05000249/LER-2002-005, High Pressure Coolant Injection System Inoperable Due to Water Hammer Event
| ML023440241 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/03/2002 |
| From: | Hovey R Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RHLTR: #02-0087 LER 02-005-00 | |
| Download: ML023440241 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2492002005R00 - NRC Website | |
text
Exe I tn S
Exelon Generation wwwexeloncorpcoM Nucear Dresden Generating Station 6500 North Dresden Road Morris, IL 60450-9765 Tel 815-942-2920 10 CFR 50.73 December 3, 2002 RHLTR: #02-0087 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 3 Facility Operating License No. DPR-25 NRC Docket No. 50-249
Subject:
Licensee Event Report 2002-005-00, "Unit 3 High Pressure Coolant Injection System Inoperable Due to Water Hammer Event" Enclosed is Licensee Event Report 2002-005-00, "Unit 3 High Pressure Coolant Injection System Inoperable Due to Water Hammer Event," for the Dresden Nuclear Power Station. This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B). "Any operation or condition which was prohibited by the plant's Technical Specifications."
Corrective actions include:
Repaired the Unit 3 High Pressure Coolant Injection (HPCI) supports, M-1187D-80 and M-1187D-83.
Vented Units 2 and 3 HPCI pump discharge piping in the X-Area, Torus Area and HPCI Pump Room.
Revised appropriate station procedures to include all high p5oint vents when venting and require venting of the HPCI pump discharge piping when lined up to the CCST.
Performed a modification on Unit 3 to eliminate potential steam voids on HPCI initiation by adding a pressure permissive on the injection valve.
Scheduled a modification to be performed on Unit 2 to eliminate potential steam voids on HPCI initiation by adding a pressure permissive on the injection valve.
Developed and implemented a Design Engineering Plan to address the knowledge and management deficiencies in the areas of problem solving, performance of operability evaluations, walk-downs, recognizing safety significance of issues without being prompted by outside agencies, identification and resolution of issues, communication, and issue management.
U. S. Nuclear Regulatory Commission December 3, 2002 Page 2 Revised NES-MS-03.2 "Evaluation of Discrepant Piping and Support Systems", to recommend expediting repair when the cause of the degradation is unknown and to include guidance on when to consider cause as an integral element of Operability Determination.
Reviewed Open Operability Determinations for Extent of Condition.
Performance managed individuals involved on challenging the quality of ACE's, Operability Determinations and being aware of compensatory actions. Reinforced expectations regarding ACE quality and operability determinations.
Developed guidance on how to properly evaluate and respond to NRC concerns and presented as a discussion topic at the Engineering Support Personnel Training session.
Developed a post-transient system walk-down process with a standard walk-down checklist and appropriate review by engineering management.
If you have any questions, please contact Mr. Jeff Hansen, Regulatory Assurance Manager at (815) 416-2800.
Respectfully, 1~Li-R. J. ovey 4ONg' Site ice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator-NRC Region IlIl NRC Senior Resident Inspector.- Dresden Nuclear Power Station
He
Abstract
On July 19, 2001, Dresden Nuclear Power Station (DNPS) personnel identified a Unit 3 High Pressure Coolant Injection (HPCI) discharge piping support in a degraded condition. An operability determination was performed, which supported continued HPCI operability. Due to perceived low safety significance, the damaged support was not immediately repaired.
Corrective actions were to restore the supports during the next scheduled maintenance window. A review of Transient Analysis Display System (TADS) data made it apparent that a hydrodynamic transient / water hammer had occurred on July 5, 2001, during an automatic initiation of the Unit 3 HPCI system. The hydrodynamic transient / water hammer event was the result of a combination of air pockets and steam voids in the discharge piping, which resulted from inadequate venting of the system. The support was repaired and the discharge piping vented on September 30, 2001. On November 16, 2001, the Nuclear Regulatory Commission (NRC) issued an Inspection Report which identified an Unresolved Item associated with the operability of the HPCI system with the degraded support. In January 2002, DNPS provided engineering analysis to the NRC and in June of 2002, the NRC transmitted a Request for Additional Information associated with the analysis. These questions were discussed in a meeting on July 25, 2002, and in subsequent teleconferences between members of Exelon and NRC. In response to these questions, DNPS performed additional evaluations. Subsequently, DNPS has been unable to demonstrate through analysis that the Unit 3 HPCI piping and supports would have met operability evaluation acceptance criteria following an additional automatic initiation. On October 4, 2002, DNPS concluded that the Unit 3 HPCI system was inoperable for the period following the hydrodynamic transient /
water hammer on July 5, 2001, until September 30, 2001.U.S. NUCLEAR REGULATORY APPROVED BY OMB NO.3150-104 COMMISSION EXPIRES 07131/2004 (7-2001)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection FACILITY NAME (1)
DOCKET NUMBER (2)
ER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL I REVISION Dresden Nuclear Power Station Unit 3 05000249 NUMBER NUMBER 2002 005 00 2 of 4 (If more space Is required, use additional copies of NRC Form 366A)(17)
A.
