IR 05000413/1998006
| ML20236Q669 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 06/05/1998 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20236Q665 | List: |
| References | |
| 50-413-98-06, 50-413-98-6, 50-414-98-06, 50-414-98-6, FACA, NUDOCS 9807200400 | |
| Download: ML20236Q669 (45) | |
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- jA 42 9'o, NUCLEAR REGULATORY COMMISSION
UNITED STATES
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%
REGION il
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$
$
ATLANTA FEDERAL CENTER
g 61 FORSYTH STREET. SW. SUITE 23 TBS
%
ATLANTA GEORGIA 30303-3415
U.S. NUCLEAR REGULATORY COMMISSION
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REGION 11
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AUGMENTED INSPECTION TEAM (AIT) REPORT
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Docket Nos:
50-413. 50-414 e
License Nos:
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t Report Nos.:
50-413/98-06. 50-414/98-06
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Licensee:
Duke Energy Corporation l
Facility:
Catawba Nuclear Station. Units 1 and 2 Location:
4800 Concord Road York. SC 29745 Dates:
May 11 - May 15. 1998 Team Leader:
K. Landis. Chief. Engineering Branch.
Division of Reactor Safety (DRS) Region II (RII)
Inspectors:
R. Moore. Reactor Inspector. DRS M. Sykes. Resident Inspector. McGuire
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P. Tam ~. Project Mana er. NRt r
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Approved by:
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8 f[
w Divisiono(fReact ohns'P. J Jdon, ector Datb Signed Safety 9007200400 900605
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PDR ADOCK 05000413 g
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SUMMARY Catawba Nuclear Station.. Units 1 and 2 NRC Inspection Report 50-413/98-06. 50-414/98-06 The Augmented-Inspection Team (AIT) reviewed the facts surrounding an event associated with degradation of the Catawba Nuclear Station (CNS) Unit 1 auxiliary feedwater (AFW) system during a rapid down-power on May 7,1998, the licensee's response to the event and licensee's event review and recovery.
In addition, the AIT' assessed generic aspects of the event to evaluate applicability to other units.
The report covers a one-week period of reactive inspec. tion by a team leader, one resident inspector, one regional inspector and a project manager from the NRC Office for Nuclear Reactor Regulation
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(NRR).
Prior to the event on May 7.1998. Catawba Nuclear Station (CNS) Units 1 and 2 I
were operating at 100 percent power.
Unit 2 was unaffected by this event.
Operators were in the process of rapidly reducing Unit 1 power following identification of an instrument air leak affecting main feedwater regulating valve ICF55. The licensee was reducing power at 25 percent / hour to approximately 30 percent power to facilitate realignment of main feedwater-flow through the affected steam generator auxiliary feedwater nozzle.
Along with the lowering of reactor power. reduced feedwater flow was passing through the condensate booster pump. Consequently, in order to maintain minimum condensate booster pump flow valve 1-CM-127 opened providing recirculation flow to the upper surge tank (UST) dome. The setpoint for the controller for valve 1-CM-127 was improperly set to approximately 14.000 gallons per minute (gpm) instead of the required 5.500 gpm. This allowed excessive heating of the UST to a peak temperature of 234 degrees F. which was well beyond the design limit for the suction to the AFW pump of 138 degrees F.
The UST is the preferred source to supply water to the suction of the AFW pumps upon automatic initiation of the AFW system.
Consequently, the AFW system was declared inoperable until the temperature of the UST was returned to within design basis, and the effects of the high temperature were evaluated.
Details of the event are further discussed in the report details and in the Sequence of Events. Attachment 2.
Doerations The combination of emergency procedures abnormal procedures, and
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Operations Technical Memorandum 97-01 provided sufficient instructions
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to the operators to maintain adequate water supply to the auxiliary feedwater pumps and thereby maintain adequate Net Positive Suction Head
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(NPSH) while preventing steam binding of the auxiliary feedwater pumps.
(Section 03.1)
Operating procedures and instructions were inadequate. in that they did
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not provide specific guidance: for operation of the digital controller:
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unplanned and unexpected condensate booster pump high recirculation flow rate to the upper surge tank; and for response to upper surge tank high temperature alarms and their effect on AFW pump operability. (Section 03.1)
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.2 not complete a timely evaluation of station procedures and subsequent procedure revisions.
(Section 03.1)
Insufficient operator and engineering staff training resulted in I
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insufficient knowledge level relative to operation of the digital controller for the condensate booster pump recirculation valve (1-CM-127). auxiliary feedwater pump suction temperature design limits and operator actions required to identify, correct, and mitigate the consequences of the unplanned and unexpected condensate booster pump high. recirculation flow rate to the' Upper Surge Tank.
The resulting il Upper Surge Tank high temperature condition caused the auxiliary feedwater system to be inoperable for approximately three hours.
(Section 04.1)
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Licensee interim and planned actions were prudent to' reduce the probability of operating with suction supply temperature outside the auxiliary feedwater system design basis. Guidance was adequate to aid operators in evaluating future similar events.
(Section 04 2)
The AIT concluded that this particular arrangement of condensate storage
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tanks used as a preferred supply for auxiliary feedwater was unique to the Duke Energy facilities.
The controls established at the McGuire and
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Oconee facilities were effective in preventing similar UST over-temperature events. The configuration of the condensate storage systems at the Oconee and McGuire Duke facilities was adequate to preclude similar UST over-temperature events.
(Section 07.1)
The Plant Operations Review Committee (PORC) had difficulty identifying
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the regulatory requirements involving non. safety and safety system interactions which were necessary to evaluate AFW system operability accurately. The AIT noted that the PORC acted as a problem-solving group and was not entirely effective at functioning in an independent oversight role during evaluations of AFW system operability following the May 7. 1998. upper surge tank over-temperature event. (Section 08.1)
The PORC reached an appropriate consensus on the sco)e and content of
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the AFW system operability evaluation and accepted t1e AFW operability determination with_the recommended compensatory actions.
(Section 08.1)
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Enaineerina
_The licensee's engineering analysis of the elevated tem)erature impact-
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on AFW pump operations was effective and demonstrated t1at the AFW aumps would have operated, sup) lying water to the steam generators with tie i
elevated upper surge tant temperatures experienced on May 7, 1998.
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Conditions did not reach'a point for steam vapor flashing to occur in l
the AFW aumas. Adequate NPSH was available at the swap over initiation point, w1ici changes the suction water supply to the assured water
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(Section El.1)
The licensee performed stress analysis on the piping and tanks exposed
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to elevated temperature. which was above the design specification values. The preliminary results indicated the code s)ecified stress tolerances were not exceeded. A system walkdown by tie team identified no visible indications of water hammer or temperature-induced stress
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damage to the piping or tanks.
(Section E1.2)
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l The licensee performed stress analysis on the piping and tanks exposed
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to elevated temperature, which was above the design specification l
values.
The preliminary results indicated the code s)ecified stress tolerances were not exceeded. A system walkdown by tie team identified
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l no visible indications of water hammer or temperature-induced stress l
damage to the piping.or tanks.
(Section El.2)
The licensee's analysis of potential safety /non-safety interactions for l
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auxiliary feedwater supply sources adequately identified potential
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mechanisms for increasing source temperatures above the value used in
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licensing basis accident analyses. Appropriate recommendations were provided to preclude an inadvertent auxiliary feedwater supply source temperature increase above the design basis limit of 138 degrees F.
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l The team concluded that, although there were limited UFSAR references to
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the AFW system temperature assumptions. the UFSAR description was adequate as indicated by secondary references in the alarm response procedure and design basis document. The licensee initiated an action item to assess the impact of the elevated AFW temperature on UFSAR accident analyses.
(Section E1.4)
The licensee initiated a Significant Event Investigation Team (SEIT) and
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performed a detailed and thorough root cause analysis of the May 7 1998. UST high temperature event. The team reviewed the SEIT findings and recommendations and assessed them to be candid probing. and
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conservative (Section E4.1)
Insufficient Trending of the high maintenance requirements on valve CM-
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127 and the Problem Investigation Process (PIP) forms which involve the upper surge tank or CH-127 resulted in the failure to detect the potential adverse conditions and system interactions between the AFW and Condensate systems.
(Section E4.1)
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Root cause determinations for several previous occurrences of high upper
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surge tank overheating, which had occurred since January 20. 1996. were inadequate and resulted in ineffective corrective actions.(Section E4.1)
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Relative to the prbviout UST high temperature events. the engineering
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staff demonstrated a poor questioning attitude and a lack of rigor in the performance of two 10 CFR 50.59 safety evaluations (July 1996 and I
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August 1997). root cause evaluations and the determination of corrective actions.
