ML20133H739
| ML20133H739 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 01/09/1997 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20133H694 | List: |
| References | |
| 50-352-96-09, 50-352-96-9, 50-353-96-09, 50-353-96-9, NUDOCS 9701170274 | |
| Download: ML20133H739 (41) | |
See also: IR 05000352/1996009
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U.S. NUCLEAR REGULATORY COMMISSION
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REGION I
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License Nos.
NPF-85
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Report Nos.
96-09
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96-09
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Docket Nos.
50-352
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50-353
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Licensee:
PECO Energy
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Correspondence Control Desk
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P.O. Box 195
Wayne, PA 19087-0195
Facility Name:
Limerick Generating Station, Units 1 and 2
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Inspection Period:
October 22,1996 through December 16,1996
inspectors:
N. S. Perry, Senior Resident inspector
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F. P. Bonnett, Resident inspector
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F. J. Laughlin, Emergency Preparedness Specialist, DRS
N. T. McNamara, Emergency Preparedness Specialist, DRS
R. L. Nimitz, Senior Radiation Specialist, DRS
D. M. Silk, Senior Emergency Preparedness Specialist, DRS
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Approved by:
Walter J. Pasciak, Chief
Projects Branch 4
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9701170274 970109
ADOCK 05000352
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additional information obtained after the connector is replaced and the old one is
inspected for indications of other damage or problems (Section E8.1).
Plant Suncort
PECO Energy continued to maintain a strong Emergency Preparedness (EP) program.
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The Emergency Plan and emergency response procedures were current and
effectively implemented. The emergency action level table for radiological releases
was found to be somewhat confusing but easily clarified. The emergency response
facilities were well-maintained and operationally ready, Management control and
involvement was very good. One EP staff position was vacant, but was slated to
be filled. All emergency response organization (ERO) training was current and all
required drills had been completed. The 1995 EP program audit was acceptable in
that it met 10 CFR 50.54(t) requirements, but it provided no substantive feedback
to EP. There were very good mechanisms in place for problem identification and
resolution, including a well-defined self-assessment prograrn (Section P).
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Overall, applied radiological controls were good including planning and preparation
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for the outage (Section R1.1). Weaknesses were identified in the control of
radioactive sources (Section R1.3). The 10 CFR 20.2002 disposal area was found
to be generally consistent with information provided to the NRC. However, a
violation of 10 CFR 50.9, involving failure to provide complete and accurate
information to the NRC in an application for disposal of slightly contaminated
flowable solids, was identified. The flowable solids were placed on a 40,000
square foot (4 feet thick) concrete stab; and the April 6,1995, submittat did not
discuss or describe the presence of the concrete pad (Section R2.1).
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01.2 Unit 2 Scram and Start-uo
a.
Scone (71707)
Control room operators manually scrammed the Unit 2 reactor on December 6, due to an
EHC oil leak from the No. 2 TCV relayed emergency trip supply (RETS) pressure switch PS-
001202D. Plant management decided to enter an one week outage to repair a number of
plant discrepancies. Operators restarted the reactor on December 13. The inspectors
reviewed the events surrounding the scram, attended various meetings, and discussed the
event with key individuals. Further, the inspectors observed shutdown activities and
portions of the startup in the control room.
b.
Observations and Findinas
The operators demonstrated a good awareness of changing plant conditior.d when the
" Turbine Control Valve Fast Closure Trip" annunciator alarmed and a coincident EHC half
scram signal occurred in the control room at 11:20 p.m. The reactor operator (RO) noted
that all TCVs were open and that there were no changes in reactor plant or balance of
plant parameters. After unsuccessfully attempting to reset the half scram, the operators
suspected a blown circuit fuse, but also directed the equipment operator (EO) to assess
conditions at the EHC skid. The EO reported that EHC reservoir level had dropped to a
negative six inches (normal level zero inches) and was continuing to dron. The control
room supervisor (CRS) assessed that EHC conditions were deteriorating and directed the.
RO to insert a manual reactor scram at 11:38 p.m.
