ML20059H472
| ML20059H472 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/1990 |
| From: | Israel S, Salah S NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20059H469 | List: |
| References | |
| TASK-AE, TASK-E90-08, TASK-E90-8 AEOD-E90-08, AEOD-E90-8, NUDOCS 9009170221 | |
| Download: ML20059H472 (10) | |
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AEOD/E90-08.
l LOW TEMPERATURE OVERPRESSURE PROTECTION:
TESTING PORVs WITH THE ALTERNATE PNEUMATIC SUPPLY
-By:
S. Salah S. Israel t
July 1990 Office for Analysis and Evaluation of Operational Data 9009170221 900910 PDR ORG NEXD PDR
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SUMMARY
i During a test of the low temperature,. overpressure protection (LTOP), system at Point Beach, Unit 1, the licensee determined that the system was inoperable because the stroke time for the t
power operated relief valve (PORV) was greater than that assumed in the safety evaluation report for the LTOP system. The delayed stroke time was caused by an inadequate nitrogen gas supply l
that is used as a backup to the normal air supply to actuate the valves. There were four others plants that reported similar problems with backup pneumatic systems since 1987.
l
- The issue of inadequate nitrogen supply was first highlighted in Information Notice 82-45.
Generally, the problem is caused by excessive pressr 4 rop or leakage in the backup gas supply lines and no surveillance on stroke time with the ba6 m gas supply. Information Notice 89 32 addressed surveillance requirements for LTOP systeins, but did not specifically include testing :
the backup pneumatic supply system.
1.
INTRODUCTION In pressurized water reactors (PWRs), the pressurizer generally has up to three power operated relief valves (PORVs) to limit system pressure rise during a transient and prevent actuation of the safety relief valves. The PORVs operate automatically or by remote manual control.
Control air to the PORVs is normally supplied by the instrument air system (IAS), which is not' safety grade.
A low-temperature, overpressure protection system mitigates low temperature, pressure transients in operating modes 4 and 5 and thus eliminates overpressure challenges to the reactor vesself Pressurizer PORVs are generally used in the LTOP system to provide (liis protection. In-compliance with the LTOP design requirements, an alternate gas supply or accumulhtors provide a backup to the IAS which normally actuates the PORVs. Degradation of a nitrogen gas system -
as a backup pneumatic supply was previously noted in an information notice in 1982 because of a series of events at the North Anna plant.-
2.
DESCRIPTION OF EVENTS L
Point Beach. Unit 1 1
During performance of test ORT 16, "PORV function test using nitrogen backup system," on May 3,1989, the opening times for the pressurizer PORVs were longer than the 2 seconds used -
in the design analysis of the LTOP system (Ref 1). The opening times measured using nitrogen
.were 5.73 seconds for one PORV and 9.41 seconds for the other. The nitrogen supply uses a -
separate gas bottle for each PORV and check valves to isolate them from the normal air supply..
The LTOP setpoint was selected on the basis of (1) an expected two-second opening time for the PORVs tnd (2) a need to keep primary pressure less than 520 psig. The acceptable PORV setpoint to meet these criteria was determined to be 425 psig. The slowest PORV opening time
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measured at this plant was ll.25' seconds. _ 'Using thii opening time, the' primary coolant system pressure was calculated to reach 835 psig for the worst shutdown transient before the PORVL
. would relieve the pressure. This calculated pressure exceeds the technical specification limits for' protecting the reactor vessel from nonductile failure (Ref. 2). The backup nitrogen system l
at Unit 2 is similar to Unit 1.
Following discovery of the nitrogen _ supply inadequacy, the licensee nude short _ term improvements by moving nitrogen regulators closer to the PORVs and adjusting the spring in the PORV valve operator to shorten the opening time. For a long term solution, the LTOP system was modified by replac%g the old nitrogen control valves with larger ones. This change enabled both Point Beach plants to meet the PORV stroke time requirements.