Plant Conditions Prior to Event:
Unit: 03 Event Date: 07-05-2001 Event Time: 1006 CDT Reactor Mode: 1 Mode Name: Run Power Level: 100 percent Reactor Coolant System Pressure: 1000 psig B.
Description of Event
On July 19, 2001, it was identified that two out of four base plate anchors for support M-1187D-80 were partially pulled out of the concrete on the underside of the 517'-6" slab, above the torus. Engineering performed an immediate extent of condition walk-down of the HPCI [BJ] pump discharge piping that could be accessed from the torus catwalk area. The engineers inspected the adjacent supports for similar damage. No other visible damage to accessible supports was identified. A corrective action program condition report (CR) was written and a prompt operability determination was completed.
On July 24, 2001, the final Operability Determination 01-031 was completed in accordance with the station's operability determination process and NES-MS-03.2, "Evaluation of Discrepant Piping and Support Systems." It concluded that the system was operable for design basis loads with the existing support damage. The conclusion of the operability determination was based on the past experience and practice that systems could be considered operable even with the failure of one support due to conservatism in design.
A work request (WR) was written to repair the support and was identified as part of the operability determination.
The WR completion was scheduled for November 1, 2001 based on the normal work control scheduling process.
Subsequently, the WR Screening Committee assigned the work request a lower priority, and the repair was rescheduled for a later date.
On July 26, 2001, a management review committee screened the CR and an apparent cause evaluation (ACE) was assigned to engineering to investigate the cause of the failed support. On August 24, 2001, the ACE was completed and approved. The ACE stated, "It is likely that the anchor deficiencies are a result of a transient (water hammer) possibly associated with the Unit 3 scram, or could be the result of another event." The ACE also stated the following corrective action: "The Dresden water hammer subject matter expert (SME) should perform a water hammer evaluation to determine if any further actions are required." This action was tracked by an action tracking item (ATI) with a due date of December 7, 2001. The completed ACE, which lacked a quality supervisory review, did not present a basis for the stated apparent cause and did not assess the impact of its conclusion on the open operability determination.
On September 26, 2001, the NRC Regional Inspector expressed concerns regarding the adequacy of the operability determination. The concerns were: (a) the failed support was not repaired, (b) there were no corrective actions in place to prevent the piping loads necessary to fail the support from recurring, (c) the system had not been vented, and (d) the Operability Determination did not consider any transient that might have failed the support.
Following additional walkdowns, on September 29, 2001, Operability Determination 01-031 was revised to remove 6redit for the two intact anchors on the damaged support. The supports were repaired on September 30, 2001, and Unit 3 HPCI pump discharge piping was vented at the high point vent per the venting procedure. Air was found, but no steam or hot water was noted. As a result of finding air, a review for past reportability was initiated.
The Unit 2 HPCI pump discharge piping was vented on October 1, 2001, and air was found. It was determined that the amount of air found in the Unit 2 HPCI system would not cause a damaging transient.U.S. NUCLEAR REGULATORY APPROVED BY OMB NO.3150-0104 COMMISSION EXPIRES 07/3112004 (7-2001)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection FACILITY NAME 1)
DOCKET NUMBER (2)
LER NUMBER 6 PAGE (3)
YEAR SEQUENTIAL REVISION I
Dresden Nuclear Power Station Unit 3 05000249 NUMBER NUMBER 2002 005 00 3 of 4 (If more space is required, use additional copies of NRC Form 366A)(17)
During this time period the Transient Analysis Display System (TADS) was reviewed for the July 5, 2001, scram.
