IR 05000277/2005008
| ML060190616 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 01/19/2006 |
| From: | Doerflein L Engineering Region 1 Branch 2 |
| To: | Crane C Exelon Generation Co, Exelon Nuclear |
| References | |
| IR-05-008 | |
| Download: ML060190616 (11) | |
Text
January 19, 2006Mr. Christopher M. CranePresident and CNO Exelon Nuclear Exelon Generation Company, LLC 200 Exelon Way KSA 3-E Kennett Square, PA 19348SUBJECT: PEACH BOTTOM ATOMIC POWER STATION UNIT 2- SUPPLEMENTALINSPECTION REPORT 05000277/2005008
Dear Mr. Crane:
On December 7, 2005, the NRC completed a supplemental inspection at the Peach BottomAtomic Power Station. The enclosed report documents the results of the inspection, whichwere discussed with Mr. B. Braun and other members of your staff on December 7, 2005.The NRC performed this supplemental inspection to assess your activities to address thePeach Bottom Unit 2 Scrams With Loss of Normal Heat Removal performance indicator (PI)
crossing the Green-White threshold in the fourth quarter of 2004. The purpose of this inspection was to assure that the causes of the performance issues associated with this PI crossing the Green-White threshold were understood, the extent-of-condition and cause were identified, and that corrective actions were sufficient. Inspection Procedure 95001, "Inspection for One or Two White Inputs in a Strategic Performance Area," was used as guidance for the inspection.Based upon the results of this inspection, the NRC determined that the problem identification,root and contributing cause evaluation, extent of condition and cause assessment, andcorrective actions for the White performance indicator were adequate. No findings of significance were identified. Therefore, consistent with NRC Inspection Manual Chapter 0305,Operating Reactor Assessment Program, the performance indicator will only be considered in assessing plant performance until it crosses below the threshold, returning it to a Green characterization.In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and itsenclosure will be available electronically for public inspection in the NRC Public Document 2Mr. Christopher M. CraneRoom or from the Publicly Available Records (PARS) component of NRC's document system(ADAMS). ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).
Sincerely,
/RA/
Lawrence T. Doerflein, ChiefEngineering Branch 2 Division of Reactor SafetyDocket No. 50-277License No. NPF-44Enclosure: NRC Inspection Report No. 05000277/20050w/Attachment: Supplemental Information cc w/encl:Site Vice President, Peach Bottom Atomic Power Station Plant Manager, Peach Bottom Atomic Power Station Regulatory Assurance Manager - Peach Bottom Associate General Counsel, Exelon Generation Company Manager, Financial Control & Co-Owner Affairs Manager Licensing, PBAPS Director, Nuclear Training Correspondence Control Desk Director, Bureau of Radiation Protection (PA)
R. McLean, Power Plant and Environmental Review Division (MD)
R. Fletcher, Maryland Department of Environment T. Snyder, Director, Air and Radiation Management Administration, Maryland Department of the Environment (SLO, MD)
Public Service Commission of Maryland, Engineering Division Board of Supervisors, Peach Bottom Township B. Ruth, Council Administrator of Harford County Council Mr. & Mrs. Dennis Hiebert, Peach Bottom AllianceTMI - Alert (TMIA)
J. Johnsrud, National Energy Committee, Sierra Club Mr. & Mrs. Kip Adams Vice-President, Licensing and Regulatory Affairs Vice-President, Operations Mid-Atlantic Senior Vice-President, Nuclear Services Director, Licensing and Regulatory Affairs J. Fewell, Assistant General Counsel 2Mr. Christopher
SUMMARY OF FINDINGS
IR 05000277/2005008; 12/05/2005 to 12/07/2005; Peach Bottom Atomic Power Station Unit 2;Supplemental Inspection of Scrams With Loss of Normal Heat Removal Performance Indicator. This inspection was conducted by two regional inspectors. No findings of significance wereidentified. The NRC's program for overseeing the safe operation of commercial nuclear powerreactors is described in NUREG-1649, "Reactor Oversight Process," Revision 3, datedJuly 2000.
