05000382/LER-1917-002, Regarding Automatic Reactor Scram Due to the Failure of Fast Bus Transfer Relays to Automatically Transfer Station Loads to Off-Site Power on a Main Generator Trip
| ML17261B215 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 09/18/2017 |
| From: | Jarrell J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| W3FI -2017-0069 LER 17-002-00 | |
| Download: ML17261B215 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3821917002R00 - NRC Website | |
text
Enteigy W3FI -2017-0069 September 18, 2017 U.S. Nuclear Regulatory Commission Attn: Document Control Desk I I 555 Rockville Pike Rockville, MD 20852 Waterford Steam Electric Station, Unit 3 (Waterford 3)
License No. NPF-38 Docket No. 50-382 Entergy Operations, Inc.
I 7265 River Road Killona, LA 70057-3093 Tel 504 739 6685 Fax 504 739 6698 jjarrelentergy.com John P. Jarrell III Manager, Regulatory Assurance Waterford 3 10 CFR 50.73
Subject:
Licensee Event Report (LER) 2017-002-00 Automatic Reactor Scram due to the Failure of Fast Bus Transfer Relays to Automatically Transfer Station Loads to Off-Site Power on a Main Generator Trip
Dear Sir or Madam:
The attached report is being sentto you as required by 10 CFR 50.73 There are no regulatory commitments contained in this correspondence.
Should you have questions regarding this report, please contact John P. Jarrell, Regulatory Assurance Manager, at (504) 739-6685.
JPJ/SWM
- lly, Regulatory Assurance Manager
Attachment:
LER 2017-002-00
W3F1-2017-0069 Page 2 cc:
Mr. Kriss Kennedy, Regional Administrator U.S. NRC, Region IV RidsRgn4MailCenter@nrc.gov U.S. NRC Project Manager for Waterford 3 April.Pulvirenti@nrc.gov U.S. NRC Senior Resident Inspector for Waterford 3 Frances.Ramirez@nrc.gov Chris.Speer@nrc.gov
Attachment to W3F1-2017-0069 Licensee Event Report 2017-002-00 (4 pages)
NRC FORM 366 (06-2016)
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (06-2016)
LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc/gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.
- 1. FACILITY NAME Waterford Steam Electric Station, Unit 3
- 2. DOCKET NUMBER 05000382
- 3. PAGE 1 OF 4
- 4. TITLE Automatic Reactor Scram due to the Failure of Fast Bus Transfer Relays to Automatically Transfer Station Loads to Off-Site Power on a Main Generator Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 07 17 2017 2017 -
002
- - 00 09 18 2017 FACILITY NAME DOCKET NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. POWER LEVEL 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 100 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 73.77(a)(1) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(5)(ii) 50.73(a)(2)(i)(C)
OTHER Specify in Abstract below or in degraded connections between the laminated shunt assemblies and the bus duct resulted in formation of gaps between the contact surfaces. Electrical arcing across these gaps over time eroded the contact surfaces which increased resistance and weakened the connection.
Failure of Fast Dead Bus Transfer:
The direct cause of the failure of the fast dead bus transfer was the Struthers Dunn (S-D) 237 Series Direct Current (DC)
Time Delay on Dropout (TDDO) relays [62] installed in the fast dead bus transfer circuitry instantaneously timed out when they were exposed to DC coil inductive kick, which prevented automatic transfer of the safety and non-safety electrical busses from the Unit Auxiliary Transformers [XFMR] to the Startup Transformers [XFMR].
The Root Cause of this event was design change procedures in effect during the development of the 1997 and 2017 modifications to the fast dead bus transfer circuitry did not include guidance that electronic devices have a greater susceptibility to DC coil inductive kick than electro-mechanical devices and did not require identification of critical characteristics for non-quality related plant changes.
The Contributing Cause of this event was the post-modification testing performed following change of the relays from Allen Bradley to Struthers Dunn did not exercise the fast dead bus transfer timing circuitry. This contributed to this condition by delaying detection of relay failure.
The inadequate design of the fast bus transfer relays resulted in a common cause inoperability of both trains of off-site power. This condition is reportable pursuant to 10 CFR 50.73(a)(2)(vii).
CORRECTIVE ACTIONS
A. Isophase Bus Overheating:
Completed corrective actions include:
a.
The Main Transformer B, Phase B isolated phase bus duct was repaired by cutting out the damaged duct sections and welding in new aluminum material. All laminated shunt assemblies were replaced using new bolting hardware.
b.
The Main Transformer B Phase A and C laminated shunt assemblies were removed, cleaned and re-installed with new bolting hardware.
c.
