United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-68: Incorrect Effective Diaphragm Area Values in Vendor Manual Result in Potential Failure of Pneumatic Diaphragm Actuators

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                         WASHINGTON, D.C.  20555-0001

                               December 19, 1996


NRC INFORMATION NOTICE 96-68:  INCORRECT EFFECTIVE DIAPHRAGM AREA VALUES IN
                               VENDOR MANUAL RESULT IN POTENTIAL FAILURE OF
                               PNEUMATIC DIAPHRAGM ACTUATORS

Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the fact that some vendors have published
incorrect values for effective diaphragm area for some spring-type pneumatic
diaphragm actuators and that use of these incorrect values may result in
safety-related air-operated valves not fully closing under design basis
conditions.  It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to
avoid similar problems.  However, suggestions contained in this information
notice are not NRC requirements; therefore, no specific action or written
response is required.  

Description of Circumstances

On October 4, 1996, Commonwealth Edison, licensee for the LaSalle County
Station, issued a notification pursuant to 10 CFR Part 21 (Accession No.
9610080102).  The notification identified the deficiency as incorrect values
for the effective diaphragm areas, as published by the original and current
valve vendors, for certain models of pneumatic actuators.

The original valve vendor, Black, Sivalls, and Bryson (BS&B), was later
purchased by  WKM Valve Division of ACF Industries, then by Muesco, and by
Anchor/Darling Valve Company.  The affected model of actuator is the Model 70-
13 pneumatic diaphragm actuator,  sizes 35, 70, 140, and 280.  The size refers
to the published diaphragm area in square inches.  The affected actuators are
either direct acting (extends the valve stem when air pressure is applied) or
reverse acting (retracts the stem when air is applied) spring return
actuators.

The Part 21 notification included an attachment providing a Nuclear Plant
Reliability Data System (NPRDS) listing of valves of the applicable model
number by plant; however, the listing may not include all of the applicable
valves and may include valves that are not safety related or that are not
required to isolate as are the primary containment isolation 


.                                                      IN 96-68
                                                      December 19, 1996
                                                      Page 2 of 3


valves at the LaSalle County Station.  Some of the valves listed are not
diaphragm actuated valves and the identification of some items is incomplete. 
The present manufacturer, Anchor/Darling Valve Company, was unable to compile
a complete listing of the actuator applications because purchase order records
from the original vendor are unavailable. 

Discussion

The licensee found discrepancies in the bench set values of the actuators
during the LaSalle County Station refueling outage that took place from
February through April 1996.  The published bench set and the actual bench set
values, indicated from testing by the plant mechanics, were inconsistent. 
"Bench set" refers to the amount of preload and final compression force placed
on the actuator spring so that the applied spring force on loss of air will
achieve the required travel of the valve stem.  Bench set adjustments are made
by applying air pressure to the actuator in accordance with the manufacturer's
published values and adjusting the spring compressive force by means of an
adjusting screw to achieve the desired relationship between air pressure and
valve stem travel.  When performing bench set testing, incomplete valve stroke
is typically indicative of a stiffer-than-expected spring.  However, testing
by the licensee indicated that the springs were within manufacturer's
tolerances and additional testing with a known spring force, a known air
supply pressure, and a known load indicated that the actual effective
diaphragm area, which relates to the force opposing the spring as well as to
the compression of the spring for proper preloading, was less than the
published values.

Anchor/Darling Valve Company was contacted by the licensee and performed a
series of tests to determine the actual effective diaphragm area.  These tests
indicated that the actual diaphragm areas of the various sizes of the Model
70-13 actuators were approximately  90 percent of the published values. 
Further testing by the licensee uncovered a contributing problem that further
reduced the effective diaphram area.  The diaphragm case consists of two
halves bolted together.  Generally one half is deeper than the other.  It was
discovered that reverse-acting actuators assembled with a deep upper half
caused unintended stretching of the diaphragm within the casing.

The licensee determined that the primary containment isolation valves would
have closed at the design-basis-accident containment pressure of 40 pounds per
square inch; however, many of the valves may not have been properly set up to
close against the normally higher system pressure under some operating
conditions.  That is, the valves may not have closed under the highest
expected differential pressure of the contained system fluid.  Further details
of the concern are in Licensee Event Report 50-373/96-011, dated October 28,
1996,  (Accession No. 9611010277).

The licensee determined which valves at the LaSalle County Station were
affected and was able to properly adjust the actuators to account for the
discrepancies between the published values for the diaphragm area and the
actual diaphragm area by (1) adjusting the bench set on the spring to achieve
the required closing force and (2) reversing the diaphragm casings so that the
deeper part of the casing was installed on the bottom with the shallower part
of the casing installed on top to prevent the diaphragm from stretching..                                                            IN 96-68
                                                            December 19, 1996  
                                                            Page 3 of 3


The licensee has not identified similar problems on actuators made by other
manufacturers, but licensees should be aware of the concern when testing and
making adjustments to the bench set of pneumatic actuators.  The proper setup
of these actuators is especially important when the attached valve is used for
isolation in a safety-related application.  Licensees may wish to review their
valves and actuators for applicability of this information.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.




                                 Thomas T. Martin, Director
                                 Division of Reactor Program Management
                                 Office of Nuclear Reactor Regulation

Technical contacts:            Patricia Campbell, NRR
                 (301) 415-1311
                 E-mail:  plc@nrc.gov

                 David Skeen, NRR
                 (301) 415-1174
                 E-mail:  dls@nrc.gov

                 Andrew Dunlop, RIII
                 (630) 829-9726
                 E-mail:  axd7@nrc.gov
Page Last Reviewed/Updated Thursday, November 21, 2013