ML20211E798
| ML20211E798 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 09/16/1997 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20211E787 | List: |
| References | |
| 50-369-97-16, 50-370-97-16, NUDOCS 9709300271 | |
| Download: ML20211E798 (9) | |
See also: IR 05000369/1997016
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U.S. NUCLEAR REGULATORY COMMISSION
REGION 11
Docket Nos.
50 369 and 50-370
License Nos.
NPF 9 and NPF-17
Report No:
50-369/97-16 and 50 370/97-16
Licensee:
Duke Energy Company
Facility:
McGuire Nuclear Station. Units 1 and 2
Location:
12700 Hagers Ferry Rd.
Huntersville, NC 28078
Dates:
July 12 - August 27, 1997
Inspectors:
M. Sykes, Acting Senior Resident inspector
M, Franovich, Resident inspector
Approved:
C. Ogle, Chief, Project Branch 1
Division of Reactor Projects
9709300271 970916
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Enclosure
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EXECUTIVE SUMMARY
McGuire Nuclear Station
NRC Inspection Report 50-369/97 16 and 50-370/97-16
This special inspection reviewed aspects of a problem involving inoperable
Unit 2 ice condenser lower inlet doors.
Enoineerina
The immediate corrective actions regarding the inoperable Unit 2 lower
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ice condenser doors were adecuate.
However, long-term corrective
actions for both Unit I and lnit 2 were not established.
An apparent violation was identified concerning the failure to comaly
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with Technical Specification requirements for the operability of t1e ice
condenser inlet doors on Unit 2 for an unknown period of time during
operation in Modes 1. 2, 3, and 4.
An apparent violation was identified concerning the failure to perform
adequate corrective actions in accordance with 10 CFR Part 50 Appendix B
Criterion XVI, in light of relevant industry operating experience at
another ice condenser facility and operational events at the McGuire
facility.
A preliminary review of industry experience and site-specific
operational events indicated that prior opportunities may have existtJ
to implement corrective actions to prevent the occurrence of the event
at the McGuire facility.
Enclosure
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Report Details
Summary of Plant Status
Unit 1 began the period at 100 percent rated thermal power.
On July 12.
power was reduced to approximately 95 percent to realign the number 3 turbine
stop valve to its normal position.
Unit 1 operated at 100 percent for the
remainder of the reporting period.
Unit 2 began the 3eriod in Mode 5 (cold shutdown) for a forced outage to
repair a failed 2) reactor coolant pump motor. While shutdown, the licensee
determined that 10 of 48 ice condenser lower inlet docrs were inoperable
because of upward ice condenser floor movement.
The licensee rep 61 red the
failed reactor coolant pump motor and the lower ice condenser inlet doors and
returned Unit 2 to power operations on July 22.
On August 4. power was
reduced to approximately 95 aercent to complete moderator temperature
coefficient measurements.
T1e unit was returned to 100 percent power on
August 5. where it continued to operate for the remainder of the reporting
period.
Review of Updated Final Safety Analvsis ReDort (UFSAR) Commitments
While performing inspections discussed in this report. the inspectors reviewed
+5 applicable portions of the UFSAR that were related to the areas inspected.
. e inspectors verified that the UFSAR wording was consistent with the
observed plant practices, procedures. and/or parameters.
III. ENALNURING
El
Conduct of Engineering
El.1
Inonerable Unit 2 Ice Condenser Lower Inlet Doors
a.
Inspection Stone (37551)
The inspectors reviewed the facts and circumstances related to a failure
to comply with Technical Specification requirements for the operability
of the Unit 2 ice condenser inlet doors.
On July 17. 1997, with the
unit in Mode 5 (cold shutdown) for a forced outage, the licensee
discovered that 10 of 48 lower inlet doors were inoperable for an
unknown period of time since the arevious Unit 2 refueling outage.
The
affected doors were mechanically )ound because the concrete floor raised
to the point where metal flashing interfered with the doors.
Prior to
restart of Unit 2. the inspectors reviewed the immediate corrective
actions initial root cause evaluations, and applicability of the
problem to Unit 1. The inspectors also reviewed station documents,
reviewed the UFSAR and design basis documents, and interviewed plant
personnel. On August 15. the licensee submitted licensee event report
(LER) 50 370/97-03 to address this event in accordance with the
requirements of 10 CFR 50.73.
Enclosure
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Observations and Findingi
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Ice Condenser System Desian
The ice condenser is a passive accident mitigation system that contains
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approximately 2.5 million pounds of borated ice.
