United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-02: Improper Installation And Testing of Differential Pressure Transmitters

                                                            SSINS No.: 6835 
                                                            IN 85-02       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                              January 11, 1985

                                   DIFFERENTIAL PRESSURE TRANSMITTERS 


All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP). 


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. 


                                                          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

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