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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 . 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). . 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. . 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 . 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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