Because the McGuire
containment has a low design pressure capability of approximately 15.0
psig, the ice condenser system condenses steam and sup3resses pressure
to ensure containment integrity during an accident.
T1e system, which
consists of ice contained within an array of approximately 1.940
baskets, has lower inlet. intermediate deck, and top deck doors that
allow passage of steam released from an accident.
Forty eight (48) lower inlet doors, which are contained in 24 bays (two
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doors per bay), are located in the lower compartment.
The inlet doors
will passively open when a differential pressure of approximately one
pound per square foot (PSF) exists between the lower containment and the
ice bed.
The design function of the lower inlet doors is to uniformly
open during a loss of coolant accident (LOCA) or steam line break in
containment 50 that the thermal energy released into the containment is
evenly absorbed by the borated ice.
These doors are adjacent to the ice
condenser floor structure.
In each bay, a thin layer of metal flashing
surrounds the bottom of the doors' frame and protects small bags of
insulation.
The ice condenser floor consists of a four inch wear slab layer of
concrete imbedded with glycol cooling coils.
The floor is cooled by one
of two floor cooling pumps that circulate glycol through the cooling
coils.
A protective layer of ice is normally on the floor.
Beneath the
wear slab is an insulation layer of foam-concrete. Combined, the floor
structure and the cooling system minimize heat entering the ice
condenser from the lower crane wall and equipment room; thereby
minimizing ice sublimation rates.
Secuence of Events
During a forced outage on July 12. several Unit 2 ice condenser inlet
doors actuated due to depressurization of upper containment when
personnel entered the containment through the upper airlock.
Through
visual ins)ection. Operations personnel discovered that one inlet door
was 12 incies open and another door was off its seat.
No ice melted
from the event: however. Operations declared the ice condenser
inoperable and a work order was developed to determine if a test of the
doors would be required prior to entry to Mode 4.
This condition was
reported to the NRC on July 12, 1997, in accordance with the reporting
requirements of 10 CFR 50.72.
On July 15. the licensee retracted the notification based on their
interpretation that a valid engineered safety feature actuation of the
lower inlet doors had not occurred since a substantial number of the
Enclosure
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- doors did not open.
On July 16. a retest of the doors was required when
maintenance personnel noticed abnormal conditions (i.e.. door bulging)
in the ice condenser.
On July 17, with Unit 2 still in Mode 5. the licensee determined that 10
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of 48 lower ice condenser inlet doors in eight of the 24 bays (two doors
per bay) were incapable of opening at a torque less than or equal to
that specified in Technical Specitications.
In Modes 1, 2. 3. and 4,
Technical Specification section 3/4.6.5.3.1 requires that the torque to
initially open each door be less than or equal to 675 inch pounds. The
inlet doors were tested per Station Procedure PT/0/A/4200/32. Periodic
Inspection of Ice Condenser Lower inlet Doors. and were found to require
more than the 15.5 lbs opening force limit (which correlates to the
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Technical Specification limit cue to the testing method).
Three of the
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5. 6, 8. quired at least 80 lbs of force to open. Inlet doors in bays 2.
doors re
and 19 through 22 were affected. On July 18. 1997, the licensee
reported this condition to the NRC in accordance with the requirements
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of 10 CFR 50.72.
The licensee's investigation revealed that the affected doors were
dragging on flashing between the floor and the bottom of the doors.
The
licensee attributed the door binding to upward movement of the floor
where the floor (wear slab) appeared to be raised by approximately 0.75
inches above its normal height. The licensee a ho discovered that ice
normally on the floor had disappeared and the floor cooling system was
degraded.
Immediate Corrective Act %n1
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Before restart of Unit 2 on July 21. 1997, immediate corrective actions
included a modification to remove a portion of the flashing that
interfered with the doors.
This left a minimum clearance of at least
2.25 inches in every bay between the floor and the remaining flashing.
occurred),perational data from Sequoyah (where a similar problem
Based on o
this modification should provide a sufficient gap under a
worst case floor movement for the remainder of the operating cycle.
The
licensee also performer' baseline measurements of the floor to monitor
future floor growth. A small amount of the bagged insulation that the
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flashing was protecting was also removed.
Removal of the insulation
increases ice sublimation rates: however, the licensee determined that
sufficient ice mass existed in the ice condenser for the remaining two
months in the fuel cycle.
The inspectors concluded that the 10 CFR 50.59 evaluation for the minor modification was adequate.
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Several of the Unit I lower ice condenser doors were examined by use of
a video camera that was lowered through the intermediate deck doors down
to the wear slab.- Video surveillance did not reveal deformation of-
flashing or concrete heave.
