United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-30, Supplement 1: Leaking Shutdown Cooling Isolation Valves at Cooper Nuclear Station

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

August 19, 1994


NRC INFORMATION NOTICE 94-30, SUPPLEMENT 1:  LEAKING SHUTDOWN COOLING
                                             ISOLATION VALVES AT
                                             COOPER NUCLEAR STATION


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 (IN) supplement to clarify the type of valve discussed in the original
notice and to alert recipients to the potential that local leak rate testing
of primary containment isolation valves with pressure applied in the direction
opposite of the accident direction may not be conservative.  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.

Background

The NRC issued IN 94-30, "Leaking Shutdown Cooling Isolation Valves at Cooper
Nuclear Station," on April 12, 1994, to alert addressees to a precursor to an
unisolable rupture of shutdown cooling piping with the potential for core
damage and release of radioactive material outside the containment.  In that
event, after receiving a high-pressure alarm for the suction piping in the
residual heat removal system, the licensee measured the leakage through the
inboard isolation valve, established a bleedoff path into the pressure
maintenance system and continued operations.  About 10 months later, the
licensee disassembled the inboard and outboard valves and found cracks in the
seating surfaces of both valves.

During the preparation of IN 94-30, the staff determined that a concern may
exist regarding the method used for testing of primary containment isolation
valves.  This concern is described below.  In addition, the NRC has received
information from Anchor/Darling Valve Company that the description of the
valves in IN 94-30, "Anchor-Darling 20-inch nominal, double-disk, flex-wedge,
gate valves," is incorrect.  The correct description is, "a 20 inch, 900
class, flex wedge gate valve," manufactured by the Anchor Valve Company before
the merger that formed the Anchor/Darling Valve Company.  In IN 94-30, the NRC
staff was concerned about the actions of the licensee after the valve leakage
was identified regardless of the valve type or manufacturer.


9408160070
.                                                        IN 94-30, Supplement
1                                                         August 19, 1994
                                                        Page 2 of 3


Description of Circumstances

On May 1, 1993, after evaluating the results of local leak rate testing for
several inboard primary containment isolation valves, the licensee for the
Cooper Nuclear Station (Cooper) determined that the testing methodology used
for Appendix J, Type C tests of certain flex-wedge gate valves could not be
relied on to be equivalent to or more conservative than testing the valves in
the accident direction.  The Type C tests for several such valves had been
performed with the pressure applied in the direction opposite to the accident
direction (reverse direction).  The licensee began corrective actions and
notified the NRC in Licensee Event Report (LER) 93-019, dated June 1, 1993.

In LER 93-019, the licensee reported that the testing of these valves in the
reverse direction was based on an incorrect interpretation of information from
the valve manufacturer.  In response to a question from the licensee regarding
the acceptability of valve test methods, the manufacturer had indicated that
testing in the reverse direction would not be expected to affect test results,
but an unqualified answer could not be provided.  Results of recent tests by
the licensee of some of the primary containment isolation valves with pressure
applied in the accident direction, indicate that testing in the reverse
direction may not be equivalent to or more conservative than testing in the
accident direction; therefore earlier test results may not be valid.

LER 93-019 indicated that Cooper Nuclear station has 65 inboard primary
containment valves of various types and from various manufacturers.  The
licensee found that 24 of those valves were of concern.  Of the 24 valves,
8 could be tested in the accident direction but, before the 1993 refueling
outage, were not.  The other 16 valves could not be tested in the accident
direction nor had testing in the reverse direction been qualified to be
equivalent or more conservative than testing in the accident direction.  For
most of these valves, the licensee qualified testing in the reverse direction
to be equivalent or more conservative or modified the testing configuration to
allow testing the valve in the accident direction.  For the remaining valves,
the licensee requested exemptions from certain Appendix J requirements to
allow leak rate testing in the reverse direction.

Discussion

Appendix J to Title 10 of the Code of Federal Regulations Part 50 requires a
program for leak testing the primary reactor containment and related systems
and components penetrating the primary containment pressure boundary.
Section III.C.1 of Appendix J specifies that, for Type C tests of valves
(local leak rate tests), the pressure shall be applied in the same direction
as that when the valve would be required to perform its safety function,
unless it can be determined that the results from the tests for a pressure
applied in a different direction will provide equivalent or more conservative
results.  This requirement is intended to ensure that test leak rates are
representative of leak rates that would be experienced under actual accident
conditions.  As described above, the licensee for Cooper found that, for some
of the primary containment isolation valves, testing in the reverse direction
was not equivalent to or more conservative than testing in the accident
direction.  .                                                        IN
94-30, Supplement 1
August 19, 1994                                                         Page
3 of 3


Related Generic Communications

NRC IN 86-16, "Failures to Identify Containment Leakage Due to
Inadequate Local Leak Rate Testing," March 11, 1986.

NRC IN 92-20, "Inadequate Local Leak Rate Testing," March 3, 1992.

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

  /S/'D BY CIGRIMES/FOR


                                      Brian K. Grimes, Director
                                      Division of Operating Reactor Support
                                      Office of Nuclear Reactor Regulation

Technical contact:  Jim Pulsipher, NRR
  (301) 504-2811

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