Operators responded to the scram well, entering the appropriate procedures and stabilizing
the reactor following the scram. Reactor !evel dropped to -25 inches which required entry
into Transient Response implementation Plan (TRIP) procedure T-101, Reactor Pressure -
Vessel Control. Reactor feed pumps (RFP) remained in service and feedwater flow was
more than adequate for operators to control reactor level. The EO isolated the affected
EHC header to the TCVs (isolating the leak), which allowed the ROs to cool down the plant
using the main turbine bypass valves. Operators placed the plant in a cold shutdown
condition on December 7.
System engineers and operators determined that the reactor protection system (RPS) had
responded appropriately, since the operators initially determined that plant parameters did
not support a half scram and suspected a blown fuse. The RETS pressure switch fell,
because its support bracket failed. This caused the 0.25 inch stainless steel tubing to the
pressure switch to fail. The pressure switch sensing low EHC pressure initiated the non-
resettable half scram signal to the RPS. The TCV did not close because the leak was small
enough to maintain sufficient oil pressure at the TCV servo's actuator disc dump valve to
prevent it from actuating.
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The TCV fast closure scram signal is generated from the RETS pressure switch that senses
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low RETS pressure at the TCV. The scram signal to RPS is an anticipatory signal to scram
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the reactor prior to a pressure and neutron flux transient that would result from a load
reject with or without bypass valves. Fast closure of the TCV is accomplished by the
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repositioning of the TCV actuator disc dump valve in the TCV se 'o redirecting actuating
oil back to the EHC reservoir.
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Control room operators maintained a professional atmosphere in the control room during
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the Unit 2 shutdown. The inspector observed the conduct and coordination of several
surveillance tests and maintenance activities being performed in the control room. The
CRS assured that the work was accomplished in an orderly fashion that did not disrupt the
conduct of operations cr cause other distractions,
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Unit 2 operators conducted the subsequent reactor startup well. The inspector observed
several shift briefings and noted that they were thorough and technically sound. Several
briefings focused on RO response to a short reactor reactivity period, which included three
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acceptable strategies for addressing the issue. Reactor ongineers were present throughout
the startup, providing assistance to the operators and monitoring core performance and
response. The reactor was made critical at 4:28 p.m. on December 13, and the generator
was synchronized to the grid on December 14,
c.
Conclusions
The inspector concluded that the operations staff response to the event, control of the unit
during the shutdown, and conduct during the startup were very good.
01.3 Unit 2 Drvwell Closeout inspection (71707)
On December 12, the inspector performed a pre-closeout inspection of the Unit 2 drywell
prior to the formal closcout inspection by plant management. The inspector verified that
materialin the drywell was properly stored, and that areas, where work had been
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performed, had been cleaned up as required. All areas inspected were found to be in good
condition, with no discrepancies identified.
O2
Operational Status of Facilities and Equipment
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O 2.1 Routine Plant Tours (71707)
The inspectors used Procedure 71707 to perform routine tours of the facility and also to
walk down accessible portions of the engineered safety feature (ESF) systems:
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Standby Liquid Control System - Unit 1
Primary Containment instrument Gas - Unit 2
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Drywell portion of Core Spray and Residual Heat Removal (RHR) Systems - Unit 2
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Emergency Diesel Generators (EDGs) - Unit 1 and 2
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Equipment operability, material condition, and housekeeping were acceptable in all cases
except for the EDGs (See Section M2.1). Several minor disciapancies were brought to
management's attention and were corrected. The inspectors identified no substantive
concerns as a result of these walkdowns.
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Report Details
Summarv of Plant Status
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Unit 1 began this inspection period operating at 100 percent power. The unit remained at
full power throughout the inspection period with exceptions for testing and the following
plant events.
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October 22
Power was reduced to 91 percent in response to a lube oilleak
at the main turbine front standard. The minor leak was from
the seal between the permanent magnet generator and front
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standard casing. Maintenance technicians repaired the leak
and reactor operators restored the unit to full power the same
day.
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November 16
Power was reduced to 60 percent to perform on-line
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maintenance on 63 hydraulic control units (HCU).
Maintenance activities were completed and the unit retumed to
full power on November 20.
