05000331/LER-2020-001-01, Notice of Unusual Event and Unit Trip Due to Loss of Offsite Power Due to High Winds
| ML20283A373 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 09/30/2020 |
| From: | Dean Curtland NextEra Energy Duane Arnold |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NG-20-0085 LER 2020-001-01 | |
| Download: ML20283A373 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iii) |
| 3312020001R01 - NRC Website | |
text
September 30, 2020 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-0001 Duane Arnold Energy Center Docket 50-331 Renewed Op. License No. DPR-49 Licensee Event Report 2020-001-01 NG-20-0085 10 CFR 50.73 On September 11, 2020, Duane Arnold Energy Center (DAEC) submitted Licensee Event Report (LER) 2020-001-00 (ML20558A229). Subsequent to filing this report, new information was discovered that met additional reporting criteria for this event.
DAEC is, therefore, submitting revised LER 2020-001-01 with additional reporting criteria and description.
Please find attached the subject report submitted in accordance with 10 CFR 50.73. This letter makes no new commitments or changes to any existing
commitments
Dean Curtland Site Director, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC cc:
Administrator, Region Ill, USNRC Project Manager, DAEC, USNRC Resident Inspector, DAEC, USNRC NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRC may not conduct or sponsor, and a oerson is not reauired to resoond to the information collection.
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Duane 7\\rnola Energy Center 05000-331 I
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- 4. Title Notice of Unusual Event and Unit Trip Due to Loss of Offsite Power Due to High Winds
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Month Day Year Number No.
N/A N/A 8
10 2020 2020 0001 01 9
30 2020 Facility Name Docket Number N/A N/A
- 9. Operating Mode N/A N/A N/A
~bstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On August 10, 2020, at 1246 CDT, while operating at 80% power, NextEra Energy Duane Arnold (DAEC)
I experienced a generator load reject and subsequent reactor scram as a result of a loss of offsite power I
(LOOP) due to extremely high winds. An Unusual Event was declared at 1258. All Safety Systems performed as designed. As a result of the LOOP, the 'A' and 'B' Emergency Diesel Generators automatically started and supplied power to the safety related busses. As a result, the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) automatically initiated and injected into the reactor. In addition, containment isolations occurred, as expected for this event. This resulted in a 4-hour event report to the NRC under 10 CFR 50.72 section 50.72{b)(2)(iv)(A) - ECCS Injection, 50.72(b)(2)(iv)(B) - RPS Actuation -
Critical, 50.72(b)(3)(iv)(A) - Valid Specific System Actuation (reference EN#54826). The NOUE was exited at 1600 on August 11, 2020. The cause of the LOOP was an extremely severe storm (called a Derecho) with heavy rains and very high winds. This event had no impact on public health or safety. There were no systems, structures, or components inoperable at the time of the event that contributed to the event. This I event is reportable pursuant to 10 CFR 50. 73(a)(2)(iv)(A), 50. 73(a)(2)(v)(C) and 50. 73(a)(2)(iii). There were no radiological releases associated with this event.
NRG FORM 366 (02-2018)
I.
Description of Event
YEAR 2020
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 001 REV NO.
- - 01 On August 10, 2020, at 1246 CDT, while operating at 80% power, NextEra Energy Duane Arnold* (DAEC) experienced a Generator Load reject and subsequent reactor scram as a result of a loss of offsite power (LOOP) due to extremely high winds. An Unusual Event was declared at 1258. All Safety Systems performed as designed.
As a result of the LOOP, the 'A' and 'B' Emergency Diesel Generators (EDGs) automatically started and supplied power to the safety related busses. In response to the expected Reactor Pressure Vessel (RPV) level transient, the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) automatically started and injected. In addition, containment isolations occurred, as expected for this event.
This resulted in a 4-hour event report to the NRC under 10 CFR 50. 72 section 50.72(b)(2)(iv)(A) - ECCS Injection, 50.72(b)(2)(iv)(B) - RPS Actuation - Critical, 50.72(b)(3)(iv)(A) - Valid Specific System Actuation (reference EN#54826).
The cause of the LOOP was an extremely severe storm ( called a Derecho) with heavy rains and very high winds. This event had no impact on public health or safety. There were no systems, structures, or components inoperable at the time of the event that contributed to the event.
The Unusual Event was exited at 1600 on August 11, 2020.
IL
Assessment of Safety Consequences
In response to the LOOP, the plant experienced a Generator Lockout, Turbine Trip and Reactor Scram. The operating crew entered the appropriate emergency procedures.