This resulted in the engineering staff failing to recognize the safety system (AFW) and non-safety system (condensate) interactions and the impact of those interactions on AFW system operability.
(Section E4.2)
Following the May 7, 1998. UST high temperature event. the licensee's
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l 10 CFR 50.59 safety evaluation was adequate for the isolation of CM-127.
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(Section E4.2)
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The actual safety significance of the Upper Surge Tank high temperature
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event was minor in that 1) the auxiliary feedwater system was inoperable for a relatively short time (approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />), 2) the auxiliary feedwater system was not called upon to perform its intended safety function, and 3) during the time of inoperability. the auxiliary feedwater pumps remained functional but degraded (still available to provide water to the steam generators (S/Gs). There was a reduced heat removal capacity for the auxiliary feedwater system during this event.
(Section E8.1)
i The regulatory significance of the Upper Surge Tank high temperature
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event was high prompting the initiation of an AIT because a safety-
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related system designed to mitigate the consequences of an accident was
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rendered inoperable by the mispositioning of a single non-safety related component, 1-CM-127.
The licensee has taken appropriate actions to provide reasonable assurance that this event will not recur in the future.
(Section E8.1)
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Reoort Details Auomented Insoection Team (AIT) Charter On May 11. 1998, an Augmented Inspection Team (AIT) was established to inspect and assess the Condensate / Auxiliary Feedwater (AFW) event of May 7. 1998, at Catawba Nuclear Station. Unit 1.
The basis for the formation of the AIT was the significant and unexplained interaction during a rapid down-power between the non-safety related condensate system and the safety-related auxiliary feedwater system, which resulted in the licensee declaring all three AFW pumps inoperable. The Augmented Inspection Team Charter Memoran im. (with Attachment) is included as Attachment 1 of this inspection report.
Summary of Plant Status and Event s
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Prior to the event on May 7, 1998. Catawba Nuclear Station (CNS). Units 1 and 2. were operating at 100 percent power.
Unit 2 was unaffected by this event.
Operators were in the process of rapidly reducing Unit 1 power following identification of an instrument air leak affecting main feedwater regulating valve ICF55. The licensee was reducing power at 25 percent / hour to approximately 30 percent power to facilitate realignment of main feedwater flow through the affected steam generator auxiliary feedwater nozzle. Along with the lowering of reactor power, reduced feedwater flow was passing through the condensate booster pump.
Consequently, in order to maintain minimum condensate booster pump flow. valve 1-CM-127 opened providing recirculation flow to the upper surge tank (UST) dome. The setpoint for the controller for valve 1-CM-127 was improperly set to approximately 14.000 gallons per minute (gpm) instead of the required 5.500 gpm.
This resulted in excessive flow and heating of the UST. when reached a peak temperature of 234 degrees F. which was well above the design limit for the suction to the AFW pump of 138 degrees F.
The UST is the preferred source to supply water to the suction of the AFW pumps upon automatic initiation of the AFW system. Consequently, the AFW system was declared inoperable until the temperature of the UST was
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returned to a point at or below design basis and the effects of the high temperature were evaluated.
Details of the event are further discussed in the report details and in the Sequence of Events. Attachment 2.
Three Catawba System Diagrams are provided for information in Attachment 3.
A trend graph of the UST and CST temperatures during this event is provided in Attachment 4.
Simulator pictures of the CM-127 digital controller are provided in Attachment 5:
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Secuence of Events
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The AIT charter required the team to develop a sequence of events associated with the specific event of concern. The AIT developed the se based on information gathered from Catawba control room logs,quence of events strip charts.
computer logs. Problem Investigation Process (PIP) forms, data printouts.
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interviews with personnel involved with the event, and from review of the licensee-generated sequence of events.
Some of the times associated with events are best approximations. The Sequence of Events is Attachment 2 of this report.
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Conduct of Operations (93800)
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l 01.1 System Descriptions l-The following is an abbreviated system description of the Condensate and-Auxiliary Feedwater Systems. The Unit 1 Condensate Storage System provides a readily available source of deaerated condensate for makeup
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to the condenser and is the preferred (although not the safety related)
source of auxiliary feedwater for makeup to the steam generators.
' Makeup to the condensate storage system is supplied to the upper surge
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tank dome from the Makeup Demineralized Water System (YM).
The upper
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I surge tank dome drains to the two upper surge tanks. Makeup to the.
condenser is su) plied by gravity. flow from the upper surge tanks.
Overflow from t1e u)per surge tanks is returned to the condensate-storage tank and subsequently pumped back to the upper surge tank dome.
The preferred sources of auxiliary feedwater supply are the upper surge tank (85.000 gallons) and the main condenser hotwell (170.000 gallons)
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on each unit.
These condensate storage tanks are not safety related.
The assured (safety related) water source for the auxiliary feedwater system is provided by the Nuclear Service Water System. Alarms are provided in the control room for high and low upper surge tank and condensate storage tank level. A summary composite flow diagram of the Condensate System is included as Attachment 3 to this report.
Operations Procedures and Documentation (93800)
03.1 _Adecuacy of-Procedures and Instructions a.
Insoection Scooe The AIT reviewed the adequacy of arocedures implemented in response to the initial high temperature in t1e upper surge tank and assessed the emergency and operating procedures actions related to steam binding of the AFW pumps. The AIT interviewed personnel and documents related to
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the upper surge tank over-temperature event, which occurred on May 7.
1998.. The documentation consisted of Operations Procedures (ops APs.
and EPs). Operations Logbooks, and 0)erator Aid Computer (0AC) point
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trends. The team also interviewed t7e Operations Shift Manager on-duty at the time of the event.
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Observations and Findinas
- The AIT reviewed Catawba Operations Procedures OP/1/A/6250/001.
" CONDENSATE AND FEEDWATER" Rev 118. and OP/1/A/6250/002 ' AUXILIARY
.FEEDWATER SYSTEM" Rev 100. that were in effect at the time of the UST overtemperature event. These system operating procedures did not discuss the 138 degrees F limit on the suction source water temperature
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to AFW and did not provide detailed instructions on the operation of the l
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digital controller for the condensate booster pump minimum flow
recirculation valve 1-CM-127 and the bumpless transfer characteristic
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controller.
Additional discussions with training personnel and reviews of applicable condensate and feedwater lessons plans revealed that the operator training did not provide specific guidance on the unique controller characteristics. During interviews with control room operators, the AIT confirmed that the specific operating characteristics of the digital controller had not been incorporated into operations training.
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t The AIT reviewed alarm response guidelines for 0AC alarm point CIA 0510 UST 'A' WTR TEMP HI and HI-HI.
The alarms were set at 130 and 134 degrees F. respectively.
The operator instructions were:
ALARM GUIDANCE HI:
Verify manual loader for the affected upper surge is set per OP/0/B/6250/07A (Auxiliary Steam System Alignment)
Ensure temperature control valve is controlling proper UST temperature HI-HI:
Notify Control Room SR0 Contact Condensate Storage System Engineer Contact Auxiliary Feedwater System Engineer to Determine Auxiliary feedwater system operability based on temperature of suction source
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The alarm response-guidelines did not included instructions to operators to check condensate booster pump minimum flow to the UST as a potential cause for the elevated UST temperature.
The AIT also reviewed several Catawba Emergency Procedures (EPs) and determined that the procedures did not include NOTES or CAUTIONS that addressed elevated auxiliary feedwater system suction sources.
The AIT presented this finding to licensee management since elevated suction source temperatures could potentially impact auxiliary feedwater system operation.
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4 The AIT also reviewed-instructions provided to operating shifts as a -
result of previously identified auxiliary feedwater system operability concerns. The licensee had developed Operations Technical Memorandum l
97-01, dated May 15. 1997, which addressed an automatic or manual actuation of the auxiliary feedwater system. The memorandum directed l
operators to enter AP/1/A/5500/06. LOSS OF S/G FEEDWATER. to maintain auxiliary.feedwater system operability. This abnormal procedure directed the operators to ensure that the AFW system realigned to the
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assured safety related source (Nuclear Service Water System) to maintain adequate NPSH to the auxiliary feedwater pumps.. The guidance provided in Operations Technical Memorandum 97-01 was adequate and had received senior licensee level ' approval from the Superintendent of Operations and the Station Manager.
