IR 05000498/1993007
| ML20035A978 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 03/23/1993 |
| From: | Beach A, Stetka T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| Shared Package | |
| ML20035A976 | List: |
| References | |
| 50-498-93-07, 50-498-93-7, 50-499-93-07, 50-499-93-7, NUDOCS 9303300301 | |
| Download: ML20035A978 (31) | |
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APPENDIX
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U.S. NUCLEAR REGULATORY COMMISSION
REGION IV
AUGMENTED INSPECTION TEAM REPORT
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NRC Inspection Report:
S0-498/93-07; 50-499/93-07 l
l Operating License:
Docket:
50-498
50-499
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Licensee: Houston Lighting & Power Company l
P.O. Box 1700
Houston, Texas 77251
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Facility Name: South Texas Project Electric Generating Station (STPEGS)
Inspection At: STPEGS
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Inspection Conducted:
February 4-24, 1993 Team Members:
R. Latta, Resident Inspector, Division of Reactor Projects, i
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Region IV
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J. Whittemore, Reactor Inspector, Division of Reactor Safety,
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Region IV A. Gautam, Sr Operations Engineer, Special Inspection Branch,
Division of Reactor Inspection and Licensing Performance, Office of Nuclear Reactor Regulation
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J. Boardman, Senior Reactor Plant Systems Engineer, Trends and
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Patterns Analysis Branch, Division of Safety Programs, Office
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for Analysis and Evaluation of Operational Data j
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Assistant i
Team Leader:
M. Satorius, Project Engineer, Division of Reactor' Projects, Region IV
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Team Leader:
T,dil S 7[73[93
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T. F. Stetka, Chief, Project Section D Date '
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Division of Reactor Projects, Region IV j
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au sac )
3/23/5l3 l
Approved:
E! Iill Beach, Director, Division of Date
i Reactor Projects, Region IV
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-9303300301 930324
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PDR AIX3CK 05000498-t
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TABLE OF CONTENTS
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1.
INTRODUCTION..........................
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1.1 General Description of Event..
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1.2 AIT formation and Tasks
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2.
AIT INSPECTION.........................
2.1 Sequence of Events....................
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2.2 Root and Contributing Causes of the TDAFWP
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Overspeed Trip Events
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2.2..I Unit 1 TDAFWP Overspeed Trip _ Events
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i 2.2.1.1 Contributing Causes for Unit 1
Overspeed Trips.............
2.2.2 Unit 2 TDAFWP Overspeed Trip Events.........
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2.3 TDAFWP Corrective and Preventive Maintenance 8'
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2.3.1 Evaluation of the Effectiveness of
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TDAFWP Surveillance Testing
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I 2.3.1.1 Pump Operability Testing
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2.3.1.2 Actuation and Response Time Testing....
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2.3.1.3 Surveillance Testing MetSodology
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2.3.2 Assessment of TDAFWP Preventive Maintenance
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2.3.3 Assessment of TDAFWP Corrective Maintenance.
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2.3.3.1 Unit 1 TDAFWP Corrective Maintenance
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2.3.3.2 Unit 2 TDAFWP Corrective Maintenance
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2.4 Design Modifications...................
2.5 TDAFWP 14 Steam Admission Drain Line Valves
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2.6 Source of Drain Line Blockage and Foreign Material
Intrusion Into Safety Related Equipment
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2.6.1 Blockage in TDAFWP 14 Turbine Casing' Drain Line...........
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' 2.6.2 Particulate Contamination' of Safety-Related.
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2 '. 7 Governor Valve and Control System
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.i 2.7.1 Governnr and Governor Valve
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2.7.2 System Control Time Coordination..........
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2.7.3 Available Technical Data..............
i 2.7.4 MOV-514 Degradation
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2.7.5 Steam Line Drain Capacity 21'
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I-l 2.8 Postmaintenance Testing...................
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2.8.1 Observation of Testing Activities'.........
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2.9 Corrective Actions Implemented and Proposed by-
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Licensee.....'...................
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PLANT RESTART 23.
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FINDINGS AND CONCLUSIONS.....................
EXIT MEETING..........................
26.
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ATTACHMENT A - Persons Contacted I
l, ATTACHMENT B - Confirmatory Action Letter l
FIGURE 1 - TDAFWP Steam Turbine Steam Admission and Drain Simplified Diagram
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(Before Modifications)
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FIGURE 2 - TDAFWP Steam. Turbine Steam Admission and Drain Simplified Diagram.
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DETAILS
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INTRODUCTION (93800)
The NRC has established a policy to provide for the timely, thorough, and
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systematic inspection of significant operational events at nuclear power i
plants. This includes the use of an Augmented Inspection Team (AIT) to i
determine the causes, conditions, and circumstances relevant to an event and j
to communicate it's findings, safety concerns, and recommendations to NRC
management.
In accordance with NRC Inspection Manual Chapter 0325, an AIT was
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dispatched to South Texas Project Electric Generating Station (STPEGS) on-February 5,1993, to review the circumstances surrounding the repetitive i
overspeed tripping of_the Unit I turbine driven auxiliary feedwater pump (TDAFWP), and the failure of the Unit 2 TDAFWP to start on. demand.
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1.1 General Description of Event On February 1, 1993, at 9:49 a.m., the Unit 1 TDAFWP 14 was tested using STPEGS's station procedure that satisfies the monthly testing requirements of Technical Specification (TS) 4.7.1.2.1.a.
When called upon to start, the pump
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tripped on overspeed and was declared inoperable at 10 a.m., and action j
statement "b" of TS 3.7.1.2 was entered. This action statement required the
TDAFWP be returned to an operable condition within the following 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, or
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the reactor be placed in the Hot Standby mode withi_n the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and the
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i Hot Shutdown mode within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The licensee began troubleshooting activities to return the pump to an operable condition.
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On February 3, 1993, STPEGS Unit 2 was operating at 100 percent power, with l
two steam driven steam generator feedwater pumps and one electric startup l
feedwater pump providing feed flow to the steam generators. At approximately
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3:23 p.m., the startup feedwater pump tripped when the pump lubricating oil
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duplex strainers were being shifted. Because the two remaining SGFW pumps
were capable of providing only 80 percent of the required feed flow at 100
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percent reactor power, control room operators immediately began to ramp down
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power.
Despite the effort of the operators, a low steam generator level was
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received in Steam Generator C.
The operators subsequently initiated a manual reactor trip, prior to receiving an automatic reactor protection system trip l
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on low steam generator level.
Following the plant trip, Unit 2 TDAFWP 24.was automatically called on to supply water to the steam generators. This pump
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started but immediately tripped on an overspeed condition. Control room l
operators were able to maintain adequate feed flow to the steam generators
using the remaining three motor-driven auxiliary feedwater pumps (MDAFWP).
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On February 4,1993, at 9:38 a.m.,
the licensee had not been successful in:
restoring TDAFWP 14 to an operable condition.
Subsequently, a Notification of
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an unusual Event was declared, in accordance with the licensee's emergency l
plan, and Unit I commenced shutting down to place the reactor in the i'
operational mode required by the TS.
l.2 AIT Formation and Tasks Region IV, in consultation with the Office of Nuclear Reactor Regulation, formed.an AIT on February 4, 1993. The AIT, which consisted of three
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' Region IV inspectors, an inspector from the Special Inspection Branch of the Office of Nuclear Reactor Regulation, an inspector from the Trends and Patterns Analysis Branch of the Office for Analysis and Evaluation of-Operational Data, and a team leader from Region.IV, was. sent to.STPEGS to gather information regarding licensee actions and to review plant response.to these events.
Prior to the arrival of the AIT, the NRC resident inspectors had monitored the licensee's preliminary response to these events..The AIT-arrived on site February 5, 1993.
The AIT tasks, which were specified in a Charter dated February 4, 1993, to Mr. T. F. Stetka from Mr. J. L. Milhoan were:
(1)
Determine the root and contributing causes, as well as the specific licensee corrective actions that have. been taken or planned for:
(a) Unit 1 TDAFWP overspeed trip on December 27, i992 (b) Unit 1 TDAFWP overspeed trip on January.28, 1993 (c) Unit 1 TDAFWP overspeed trip on February 1, 1993 (d) Unit 2 TDAFWP trip while being secured on January 23, 1993 (e) Unit 2 TDAFWP overspeed trip on February 3, 1993
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For the February 3,1993, Unit 2, reactor trip and TDAFWP 24 overspeed trip, also determine the sequence of events.
In addition, ascertain whether there have been any other TDAFWP trips that may not have been appropriately documented by the licensee.
(2)
Review the auxiliary feedwater system preventive maintenance activities.
relative-to both TDAFWPs, including subcomponents and related support
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systems.
For both TDAFWPs, develop a chronology and description of all
problems for which troubleshooting and corrective maintenance have been
performed, including a determination of whether there have been undocumented troubleshooting and corrective maintenance activities
performed. Document all actions taken or planned (including the j
completion or schedJled completion dates)' to resolve each-of these.
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problems, including the planned implementation of any design j
modifications.
a (3)
Determine why the TDAFWP 14 steam admission line drain-valves were not verified ~open pr.ior to the Unit I startup from the fourth refueling outage, as well as the effect that this condition may have had~ relative
'to the operation of TDAFWP-14.
Verify what the ' source of. blockage was l
in the TDAFWP 14 turbine casing drain line. and ascertain the manner in-
which the line became! blocked.
