Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 87-02
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
January 13, 1987
Information Notice No. 87-02: INADEQUATE SEISMIC QUALIFICATION OF
DIAPHRAGM VALVES BY MATHEMATICAL
MODELING AND ANALYSIS
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit.
Purpose:
This notice is provided to alert recipients to a potential problem
pertaining to seismic qualification of safety-related diaphragm valves.
These valves were furnished as qualified by mathematical analysis based on
an inadequate model; the results of later tests showed that the actual
lowest natural frequency of the valve may be less than that required by the
purchase specification.
It is expected that recipients will review this information for
applicability to their facilities and consider actions, if appropriate, to
preclude a similar problem from occurring at their facilities. However,
suggestions contained in this notice do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances:
On December 27, 1984, ITT Engineered Valves (formerly Dia-Flo Division of
ITT Grinnell Valve Co., Inc.) notified purchasers of air-operated valves
with extended operator structures that such valves had been determined by
test to have natural frequencies less than 33 hertz. The notification was
directed to nuclear power plant owners or suppliers who had purchased valves
to specifications requiring the valves to have all natural frequencies equal
to or greater than 33 hertz as demonstrated by analysis or test.
The natural frequencies of these valves had been originally determined by
analysis. Subsequent information obtained from testing similar valves
disclosed that the natural frequency of air-operated valves with extended
structures is less than 33 Hz. ITT Grinnell undertook a testing program that
included fragility testing to provide data for evaluating the
characteristics and capabilities of the valves. On the basis of the
fragility testing results, Grinnell drew the generic conclusion that there
was not a safety problem related to valve functionality; this conclusion
,was presented in the December 27, 1984 notification. No notification of
this problem under 10 CFR Part 21 was made at that time; however, a
notification under 10 CFR Part 21 subsequently was received by the NRC from
one power plant.
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IN 87-02
January 13, 1987
Page 2 of 3
The NRC staff reviewed the test reports obtained from ITT Grinnell and
reviewed the design applications and field installations of such valves to
see if they agreed that there was adequate justification, for a generic
conclusion that no safety problem existed. The NRC staff concluded that
generic acceptance of the valves could not be determined and informed ITT
Grinnell that a Part 21 notification should be issued. As a result, on
October 10, 1986 ITT Grinnell issued two Part 21 notices, one for diaphragm
valves with air operators on extended structures and one for diaphragm
valves with Limitorque operators.
The Part 21 notices point out that, in addition to valve considerations, the
piping systems containing these valves and the associated piping supports
also may be affected by the change in frequency and that an evaluation of
the analysis methods used to qualify the valves and of the potential impact
on a system may be required.
Discussion:
The natural frequencies of the diaphragm valves are reflected in the
mathematical model and are used for dynamic analyses of those systems
requiring dynamic analysis. Therefore, these results of dynamic analysis
using the model affect predicted accelerations and forces on the valve and
its operator, stresses in the piping, and forces on the pipe supports.
The test results, reported in the Part 21 notices, for valve fragility in
terms of acceleration "g" levels are consistent with those that the NRC
obtained from review of the ITT test report data. Although the high g levels
for fragility of the valves are impressive, no generic conclusion of valve
acceptability can be made because (1) the large range of capability in g
levels included in the purchase specifications (0.15g to 4.5g) and (2) the
possibility of amplified response at frequencies less than 33 Hz can result
in unacceptable installations. Except for cases where the valve operators
are supported directly, no basis can be found for considering piping and
supports to be unaffected by the change in frequency.
Although the information provided above deals with diaphragm valves
manufactured by ITT Grinnell, there are indications that similar problems
may exist in valve/actuator assemblies sold by other manufacturers. The
difference between the original ITT Grinnell analysis and the test results
illustrates the difficulty in analytically determining the natural frequency
of the valve/actuator assembly. To provide valid results, the analytical
model must accurately reflect the flexibility of the connection between the
actuator and the valve. This may require confirmatory experimental data.
Thus it appears that a potential problem with the validity of valve
qualification and piping analysis can exist for cases where valve seismic
qualification was performed by analytical methods that were not confirmed by
test results. This problem appears to be more common for diaphragm valves
that have a predicted natural frequency of less than 55 Hz and that have
heavy extended operators with flexibility in the interface between the valve
and the operator structure.
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IN 87-02
January 13, 1987
Page 3 of 3
This information is being made available to licensees to provide insight to
a problem which may exist in systems with diaphragm valves other than those
specifically addressed in the Part 21 notices from ITT Grinnell. No specific
action or written response is required by this information notice. If you
have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: John R. Fair, IE
(301)492-4509
Attachment: List of Recently Issued IE Information Notices
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