1. Background and Diablo Canyon Initiatives
Open Phase Conditions
Background and Diablo Canyon Initiatives
Yves Nembo
Supervisor, Design Engineering PG&E
June 21, 2016

2. Overview Open Phase Conditions (OPC) Global Operating Experience
NRC Actions
Industry Follow-up Actions
DCPP Initiatives
Schedule / Path Forward
Introduce yourself! Lead by saying we have not experienced an OPC;

3. What is an Open Phase Condition (OPC)?
Loss of one or two of the three phases (with or without ground), on the high voltage side of a transformer connecting a General Design Criterion 17 (GDC 17) offsite power circuit to the transmission system.

4. Open Phase Condition ` Connections Of Interest
IEEE Std – IEEE Standard for Preferred Power Supply (PPS) for Nuclear Power Generating Stations (NPGS).
Figure 4 – Example of an enhanced PPS design
Source: IEEE Std

5. Why Do OPCs Matter?
An Open Phase Condition creates unbalances (sequence voltages and currents) in the plant AC electrical distribution system.
If undetected for an extended period of time, an OPC could lead to:
Overheating running motors and serious damages to rotating machines
Protective device actuation and lock out

6. Global Operating Experience
Thirteen open phase events between
6 Internationally
7 in United States
Open Phase Conditions at Byron Nuclear Generating Station, Illinois:
Byron Unit 2 – January 30, 2012
Byron Unit 1 – February 28, 2012
US: 6
Europe: 4
Canada:1
Other: 1
OPC OEs due to either a failure of insulators & switchyard connections or malfunctions of breakers
Oconee Nuclear Station, Units 1 and 3 – December 2015
Dungeness B, UK - April 2014
Forsmark, Unit 3, Sweden – May 30, 2013
Bruce Power, Unit 1, Canada – December 22, 2012
Byron Station, Unit 1 – February 28, 2012
Byron Station, Unit 2 – January 30, 2012
Beaver Valley, Unit 1, US – November 1, 2007
Dungeness A, UK – May 14, 2007
Vandellos, Spain – August 9, 2006
Fitzpatrick/and Nine Mile Point, US – December 19, 2005
Koeberg, South Africa – November 11, 2005
South Texas Project Unit 2, US – March 1, 2001

7. Byron OPC Events
Initiated by a failed inverted/underhung porcelain insulator
Rendered offsite power supply circuits inoperable
Resulted in automatic reactor trip or electrical transients
Revealed design vulnerability of offsite power circuit to OPCs
Potential noncompliance with General Design Criteria 17 (GDC 17)
OHIO Brass Insulator (Underhung type)

8. NRC Actions
Information Notice : Design Vulnerability in Electric Power System - Informs licensees of the Byron OE as well as other similar OPC events at other plants
Bulletin : Design Vulnerability in Electric Power System - Requires licensees to confirm compliance with 10CFR50.55a(h)(2), 10CFR50.55a(h)(3), and GDC 17
BTP 8-9: Open Phase Conditions in Electric Power System - Provides design criteria and guidance to NRC staff in reviewing various actions related to OPC design vulnerability
Will be used for future licensing actions to verify compliance with applicable regulations related to electric power systems
Pending NRC Actions:
OPC Petition:
Interim Enforcement Policy for OPC

9. Industry Stakeholders: INPO Actions
INPO IER L (Rev.0 & Rev.1): Automatic Reactor Scram Resulting from a Design Vulnerability in the 4.16-kV Bus Undervoltage Protection Scheme
Distributed February 16, 2012
Required prompt interim compensatory actions to detect OPCs
Required implementation of procedural guidelines to help operators promptly diagnose and mitigate OPC symptoms
Required identification of long-term solutions to provide automatic protection from OPCs