Unit 2 began this inspection period operating at 100 percent power with the six*.h stage
feedwater heaters removed from service for end-of-cycle (EOC) coastdown operations.
Operators removed the fifth stage feedwater heaters from service on November 6, to
maintain full power operation. Operators manually scrammed the reactor on December 6,
in response to an electro-hydraulic control (EHC) oil leak at the No. 2 turbine control valve
(TCV). After completing a one week maintenance outage, operators restarted the reactor
on Decembsr 13. The unit was operating at 29 percent power when the period ended,
with plant personnel trying to identify the source of air in-leakage to the main condenser..
l. Operations
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Conduct of Operations'
01.1 General Comments (71707)
Using Inspection Procedure 71707, the inspectors conducted frequent reviews of ongoing
plant operations. In general, PECO Energy's conduct of operations wres professional and
safety-conscious. Operators conducted normal activities including shift turnovers and pre-
shift briefings well. Operators continued to demonstrate good communication skills and
control of several plant evolutions, including the Unit 1 on-line HCU maintenance and
removal of the fifth stage feedwater heaters at Unit 2. Operators responded well to
stabilize plant conditions following the Unit 1 power decrease on October 22, and the Unit
2 scram.
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' Topical headings such as 01, M8, etc., are used in accordance with the NRC standardized
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reactor inspection report outline. Individual reports are not expected to address all outline
topics.
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Quality Assurance in Operations
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07.1 Self-Assessment Activities (71707)
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During the inspection period, the inspectors reviewed or attended multiple self' assessment
activities, including.
the December 5, regularly scheduled Nuclear Review Board (NRB) meeting;
various Plant Operations Review Committee (PORC) meetings and meeting minutes;
the November 27, EDG Branch critique of the D-14 shutdcwn during its routine
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surveillance test to investigate an unusual vibration and noise;
various quality verification and independent safety engineering group reports.
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The NRB and PORC reviewed several activities related to safe station operation. PORC
scheduled several special meetings to discuss root causes and corrective actions for the
Unit 2 scram (see Section E1.2), and corrective actions necessary to implement, to achieve
compliance with the facility operating license regarding a safe shutdown fire (see Section
E1.3). The members of the NRB and PORC actively participated in the meeting with open
discussions on the plant issues while maintaining a focus on safety. The inspector
concluded that the self-assessment activities were effective.
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ll. Maintenance
M1
Conduct of Maintenance
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M 1.1 2A Core Sorav Trio Unit Replacement 62707
The inspector observed activities associated with the replacement of the Unit 2, A core v
spray trip unit. Instrumentation and control (l&C) technicians troubleshooting the 2A core
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spray trip unit were very knowledgeable and technically competent in accomplishing the
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activity. The l&C technicians were members of the Limerick Fix-It-Now (LFIN) team. The
technicians determined that the trip unit was intermittently causing a channel gross fail
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signal and replaced the trip unit.
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The technicians also identified several questionable ground connections that appeared
loose in back of the core spray logic panel. The technicians notified their supervisor who
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initiated an action request to have all cabinet ground connections tightened at a future time
because of system interaction concerns with other operable systems. The ground strip in
the cabinet affects signal common busses on the trip unit racks which could cause
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spurious loss of coolant accident (LOCA) signals in other emergency core cooling systems.
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Maintenance planning assessed that the existing ground connections were adequate and
would be addressed during the upcoming refueling outage.
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The LFIN performed the troubleshooting and trip unit replacement activities safely. A good
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questioning attitude was demonstrated by technicians.
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M1.2 Maintenance Outaae - Unit 2
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Scooe (62707)
As a result of the Unit 2 scram on December 6, plant management decided to implement a
week long maintenance outage. The scope of the outage was to repair the EHC leak,
replace leaking safety relief valves (SRV), repair other leaking valves located in the drywell,
and address seventeen main control room deficiencies. The inspectors reviewed and
observed activities throughout the outage.
b.
Observations and Findinas
Maintenance technicians executed repairs to all RETS pressure switches on all four TCVs.
