Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 8, 1988
Information Notice No. 88-73: DIRECTION-DEPENDENT LEAK CHARACTERISTICS
OF CONTAINMENT PURGE VALVES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to a potential
problem regarding unexpected direction-dependent leakage through containment
purge valves. 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 do not constitute NRC requirements; therefore, no specific action or
written response is required.
Description of Circumstances:
On May 18, 1988, during the performance of a Diablo Canyon Unit 1 containment
integrated leak rate test (ILRT), the licensee discovered that the 48-inch
purge system valves inside containment did not have adequate leakage integrity
(Licensee Event Report 50-275/87-25). The licensee then successfully
performed a local leak rate test (LLRT) on the purge supply and exhaust
penetrations by pressurizing the volume between the inboard and outboard
isolation valves. Although the LLRT was apparently a success, the valves
inside containment were pressurized from the direction opposite to the one
required for them to perform their safety function. The licensee determined
earlier that this practice was acceptable, based on information and test data
supplied by the manufacturer stating that pressure could be applied to the
valve from either direction and the valve would be leaktight.
The discrepancy between the ILRT and LLRT findings indicated that the LLRT
methodology of pressurizing the volume between the isolation valves did not
adequately confirm the operability of the inside valve.
The licensee's subsequent investigation found that the valves, Fisher Series
9200 butterfly valves, have a tapered seat that gives them a directionally
dependent leakage characteristic. The valves inside containment are oriented
so that the discs face outward. Pressure from containment tends to unseat the
disc gaskets, whereas pressure from the opposite direction tends to seal
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September 8, 1988
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the gaskets against the tapered valve seats. The valves were purchased
because the manufacturer had specified that they could seal in either
direction. The licensee reversed the inboard purge valves in Unit 1 and made
a commitment to do the same for Unit 2.
Discussion:
Section III.C, "Type C tests," of Appendix J, "Primary Reactor Containment
Leakage Testing for Water-Cooled Power Reactors," to 10 CFR Part 50 states
that for containment isolation valve local leak rate testing, "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." LLRT results could be misleading if
the assumption that an isolation valve does not have directionally-dependent
leakage characteristics is not true. Direction-dependent leakage could be a
characteristic of valves other than the make and model used at Diablo Canyon.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: James C. Pulsipher, NRR
(301) 492-0877
Attachment: List of Recently Issued NRC Information Notices
. Attachment
IN 88-73
September 8, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-72 Inadequacies in the Design 9/2/88 All holders of OLs
of dc Motor-Operated Valves or CPs for nuclear
power reactors.
88-71 Possible Environmental 9/1/88 All holders of OLs
Effect of the Reentry or CPs for nuclear
of COSMOS 1900 and power reactors,
Request for Collection fuel cycle
of Licensee Radioactivity licensees, and
Measurements Attributed Priority 1
to That Event material
licensees.
88-70 Check Valve Inservice 8/29/88 All holders of OLs
Testing Program or CPs for nuclear
Deficiencies power reactors.
88-69 Movable Contact Finger 8/19/88 All holders of OLs
Binding in HFA Relays or CPs for nuclear
Manufactured by General power reactors.
Electric (GE)
88-48, Licensee Report of Defective 8/24/88 All holders of OLs
Supplement 1 Refurbished Valves or CPs for nuclear
power reactors.
88-68 Setpoint Testing of Pres- 8/22/88 All holders of OLs
surizer Safety Valves with or CPs for nuclear
Filled Loop Seals Using power reactors.
Hydraulic Assist Devices
88-67 PWR Auxiliary Feedwater Pump 8/22/88 All holders of OLs
Turbine Overspeed Trip or CPs for nuclear
Failure power reactors.
88-66 Industrial Radiography 8/22/88 All NRC industrial
Inspection and Enforcement radiography
licensees.
88-65 Inadvertent Drainages of 8/18/88 All holders of OLs
Spent Fuel Pools or CPs for nuclear
power reactors and
fuel storage
facilities.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