Tie combination of E3s,'APs. and Operations l
Technical Memorandum 97-01 were adequate to maintain NPSH and prevent steam binding of the auxiliary feedwater pumps. Operations Technical Memorandum 97-01 was used to com)ensate for an inadequate procedure in-lieu of performing a procedure c1ange. Additionally, needed revision of AP/1/A/5500/06. LOSS OF S/G FEEDWATER. had been untimely, in that the revision was not completed at the time of this inspection which.was approximately one. year after issuance of Operations Technical Memorandum 97-01.
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Conclusion The combination of emergency procedures, abnormal procedures, and Operations Technical Memorandum.97-01 provided sufficient instructions to the operators to maintain adequate water supply to the auxiliary feedwater pumps and thereby maintain adequate Net Positive Suction Head (NPSH) while preventing steam binding of the auxiliary feedwater pumps.
Operating procedures and instructions were inadequate, in that they did not provide specific guidance: for operation of the digital controller:
for identifying. correcting, and mitigating the consequences of the unplanned ~and unexpected condensate booster pump high recirculation flow rate to the upper surge tank: and for response to upper surge tank high temperature alarms and their effect on AFW pump operability.
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Operations Technical Memorandum 97-01 was used to compensate for j
inadequate procedures instead of revising the procedures.
The licensee
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did not complete a timely evaluation of station procedures and
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subsequent procedure revisions.
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Operator Knowledge and Performance (93800)
04.1 Doerator Performance Durina the Event a.
Insoection Scone The AIT reviewed operator logs, licensee interviews, computer logs, and maintenance work orders and developed a sequence of events for the upper surge tank over-temperature event.
In addition the AIT conducted
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interviews with the Operations Shift Manager who was on shift during the
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Observations a d Findinas On April 17. 1998. Operations issued what is commonly called a clearance or tagout and at CNS is called a Removal and Restoration (R&R).
The purpose of R&R 18-754 was to investigate high condensate system dissolved oxygen content. The R&R included placing the controller for vahe 1-CM-127 in the manual control mode with the valve closed.
Following completion of the investigation into the dissolved oxygen content, the controller was returned to the automatic control mode and the valve remained closed.
No specific instructions were included in
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the R&R to verify proper valve automatic setpoint.
The R&R indicated that the final valve position was automatic control and closed.
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information was noted as to the as-left setpoint.
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l On May 7.1998. 03erators were reducing power at approximately 25%/hr in accordance with A3/1/A/5500/009. Rapid Downpower, to repair an instrument air leak at feedwater regulating valve KF55. After securing the 'A' main feedwater pump the Operator Aid Cower point for UST A WTR TEMP HI and HI-HI came into alarm.
Due to numerous other alarms resulting from the rapidly changing plant conditions and the lack of knowledge of the importance of maintaining UST temperature less than 138 degrees F. the operator at the controls decided to delay the detailed evaluation of this alarm until the rapid down power was completed.
l Prior to reactor power being stabilized, an extra reactor operator referred to the alarm response guidelines to identify a potential cause for the unexpected alarm. The alarm response directed operators to verify auxiliary steam supply valves closed to the upper surge tank.
Operators confirmed auxiliary steam valve positions and continued the downpower evolution. The alarm response guideline did not provide any specific operator instructions to check condensate inputs as a potential heat source for Unit 1 Upper Surge Tank. The procedure in use.
AP/1/A/5500/09. Rapid Downpower did not address elevated auxiliary feedwater suction source temperatures.
Elevated Condensate Storage System temperatures were not identified as concerns in any of the Catawba Emergency. Abnormal or Operating procedures.
Indications of
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level fluctuations were also noted during this evolution in both the
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. main condenser hotwell and upper surge tank. A reactor operator was
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l dispatched to' check local UST and CST level indications. The operator
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contacted the control room noting that the steam was being released to l _
the turbine building basement from the CST vent line and confirmed that the local level indications were erratic.
The reactor operator returned to the control room and investigated l
actual UST and CST temperature information using the OAC point.
The OAC
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indicated that UST and CST temperatures were near 200 degrees F and rising. The operators checked additional control room indications and identified that the controller for valve 1-CM-127 the condensate booster
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pump minimum flow recirculation valve was set at approximately 14.000 gpm. The operator referred to the similar controller for Unit 2 which indicated a setpoint of 5.500 gpm.
Operators contacted engin7ering and
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checked operating procedures to determine if the setpoint had been revised. No revisions were identified.
Per the direction of the OSM.
the 1C condensate booster pump was secured to reduce condensate L
pressure / flow and makeup demineralized water was added to the UST.
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'C' heater drain tank pumps were also secured.
Operators noticed valve 1-CM-127 was. closing.
Engineering confirmed that the accurate controller setpoint was 5.500 gpm. Operators adjusted the setpoint to
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5.500 gpm. Operators then took manual control and closed ICM127.
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condensate storage tank pumps were secured per direction of OSM.
Approximately one hour after closing 1-CM-127 UST temperatures _ returned
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to less than 138 degrees F.
Because of the potential impact on the condensate system (civil and mechanical). the OSM contacted CNS engineering and regulatory compliance to discuss operability of the l
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l system following the UST over-temperature. After approximately 50 minutes, the decision was made to declare all three auxiliary feedwater pumps inoperable until further evaluation could be completed. The licensee entered TS LC0 3.7.1.2 action c which required that at least one AFW pump be immediately restored to operable status.
-The licensee made event notification (No.
34191) at 6:42 pm on May 7, 1998, to notify the NRC of the AFW system being in an unanalyzed condition due to elevated suction source water temperature.
The following table contains an abbreviated operator response time line.
Doerator Resoonse Time Line
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UST Hich Temperature Event of May 7: 1998
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TIME EVENT SEQUENCE TIME TOTAL TIME-HR/ MIN
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i 1425 First 0AC alarm of UST high
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temperature 1430 UST > 138 degrees F-
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1454 SR0s informed of high
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temperature 1515 Engineering called for
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1531 First mitigation action
1 hr. G min.
(secured "C" condensate booster pump)
1713 Last mitigation action 1 hr. 42 min.
2 hrs. 48 min.
(secured CST pumps)
173r Last alarm clears (UST ~A")
3 hrs. 5 min.
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Conclusion Insufficient operator and engineering staff training resulted in insufficient knowledge level relative to operation of the digital controller for the condensate booster pump recirculation valve (1-CM-127), auxiliary feedwater pump suction temperature design limits, and operator actions required to identify, correct, and mitigate the consequences of the unplanned and unexpected condensate booster pump high recirculation flow rate to the Upper Surge Tank. The resulting Upper Surge Tank high temperature condition caused the auxiliary feedwater system to be inoperable for approximately three hours.
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04.2 Interim and Planned Actions To Prerlude Recurrence a.
Insoection Scooe The AIT reviewed and assessed licensee interim and planned actions to preclude recurrence in either unit.
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Observations and Findinas The licensee's interim and planned actions to preclude recurrence are listed below. An Operations Information Notice dated May 13. 1998, was issued to describe the actions prescribed by the Plant Oversight Review Committee (PORC) as a result of this event.
The licensee issued tagouts18-973, 18-975,28-498, and 28-501 for
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Unit 1 and Unit 2 which isolated auxiliary steam and condensate inputs to the UST and CST on May 11, 1998.
An immediate training package ("Just in Time" training) was issued
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to operating crews, specifying design characteristics of the digital controllers and identifying expected operator actions in response to auxiliary feedwater suction source temperatures
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exceeding 120 degrees F.
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The 'C' heater drain pumps were not to be operated below 70%
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power.
The condensate storage system was maintained in constant overflow
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to provide good mixing and cooling of preferred auxiliary feedwater sources and 3rovide a leading indicator of UST temperature increase t1 rough the monitoring of CST temperature.
l Operations Procedure OP/1/A/6250/001, Condensate and Feedwater.
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was revised to incorporate adequate instructions on the CM-127
digital controller operation.
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!
The ala-response guideline was revised to include 1-CM-127 as a
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,
potentia: source for UST elevated temperature and the alarm setpoint was reduced to 120 degrees F.
A label was installed on the control board to caution operators
.
that manual mode "M" changes the setpoint and to refer to the CM
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OP for operation in manual mode.
Immediate training was provided on 1-CM-127 digital controller
.
operation for crews prior to assuming on-shift duties.
The 1-CM-127 digital controller was added to the Semi-Daily
.
,
Operations turnover surveillance checklist.
'
The licensee issued an Operations Information Notice to implement
.
the compensatory actions specified by the Plant Oversight Review Committee (PORC) until engineering evaluations can be completed
,
and final procedure revisions implemented.
i AFW was specified to be declared inoperable if the UST CST. or
-
hotwell temperature exceeded 130 degrees F per the Operations Information Notice.
.
c.
