IR 05000317/2007006
| ML070610074 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 02/28/2007 |
| From: | Rogge J Engineering Region 1 Branch 3 |
| To: | Spina J Calvert Cliffs |
| References | |
| IR-07-006 | |
| Download: ML070610074 (11) | |
Text
ary 28, 2007
SUBJECT:
CALVERT CLIFFS NUCLEAR GENERATING STATION - NRC SUPPLEMENTAL INSPECTION REPORT 05000317/2007006 and 05000318/2007006
Dear Mr. Spina:
On January 25, 2007, the U.S. Nuclear Regulatory Commission (NRC) completed a supplemental inspection at the Calvert Cliffs Nuclear Power Plant Units 1 and 2. The enclosed report documents the inspection results that were discussed on January 25, 2007, with you and other members of your staff.
The NRC performed this supplemental inspection to assess your evaluation of a low to moderate (White) safety significant finding related to an incorrect circuit breaker setting that would have impacted the ability of the Unit 1 1A emergency diesel generator to perform its intended safety function under certain design basis conditions. The supplemental inspection was conducted to determine if the root and contributing causes of the finding were understood, to assess the extent of condition review, and to determine if the corrective actions were sufficient to address causes and prevent recurrence. The inspection was conducted in accordance with Inspection Procedure 95001, Inspection for One or Two White Inputs in a Strategic Performance Area, and examined activities conducted under your license as they relate to safety and compliance with the Commissions rules and regulations and with the conditions of your license. The inspection included a review of your Reply to a Notice of Violation, EA-06-198, dated November 27, 2006.
Based on the results of this inspection, we concluded that you have adequately completed a root cause analysis of the performance deficiency and have identified and implemented appropriate corrective actions. No findings of significance were identified. Given your acceptable performance in addressing the cause of the circuit breaker trip, the White finding associated with this issue will only be considered in assessing Unit 1 plant performance for a total of four quarters in accordance with the guidance in Inspection Manual Chapter (IMC) 0305, Operating Reactor Assessment Program.
In accordance with 10 CFR 2.390 of the NRCs Rules of Practice, a copy of this letter and its enclosure will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records (PARS) component of NRCs document system (ADAMS). ADAMS is accessible from the NRC Website at http://www.nrc.gov/reading-rm/adams.html (The Public Electronic Reading Room).
Sincerely,
/RA/
John F. Rogge, Chief Engineering Branch 3 Division of Reactor Safety Docket Nos. 50-317 50-318 License Nos. DPR-53 DPR-69
Enclosure:
Inspection Report 05000317/2007006 and 05000318/2007006 w/Attachment: Supplemental Information
REGION I==
Docket Nos. 50-317, 50-318 License Nos. DPR-53, DPR-69 Report Nos. 05000317/2007006 and 05000318/2007006 Licensee: Constellation Generation Group, LLC Facility: Calvert Cliffs Nuclear Power Plant, Units 1 and 2 Location: 1650 Calvert Cliffs Parkway Lusby, Maryland 20657-4702 Dates: January 23 - 25, 2007 Inspector: Larry Scholl, Senior Reactor Inspector, DRS Approved by: John F. Rogge, Chief Engineering Branch 3 Division of Reactor Safety i Enclosure
SUMMARY OF FINDINGS
IR 05000317/2007006, 05000318/2007006; 01/23/2007 - 01/25/2007; Calvert Cliffs Nuclear
Power Plant, Units 1 and 2; Supplemental Inspection; IP 95001, Inspection for One or Two White Inputs in a Strategic Performance Area.
The inspection was conducted by a regional inspector. The NRCs program for overseeing the safe operation of commercial nuclear power reactors is described in NUREG-1649, Reactor Oversight Process, Revision 3, dated July 2000.
Cornerstone: Mitigating Systems
The NRC performed this supplemental inspection, in accordance with Inspection Procedure 95001, to assess the licensees evaluation associated with the incorrect overcurrent trip set point for the supply circuit breaker to Unit 1 1MCC123. This performance issue was previously characterized as having low to moderate risk significance (White) in NRC Inspection Reports 05000317/2006012 and 05000318/2006012.
Constellations evaluation of the issue included performing a formal root cause analysis to identify the root and contributing causes associated with the improper circuit breaker trip set point and to identify corrective actions to address these causes.