Turkey Point. Unit 3 On September 13,1988,' the licensee determined that the PORV opening time exceeded the design basis values of 2.0 seconds for the mass input case and 3.0 seconds for the heat input case (Ref. 3). Data on PORV opening times range from 2 to_6 seconds since the initiation of the inservice testing (IST) of the PORVs in 1984. The nded opening times were caused by undersized control air and nitrogen ba(
g,.,
s the PORV actuators.
Some of the corrective actions taken by the licensee were:
1.
The safety injection system is isolated from the reactor coolant system (RCS) at temperatures less than 380 degrees F.
2.
Procedures tag out one of the three charging pump breakers to prevent a third charging pump from operating when the RCS temperature is less than 285 degrees F.
3.
Procedures maintain a pressurizer bubble with RCS temperatures greater than' 200 degrees F.
4.
At RCS temperatures less than 275 degrees F, pmcedures do not permit starting a reactor coolant pump unless the steam generator secondary water temperature is less than 10 degrees F above.the RCS temperature.
5.
Increased the size of the Unit 3 PORV instrument air and nitrogen supply lines to decrease the PORV stroke time.
Indian Point. Unit 2 The plant was at cold shutdown for a refueling outage. The backup nitrogen supply system to the PORVs was inoperable during a test conducted on November 8,1987-(Ref 4).
Each PORV is provided with a separate safety related backup nitrogen supply which uses accumulators. The basis for the size of each backup nitrogen accumulator is 200 cycles of valve
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10 operation which is the number of cycles required to_ miticate the worst case overpressure transient with no operator action for ten minutes (as reported in.the LER).
The backup nitrogen system failed the test because of the following:
1.
Check valves did not prevent backflow to the r.ormal nitrogen system.
2.
Nitrogen consumption per stroke was excessive.
Normal equipment wear was the cause of the check valve failure and system leaks. De check j
valves were replaced and system leaks were repaired by the licensee.
j San Onofre. Unit 1
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The licensee determined that the backup nitrogen system (BNS) design was not fully implemented in the design and installation of the system (Ref. 5) A surveillance test of the BNS supply to the PORVs was not performed during mode 5 operations. Although the PORVs were capable of functioning on instrument air, adequate backup nitrogen was not assured in mode 5 since the.
surveillance was not performed. Procedural changes now confirm the adequacy of the BNS during mode 5 operation.
1 3.
DISCUSSION The LTOP system is designed to mitigate overpressure transients while the reactor is water solid.
In particular, it is designed to preclude the pressure vessel from exceeding the pressure associated with vessel failure at low-temperature. Many plants rely on their PORVs to provide the necesJ sary relief. The set point on the valves is on the order of 300 to 400 psi and they are armed in modes 4 or 5 in anticipation of water solid operation.when the plant is cooled down or heated l
up.
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The PORV setpoints for LTOP were established in the late 1970s in response to a concern about.
vessel failure during low temperature operation _. Mass addition and heat addition transients were examined to identify the most limiting conditions. Generic calculations for Westinghouse plants used a 3 second opening time for the PORVs in the LTOP analyses (Ref. 6)..The 3 second opening time Neludes a 0.6 second delay before the valve actually moves. Thus, 3 seconds could be a criterion for the surveillance test of the PORV stroke time, although longer stroke times may actually be acceptable for individual plants.
The LTOP system has to meet single failure and seismic requirements which dictate an alternate gas supply to actuate the PORVs because the air system is not safety grade. Some plants use an accumulator with a check valve for each PORV and others use a nitrogen gas supply as the alternate. An analysis performed for San Onofre, Unit 1, (Ref. 7) indicated that the limiting transient was an isolation of the letdown system while the charging pumps continued to operate.
This event could be caused by a loss of air which is used to actuate the isolation valve in the letdown system. At the same time, the loss of air would defeat the LTOP system if there wasn't 3
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an alternate pneumatic supply. Thus, the need for an alternate gas apply has a mechaninc basis,
as well as a regulatory design basis.
