05000277/LER-2022-001, Automatic Reactor Scram Due to Loss of Power to Both RPS Buses
| ML22196A020 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 07/15/2022 |
| From: | Henry D Constellation Energy Generation |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CCN: 22-56, ENS 55899 LER 2022-001-00 | |
| Download: ML22196A020 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2772022001R00 - NRC Website | |
text
Constellation0 CCN: 22-56 July 15, 2022 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 10 CFR 50.73 Peach Bottom Atomic Power Station (PBAPS) Unit 2 Subsequent Renewed Facility Operating License No. DPR-44 NRC Docket No. 50-277
Subject:
Licensee Event Report (LER) 2-2022-001-00 Automatic Reactor Scram due to Loss of Power to Both RPS Buses
Reference:
ENS 55899 The subject report is being submitted in accordance with 1 O CFR 50.73(a)(2)(iv)(A) for actuation of the Reactor Protection System, Containment Isolation Signals affecting multiple Main Steam Isolation Valves, Emergency Core Cooling Systems and Reactor Core Isolation Cooling.
There are no commitments contained in this letter. If you have any questions, please contact the Peach Bottom Regulatory Assurance Manager, Wade Scott at (717) 456-3047.
Respectfully,
~_,...,____, -2' David A. Hen~
Site Vice President Peach Bottom Atomic Power Station Enclosure cc:
USNRC, Administrator, Region I USNRC, Senior Resident Inspector W. DeHaas, Commonwealth of Pennsylvania S. Seaman, State of Maryland B. Watkins, PSE&G, Financial Controls and Co-Owner Affairs
Abstract
On 5/16/22 at 1537 hours0.0178 days <br />0.427 hours <br />0.00254 weeks <br />5.848285e-4 months <br />, the Unit 2A reactor protection system motor generator set (RPS MG set) tripped in response to grid perturbations, causing a half scram condition as expected. At 1552 hours0.018 days <br />0.431 hours <br />0.00257 weeks <br />5.90536e-4 months <br />, Unit 2 experienced an automatic scram and Group 1 isolation. The scram was the result of a self-revealing technical human performance event during the execution of a procedure to return 2A RPS to service. The loss of both RPS buses resulted in a reactor scram, Primary Containment Isolation System Group 1 Isolation (main steam isolation valve closure), safety relief valve actuation, and loss of the normal heat sink. Emergency Core Cooling Systems were utilized to maintain reactor pressure vessel level and pressure.
At no time was there a public safety risk and there were no safety consequences as a result of the event. All control rods inserted, and all safety systems performed as expected. Operations safely stabilized Unit 2 and brought it to a cold shutdown condition. The root cause of this event was a breakdown in technical human performance, which led to directing the wrong procedure steps and resulted in a reactor scram. Immediate corrective actions included increased oversight and reinforced stop work criteria. Longer term corrective actions include procedure and training enhancements.
(See Page 3 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/)
Safety Consequences
The scram and response was completed without complication and resulted in no safety consequences. At no time was there a public safety risk. The operations crew responded correctly and plant SSC responded as designed in response to the event. Although the primary heat sink was lost due to closure of the MSIVs, decay heat was adequately managed with the use of other safety systems as described above. The event was within the analysis of UFSAR Chapter 14, Plant Safety Analysis. There was not a release of radioactivity as a result of this event.
Corrective Actions
The root cause of this event was determined to be a technical human performance event. While operating in knowledge-based thinking, licensed operators had breakdowns in technical human performance. This led to directing the wrong procedure steps and caused a reactor scram. Contributing causes identified included not establishing a deliberate and focused pace once plant conditions stabilized due to an elevated sense of urgency and inconsistent use of human performance tools. Immediate corrective actions included increased supervisory oversight and peer checks and reinforcement of stop work criteria. Corrective actions also include procedure enhancements and ensuring reviews of contingency plans for longer system outage windows. Additionally, training will be used to reinforce the transition from transient to normal operations as well as appropriate pace control, teamwork and technical human performance standards.
Previous Similar Events
Peach Bottom has not experienced a scram due to a human performance or technical human performance event in at least 10 years.