Conclusion Licensee interim and planned actions were prudent to reduce the probability of operating with suction supply temperature outside the
'
auxiliary feedwater system design basis.
Guidance was adequate to aid operators in evaluating future similar events.
07.1 Generic Acolicability a.
Insoection Scone I
The AIT assessed the generic aspects of operations / engineering that may have applicability to other licensed facilities. The AIT focused on the potentially adverse system interactions between safety and non-safety
,
b
-
systems related specifically to Condensate and Feedwater System interaction with the Auxiliary Feedwater System.
b.
Observations and Findinas The AIT observed that this particular arrangement of condensate storage tanks used as a preferred supply for auxiliary feedwater was unique to l
the Duke Energy facilities.
Both Oconee and McGuire Nuclear Stations l
were designed with similar condensate storage systems; however.
administrative controls had previously been established to prevent UST over-temperature due to condensate booster pump recirculation flow.
The Oconee Nuclear Station operates with the condensate booster pump minimum flow recirculation valve closed and the main controller in l
l l
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manual.
The Oconee UST dnx not have auxiliary steam inputs.
Main Feedwater recirculation to the UST. used during long cycle cleanup, was normally closed and did not have an automatic open feature.
McGuire Nuclear station had also established administrative controls to isolate the condensate booster minimum flow recirculation valve isolated.
Following the May 7.1998, the licensee removed power from the valve to prevent spurious operation. Auxiliary steam heating remains available as a temperature control mechanism. The auxiliary steam temperature control valve was normally closed and had been evaluated to be a low capacity heat source which would provide ample time for operator intervention in the event of a control valve failure.
c.
Conclusions The AIT concluded that this particular arrangement of condensate storage tanks used as a preferred supply for auxiliary feedwater was unique to the Duke Energy facilities. The controls established at the McGuire and Oconee facilities were effective in preventing similar UST over-temperature events.
The configuration of the condensate storage systems at the Duke facilities was adequate to preclude similar upper surge tank over-temperature events.
08.1 Plant Ooerations Review Committee (PORC)
a.
Insoection Scoce The AIT attended selected special meetings of the Catawba PORC to assess licensee performance in evaluating complex issues involving several onsite groups that impact plant safety and nuclear station operation.
b.
Observations and Findinas The AIT observed portions of special meetinas of the Catawba PORC held to discuss operability of the AFW system following the May 7.1998 UST overtemperature event.
During the PORC meetings conducted between May 11 - May 15, 1998, the AIT noted that the PORC acted as a problem-
,
_
solving group and was not entirely effective at functioning in an independent oversight role. The PORC had difficulty maintaining sufficient independence from the detailed evaluation of the issues, so the PORC could provide adequate oversight.
A clear distinction between
~
the problem-solving function of station management and the oversight function of PORC was not drawn.
The licensee also had difficulty identifying regulatory requirements involving non-safety and safety system interactions necessary to evaluate AFW system operability accurately. This lack of understanding resulted in unclear expectations of station organizations and delayed completion of formal operability determinations.
Ultimately. the station organizations completed the evaluation and made the necessary recommendations to the PORC. which was accepte.
1.
.
.
c; C'onclusion
.r The Plant Operations Review Committee (PORC) had difficulty identifying
'the regulatory requirements involving non-safety and safety system
. interactions which were necessary to evaluate AFW system operability accurately.
The AIT noted that the PORC acted as a problem-solving group and was not entirely. effective at functioning in an independent oversight role during evaluations of AFW system operability following
,the May 7. 1998. upper surge tank over-temperature event.
The PORC reached an appropriate consensus on the sco)e and content of the AFW system operability evaluation and accepted t7e AFW operability determination with the recommended compensatory actions.
l II. Engineering
'
El-Conduct of Engineering (93800)
E1.1 Assessment of the Thermo-Hydraulic Interaction Between the Unoer Storace-Tank (UST) and AFW Suction Sucolv (Imoact on AFW Pumo Doeration)
a.
Insoection Scooe.
The team assessed the thermo-hydraulic interaction between the u)per surge tank-~and AFW pump suction supply including the impact of tais event on the swapover'of AFW sources. The team reviewed the licensee's evaluation of the impact of the higher temperature AFW supply source on AFW pump operation'.
b.
Observations and Findinas The licensee's evaluation included a run of the AFW system hydraulic flow model with inputs consistent with system conditions during the UST high temperature event. The original system hydraulic flow model' was documented in Calculation CNC 1223.42-00-0040. Catawba Nuclear Station.
Unit 1. Auxiliary Feedwater System CA System Res onse to Chapter 15 Accidents. Revision 3.
The team verified the mo el was consistent with b
the as-built configuration for the portions of the piping between the AFW pumps and the supply sources. The following as-built drawings were reviewed:
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.
L CN-1490-CS 010. Turbine Building (TB) Condensate Storage System, revision 8 CN-1490-CA 005. TB AFW System, revision 6 CN-1492-CA 023. Auxiliary Building (AB) AFW System, revision 15 CN-1497-CA 027. AB AFW System (including recirculation). revision
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CN-1492-CA 19. AB AFW System (including Recirculation revision 8 CN-1492-CA 20. AB AFW System (including recirculation), revision
The elevated AFW temperature run was documented as "CA System Model with Elevated UST Temperature, dated 5/12/98." The accident used in this model was the steamline break accident.
This accident provided the greatest flow demand for the analyzed accidents. (2312 gpm). The input conditions for the model run were consistent with the plant conditions during the elevated UST temperature event. The output of the model provided the projected pressure at each AFW pump suction and the net positive suction head (NPSHa) available. These pressure and NPSHa
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values were compared to the saturation pressure (Psat) for the highest CST temperature in the event and the NPSH required (NPSHr) for the pumps.
The model determined that the existing pressures at the pump suctions was greater than Psat - therefore no steam /va)or binding was anticipated, and the NPSHa was greater than tie NPSHr for the AFW pumps.
These values are shown in the following table:
AFW Pump Pressure Psat NPSHa NPSHr MDAFW-A 39.76 psia 22.8 psia 40.3 ft 19 ft
!
l MDAFW-B 39.72 psia 22.8 psia 40.2 ft 27 ft TDAFW 39.68 psia 22.8 psia 40.1 ft 15 ft i
!
!
The model demonstrated that these conditions exist up to the point where l
the UST is emptied in approximately 35 minutes.
The values are based on
<
l an elevation at the bottom level of the UST.
The licensee also evaluated system conditions at the AFW pump suction at (
the assured source (RN) swa) over initiation point which corresponds to
?
~
the 560 foot elevation in tie piping between the UST and the pump i
suction. At 230 degrees F water temperature the pressure at the AFW pump suction was predicted by the analysis to be 26.9 psia which was greater than the 22.8 psia Psat for 230 degrees F.
Therefore, vapor flashing was not a concern when water level was at the RN swap over point.
'
The licensee noted that plant conditions 10 minutes into the accident scenario would not require full AFW flow and water temperature would be less than 212 degrees F.
The faulted S/G would be isolated and AFW flow would be to the remaining S/Gs at full pressure reducing flow requirements and subsequent NPSHr to approximately 12 feet.
Because of saturated conditions in the UST pressure can be conservatively assumed to be atmospheric and a conservative temperature of 212 degrees F was J
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assumed. A calculation of static fluid condition in the supply piping at 212 degrees F yields a NPSHa of 28 ft which exceeds the maximum
,
l required NPSH of 12 ft. for the anticipated flow conditions.
l The licensee's Abnormal Procedure for Loss of Steam Generator (S/G)
'
Feedwater. Rev. 17. AP/1/A/5500/06 is required to be referenced when an auto start of the AFW system occurs.
This procedure requires verification and monitoring of AFW supply sources. The actions of the l
procedure would be addressed within minutes of AFW auto initiation:
therefore, actions would be initiated to establish an alternate supply
. source before the UST was emptied.
c.
Conclusion
,'
The team concluded that licensee's engineering analysis of the elevated temperature impact on AFW pump operations was effective and demonstrated that the AFW pumps would have operated, supplying water to the steam generators with the elevated upper surge tank temperatures experienced on May 7, 1998.
Conditions did not reach a point for steam vapor flashing to occur in the AFW aumas.
Adequate NPSH was available at the swap over initiation point, w11c1 changes the suction water supply to the assured water source (RN).
E1.2 Imoact of Exceedino Desian Temperature Specification for Pioina and l
Tanks l
a.
Insoection Scoce l
l The team reviewed the licensee's analysis of exceeding the desian l
temperature for condensate system piaing and tanks.