Performed a complete inspection and torque check for all laminated shunt assemblies to identify any other degraded bolted connections and adjusted torque as needed.
Corrective actions planned include:
a.
Revise preventive maintenance strategy for isophase bus based on EPRI and industry recommendations to include shunt assembly torque checks, regular bus inspections, thermography scans, and corona scans.
b.
Revise the site procedure for inspection of the isophase busses and ducting based on engineering input.
B. Failure of Fast Dead Bus Transfer:
Completed corrective actions include:
a.
The installation of a suppression diode in parallel with fast bus transfer relay. (Corrective Action to Prevent Recurrence) b.
The Struthers-Dunn relays were removed from service and replaced with Allen Bradley relays.
c.
Entergy Nuclear Fleet has adopted the Standard Design Process in accordance with IP-ENG-0001, Revision 0, Standard Design Process.
d.
Fast Dead Bus Transfer engineering change test procedure was developed during troubleshooting and was performed following re-installation of the Allen Bradley relays and the installation of flyback diodes.
Corrective actions planned include:
a.
Verify that all Allen-Bradley 700RTC relays installed in the plant are immune to the effects of inductive kick. If any
Allen-Bradley relays are discovered to not be immune to the effects of Inductive kick, generate additional actions to correct the lack of immunity.
b.
Review and verify the existing EMC qualifications of currently installed Allen-Bradley 700RTC relays to ensure that they are appropriate for their operating environment. If any Allen Bradley relays are discovered to not be appropriate for their operating environment, generate additional corrective actions to correct the deficiency.
c.
Anchor surge suppression/flyback diodes into design basis drawings and the Fast Dead Bus Transfer circuit Control Wiring Diagrams to ensure they are not removed if the Fast Dead Bus Transfer circuit is modified. (Corrective Action to Prevent Recurrence)
SAFETY EVALUATION Technical Specification (TS) 3.8.1.1 requires two physically independent circuits between the off-site transmission network and the on-site Class 1E distribution system to be operable. The operability of the electrical distribution systems during operation ensures that sufficient power will be available to supply the safety-related equipment required for (1) the safe shutdown of the facility, and (2) the mitigation and control of accident conditions within the facility. The minimum specified independent and redundant A.C. and D.C. power sources and distribution systems satisfy the requirements of General Design Criterion 17 of Appendix A to10 CFR Part 50. The fast dead bus transfer system is required to be functional per the Waterford 3 FSAR to support the operability of off-site power.
The Struthers-Dunn relays were installed in the fast dead bus transfer circuit in May of 2017, and were required to be functional on June 2, 2017, at 1902, when the main generator was paralleled to the grid and loads were transferred to the Unit Auxiliary Transformers at the conclusion of Refueling Outage 21. Both trains of the offsite transmission network have been inoperable from that time until the time of the generator trip on July 17, 2017. Action e of TS 3.8.1.1 requires restoration of one of the inoperable offsite A.C. circuits to OPERABLE status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Because of this, Waterford 3 was not in compliance of TS 3.8.1.1 for 45 days.
The inoperability of both trains of off-site electrical distribution is a reportable condition pursuant to 10 CFR 50.73(a)(2)(v)(A) and (D).
The non-compliance with Technical Specifications is a reportable condition pursuant to 10 CFR 50.73(a)(2)(i)(B).
The safety significance determination of this event is still being determined. The safety significance will be included as a planned update to this LER.
PREVIOUS OCCURRENCES
CR-WF3-2015-3566: Failure of B Fast Dead Bus Transfer during Plant Scram on June 3, 2015. (Reported under LER 2015-005-00 and 2015 005-01.)
Directly following a manual plant scram on June 3, 2015, due to a secondary system malfunction, a loss of off-site power occurred on the B Train due to the failure of the fast dead bus transfer relays on the B train. The Apparent Cause of this event was determined to be Unknown Equipment Cause (FEUU). A contributing cause was that the 1997 Plant Change was due to a Design Change That Was Not Adequate (FE18) because a latent design deficiency did not take into account the observed failure mode where a two coil design allowed one coil to fail preventing the fast dead bus transfer function (timed contacts) without actuating the contacts for the alarm circuit.
From this event, all fast dead bus transfer relays were replaced with new Allen -Bradley relays. Preventative Maintenance strategies were revised to replace the relays on a three (3) year frequency.
The corrective actions from this earlier event did not correct the issue and prevent recurrence because the nature of the relay failure was not determined conclusively. Corrective actions were assigned from the apparent cause without a solid understanding of the causal factors for the respective failure.