United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-32, Supplement 1: Surveillance Testing of Low-Temperature Overpressure-Protection

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              February 12, 1991


Information Notice No. 89-32, SUPPLEMENT 1:  SURVEILLANCE TESTING OF 
                                                 LOW-TEMPERATURE 
                                                 OVERPRESSURE-PROTECTION 
                                                 SYSTEMS


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose:

This information notice is intended to alert addressees to potential 
problems resulting from the lack of testing of the ability of the 
low-temperature overpressurization protection system (Ltop) to perform its 
safety-related function using the alternative pneumatic supply system for 
operation of the power-operated relief valves (PORVs).  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 do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Background:

Information Notice 89-32 (Reference 7) discussed the lack of testing of 
PORVs in the Ltop mode; citing inspection results at the Beaver Valley, 
Turkey Point, and Harris nuclear power stations.  The issue of 
low-temperature overpressurization protection first arose in 1976.  Many 
licensees established procedures and proposed systems to mitigate postulated 
overpressure events.  The main concern was meeting fracture toughness 
requirements during heating and cooling of the reactor coolant system.  Most 
licensees' proposed systems consisted of manually enabled low-pressure 
setpoints on the existing PORVs governed by procedures and technical 
specifications. 

Most PORVs are provided with a primary pneumatic supply system, usually the 
plant's nonsafety-related instrument air system, and a backup pneumatic 
supply system, often a safety-related nitrogen system.  Most testing of the 
Ltop function is performed using the nonsafety-related primary supply, which 
does not confirm the safety-related aspects of the Ltop function.  Since 
1982, the NRC has received 12 licensee event reports (LERs) of degraded 
safety-related nitrogen and/or air supply systems used for actuating PORVs 
in the Ltop mode.  





9102060144
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                                                  IN 89-32, Supplement 1
                                                  February 12, 1991
                                                  Page 2 of 4


Four of the most recent events (since 1987) are discussed in detail in a 
recent NRC report (Reference 1).  The following discussion includes synopses 
of all 12 events. 

Description of Circumstances:

Point Beach 1  On May 3, 1989, during a test of the Ltop system, the opening 
stroke time of the PORV using the nitrogen gas supply system exceeded the 
design calculation because of an excessive pressure drop in the nitrogen 
lines (LER 50-266/89-05).  The PORVs had opening times of about 6 seconds 
and 10 seconds instead of the 2 seconds assumed in the analysis.  The 
slowest time measured during the life of the plant was about 11 seconds.  
With this slow opening time, the reactor coolant system (RCS) pressure could 
increase to 835 psig, well above the technical specification limit for low 
RCS temperature conditions.  To ensure sufficient PORV stroke speed, the 
licensee replaced the existing nitrogen supply control valves with larger 
ones and modified the PORV spring.

Turkey Point 3  On September 13, 1988, the PORV opening time exceeded the 
design values of 2.0 seconds for mass input and 3.0 seconds for heat input. 
The licensee attributed the cause to undersized control air and nitrogen 
backup supply lines to the PORV actuators (LER 50-250/88-21).  Since the 
licensee first performed the tests in 1984, the PORV stroke times varied 
from 2 to 6 seconds.  To correct these problems, the licensee enlarged the 
supply lines.  

San Onofre 1  On March 21, 1988, the licensee determined that no testing 
requirement existed to assure the operability of the backup nitrogen supply 
system for the PORV in Operational Mode 5 (LER 50-206/88-06).  The licensee 
modified procedures to include such a requirement.

Indian Point 2  On November 18, 1987, the licensee found that the backup 
nitrogen supply system to the PORV was inoperable during a test (LER 
50-247/87-15).  The backup nitrogen system failed the test because check 
valves did not prevent backflow to the normal nitrogen system and nitrogen 
consumption during each stroke was excessive.  Normal equipment wear caused 
the check valve failure and system leaks.  The licensee replaced the check 
valves and repaired system leaks. 

Catawba 1  On March 11, 1987, the licensee declared the pressurizer PORVs 
inoperable because the instrument air and nitrogen lines were incorrectly 
connected across trains (LER 50-413/87-12).

Robinson 2  On December 15, 1984, the licensee discovered that the Ltop 
system drawing, operating work procedures, and operating procedures were 
incorrect after the PORVs had been returned to operable status.  Both PORVs 
were inoperable for one hour while a common accumulator was out of service 
(LER 50-261/84-12).

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                                                  IN 89-32, Supplement 1
                                                  February 12, 1991
                                                  Page 3 of 4


North Anna 1  On October 9, 1983, the licensee took an excessively leaking 
train of the Ltop system out of service because of the unavailability of a 
nitrogen makeup supply.  This supply was unavailable because the liquid 
nitrogen plant normally used for makeup had a vent valve malfunction (LER 
50-338/83-71).

North Anna 2  On May 15, 1983, a relief valve downstream of a nitrogen 
supply tank for the pressurizer PORV lifted, reducing the supply pressure 
below the minimum required for PORV operation (LER 50-339/83-33).

North Anna 2  On April 6, 1983, leakage in the nitrogen supply system for 
the pressurizer PORV reduced the supply pressure below the minimum required 
for PORV operation (LER 50-339/83-30).

Surry 1  On February 9, 1983, the licensee declared both pressurizer PORVs 
inoperable during cold shutdown with the overpressure mitigating system 
enabled because of low air pressure in the backup bottled air supply system 
(LER 50-280/83-12).

North Anna 1  On December 7, 1982, one of the relief valves for the nitrogen 
supply tank leaked excessively, reducing the supply pressure below the 
minimum required for PORV operation (LER 50-338/82-91).