Additionallythe l
team performed a field walkdown of t1e piaing and tanks to assess l
indications of visible damage from water lammer or temperature induced stress.
b.
Observations and Findinas The team's walkdown of the piping and tanks identified no indications of
,
_.
water hammer or temperature stress.
The design piping specification for temperature was exceeded for the non-safety related condensate tanks and piping, which provided the preferred suction supply source for the AFW pumps. The safety related piping was not ex)osed to the higher
-
temperature due to the static condition of t1e system during the event duration.
Approximately 4 gpm flow through the TDAFW pump cooler did not result in increased temperature in the safety related piping adjacent to the pumps.
The condensate piping was Duke Class G which corresponded to ANSI B31.01. code criteria. The piping criteria was 75 psia and 212 degrees F.
Based on the saturation pressure of the noted 25 psig CST tank pressure during the event, the licensee analyzed the piping at 267 degrees F.
The analysis method was to input the higher temperature and recalculate the piping stress calculations to verify the calculated stress was less than the allowable. The preliminary results f
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%
demonstrated that the B31.1 code stress allowance was not exceeded.
The calculations were in the review and approval stage during the inspection.
The following piping stress calculations were revised:
CNC-1206.02-75-2004. Drain from UST Dome Connection A to UST le and Ib Connection B1 problem CSA. rev.4 i
CNC-1206.02-75-2011. USTs la and 1b to Condenser Auxiliary l
Electrical Boiler FDWPs and Aux FDWP supply - problem CSB rev.7 i
CNC-1206-02-75-2013. Vent from Upper Surge Tanks la and 1b to Upper Surge Dome Tank. rev.4 CNC-1206.02-75-2016. Upper Surge Dome Tank to Condensate Storage Tank Piping Analysis Problem CSD. rev. 6 CNC-1206.02-75-2019. UST Vent to Condenser Connection 56. rev. 2 The tanks were qualified to ASME Section VIII code criteria and were analyzed for stress on the shell, supports and penetrations at the elevated temperatures. The tank specification was 75 psia and 212 degrees F.
The tank stress components were calculated for the elevated temperature values. The following stress calculations were revised:
CNC-1148.00-05.0001. Upper Surge Tanks-System C5. rev.4 CNC-1148.00-05.0002. Catawba Units 1 and 2 Condensate Storage Tanks, rev.4 CNC-1148.00-05-0003. Catawba Units 1 and 2. Upper Surge Dome Tank, rev. 2 The calculations were in the review and approval stage during the inspection.
The preliminary results indicated the code allowable stress tolerances were not exceeded.
c.
Conclusion
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~
The team found that the' licensee performed stress analysis on the piping and tanks exposed to elevated temperature which was above the design specification values. The preliminary results indicated the code
-
specified stress tolerances were not exceeded. A system walkdown by the team identified no visible indications of water hammer or temperature
,
induced stress damage to the piping or tanks.
l I
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E1. 3 Assess Potential Interactions Between Safety and Non-Safety Related AFW S_ources a.
Insoection Scone The team reviewed the licensee's actions to identify potential safety /non-safety interactions for AFW sup)1y sources.
In particular, this addressed the potential to increase A W supply source temperatures i
above the 138 degrees F value used in accident analysis.
b.
Observations and Findinas I
The inspectors noted that the licensee's methodology for assessing these
'
'
interactions was to identify supply source inputs on the system piping flow drawings and evaluate the potential for increasing the tem)erature of these sources.
The team performed a parallel review using t1e following system flow diagrams:
CN-2595-1.0, Flow Diagram of Auxiliary Steam System. rev.3 CN-2590-1.6. Flow Diagram of Condensate System, rev. 10 CN-1595-1.0. Flow Diagram of Auxiliary Steam System, rev. 9 CN-1590-1.6. Flow Diagram of Condensate System. rev.11 CM-1590-2.0, Flow Diagram of Condensate Storage System, rev.10 The AFW sources evaluated for het.t up included the UST main condenser hot well, service water (assured source) and condenser circulating water (Station S W kout source).
The UST heat up from a CM-127 failure and main condenser beat up due a C-9 permissive relay failure which would arm the steam dumps were the major heat up mechanisms.
Interim actions to address heat up mechanisms included isolation of CM-127. isolation of UST auxiliary steam input and increased temperature monitoring of tanks and piping.
For main condenser heating to occur from the C-9 permissive relay failure, multiple other failures were required which included loss of the circulating water pumps.
Compensatory actions to 3reclude AFW supply source heat up are discussed in detail in paragrapa D4.2 and are addressed specifically in the licensee *s AFW operability evaluation.
No other potential safety /non-safety interactions were identified other
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than mechanisms for increased AFW supply source temperature.
c.
Conclusion
, _
The team concluded that the licensee's analysis of potential safety /non-safety interactions for auxiliary feedwater supply sources adequately identified potential mechanisms for increasing source temperatures above the value used in licensing basis accident analyses. Appropriate recommendations were provided to preclude an inadvertent auxiliary feedwater supply source temperature increase above the design basis limit of 138 degrees F.
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15 E1.4 Adecuacy of UFSAR as it Related to Description of Systems Involved in the Event a.
Insoection Scope The team reviewed the applicable sections of the UFSAR to assess the adequacy of the descriptions as related to this event. The team reviewed the UFSAR dated May 2.1997. Technical Specifications, and related licensing documents.
'
b.
Observations and Findinas The team reviewed the Catawba Updated Final Safety Analysis Report
'
(UFSAR). Section 10.4.7. Condensate and Feedwater Systems, and Section
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10.4.9. Auxiliary Feedwater System. The team also reviewed identical sections in the Catawba Final Safety Analysis Re) ort (FSAR). These documents showed no substantive differences in tie way the subject systems were described. The team also reviewed the Catawba Safety Evaluation Report (SER. NUREG-0954 dated February 1983) and its supplements and found that the staff has accepted the systems as described in the UFSAR.
The UFSAR, therefore, documented the licensing bases of the condensate. feedwater, and auxiliary feedwater systems. As I
far as auxiliary feedwater was concerned, the licensing basis specifies a temperature range of 40 to 138 degrees F.
Accordingly, the licensee appropriately analyzed the UFSAR Chapter 15 transients and accidents with this licensing basis temperature range.
The May 7. 1998 event resulted in an u)per surge tank (UST) water temperature of higher than 138 degrees :. up to 234 degrees F for a period of approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, leading the licensee to declare that the entire auxiliary feedwater system inoperable for Unit 1.
Technical Specifications Section 3.7.1.2. Action c. specifies that "[with three auxiliary feedwater pumps inoperable, immediately initiate corrective action to restore at least one auxiliary feedwater pump to OPERABLE l
status as soon as possible." The licensee reduced the UST water temperature to below 138 degrees F within approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> complying with the TS action statement.
Following an assessment of the impact of the condensate system high temperature on auxiliary feedwater
^
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system operability; the' licensee declared two AFW pumps operable the next morning at 5:55 am on May 8, 1998.
The team therefore had no
.
concern with meeting the technical specification licensing requirements.
UFSAR Section 9.2.6. Condensate Storage System provided a brief.
general description of the system, with no reference to the 138 degrees F AFW supply criteria.
UFSAR Table 9-14. Condensate Storage System Design Parameters, specifies the design temperature for the tanks at 212 degrees F.
This was consistent with the value on the tank drawing.
!
I UFSAR Section 10.4.7. Condensate and Feedwater System, discussed the operation of the condensate and feed system with respect to design I
_ _ _ _ _ _ _
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16-functions and system description, but included no specific reference to the.138 degrees F criteria for AFW supply source.
It did include a-reference to UFSAR section 10.4.9. Auxiliary Feedwater System.
'
UFSAR Section 10.4.9. described the AFW system design base and system function in greater detail.
In Section 10.4.9.2. System Description.
the last sentence, stated. "The CA system is designed to supply 40 degrees F to~138 degrees F water to the SG nozzles in the pressure range from ND system cut-in conditions..."
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.
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UFSAR Section 10.4.9.1. Design Bases, stated. " Maximum auxiliary feedwater temperature at Catawba may reach 138 degrees F based on maximum operating condenser pressure of 24.0 inches Hg vacuum.
l l'
UFSAR Section 15.2.8.2. Feedwater System Pipe Break, Analysis of effects and consequences referenced 138 degrees F as the temperature of
.
feedwater injected during this accident condition.
l The team reviewed the DBD and noted one reference to AFW supply source
'.
temperature. CNS-1592-CA-00-0001. Auxiliary Feedwater System Design Base Specification. Rev.10. Section 20.3.4. System Flow Requirements.
stated that for the required flows assumed in the accident analysis.