Information Notice no. 82-45 (Ref. 8) identified deficiencies in the LTOP. system at several' plants. These deficiencies ' included low nitrogen pressure to both. PORV actuators that was observed at the North ' Anna plants on several occasions. leakage and limited bottled gr.s in the backup nitrogen supply to the PORVs resulted in degraded supply pressure and rendered the.
LTOPs useless. It was also noted that similar results could occur because of excessive leakage in those systems that employ accumulators in the alternate gas supply system. The information notice suggested that periodic inspection or surveillance may be needed to detect excessive leakage and to ensure operability of the backup pneumatic supply.
Recently, Information Notice No. 89-32 (Ref. 9) noted that stroke time testing in the open.
direction was not being evaluated at three. sites - Beaver Valley, Turkey Point, and Sheeson Harris. This notice addressed the fact that the opening times of the PORVs identified in the LTOP design were not included in the inservice test program.
This study is also concerned with opening times for the PORVs, specifically when the alternate pneumatic supply is used. The four operating events referenced in Section 2 all highlight -
deficiencies h the nitrogen backup supply. Either the PORVs weren't tested with the backupL supply, they were tested and failed the stroke time criterion, or they were incorrectly connected.'
3' All of these situations, includirg the eight additional events listed in the appendix, represent licensee oversights with respect to maintaining this safety system in compliance with its design requirements. These oversights occurred subsequent to the IN 82-45 which specifically identified; concerns with the nitrogen backup supply, but prior to IN 89-32 'which was concerned with PORV testing in general.
i The staff has deveMped a draft generic letter on 'PORVs, their block ' valves, and LTOP requirements (Ref.10. The letter discusses resolution of generic issues 70 and 94 which are -
3 concerned with PORVs. The requirements contained in the draft letter do not address details such as verification of the backup pneumatic supply for the PORVs.. A review of sample Technical Specifications shows that testing of the LTOP system with the backup pneumatic-supply is not always required, a
4.
FINDINGS 1.
Problems with backup nitrogen supply to PORVs reduce the ability of the LTOP to meet design requirements.
2.
Backup nitrogen problems were discovered by testing PORV stroke times.
3.
Backup pneumatic supply problems connected with the LTOP system may be' due to restricted flow.
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CONCLUSIONS I
Many Westinghouse plants utilize PORVs to protect the pressure vessel from low-temperature -
overpressurization when shutdown and in a water solid condition. Part of the regulatory :
requirements for the LTOP system is an alternate pneumatic supply to backup the normal air supply needed to actuate the PORVs. - Some plants use a bottled nitrogen Wpply and others use an accumulator with associated check valve to provide the alternate pneumatic supply. A.
number of operational events have indicated that the alternate pneumatic supplies are not being maintained in compliance with their design functions.
6.
REFERENCES l
1.
Wisconsin Electric Power Company, Licensee Event Report 266/89-05, j
Point Beach, Unit 1, June 2,1989.
2.
Wisconsin Electric Pov er Company Facil_ity Operating License Appendix A, 1-Technical Specification Section 15.3.1, Amended January 10,1990.
3.
Florida Power and Light, Licensee Event Report 250/88-21, Turkey Point,.
Unit 3, September 5,1988.
4.
Consolidated Edison, Licensee Event Report 247/87-15, Indian Point, Unit t
2, December 18, 1987.
5.
Southern California Edison, Licensee Event Report 206/88-06, San Onofre, Unit 1, April 21,1988.
6.
Westinghouse Electric, " Pressure Mitigating System Transient Analysis -
Results," July 1977.-
7.
Letter from D. Crutchfield (NRC) to R. Dietch (SCE), dated October 28,1982.
8.
U.S. Nuclear Regulatory Commission, Office of Inspection and Enforce-ment, Information Notice No. 82-45, "PWR Low Temperature Overpressure Protection," November 19, 1982.
9.
U.S. Nuclear Regulatory Commission, Office of Inspection and Enforce-ment, Information Notice No. 89-32, " Surveillance Testing of Low-1 Temperature Overpressure-Protection Systems," March 23,1989, t
10.
