05000391/LER-2020-003, Re Low RHR Flow in Mode 6 Results in a Condition Prohibited by Technical Specifications
| ML20356A291 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 12/21/2020 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WBL-20-064 LER 2020-003-00 | |
| Download: ML20356A291 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3912020003R00 - NRC Website | |
text
mil Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 WBL-20-064 December 21, 2020 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391 10 CFR 50.73
Subject:
Licensee Event Report 391/2020-003-00, Low RHR Flow in Mode 6 Results in a Condition prohibited by Technical Specifications This submittal provides Licensee Event Report (LER) 391/2020-003-00. This LER provides details of Human Performance errors that resulted in Mode 6 operation with low Residual Heat Removal (RHR) loop flow. This event is being reported as a condition prohibited by plant Technical Specifications in accordance with Title 10 of the Code of Federal Regulations (10 CFR) part 50. 73(a)(2)(i)(B).
There are no new regulatory commitments contained in this letter. Please direct any questions concerning this matter to Tony Brown, WBN Licensing Manager, at (423) 365-7720.
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J Watts Bar Nuclear Plant
U.S. Nuclear Regulatory Commission WBL-20-064 Page 2 December 21, 2020
Enclosure:
LER 391-2020-003-00 Low RHR Flow in Mode 6 Results in a Condition prohibited by Technical Specifications cc (w/o Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Region II
ENCLOSURE Tennessee Valley Authority Watts Bar Nuclear Plant Unit 2 LER 391-2020-003-00 Low RHR Flow in Mode 6 Results in a Condition prohibited by Technical Specifications
Abstract
On November 7, 2020, at 1315 Eastern Standard Time (EST) it was discovered that Technical Specification (TS) Requirement 3.9.5, Residual Heat Removal (RHR) and Coolant Circulation - High Water Level, for Unit 2 was not met prior to Mode 6 entry. 2B RHR pump flow was 2100 Gallons Per Minute (GPM) contrary to Surveillance Requirement (SR) 3.9.5.1 flow requirement of >/= 2500 GPM. As a result, TS Limiting Condition for Operation (LCO) 3.9.5. Condition A was entered and subsequently exited once flow was raised to 2600 GPM.
This event was the result of Operations personnel failing to verify the applicable TS LCO was met prior to a plant Mode change. Corrective actions to prevent recurrence include coaching involved personnel and revising the applicable surveillance procedure for RHR flow in MODE 6.
I.
Plant Operating Conditions Before the Event
Watts Bar Nuclear Plant (WBN) Unit 2 was defueled (NO Mode) with water cavity level 24 2 inches above the reactor vessel flange.
II.
Description of Event
A. Event Summary
On November 7, 2020 at 1315 Eastern Standard Time (EST) during a Control Room board walk down it was identified that Technical Specifications (TS) Requirement 3.9.5, Residual Heat Removal and Coolant Circulation - High Water Level, was not met for the current
plant conditions
Unit 2, 2B Residual Heat Removal (RHR) [EIIS:BP] pump [EIIS:P] flow indicator[EIIS:FI] indicated 2100 Gallons Per Minute (GPM). This was below the required value of >/= 2500 GPM stated in TS Surveillance Requirement (SR) 3.9.5.1. As a result, TS Limiting Condition for Operation (LCO) 3.9.5 Condition A was entered and subsequently exited after flow was raised to 2600 GPM to comply with the TS SR.
At time of discovery, Unit 2 was in Mode 6 and the refueling cavity was filled to elevation 749 2 (24 2 above the reactor vessel flange) with dilution protection in place per Surveillance Instruction (SI), 2-SI-62-1, Uncontrolled Boron Dilution Paths. The 2B RHR system was maintaining Reactor Coolant System (RCS) [EIIS:AB] temperature in accordance with 2-GO-7, Refueling Operations, with higher flow capacity available at all times. There were no challenges to temperature or boron mixing noted during fuel handling activities.
This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event When Unit 2 entered Mode 6, the in service RHR system was in service with loop flow of 2100 GPM. This did not meet the Surveillance Requirement 3.9.5.1 Verify one RHR loop in operation and circulating reactor coolant at a flow rate of >/= 2500 GPM.