,
l
~... the AFW temperature is assumed to be between 70 and 138 degrees F."
l The limited references to the AFW source temperature assum3tions in the UFSAR may have impacted the licensee's identification of tie 138 degrees F AFW temperature criterion..However, the reference to the 70-138 degrees F range as a design base value in the OAC' alarm response
. guideline indicated that adequate reference was available. The 70-138 degrees F AFW range was initially provided to the design organization as the anticipated operator range of the condensate storage system.
The upper limit was based on the saturation temperature for the expected worst case main condenser vacuum during operation. The UST is vented to the main condenser by 16" diameter piping, therefore the UST was anticipated to be in saturated conditions for 24 inches Hg vacuum which
,
is 138 degrees F.
This value was the input to the design accident
!
analysis.
The 138 degrees F temperature limit was not based on limits established by the accident analysis. however the elevated AFW supply l
~
I temperature condition resulted in the station being outside the analyzed
'
condition for the approximately 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> period the UST was at elevated temperatures.
.
The licensee identified the accident analyses which used the 138 degrees F value as design input. These included the following:
UFSAR Section 15.2.6 - Loss of Non-Emergency AC Power UFSAR Section 15.2.7 - Loss of Normal Feedwater UFSAR Section 15.2.8 - Feedwater Line Break UFSAR Section 15.3.3 - Locked Rotor UFSAR Section 15.4.3 - Single Uncontrolled Rod Withdrawal UFSAR Section 15.4.8 - Rod Ejection
.
I
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UFSAR Section 15.6.3 - Steam Generator Tube Rupture l
UFSAR Section 15.6.5 - Loss of Coolant Accidents l
UFSAR Section 15.8 Anticipated Transients Without Scram
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(Generic Analyses)
,
.The-licensee included an action item in their event evaluation to address the impact on accident analysis of elevated AFW temperature.
The design engineering organization indicated this assessment would require several' months to complete. As the system was returned to less than.138 degrees F and compensatory actions were implemented there was.
no safety concern related to the completion of the accident analysis assessment.
s c. ' Conclusion
'
Tha team concluded that. although there were limited UFSAR references to the AFW system temperature assumptions. the UFSAR description was adequate as indicated by secondary references in the alarm response
,
procedure and design basis document. The licensee initiated an action J
item to assess the impact of the elevated AFW temperature on UFSAR accident analyses.
E4.
Engineering Staff Knowledge and Performance (93800)
E4.1 Significant-Event Investigation Team Root Cause Analysis a.
Insoection Stone Inspect licensee activities related to event investigation such as root cause analysis and precursor event reviews.
b Observations and Findinas The NRC AIT independently conducted a root cause analysis with the following results.
I ROOT CAUSE:
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'
Insufficient operator and engineering staff training which
~
.
resulted in insufficient knowledge level relative to:
how to operate the digital controller for CM-127
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_ full understanding of dynamic system interaction -
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!
condensate to auxiliary feedwater.
what-the Auxiliary Feedwater system suction temperature
-
l design limits were (temperature limits of 70-138).
l
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determining the time of entry into the LC0 (i.e.. When did the system become inoperable?). and
-
understanding how exceeding the system design temperature-limit affects system operability.
,
.
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i
Inadequate procedures, instructions, and guidelines for:
-
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operation of the digital controller (OP/1/A/6250/04 Condensate and Feedwater System) regarding the bumpless transfer feature which changes the setpoint and must be reset manually and
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operator response guidelines (controlled by OMP 2-13) for high UST "A" temperature. At the time of the event.
l Operator Aid Computer point C1A0510 UST WTR TEMP HI and HI-l HI alarm response guideline did not provide any specific e
operator instructions to check condensate inputs as a potential heat source for Unit 1 Upper Surge Tank, although
,
,
the day before the event a note was added to the computer.
l CONTRIBUTING CAUSAL FACTORS:
Inadequate implementation of the 10 CFR 50.59 evaluation process
.
on two occasions: 1) isolation of CM-127 (7/7/96) and 2) restoring use of CM-127 (8/28/97).
Both 10 CFR 50.59 Evaluations were o)portunities to perform a detailed evaluation of the impact of t7e condensate system on the auxiliary feedwater system.
This factor is discussed in more detail in paragraph E4.2.
Inadequate implementation of design basis limits into ]rocedures
.
and instructions which are used to prevent exceeding tiose design basis limits (such as accident analysis assumptions like that of 70 - 138 degrees F AFW inlet temperature).
Insufficient Trending of the high maintenance requirements on
.
Valve CM-127 and the PIPS which involve the UST or CM-127 resulted in the failure to detect the potential adverse conditions and system interactions between the AFW and Condensate systems.
Robust trending should have prompted a focused evaluation of the causal factors and adverse system interactions which could result from the overtemperature conditions in the UST on the AFW system.
Operating Experience Reviews: Large number of PIP reports relating
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to CM-127 with some involving high temperature alarms on the UST -
6 previous pr'ecursor events from 1/20/96 to 1/11/98.
Inadequate root cause determination and subsequent corrective
-
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actions on the previous occurrences of high UST temperature failed to correct a condition adverse to quality, once identified, since January 20. 1996.
Insufficient configuration control when changing mode of operation
-
of the unique controller for CM-127.
Com31exity of the design of the condensate system as it interfaces
.
wit 1 the auxiliary feedwater system.
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The OAC alarm was not an annunciator alarm on the main control
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board commensurate with the importance of the UST temperature.
. Lack of questioning attitude of operators over approximately-a two
.
week period when the CM-127 controller visual display was indicating other than normal conditions for the controller setpoint.
c.
Conclusion
'
The t'eam noted that the licensee initiated a Significant Event Investigation Team (SEIT) and performed a detailed and thorough root cause analysis of the May 7. 1998. UST high temperature event. The team
'
'
reviewed the SEIT findings and recommendations and assessed them to be candid.-probing, and conservative.
The team concluded that insufficient Trending of the high maintenance requirements on valve CM-127 and the Problem Investigation Process (PIP)
l forms which involve the upper surge tank or CM-127 resulted in the failure to detect the )otential adverse conditions and system interactions between tie AFW and Condensate systems.
l-
'The team also found that inadequate root cause determinations for L
several previous occurrences of high upper surge tank overheating, which
!
had occurred since January 20. 1996. were inadequate and resulted in l
ineffective corrective actions.
l E4.2 Significant Event Investigation Team Review of Precursor Events a.
Insoection Scoce Inspect licensee activities related to event investigation such as review of precursor events.
b.
Observations and Findinas Inspection of the licensee's records (PIP 1-C-96-0145) indicated that on L
.
January 20.1996. Unit 1 experienced a similar incident where UST temperature exceedbd the auxiliary feedwater design temperature for i
a) proximately 98 minutes with a peak temperature of 211 degrees F.
Had L
tie auxiliary feedwater system been actuated at this time, the water L-temperature would have exceeded the design temperature for the suction l
of the AFW pumps (FSAR Tables 10 4.9-1 and 10.4.9-2 specify the pump design tem]erature as 138 degrees F).
The licensee's records do not indicate tlat the licensee was aware that the UST was beyond its licensing / design basis. The licensee did not take adequate measures to prevent future recurrence. The investigation revealed that engineering staff assumed that since the UST was connected by a 16 inch line to the Condenser Hotwell, that the maximum temperature that the UST could reach was saturation temperature for 24 inches vacumn.
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On January 11. 1998, the UST temperature reached a maximum of 135 degrees F and remained near this value for four days until the licensee closed the isolation valve 1CM-126.
No PIPS were initiated by the licensee.
This event similarly did not prompt the licensee to take adequate measures to prevent future recurrence.
Relative to these UST high temperature events, the engineering staff demonstrated a poor questioning attitude and lack of rigor in the performance of root cause evaluations and determination of corrective actions.
The team reviewed the licensee's Procedure OP/2/A/6250/01, dated July 11. 1996, and its associated screening for 10 CFR 50.59 evaluation.
'
With this procedure. the practice of operating with 5.500 gpm
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recirculation to the UST was suspended by isolating valve 2-CM-127 (Unit 2). The licensee's 10 CFR 50.59 evaluation was accomplished, when the procedure change was " screened" for Jossible unreviewed safety questions. The licensee concluded tlat a detailed 10 CFR 50.59 evaluation was not required.
The screening questions were as follows:
~1.
Does the activity change the facility as described in the SAR?
2.
Does the activity change procedures, methods of operation. or alter a test or experiment as described in the SAR?
3.