The inspector reviewed videos of both Unit
I and Unit 2 to verify the licensee's surveillance results.
Floor ice
and beam cooler frost were significantly present in the Unit 1 ice
condenser.
The licensee also reviewed historical ice basket data,
determining that Unit 1 did not have significant ice melt events
comparable to the Unit 2 events discussed below.
On August 19. the
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Enclosure
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system engineer informed the inspector that removal of the door frame
flashing on Unit I was placed on the Unit 1 forced outage list to be
performed at the next opportunity as testing warrants.
Anoarent Cause. Review of Industry Experience. and Operatinn Exoerience
Water intrusion, freezing, and expansion in the floor concrete coupled
with subsequent freeze and thaw cycles are the likely phenomena causing
the concrete to hea/e upward. The licensee identified several Unit 2
0)erational events and design attributes that may have contributed to
t7e problem. Two events in 1993 resulted in some of the ice melting.
The first event involved feedwater valve 2CF-130, where a maintenance
error caused high temperature and pressure feedwater to be released into
containment. The second event involved a loss of offsite )ower event
where reactor coolant was released into containment when t1e pressurizer
relief tank rupture disk ruptured.
In 1994, the licensee intentionally
performed an aggressive wall panel defrost in Unit 2 ice condenser bays
18 through 24 that may have also introduced water into the concrete
flooring. Additionally, the licensee postulated that the design of the
floor cooling system did not account for localized heat loads from the
On July 20, 1997, the licensee discovered that the performance of the
floor cooling system was degraded for some period of time following the
last Unit 2 refueling outage.
Video surveillance of Unit 2 revealed
that no ice was present on the concrete wear slab, and virtually no
frost was present on the beam cooler lines that remove residual heat.
Normally, a protective coat of at least 0.25 inches of ice is on the
floor and heavy frost is accumulated on the beam coolers.
The lack of
ice and frost on these components was a self-revealing condition
indicative of degraded floor cooling system performance.
Together,
these events may explain the concrete heave in the bays that were
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affected.
On July 29, the inspectors interviewed the ice condenser system
engineer.
The inspectors questioned the system engineer on past
corrective actions at McGuire to address a similar event that occurred
at the Sequoyah facility in 1992. Apparently. McGuire personnel in 1992
did not perceive that the floor problems at Sequoyah applied to McGuire
because:
(1) the concrete floor at Secuoyah was severely cracked and
the floor noved in multiple planes; anc (2) water intrusion at Sequoyah
was the result of intentional floor defrosting and floor cleaning
practices that were not performed at the McGuire facility.
The inspectors also asked if any baseline measurements of floor
dimensions or special efforts to monitor floor growth were established
in view of both the Sequoyah event and the ice melt events that had
occurred at McGuire since then.
No floor measurements had been taken,
nor was additional monitoring-established beyond the regular Technical
Specification required door surveillances that are performed once every
eighteen months.
In 1992, the licensee did examine the condition of the
wear slab and concluded that the cracking expe enced at Sequoyah was
not evident at McGuire.
The licensee also stated that, unlike what was
Enclosure
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experienced at Sequoyah. the current condition of the Unit 2 floor
indicates movement in a single slane. The inspectors noted that the
licensee did not determine if t7e Sequoyah floor cracking had exhibited
movement in a single plane before the severe cracking of the concrete
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occurred.
During the July 29 interview the system engineer informed the
inspectors that the setpoint for the temperature controlled glycol / floor
cooling flow valve had drifted from 12*F to 19'F.
The licensee believes
that this degradation aggravated the condition of the floor: however.
the licensee maintained that the ice on the floor did not melt.
The inspectors interviewed the instrumentation and controls (I&C)
engineer and ice condenser system engineer on the procedare usS1 to
calibrate the glycol bleed controller for floor cooling. The inspector
expressed concern that inadequate performance of the floor cooling
system may create a source of water (from ice normally on the floor)
that could be absorbed Dy the concrete. The 1&C engineer informed the
inspector that the system had never been calibrated and is run to-
failure.
The licensee also postulated that the floor ice had sublimated
away and did not melt as evidenced by boron residue on the floor.
However, the inspectors' examination of the video also revealed boron
residue streams near the floor drains. which may indicate that an ice
melt had occurred.
The inspectors also questioned if a mispositioned valve may have
inadvertently isolated glycol to the floor cooling coils during
maintenance and train swaps. Some plant drawings indicate that the idle
pump had its associated discharge valve normally closed.
Operations
responded that the train swap practice for the floor cooling system did
not require valve closure and the valves were not referenced in the
procedure for train swaps.