Memorandum from E. Beckjord (RES) to F. Gillespie (NRR), dated November 16, 1989.
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Page No.
1 ENCLOSURE 1 OTHER LTOP EVENTS INVOLVING NITROGEN SINCE 1982
.t Plant Name LER No.
Event.
Description of Event Date
. POINT BEACH 1 266/89-005 05/03/89 Durjng a test of the LTOP system, the' system'was inoperable using nitrogen gas as operating gas because-the opening stroke time' for the valve was in excess'of that assumed in the design calculations.
The problem.was excessive. drop in nitrogen lines.
l TURKEY POINT 3 250/88-021 09/13/88-PORV opening, time exceeded the design values of 2.0 seconds.for the mass input case and 3.0-seconds for the'heatiinput case.
Cause was attributed to undersized = control air and nitrogen backup supply lines to.
the PORV actuators.
SAN ONOFRE 1 206/88-006 03/21/88 It was determined that the backup nitrogen supply.for the PORV, had no requirement for testing in-mode 5 operations to assure operability.of-the backup gas system.
INDIAN POINT 2 247/87-015 11/18/87 The backup nitrogen supply system to the PORVs system was found to L
be inoperable during test. Check valves failed to prevent backflow to the non-safety nitrogen system and the nitrogen consumption per valve stroke was greater than
- 7alized.
CATAWBA 1 413/87-012 03/11/87 The: pressurizer PORVs were declared inoperable because the-instrument air and nitrogen lines were incorrectly connected ~
accross trains.
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ENCLOSURE'1 OTHER LTOP-EVENTS INVOLVING NITROGEN SINCE 1982 Plant Name LER No.
Event Description of Event =
-Date ROBINSON 2 261/84-012 12/15/84.When PORVs returned to operable 7
status,-it was discovered that the LTOP system drawing,.
operating work procedures, and
. operating procedures were incorrect. Both PORVs were l
-inoperable for 1 hr.while accumulator which supplies PCV-455C, was out of service.
NORTH ANNA 1 338/83-071.10/09/83 One train of the LTOP system was taken out of service.-Because vent valve malfunction in the liquid nitrogen plant made it, unavailable for nitrogen makeup.
Leakage'-in the A LTOP train bled down the limited stored nitrogen makeup supply.-
NORTH ANNA 2 339/83-033 05/15/83 Pressure in nitrogenLsupply tank B for pressurizer.PORV: dropped below minimum pressure required I
for PORV operation. Low pressure L
resulted from'the downstream nitrogen supply (tovPORV) relief valve. lifting.
NORTH ANNA 2-339/83-030 14/06/83 Nitrogen' supply tank B pressure for-presurizer PORV dropped below the minimum pressure for operability. Leakage in pressurizer PORV nitrogen supply system caused the B' supply tank to depressurize.
I SURRY l 280/83-012 02/09/83 At cold shutdown and overpressure mitigating system in enable,.both pressurizer: PORVs were declared' inoperable due to low air-pressure in-the back up bottle air supply l
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Event Description of Event Date NORTH ANNA 1 338/82-091 12/07/82-Pressure in the B_ nitrogen reservoir for a pressurizer PORV dropped.below the minimum-pressure required to maintain the PORV operable.-This' event'was caused by excersive nitrogen-leakage through' the B reservoir relief valve.
SURRY 1 280/82-106 10/02/8? Both pressurizer PORVs were declared inoperable.;One hadia leaking diaphram and'the other-was inoperable due to low air pressure in its-back up bottle air supply caused by a. leak in the-check valve separating it fromethe instrument air.
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Draft Supplement to Information Notice 89-32 Descriotion of Circum =tances Eoint Beach: During performance of a functional test of the nitrogen backup system for the PORVs in 1989, the opening times for_ the PORVs were longer than those used for the safety -
analysis of the low-temperature, overpressurization system. The opening times _were 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, it was_-
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. determined that the overpressure transient could reach 835 psig which is well above the technical' specification limit for brittle failure at low temperatures. The licensee replaced nitrogen control valves with larger ones to achieve adequate actuator pressure at the PORV and modified the,
PORV spring to ensure meeting the PORV stroke time.