Does the activity appear significant enough to require inclusion in the SAR?
4.
Could the activity adversely affect any system, structure, or component necessary to operate the plant in accordance with the SAR?
5.
Does the activity perform a test or experiment that is NOT described in the SAR?"
The screening process used for the July 1996 procedure change failed to recognize Item 3 of UFSAR Section 10.4.7.5.2 which stated that the
" Condensate recirculation control valve CM-127 is controlled by condensate flow and the number of hotwell and condensate booster pumps running to provide a minimum flow recirculation path for the pumps." As a result of this failure to recognize the content of item 3. the licensee erroneously concluded that closing or isolating valve CM-127
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did not represent a charige to the condensate system or a change to the methods of operation of the condensate system as described in the UFSAR and, therefore, concluded that a 50.59 evaluation was not warranted.
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With regard to question 4 above. this event demonstrated that the change in operation of CM-127 could adversely affect the auxiliary feedwater system which is necessary to operate the plant in accordance with the SAR.
This 10 CFR 50.59 screening failed to answer yes to questions 1.
2. and 4 of the screening for US0 evaluation applicability.
An answer j
of yes to any one of the five questions requires a more detailed 10 CFR 50.59 evaluation to determine if a US0 exists.
In August of 1997, the licensee performed another 50.59 screening to open and unisolate 2-CM-127.
Since the condensate recirculation line
I eles being returned to its original configuration. the licensee assumed l
that no 50.59 evaluation was necessary.
Again, this 10 CFR 50.59
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screening failed to answer yes to question 4 of the screening for USQ evaluation applicability. An answer of yes to any one of the five questions requires a more detailed 10 CFR 50.59 evaluation.
The team also reviewed the revision. dated May 9. 1998 of Procedure OP/2/A/6250/001 that was performed to close and isolce CM-127.
This included a review of PIP 0-C-98-1726. which evaluated compensatory actions to maintain the auxiliary feedwater system OPERABLE but degraded by isolating valve CM-127 of each unit.
This action is similar to that specified by OP/2/A/6250/01. except this time the licensee performed a full 10 CFR 50.59 evaluation based on the UFSAR description in Section
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10.4.7.5.2.
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For the 1998 revision to the procedure for again closing CM-127. the licensee correctly recognized that Item 3 of UFSAR Section 10.4.7.5.2.
did describe the operation of CM-127 and that operation with this valve closed or isolated did result in a change to the condensate system as described in the UFSAR.
Therefore, the licensee appropriately concluded that a 10 CFR 50.59 safety evaluation was necessary to close or isolate CM-127. The team concluded that the licensee's 10 CFR 50.59 safety evaluation was adequate.
c.
Conclusion The AIT concluded that, relative to the previous UST high temperature events the engineering staff demonstrated a poor questioning attitude and a lack of rigor in the performance of two 10 CFR 50.59 safety evaluations (July 1996 and August 1997). root cause evaluations and the determination of corrective actions.
This resulted in the engineering staff failing to recognize the safety system (AFW) and non-safety system (condensate) interactions and the impact of those interactions on AFW system operability.
Following the May 7. 1998. UST high temperature event. the licensee's 10 CFR 50.59 safety evaluation was adequate for the isolation of CM-127.
E8'
Miscellaneous Engineering Issues (93800)
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E8.1 Safety Significance Assessment of the Unit 1 Unoer Surce Tank Over-
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Temperature Event The actual safety significance of the upper surge tank high temperature event was minor in that 1) the auxiliary feedwater system was inoperable for a short time (approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />). 2) the auxiliary feedwater system was not called upon to perform its intended safety function, and 3) during the time of inoperability, the auxiliary feedwater pumps remained functional but degraded (still available to provide water to the steam generators).
There was a reduced heat removal capacity for the auxiliary feedwater system during this even __
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The regulatory significance of the upper surge tank high temperature event was high prompting the initiation of an AIT because a safety-related system designed to mitigate the consequences of an accident was rendered inoperable by the mispositioning of a single non-safety related componeni;. 1-CM-127.
The licensee has taken appropriate actions to provide reasonable assurance that this event will not recur in the future.
III. Manaaement Meetinas
X1 Exit Meeting Summary The team held a public exit meeting on May 15.' 1998, at the Catawba
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site.
There was media coverage of the exit meeting.
The team leader i
presented the inspection results to members of licensee management and the licensee acknowledged the findings presented.
No proprietary information was identified. The team concluded that during the event, the AFW system remained capable of performing the safety function of providing water to the steam generators but was degraded in that water would have been provided at a higher temperature than design.
PARTIAL LIST OF PERSONS CONTACTED Licensee T. Baumgarner. Operations Supervisor M. Birch Safety Assurance Manager R. Glover Operations Superintendent P. Herran. Engineering Manager C. Hood. Condensate System Engineer G. Horne. Design Engineering R. Jones. Station Manager M. Kitlan. Regulatory Compliance Manager T. Moore. Design Engineering G. Peterson, Catawba Site Vice-President M. Tuckman. Executive Vice-President. Nuclear Generation Significant Event Investigation Team (SEIT) Members J. Davis. Team Leader E. Blough
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M. Chernoff R. Freudenberger G. Ford G. Gibert L Saunders A. Smith D. Sweigart D. Tower i
E. Blough
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l J.
Jaudon. Director. Division of Reactor Safety. Region II. USNRC l
INSPECTION PROCEDURE USED IP 93800:
Augmented Inspection Team Implementing Procedure LIST OF ACRONYMS USED CFR
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Code of Federal Regulations DBD Design Basis Document
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ECCS -
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ESF Engineered Safety Feature
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LC0
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Limiting Condition for Operation NSD
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Nuclear System Directive Nuclear Station Modification NSM
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0ATC Operator at the Controls
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OMP
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Operations Management Procedure OSM Operations Shift Manager
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Problem Investigation Process PSIA -
Pounds per Square Inch. Absolute PSID Pounds per Square Inch Differential
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TS Technical Specification
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UFSAR -
Updated Final Safety Analysis Report USO Unreviewed Safety Question
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UST Upper Surge Tank
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WCC Work Control Center
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Work Order
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AUGMENTED INSPECTION TEAM CHARTER
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Attachment 1
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>* aeog'o-UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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REGION il n
y ATLANTA FEDERAL CENTER
t 61 FORSYTH STREET. SW, SUITE 23T85
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ATLANTA GEORGIA 30303-3415
...o May 11, 1998 MEMORANDUM T0:
Kerry D. Landis Team Leader gmente nspection Team
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FROM:
K is A eyes egiona. t ei C rator
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SUBJECT:
AUGMENTED INSPECTION TEAM CHARTER
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An Augmented Inspection Team (AIT) has been. established to inspect and assess the Condensate / Auxiliary Feedwater (AFW) event of May 7. 1998. at Catawba Unit 1.
The team composition is as follows:
Team Leader:
K. Landis Members:
M. Sykes (Operations)
R. Moore (Engineering)
P. Tam (Licensing)
The bases for the formation of the AIT are the significant and unexplained interactions during a normal down-power between the non-safety related condensate system and the safety-related auxiliary feedwater system, which resulted in the licensee declaring all three AFW pumps inoperable.
The objectives of the inspection are to: (1) determine the facts surrounding the specific event: (2) assess licensee res)onse to the event: (3) assess generic aspects of operations / engineering tlat may have applicability to other facilities: (4) oversee licensee activity during their event review; and (5)
interface with other on-site entities as needed.
For the period during which you are leading this inspection and documenting the results, you will report directly to me. The guidance in Inspection Manual Chapters 0325 and 0610 apply to your inspection and the report.
If you have any questions regarding the objectives or the attached charter, contact me.
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Attachment: AIT Charter
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cc w/att:
L. Callan. ED0 C. Casto. RII H. Thompson. DEDO J. Jaudon. RII S. Collins. NRR B. Mallett RII T. Martin, AEOD L. Plisco RII J. Zwolinski, NRR R. Carroll. RII l
H. Berkow. NRR C. Ogle. RII
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M. Tschiltz. OEDO D. Roberts. RII P. Tam. NRR L-
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AUGMENTED INSPECTION TEAM CHARTER CATAWBA NUCLEAR STATION CONDENSATE /AFW EVENT
- The objectives of the inspection are to: (1) determine the facts surrounding
'the specific event: (2) assess licensee res)onse to the event: (3) assess i
generic aspects of operations / engineering tlat may.have applicability to other
. facilities: (4) oversee licensee activity during their event review; and (5)
interface with any other on-site' entities. To accomplish these objectives.
l the.following will'be performed:
Monitor and review licensee activities related to event investigation e'
such as root cause analysis and precursor event reviews.
