05000286/LER-2012-001, Regarding Common Cause Inoperability of Both Trains of Motor Driven Auxiliary Feedwater (AFW) Pumps Due to Inability to Control AFW Regulating Valves After Isolation of Nitrogen Backup
| ML12107A026 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 04/02/2012 |
| From: | Ventosa J Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-12-040 LER 12-001-00 | |
| Download: ML12107A026 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2862012001R00 - NRC Website | |
text
- Entergy Indian Point Energy Center 450 Broadway, GSB P.O. Box 249 Buchanan, N.Y. 10511-0249 Tel (914) 254-6700 John A. Ventosa Site Vice President NL-12-040 April 2, 2012 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop O-P1-17 Washington, D.C. 20555-0001
SUBJECT:
Licensee Event Report # 2012-001-00, "Common Cause Inoperability of Both Trains of Motor Driven Auxiliary Feedwater (AFW) Pumps Due to Inability to Control AFW Regulating Valves After Isolation of Nitrogen Backup" Indian Point Unit No. 3 Docket No. 50-286 DPR-64
Dear Sir or Madam:
Pursuant to 10 CFR 50.73(a)(1), Entergy Nuclear Operations Inc. (ENO) hereby provides Licensee Event Report (LER) 2012-001-00. The attached LER identifies an event where there was a common cause inoperability of both trains of motor driven auxiliary feedwater (AFW) pumps due to an inability to control AFW regulating valves after a loss of nitrogen backup, which is reportable under 10 CFR 50.73(a)(2)(vii). This condition was recorded in the Entergy Corrective Action Program as Condition Report CR-IP3-2011-04651.
There are no new commitments identified in this letter. Should you have any questions regarding this submittal, please contact Mr. Robert Walpole, Manager, Licensing at (914) 254-6710.
Sincerely, cc:
Mr. William Dean, Regional Administrator, NRC Region I NRC Resident Inspector's Office, Indian Point 3 Mrs. Bridget Frymire, New York State Public Service Commission LEREvents@inpo.org
Abstract
On October 11, 2011, following completion of a 2 year inspection/overhaul of the Auxiliary Feedwater System (AFWS) nitrogen backup (BU) supply pressure regulator (IA-PCV-1276),
the set pressure was increased to the set pressure of relief valve RV-1284 while performing the post maintenance (PM) test (PMT).
RV-1284 lifted, chattered and the disc and seat were damaged.
When valve PCV-1276 was returned to service, RV-1284 was found to be leaking and the system was isolated which resulted in the unavailability of the AFWS nitrogen BU system.
An assessment was conducted on required actions as a result of isolating nitrogen BU.
At 18:30 hours, a dedicated operator was stationed in the Auxiliary Boiler Feed Pump building for manual operation of the AFWPs discharge flow control valves (FCV) to mitigate any events that could result in loss of the normal instrument air (IA) supply.
Under Design Basis Accident (DBA) events, the IA system (IAS) is not credited as its function to supply AFWS valves is not classified as safety related.
Without IA, the BU nitrogen system is relied upon to operate the AFWS including the AFWP FCVs.
When the AFWS nitrogen BU is unavailable, a dedicated operator is required to manually operate the AFWPs FCVs.
The direct cause of the unavailable nitrogen BU was RV-1284 chattering due to inadequate PMT work order (WO) instructions for control of air regulator set-pressure following overhaul.
The apparent cause of operators not recognizing the need to station an operator locally prior to isolating the AFWP nitrogen BU supply was inadequate procedural basis and licensing bases documents (UFSAR, TS Basis, TRM) from a missed opportunity from a previous event.
Corrective actions include RV-1284 replacement, revision of model PMT WOs with guidance on regulator set pressures, revision of TS Basis, TRM, UFSAR, DBD, applicable System Descriptions, Operations procedures and lesson Dlans.
The event had no sianificant effect on public health and safety.
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In accordance with UFSAR Section 9.6.3 the IAS was designed such that IA shall be available under all operating conditions, all essential systems requiring air during or after an accident shall be self supporting, and after an accident the air system shall be re-established.
Those items essential for safe operation and safe cooldown are provided with air reservoirs or gas bottles.
These supplies will enable the equipment to function in a safe manner until the air supply is re-established or other means of control are made available.
The IAS is backed up by the Station air system.
The unavailability of both IA and the nitrogen backup for the AFWS results in the following: AFWP FCVs [FCV-405 (A-D) and FCV-406 (A-D) fail open ensuring AFW flow to the SGs.
Amptectors trip of the MD AFWPS after several minutes under worst case conditions under high HP/amperage demand unless the FCVs are locally throttled.
The pressure control valves for steam supply to the TD AFWP (PCV-1310A and 1310B) fail open insuring steam supply to the AFWP turbine.
The TD AFWP steam supply pressure control valve (PCV-1139) fails open ensuring steam supply to the TD AFWP.
TD AFWP speed control valve (HCV-1118) fails open to the mechanical governor maximum speed.
The TD AFWP has a mechanical governor which will establish the design speed and prevent overspeed.
The TD AFWP with no IA or nitrogen BU will provide adequate FW flow to the SGs to meet accident requirements.
All the referenced valves have hand wheels for local control.
Loss of IA (low pressure) and low nitrogen pressure will alarm in the control room alerting the operators for the need of manual actions.
Alternate shutdown capability to comply with 10CFR50, Appendix R has one scheme that makes use of the local control station in the Auxiliary Feedwater (AFW)
Pump Room to shutdown the plant following a fire.
For a safe shutdown following a postulated fire event, no credit is taken for the availability of the IA system to support operation of the AFWP FCVs.
Further, no credit is taken for the availability of either the IA or nitrogen backup systems for a postulated fire event within the AFW Pump Room itself.
Local operation of the AFWPs can be accomplished in the AFW Pump Room for the TD AFWP and at the emergency switchgear (in the Control Building), for the MD AFWPs, if necessary.
Prompt Operator action to manually operate the FCVs would be available, except during an actual fire within the AFW Pump Room.
The AFW Pump Room contains both MD AFWPs and the TD AFWP and is provided with automatic fire detection and a fixed suppression system, and a hose station outside the room.
Fire suppression capability in the room is provided by an area wide automatic wet pipe sprinkler system, portable fire extinguishers, and by fire hose from nearby yard hydrants.
For a loss of both IA and nitrogen supplies, the AFWPs would operate in the manner previously discussed, and AFW flow control valves for the selected AFW pump(s) would be manually operated in accordance with existing procedures following operator re-entry to the AFW Pump Room.
An assessment was performed to determine the impact of the condition on Incremental Core Damage Probability (ICDP) and Incremental Large Early Release Probability (ILERP).
The assessment considered the case of both MD AFWPs being inoperable for a period of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to bound the time from initiation of the condition report for nitrogen BU system isolation to the time a dedicated operator was stationed at the AFWPs.
The assessment yielded an ICDP of 1.18E-7 and an ILERP of 1.78E-8.
Based on these results, the unavailability of the two MD AFWPs for the two hour period does not represent a significant risk impact when compared to the guidance provided in NUMARC 93-01 or Regulatory Guide 1.177.