the impact-induced
response spectrum from the ABAQUS calculation. It is then
compared to the design-basis seismic spectrum to show that
the impact-induced response spectrum does not cause more
damage to the shutdown mechanism. The impact-induced
response spectrum is derived in this analysis by using the
acceleration history of a surface point of the pool concrete
slab close to the HFIR vessel.
2. ANALYSIS OF THE PROBLEM
The two-dimensional finite element model for the
reactor and the nearby structure is sketched and shown in
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Chang, S.J. Impact induced response spectrum for the safety evaluation of the high flux isotope reactor, article, May 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc676362/m1/4/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.