Determine 'whether other safety-related
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equipment may be affected by the same foreign material that was-
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deposited in the TDAFWP 14 turbine casing drain line.
If other-i equipment is affected, determine what actions ~are being taken to resolve-l such a condition.
(4)
Verify that theLTDAFWP governor valve control systems are functioning as l
intended.
Quantify the seat leakage associated with both trip and i
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throttle valves and the effect of this seat leakage on the operation of both TDAFWPs.
Assess the acceptability of continued plant operation i
with these valves in a degraded condition.
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Review the postmaintenance testing (PMT) for both pumps and the basis i
for the operability determinations. prior to the pumps being returned ~to
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an operable status.
2 AIT INSPECTION l
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The inspection effort began with a briefing by the licensee's Response-Team,
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which was formed by plant management following the occurrence of the event.s, t
and notification that an AIT would be dispatched. The briefing included.the" i
licensee's investigation into the events and their findings to date. The AIT-
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found this briefing to be limited in scope, as the Response Team had not been
formed until nearly 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the last event occurred.
The initial i
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licensee response did not appear to have been aggressive in the determination of the causes of the TDAFWP overspeed trips or in the diagnosis of. required
corrective actions for restoration. The AIT noted.that the licensee had
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conducted relatively few personnel interviews and gathered little data i
relevant to root cause determination.
It was noted that the licensee had not
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developed a timeline for the events.
l The AIT inspection included a review of plant logs, numerous interviews with
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personnel, a review of plant procedures and maintenance' records, a review of pertinent vendor information, walkdowns of both TDAFWPs, observations of
ongoing maintenance and testing activities, and a review of the STPEGS design.
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criteria.
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2.1 Seauence of Events
The AIT developed the following sequence of events based on its review of'the-licensee's logs, personnel interviews, and briefings by the Response Team.'
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t December 8-9, 1992
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Unit 1 I
a TDAFWP 14 was restored to service following a refueling outage.
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number of problems were encountered during testing, including speed oscillations, condensate entrained in the supply steam,.and overspeed.
i trips. Unit restart was postponed, due to a leaking seal weld on a l
control rod drive mechanism.
December 16. 1992
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Unit 1 i
The TDAFWp 14's steam admission and.;ip/thottle valve, Motor-0perated
Valve (MOV)-514, was disassembled to repair previously identified ' seat
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leakage. After' disassembly and the-licensee's discovery that no repair
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parts were obtainable, MOV-514 was reassembled, without any corrective l
maintenance being completed.
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i December 27. 1992
l Unit 1 i
Surveillance Procedure OPSP03-AF-0007, Revision 7, " Auxiliary' Feedwater
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Pump 14/24 Inservice Testing," the monthly surveillance that i
demonstrates operability in accordance with TS 4.7.1.2.1.a.2, was conducted and TDAFWP 14 tripped on an overspeed condition.
After a
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local manual start and a second remote start from the control' room, the
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surveillance procedure was repeated. On this attempt the pump
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A reactor trip was manually initiated by operators when a feedwater j
regulating valve failed shut and could not be reopened from the control
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room, causing steam generator levels to decrease. TDAFWP 24 started, on-j demand, and was later secured wher. no longer requi' red, in accordance
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with the licensee's emergency operating procedures.
January 8. 1993 i
i Unit 2 Surveillance Procedure OPSP03-AF-0007 was completed satisfactory.
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January 23. 1993-l Unit 2 ntor trip occurred following a turbine trip when a main. turbine and
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generator feedwater pump turbine. electrohydraulic control (EHC)
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s32 tem pipe, which was common to both turbines, failed. TDAFWP 24
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l started, on demand, and was later secured _when no' longer required.
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After the pump was secured, problems occurred when operators attempted to relatch MOV-514 from the control room. TDAFWP 24 was declared -
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inoperable, while the unit was shut down for repair of the EHC pipe.
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January 252 1993'
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_. Unit 2
The EHC pipe failure was repaired. A significant amount of troubleshooting and testing was conducted on' TDAFWP 24 to resolve the -
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MOV-514 relatch problem and another speed control problem that was:
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identified-during the testing. After successfully completing Surveillance Procedure OPSP03-AF-0007, TDAFWP 24 was declared operable and the unit restarted.
January 28. 1993 i
Unit I
i When initially starting TDAFWP 14 for the monthly operability
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surveillance in accordance with Procedure OPSP03-AF-0007, the pump-
tripped on overspeed, and was subsequently declared ' inoperable.
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January 28-30. 1993 i
i Unit 1 j
An extensive testing and troubleshooting effort was conducted by the licensee to determine the problem with TDAFWP 14.
Numerous pump starts'
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were completed.
Several problems with overspeed tripping, speed control-
and oscillations, and the ability to maintain ~ rated, full-load steady-
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state speed were identified. TDAFWP 14 ven6or support was retained to
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assist in the troubleshooting and problem resolution.
January 30. 1993-l
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Unit 1 l
TDAFWP 14 was declared operable following successful completion of l
Surveillance Procedure OPSP03-AF-0007.
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Unit 2
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Operators disclose to licensee managers that maintenance was conducted
on TDAFWP 24 on January 25, 1993, by unauthorized and unqualified i
personnel; as a result, the pump was ' declared inoperable.
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unauthorized maintenance was reworked and'the pump tested'in accordance j
with Surveillance Procedure OPSP03-AF-0007 and declared operable.
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February 1. 1993 l
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Unit 1
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At 9:49 a.m., TDAFWP 14-was tested using Surveillance;
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Procedure OPSP03-AF-0007. The pump was tested in order to' ensure operability, following several problems encountered in the previous several days. When called upon to start, the pump tripped on overspeed1 and was declared inoperable at 10 a.m.
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February 3, 1993
Unit 2 At approximately 3:23 p.m., a reactor trip occurred and TDAFWP 24 I
started but immediately tripped on an overspeed condition.
'f February 4. 1993 i
Unit 1
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At 9:38 a.m., the unit commenced a shutdown to place the reactor in the mode required by TS because TDAFWP 14 had not been restored to an operable condition within the allowed TS outage. time.
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2.2 Root and Contributino Causes of the TDAFWP Overspeed Trio Events
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2.2.1 Unit 1 TDAFWP Overspeed Trip Events
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No definitive root cause was identified for TDAFWP 14 overspeed trips. A
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number of' contributing causes have been identified; each contributing cause,
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taken alone, was not considered sufficient to have resulted in the overspeed problems that occurred December 27, 1992, January 28, 1993, or February 1, i
1993. However, the AIT determined that the most probable cause of th
overspeed trips was due to the misadjustment of the governor val e linkage.
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l 2.2.1.1 Contributing Causes for Unit 1 Overspeed Trips The AIT determined that MOV-514 was leaking by it's seat, had been in this
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condition for nearly 1 year, and had been identified and documented as a deficiency by the system engineer since March 1992. This created tne potential for condensate collecting in the turbine casing.
In addition, about
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t I 1/2 quarts of water, which collected in the casing upstream of the turbine wheel, was not designed to drain from the casing. -Although not considered by i
the turbine vendor to be of sufficient quantity to cause overspeed trips, the
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presence of this water and its potential for becoming entrained and water
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slugging the turbine could have reduced the margin during startup to reach the overspeed trip point.
The AIT also determined that this leakage could have.
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further reduced the time for the governor valve to gain control of the turbine
speed due to the " pre-pressurizing" effet;t the leakage created in the turbine
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casing.
This effect would cause a faster acceleration of the turbine wheel
upon initiation of steam into the turbine casing.
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Review of the as found condition of the governor valve indicated that the closed position.was misadjusted approximately 1/16 inch (10 percent of full i
travel) off the closed seat during the last outage (mid-September to late
' December 1992). This misadjustment had two impacts:
(1) When tne governor valve closed to slow the turbine, it was 10 percent behind, or further open
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than, the governor's demanded position; and (2) with MOV-514 leaking-by, steam
was being admitted into the turbine and, although not sufficient to cause the i
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i turbine to turn, did permit a faster rate of. steam admission into the turbine-l once a start signal.was present.
In addition, the governor valve's slightly
open position would also tend to challenge the governor's ability to -slow the -
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turbine prior to an overspeed condition being reached.
!J The AIT determined that the opening of MOV-514 on the turbine start signal could have contributed to TDAFWP 14 overspeed trips. The original design I
configured MOV-514 as a normally open valve with the outside containment
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isolation valve, MOV-143, normally closed (see Figure 1). The outside containment isolation valve was to receive an open command on the turbine-
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start sigt.al, thus starting the turbine. This configuration was changed
during Unit 1 prestartup testing to leave MOV-143 normally open and have MOV-I 514 open on the turbine start signal because the licensee was unable to achieve proper system operation. with the original configuration.
Valve MOV-
'I 514 fully opens in approximately 10 seconds but, in about 3 seconds, provides i
sufficient steam to operate the TDAFWP, resulting in the governor being required to control turbine speed in less than this amount of time. MOV-143,
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as designed, opens in.20 to 30 seconds, which would have provided an additional margin. for the governor valve to control turbine. speed., In-j
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addition, with MOV-514 closed and MOV-143 open, an additional = 97-foot run of j
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4-inch steam piping was at system operating temperature and pressure
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(saturated steam at 1100 psia).
This created an additional uncalculated 3;
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condensate load that the single steam line drain must accommodate since the design calculations for the steam line drain capacity were based on the
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original design (i.e., MOV-143 closed and MOV-514 open).
