ML22301A167

Presentation 5 - Oconee Trip and Notification of Unusual Event on February 5, 2022

ML22301A167
Person / Time
Site:	Oconee
Issue date:	02/05/2022
From:	Kenneth Kolaczyk, Jared Nadel Duke Energy Carolinas, NRC/NRR/DRO/IRAB
To:
References
Download: ML22301A167 (28)

Text

Oconee Trip and Notification of Unusual Event on February 5, 2022 Presented by:

Jared Nadel, Oconee SRI

Oconee Nuclear Plant Facts 3 Unit site of Babcock and Wilcox (B&W) Pressurized Water Reactors (2568MWt)

B&W plants have once through steam generators (straight tube, produce superheat, low feedwater inventory at full power)

The B&W integrated control system (ICS) uses process inputs from both the primary and secondary systems to control Tave, reactor power, feedwater flow, and turbine steam pressure, (and much more) automatically from very low power (~3%) to full power.

The Emergency Feedwater (EFW) Pumps (aka Aux Feedwater) are not normally required on a routine trip and do not auto-start on a plant trip if main feedwater pumps remain available

Timeline of Events All 4 RCP Breakers First fire open simultaneously alarm in West Fire brigade reports

-> RPS RCP/Flux Penetration no flame/fire, but Ratio Trip -> Rx Trip Room cannot determine Second fire NOUE source of smoke alarm in West Declared 2RIA-45, Aux building Penetration (fire >15 min) vent stack radiation NOUE Room alarm spikes declaration is exited 0343 0345 0348 0350 0357 0419 0811 February 5, 2022

Timeline of Events RCPs are restarted to U2 startup Licensee decides to U2 startup is prevent natural approved by shutdown to mode 5 approved circulation cooldown to licensee after to replace safety valve (second time) mode 4 cause identified RCS draining for 2RC-67 2RC-67 PRZ safety removal valve declared 24/7 NRC onsite results in inoperable (unit still coverage begins Yellow risk in mode 3) 6th @0617 6th @1800 7th @1900 8th @0323 8th @0630 10th @1015 11th @1800 February 2022

Timeline of Events Temperature transient After manually at 3% power causes inserting the stuck rod, U2 starts up after A fault in the MFP the ICS to drive rods it cannot be withdrawn CRDM replacement speed controller in, taking Rx subcritical past 19% and enters mode 1 causes loss of SG (mode 3) level and auto-start of During rod insertion Licensee decides to EFW pumps during on shutdown, group shutdown to mode 5 mode 3 heat up (not 1 rod 5 becomes to replace CRDM for reported under 50.72) stuck at 97%

U2 enters stuck rod mode 2 13th @1625 14th @1000 14th @1106 14th @1300 15th @0700 15th @1400 21st @0937 February 2022

Timeline of Events Fleet independent Comprehensive review of plant review team is stood up equipment, procedures, and to monitor U2 recovery maintenance occurs with a U2 at 100%

and startup focus on eliminating and power mitigating single point vulnerabilities and risk and U2 in mode 1 U2 manual Rx trip due to lowering SG level preventing another U2 trip caused by feed reg valve going closed U2 in mode 2 21st @2207 22nd @1300 22nd 26th 26th @2342 27th @0039 28th February 2022

6900V Auxiliary Power System CT1 1T 2T CT2 CT3 3T SU N SU N N SU N SU SU N SU N 1TA 1TB 2TA 2TB 3TA 3TB M M M M M M M M M M M M 1A1 1B1 1A2 1B2 2A1 2B1 2A2 2B2 3A1 3B1 3A2 3B2 Unit 1 Reac tor Coolant Pumps Unit 2 Reac tor Coolant Pumps Unit 3 Reac tor Coolant Pumps

Oconee OTSG Feed Flow Paths Diagram

• Green - Flow path at power

• Blue - Flow path after Rx Trip with RCPs

• Yellow - Flow path after Rx trip without RCPs

Group 1 Rod 5 Lead Screw with Foreign Material (setscrew)

Group 1 Rod 5 CRDM foreign material damage U2 Trip February 21, 2022 U2 Trip February 21, 2022

Event Response by the Numbers 0 - Special Inspections 1 - Notification of Unusual Event 1 - LIV - 50.72 violation for missing the 4hr RPS actuation reporting requirement by minutes 2 - Plant Trips (one automatic, one manual, neither was complicated) 2 - Shutdowns to mode 5 2 - Automatic actuations of EFW on low steam generator level (dryout protection) 4 - Green/SL IV NCVs -

• Inadequate coatings in West Penetration Room (NOUE on 2/5/22)

• Failure to respond to main feed pump speed controller alarm (2/21/22 manual trip)

• Two examples of 50.72 failure to report for EFW dryout protection actuations (on 2/13/22 and 2/21/22) 4 - Additional inspectors sent to the site for coverage help (plus more assisting remotely) 23 - Forced outage length in days 27 - Potential PDs investigated by the residents

Lessons Learned

• Single point vulnerability (SPV) program weaknesses: Fuse was an identified SPV; Reviewed only once; Not mitigated due solely to cost considerations

• Use of technology: Custom MS Teams Channel; Hybrid resident office response; MCR event communication; The power of too much information

• Licensee specific sensitivities: New site management with short time in role, Rapid restart cadence; The power of NRC influence;

Questions?