Surry 1  On October 2, 1982, the licensee declared both pressurizer PORVs 
inoperable.  One train had a leaking diaphragm in the supply tank.  In the 
other train, a check valve separating the backup bottled air supply from the 
instrument air system leaked excessively (LER 50-280/82-106).

Discussion:

The standard technical specifications do not explicitly require the testing 
of the Ltop system while using the backup safety-related pneumatic supply 
system, and the individual plant technical specifications may or may not 
explicitly require such testing.  However, such testing is important to 
assure that the Ltop system can perform its safety-related function in 
general and that the PORV stroke times conform with safety analyses in 
particular.  The NRC has issued Generic Letter 90-06, "Resolution of Generic 
Issue 70, 'Power-Operated Relief Valve and Block Valve Reliability,' and 
Generic Issue 94, 'Additional Low-Temperature Overpressure Protection for 
Light-Water Reactors,' Pursuant to 10 CFR 50.54(f)," June 25, 1990, 
requesting changes in plant technical specifications to correct this 
deficiency.

Air-operated components or systems used to perform safety-related functions 
other than the Ltop function described herein have been noted to fail in the 
same way, namely because of insufficient supply pressure.  The NRC has also 
issued information notices describing safety-related problems caused by 
excessive supply pressure.  Attachment 1 lists previously issued generic 
communications addressing pneumatic systems and relief valves.  However, the 
scope of Attachment 1 does not include pneumatic problems that may have been 
described before for safety valves or contaminated air systems.  It should 
be noted that Generic Letter No. 88-14, "Instrument Air Supply System 
Problems Affecting Safety-Related Equipment," August 8, 1988, requested 
testing to verify that accumulators and backup pneumatic supply systems will 
perform as intended.
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                                                  IN 89-32, Supplement 1
                                                  February 12, 1991
                                                  Page 4 of 4


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




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


Technical Contacts:  Vern Hodge, NRR
                     (301) 492-1861

                     Sagid Salah, AEOD
                     (301) 492-4432

                     Sanford Israel, AEOD
                     (301) 492-4437


Attachments:  
1.  List of References
2.  List of Recently Issued NRC Information Notices 
.

                                                  Attachment 1
                                                  IN 89-32, Supplement 1
                                                  February 12, 1991
                                                  Page 1 of 2


                             LIST OF REFERENCES


     1.   "Low-Temperature Overpressure Protection:  Testing PORVs with the 
          Alternate Pneumatic Supply," AEOD/E90-08, NRC Office for Analysis 
          and Evaluation of Operational Data, July 1990.  A copy of this 
          report is available in the NRC Public Document Room, 2120 L 
          Street, N.W., Washington DC.

     2.   Bulletin No. 80-01:  "Operability of ADS Valve Pneumatic Supply," 
          January 11, 1980

     3.   Circular No. 79-22:  "Stroke Times for Power Operated Relief 
          Valves," November 16, 1979

     4.   Generic Letter No. 90-06:  "Resolution of Generic Issue 70, 
          'Power-Operated Relief Valve and Block Valve Reliability,' and 
          Generic Issue 94, 'Additional Low-Temperature Overpressure 
          Protection for Light-Water Reactors,' Pursuant to 10 CFR 
          50.54(f)," June 25, 1990 

     5.   Generic Letter No. 88-14:  "Instrument Air Supply System Problems 
          Affecting Safety-Related Equipment," August 8, 1988

     6.   Information Notice No. 89-38:  "Atmospheric Dump Valve Failures at 
          Palo Verde Units 1, 2, and 3," April 5, 1989

     7.   Information Notice No. 89-32:  "Surveillance Testing of 
          Low-Temperature Overpressure-Protection Systems," March 23, 1989

     8.   Information Notice No. 89-26:  "Instrument Air Supply to 
          Safety-Related Equipment," March 7, 1989

     9.   Information Notice No. 89-07:  "Failures of Small-Diameter Tubing 
          in Control Air, Fuel Oil, and Lube Oil Systems Render Emergency 
          Diesels Inoperable," January 25, 1989

     10.  Information Notice No. 88-24:  "Failures of Air-Operated Valves 
          Affecting Safety-Related Systems," May 13, 1988

     11.  Information Notice No. 86-51:  "Excessive Pneumatic Leakage in the 
          Automatic Depressurization System," June 18, 1986

     12.  Information Notice No. 86-50:  "Inadequate Testing to Detect 
          Failures of Safety-Related Pneumatic Components or Systems," June 
          18, 1986

     13.  Information Notice No. 85-84:  "Inadequate Inservice Testing of 
          Main Steam Isolation Valves," October 30, 1985

     14.  Information Notice No. 85-35:  "Failure of Air Check Valves to 
          Seat," April 30, 1985

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                                                  Attachment 1
                                                  IN 89-32, Supplement 1
                                                  February 12, 1991
                                                  Page 2 of 2


     15.  Ibid., Supplement 1, May 17, 1988

     16.  Information Notice No. 82-45:  "PWR Low Temperature Overpressure 
          Protection," November 19, 1982

     17.  Information Notice 82-25, "Failures of Hiller Actuators upon 
          Gradual Loss of Air Pressure," July 20, 1982

     18.  Information Notice No. 82-17:  "Overpressurization of Reactor 
          Coolant System," June 11, 1982

     19.  Information Notice No. 80-30:  "Potential for Unacceptable 
          Interaction between Control Rod Drive Scram Function and 
          Non-Essential Control Air at Certain GE BWR Facilities," August 
          19, 1980

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