05000298/LER-2007-004, Re Manual Reactor Trip Due to Hydraulic Control Unit Valve Bonnet Leak Into Reactor Building
| ML072010015 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/16/2007 |
| From: | Michael Colomb Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2007053 LER 07-004-00 | |
| Download: ML072010015 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982007004R00 - NRC Website | |
text
N Nebraska Public Power District Always there when you need us NLS2007053 July 16, 2007 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2007-004-00 Cooper Nuclear Station, NRC Docket 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2007-004-00.
Sincerely, Michael J. Colomb General Manager of Plant Operations
/em Enclosure cc:
Regional Administrator w/enclosure USNRC - Region IV Cooper Project Manager w/enclosure USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/enclosure USNRC - CNS SRAB Administrator w/enclosure NPG Distribution w/enclosure INPO Records Center w/enclosure SORC Administrator w/enclosure CNS Records w/enclosure COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax:. (402) 825-5211 www.nppd.com
ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS@
ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS0 Correspondence Number: NLS2007053 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory
commitments
Please notify the Licensing Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.
COMMITMENT
COMMITTED DATE
COMMITMENT
NUMBER OR OUTAGE None I
I.
4 4.
4 4.
Procedure 0.42 Revision 21 Page 18 of 25
Abstract
On 5/19/2007 at 00:25 CDT, Cooper Nuclear Station (CNS) was in Mode 1 at 50%
Power in Single Loop Operation when a small water leak developed from a Control Rod Drive Hydraulic Control Unit (HCU) directional control valve (DCV) during maintenance.
The leak degraded to the point of a visible steam plume, and prompted a precautionary Reactor Building evacuation. After several unsuccessful attempts to isolate the leak operators made the conservative decision to remove the unit from service. At 02:12 CDT, the operators manually scrammed the reactor. Control rods inserted normally. A Group 2 Primary Containment isolation signal isolated required systems. The scram was uncomplicated with systems functioning as required. No off-site releases occurred due to the HCU valve leak which stopped after the scram. The manual scram and controlled shutdown were not nuclear risk significant. Leakage past a manual isolation valve is the most probable direct cause of the DCV internal pressure. The cause of the leak was that tag-out implementation and acceptance for maintenance did not require verification that HCU was de-pressurized, nor were contingencies in place if it was not.
Corrective actions are being tracked in CNS's corrective action program.
NRI" FORM 366 (6-2004)
(If more space is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of Form 366A) reported this under 50.72(b)(2)(iv)(B) as a 4 Hour (Hr) Emergency Notification System (ENS) Notification and under 50.72(b)(3)(iv)(A) as an 8 Hr ENS Notification.
SAFETY SIGNIFICANCE
The manual scram and controlled shutdown that resulted from the leak in HCU 26-27 was not a nuclear risk significant event. Mitigating equipment responded as expected.
The leak did not impact functionality of any equipment and stopped after the plant shutdown. Therefore, this event resulted in negligible change in core damage frequency.
CAUSE
The root cause was that neither the Clearance Order (i.e. Tag-Out) implementation, nor the acceptance of the system for maintenance required explicit, positive verification that the system energy source was isolated, and neither process identified contingency actions in case the system was still pressurized. Leakage past one of the manual isolation valves (CRD-V-101) is the most probable direct cause of the pressure persisting internal to CRD-V-122 (HCU 26-27).
'CORRECTIVE ACTION - The following actions are being tracked in the CNS Corrective Action Program.
A.
Revise the Clearance Order process to require verification of hazardous, off-normal, mode changed, or unusual system isolation prior to system release for maintenance, and to include identified contingency actions in case the system energy source cannot be isolated. Include maintenance verification by positive actions that the isolated system energy has been removed.
B.
Inspect CRD-V-1 01 (HCU 26-27) to determine if there is any mechanical degradation which could explain the leakage associated with this event. Develop and implement corrective actions for leakage based upon the results of the inspection.
PREVIOUS EVENTS There have been no reportable events identified in the past 7 years related to HCU leaks.
NRC FORM 366 (1-2001)