10. Industry Stakeholders: NEI Actions
NEI 13-12: Open Phase Condition Industry Guidance Document
Established industry-led OPC Task force
Organized various OPC Working Group Workshops
Issued a new industry guidance document for OPC
Coordinated with the industry’s Chief Nuclear Officers to commit to address OPC and ensure safety margins

11. OPC Initiatives at DCPP
Active engagement in various industry task forces
Comprehensive design comparison:
Different insulators in the switchyards/offsite power circuits to the plant.
Key differences in the physical arrangement of vulnerable conductors and structures
Minimal configuration-based risk as compared to Byron configuration
Adopted compensatory measures:
Operating procedure revised to provide guidance in diagnosing OPCs
Daily inspections of equipment
Safety is the highest priority at Diablo Canyon; we took immediate action to assess conditions and implement mitigations to guard against OPC.
Reviews and analyses of offsite power circuits and existing protection schemes concluded current design is susceptible to undetected OPCs.
- PG&E does not utilize Ohio Brass insulators in the switchyards or the offsite power circuits to the plant.
- Except for 230 kV disconnect switches; the DCPP switchyard design does not employ suspended post insulators.
- The use of rigid bus bar in the DCPP switchyards is limited to straight line sections only (i.e. no "S" configurations). Expansion joints are also used to minimize growth / shrink affects.
- These key differences in the physical arrangement of vulnerable conductors and structures continue to demonstrate minimized configuration-based risk as compared to the Byron configuration.

12. Initiatives at DCPP Immediate Interim Corrective Actions:
Operating procedure revised to provide guidance in diagnosing OPCs
Implemented switchyards monitoring via daily operator rounds
Long Term Corrective Actions:
Committed to develop and implement OPC Detection Design Changes on start-up transformers and generator step-up transformers
NRC Commitment DCL
DCPP is committed to the following Open phase Detection implementation schedule:
Unit 1 – 1R20 forecasted to be completed in June Trip functions will be enabled by June 30, 2018.
Unit 2 – 2R20 forecasted April Trip functions will be enabled by December 31, 2018.

13. Path Forward & Schedule
Develop and Implement an OPC Detection and Protection Design Change
Phase 1: Alarm Only – To verify the dependability of the system settings.
Phase 2: Trip Functions Enabled
Implementation Schedule
Unit 1 – 1R20 completion forecast. Trip functions enabled by mid-2018.
Unit 2 – 2R20 completion forecast. Trip functions enabled by Dec
NRC Commitment DCL
DCPP is committed to the following Open phase Detection implementation schedule:
Unit 1 – 1R20 forecasted to be completed in June 2017 (Alarm Only). Trip functions will be enabled by June 30, 2018.
* Unit 1 Mod ~ 40% complete
* No adverse schedule issues at the moment.
Unit 2 – 2R20 forecasted April 2018 (Alarm Only). Trip functions will be enabled by December 31, 2018.
* Unit 2 scoping meeting scheduled for 11/10/16.
* Timing selected to allow incorporation of Unit 1 lessons learned.

14. NRC Reference Documents
Ref. No.
NRC ADAMS
Accession No.
Document Title 1 ML
NRC Information Notice , “Design Vulnerability in Electric Power System,” dated March 1, 2012 2
ML12074A115
NRC Bulletin , “Design Vulnerability in Electric Power System,” dated July 27, 2012 3
ML15057A085
Branch Technical Position 8-9, dated July 2015 4 ML
RIS , Revision 1, “Adequacy of Station Electric Distribution System Voltages” 5
ML16050A212
2.206 Petition on Current Operating Nuclear Power Plants - Open Phase Conditions in Electronic Power System which Lead to Loss of Safety Functions of both Offsite and Onsite Power Systems (NRC Bulletin ) 6
ML16069A214
NRR initial response to OPC petition (ML16050A212)
NRC Reference Documents

15. Thank You
Yves Nembo
Safety is the highest priority at Diablo Canyon; we took immediate action to assess conditions and implement mitigations to guard against OPC.