The EDG's quickly re-energized tlie safety-related electrical busses and restored power. The Reactor Protection System (RPS) power was never lost as the EDG's were able to recover power to the essential buses quickly. This prevented a Main Steam Isolation Valve (MSIV) isolation signal and thus allowed the Main Condenser to remain available post event.
As expected for this event, RPV level dropped below L2 setpoint (119.5") initiating the HPCI and RCIC systems. Reactor level recovered quickly. The Low Low Set System functioned as designed initially opening two primary system relief valves to control reactor pressure.
NRG FORM 3668 (02-2018)
Page 2 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020
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LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http:/lwww.nrc.gov/readinq-rm/doc-collections/nuregs/staff/sr1022/r3l)
, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
~- DOCKET NUMBER YEAR Duane Arnold Energy Center 05000-331 2020
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 001 Operators were quickly able to establish pressure control initially via Steam Line Drains and RCIC and establish a cooldown rate.
Both recirculating pumps tripped when power was lost to their associated non-safety related electrical busses. The operators followed procedures for cooldown with no forced circulation in the core. When Shutdown Cooling was placed in service, forced circulation was re-established which resulted in exceeding the bottom head cooldown limits of 100 degrees per hour. This was anticipated and could not be avoided.
On August 12, a small cut was discovered in the Reactor Building 5th floor wall that was the result of storm damage. A test of the Secondary Containment boundary was conducted to determine the effect of the cut. The vacuum able to be drawn on secondary containment with one train of Standby Gas Treatment.System (SGTS) was 0.24 inches of water. The vacuum required to be drawn by Technical Specification Surveillance Requirement is 0.25 inches of water. Secondary Containment was declared inoperable with the plant not in the mode of applicability (Mode 4, Cold Shutdown). During a review of past operability of Secondary Containment, it was determined that the cut in the Reactor Building wall likely existed during the period the plant was cooling down in Mode 3, Hot Shutdown. Secondary Containment is required to be operable in Mode 3.
DAEC design basis documents state the design safety criteria for SGTS is to "limit exfiltration from the secondary containment during periods of primary and/or secondary containment isolation" and "to control outward leakage of the atmosphere from the secondary containment". Therefore, the safety function of SGTS and Secondary Containment was maintained by the ability to draw a substantial vacuum of 0.24 inches of water with the cut in the Reactor Building wall. Although the safety function of Secondary Containment and SGTS was maintained throughout this event, the reporting criteria in NUREG-1022 for 50.73(a)(2)(v)(C) states"... a report is required when 1) there is a determination that the SSC is inoperable in a required mode or other specified condition, 2) the inoperability is due to... equipment failures..., and 3) no redundant equipment in the same system was operable." Since Secondary Containment was declared inoperable, it meets the reporting criteria outlined in NUREG-1022.
This event did not result in a Safety System Functional Failure.
REV NO.
- - 01 Page 3 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/readinq-rm/doc-collections/nuregs/staff/sr1022/r3[)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Duane Arnold Energy Center 05000-331 Ill.
Cause of Event
YEAR 2020
- 3. LERNUMBER SEQUENTIAL NUMBER
- - 001 The cause of the LOOP was an extremely severe storm (called a Derecho) with heavy rains and very high winds. Wind speeds exceeded 80 mph for over 20 minutes with peaks on site at greater than 100 mph. The National Weather Service later estimated wind speeds were likely near 130 mph. These winds resulted in all 6 off site power sources (4 - 161 kV and 2 - 345 kV) coming into the DAEC switchyard being damaged or downed. A separate offsite 69 kV line which feeds non-essential plant loads was also damaged.
IV.
Corrective Actions
REV NO.
- - 01 The high winds experienced on August 10, 2020 were not considered a beyond design basis event. The systems and components responded as designed and the overall peak wind speeds were within the Design Basis Tornado. The damage observed coincides with the amount of damage expected for the event. Given this event was outside the control of the station staff and that all components worked as designed, no additional corrective actions beyond repair/recovery efforts related to the wind storm are needed.
V.
Additional Information
Previous Similar Occurrences:
A review of NextEra Energy Duane Arnold LERs from the previous 5 years identified the following event:
LER 2018-004 -Automatic Reactor Scram due to Feedwater Regulating Valve Failure LER 2019-001 -Automatic Reactor Scram due to Loss of Feedwater EIIS System and Component Codes:
EB - Medium-Voltage Power System
Reporting Requirements
This activity is being reported pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A),50.73(a)(2)(iii), and 50.73(a)(2)(v)(C). Page 4 of 4