The pressure switches were remounted on modified brackets and all stainless steel tubing
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to each pressure switch was replaced. Further, l&C technicians identified a possible failure
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of the flexible hoses connecting the EHC supply header to the TCV servo valves and these
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were replaced. The hoses displayed small bubbles under the outer layer of the hose
material. Subsequent testing at Valley Forge Laboratories determined that the hoses had
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not mechanically failed.
Due to excessive tailpipe temperatures on three SRVs, plant management directed that the
E, G, and H SRVs be replaced. Technicians performed the work well, using the appropriate
procedures and work orders. No discrepancies were noted.
Technicians discovered a substantial leak from the bearing cap of the 2A core spray
testable check valve, HV-052-2F006A. The valve is an inboard primary containment
boundary valve, but the leak did not affect downstream core spray piping. Operators
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assessed that the leak was a substantial contributor to the drywell leakage that had been
slowly increasing prior to the shutdown, and that the leak did not affect the valve's
operability. Technicians replaced the bearing cap gasket which stopped the leak. This
was determined during various drywell walkdowns during the performance of the reactor
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pressure vessel hydrostatic test on December 11. Engineers determined that localleak rate
testing was not required for the repair because the valve internals were not disturbed.
Several other activities were accomplished during the outage including, repair of the 2C
RFP casing drain leaks, replacement of clogged drywell unit cooler condensate flow
elements, and replacement of a degraded circulating water pump expansion joint. The
inspector observed these activities and had no concerns.
c.
Conclusions
The inspector concluded that the maintenance outage at Unit 2 was conducted very well.
Many work activities were safely and successfully completed without incident.
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The inspector noted that foreign material exclusion (FME) measures were adequate, but
questioned the implementation of FME controls during short breaks. The inspector
identified that the upper crankcase or fittings were not covered. These concerns were
immediately addressed by the maintenance personnel. The Maintenance Director informed
the inspector that measures are being established to implement FME controls consistently
during diesel outages.
The D24 EDG failed to shut down during a post-maintenance break-in run. The EO
identified a fuel oilleak at the No.10 cylinder and attempted to shut down the EDG using
the emergency stop pushbutton located on the diesel. l&C technicians identified a faulty
contact on the engine trouble shutdown relay that energizes the shutdown relay. The
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control room supervisor (CRS) determined that the failed engine trouble shutdown relay
was e achnical specification (TS) required component; however, the EDG was currently
inoperable for the outage. The system manager initiated a troubleshooting control form to
test the other engine trouble shutdown relays and verified their operability on the remaining
seven EDGs.
The Woodward governor replacement went well. The governor was replaced to address a
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speed oscillation problem. Control room operators had observed some hunting and speed
oscillations during normal operations when D24 was carrying the bus and isolated from the
grid. Attempts to tune the governor had not been successful in resolving this problem.
Following the governor replacement, l&C technicians and the system manager tuned the
new governor. The inspector observed the activities, which were well controlled. A
special test was written to demonstrate proper operation of the governor in both the droop
and isochronous modes of operation. The inspector reviewed the procedure and safety
evaluation (10 CFR 50.59) and had no concerns. The system manager successfully
directed the test from she control room, but noticed that the hunting problem had not been
completely resolved.
During the Unit 2 maintenance outage, the CRS removed the D24 EDG from service for
maintenance technicians and the system manager to further investigate the governor
hunting. A knuckle in the linkage arm between the governor unit and engine demonstrated
excessive freedom of movement, approximately 3-4 mils. This fitting is required to be
tight. The loose knuckle introduced a delay in engine response to changes in spaed
causing the governor to overreact to frequency changes. This loose knuckle was replaced.
The D24 EDG performed well during the post-maintenance surveillance test. The D24 EDG
was extensively tested during the performance of ST-1-092-114-2, D24 Diesel Generator
4KV Safeguards Loss of Power Logic System Function Test. The inspector observed the
entire test which demonstrated the EDG's ability to start upon either or both Loss of
Offsite Power (LOOP) and Loss of Coolant Accident (LOCA) signals. Further, the test
demonstrated the EDG's ability to continue running after a complete load shed and the loss
of the largest post-LOCA load (RHR pump).