2.2.2 Unit 2 TDAFWP Overspeed Trip Event j
The root cause of the TDAFWP 24 overspeed trip.was determined to be an incorrect valve line-up, in conjunction with an inoperable,' or at a minimum
'i degraded, steam trap.
These. valves and steam trap are located in the drain
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line from the turbine steam supply line. This steam trap was located..
i downstream of Valves 2MS-148 and.2MS-218.
In' addition to accepting condensate
from the steam line drain, drainage from the MOV-514 above seat condensate j
drain line was also piped into this common drain line to the condenser (see
Figure 1).
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In April 1992, the steam trap bypass valve (2MS.-517) was opened and
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independently verified by two nonlicensed reactor plant operators. : This
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action was taken in accordance with a field change to valve lineup' Procedure
2 POP 03-AF-0001, Revision 04, "Auxil.iary Feedwater.".The field change-.had been.
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generated because of the identified degraded condition of-the steam trap and
the potential for the trap to stop passing condensate. Although' bypassing the
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trap, this action.did ensure that any. condensate buildup.would: be removed from j
the steam admission piping.. Later in April 1992, at a time that-the slicensee was not able to specifically determine, Valve 2MS-517 was shut in order to re-
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establish flow through the trap and permit the trap to perform its function of j
passing condensate.
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Based on historical thermal data collected on the trap and the associated i
drain piping, the trap, although in a degraded condition, continued to perform j
its function until late January 1993. At that time, the trap degraded to a
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point that it no longer was able to pass condensate.
This resulted in
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t condensate from the steam line being trapped in the steam admission piping and becoming entrained in the turbine supply steam when the TDAFWP received a
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start signal, consequently causing an overspeed of the TDAFWP on February 3,
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1993.
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Other contributing causes for the TDAFWP overspeed trips in Unit 2, which were
also common to the Unit 1 TDAFWP problems included excessive. seat leakage in
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MOV-514, and the use of MOV-514 in lieu of MOV-143 as the steam admission i
valve.
2.3 TDAFWP Corrective and Preventive Maintenance
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i 2.3.1 Evaluation of the Effectiveness of TDAFWP Surveillance Testing procedures for conducting surveillance testing for the TDAFWPs.
Specifically,.
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The AIT reviewed the facility license requirements for surveillance and the AIT attempted to determine if previous past testing activities were being j
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conducted with the pump in it's normal standby condition. This was an j
important criteria since there was evidence that once the turbines were
warmed, either through operation or previous start attempts, the overspeed.
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i occurrences would no longer occur.
The AIT also reviewed past surveillance testing of the auxiliary feedwater (AFW) system as related to the TDAFWPs.
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The AIT requested that the licensee provide the documentation of monthly and
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quarterly surveillance testing for the past 2 years. The licensee was also
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requested to provide the documentation for 18-month (refueling) actuation and
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response time testing and the control room logs for the times relating to this j-testing since the plants had been licensed.
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2.3.1.1 Pump Operability Testing-j TS 4.7.1.2.1.a provided the surveillance requirements for the auxiliary
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feedwater system. There were no actual quarterly requirements, but testing
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was performed for some equipment on a staggered monthly test basis, and the
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procedures stipulated that these tests be performed quarterly. The only
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requirements of interest to the AIT were the surveillance requirements to i
assure 15 operability of the TDAFWPs. Procedure 1/2 PSP 03-AF-0007, Revision 6, i
" Auxiliary Feedwater Pump 14/24 Inservice Testing," provided the-detailed j
instructions to perform the monthly measurement of the TDAFWP discharge
pressure and flow. The testing performed by this procedure satisfied the i
surveillance requirements of TS 4.7.1. 2.1.a.2.
The testing also satisfied
.j other surveillance requirements associated with the positions of automatic.and j
nonautomatic system valves.
The monthly pump operability test could also-be
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performed utilizing Procedures 1/2 PSP 03-AF-0008, Revision 6, " Auxiliary
Feedwater Pump 14/24. Reference Testing."
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A review of Surveillance Test Procedure PSP 03-AF-0007: revealed'that the
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operator was required to start the IDAFWP from the control room. The pump was started by operating the control switch for the MOV-514 steam admission
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valve. This action caused MOV-514 to stroke fully open. There was no prerequisite to warm the system or turbine (and thereby place it in other than
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it's normal standby condition) prior to starting from the control room.
However, the procedure contained no precautionary statement that would preclude performing the test on a warm system. Also, based on Procedure PSP 03-AF-0007, a turbine trip on startup would not invalidate the operability test as long as the pump could be started on a. subsequent attempt.
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The only operability. requirements related to the TDAFWPs were to assure that they produced the required pressure and flow during steady state conditions.
t after a successful start from the control room.
Procedural prerequisites required the monthly operability surveillance test to be conducted in plant Modes 1, 2, or 3 with at least 1000 psig main steam pressure.
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The AIT reviewed all operability testing of both units performed in accordance with Procedure PSP 03-AF-0007 for the past 2 years. The reviews consisted of j
both record reviews and interviews with licensee personnel. The documentation
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indicated that the licensee had performed all the required surveillances, and
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that the surveillance conducted had met the license requirements for
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satisfactory operability determinations.
Several test documents indic,ced f
that the initial testing had revealed anomalies which constituted ar
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unsatisfactory test.
The followup to these findings generally re*;ealed an
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installed instrument out of calibration, minor misadjustment, or faulty measuring and test equipment. All followup testing had been prrformed satisfactorily and the license requirements for the determinat,on of equipment
operability had been met. As the result of these reviews and interviews, the
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AIT determined that the monthly and quarterly testing was appa,ently conducted
with the turbines in their normal standby condition.
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2.3.1.2 Actuation and Response Time Testing The AIT reviewed the license requirements for actuation and response time i
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testing related to the TDAFWPs. TS 4.7.1.2.1.b, which stated in part that
"each AFW pump starts as designed automatically upon receipt of an Auxiliary j
Feedwater Actuation test signal," required a startup test of the AFW system to
be performed every 18 months.
Other surveillance requirements included.the l
verification of automatic flow path alignment and delivery. of required flow to l
each steam generator.
The AIT reviewed the licensee's procedure to conduct the required TS surveillance requirement. Testing was conducted in accordance with
Procedure PSP 03-50-00190, Revision 0, " Turbine Driven Auxiliary Feedwater Pump
Actuation.And Response Time Test." Several system responses were measured l
during this test to provide assurance that the system would deliver the
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required feedwater flow within the required time. TDAFWP response was measured by accurately measuring the elapsed time between test signal
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initiation and the attainment of 550 gpm of feedwater flow to the steam
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generator. The acceptance criteria for this response was a maximum elapsed l
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I time of 45 seconds. The procedure prerequisites for testing were that the'
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system be aligned for automatic operation with at least 1000 psig steam i
pressure in plant Modes 1, 2, or 3.
The procedure did not specifically
preclude or allow testing on a warm system or turbine.
Since the plants had been licensed, these response time tests had been
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conducted three times on Unit I and one time on Unit 2.
The test was
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routinely conducted just. prior to entering or upon exiting-a refueling outage.
r The AIT reviewed the four completed tests that had been conducted on both l
units and the control room logs for the time period surrounding the tests.
Unit 1 TDAFWP Actuation and Response Time Testing The first test conducted was performed on February 28, 1989. The control room i
log indicated that the response test was commenced at 5:59 a.m. and completed-
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satisfactorily at 12:30 p.m..
The logs indicated that a satisfactory AFW feed
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flow verification test was performed at 2:51 a.m., but there was no indication
of the pump or pumps that were used for this test.
Additionally, one log.
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entry stated that MDAFWP 12 was started and MDAFWP 11 was stopped in support of the response test at 9:45 a.m.
The AIT was unable to determine, through j
review of the documentation, whether the TDAFW pump had been operated prior to
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the initiation of response time testing.
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The second response test was conducted on March 31, 1990.
This testing was
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The documentation for this j
test indicated that all MDAFWPs tested satisfactorily, and the TDAFWP was not tested. According to the control room log, the TDAFWP was declared inoperable
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prior to the initiation of testing. The log entry declaring pump.
inoperability referenced Service Request (SR) AF-83585, which was submitted to obtain maintenance support for overspeed trip testing.
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l A second attempt to test the response of the TOAFWP was conducted on June'll,
1990, upon entering operational Mode 3 after the outage.
The control room log
indicated that the response time test for the TDAFWP was commenced 55 minutes i
after the successful completion of the monthly operability test. This i
indicated that the system and turbine would have been. warm prior.to the j
response _ time testing. A log entry during the testing indicated that the i
TDAFWP had tripped on overspeed during startup after having been secured
during testing. This trip was attributed to high turbine governor oil l
pressure which had not sufficiently decayed in the short time the pump had l
been stopped. The pump was started successfully on the next attempt. The j
testing had not been conducted with the pump in it's normal standby condition, j
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A third actuation and. response time test was conducted on March 30, 1991. The AIT noted that control room log entries fixed the start of testing at 4:16 a.m., March 30, 1991, and the satisfactory completion of testing at 2:15
.a.m., on March 31, 1991.
The only entries regarding the AFW system during the test' period were the starting'and stopping of MDAFWP 12 in support of the response testing. The AIT could not determine from logs or test documentation why the actuation and response time test took 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> to complete.
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Unit 2 TDAFWP Actuation and Response Time Testing Actuation and response. time testing had been conducted on one occasion since
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the full power license had been granted. Testing was attempted on September 16, 1991, while preparing to enter a scheduled refueling' outage.
