Information Notice No. 85-23:Inadequate Surveillance and Postmaintenance and Postmodification System Testing
SSINS No.: 6835
IN 85-23
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 22, 1985
Information Notice No. 85-23: INADEQUATE SURVEILLANCE AND
POSTMAINTENANCE AND POSTMODIFICATION
SYSTEM TESTING
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is to alert addressees of several instances pertain-
ing to improper system modifications, inadequate postmodification system
testing, and inadequate surveillance testing recently detected at the
McGuire nuclear power facility.
It is expected that recipients will review the information contained in this
notice for applicability to their facilities and consider actions, if appro-
priate, to preclude similar problems 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 November 1, 1984, Duke Power Company (DPC) informed the NRC that the four
Rosemont differential pressure transmitters that control the closing of four
isolation valves of the upper-head injection (UHI) system at McGuire Unit 1
were improperly installed (i.e., the impulse lines were reversed when the
original Barton reverse-acting differential pressure switches were replaced
with Rosemont direct-acting differential pressure transmitters during April
of 1984). As a result, the UHI isolation valves failed to close during
draining of the accumulator when the water level in the UHI accumulator
reached the set point. In addition to the improper installation, the
postmodification testing was limited to a dry calibration method that does
not use the actual reference leg of the accumulator; therefore, the
installation error was not detected by the postmodification test.
Consequently, the plant was operated for approximately five months with the
UHI isolation valves inoperable.
The McGuire UHI system design includes a separate nitrogen accumulator that
supplies pressurized nitrogen to force the water from the UHI accumulator
into the reactor vessel during the initial phase of a design-basis loss-of-
coolant accident (LOCA). Thus, if a design-basis LOCA had occurred while the
UHI isolation valves were inoperable, the UHI system would have been actu-
ated; however, the UHI isolation valves would not have closed when the water
in the
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IN 85-23
March 22, 1985
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UHI accumulator had been depleted. As a result, nitrogen gas could have been
injected into the reactor vessel during the course of a design-basis LOCA.
Under such conditions, and using Appendix K assumptions, DPC's analysis
indicated that the peak cladding temperature of 2200F most likely would
have been exceeded and that the worst-case increase in containment pressure
could have resulted in exceeding the design pressure by 2 psi.
A related but separate event involved the establishing of the set points for
closing the UHI isolation valves. On February 14, 1984, DPC approved the use
of a dry calibration method, which would establish the trip set point for
closing the UHI isolation valves relative to the bottom of the UHI water
accumulator tank. However, a 24-inch nonconservative error in the trip set
point occurred at McGuire Units 1 and 2 when the responsible instrument
engineer misinterpreted the tank measurements made by instrument
technicians. Because the dry calibration method does not use the actual
process leg of the UHI accumulator, this error was left undetected at both
units for several months. The calibration error was finally detected on
November 2, 1984, while DPC personnel were taking "as-found" data in
response to the previous error involving the incorrect installation of the
differential pressure transmit-ters. The consequences of this event would be
the early isolation of the UHI water accumulator during a design-basis LOCA,
resulting in less water being delivered to the vessel than assumed in the
analysis.
A completely unrelated event involved the inoperability of two of the four
overpower delta temperature reactor protection channels at McGuire Unit 2.
This defect was discovered on November 26, 1984, by a DPC engineer while
performing a posttrip review of a reactor scram in which signals of the two
affected channels responded contrary to that expected. This event was caused
because an electrical jumper was not installed on two of the four overpower
delta temperature input logic cards. The purpose of the jumper is to ensure
that the overpower delta temperature system provides protection for decreas-
ing temperature, as might be expected on a steam line break. DPC's surveill-
ance tests only verified that protection would be provided for increasing
temperature, but not for decreasing temperature. This defect was left unde-
tected for an unknown period of time, but most likely it had existed since
initial plant startup. Subsequent investigations revealed that in addition
to inadequate testing, there was an absence of instructions and descriptions
of the required jumpers.
The above examples illustrate the need for thorough reviews and detailed
attention to plant surveillance and postmaintenance and postmodification
tests, to ensure that they accomplish the required verification of system
function.
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March 22, 1985
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No specific action or written response is required by this information
notice; however, if you have any questions regarding this notice, please
contact the Regional Administrator of the appropriate NRC regional office or
the technical contact listed below.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: I. Villalva, IE
(301) 492-9007
H. Dance, RII
(404) 221-5533
Attachment: List of Recently Issued IE Information Notices
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