Information Notice No. 89-32: Surveillance Testing of Low-Temperature Overpressure-Protection

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                 March 23, 1989

                                   OVERPRESSURE-PROTECTION SYSTEMS


All holders of operating licenses or construction permits for 
pressurized-water reactors (PWRs).


This information notice is being provided to alert addressees to potential 
operability problems due to lack of inservice testing of power-operated relief
valves (PORVs) in their low-temperature overpressure-protection (Ltop) mode.  
It is expected that recipients will review the information for applicability 
to their facilities and consider actions, as appropriate, to avoid similar 
prob-lems.  However, suggestions contained in this information notice do not 
consti-tute NRC requirements; therefore, no specific action or written response 
is required.  

Description of Circumstances:

Beaver Valley:  During an inspection (Inspection Report No. 50-334, 
412/86-20), NRC inspectors noted that technical specifications (TS) require 
that over-pressure protection be provided by two PORVs with a nominal trip 
setpoint of less than or equal to 350 psig whenever the temperature of a 
non-isolated reactor coolant system (RCS) cold leg is less than or equal to 
275�F.  The TS surveillance requirement only addresses stroking the operable 
PORV each time the plant enters Mode 5 (cold shutdown) unless that PORV has 
been tested within the preceding three months.  

The licensee analyzed two cases for an overpressure accident scenario:  (1) a 
mass input case and (2) a heat input case.  The most restrictive PORV opening 
time was identified as the mass input accident which would require a valve to 
open within 2.5 seconds.  An NRC safety evaluation report (SER) dated April 4, 
1983 found this analysis to be acceptable.  A review of the licensee's mainte-
nance surveillance procedure indicated that the nominal trip setpoint of less 
than or equal to 350 psig was addressed, but the stroke time was not.

Plant TS and procedures had not implemented PORV stroke times as assumed in 
the analysis.  The licensee performed an evaluation using data from the 
station's ASME Valve Stroke Log, when compared to SER stroke time assumptions.  
The licensee 

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concluded that the resulting maximum RCS pressure would still have been within
specified limits.  However, the licensee initiated several procedural improve-
ments to address PORV stroke testing.

Turkey Point:  The staff inspected the licensee's overpressure mitigation 
system (OMS) (Inspection Report Nos. 50-250, 251/88-14 and 88-26).  The PORV 
electronics operability and setpoints are verified before being aligned for 
low-pressure operations.  The inspectors reviewed the stroke times for the 
Unit 3 and 4 PORVs from May 1984 through May 1988.  These tests were performed 
in accordance with the licensee's inservice test (IST) program.  The IST 
require-ment for each PORV is to fully stroke within 15 seconds.  The stroke 
times reviewed ranged from less than 2.0 seconds up to 6.41 seconds.  These 
stroke times are well below the 15-second IST criterion.  However, in analyses 
sup-porting license amendments, a relief valve opening time of 2.0 seconds was 
assumed in calculating the setpoint overshoot for the mass input case.  The 
heat input case assumed a relief valve opening time of 3.0 seconds.  The PORVs, 
on average, were not meeting the design-basis stroke time.  

The licensee requested relief from the TS requirement in order to prepare for 
the eventual refueling outage that would place one of the units within the 
operating regime of the OMS.  The request extended to the next refueling 
outage for each of the units in order to allow the licensee time to resolve 
this issue.  The licensee requested that Westinghouse perform an analysis to 
determine the magnitude of the overshoot considering the following transients:  
1) the start of an idle reactor coolant pump with the secondary water 
temperature of the steam generator less than or equal to 50�F above the RCS 
cold-leg temperature; 2) the start of a high pressure safety injection pump 
and its injection into a water-solid RCS and 3) the inadvertent start of two 
charging pumps with a loss of letdown.  The safety evaluation demonstrated 
that with a PORV opening stroke time up to 3.45, the OMS could mitigate the 
most limiting transient (spurious start of a SI pump).  The licensee has 
completed a design change for Unit 4 and is planning to implement the design 
change on Unit 3 during the next refueling outage.  This design change will 
ensure that the PORVs will open in time to prevent exceeding the 10 CFR 50, 
Appendix G limits. The surveillance procedures supporting the TS were changed 
so that future stroke time testing will use an acceptance criterion that is 
consistent with the design basis. 