The inspector observed that no hunting or oscillations occurred during the test, during
parallelling operations with offsite power, or during various generator loading conditions.
The system manager directing the surveillance test maintained good control, as well as the
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M1.3 Hydraulic Control Unit On-line Maintenance - Unit 1
a.
Insoection Scoce (62707)
PECO Energy's Nuclear Maintenance Division (NMD) performed an on-line maintenance
outage on selected Unit 1 hydraulic control units (HCUs) beginning on November 16. The
maintenance focused on rebuilding or replacing various HCU components including the
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scram pilot valves and the inlet and outlet scram valve diaphragms. Maintenance
technicians used maintenance procedure M-047-027, rev. 6, Preventive Maintenance for
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HCUs, throughout the activities. NMD technicians rebuilt 63 HCUs over a four day period,
completing the activity on November 20. The inspector observed the activities performed
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at the HCUs.
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b.
Observations and Findinas
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Work Activities were planned, coordinated, and exe= ted well between the Operations and
NMD Departments, and the reactor engineering staff. Operators and reactor engineers
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performed a large number of control rod manipulations without error. Further, NMD
personnel performed clearance and tagging responsibilities, maintenance activities, and
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HCU restoration without error. Following HCU restoration, operators performed scram time
testing to verify the control rod's operability. No discrepancies were identified.
During the maintenance activities, NMD technicians identified two degraded components
on two different HCUs. A scram valve position limit switch which indicates valve position
in the control room and a broken terminal board were replaced. The inspector observed
that the technicians exercised caution and appropriate controls during the repairs.
Radiological controls were noted to be very good.
c.
Conclusion
NMD had established good control and oversight of the work activities. Technicians and
operators completed the activity without error or challenge to safe plant operations.
M1.4 D-24 Diesel Overhaul and Testina
a.
Scoce (62707)
From November 18 through 24, maintenance personnel performed the 18 month
inspection, testing and general maintenance on the D24 EDG. The scope of the outage
included the replacement of the Woodward governor. The inspectors observed portions of
the maintenance work and post-maintenance testing, including special test SP-173, D24
Diesel Generator Governor Test and ST-1-092-114-2, D24 Diesel Generator 4KV
Safeguards Loss of Power Logic System Function Test.
b.
Observations and Findinas
The maintenance technicians performed the outage well. The inspector observed that
work activities were well controlled, with improved housekeeping practices implemented.
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coritrol room staff that coordinated the various sections of the test to prevent disruptions
in the control room.
c.
Conclusions
The inspectors concluded that the Limerick staff performed the 18 month inspection and
maintenance of the D24 EDG well. Improved housekeeping practices during the outage
were observed, but FME controls although adequate, need to be improved. The persistent
effort of plant personnel to identify the cause and correct the oscillation problem was
notable. The operations and technical staffs' performance of the LOOP /LOCA surveillance
test was very good.
M1.5 General Comments on Surveillance Activities (61726)
The inspectors observed selected surveillance tests to determine whether approved
procedures were in use, details were adequate, test instrumentation was properly
calibrated and used, technical specifications were satisfied, testing was performed by
knowledgeable personnel, and test results satisfied acceptance criteria or were properly
dispositioned.
The inspectors observed portions of the following surveillance activities:
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D14 and D24 overspeed tests
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various EDG monthly tests
Unit 2 control rod scram timing
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D24 special test (SP)-173
Unit 1 standby liquid control pump, valve and flow test
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D24 loss of power logic system function test
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Unit 1 reactor core injection cooling quarterly test
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security system static inverter test
Observed surveillance tests were conducted well using approved procedures,and were
completed with satisfactory results. Communications between the various work and
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support groups were good, and supervisor oversight was good.
M2
Maintenance and Material Condition of Facilities and Equipment
M2.1 Emeraency Diesel Generator Material Condition
a.
Scope (62707)
During this inspection period, the inspectors conducted thorough walkdowns of all eight
EDGs. The inspectors observed the general conditions of the EDGs and verified that no
conditions existed which would adversely affect the operation of the EDGs, or cause it to
be inoperable.