Engineering personnel concluded the HPCI system had experienced a hydrodynamic transient / water hammer on July 5, 2001.
October 17, 2001, a CR was issued to document the July 5, 2001, HPCI pressure and flowrate transient data and its impact on Operability Determination 01-031. From the period between October 2001 and October 2002, numerous communications between Exelon and the NRC were conducted. Although the support had been repaired and the discharge piping vented, engineering performed detailed analyses assuming the pipe support was in a degraded condition and the system not properly vented in order to determine past reportability of the condition. Subsequently, DNPS has been unable to demonstrate through analysis that the Unit 3 HPCI piping and supports would have met operability evaluation acceptance criteria following an additional automatic initiation.
Thus, it has been concluded that the Unit 3 HPCI system was inoperable for the period following the hydrodynamic transient / water hammer on July 5, 2001, until September 30, 2001.
C.
Cause of Event
Two root causes were identified as a result of this event. One root cause addressed the cause of the damage to the support and the other addressed the station's management of the issue. The root cause of the HPCI support failure was a hydrodynamic transient / water hammer during the system actuation on July 5, 2001, due to air pockets and steam voids in the HPCI pump discharge piping. The cause of the air pockets was due to inadequate venting of the system. The root cause of the management issues was the failure of Design Engineering to evaluate the HPCI operability issue from the proper safety perspective because the focus was on demonstrating operability and not on recognizing the extent of the degraded condition, which resulted in untimely corrective actions. Corrective actions to prevent recurrence are: (1) to implement modifications and revise appropriate procedures as required, to ensure that air/steam voids do not recur and (2), to develop and implement a Design Engineering Excellence Plan to address the management issues and knowledge deficiencies.
D.
Safety Analysis
This event has been determined to be of low to moderate safety significance. This result is based on an assumption that the HPCI discharge piping stresses would exceed operability limits if HPCI injected during the period of approximately 80 days during which the support was degraded and the potential for an additional hydraulic transient existed. The Automatic Depressurization, Isolation Condenser [BL], Low Pressure Coolant Injection [BO], and Core Spray [BM] systems were operable and available, except for short periods during maintenance (within Technical Specification compliance), to provide reactor pressure / inventory control under postulated design basis accident conditions.
E.
Corrective Actions
The Unit 3 HPCI supports M-1187D-80 and M-1187D-83 were repaired.
The Unit 2 and 3 HPCI pump discharge piping in the X-Area, torus Area and HPCI pump room was vented.
Appropriate station procedures were revised to include all high point vents when venting and require venting of the HPCI pump discharge piping when lined up to the CCST.
A modification was performed on Unit 3 to eliminate potential steam voids on HPCI initiation by adding a pressure permissive on the injection valves. A similar modification will be performed on Unit 2.U.S. NUCLEAR REGULATORY APPROVED BY OMB NO.3150-0104 COMMISSION EXPIRES 07131/2004 (7-2001)
Estmated, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
FACILITY NAME (1)
DOCKET NUMBER (2)
ER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL I REVISION Dresden Nuclear Power Station Unit 3 05000249 NUMBER NUMBER 2002 005 00 4 of 4 (If more space is required, use additional copies of NRC Form 366A)(17)
Developed and implemented a Design Engineering Plan to address the knowledge and management deficiencies in the areas of problem solving, performance of operability evaluations, walk-downs, recognizing safety significance of issues without being prompted by outside agencies, identification and resolution of issues, communication, and issue management.
NES-MS-03.2 'Evaluation of Discrepant Piping and Support Systems," was revised to recommend expediting repair when the cause of the degradation is unknown and to include guidance on when to consider cause as an integral element of operability determinations.
Open operability determinations were reviewed for extent of condition.
Performance managed individuals involved on challenging the quality of ACE's, Operability Determinations and being aware of compensatory actions. Reinforced expectations regarding ACE quality and operability determinations.
Developed guidance on how to properly evaluate and respond to NRC concerns and presented as a discussion topic at the Engineering Support Personnel Training session.
A post-transient system walk-down process was developed with a standard walk-down checklist and appropriate review by engineering management.
F.
Previous Occurrences
None G.
Component Failure Data
N/A