Based on the results of this inspection, the inspector concluded that Constellation completed a thorough evaluation of the performance deficiencies associated with this finding and implemented appropriate corrective actions to address the related causes. Given Constellations acceptable performance in addressing the improper circuit breaker trip set point, the White finding associated with this issue will only be considered in assessing Unit 1 plant performance for a total of four quarters in accordance with the guidance in IMC 0305, Operating Reactor Assessment Program.
ii
REPORT DETAILS
INSPECTION SCOPE
The U.S. Nuclear Regulatory Commission (NRC) performed this supplemental inspection to assess Constellations evaluation of the root and contributing causes for the trip of the feeder circuit breaker for safety-related motor control center 1MCC123 on March 24, 2006. This motor control center (MCC) supplies 480 volt power to the 1A emergency diesel generator support equipment which include radiator cooling fans and building ventilation fans. The circuit breaker trip was due to inadequate design controls that resulted in an improper short-time overcurrent trip set point combined with the normal drift of the trip unit set point. As a result, the EDG would not have been able to perform its safety function following a loss of offsite power (LOOP) under certain conditions. The 0C EDG was similarly affected, but to a lesser degree since the amount of trip set point drift was found to be less than that of the 1A EDG.
This performance issue was previously characterized as a finding with low to moderate safety significance (White) in NRC inspection report numbers 05000317/2006012 and 05000318/2006012 and is related to the mitigating systems cornerstone in the reactor safety strategic performance area. The inspector performed a walk-down of the affected EDGs, interviewed selected Constellation staff, and reviewed documents pertaining to the root cause evaluation and corrective actions for the event. The inspector also reviewed the corrective actions to ensure the actions addressed both the root and contributing causes for the identified performance deficiencies. The inspection also included a review of the adequacy of Constellations Reply to a Notice of Violation, EA-06-198, dated November 27, 2006, and Licensee Event Report 2006-001, 1A Emergency Diesel Generator Feeder Breaker Tripped Due to Low Design Set Point, Revision 1.
EVALUATION OF INSPECTION REQUIREMENTS 02.01 Problem Identification a.
Determination of who identified the issue and under what conditions.
The circuit breaker trip was a self-revealing finding identified during the performance of an EDG surveillance test on March 24, 2006. During surveillance and test procedure (STP) O-004A-1, Unit 1 A-Train ESF Test, a loss-of-offsite-power is simulated, the EDG starts and powers the both the 4 kV bus loads and 1MCC123. Due to the low set point and the effects of the trip unit (Amptector) drift, the inrush current when the MCC energized exceeded the short-time overcurrent set point, tripping the feeder breaker.
b. Determination of how long the issue existed and prior opportunities for identification
.
Constellations evaluation determined that the improper overcurrent trip set point was established as the result of a design error when the 1A and 0C were installed by a plant modification in 1996. Prior opportunities for identification would have been during the modification design development and design reviews and/or during post-modification testing. However, neither the design reviews or the post-modification test were sufficiently rigorous to identify the deficiency. Both the design agent and CCNPP design acceptance reviews failed to identify the problem. The post-modification test was not conducted in a manner that ensured the breaker would be subjected to the maximum possible level of inrush current during the MCC energization. For example, the number of building ventilation fans that start simultaneously is dependent on the building temperature at the time of the EDG start following a LOOP. At low temperatures one will start and the number of additional starts increases as room temperature increases. All four fans would start simultaneously at a design room temperature of 105EF.
The problem was not identified during previous surveillance tests because, due to ambient temperature conditions, only one building ventilation started during those tests.
Additionally, and at the time of those tests, the amount of Amptector set point was not sufficient to cause a trip at the reduced current levels associated with at single fan start.
c.
Determination of the plant-specific risk consequences and compliance concerns associated with the issue.
Constellations Root Cause Analysis Report, Rev. 1, estimated that the MCC feeder breaker would have tripped approximately 70% of the times the EDG would have started between March 24, 2005, and March 24, 2006, resulting in an increase in core damage frequency (CDF) of approximately 5E-6. The NRCs risk evaluation reached similar conclusions.
02.02 Root Cause and Extent of Condition Evaluation a.
Evaluation of methods used to identify root cause and contributing causes.
To evaluate this issue, Constellation used a modified Kepner-Tregoe Problem Analysis for the equipment-related analysis. They used Problem Analysis, Why Staircase, and Cause-Effect Analysis for the human performance-related analysis. The inspector determined that Constellation used appropriate methods to identify the root and contributing causes.
b.
