05000247/LER-2016-006, Regarding Technical Specification Prohibited Condition Due to Inoperable 138 Kv Offsite Circuits Caused by a Disconnected Safety Injection Signal to the Station Auxiliary Transformer Load Tap Changer
| ML16159A192 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/27/2016 |
| From: | Ferrick J Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-16-061 LER 16-006-00 | |
| Download: ML16159A192 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2472016006R00 - NRC Website | |
text
- =~ Entergx NL-16-061 May 27, 2016 U.S. Nuclear Regulatory Commission Document Control Desk 11545 Rockville Pike, TWFN-2 F1 Rockville, MD 20852-2738 Indian Point Energy Center 450 Broadway, GSB P.O. Box 249 Buchanan, N.Y. 10511-0249 Tel (914) 254-5066 John Ferrick Director, Regulatory &
Performance Improvement
SUBJECT:
Licensee Event Report# 2016-006-00, "Technical Specification Prohibited Condition Due to Inoperable 138 kV Offsite Circuits Caused by a Disconnected Safety Injection Signal to the Station Auxiliary Transformer Load Tap Changer" Indian Point Unit No. 2 Docket No. 50-247 DPR-26
Dear Sir or Madam:
Pursuant to 10 CFR 50.73(a)(1), Entergy Nuclear Operations Inc. (ENO) hereby provides Licensee Event Report (LER) 2016-006-00. The attached LER identifies an event where there was a Technical Specification (TS) Prohibited Condition due to an inoperable 138 ~V offsite power system caused by the Station Auxiliary Transformer (SAT) Load Tap Changer (L TC) not capable of automatically adjusting voltage to maintain required voltage as a result of finding the Safety Injection signal links disconnected. Technical Specification 3.8.1 (AC Sources Operating) specifies, in part, that two qualified circuits between the offsite transmission network and the onsite AC Electrical Power distribution system shall be operable. Operability of the offsite power sources requires the ability to provide the required capacity during design basis conditions. The AC electrical distribution system relies on the SAT L TC to automatically adjust the voltage on 480 volt vital busses for the system to perform as designed. This condition is reportable under 10 CFR 50. 73(a)(2)(i)(B). This condition was recorded in the Entergy Corrective Action Program as Condition Report CR-I P2-2016-02293.
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NL-16-061 Page 2 of 2 There are no new commitments identified in this letter. Should you have any questions
- regarding this submittal, please contact Mr. Robert Walpole, Manager, Regulatory Assurance at (914) 254-6710.
Sincerely, JF/cbr Attachment: LER-2016-006 cc:
Mr. Daniel H. Dorman, Regional Administrator, NRC Region I NRG Resident Inspector's Office Ms. Bridget Frymire, New York State Public Service Commission
Abstract
MANUFACTU REA.
MONTH 07 REPORTABLE TOEPIX DAY YEAR 31 2016 On March 9, 4016, during shutdown for a refueling outage, while performing testing of the safety injection (SI) system, the Station Auxiliary Transformer (SAT) Load Tap Changer (LTC) failed to increase per design upon actuation of an SI signal.
The condition was acceptable for the current mode but is unacceptable when the offsite AC electric power distribution and SI System is required to be operable.
An investigation was performed and it was. discovered on March 28, 2016, that the SAT control cabinet terminal blocks Wl05 and Wl06 had their links open thereby preventing proper operation of the LTC.
A review of tests and Work Orders (WO) did not identify any previous failed tests or any WO with instructions to open the links.
The last successful test of LTC operation was performed on February 26, 2014.
The direct cause of the event was open links for the SAT LT~ SI signal.
The most probabl~ apparent cause was maintenance activities by either IPEC or supplemental personnel that left the SAT states links Wl05 and Wl06 open during the 2014 spring outage (2R21).
A review was performed of 42 Work Order (WO) tasks conducted during the 2014 spring outage.
None of the WO tasks required work on the SAT LTC links or required work in the specific area of the states links.
Corrective actions
included closure of the SAT LTC Terminal Block states links and testing.
The control links for the Unit 3 SAT will be inspected to verify they are in the correct position.
All troubleshooting work brders will require concurrent verification that any equipment manipulation is restored to its original configuration.
The SAT LTC Preventive Maintenance (PM) procedure will be revised to insure steps are added to require independent verification for all LTC SI logic control link manipulation.
The event had no significant effect on public health and safety..
(If mf>re space is required, use addition~/ copies of (ti more space is required, use additional copies of NRG Form 366A) (17)
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Event Analysis
LEA NUMBER (6)
I SEQUENTIAL I REVISION NUMBER NUMBER-006 00 PAGE (3) 4 OF 4
The event is reportable under 10 CFR 50.73(a) (2) (i) (B).
The licensee shall report any operation or condition which was prohibited by the plant's TS. *This condition meets the reporting criteria because Technical Specification 3.8.1 (AC Sources-Operating) specifies the following AC electrical sources to be operable in modes 1,2,3 and 4:
- 1) Two qualified circuits between the offsite transmission network and the onsite AC electrical power distribution system, and 2) Three diesel generators capable of supplying the onsite power distribution subsystem.
TS 3.8.1 has a Note that the automatic transfer function for the 6.9 kV buses shall be operable whenever the 138 kV offsite circuit is supplying 6.9 kV bus 5 and 6 and the UAT. is supplying 6.9 kV buses 1,2,3 and 4.
Qualified offsite circuits are those that are described in the UF~AR and are part of the licensing basis for the unit.
Each offsite circuit must be capable of maintaining rated frequency and voltage, and accepting required loads during an accident, while connected to the Engineered Safety Features buses.
UFSAR Section 7.5.2.1.12.1 discusses the SAT LTC SI signal feature.
With the SAT LTC SI actuation signal disconnected, the 138 kV offsite circuit is no longer a qualified circuit therefore is inoperable.
With the as-found LTC condition, an event resulting in an SI and fast bus transfer could cause the secondary voltage to drop below the degraded voltage setpoint for more than 10 seconds, resulting in a separation of the safety buses from offsite power (LOOP).
Past Similar Events A review was performed of the past three years of Licensee Event Reports (LERs) for events reporting a.TS violation due to inoperable 138 kV offsite power distribution system.
No LERs were identified.
Safety Significance
This event had no effect on the health and safety of the public. There were no actual safety consequences for the event because there were no accidents or events during the degraded condition.
There were no significant potential safety consequences of this event.
A probabilistic risk evaluation was performed for failure of the SAT LTC to increase to the required voltage following actuation of a SI signal.~~he risk evaluation for the SAT LTC boosting function involved estimating the increase in core damage frequency (CDF) and large early release frequency (LERF) using a baseline case which only includes initiating events that generate an SI signal.
Pending the outcome of further investigations, the time of consideration was conservatively determined to be since the SAT LTC was last verified to be operable for SI actuations on February 26, 2014.
Even in this situation, the results of the risk evaluation concluded the risk impact associated with the failure of the SAT LTC to increase voltage following an SI signal is non-risk significant per NRC Regulatory Guide 1.174 (i.e., the increase in CDF is less than lE-6/year and the increase in LERF is less than lE-7/year).