05000416/LER-2015-001, Regarding Automatic Actuation of the Reactor Protection System (RPS) Due to a Fault in the Protective Relaying Circuitry on the B Main Transformer
| ML15098A601 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 04/08/2015 |
| From: | Nadeau J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GNRO-2015/00019 LER 15-001-00 | |
| Download: ML15098A601 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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 |
| 4162015001R00 - NRC Website | |
text
~
===Entergy GNRO-2015/00019 April 08, 2015 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
P.O. Box 756 Port Gibson, MS 39150 James Nadeau Manager, Regulatory Assurance Grand Gulf Nuclear Station Tel. (601) 437-2103
SUBJECT:
Licensee Event Report (LER) 2015-001-00 Automatic Actuation of the Reactor Protection System (RPS) Due to a Main Turbine Trip Grand Gulf Nuclear Station Docket No. 50-416 License No. NPF-29
Dear Sir or Madam:
Attached is Licensee Event Report (LER) 2015-001-00 which is a 60 day final report. This report is submitted in accordance with Title 10 Code of Federal Regulations 50.73(a)(2)(iv)(A).
This letter contains no new commitments. If you have any questions concerning this submittal, please contact Mr. James Nadeau at (601) 437-2103.
Sincerely, JJN/ss
Attachment:
Licensee Event Report (LER) 2015-001-00
GNRO-2015/00019 Page 2 of 2 cc:
U.S. Nuclear Regulatory Commission ATIN: Mr. A. Wang, NRR/DORL (w/2)
Mail Stop OWFN8 B1 Rockville, MD 20852-2738 U.S. Nuclear Regulatory Commission ATIN: Mr. Marc Dapas (w/2)
Regional Administrator, Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector
- Grand Gulf Nuclear Station Port Gibson, MS 39150
Attachment to GNRO-2015/00019 Licensee Event Report (LER) 2015-001-00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (O1-2014) digits/characters for each block) the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 13. PAGE Grand Gulf Nuclear Station, Unit 1 05000416 1 of 5
- 4. TITLE Automatic Actuation of the Reactor Protection System (RPS) Due to a Fault in the Protective Relaying Circuitry on the "B" Main Transformer.
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER NUMBER NO.
MONTH DAY YEAR N/A 05000 N/A 02 07 2015 2015 - 001 - 00 04 07 2015 FACILITY NAME DOCKET NUMBER N/A 05000 N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii) 1 D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4) 100 D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(C)
D OTHER D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(v)(D)
Specify in Abstract below or in
EVENT CAUSE
- 2. DOCKET 05000416
- 6. LER NUMBER YEAR ISEQUENTIAL I NUMBER 2015-001-00 REV.
NO.
- 3. PAGE 3 of 5 The direct cause was a fault in the protective relaying circuitry on the "B" main transformer high voltage current transformer. The fault tripped the turbine differential relay generating a generator lockout signal to the main turbine, tripping it offline.
CORRECTIVE ACTIONS
The faulted cables and other similar cables were determinated and alternate wiring and conduit was installed The extent of condition involved replacing the wiring and conduit for the protective circuitry on both the high voltage and low voltage sides on all three recently installed single phase main transformers.
SAFETY SIGNIFICANCE
The event posed no threat to the health and safety of the public as RPS performed as designed. All safety systems responded as expected. No Technical Specification safety limits were challenged or violated. There were no ECCS actuations or malfunctions. The end of cycle/recirculation pump trip (EOC/RPT) to slow speed did occur as expected.
The main steam isolation valves (MSIVs) [ SB ] operated as expected based on plant conditions. The operating crew entered the appropriate emergency and off normal procedures, as applicable. There was no radiological release or industrial safety hazard during the event.
BASIS FOR REPORTABILITY This Licensee Event Report (LER) is being submitted pursuant to Title 10 Code of Federal Regulations 50.73(a)(2)(iv)(A) for an automatic actuation of the Reactor Protection System. Telephonic notification was made to the U.S. Nuclear Regulatory Commission (NRC) Emergency Notification System (ENS) on February 7, 2015, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the event, pursuant to 10CFR50.72(b)(2)(iv)(B) for RPS actuation.
SIMILAR EVENTS
Since the installation of the transformers in April 2012, there were two RPS SCRAMs on main turbine [TA] trips associated with CTs. These two events involved the current transformer for the main generator. The causes and corrective actions for each of these events were reviewed and it has been concluded that the corrective actions associated with these events would not have prevented the February 7, 2015 reactor SCRAM as reported in this licensee event report.
LER-2012-008-00 document the December 29,2012 RPS actuation and reactor SCRAM. A second RPS reactor SCRAM was documented in LER 2013-001-00. The cause of both SCRAMS was because there was a partial grounding due to an inadequate clearance between the micarta plate bolts and the bottom of the current transformer as part of the physical installation of the CTs into the main generator bus work. Although these two events were attributed to installation techniques, the causes of the events were different. One was a structural/mechanical installation and the other was associated with concealed control wiring by the supplier.
MAIN TRANSFORMER DESCRIPTION:
The main transformers were installed in April 2012 to support extended power uprate (EPU). They are 510MVA, single phase, delta/wye configured step-up transformers, supplied 1525MVA from the main generator. They have a nominal low voltage rating of 22kV and the secondary high voltage windings supply 500kV to the switchyard. The main transformer relay protection system interfaces with the plant protection logic, computer and event recorder.
Failure of the main transformers will not inhibit any plant safety-related system or prevent safe shutdown.
BACKGROUND ON INITIATING EVENT:
The high voltage side (500kV) CT wiring is normally grounded in the 801 panel in the control room. An unintentional, high voltage CT Wiring ground developed inside the conduit mounted on top of "B" main transformer. The high voltage CT provides input to the transformer differential relay located in the control room. The differential relay is a protective relay that compares the difference in power between the high voltage side and low voltage side (22kV) of the transformer. The transformer is protected by actuation of the transformer differential relay and generator trip.
SUMMARY:
The trip signal was generated by the following events
- 1. A ground developed on the high voltage CT wire inside the conduit on top of the transformer. This ground created circulating ground currents between the normal ground in the control panel and the fault location on top of the transformer. This current caused localized heating that resulted in melting the other wiring in the conduit.
- 2. The change in current through the high voltage CT, without a change in the low voltage CT current, was detected by the transformer differential relay, resulting in relay actuation and subsequent generator trip.
Note: simplified for illustration Low Side Main High Side Transformer CT's Transformers Transformer CT's
][
<">0°1 I
I I
PhaseC Generator Cy
][
r T
I I
I Phase A
~r
~
I I
~L I
Phase B
~
~
~"
~0(c,
.~,('j
~...
- 2. DOCKET 05000416
, 6. LER NUMBER YEAR SEQUENTIAL REV.
NUMBER NO.
2015-001-00
- 3. PAGE 5 of 5 Corrective actions were taken to replace wiring and conduit I Damaged wiring was in pull box '3.
'l':f.\\;'~":C:,:JZJf>!1,~'j;,;\\,,,,:g.:1~7"::~;;';;i~,1