Develop a sequence of events associated with the event.
- Review the adequacy of the procedure (s) implemented in response to the
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initial high temperature in the upper surge tanks. Assess emergency and operating procedure actions related to steam binding of the AFW pumps.
Assess the thermo-hydraulic interaction ~between the up)er surge tank and
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AFW pump suction supply.
Include in this assessment t1e impact of this event on the swapover of AFW sources.
Assess any other potential interactions between the safety and non-
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safety-related AFW suction sources.
L Review and assess licensee interim and planned actions to preclude
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. recurrence in either unit.
Review the adequacy of the UFSAR as it relates to the description of the
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systems involved in this event-.
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Document the inspection, findings and conclusions in an inspection report
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within 30 days of the completion of the inspection.
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SEQUENCE OF EVENTS DATE/ TIME ITEM DESCRIPTION The following sequence of events was developed by the AIT using plant data and independently verified licensee information produced during the investigation of the event.
January 20. 1996 Freezing instrumentation resulted in the UST exceeding design basis temperature of 138 degrees F for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and reached a maximum temperature 222 degrees F.
Impact on auxiliary i
feedwater system not recognized by Operations / Engineering.
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January 11. 1998 UST temperature exceed 135 degrees F for approximately four days due to ICM127 leakage.
Februarv 5. 1996 PIP initiated to document that ICM-127 could initiate secondary transients and affect reactivity (PIP 0-C96-0261).
July 11. 1996 (Approximate date) Procedures changed to maintain 1(2)CM-126 closed to isolate 1(2)CM-127 anytime a feed pump is in operation (PIPI-C96-0145).
Procedure changes received an inadequate 10CFR 50.59 screening.
May 7. 1997
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Water hammer in Unit 2 Upper Surge Tank dome attributed to leak by of 2CM-127 (PIP 2-C97-1562).
UST temperature did not exceed the CA suction design basis temperature of 138 during this event:
however, the CST temperature did exceed 138 on three occasions during this event.
Julv 9. 1997 As a result of Unit 2 trip, on 6-26-97. it was decided to restore 1(2)CM-127 to operation.
Attachment 2
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Julv 26. 1997
During a Unit 2 manual reactor trip. the CFPT's tripped on low
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suction pressure.
Had 2CM-127 been open (as decided in July 9, 1997 event). CFPT's may not have tripped (PIP 2-C97-2800).
Auaust 28. 1997 Operations procedures changed to unisolate 1(2)CM-127 during all modes of operation.
Procedure change received an inadequate 10CFR50.59 screening.
l January 11. 1998 i
During power escalation.1CM-127 was identified as leaking. Work Order (W/0) 98007155 was initiated.
No PIP was initiated.
Between January 11 and January 15. temperature ranged from 110 degrees F to 135 degrees F.
Aoril 3. 1998
)
Removal and Restoration (R&R) Tagout 18-673 placed for troubleshooting Dissolved Oxygen problem by 'C' shift.
ICM-127 placed in manual and tagged closed.
Aoril 17. 1998 Unit 1 SRO ordered (approved the R&R to be placed) R&R 18-754 The Removal Remarks section stated: " Record 1CM127 initial position prior to going to manual and closing."
In response the Unit 1 SRO recorded the initial position as auto and closed.
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U1 OATC placed ICM-127 in manual and closed per R&R.
(This action caused the controller to go to the setpoint of approximately
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14.000 gpm.)
U1SRO placed 1CM-127 in automatic and closed.
The Remarks in the Restoration Section stated " Return ICM127 to initial position:~.
The controller setpoint was not adjusted and remained approximately 14.000 gpm.
NOTE: With this setting. ICM-127 will begin opening anytime Condensate Booster Pump flow decreases below approximately 14.000 gpm.
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Hav 7. 1998 1155 Unit 1 operators began raaid power reduction at a rate of 25% per hour'in accordance with A)/1/A/5500/09. Rapid Downpower. Revision 7 to allow for realignment of main feedwater due to malfunction of main feedwater. regulating valve ICF55,
1415 At approximately 48 percent reactor power, the licensee shutdown
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l and secured the 1A main feedwater pump per procedure.
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1418 Operators complete closure of the main-feedwater recirculation
. valve.
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1CM127 opens to approximately 50%.
~1422 0AC point C1D2324. UST INVENTORY RECOMMENDED CAPACITY alarmed due to unknown.
(Potentially high flow or high temperature)
1425 OAC point C1A0510 UST A WTR TEMP HI alarmed.
(Setpoint 130 degrees F)
'1427 OAC point CIA 0510 UST A WTR TEMP HI-HI alarmed. (Setpoint 134 degrees F)
1439 UST B WTR TEMP HI alarmed. -(Setpoint 130 degrees F)
UST LOW LEVEL annunciator alarmed on main control room annunciator Janel (Only annunciated indication of UST conditions)
Reactor operator dispatched to check UST and CST level locally UST level fluctuating between -0 and 100 percent Operator returned to control room and notified CRSR0 1454 Operator checks alarms to research UST high temperature alarm.
Temperature indicating approximately 200 degrees F.
Notifies i
CRSR0 and OSM.
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OSM directed R0 to return to UST to check for indications of water
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hammer.
l ICM127 setpoint found at 14000 gallons per minute.
1515 Engineering contacted for guidance.
Procedures also checked for possible setpoint change.
j 1531 1 'C' Condensate Booster Pump secured per direction of OSM 1532 OAC Point CIA 0510. UST A WTR TEMP indicates 234 degrees F
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1541 Demineralized makeup water aligned to UST for cooling at - 125 gallons per minute
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1559 1C1 Heater Drain Pump secured 1605 1C2 Heater Drain Pump secured 1608: 1CM127 starts to close Setpoint returned to 5500 gallons per minute per discussions with engineering.
ICM127' closed to approximately 18 percent. operators took manual control and closed ICM127.
l 1628 1CM127 fully closed
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1713 Condensate storage Tank pumps secured per direction of OSM.
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1730 UST temperature reduced to less than 138 degrees F
.
1843 NRC H00 advised that all 3 pumps were declared inoperable as of 1745
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May 8. 1998 0500 PORC Meeting to review operability performed on the AFW System
0555.0PS accepted the AFW operability evaluation with one pump inoperable 0939 Commenced power increase from 30% to 100%
i 1645 Conference call between MGT. ENG. OPS. and NRC held.
Due to single failure concerns, licensee management decided to terminate
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power increase at.85% and isolate ICM-127 and 2CM-127.
l Engineering team organized to evaluate single failure issues.
I
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_ Event Investigation requested by Safety Assurance Manager.
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' May 9.1998 -
1547 ENS notification (Event 34191) updated to report that Auxiliary Feedwater System was not adversely affected.by the event and that 1(2)CM-127 have been isolated.
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May 10. 1998 Licensee establishes a Significant Event Investigation Team to review the events leading to and subsequent to the May 7, 1998 UST over-temperature event.
May 11. 1998
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NRC Region II AIT arrives at CNS to investigate May 7.1998 event and provide oversight of licensee investigation process.
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I CATAWBA SYSTEM DIAGRAMS l
1.
CM/CF/CS SUMMARY COMPOSITE FLOW DIAGRAM 2.
SUMMARY FLOW DIAGRAM AUXILIARY FEEDWATER SYSTEM (CA) UNIT 1 3.
CA SUCTION PIPING ELEVATIONS
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TREND GRAPH OF TANK TEMPERATURES
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SIMULATOR PICTURES OF 1 CM-127 CONTROLLER
PICTURE SUBJECT cm127a The first simulator picture (cm127a) is of the CM-127 digital controller as it would normally look during routine at power operation.
The left red bar is the setpoint indication at 5500 gpm, and the right bar is the 3rocess feedwater flow which indicates 13905 gpm any time t1e feedwater flow exceeds that value.
This )icture shows the indications, which should be very familiar to tie control room operators.
The caution sign at the bottom of the controller face was added after the May 7. 1998. UST
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cm127b The second simulator picture (cm127b) is of the CM-127 digital controller as' it was during approximately a two week period of o)eration prior to the May 7,1998. UST high temperature event.
T1e left red bar (at full scale) is the setpoint indication at approximately equal to the maximum process flow indication of 13905 gpm and the right bar is the process feedwater flow which indicates 13905 gpm any time the feedwater flow exceeds that value.
This picture shows the indications which should have alerted the control room operators to an abnormal indication.
Again, the caution sign at the bottom of the controller face was added after the May 7. 1998. UST high temperature event.
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