Cornerstone: Initiating Events
The U.S. Nuclear Regulatory Commission (NRC) performed this supplemental inspection toassess Exelon's evaluation in response to a White performance indicator (PI) in the initiating events cornerstone. Peach Bottom Unit 2 crossed the threshold from Green to White for Scrams With Loss of Normal Heat Removal in the fourth quarter of calendar year 2004. This supplemental inspection assessed Exelon's problem identification, cause evaluation and corrective actions associated with the Unit 2 Scrams With Loss of Normal Heat Removal PI.
Based on the results of this inspection, no findings of significance were identified.Overall, the inspectors concluded that Exelon adequately addressed the problem identificationand problem resolution attributes of NRC inspection procedure 95001. The inspectors did notidentify any common root causes for the three scrams. Minor weaknesses were noted associated with root cause characterization, and the timeliness and adequacy of documenting potentially similar problems in the corrective action program. None of these weaknesses adversely impacted Exelon's conclusions or corrective actions. Some examples of these problems were similarly identified and discussed in Exelon's focused area self assessment, which was completed several weeks prior to the NRC's supplemental inspection.Therefore, consistent with the guidance in NRC Inspection Manual Chapter (IMC) 0305,Operating Reactor Assessment Program, the performance indicator associated with Loss of Normal Heat Removal will only be considered in assessing plant performance until it crosses below the threshold, returning it to a Green characterization.
Enclosure
REPORT DETAILS
01INSPECTION SCOPE (IP 95001)The U.S. Nuclear Regulatory Commission (NRC) performed this supplementalinspection in accordance with NRC Inspection Procedure (IP) 95001, "Inspection ForOne or Two White Inputs in a Strategic Performance Area," to assess Exelon's problem identification, cause evaluation and corrective actions associated with the Peach BottomUnit 2 Unplanned Scrams with Loss of Normal Heat Removal Performance Indicator (PI). This performance indicator was characterized as White in the fourth quarter 2004.
A total of three scrams with loss of normal heat removal caused the performance indicator to cross the Green - White threshold on this occasion. A summary of the three scram events, including the licensee identified root or apparent cause, and correctiveactions to prevent recurrence, are listed below:*On December 21, 2002, an electro-hydraulic control (EHC) system circuit cardfailure resulted in a closure of main steam isolation valves (MSIV) and a scram.
Exelon concluded that the circuit card failure was caused by a manufacturing defect in a component on the circuit card. The circuit card had been installed three months earlier. The corrective actions included ensuring there were no similar defective components installed on circuit cards at Peach Bottom.*On July 22, 2003, a main generator lockout and scram occurred as a result of aground fault caused by a piece of broken fan belt in the isophase bus duct cooling system. Exelon concluded that a design weakness existed in that therewere no debris guards to prevent intrusion of fan belt material into the fan suction. The corrective actions included installing debris guards.*On December 22, 2004, an EHC system circuit card failure resulted in a closureof MSIVs and a scram. Exelon concluded that the circuit card failure was caused by a manufacturing defect associated with a particle of solder that was deposited across two of the traces on the card. The circuit card had been installed three months earlier. The corrective actions included inspecting all circuit cards prior to installation for the existence of similar solder deposits on the circuit traces.02 EVALUATION OF INSPECTION REQUIREMENTS02.01 Problem Identificationa. Determination of who identified the issue and under what conditionsThe White Unplanned Scrams With Loss of Normal Heat Removal PI was self revealingthrough Exelon's collection of PI data taken in support of the NRC's reactor oversightprogram. Each of the three reactor scrams with loss of normal heat removal that caused the PI to cross the Green-White threshold were also self-revealing.
