ML24302A210
| ML24302A210 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 11/13/2024 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| Download: ML24302A210 (3) | |
Text
NRC Staff Proposed Scenarios for November 13, 2024, Workshop RE: TSTF-585, Revise LCO 3.0.3 to Require Managing Risk
- 1. Unit 1 is a BWR-4 with Mk-1 containment1 that is operating at 100% thermal power. high pressure coolant injection (HPCI) system was taken out of service for planned maintenance and declared inoperable on Monday at 0100 and the unit is currently in LCO 3.5.1 Condition C.
On Wednesday at approximately 1749, the unit experienced a loss of Reactor Protection System (RPS) Bus 1A. Primary Containment Isolation System (PCIS) Groups 2, 3, 6, and 8 isolated in response to this event. The PCIS isolations caused the initiation of Standby Gas Treatment (SBGT) trains A, B, and C, and Control Room Emergency Ventilation (CREV) subsystem A. The unit declared reactor coolant system (RCS) leakage detection instrumentation inoperable and entered TS LCO 3.4.5 condition A, B, and D with required action D.1 to enter LCO 3.0.3 immediately. The unit entered TS LCO 3.0.3 with required actions to be in Mode 2 within 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, Mode 3 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 4 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. Upon investigation, it was discovered that an age-related overheating condition resulted in the failure of the 1A RPS Motor Generator (MG) set, causing the feeder beaker from the 1A 480v Remote Motor-Operated Valve distribution board to trip.
On Wednesday at 1830, while attempting to swap RPS Bus 1A to its alternate power supply, the equipment operator and field supervisor were unable to close the breaker from RPS Bus 1A to its alternate power supply. Electrical maintenance was contacted, and at 1903 hours0.022 days <br />0.529 hours <br />0.00315 weeks <br />7.240915e-4 months <br /> it was identified that the breaker handle linkage had broken and is unable to engage and close the breaker. A station duty team call was held, and it was determined that replacement parts wont be on site until Friday at 0200 at the earliest.
Please walk through the how the licensee would respond using the proposed LCO 3.0.3 revision. Specifically,
- a. What actions does the Shift Manager and Control Room Supervisor take?
- b. What would be the likely outcome of the risk assessment required by LCO 3.0.3.
- c. Would the risk assessment be documented? If so, please provide a sample risk assessment.
- d. Will Unit 1 qualify for additional time (up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) to restore, or will it initiate a shutdown?
- e. What administrative controls for risk management would be put in place?
Then, Thursday at 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br />, high winds of over 96 mph (triggering increase in online risk due to potential loss of offsite power (LOOP)) are detected on the stations meteorological tower.
- f.
Would another risk assessment be reperformed? What would the results be?
- g. Can Unit 1 remain at full power?
1 Based on Browns Ferry
- h. What additional administrative controls for risk management would be put in place?
- 2. Unit 1 is a BWR-3 with Mk-1 containment2 at a dual-unit site operating at 100% thermal power. Division 2 of low-pressure coolant injection (LPCI) system was taking out of service for planned maintenance and declared inoperable on Monday at 0100 and the unit is currently in LCO 3.5.1 Condition B. The work includes 4kV breaker preventive maintenance, LPCI logic system functional testing, and installation of new pump discharge pressure taps and gauges.
Maintenance is completed and Operations begins the post-maintenance testing of Division 2 LPCI to declare operability. On Wednesday at 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br />, while running the 1C and 1D LPCI pumps, the new pressure tap installed for the 1D LPCI pump fails upstream of the isolation valve and heavily sprays water onto the Division 2 1B Core Spray pump that is located adjacent to it, soaking the pump motor. Secondary splashing also wets the 1C and 1D LPCI pumps which leads to an overcurrent trip of the 1D LPCI pump. Operations secures the 1C pump and begins assessing the condition of the impacted equipment. Division 1 Core Spray is declared inoperable at 1900 on Wednesday based on the significant wetting that occurred, and LCO 3.5.1 Condition K is entered, requiring entry into LCO 3.0.3.
- a. What actions does the Shift Manager and Control Room Supervisor take?
- b. What would be the likely outcome of the risk assessment required by LCO 3.0.3.
- c. Would the risk assessment be documented? If so, please provide a sample risk assessment.
- d. Will Unit 1 qualify for additional time (up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) to restore, or will it initiate a shutdown?
- e. What administrative controls for risk management would be put in place?
Drying, diagnostics, and any repairs of the 1B Core Spray pump and the 1C LPCI pump is expected to take 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Drying, diagnostics, and repairs of the 1D LPCI pump, based on initial Electrical Maintenance and Engineering assessment is expected to take at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
At 1245 on Thursday, storms move through the area, and a lightning strike in the switchyard results in a trip of the unit 1 Reserve Aux Transformer. Fast bus transfer occurs successfully, and all unit 1 loads are now fed from the Unit 1 Unit Aux Transformer fed from the Unit 1 Main Generator. Unit 1 enters LCO 3.8.1 Condition A for an inoperable offsite circuit.
- f.
What actions does the Shift Manager and Control Room Supervisor take?
- g. Would another risk assessment be reperformed? What would the results be?
- h. Can Unit 1 remain at full power?
- i.
What additional administrative controls for risk management would be put in place?
2 Based on Quad Cities
- 3. Unit 1 is a Westinghouse 4-loop pressurized-water reactor (PWR)3 at a dual-unit site and is operating at 100% thermal power. Essential Service Water (SX) at this site has the ability to be cross tied between both units. The 1A SX was taken out of service for planned maintenance and declared inoperable at 0030 on Monday. The licensee enters LCO 3.7.8 Condition A for one SX train inoperable, LCO 3.8.1 Condition B (required by the Notes for Required Action A.1 in LCO 3.7.8) for the 1A emergency diesel generator being made inoperable by SX, and LCO 3.7.8 Condition B for Unit 2 for an opposite (Unit 1) unit SX train inoperable.
At 0930 on Tuesday, the system engineer performing a thermography walkdown identified the auto start relay for the 1B Essential Service Water pump has significantly elevated temperatures. Further investigation by instrument maintenance technicians shows significant degradation and state the relay wont operate as designed to auto start the 1B SX Pump. In this condition, the 1B train could not pass SR 3.7.8.5 which requires verification that each unit-specific SX pump starts automatically on an actual or simulated actuation signal.
- a. What actions does the Shift Manager and Control Room Supervisor take?
- b. What would be the likely outcome of the risk assessment required by LCO 3.0.3.
- c. Would the risk assessment be documented? If so, please provide a sample risk assessment.
- d. Will Unit 1 qualify for additional time (up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) to restore, or will it initiate a shutdown?
- e. What administrative controls for risk management would be put in place?
At 1930 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.34365e-4 months <br /> on Tuesday, the unit equipment operator identifies loud noises coming from the 1B SX pump. The noise is getting louder, and vibrations are increasing. The operating crew secures the 1B SX pump to prevent further damage.
- f.
What actions does the Shift Manager and Control Room Supervisor take?
- g. Would another risk assessment be reperformed? What would the results be?
- h. Can Unit 1 remain at full power?
- i.
What additional administrative controls for risk management would be put in place?
- j.
If plant staff were unable to determine the probable cause of the high vibrations of the 1B SX pump within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, how would the licensee respond?
3 Based on Braidwood