United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-02: Inadequate Seismic Qualification of Diaphragm Valves by Mathematical Modeling and Analysis

                                                         SSINS No.: 6835 
                                                         IN 87-02       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                              January 13, 1987

                                   DIAPHRAGM VALVES BY MATHEMATICAL 
                                   MODELING AND ANALYSIS 


All nuclear power reactor facilities holding an operating license or a 
construction permit. 


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. 


                                                            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. 


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.

                                                            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 

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