United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-90, Supplement 1: Pressurizer Safety Valve Lift Setpoint Shift

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                                April 3, 1991

                                                 LIFT SETPOINT SHIFT


All holders of operating licenses or construction permits for nuclear power 


Information Notice (IN) No. 89-90 was issued to inform licensees about 
possible problems resulting from operating pressurizer safety valves in 
environments different from that used to establish the safety valve lift 
setpoints.  The IN primarily focused on problems encountered when valves 
were operated with a loop seal containing water after setting the safety 
valve lift setpoints using steam under the seat.

This supplement to IN 89-90 alerts addressees to an additional factor that 
may affect the lift setpoint of all safety (relief) valves.  In particular, 
this problem can affect large steam relief valves such as pressurizer safety 
valves, main steam safety valves (MSSV), and boiling water reactor (BWR) 
safety/relief 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 supplement do not constitute NRC requirements; 
therefore, no specific action or written response is required.

Description of Circumstances:

On May 28, 1989, a pressurizer safety valve failed open at the V. C. Summer 
Nuclear Station, requiring the operators to initiate a manual reactor trip 
due to the rapid depressurization of the reactor coolant system (RCS).  The 
safety valve reseated before the pressure reached the safety injection 
initiation setpoint of 1850 psig.  RCS pressure was then stabilized at 
approximately 2000 psig. 

On July 15, 1990, a MSSV lifted for roughly 2 minutes at approximately 1025 
psia at the San Onofre Nuclear Generating Station (SONGS).  The minimum 
setting for this valve is 1103 psia, with a nominal setting of 1114 psia.  
Further testing at SONGS revealed that 4 other recently refurbished MSSVs 
were lifting at pressures of between 20 to 30 psi below their respective 
minimum settings.


                                                  IN 89-90, Supplement 1
                                                  April 3, 1991
                                                  Page 2 of 3


Utilities have indicated that setpoint shifts can be caused by changes in 
temperature of the safety (relief) valve body and bonnet.  Anything that 
causes an increase in the temperature of the valve results in the expansion 
of the body and elongation of the bonnet.  This relieves spring pressure and 
reduces the lift setpoint of the valve.  ASME OM Code-1990, Appendix I 
(previously ASME/ANSI OM-1987 Part 1), "Requirements for Inservice 
Performance Testing of Nuclear Power Plant Pressure Relief Devices," 
discusses the importance of ambient conditions for relief valve testing.

Personnel at San Onofre and at V. C. Summer Nuclear Station determined that 
the installation of insulation on the valve can inadvertently increase the 
temperatures of the valve body and bonnet.  If the valve is tested and the 
lift setpoint is adjusted in an uninsulated condition, the addition of 
insulation after the valve is installed can cause a subsequent unanticipated 
increase in valve body temperature and a resultant decrease in the lift 
setpoint.  At the Calvert Cliffs Nuclear Power Plant, personnel determined 
that the safety valve setpoint shifted from 60 to 150 psi for a 120xF change 
in valve body temperature.  Personnel at the Millstone Nuclear Power 
Station, Unit 3, indicated that a significant reduction in the lift setpoint 
of a safety valve was caused by setting the valve at a lower temperature 
than the actual inservice operating temperature.  At Arkansas Nuclear One, 
Unit 2 (ANO-2), a pressurizer safety valve was refurbished and adjusted at 
Wyle Laboratories utilizing valve temperature profile data provided by ANO-2 
based on measured valve temperatures.   After installation of the valve, and 
plant heatup to hot standby, personnel found that the lift setpoint for the 
safety valve had decreased by 25 psi, possibly due to actual valve 
temperatures which were higher than those previously recorded.  The 
temperature error at ANO-2 was attributed to the use of hand-held measuring 
devices instead of thermocouples that could be mounted on the valve for more 
accurate temperature monitoring.  In addition, changes in the valve's 
insulation may have contributed to the setpoint shift.  These events show 
that it is critical that the valves be tested under the same ambient 
conditions that will exist in the plant during operation.  

Other factors that may possibly affect the lift setpoint of relief valves 
are discussed in a recent engineering report from the Office for Analysis 
and Evaluation of Operational Data (AEOD).  This report, Engineering 
Evaluation Report E90-09, "Additional Factors Affecting the Lift Setpoint of 
Pressurizer Safety Valves," was issued in October 1990.  The report 
documents root causes of relief valve setpoint shifts as reported by 
licensees in licensee event reports (LERs).  The root causes discussed in 
the report have not all been corroborated by independent testing, so some 
caution should be exercised in using this information.

Westinghouse and the Westinghouse Owners Group performed testing on safety 
valves in November and December of 1990.  These tests used steam, loop 
seals, and nitrogen on the valve disk.  The intent of this testing was to 

                                                  IN 89-90, Supplement 1
                                                  April 3, 1991
                                                  Page 3 of 3

determine the magnitude of the error in lift setpoint associated with 
testing the valves with these various mediums.  These tests may help to 
clarify some of the factors affecting relief valve setpoints.  A further 
supplement to this notice will be issued, if appropriate, after the results 
of these tests have been issued and reviewed.

Related Generic Communications:

Previous information notices issued on related topics include IN 86-56, 
"Reliability of Main Steam Safety Valves", IN 86-92, "Pressurizer Safety 
Valve Reliability", and IN 88-68, "Setpoint Testing of Pressurizer Safety 
Valves with Filled Loop Seals Using Hydraulic Assist Devices", as well as IN 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 

                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  L. Mark Padovan, AEOD
                     (301) 492-4445 

                     Andrew J. Kugler, NRR
                     (301) 492-0834

Attachment:  List of Recently Issued NRC Information Notices
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