Level of detail of the root cause evaluation.
The inspector determined that the level of detail of the root cause analysis was sufficient for the issue. In addition to addressing the cause of the incorrect short-time overcurrent trip set point, Constellation performed a review of Amptector calibration data for numerous circuit breakers to ensure there was not a programmatic issue with the set point drift.
c.
Consideration of prior occurrences of the problem and knowledge of prior operating experience.
Constellations evaluation included a consideration of previous internal and external operating experience that may be applicable to this issue. A number of internal and external events were reviewed; however, none of the issues would have afforded an opportunity to prevent this event.
d.
Consideration of potential common causes and extent of condition of the problem.
The inspector found that Constellations evaluation properly addressed extent of condition for both the equipment issues and the human performance issues. After identification of the set point issue with the MCC for the 1A EDG, the same problem was identified with the 0C EDG which is of similar design and was installed at the same time as the 1A EDG. Although the condition was not expected to affect the originally installed Fairbanks Morse EDGs, their associated MCC feeder breaker overcurrent trip set points were reviewed and found to be satisfactory. The extent-of-condition review was then expanded to include a determination of available margin for the 4160 volt and 480 volt safety-related bus feeder overcurrent trip set points. All bus feeder breaker set points were found to be acceptable.
02.03 Corrective Actions a.
Appropriateness of corrective actions.
Constellation took immediate corrective actions to increase the set points of MCC feeder circuit breaker 1BKR52-1703 and 0BKR52-0703 short-time overcurrent trip from 2400 amps to 3600 amps. Additional actions were subsequently taken to provide training to site engineers in the areas of owner acceptance review expectations regarding vendor design bases assumption verification and the use and preparation of Engineering Test Procedures for post-modification testing. The inspector concluded that the corrective actions were appropriate.
b.
Prioritization of corrective actions.
The inspector reviewed the prioritization of corrective actions and verified that all required actions had been completed within an appropriate time. Associated engineering documents had also been updated at the time of the inspection.
c.
Establishment of schedule for implementing and completing the corrective actions.
Constellations evaluation provided dates for completion of corrective actions. The inspector reviewed the status of corrective actions and found that all required actions had been completed. One action which remains incomplete is to increase the overcurrent trip time delay setting. This action is considered to be an additional enhancement and will be implemented during the next scheduled performance of the trip point test. The inspector reviewed this issue and concluded that increasing trip unit current level set point would be sufficient to prevent recurrence, without increasing the time delay.
d. Establishment of quantitative or qualitative measures of success for determining the effectiveness of the corrective actions to prevent recurrence.
The inspector found that Constellations root cause report contains appropriate actions to assess the effectiveness of corrective actions. The actions include verification there are no additional breaker trips, no condition reports related to vendor modifications that are caused by improper review of assumptions, and no conditions reports result that are related to inadequate Engineering Test Procedure scopes.
MANAGEMENT MEETINGS
Exit Meeting Summary
The results of this inspection were discussed with Mr. James Spina and other members of the Calvert Cliffs staff at the conclusion of this inspection on January 25, 2007.
Following the exit meeting, a Regulatory Performance Meeting was conducted, by conference call, in accordance with Inspection Manual Chapter 0305, Operating Reactor Assessment Program, and focused on the performance deficiencies associated with this issue and corrective actions to prevent recurrence. No proprietary information was discussed.
ATTACHMENT
SUPPLEMENTAL INFORMATION
KEY POINTS OF CONTACT
NRC Personnel
- S. Kennedy, Senior Resident Inspector, Calvert Cliffs
- M. Davis, Resident Inspector, Calvert Cliffs
- B. McDermott, Chief, Projects Branch 1, DRP
Licensee Personnel
- S. Loeper, System Manager
- J. Mark, Design Engineer
- A. Simpson, Senior Engineer, Regulatory Matters
- M. Simpson, Principal Engineer, Plant Engineering Section
ITEMS OPENED, CLOSED, AND DISCUSSED
Closed
- 05000317/2006012-01 VIO Failure to Adequately Control the Design of the 1A EDG Feeder Breaker for Essential EDG Support Systems
- 05000317, 318/2006001-01 LER 1A Emergency Diesel Generator Feeder Breaker Tripped Due to Low Design Set Point