Turkev Point. Unit 3: In 1988 it was determined that the stroke times for the PORV varied from 2 to 6 seconds since initiation of the tests in 1984 instead of the 2 and 3 second opening times assumed in the safety analyses for low-temperature overpressurization events. These delays were attributed to undersized control air and nitrogen backup supply lines to the PORV actuators. The licensee enlarged the supply lines to decrease the PORV opening times.
San Onofre. Unit 1: The licensee determined that there was no provision for testing the backup nitrogen supply. system in mode 5 operation.
Procedures _ were modified to confirm the operability of the backup system in operating mode 5.
Indian Point. Unit 2: The backup nitrogen supply system to the pressurizer PORVs, which are used for the LTOP system, was found to be inoperable during a test conducted in 1987. Check valves failed to prevent backflow to the non-safety grade nitrogen system and.the nitrogen consumption per valve stroke was greater than expected. The check valves were replaced..
Discussion The issue in these situations is confirmation that the PORV will operate consistent with the assumptions used in the low-temperature, overpressure protection analyses.. In particular, 4
assurance that the PORV opening times, using the alternate pneumatic supply, comply with the safety analyses. Performance of surveillance tests using the alternate supply is consistent with conducting stroke time tests using the normal air supply to actuate the PORVs.
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IN 82 -
UNITED STATES hUCLEAR REGULATORY COMMISSION gh i
0FFICE OF INSPECTION AND ENFORCEMENT WASHINGTON.'DC 20555.
November 19, 1982 IE INFORMATION NOTICE NO. 82-45:
PWR LOW TEMPERATURE OVERPRESSURE PROTECTION Addressees:
All pressurized water reactors-(PWRs) holding an operating. license (0L) or l
construction pemit (CP).
Purpose:
l This notice is to provide PWR licensees and construction pemit holders with l
pertinent information related to operation of the low temperature overpressure l -
protection system. This infomation. updates that presented in Information l
Notice No. 82-17 (June 10, 1982) and reflects.the initial findings of PRC staff' review'of operating experience, Licensee Event Report:, and._ technical specifications related to low temperature overpressure protection. NRC staff review of this issue is continuing.. Recipients of this information notice should review the infomation herein for applicability to their facilities.-
i No specific action or response is required at this time.
Description of Circumstances:
In August of 1976, the issue of low temperature overpressure protection was raised and licensees initiated procedures and proposed systems to mitigate postulated overpressure events. The main concern was with the low temperature modes of cooldown and heatup, during which overpressurization could cause brittle fracture of the reactor vessel.
In most cases, licensees proposed a manually enabled low pressure setpoint-on the existing pressurizer power-operatea relief valves (PORVs) supplemented by procedures and technical specifications.
t The low temperature overpressure events at Turkey Point Unit 4, on November 28 and 29,1981'have been designated.by the Comission as abnomal occurrences.
These events were described in IE Infomation Notice No. 82-17.: The events were caused by failure of the backup train of the low temperature overpressure protection system (LTOPS) because of inadequate surveillance and valve lineup.
procedures.
Following the Turkey Point events, investigation of the.contri-buting factors led to a review of the Turkey Point Unit 4 LTOPS surveillance procedures which showed that the surveillance requirement did not include a test of the complete instrument channel.
Staff review of LERs indicates that no overpressure events similar to those at Turkey Point have occurred at operating.PWRs since 1978.
However, events have i
occurred in which both trains of LTOPS have been inoperable simultaneously, emet 97 m 3p
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IN 82 45-
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' l Novetter :19,1982 Page 2 of 3 The following causes have each resulted apparently from comon cause factors.in both LTOPS trains being inoperable r
Operation with both PORVs isolated (block valves closed) because 1,
of known PORY leakage.
at the Salem 2 plant, the PORV block 18, 1981 On. June 12 and again on Junevalves were closed because of leaking LTOP 4
trains inoperable. Also, on December 12, 1978 during plant heatup, a technician troubleshooting the f ailure of one To stop the train of LTOPS pulled fuses which caused both PORVs to o PORVs were returned to service within 15 minutes.