2Enclosureb. Determination of how long the issue existed, and prior opportunities for identificationThe inspectors concluded that the prior opportunities for identification were appropriatelyassessed in the root cause evaluations, as applicable. For example, Exelon concluded that the root cause evaluation for the December 21, 2002, EHC card failure provideddetails regarding opportunities to have learned from prior similar circuit card failures in EHC.c. Determination of the plant-specific risk consequences and compliance concernsThe risk significance was addressed as part of the investigations associated with each of the three events. The licensee determined that the events were of very low risksignificance. The inspectors agreed with this determination based on a review of the individual events. The NRC performed a special inspection for the EHC circuit cardfailure in December 2002; the results of this inspection are documented in NRC Inspection Report 05000277/2003007. The inspectors concluded that Exelon adequately addressed the problem identificationattributes of inspection procedure 95001.02.02 Root Cause and Extent of Condition Evaluationa. Evaluation of methods used to identify root causes and contributing causesExelon used a combination of event and causal factor, barrier analysis, cause and affectanalysis, and complex trouble shooting techniques to evaluate the issues. The inspectors found the evaluation methods to be acceptable.Noting that the NRC had previously performed a supplemental inspection for unplannedscrams and reviewed two of the three events (NRC Inspection Report05000277/2004011), Exelon performed a pre-inspection assessment of the individual and aggregate actions taken to address the December 2004 event, and a review of the corrective actions for the December 2002 and July 2003 events. The inspectors determined that the deficiencies identified in the assessment were adequatelyaddressed.The inspectors did not identify a common cause for the three scrams. However, theinspectors identified a minor weakness related to the effectiveness of evaluating potentially similar issues in Exelon's corrective action program. Examples of this problem were identified and discussed in the Exelon's self assessment.Exelon did not perform a separate common cause analysis in response to the White PI,although key elements of a common cause analysis were contained in the December 2004 event evaluation. Since there was no common cause analysis, the inspectors independently evaluated the cause analysis for each of the three scrams.
3Enclosureb. Level of detail of the root cause evaluationOverall, the inspectors found the level of detail of the root cause evaluations wasacceptable. However, there was one observation associated with Exelon's root cause characterization, as described below.Based upon interviews and data reviewed, the inspectors observed that some rootcause conclusions appeared to be driven by the corrective action process rather than the root cause evaluation. Specifically, some licensee staff indicated that in order for acause to be called the root cause, there had to be an adverse condition that was licensee-correctable with an associated corrective action to prevent recurrence (CAPR)assigned. Procedurally, this is not a requirement as some adverse conditions, such as an undetectable manufacturing defect, is not licensee-correctable. This misconception led to some of the root causes for the events being incorrectly labeled as contributing causes. For instance, the December 2002 event was determined to be due to a faulty subcomponent on a circuit card, specifically an operating amplifier, but Exelon determined that the root cause was the EHC system design was not fault tolerant. Theassociated CAPR for this root cause was an assignment to replace the EHC system with a digital, fault tolerant system. Subsequently, the station reevaluated the root cause forthis event and determined that the previously identified root cause was too broad andcould not be corrected in a timely manner. Exelon appropriately recharacterized the root cause to be the manufacturing defect, although there was not a specific CAPR associated with it.The inspectors characterized this as a weakness in that an incorrect root causedetermination can potentially lead to ineffective corrective actions. Nonetheless, in the evaluations reviewed, the inspectors found that the actual root causes and contributingcauses were associated with appropriate corrective actions.c.Consideration of prior occurrences of the problem and knowledge of prior operatingexperienceOverall, the root cause reports associated with the individual events considered prioroccurrences and similar problems where applicable. The inspectors did not identify any additional examples in which prior occurrences of the problem or prior operating experience was not considered. d. Consideration of potential common causes and extent of condition of the problemOverall, the inspectors determined that the extent of condition and cause reviews wereadequate. However, in some instances, the inspectors identified minor weaknesses where the reviews were not effectively focused. One example includes the following: One aspect of the extent of cause review for the December 2002 EHC circuit cardfailure was weak regarding the contributing cause of not generating condition reports for previous similar operating amplifier failures. The Exelon investigation found that condition reports were not written because