This test failed because, upon test signal initiation TDAFWP 24 tripped en
satisfactorily. The testing for TDAFWP 24 was postponed until the unit had
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completed the outage on December 10, 1991. The control room log did not
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indicate a start time for the 18 month response time test but stated that the l
monthly operability test commenced at 11:30 p.m. on December 10, 1991. The i
I TDAFWP was started and logged running at 11:45 p.m., apparently for the.
operability test.
This entry also stated that the running pump speed was j
measured at 3420 rpm and was readjusted to run at the reference speed of
3595 rpm.
Log entries for December 11, 1991, stated that operability and j
response time testing was completed at 1:57 a.m. and 2 a.m., respectively.
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i The results of both. tests were logged as satisfactory.
'From al.1 data available to the AIT, it appeared that the response time testing had been
- conducted with the system in other than it's normal standby condition.
I 2.3.1.3 Surveillance Testing Methodology
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The AIT reviewed other documentation to determine if the~ licensee was o
performing testing in accordance with license requirements. These documents
included the design basis for the AFW system, accident analysis for loss of
all AC power, and Updated Safety Analysis Report. The Updated Safety Analysis l
Report chapters reviewed included those on system design and initial startup
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testing. The AIT was unable to le ate any requirement to test the system with i
the pumps in a normal standby condition. Design specifications and I
requirements only required that the TDAFWP deliver the design flow rate within -
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a short time of receiving a demand signal.
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2.3.2 Assessment of TDAFWP Preventive Maintenance
The AIT requested that the licensee provide preventive maintenance records for h
the TDAFWP turbines, the MOV-514 valves, the speed control system, and the
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drain system steam traps for the previous ~2 years.
This review provided the
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I AIT with assurance that scheduled maintenance was being accomplished on schedule. A record of previously scheduled maintenance and related SRs indicated that problems were being identified. However, it was also noted
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that work documents were being generated only to correct the symptomatic
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deficiencies identified during the preventive. maintenance inspections and that
no generic implications were being addressed.
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l 2.3.3 Assessment of TDAFWP Corrective Maintenance
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The AIT reviewed corrective maintenance documents relating to both TDAFWPs for i
adequacy of procedures, problem identification, root cause analysis, and
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corrective action followup.
In addition, the AIT developed a chronology of r
significant corrective maintenance that had been performed on both TDAFWPs
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I since the units had been licensed. Work documents for review were selected-
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from a printout provided by the licensee that listed all corrective'
.j maintenance performed on the pumps. The chronology consisted of only that l
maintenance that was conducted on the turbine, MOV-514, steam _ admission line,
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turbine drain system, and turbine speed control system.
This review indicated that there had been no significant corrective l
maintenance conducted on the steam admission line or the turbine drain system.
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2.3.3.1 Unit 1 TDAFWP Corrective Maintenance I
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The AIT reviewed 24 corrective maintenance SRs for TDAFWP 14 performed from
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1988 through the end of 1992. Based on the chronology of the maintenance l'
reviewed, this pump did not have any overspeed trips prior to December 27,
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1992. Maintenance performed on the TDAFWP was found adequate, with one exception.
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' From December 1990 through August 1991 there had been three instances of
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deterioration of the tappet holder and ball in the overspeed trip. assembly.
SR AF-128755, dated December 4,1990, indicated that the ball in the tappet j
W der had deteriorated and had to be replaced.
SR AF-133781, dated.
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December 1,1990, indicated that the manual trip lever plunger had dirt and
sawdust' jammed around the' stem and that the turbine wouTd'not reset after a
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trip (during testing).
SR AF-111940, dated August 27, 1991, indicated that the tappet had the ball stuck in the trip position, causing resistance to the j
mechanical overspeed trip plunger.
In each instance the assembly was
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repaired; however, no station problem report (SPR) was' issued, anif no action j
was taken to highlight.the deficiency to prevent recurrence of the problem.
The issuance of an SPR provides the mechanism to assure that problems are
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l investigated, appropriate corrective actions are implemented, and generic implicatiens are addressed so that the problem does not recur.
l 2.3.3.2 Unit 2 TDAFWP Corrective Maintenance i
The AIT identified two maintenance items that pertained to MOV-514.
One item
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previded for a hydrostatic retest of the ASME Class 3 flange weld on the inlet
5 # of the valve. The second item required the retorque of the valve bonnet -
l to stop a valve bonnet steam leak. These two efforts were successful.
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A number of SRs had been written to address problems with the turbine i
overspeed trip mechanism.
In December 1990, the turbine overspeed trip mechanism' failed to trip the turbine during a test. The mechanism was repaired during a subsequent outage and tested satisfactorily prior to being j
returned to operable status.. During preventive maintenance in February 1991,
-l the licensee identified a sticking overspeed trip reset plui,ger. The
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identified problem involved difficulty in resetting the overspeed trip mechanism. The trip mechanism was disassembled, cleaned, and re-assembled
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with a new ball-and tappet assembly. The S?. indicated that the tappet
clearan:e;was also changed during this repair.
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During the September 1991 actuation and response time test discussed in i
Section 2.3.1.2 of this report, which resulted in a-turbine overspeed. trip,
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licensee personnel were unable to reset the overspeed trip mechanism. The
work document indicated the presence of a thick, tarry substance which
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interfered with plunger operation. The mechanism was disassembled, cleaned, and reassembled. The trip mechanism was successfully tested in December.1991 upon completion of the outage. However, there was no indication that any
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followup was performed (e.g., issuance of an SPR) to assess the cause of the overspeed trip that occurred during the original testing.
It appeared that
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the testing sequence employed for the December actuation and response time testing was performed with the turbine in other than a normal standby
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condition and, therefore, may have masked the continuing problem. Another occurrence of a sticking overspeed trip plunger was identified in March 1992 when the trip mechanism would not reset after a manual trip. Again, the
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problem was determined to be an oil varnish buildup on the trip mechanism.
q Work records indicated that the licensee's maintenance organization changed oil in the turbine oil reservoir three times in a 6-month period from February l
to August 1991.
The reason for changing the oil was because the preventive maintenance program had identified high acid content in the oil. None of the work documents for changing the oil indicated that an SPR or other corrective
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actions had been initiated.
In addition, the craftsperson performing the
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initial oil change identified the presence of a thick, g'reasy-substance in the
bottom of the reservoir and removed the substance to the extent possible.
The oil was changed again, in March 1992, during the repair of the trip plunger.
Again there was no followup action taken to address the identified problem.
An SR dated in December 1992 indicated that the turbine oil was changed to a different type.
i A recent S1 issued in late January 1993 addressed a problem identified when
-the control room turbine trip switch was actuated and caused a mechanical
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overspeed trip of the turoine. While actuation of.this switch should have l
caused a turbine trip, it should not have actuated the mechanical overspeed
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trip mechanism. The AIT determined that the licensee's effort to make
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adjustments to alleviate this problem resulted in the overspeed trip linkage
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being adjusted into an out-of-tolerance condition.
A second SR was issued to
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correct the out-of-tolerance conditions.
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The AIT concluded, in conjuction with the licensee's investigation of this occurrence, that the out-of-to'erance conditions were caused or exacerbated by
unauthorized and unqualified licensee personnel making linkage adjustments.
l 2.4 Design Modifications in response to the overspeed tripping events, the licensee plans to implement
the following modifications for both Units 1 and ? rrior to startup (refer to Figures 1 and 2).
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Installation of covers on the AFW turbine steos e' 1st stacks to
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prevent precipitation and foreign objects from being introduced into the l
stack.
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Rerouting of the high pressure stem leak off drain line for MOV-514 from
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a combined drain with the turbine casing drain to a separate floor i
drain.
This will provide an alternate drain path and prevent the l
potential of a buildup of water in the turbine casing due to back
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pressure in the drain line caused by this stem leak off.-
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c Drilling of weep holes in Orifice Plate F0-7357B located in the MOV-514
below seat drain line that runs horizontally.
These holes will prevent i
a buildup of water behind the orifice plates in the line and allow for i'
more complete drainage of the line to the sump.
Replacement of inoperable Steam Traps 9S141MTR001A and 9S142MTR001A with
spool pieces. This will insure that this line remains open to the
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condenser.
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Slowing the opening speed of MOV-514 so as to allow the turbine governor j
more time to react and maintain the design speed of the turbine. The I
valve currently fully opens in approximately 10 seconds and, within
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approximately 2-3 seconds of the opening command, provides enough steam
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to run the turbine. The modification slows the opening of the valve to
20 seconds.
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b 2.5 TDAFWP 14 Steam Admission Drain Line Valves l
i Subsequent to the overspeed trip of TOAFWP 14 on February 1,1993, the i
licensee conducted extensive repair and troubleshooting activities. One
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aspect of this process involved the evaluation of the steam admission drain
line Valves IMS-148 and IMS-218, which were determined to be partially closed j
rather than fully open as specified on applicable system line-up
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Procedure IPOP0Z-AF-0001, Revision 11, " Auxiliary feedwater."
In order to j
confirm the actual position of these valves, which are 1-inch manual gate
valves, radiographic examination was performed by the licensee.
Based on the
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results of these radiographs, it was determined that Valve IMS-148 was only
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20 percent open and that Valve IMS-218 was 80 percent open.
Based on the review of corrective work documents by the AIT for these valves, l
this condition was caused by binding in the stem of the valves.
