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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