Shearon Harris:  NRC inspectors assessing operational performance (Inspection 
Report No. 50-400/88-34) noted a discrepancy concerning the testing of the 
pressurizer PORVs.  An IST procedure specified that the PORVs were to be 
stroke tested from the open to closed position with a maximum stroke time of 
2.0 seconds.  The licensee tested the PORVs in accordance with an 18-month 
surveil-lance test for pressurizer PORV operability.  Although no safety 
analysis credit was taken for the PORVs at power operation, they were required 
to provide overpressure protection (by opening on demand) during 
low-temperature operation.  Shearon Harris utilizes two of the three PORVs for 
the Ltop system.

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The design basis of the licensee's Ltop is to protect the RCS from 
overpressure when the transient is limited to:  (1) start of an idle reactor 
coolant pump with secondary-side water temperature less than 50�F above RCS 
cold-leg temper-ature or (2) start of a charging safety injection pump and its 
injection into a water-solid RCS.  The PORV setpoints were calculated to 
maintain the RCS below the maximum allowable system pressure given in 10 CFR 
50 Appendix G.  The setpoint calculations assumed a valve opening time of 2.0 
seconds in determin-ing the possible overshoot.  The inspectors noted that if 
the actual valve opening times were greater than 2.0 seconds, then the 
pressure overshoot could be greater than originally calculated.  A significant 
increase in valve opening time could result in the 10 CFR 50 Appendix G limits 
being exceeded during a design-basis transient.

The PORVs were stroked in the open direction so that the licensee could 
perform the time-to-close test.  However, the surveillance procedure did not 
require that the time to open be determined, and this was not done.  


The basic issue in these three cases is that the licensee's inservice testing 
of its low-temperature overpressure-protection (Ltop) systems may be inade-
quate.  Stroke time requirements used in analyses of the licensee's Ltop 
systems were not being transferred into IST requirements and eventually into 
surveillance test procedures.  The ASME Code, Section XI, paragraph IWV-3400, 
requires valves to be exercised to the position required to fulfill their 
function.  Therefore, not testing the Ltop PORVs in the open direction is a 

No specific action or written response is required by this information notice. 
If you have any questions about this matter, please contact one of the tech-
nical contacts listed below or the Regional Administrator of the appropriate 
regional office.  

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

Technical Contacts:  Milton Shymlock, RII
                     (404) 331-5542

                     Thomas McElhinney, Res. Insp., Turkey Pt.
                     (305) 245-7669

Attachment:  List of Recently Issued NRC Information Notices
..                                                            Attachment 
                                                            IN 89-32
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                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

89-31          Swelling and Cracking         3/22/89        All holders of OLs
               of Hafnium Control Rods                      or CPs for PWRs 
                                                            with Hafnium 
                                                            control rods. 

89-30          High Temperature              3/15/89        All holders of OLs
               Environments at                              or CPs for nuclear
               Nuclear Power Plants                         power reactors.

89-29          Potential Failure of          3/15/89        All holders of OLs
               ASEA Brown Boveri                            or CPs for nuclear
               Circuit Breakers                             power reactors.
               During Seismic Event

89-28          Weight and Center of          3/14/89        All holders of OLs
               Gravity Discrepancies                        or CPs for nuclear
               for Copes-Vulcan                             power reactors.
               Air-Operated Valves

89-27          Limitations on the Use        3/8/89         All holders of OLs
               of Waste Forms and High                      or CPs for nuclear
               Integrity Containers for                     power reactors, 
               the Disposal of Low-Level                    fuel cycle 
               Radioactive Waste                            licenses and 
                                                            certain by-product
                                                            materials licenses.

89-26          Instrument Air Supply to      3/7/89         All holders of OLs
               Safety-Related Equipment                     or CPs for nuclear
                                                            power reactors.

89-25          Unauthorized Transfer of      3/7/89         All U.S. NRC 
               Ownership or Control of                      source, byproduct, 
               Licensed Activities                          and special 
                                                            nuclear material 

89-24          Nuclear Criticality Safety    3/6/89         All fuel cycle
                                                            licensees and 
                                                            other licensees 
                                                            possessing more 
                                                            than critical 
                                                            mass quantities of 
                                                            special nuclear 
OL = Operating License
CP = Construction Permit 

Page Last Reviewed/Updated Friday, May 22, 2015