Review of the
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v, ' dor manual for these valves by the AIT indicated that these valves are l
Borg-Warner, SH-105, 1500 psi rising stem gate valves with needle bearings in l
the valve stem-to-yoke bushing. The vendor manual did not stipulate any
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preventive maintenance for these valves and, therefore, no maintenance was l
performed on these valves. This lack of maintenance caused the valve stem
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needle iw rings to seize, making valve operation difficult. As a result, the
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valves could not be fully opened.
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i The inspectors reviewed the TDAFWP valve checklist, which was performed on I
December 8, 1992, to align the system for operation. This review indicated
that the subject valves had been independently verified as open in accordance i
with the governing requirements of Station Procedure OPG P03-ZA-0010, Revision 15, " Plant Procedure Adherence and Implementation and Independent Verification."
It was also determined that operations deparatment personnel-t had initiated SR MS-1-156957 on November 28, 1992, which documented that
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Valve IMS-148 was difficult to operate; however, this corrective maintenance l
activity was assigned a relatively low priority rating and, therefore, was not i
repaired.
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I Based on the AIT's reviews of the valve checklist, field examination of the
affected components, and interviews with the reactor plant operators who
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aligned the system, it was determined that the operators believed that the
drain valves had been properly aligned for service and that a slight variation i
in stem height on the valves would not have provided a definitive indication i
that the valves were not fully open.
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It was also determined that the operational impact of Valves IMS-148 l
and IMS-218 being less than fully open would have had a negligible impact on-j the operations of TDAFWP 14. This conclusion was based on the fact that the i
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area available for steam flow through Valve IMS-148 was significantly greater, l
than the area afforded by a 1/8-inch flow orifice which is located immediately
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down stream of the subject drain valves.
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2.6 Source of Drain Line Blockage and Foreign Material Intrusion Into Safety Related Equipment i
2.6.1 Blockage in TDAFWP 14 Turbine Casing Drain Line
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The AIT evaluated the source of the reported blockage in the TDAFWP 14 turbine
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casing drain line, which was identified during the performance of
a SR AF-10169794.
The AIT determined that there was no blockage in the turbine
casing drain line.
The only blockage identified was a gritty, foreign
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material that had plugged the orifice in the TDAFWP exhaust stack drain line
(see Figure 1).
This drain line was installed to permit drainage of condensate or rain water that could collect in the exhaust stack to a floor
sump.
Originally this condition was thought to have permitted water to
collect in the turbine casing; however, further investigation determined that
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this condition, although a deficiency, did not contribute to the TDAFWP v
This blockage only affected TDAFWP 14 since only this pump
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had an orifice in this drain line.
The orifice, a hole drilled in a pipe cap
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that was installed on the end of the drain line, had been removed from the
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Unit 2 TDAFWP turbine exhaust stack drain line.
Based on the review of the preliminary charcal analysis of this granular
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material, it appeared to match the constituents contained in sand blast grit
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with the addition of iron oxide witn some zinc content (approximately i
15 percent). The source of this granular material was most likely from sand-
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c blasting of the reactor containment structures which was performed from May to June of 1990 for Unit I and December of 1989 for Unit 2.
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2.6.2 Particulate Contamination of Safety-Related Equipment
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With respect to other safety-related equipment which could have been adversely.
j affected by the same foreign material, the AIT reviewed the results of the
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licensee's evaluations. These evaluations, which were documented on several.
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Houston Lighting & Power Company office memorandums dated February 9 and 10, 1993, provided the results of extensive system walkdowns of the following l
areas in Units 1 and 2:
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Power Operated Relief Valve (PORV) exhaust stacks
Main steam safety valve exhaust stacks and discharge piping
AFW pump rooms
Isolation valve compartments l
l AFW storage tanks
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Heating, Ventilation, and Air Conditioning intake 'and exhaust openings
for the electrical auxiliary building, control room envelope, mechanical auxiliary building, reactor containment building, and fuel handling
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building The results of these examinations generally indicated that the areas were free
of foreign material except for a buildup of debris inside the containment
penetration flue head in the isolation valve compartments and debris found in
'the Unit 2 exhaust stacks for the Train A main steam safety valves. The AIT
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determined that the debris in the containment penetration flue head did not i
affect the condition of the penetration.
In addition, the AIT reviewed the
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licensee's evaluations of the potential adverse affects associated with the particulate and corrosion products identified in the Unit 2 Train A main steam safety valve discharge pipes and stacks.
Based on the review of surveillance test results subsequent to the sand blasting of the Units 1 and 2 reactor containment buildings, it was determined that all of the main steam safety valves have had their setpoints verified. All 20 of the Unit 1 main steam
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safety valves were tested satisfactorily during Refueling Outatge IRE 03
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(March 29,1991) and 6 were satisfactorily retested during Refueling Outage IRE 004 (September 19, 1992).
Correspondingly, all 20 Unit 2 main steam safety
valves were tested during Refueling Outage 2RE01 (September. 28, 1990) and 4 were subsequently tested acceptably during Refueling Outage 2RE02 (September 14,1991). Therefore, it was determined by the AIT that the main steam safety valves for Units 1 and 2 were not adversely impacted by the reported particulate and corrosion products.
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The AIT also reviewed the licensee's evaluations of historical data related to
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sand / grit induced component failures to determine if other adverse conditions had been identified.
This review involved a selected examination of the
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licensee's Nuclear Plant Reliability Data System (NPRDS) for the following categories:
Contaminated / Dirty Components
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Particulate Contaminates
I Foreign / Incorrect Material
i Based on the review of the NPRDS data within these areas, the AIT determined l
that particulate intrusion had been a contributing factor in component failures on at least three other occasions. The first instance involved the TDAFWP 14 manual overspeed trip lever which was reported as jammed.
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Specifically, as a result of the' accumulation of dirt / sawdust on the manual l
trip lever, the turbine could not be reset subsequent to a trip on December 1, t
1990. No analysis was performed on the granular material by the licensee and i
the root cause of this condition was characterized on NPRDS as indeterminate.
l Absent the chemical analysis of this granular material, the AIT was unable to ~
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determine if this specific case was related to the foreign material which was found in the TDAFWP 14 turbine exhaust stack drain line/ ~
The second occurrence involved grit which was identified in the feedwater l
isolation valve,1FWFV7144-0P, air-operated hydraulic pump. This condition,
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which was originally identified on March 3,1989, was ultimately documented on
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SPRs 90-00010 and 90-0189. As determined by the AIT, the original failure of.
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the solenoid pump valves was-attributed to excessive contaminants (silica) in the hydraulic fluid used in these valves; however, the source of the foreign
material was not -identified by the licensee.
Subsequent deficiencies associated with the feedwater isolation valve solenoid pump valves were
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experienced.
However, these conditions were primarily attributed to the breakdown of the hydraulic fluid and not particulate contamination.
The third instance of component failure associated with particulate contamination involved the Unit 2 steam generator PORV, C2MSPV7431-0P.
This condition, which was identified on May 23, 1991, and again on December 14,
- 1991, involved particulate contamination of the hydraulic fluid which clogged the solenoids on the associated valve operator. As described in the NPRDS data base, the definitive source of the particulates was. unknown and the corrective actions initiated by the licensee involved flushing the affected-
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components and replacing the hydraulic fluid.
Although the AIT could not establish any co,alusive correlaticm between the
granular material discovered in the TDAFWP 14 turbine exhaust stack drain line and the previously cited examples of particulate contamination, it was-determined that the licensee had not rigorously pursued effective corrective actions on root cause analyses for these examples of equipment failure.
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-18-The inspectors also reviewed the licensee's NPRDS data associated with f ailures of critical components in the isolation valve compartments (the compartments where the TDAFWPs are located), including all the AFW pumps, steam generator PORVS, main steam isolation valves, and feedwater isolation valves.
Based on the results of this review, no additional examples of component failures related specifically to particulate contamination were identified.
2.7 Governor Valve and Control System DRESSER-RAND (Terry-Turbodyne) factory and service representatives, as well as Woodward Governor Company factory and field service representatives, were on site to review and analyze the TDAFWP control system concerns and to provide technical direction.
DRESSER-RAND is the successor company to Terry who supplied these governor valves with the turbines.
2.7.1 Governor and Governor Valve A Woodward Governor Company field service representative stated that, when he inspected the Unit 1 TDAFWP 14 on January 29, he found the governor-valve-to-governor-servomechanism mechanical linkage out of adjustment by.060
.080 of
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an inch in the direction that would prevent the governor valve from completely closing.
He further stated that this condition alone co'uld result ir. an overspeed of the TDAFWP during a quick-start.
The Woodward type PGA governors for both units were returned to the factory while the AIT was on site.
They were refurbished to their original design condition.
The governor valves were refurbished on site under the direction of DRESSER-RAND representatives.
The acceptability of the governor control systems was ultimately verified as being satisfactory by operation of the Unit 2 TDAFWP 24 with a DRESSER-RAND representative present.
At the completion of the AIT inspection, refurbishment of the Unit 11DAFWP governor valve had not yet been completed.
Restoration of the TDAFWPs included setting
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the governor-valve-to-governor-servomechanism mechanical linkage, the governor droop linkage, and the mechanical overspeed trip mechanism and linkage.
During restorction of the Unit 1 and 2 TDAFWPs, the turbine overspeed trip mechanism tappets and tappet nuts were found to be deteriorated and were repl aced.
This required a readjustment of the overspeed trip mechanisms. The spring tension in the overspeed trip mechanism linkage required adjustment.