2.
Operator error during maintenance.
et the Surry 2 plant, one train of LTOPS was inoperable On May 21, 1981 because of a wiring error while the isolation valve for the pressureAlso, on May 6,.
transmitter for the second train of LTOPS was closed.
1980 at the Ginna plant, during post-installation test of the reactor vessel head vent, OC power switches for both trains of LTOPS were found to the off position.
Isolation and venting of instrument air to the PORV actuators during 3.
integrated leak rate testing. (ILRT) at the Zior. 2 plant, the accumulators for both PORVs were vented and the instrument air source-was isolated, rendering b On June 18, 1980 of LTOPS inoperable.
f Surry 2 plant the LTOPS was inoperable due to ILRT.
~27, 1980 at the to block both PORVS open during the ILRT. Also, on May i
Low nitrogen pressure to both PORV actuators.
4.
On numerous occasions at North Anna 1 and 2, leakage in the backup nitro-I gen supply to the PORVS degraded the nitrogen supply pressure and re j.
l the LTOPS innperable.
The events involving low nitrogen pressure were caused Although, these events occurred in a LTOPS where the backup air supply is bottled nitrogen, the events could have direct applicability f
Because these air-operated systems are normally continuously supplied from the plant air compressors, even when in shutdown, the lack loss of air.
effectiveness of the pneumatic system and the air accumulators may not be discovered unless the plant experiences a loss-of-air event or unless the normal air supply to the accumulators is deliberately interrupted to perfonn an in these cases, periodic inspection or surveillance may operability check,be needed to detect excessive leakage and to ensure opera pneumatic supply.
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o IN 82-45 November 19, 1982 Page 3 of 3 In addition to instances in which both LTOPS trains were found to be inoperable, some LTOPS may have been in a degraded condition as a result of failure to update the LTOPS setpoints to correspond to changes -in the Appendix G tempera-ture pressure limits.
This condition was found at both Kewaunee and Turkey
- Point, if you have ais 49estions regarding these matters,'please contact the adminis-trator of the gyropriate Regional Office or this office.
Edward L. Jordan, Director Division of Engineering and Quality. Assurance Office of Inspection and Enforcement Technical
Contact:
- Geor e F. Lanik, IE 1
(301 492-9636
Attachment:
List of Recently Issued Information Notices 4
- SEE PREVIOUS CONCi!RRENCES
- DE0A:lE
- 0EQA:lE
- PSB:lE
- 0:
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GFLANIK WRMILLS RSANDERS ELJORD N 11/ /82 11/ /82 11/ /82 11//4/82
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UNITED STATES NUCLEAR REGULATORY C08911SS10N OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C.
20555 March 23,1989 NRC INFORMATION NOTICE NO. 99-32: SURVEILLANCE TESTING OF LOW-TEMPE C/ERPRESSURE-PROTECTION SYSTEMS
_ Addressees:
All holders of operating licenses or construction pemits for pressurized-water reactors (PWRs).
Purpose:
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 infomation-for applicability to their facilities and consider actions, as appropriate, to avoid similar prob.
lems.
However, suggestions contained in tnis infomation notice do not consti-t tute NRC requirements; therefore, no specific action or written response is required.
j Description of Circumstances:
Beaver Valley:
Ouring an inspection (Inspection Report No.
NE inspectors noted that technical specifications (TS) require that over-50-334,412/86-20),
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.
surse111ance requirement only addresses stroking the operable PORY each time The TS
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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:
mass input case and (2) a heat input case.
(1) a
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The most restrictive PORV opening time was identified as the mass input accident which would require a valve'to open within 2.5 seconds.