- (1) Exelon staff was not aware of the 4Enclosureprocedure requirement to do so, and
- (2) for not applying engineering fundamentals. These errors were attributed to poor change management in that maintenance personnel were not aware of the rework procedure requirements. The Exelon staff at Peach Bottom missed the opportunity to develop broader corrective actions for change management problems until prompted by assessments of several external groups, including Exelon Nuclear Oversight and the corporate Nuclear Safety Review Board, about a year later.Overall, regarding the root cause and extent of condition evaluations, the inspectorsconcluded that Exelon adequately determined and corrected the root causes of theevents. Exelon addressed the inspectors' observation related to the adequacy of correctly labeling the root and contributing causes by initiating Condition Report 430987 in their corrective action program.02.03 Corrective Actionsa. Appropriateness of corrective actionsExelon implemented appropriate and timely corrective actions to repair the equipmentdeficiencies associated with each of the reactor scrams. They also instituted adequate barriers or other corrective actions to address the issues that were related to other thanequipment problems (e.g., process and procedure changes).b. Prioritization of corrective actionsThe proposed corrective actions were prioritized commensurate with safety significance. The inspectors identified minor weaknesses related to corrective action timeliness, and one example is described below:Corrective actions for one of the contributing causes associated with the brokenisophase bus duct cooling fan belt (July 2003 scram) were not timely. Specifically, the installation of matched belt sets on all isophase cooling fans, which will minimize beltfailures, was not completed on Unit 3 until September 2004, more than a year after the event.c.Establishment of a schedule for implementing and completing the corrective actionsThe inspectors determined Exelon's schedule for implementing and completingcorrective actions was adequate.d. Establishment of quantitative or qualitative measures of success for determining theeffectiveness of the corrective actions to prevent recurrenceThe corrective action plans for the three events included effectiveness reviews;however, most of these reviews were not completed prior to the end of this inspection.
5EnclosureThe inspectors concluded that sufficient actions have been taken to reasonably preventrecurrence of similar events. This conclusion is also supported by the fact that there were no additional scrams as of the conclusion of this inspection.03 MANAGEMENT MEETINGS 03.01Exit Meeting SummaryThe results of this inspection were discussed with Mr. B. Braun, Site Vice President, andother members of Exelon management and staff at the conclusion of this inspection on December 7, 2005. No proprietary information was received as part of this inspection.03.02Regulatory Performance MeetingIn accordance with the requirements of Manual Chapter 0305, the exit meeting alsoserved as a Regulatory Performance meeting, with Mr. Richard J. Conte, OperationsBranch Chief, NRC Region I, meeting with Mr. B. Braun and other members of thelicensee staff.ATTACHMENT:
SUPPLEMENTAL INFORMATION
KEY POINTS OF CONTACT
Exelon Generation Company
- D. Henry, Manager, Business Support
- B. Woodard, System Engineer
- D. Foss, Regulatory Assurance
- C. Behrend, Senior Manager, Engineering
- J. Mallon, Manager, Regulatory Assurance
DOCUMENTS REVIEWED
Corrective Action DocumentsCR
- 430987,
- CR 248779Root Cause Report for
- CR 137110, "Failed EHC Card Caused Unit 2 Reactor Scram andprimary containment isolation system Group I Isolation" (12/21/02 event)Root Cause Report for
- CR 168589, "Unit 2 Scram Due to Generator Lock Out (Isophase BusCooler Belt foreign material exclusion)" (7/22/03 event)Root Cause Report for
- CR 336743, "Primary Containment Isolation System Group I IsolationDue to High Main Steam Line Area Temperature" (7/22/03 event)Root Cause Report for
- CR 285024, "Reactor Scram due to malfunction of an Electro HydraulicControl System Pressure Setpoint Card," (12/22/04 event) Procedures and Other DocumentsLS-AA-125, Corrective Action Program Procedure, Rev. 9LS-AA-125-1001, Root Cause Analysis, Rev. 5