05000298/LER-2010-004, Regarding Loss of Safety Function for Emergency Diesel Generators
| ML103270041 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 11/18/2010 |
| From: | Dori Willis Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2010094 LER 10-004-00 | |
| Download: ML103270041 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2982010004R00 - NRC Website | |
text
N Nebraska Public Power District Always there when you need us NLS2010094 November 18, 2010 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2010-004-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2010-004-00.
Sincerely, emetrius L. Willis General Manager of Plant Operations hJo Attachment cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/attachment USNRC - CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment SORC Chairman w/attachment CNS Records w/attachment COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5217 ww.wnppd.com
)J
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BYOMB NO. 3150-0104 EXPIRES 10/31/2013 (10-2010)
Estimated burden per response to comply with this mandatory information collection request: 80 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA/Privacy Service Branch (T-5 F53), U.S. Nuclear Regulatory Commission, LICENSEE EVENT REPORT (LER)
Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs NEOB-10202, (See reverse for required number of (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means digits/characters for each block) used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Cooper Nuclear Station 05000298 1 of 4
- 4. TITLE Loss of Safety Function for Emergency Diesel Generators
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH: DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
__05000 FACILITY NAME DOCKET NUMBER 08 19 2010 2010
- - 004 00 11 18 21 50
~05000
- 9. OPERATING MODE 1i. THIS REPORT IS SUBMITTED PURSUANT TO THF REOUIREMENTS OF 10 CFR 6: (Chek.k all that annlv) 1l 20.2201(b)
[] 20.2203(a)(3)(i)
F] 50.73(a)(2)(i)(C)
EL 50.73(a)(2)(vii)
EL 20.2201(d)
El 20.2203(a)(3)(ii)
L7 50.73(a)(2)(ii)(A)
LI 50.73(a)(2)(viii)(A)
LI 20.2203(a)(1)
El 20.2203(a)(4)
Z 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
LI 20.2203(a)(2)(i)
EL 50.36(c)(1)(i)(A)
EL 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
El 20.2203(a)(2)(ii)
LI 50.36(c)(1)(ii)(A) lI 50.73(a)(2)(iv)(A)
LI 50.73(a)(2)(x)
- 10. POWER LEVEL LI 20.2203(a)(2)(iii)
ED 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100 El 20.2203(a)(2)(iv)
EL 50.46(a)(3)(ii)
L] 50.73(a)(2)(v)(B)
El 73.71(a)(5)
LI 20.2203(a)(2)(v)
[3 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(C)
EL OTHER LI 20.2203(a)(2)(vi)
LI 50.73(a)(2)(i)(B)
[
50.73(a)(2)(v)(D)
Specify in Abstract below or in PLANT STATUS Cooper Nuclear Station (CNS) was in Mode 1, Power Operations, at 100% power at the time of discovery.
BACKGROUND The purpose of the standby (emergency) Alternating Current (AC) power system [EIIS: EK] is to provide a single failure proof source of on-site AC power adequate~for maintaining the safe shutdown of the reactor following abnormal operational transients and postulated accidents.
This system consists of two independent AC power sources, the Emergency Diesel Generators (EDG) [EIIS: DG].
Each EDG shall be capable of automatic start at any time and.capable of continued operation at rated load, voltage, and frequency until manually stopped.
Each EDG is housed in completely independent, separated rooms, together with respective auxiliary systems which are provided independently in all respects for each unit. The rooms are connected by doors [ElIS: DR] which are nonlouvered, steel doors. Each EDG room is designed as a Class I Seismic building.
CNS Technical Specifications require that two EDGs be operable when the plant is in Modes 1, 2, or 3, and that one DG be operable when the plant is in Modes 4 or 5.
EVENT DESCRIPTION
On August 19, 2010, at 10:05, Central Daylight Time (CDT), both EDG Doors N103 and N104 were propped open in support of planned maintenance on EDG2, which had been declared inoperable. The doors were propped open to allow a hose to run from the Turbine Building through EDGI room and into EDG2 room to support draining of the EDG2 jacket water system.
Door N103 is a Steam Exclusion Barrier (SEB) rated door located on the Turbine Building side of EDGI room. If a main steam line rupture were to occur in the Turbine Building, the steam could enter EDG1 room through the propped open Door N103.
At the time of the event, Operations determined EDGI system to be operable based on existing guidance documents. These existing guidance documents allowed for compensatory actions to be put in place to assure operability of EDG1 when Door N103 is left open. As a compensatory measure, per guidance documents in place at that time, a Security Officer was posted on the Turbine Building side of Door N103 to pull the hose and close the door in the event of steam leakage from the Turbine Building. Doors N103 and N104 were closed at 11:10 CDT upon completion of draining EDG2 jacket water system.
Based on initial review of the CNS Environmental Qualification Program Basis Document, Section 3.3.2.4.2, completed on September 21, 2010, the EDG rooms had not been evaluated or analyzed for a High Energy Line Break environment; therefore, with Door N103 propped
open, the plant was in an unanalyzed condition that had the potential to degrade plant safety.
Consequently, new information concerning the basis for the guidance documents was made available and Operations conservatively determined that by having Door N103 propped open, reasonable assurance was lost that the EDGI would fulfill its safety function.
Prior to this event, the issue of door impairments had been periodically documented in notifications and conditions reports. However, they were consistently dispositioned using Probabilistic Risk Assessment (PRA) evaluations. Consequently, CNS guidance documents dealing with the temporary impairment of SEB boundary doors were based upon the incorrect method of PRA, which also contained a latent presumption of operability. These guidance documents were then provided to the Operations staff for execution. At anytime work was planned in accordance with these guidance documents, the EDGs were inadvertently inoperable whenever Door N103 was propped open during Modes 1, 2, or 3.
BASIS FOR REPORT This event is being reported as an operation or condition that resulted in an unanalyzed condition that significantly degraded plant safety per 10 CFR 50.73(a)(2)(ii)(B); and also as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident per 10 CFR 50.73(a)(2)(v)(D).
SAFETY SIGNIFICANCE
The safety significance associated with this condition is considered negligible. The potential impact of this condition is limited to pipe breaks outside of containment. Therefore, EDG1 was available to respond to all other events during the short duration in which EDG2 was inoperable and Door N103 was open. There was no other impact to structures, systems or components that were needed to achieve safe shutdown, or mitigate potential accidents, transients and special events described in the Update Safety Analysis Report. The likelihood of occurrence of pipe breaks outside of containment during the time Door N103 was open resulted in a negligible increase to the core damage frequency reflected in the CNS PRA model.
This event is a safety system functional failure.
CAUSE
The root cause of the event was that impairment of Door N103 (a SEB door) for maintenance activities was evaluated using procedural guidance based upon a PRA rather than performing an operability evaluation.
CORRECTIVE ACTION
The procedure was revised to include specific guidance regarding the operability statements for impaired SEB doors.
The following corrective actions are being tracked in the Corrective Action Program and are not regulatory commitments:
Training materials will be prepared for Shift Technical Engineers and Senior Reactor Operators use that explains and clarifies when PRA can be used, and when the assessments cannot be used. Additionally, training will be delivered to an identified target population in Engineering to recognize the limitation of using PRA.
In addition, an evaluation of the effects of a High Energy Line Break on the environment in the EDG rooms will be performed.
PREVIOUS EVENTS There have been no events reported in the last three years related to SEB doors.
ATTACHMENT 3 LIST OF REGULATORY COMMITMENTSC 4 ATTACHMENT3 LIST OF REGULATORY COMMITMENTSNO Correspondence Number:
NLS2010094 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
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