Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No: 6835
IN 86-16
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
March 11, 1986
Information Notice No. NO 86-16: FAILURES TO IDENTIFY CONTAINMENT LEAKAGE
DUE TO INADEQUATE LOCAL TESTING OF BWR
VACUUM RELIEF SYSTEM VALVES
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is to alert recipients to a potentially significant problem
involving the failure to conduct adequate local leak rate tests of
containment isolation valves It is expected that recipients will review
this information for applicability to their facilities and consider actions,
if appropriate, to preclude a similar problem occurring at their facilities
However, suggestion contained in this notice do not constitute NRC
requirements; therefore, no specific action or written response is required
Past Related Correspondence:
IE Circular 77-11, "Leakage of Containment Isolation Valves with Resilient
Seals" September 6, 1977 Information Notice 79-26, "Break of Containment
Integrity", November 5, 1977 Information Notice 85-71, "Containment
Integrated Leak Rate Tests", August 22, 1985
Description of Circumstances:
During containment integrated leak rate testing, three plants had excessive
leakage associated with the torus-to-reactor-building vacuum breaker valves
In all of these cases, the leakage was not detected by the local leak rate
test procedure because the valves were not tested with pressure applied in
the direction assumed for an accident
Browns Ferry 2
Browns Ferry Unit 2 conducted a containment integrated leak rate test in
February 1983 that failed because of an excessive leak rate of about twice
the allowable limit of 15 percent per day (075La) The leakage path was
found to be through a flange seal on a valve in the
torus-to-reactor-building vacuum breaker system This valve (designated FCV
64-20) is a butterfly valve bolted
8603050397
IN 86-16
March 11, 1986
Page 2 of 3
into an 18-inch line connecting directly to the torus The leakage through
the flange seal was reduced to an acceptable rate by tightening flange
bolts Local leak rate testing, which is required to be performed every 2
years, is done by applying pressure between FCV 64-20 and a flapper-type
check valve that is located on the reactor building side of the butterfly
valve However, the leaking flange was on the torus side of FCV 64-20
Consequently, the valve flange was not included in the local testing, but
was tested only during the integrated testing which is done every 3 to 4
years
Peach Bottom 2
Peach Bottom Unit 2 conducted a containment integrated leak rate test in
June 1985 that produced an excessive leak rate of about three times the
allowable limit of 0375 percent per day Most of the leakage was found to
be going through the stem seal of valve AO-2502B, an air-operated butterfly
valve located adjacent to the torus in the vacuum breaker line An
apparently successful local leak rate test performed on this valve prior to
the integrated test had failed to detect the leakage Local leak rate
testing is done by applying pressure between valve AO-2502B and the check
valve located between the reactor building and this valve However, the
valve stem for AO-2502B is located on the torus side of the valve and, as in
the Browns Ferry case, this leak path was not subject to the local leak rate
test pressure
Duane Arnold
During a containment integrated leak rate test at Duane Arnold in July 1985,
difficulty was experienced in establishing the test pressure The problem
was found to be caused by leakage through a hole left by a plug that was
missing from the body of isolation valve CV4305 This valve was part of the
torus-to-reactor-building vacuum breaker system and was located on the torus
side of the vacuum breaker line The plug had evidently been removed during
maintenance conducted on the valve during the same outage as the integrated
test An apparently successful local leak rate test, conducted on the valve
after the maintenance, had failed to detect the hole This failure was due
to the fact that the hole was located on the torus side of the valve disc,
and the test pressure had been applied to the other side of the valve
Discussion:
NRC regulations (10 CFR 50, Appendix J, Section III C1) require that local
leak rate test pressure be applied in the same direction as that which would
exist when the valve would be required to perform its safety function,
unless it can be determined that the results from tests for a pressure
applied in a different direction will provide equivalent or more
conservative results Many facilities experience problems in applying this
rule because of the difficulty of applying a local test pressure for large
isolation valves connected directly to primary containments After the
Browns Ferry test failure, TVA identified 14 containment isolation valve
flanges on each of the Browns Ferry units that were not being tested under
the local leak rate test procedures then in use After the Peach Bottom
test, two valves on Unit 2 and five valves on Unit 3 were found to be
oriented so that the valve stems were not being subjected to local leak rate
test pressure
IN 86-16
March 11, 1986
Page 3 of 3
There are modifications and test techniques that can be applied to cause the
local leak rate test to produce "equivalent or more conservative results"
For example, at Browns Ferry, TVA is committed to solving the valve flange
problem by installing double seals (gaskets) on the problem flanges Local
leak rate test pressure can be applied between the seals to produce a local
test that can be considered equivalent to or more conservative than internal
pressurization This technique may also be used on valve stems that are
designed to permit double seals In some situations valve stem seals may be
included in the normally pressurized boundary by turning the valve around
without reducing the effectiveness of the valve In some cases special test
devices such as a blank flange may be used to seal the line inboard of the
inner isolation valve
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: Don Kirkpatrick, IE
(301) 492-4510
Attachment: List of Recently Issued IE Information
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