After the Unit 2 TDAFWP 24 turbine restoration, a slow startup using MOV-514 to manually admit steam to the turbine was commenced.
The TDAFWP began unacceptable oscillations as its speed reached 3000 rpm.
The cause of the speed oscillations was determined to be the governor buffer springs in that they were not suf ficiently rigid to prevent the oscillations from occuring.
The governor from Unit 1 TDAfWP 14 was installed on Unit 2 TDAFWP 24 after the turbine oscillated, and the Unit 2 TDAFWP 24 governor was subsequently installed on Unit 1.
The buf fer springs were replaced with stronger springs which ended the oscillations.
A Woodward Governor Company factory
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representative stated that the installed buffer springs were the same ones
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that were originally installed -at the Woodward Governor. company factory and used for the TDAFWP operation since startup.
He stated that the oscillations-I were the result of a change in the dynamics of TDAFWP operation (flow path,-
d discharge pressure, etc ).
He also stated that the heavier buffer springs:
l installed should prevent TDAFWP turbine speed oscillations during the operational conditions that the Woodward Governor Company factory
representative was aware of.
j
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Additionally, a DRESSER-RAND representative stated that the Woodward Governor
!
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' Company governor remote speed control bellows air connection on Unit 2 TDAFWP (which is not used at STP) was capped.
He stated that capping this connection
- l permits room temperature variations to cause fluctuations in pressure on the y
bellows that changes turbine speed. He stated that for the Unit 2 TDAFWP,-..
.
with an initial turbine speed setting of 3600 rpm and the room cool, a speed-l drop of 120 rpm could be expected as the room heated to normal temperature.
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The connection was uncapped and the phenomenon stopped.
Subsequently, the Unit 2 TDAFWP operated satisfactorily.
!
2.7.2 System Control Time Coordination j
Time coordination between the turbine steam inlet valve, MOV-514,' and the l
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governor valve was reviewed since, as discussed in Secti'on 2.2.1.1 of this
report, rapid opening of MOV-514 could result in steam flow' causing an,
i overspeed trip before the governor valve could control turbine speed.
j As initially designed for both units, the TDAFWP steam inlet stop valve was l
MOV-143, a stop-check valve, which is located approximately 97 feet' upstream l
of MOV-514, which was adjacent to the turbine governor valve.
Subsequently,
MOV-514 was reconfigured as the TDAFWP steam inlet stop valve during start-up.
testing because of TDAFWP overspeed trips apparently caused by condensate in j
the steam line between MOV-143 and MOV-514. MOV-143 was designed to fully-t open in 20-30 seconds.
The licensee could not provide the AIT with data on
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the design steam flow through MOV-143 as a function of amount of valve opening i
(valve stem travel).
The licensee also could not provide this steam flow.
r versus valve position data for MOV-514, though the licensee indicated that d
MOV-514 could pass sufficient flow to permit design operation of the'TDAFWPs
!
within 3 seconds after the valve disc leaves its seat.
The rapid opening of i
MOV-514 and the lack of design information on the steam flow characteristics-
through the valves were the basis for the concern with the coordination of-the opening af MOV-514 and the ability of the governor valve to control turt'ine _
speed during quick-starts.
-l i
The TDAFWP governor valve opens to'its maximum position as a turbine coasts
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down, when inlet steam is secured, and remains in that position until a turbine start. The governor valve is designed to assume speed control during-startup when the turbine speed reaches the governor's minimum speedLsetting.
l (approximately 2000 rpm). The turbine accelerates rapidly to the minimum-
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speed setting. At that time the governor valve begins to close to control
' turbine speed. The turbine, however. overshoots the minimum. speed, starts t'o-l
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slow'down (as the governor valve closes) and then accelerates again as the
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governor valve opens in response to the governor's controlled increase to
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rated speed.
To reduce the possibility of turbine overspeed at this time, the s
governor contains a governor oil flow' restriction, called a ramp bushing.
.
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This bushing controls and limits the time for the turbine to reach rated speed to 28-32' seconds after the governor gains control.
If inlet steam flow is
,
excessive during a quick-start, the governor valve can not'close sufficiently
to limit speed before the turbine overspeeds. At STPEGS, rated turbine speed
.:
is 3598 rpm, plus or minus 5 rpm, with the mechanical overspeed trip set at 4044-4144 rpm.
2.7.3 Available Technical Data j
The licensee's Terry Turbine Manual (which was the licensee's only identified source of approved data on the installed Woodward governor) appeared to be a
commercial grade 1975 manual with a 1978 update and some additional changes.
The information contained in the manual on setting.the governor-valve-to-
governor-servomechanism mechanical linkage, the governor. droop linkage, and
,
the mechanical trip mechanism and linkage appeared to be ' marginally acceptable
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at.best, which could result in inaccurate settings.
The licensee's procedures.
for setting these linkages was requested. The. maintenance manager could
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identify no specific procedures.
The licensee responded to this request for the governor-valve-to-governor-servomechanism mechanical linkage only, by i
stating that the Terry turbine manual was available and contained the
'
necessary instructions.
The instructions from this manual were shown to a
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DRESSER-RAND factory representative for his opinion regarding the use of these instructions to set the linkages. He indicated that the instructions were
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adequate when used by properly trained per:;onnel. The AIT did not, identify
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any formal training in the setting of these linkages.
The licensee indicated that they will use DRESSER-RAND representatives to perform linkage adjustments until their~own personnel are properly trained.
e
,'
The licensee possessed an uncontrolled copy of EPRI/HUMAC manual " Terry Turbine Control Guide" (EPRI NP-6909s), dated September 1990. This manual was
!'*
prepared to provide necessary details on maintenance and adjustment of' Terry turbine controls not available in the commercial grade Terry turbine manuals-
!
available at sites such as STPEGS.
Based on review of procedures and i
discussions with licensee personnel, the AIT determined that this manual had i
not been used for maintenance and adjustment of TDAFWP turbine controls.
It
';
was noted that the licensee had used a DRESSER-RAND service representative and j
a Woodward Governor Company field representative for certain work on the j
TDAFWP turbines and' governors, but not for all work.
2.7.4 MOV-514 Degradation
Both Units 1 and 2 MOV-514 valves.were refurbished and returned to their design condition.(no greater than 8 cubic centimeters per hour.. seat: leakage)
{
while the AIT was on site.
Prior to refarbishment, these-valves were tested.
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on site for seat leakage using a low capacity hydrostatic test pump. During these tests, seat' leakage on MOV-514 for Unit I was 0.7.gpm.
The leakage on l
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MOV-514 for Unit 2 was 0.3 gpm.
These leakage rates could have been affected l
by'the capacity of the test pump. These leakage tests were not performed at.
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~ he rated pressure of the valves. These valves are designed so that steam'-
t-inlet pressure above the disk provides a force'that tends to reduce seat
.;
leakage, with this effect being greater at higher pressures. At low
'
pressures,. seat leakage could be increased because of'the lack of closing-pressure above the disk.
As discussed in Section 2.2.1.1 of this report, the MOV-514 degradation could a
have contributed to the overspeed trips of the pumps because of the excessive-l steam leakage into the turbine casing.
2.7.5 Steam Line Drain Capacity j
The drain calculation for the steam inlet line between Valves MOV-143 and
'
MOV-514 provided to the AIT was performed at the time that MOV-143 was the
steam admission valve for the TDAFWPs.
It indicated that warming the line hetween M9V-143 and MOV-514 would generate approximately 125 pounds of
condensate, and that, with this steam line warm, the steady state ccndensate
formation rate would be approximately 25 lb/hr.
The calculation indicated i
.
that there was adequate drainage for this condensate on an hourly basis, but
,
stated that warm up should not exceed the capacity of the drainage system.
With the present AFW system design using MOV-514 as the TDAFWP. steam admission valve, this drain design means that, when MOV-143 has been closed for maintenance or containment isolation and the line has cooled down, the TDAFWP
>
is not operable until the drain system has been able to remove the condensate generated during warmup of the line.
This had not been controlled by the
'
licensee, but the AIT was informed that this condition would be procedurally i
controlled in the future.
t 2.8 Postmaintenance Testing (PMT)
.
The AIT verified PMT and the basis for the operability of the TDAFWPs prior to their being returned to an operable status.
>
SRs did not identify the PMTs that established the operability of the TDAFWPs
prior to the pumps being returned to an operable status. The only means~to-establish the basis for operability was to match the dates of PMT data sheets with the' dates of SRs.
PMTs establishing operability were found in place,
!
however, in some instances the AIT found it very cumbersome to determine the
!
as-installed status of the selected equipment.
It was _also noted that SPRs had not been initiated for problems affecting the overspeed trip mechanism.
!
Maintenance records also indicated that housekeeping problems affected the operation of the overspeed trip mechanism.
'
The AIT's review of monthly, quarterly, and ref ueling outage surveillances, to determine the licensee's bases for determining operability, indicated that
these surveillances have satisfied license conditions.
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2.8.1 Observation of Testing Activities The AIT witnessed portions of the testing of TDAFWP 24, following completion of the corrective actions developed as the result of the overspeed tripping i
event.
These activities, which were controlled by Procedure OPEP07-AF-0013,.
Revision 0, " Auxiliary Feedwater Pump 14(24) Special Post Maintenance Test,"
l included the operational testing of the overspeed trip mechanism, MOV-514 l
above seat drain flow path verification, a baseline temperature survey, and
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setting of the turbine overspeed trip mechanism.