On August 19 the inspector identified information in the UFSAR
regarding the consequences of water on the floor of the ice condenser.
UFSAR section 6.2.2.1.3 states that ..the effects of water on the floor
and insulation [are) negligible."
The licensee initiated PIP-0M 97-
3070 to incorporate into the UFSAR industry and site-specific experience
regarding water intrusion and temperature swing effects,
Preliminary Review of Safety Sianificance
To evaluate the short-term containment res)onse, the licensee performed
special scoping loss of coolant accident ( 0CA) analyses using the
GOTHIC computer code to demonstrate that the ice condenser would have
)erformed its safety function during design basis accidents.
Up to 16
'
) locked doors were assumed for a range of pipe break sizes.
The results
demonstratedthatgeakcontainmentsteampressureswouldnotexceedthe
design pressure.
ihe inspector performed a preliminary review of LER
50-370/97-03 and noted to the licensee that an evaluation of post-
accident hydrogen (e.g.. degraded core, radiolysis of core and sump
water, corrosion of aluminum and zinc. etc.) nad not been performed.
/ccording to UFSAR section 6.2.7. 12 igniters are located in the ice
Encicsure
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condaser. The inspectors were concerned that blockage of tra lower
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inlet doors may impact the distribution of hydrogen in containment and
reduce the hydrogan mitigation systeT s effectiveness in preventing a
detc.nable concentration during an accident.
The licensee acknowledged
the inspector's concern.
C.
(onclusions
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The inspectors concluded that the licensee's immediate corrective
actions regarding the inoperable Unit 2 lower ice condenser doors were
adequate. At the end of the inspection period. long-term corrective
actions for both Unit I and Unit 2 were not established.
As a result of the degraded condition, two apparent violations were
identi fied.
The first apparent violation is related to a failure to
comply with iechnical Specification requirements for the operability of
^he ice condenser inlet doors on Unit 2 for an unknown period of time
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W rino o pratica in Modes 1. 2, 3. and 4.
This is identified as
cr;arent da),nion (EEI) 50 370/97-16-01. Failure to Comply With
Technical ipecificatieri Requirements for Ice Condenser Lower Inlet
Doors.
The second apparent violation is related to a failure to perform
adequate corrective actions in accordance with 10 CFR Part 50 Appendix B
Criterion XVI, in light of relevant industry operating experience at
another ice condenser facility and operational events at the McGuire
facility. A preliminary review of industry experience and site-specific
operational events indicates that prior opportunit.es may have existed
to implement :orrective actions to prevent the occurrence of the event
at the McGuwe facility. This is identified as EEI 50-370/97-16 02.
Failure to Implement Effective Corrective Actions to Prevent Ice
Condenser Lower Inlet Door Binding.
Enclosure
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Y. Management Heetinos
X1
Exit Heeting Summary
The inspectors 3 resented the inspection results to members of licensee
management at tie conclusion of the inspection on August 7.1997. The
licensee acknowledged the findings presented.
The inspectors asked the licensee whether any materials examined during
the inspection should be considered proprietary.
No proprietary
iaformation was identified.
On August 27. a phone exit was held between
the acting branch chief and the site vice president to inform the
licensee of the two apparent violations.
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Enclosure
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PARTIAL LIST OF PERSONS CONTACTED
Licensee
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Barron B.
Vice President. McGuire Nuclear Station
Cross, R.. Regulatory Compliance
Dolan. B.. Manager. Safety Assurance
Geddie. E., Manager. McGuire Nuclear Station
Herran. P.. Manager. Engineering
Cash. M., Manager. Regulatory Compliance
Thomas, K.. Superintendent. Work Control
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Travis. B. . Manager. Mechanical-Systems Engineering
Tuckman
M., Senior Vice President. Nuclear Duke Power Company
Spada. R.. System Engineer. McGuire Nuclear Station
Knost. J., System Engineer. McGuire Nuclear Station
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S. Shaeffer. Acting Chief. Branch 1. Division of Reactor Projects
M. Sykes. Acting Senior Resident Inspector. McGuire
M. Franovich. Resident Inspector. McGuire
INSPECTION PROCEDURES USED
IP 375S1:
Onsite Engineering
ITEMS OPENED CLOSED, AND DISCUSSED
OPENED
50 370/97-16-01
Failure to Comply With Technical
Specification Requirements for Ice
Condenser Lower Inlet Doors.
50-370/97-16 02
eel
Failure to Implement Effective Corrective
Actions to Prevent Ice Condenser Lower
Inlet Door Binding.
Enclosure
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