Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-02
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
January 11, 1985
Information Notice No. 85-02: IMPROPER INSTALLATION AND TESTING OF
DIFFERENTIAL PRESSURE TRANSMITTERS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice provides notification of a potentially significant
problem pertaining to the improper installation and inadequate functional
testing of differential pressure transmitters. Such conditions occurred at
the McGuire Nuclear Station, Unit 1, when the Barton differential pressure
switches utilized to control the isolation valves of the upper head
injection (UHI) system were replaced with Rosemont differential pressure
transmitters. It is expected that recipients will review the information
contained in this notice for applicability to their facilities and consider
actions, if appropriate, 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 informed the NRC that the UHI
isolation valves failed to close when the UHI water accumulator was drained
at its McGuire Nuclear Station, Unit 1. At that time, the plant was shut
down because the nitrogen content of the water in the UHI accumulator
exceeded the limit permitted by its technical specifications. Subsequent
investigations revealed that the four differential pressure transmitters
used to sense the level of water in the UHI accumulator and initiate
automatic closure of the isolation valves on a predetermined level had been
improperly installed. As a result, the isolation valves did not
automatically close when the water level in the UFII accumulator reached the
set point.
The McGuire UHI system design includes a separate nitrogen accumulator that
supplies pressurized nitrogen to force the water from the UHI water
accumulator into the reactor vessel during the initial phase of a
design-basis loss-of-coolant accident (LOCA). Thus, if the UHI isolation
valves fail to close during the course of a design-basis LOCA, nitrogen
could be injected into the reactor vessel. To prevent such an event, the
differential pressure transmitters are designed to initiate automatic
closure of the UHI isolation valves when the water in the UHI accumulator
reaches a predetermined level.
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IN 85-02
January 11, 1985
Page 2 of 2
During April of 1984, the McGuire Nuclear Station, Unit 1, Barton
reverse-acting differential pressure switches were replaced with Rosemont
direct-acting differential pressure transmitters to improve the accuracy and
repeatability of the UHI water accumulator level sensing system. However,
the Rosemont differential pressure transmitters were not properly installed
in that the impulse lines were not connected to the appropriate transmitter
ports. Several factors contributed to the improper installation, including
inadequate installation instructions. The major contributor was inadequate
functional testing of the UHI system after it had been modified in that the
post-modification tests were limited to calibration tests of the
differential pressure transmitters. These calibration tests were performed
with the transmitters isolated from the impulse lines. Consequently, the
tests only verified that the transmitters would provide the required output
signal for a given differential pressure, but they lid not demonstrate that
the transmitters sensed the differential pressures associated with water
level changes in the UHI water accumulator. Thus, the differential pressure
transmitters were not only improperly installed, but the error was not
detected until this event. If a design-basis LOCA had occurred during this
period, the UHI system would have been actuated, but the UHI isolation
valves would not have closed when the water in the UHI water accumulator had
been depleted and nitrogen gas could have been injected into the reactor
vessel during the course of the LOCA.
Similar installation errors have been addressed in Information Notice No. No.
84-45, "Reversed-Differential Pressure Instrument Lines." However, the
majority of events described in that information notice occurred in boiling
water reactors during plant construction and were detected by functional
tests performed before commencing power operation. In contrast, the event
described in this infomation notice occurred at a pressurized water reactor
and was undetected during approximately 5 months of power operation.
No specific action or written response is required by this information
notice; however, if you have any question 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 Contact: I. Villalva, IE
(301) 492-9007
F. R. McCoy, RII
(404) 221-2689
Attachment:
List of Recently Issued IE Information Notices
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