Based on the results of these activities, it was determined that the licensee had developed and implemented appropriate procedural controls, that the temporary test equipment
was properly calibrated, and that the system was correctly aligned to support
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the test configuration.
It was also ascertained that the test personnel were j
properly briefed prior to the initiation of verification evolutions, and that
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manufacturers representatives from both the turbine and the MOV-514 valve suppliers were present during conduct of PMT. Test discrepancies associated
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with the setting of the mechanical overspeed trip mechmism were properly
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addressed and, at the conclusion of these activities, was determined that
the_specified acceptance criteria had been satisfied.
40 deficiencies were
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identified and, in general, these confirmatory testing activities were well
controlled and executed.
.
2.9 Corrective Actions Implemented and Proposed by Licensee l
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As a result of the licensee's root cause determinations, a series of corrective actions was developed.
In addition to the plant modifications i
listed in Section 2.4 of this report, these corrective actions included-
'
t Locking cpen the steam trap bypass valve (MS-517), in addition to I
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verifying that system valve lineups for this system are correct.
<
U-Refurbishing the following components to original condition:
-MOV-514
,
-Governor Valve-Governor
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Establishing a reference point (based on the system return to normal
standby conditions) to be used as a required starting point for all future TDAFWP operability det3rminations.
>
Utilizing the vendor representatives to revise the maintenance,
operating, and surveillance procedures to reflect the as designed l
adjustments and operating requirements. This included revising the
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TDAFWP control linkage setting procedures'using vendor information.
i Performing an analysis to ensure that the TDAFWP drain system is
adequate to handle expected drainage conditions and change the operating
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procedure to ensure that the' upstream steam drain valves remain clear-
.i and capable of draining condensate out of the-steam lines.
Conducting site-wide training to address:
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Unauthorized maintenance and management's expectations regarding
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maintenance performed by operators.
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Valve line-ups and the methods.of checking valve position.
'
3 PLANT RESTART On' February 5,1993, the NRC issued a Confirmatory Action Letter to the i
Houston Lighting & Power Company to describe the actions that would be
'
required by the licensee prior to taking the-reactor critical.
The Confirmatory Action Letter is provided as Attachment B.
This letter requiris i
that the licensee brief the NRC staff of the results of the efforts to correct
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the overspeed trip conditions that affected the TDAFWP.
,
4 FINDINGS AND CONCLUSIONS i
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The AIT had the following findings and conclusions:
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(1)
With respect to the root and contributing causes for the TDAFWPl
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overspeed trips, the AIT's findings are consistent with the licensee's-
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finding s..
In general these root and contributing causes-are as follows:
For the Unit 1 TDAFWP 14, no definitive root cause was identified.
+
o However, the AIT considered the misadjustment of the governor-
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valve linkage to be the most probable cause-of the overspeed trips. This misadjustment, which occurred during.the previous.
I plant outage, reduced the governor's ability to control turbine speed.
.
for the Unit 2 TDAFWP 24 overspeed trip, the root cause was
o determined to be a condensate build up upstream of MOV-514 caused.
by an incorrect valve lineup combined with an inoperable'or i
degraded steam trap in the drain line for the steam admission
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line.
This caused a slug of water to enter the turbine and result in a turbine overspeed.
Contributing causes for these trips that affected both TDAFWPs l
o included:
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The use of MOV-514 as the steam admission valve in lieu of-
MOV-143. This. usage created a problem with the opening time
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coordination between MOV-514 and the ~ governor valve.
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i also. created addit'ional demands on the steam admission line-l drain system which could have resulted-in a condensate
buildup in this line.
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Excessive seat leakage past MOV-514 which~had the potential-l of reducing the governor control margin.
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(2)
The AIT ascertained that there were two TDAFWP trips that were
.;
attributed to an overspeed condition prior to the December 27, 1992, through February 3, 1993 events. One of these trips occurred on,
{
i TDAFWP 14 on June 11, 1990, and was attributed:to a low governor oil pressure that results when a turbine restart is attempted prior to
'f allowing the oil pressure to bleed off from the governor. The other
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trip occurred on TDAFWP 24 on September 16, 1991, and was' attributed.to I
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a mechanical overspeed trip.
Effective followup was not conducted to'-
determine the reason for this overspeed trip during the response time i
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test conducted prior to the first refueling outage.
Followup to correct
!
the problem with the sticking overspeed trip plunger ~was slow and considered to be less than adequate.
i (3)
The AIT concluded that the licensee's Preventative Maintenance' program l
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was being accomplished for the TDAFWPs. The AIT also concluded that the
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licensee had performed the proper corrective maint'enance on both unit's
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TDAFWPs, when the need for maintenance was identified 'However, it appeared that the corrective maintenance program was only correcting
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specific problems. The AIT~also noted that maintenance was not performing root cause analyses to assure that equipment re' liability L
,
problems were being pursued when identified. As a result,'it was
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evident that recurring problems were not being addressed.
It was-also-evident that these problems are not being pursued because they are not-l being entered into the corrective action system (as evidenced by'the
!
lack of issuance of SPRs).
[
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q With the exception of the undocumented control linkage adjustment i
activities that occurred on January 25 on the Unit 2 TDAFWP 24, the AIT
did not identify any other examples of such activities ~.
(4)
The AIT's ruiew of' the shut steam admission line drain. valves for the
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Unit 1 TDAFWP 14 indicated that these drain valves were not fully ~ closed i
as originally thought, but were instead partially open. The valves were
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not fully open, however, even though verified open, due to seizing of;
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the hand wheel bearings.
This situation caused the operators to conclude that the valves were fully open when, in actuality,. they.were
'
not. This bearing' seizure was caused by a lack of maintenance on these
,
valves even though an SR, written'in November 1992, identified the'hard
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working valves. The All concluded that the partially open condition of-
.these valves had.a negligible affect on the overspeed trip occurrences i
on TCAFWP 14.
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I (5)
The AIT concluded that the turbine casing drain valves were not blocked
'
and that the only blockage was in the turbine exhaust stack drain on the l
Unit 1 TDAFWP 14. The AIT noted that the most probable cause of the foreign material found in this drain was sand blasting material that was the result of sand blasting of the reactor containment buildings in the _
late 1989 to mid-1990 time frame. With respect to other safety-related i
i equipment, which could have been adversely affected by the particulate contamination, it appears that most equipment was not affected.
.
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However, the AIT did identify three historical examples of component failures which could be attributed to such contamination.
These examples, which included the TDAFWP 14 manual overspeed trip. lever, feedwater isolation valve hydraulic pump solenoid valve failures, and
,
,
the Unit 2 Steam Generator C PORV solenoid valve hydraulic fluid,
-
generally indicated a lack of rigorous pursuit by the licensee to l
determine the root causes and generic implications of the particulate I
contamination.
(6)
The AIT determined that the turbine speed control systems did not i
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operate as intended.
The licensee has committed that they will reset
'
the linkage using the appropriate vendors to assure that they are
!
properly set _and will verify that the linkage is adjusted correctly
_,
,
during subsequent turbine testing.
In addition, future adjustments to the turbine speed control system will be accomplished with the
assistance of appropriate vendors until necessary plant procedures are
verified as adequate and personnel are properly trained to make such adjustments.
,
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. (7)
The AIT determined that the leakage for MOV-514 was considerably above the manufacturer's acceptance criteria.
It was noted that the valves
.
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have been repaired so that they are within the proper acceptance criteria and that the licensee committed that plant operation will not
,
be conducted with degraded valves.
The AIT considered that this_ seat
,
leakage reduced the margin during the pump startup such that the
potential for the overspeed was increased.
.
(8)
The licensee's determination of the turbine's drain system capacity
>
indicates that the system is capable of keeping the steam admission line
~
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drained of condensate during normal conditions. The licensee also determined that a potential for a condensate buildup in this line, which_
i could exceed the capacity of the drain system, could occur if valve
.
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MOV-143 is closed for an activity, such as maintenance or for a
'
containment isolation, and the line is allcsed to cooldown.
To mitigate this condition, the licensee committed to revise procedures to assure
.
that such an evolution is properly controlled and that this condensate
buildup potential is considered.
j
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.
(9)
The license ^, PPT activities were found to be appropriate for the
,
maintenance tonaucted.
In general, the PMTs reviewed by the AIT were l
technically adequate and licensee personnel were technically
-
knowledgeable in their performance.
It was noted that PMTs did not i
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i identify applicable 5Rs which made it difficult 'to establish the criteria for determining 'postmaintenance operability.
,
s The AIT noted that the refueling outage (18-month) test had been performed three times.on Unit I and one time on Unit 2.
The AIT also noted, however, that-there was a wide variance.in the testing conditions
.
which could have masked turbine performance degradation.
The AIT.
I determined that only one of these five' tests was performed under actual
.(
normal standby conditions.
The licensee has committed to revise procedures to insure that all future testing is commenced with the -
TDAFWPs in their normal standby condition.
,
As the re.sult of these reviews, it appears that the Unit 1 TDAFWP 14'was?
[
in an inoperable condition since a return to power from the refueling
.;
outage that ended in December 1992.
.!
(10) The AIT reviewed the licensee's reactive corrective action plans and plant modification plans and found them to be appropriate. These plans
'
are listed in Sections 2.4 and-2.9 of this report, respectively.
The-i licensee has committed to complete these plans and modifications prior-
,
to taking the reactors critical.
.
.
(11)
In addition to the findings identified as the result of the charter-i driven inspection activities, the AIT noted the following other
!
weaknesses:
,
!