Page 3 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 2 05000-391 YEAR SEQUENTIAL NUMBER REV NO.
2020
- - 003
- - 00
C. Dates and approximate times of occurrences
Date Time (EST)
Event 11/6/20 0354 Unit 2 entered Mode 6 Refueling, with refueling cavity level 749 2 (24 2 above the reactor vessel flange).
11/7/20 1315 Operator noticed that 2B RHR flow did not meet the minimum flow requirement as required by TS SR 3.9.5.1. TS LCO 3.9.5 Condition A was entered and subsequently exited when 2B RHR flow was raised to 2600 GPM to comply with the TS requirement.
D. Manufacturer and model number of each component that failed during the event
No equipment failures occurred during the event.
E. Other systems or secondary functions affected
TS 3.9.5 Bases states that at least one RHR loop must be operable and in operation to provide:
a. Removal of decay heat b. Mixing of borated coolant to minimize possibility of criticality c. Indication of reactor coolant temperature During the short period when Unit 2 was in a RHR low flow condition there were no challenges to temperature control, reactivity changes, or indications of temperature stratification. No other systems or secondary functions were affected.
F. Method of discovery of each component or system failure or procedural error
This event was discovered by Operations personnel while performing a Control Room board walk down verifying systems parameters.
G. Failure mode, mechanism, and effect of each failed component No equipment failures occurred during the event.
H. Operator actions
TS LCO 3.9.5 Condition A was entered and subsequently exited when 2B RHR flow was raised to 2600 GPM to comply with the TS SR 3.9.5.1 requirement.
I.
Automatically and manually initiated safety system responses
None required.
Page 4 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 2 05000-391 YEAR SEQUENTIAL NUMBER REV NO.
2020
- - 003
- - 00 III.
Cause of the Event
A. Cause of each component or system failure or personnel error
There was no equipment failures associated with this event.
No root cause was performed. This event was the result of Operations personnel not verifying that the correct TS LCO was met prior to a plant Mode change.
IV.
Analysis of the Event
At the time of discovery, the 2B RHR system was maintaining RCS temperature within the refueling limits with higher flow capacity available at all times. Dilution protection was in accordance with, SI 2-SI-62-1, Uncontrolled Boron Dilution Paths, and there were no challenges to temperature control or water mixing noted during fuel handling activities.
A flow reduction safety evaluation from 2500 GPM to 2000 GPM has been performed. Based on that evaluation, none of the parameters evaluated for the midloop would be any worse at higher vessel levels; therefore, the condition is bounded by the safety evaluation.
V.
Assessment of Safety Consequences
There were no actual safety consequences as a result of this event.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event.
Not Applicable.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident The lower RHR flow did not challenge decay heat removal capability or prevent thermal and boron stratification in the core.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service Not Applicable.
Page 5 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 2 05000-391 YEAR SEQUENTIAL NUMBER REV NO.
2020
- - 003
- - 00 VI.
Corrective Actions
This event was entered into the Tennessee Valley Authoritys (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1650648.
A. Immediate Corrective Actions
Upon Discovery, RHR flow was immediately raised to comply with the required TS value.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future A corrective action to provide training and coaching for the operators involved has been completed.
A corrective action to revise procedures 2-SI-0-2A-06, 1900-0700 Shift and Daily Surveillance Log Mode Six, and 2-SI-0-2B-06 0700-1900 Shift and Daily Surveillance Log Mode Six has been developed to clarify cavity level and RHR flow requirements. The proposed procedure revisions will clearly distinguish the TS requirement reducing the likelihood of a repeat occurrence.
VII.
Previous Similar Events at the Same Site
LER 391-2018-004-00, Failure to Implement Annunciator Response Process Results in a Condition Prohibited by Technical Specifications. The cause evaluation for this event determined that on-shift operators were not properly implementing TVAs annunciator response process.
LER 390-2017-011-00, Failure to Enter Technical Specification 3.6.3 for Containment Isolation Valve. The cause evaluation for this event determined that the failure to enter the inoperable valve into the TS tracking program was a human performance error limited to a single individual.
The event described in this LER is different in that no alarm indications were available for operators and there were no human performance errors using the inoperable equipment tracking and log system.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.
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