1983 found this analysis to be acceptable.An NRC safety evaluation report (SER) dated April 4, l
A review of the licensee's mainte-nance surveillance procedure indicated that the nominal trip setpoint of less than or ecual to 350 psig.was addressed, but the stroke time was not.
i Plant TS and procedures had not implemented PORV stroke times as assuraed 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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IN 89-32 i
March 23, 1989 Page 2 of 3 concluded that the resulting maximum RCS pressure would still have been within specified limits.
i ments to address PORY stroke testing.However, the licensee initiated several pe Turkey Point:
The staff inspected the licensee's overpressure ritigation system (OM5) (Inspection Report Nos. 50-250, 051/88-14 and 88-26). The PORY electronics operability and setpoints are verified before being aligned for low-pressure operations.
3 and 4 PORVs from May 1984 through May 1988.The inspectors reviewed the strok accordance with the licensee's-inservice test (IST) program.These tests were perform
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ment for each PORV is to fully stroke within 15 seconds.. The stroke timesThe IST require
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reviewed ranged from less than 2.0 seconds up to 6.41 seconds.
times are well below the 15-second IST criterion.
These stroke porting license amendments, a relief valve openin9 time of 2.0 seconds wasHowever
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heat input case assumed a relief. valve opening time of 3.0 seco The 4
The PORVs, on average, were not meeting the design-basis stroke time, the eventual refueling outage that would place one of the u operating regime of the OMS.
for each of the units in order to allow the licensee time to resolve thisThe r issue.
the magnitude of the overshoot considering the following transie start of an idle reactor coolant pump with the secondary water temperature 1) the 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 pumps with a loss of letdown. injection into a water-solid RCS and 3) the inadv The safety evaluation demonstrated that with a t
PORV opening stroke time up to 3.45, the OMS could mitigate the most limiting transient (spurious start of a SI pump).
during the nort refueling outage. change for Unit 4 and is planning This design change will ensure that the PORVs will opea in time to prevent exceeding the 10 CFR 50, Appendix G limits The surveillance procedures supporting the TS were changed so that future stroke tme testing will use an acceptance criterion that is consistent with the design basis.
essing operational perfonnance (Inspection Rep r N 5
00/
-34 ed a pressuriter PORVs An IST re ancy c neerning the: testing of the testedfromtheohntocloedDoifon ed that the PORVs were to be stroke t
seconds.
The licensee tested the PORVs i time of 2.0 lance test 'or pressurizer PORV operabilit
- Ndancewithan18-monthsurveil-credit was taken for the PORVs at power opM t1on. they were required toe y analysis l
provide overpressure protection (b operation.
Shearon Harris utilize the h e 04 s rt l
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IN 89-32 March 23,1989 Page 3 of 3 The design basis of the licensee's LTOP is to protect the RC5 from overpressure when the transient is limited to:
(1) start of an idle reac?.or 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 itr injection into a water-solid RCS.
The PORY setpoints were calculated to maintain the RCS below the maximum allowable system pressure given in 10 CFR 50 Appenoix 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 viive opening times were greater than 2.0 seconds, then the pressure overshoot could be greater than originally calculated.
time could result in the 10 CFR 50 Appendix G limits being exceeded during design-basis transient.
The PORVs were stroked in the cpen direction so that the licensee could perfonn the time-to-close test.
that the time to open be determined, and this was not done.However, the surveilla Discussion:
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-Stroke time requirements used in analyses of the licensee's LTOP quate.
systems were not being transferred into IST requirements and eventually into surveillance test procedures.
requires valves to be exercised to the position required to fulfill theirThe ASM function.
Therefore, not testing the LTOP PORVs in the open direction is a Concern.
No specific action or written response is required by this information notice, if you have any cuestions about this matter, please contact one of the tech-nical contacts listed below or the Regional Administrator of the appropriate regional office.
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< -:r.-r Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: Milton Shymlock, Rf!
(404) 331-5542 Thomas McElhinney, Res. Insp., Turkey Pt.
(305) 245-7669 A22a chtrent:
List of Pecently Issued NRC Information Notices
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