The team noted that the control room logs typically did not i
o identify mode changes, plant heatup or cooldown conditiort, and;
were inconsistent in their logging of test procedure initiation or j
completion.
]
The team also noticed examples of poor documentation of. work
'
o activities.
Examples were an absence of reasons for changes to.
procedures and surveillance data sheets that indicated anomalies-
. :
with no explanation for these anomalies.
]
As mentioned throughout this report, the team noted_that, with i
a perhaps one exception, no SPRs were written to identify previous
!
problems with this equipment.
This appears to be indicative of
- !
too high a threshold for the implementation of these reports.
A
>
failure. to write these reports prevents station problems from
being properly dispositioned for root cause determinations,
.
generic applicability, and appropriate corrective actions.
l 5 EXIT MEETING
-
An_ exit; meeting was held on February 11, 1993, with the personnel listed in Attachment A to diseminate the AIT's interim findings prior to the team's -
_r departure from the site. A member of the AIT returned-to the site and~
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i remained onsite for the period-of February 16-19, 1993, to observe TDAFWP
.
testing activities In addition, the site resident inspectors continued to.
observe TDAFWP testing after the team member's departure from the site.
A.
'
public exit meeting was held at the conclusion of the inspection on..
'
February 24, 1993, with the personnel listed in-Attachment B.
At this meeting-
.
'!
the team leader summarized the scope.and-findings.of this inspection as
_
,
delineated in 'this report.
The licensee did not identify'as proprietary.any
'
information used in the, performance of this inspection.
,
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n ATTACHMENT A
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' PERSONS CONTACTED
"The AIT contacted the following persons during this i.nspection.
In addition
to these personnel, the AIT contacted other licensee personnel during the
.,
inspection.
j HL&P
,
i M. Kanavos, Mechanical Engineering
M. Coughlin, Sr. Licensing Engineer i
W. Humble, Plant Engineering
L. Jones,-Plant Operator
D. Valley, Quality Assurance
.
J. Sharpe, Plant Maintenance Manager
E. Halpin, Manager, Technical Support
!
V. Starks, Design Engineer j
0. Leazar, Plant Engineering l
J. Johnson, Quality Assurance i
H. Stricklin, Quality Assurance
.!
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- R. Dally-Piggott,. Engineering Specialist, Licensing
- J. Robbins, Organizational Development Consultant l
- M. Coughlin, Senior Licensing Engineer
. - _
- D. Hall, Group Vice President, Nuclear
'!
- H. Pate, Senior Licensing Specialist
!
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- C. Keen, Construction Engineering Specialist, Licensing
.
- K. Christian, Manager, Plant Operations j
- W. Kinsey, Vice President, Nuclear Generation
'j
- G. Parkey, Plant Manager.
- T. Meinicke, Manager,. Planning Assessment i
- S. Rosen, Vice President, Nuclear Engineering
- W. Jump, Gereral Manager, Nuclear Licensing
- R. Graham, lead Instructor, Licensed Operator Training
--
- T. Jordan, General Manager, Nuclear Engineering
- D. Leazar, Manager, Plant Engineering
-
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- F. Rehkugler, Director, Quality Assurance
'
- M. Pacy, Design Engineering o
- W. Wagner, Manager, Professional Reactor Operators' Association
'
'
- M. Wisenburg, Assistant to Group Vice President
'
- C. Bowman, Administrator, Corrective Action
- F. Mallen, Manager, Planning & Assessment
'
- D..Wohleber, Director, RMS and Administration
!
- T. Underwood, Maintenance Manager t
- M. Chakravorty, Executive Director, NSRB
- D. Denver, General Manager, Nuclear Assurance
- L. Earls, Technical Services Representative j
- J. Soward, Manager, Nuclear Quality Control and Material Testing
- J.
Gruber, Manager, AFW Team.
.
- A. Harrison, Supervising Engineer, Nuclear Licensing
,
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- **S. Rosen, Vice President, Nuclear Engineering
!
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- S. Head, Deputy General Manager, Licensing i
- H.' Hernandez, Acting.ISEG Manager
- M. Kanavos, Manager, Mechanical / Nuclear Division
- C. Walker, Manager, Public Information i
i Woodward Governor Company
~'
R. Witt, Senior. Staff Engineer V. Hobbs, Company Representative H. Norman, Company Representative-
,
T. Johnson, Governor Foreman for Gerhardt's
,
r DRESSER-RAND i
C. Slater, Service Engineer B. Sweeny, Service Engineer E. Grandusky, Service Engineer
.[
B. Miller, Service Representative NRC
_,
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- A. Gautam,-Senior Operations Engineer, NRR
'
- J.-Boardman, Senior Reactor Systems Engineer, AE00
- M. Satorius, Project Engineer, Project Section D
-
- R. Evans, Resident Inspector ~
,
- J. Tapia, Senior' Resident Inspector
- A. Beach, Director, Division of. Reactor Projects
_
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- A. Howell, III, Deputy Director, Division of Reactor-Safety
- J.
Gilliland, Public Affairs Officer
,
Energy Services, Inc.
- J.. Richardson, Senior Vice President
[
Owners Group
- B. McLaughlin, Owners Representative, Central.Pcwer and Light Company
,
- T. Puckett, Owners Representative, Central Power and Light Company -
- M._ Hardt, Director, Nuclear Division, City Public Service of San Antonio
'
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Newman & Holtzinger
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- W.
Baer, Attorney Applied Radiological Controls
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- J.
Miller, Administrative Assistant
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- P. Salter, Pilot,'KSAT, Channel =12, San Antonio,. Texas j
- K. Gieske, Photographer, KSAT, Channel 12, San Antonio, Texas
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- J. Degollado, Reporter, KSAT,. Channel 12, San Antonio, Texas i
- Indicates personnel attending the February 11,:1993, exit meeting
2" Indicates personnel attending the February 24, 1993, exit meeting
- Indicates personnel attending both exit meetings
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02/05/93-15:56 P IO-US IRC FTS 728-8278
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UNITED STATES
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NUCLEAR' REGULATORY COMMISSION g-
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ATTACHMENT B j
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5-en avan ei.azA on ve. suite 4eo ARUtvGTON. TEXA5 76DM 8064 l
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FEB - 51993
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Docket 50-498
50-499
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License NPF-76 NPF-80 CAL 4-93-04
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Houston Lighting & Power Company ATTN: Donald P. Hall, Group
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Vice President, Nuclear
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P.O. Box 1700 Hour. ton, Texas 77251
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SUBJECT: CONFIRMATORY ACTION LETTER l
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Pursuant. to our telephone conversation un February 4,1993, i.t is our'
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understanding that South Texas Project. Units 1 and 2, will.not be'taken.
critical until you have' briefed the NRC' staff of the results of your efforts i
to correct the overspeed trip condition that is affecting the turbine-driven auxiliary feedwater pumps.
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Pursuant to Section 182 of the Atomic Energy Act, 42 U.S.C; 2232,- and -
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10 CFR 2.204, you-are required to notify me immediately if your understanding differs from that set forth above.
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Issuance of this Confirmatory Action Letter does not preclude issuance of an'
.i order formalizing the above commitments or requiring other actions on the part
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of the licensee. Nor does it preclude the NRC from taking enforcement action
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for violations of. NRC requirements that may have prompted the issuance ~ of this letter, in addition, failure to take the actions addressed in this Confirmatory Action Letter may result in enforcement action.
l The responses directed by this letter are not subject to the clearance.
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procedures of the Office of Management and Budget as required by the Paperwork-
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leduction Action of 1980, Pub. L. No.96-511.
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- CERTIFIED MAIL - RETURN RECEIPT REQUESTED
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02.'05'93-15:57 P 19 U3 NFC FT5 725-E278 032
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In accordance with 10 CFR 2.790 of the NRC's " Rules of Practice," a copy of.
this letter will be placed in the NRC Public Document Room.
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Sincerely,
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cc:
Houston Lighting & Power Company ATTH: William J. Jump, Manager Nuclear Licensing
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P.O. Box 289 Wadsworth, Texas 77483
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City of Austin
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Electric Utility Department i
ATTN:
J. C. Lanier/M. B. Lee
P.O. Box 1088 Austin, Texas-78757
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City Public Service Board ATTH:
R. J. Costello/M T. Hardt
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P.O. Box 1771 i
San Antonio, Texas 78296 l
Newman & Holtzinger, P. C.
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ATTN: Jack R. Newman', Esq.
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1615 L Street, NW l
Washington, D.C.
20036 t
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Central Power and Light Company
ATTN:
D. E. Ward /T. M. Puckett
P.O. Box 2121 Corpus Christi, Texas 78403 INPO Records Center
1100 circle 75 Parkway
- Atlanta, Georgia 30339-3064 l
Mr. Joseph M. Hendrie 50 Bellport Lane
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Bellport, New York 11713
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~ 02/05/93-15:57 P IU US tFC FTS 723-8278 003
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f-3-Bureau of Radiation Control State of Texas 1101 West 49th Street Austin, Texas 78756 Judge, Matagorda County Matagorda County Courthouse 1700 Seventh Street Bay City, Texas 77414
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Licensing Representative
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Houston Lighting & Power Company
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Suite 610 Three Metro Center Bethesda, Maryland 20814
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Houston Lighting & Power Company ATTN:
Rufus S. Scott, Associate
General Counsel P.O. Box 61867
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i Houston, Texas 77208 NRC Public Document Room Texas Radiation Control Program Director
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