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At 1258 CDT on August 10, 2020, Duane Arnold Energy Center declared an Unusual Event due to a loss of offsite power due to high winds. The event at the single unit plant resulted in an automatic scram from 82 percent power (Mode-1) to zero percent power (Mode-3). They are headed to Mode-4. There is damage on site, but the Reactor Building is intact. All rods inserted and cooling is being addressed via Reactor Core Isolation Cooling (RCIC) for level control and Safety Relief Valves are removing decay heat to the torus. Both Standby Diesel Generator are running. The licensee notified the NRC Resident Inspector, the Iowa Department of Emergency Management, and the Linn County and Benton County Emergency Management agencies. Notified DHS SWO, FEMA Operations Center, CISA Central, FEMA NWC (email), DHS Nuclear SSA (email), and FEMA NRCC SASC (email).

• * * UPDATE ON 08/10/2020 AT 1554 EDT FROM CURTIS HANSEN TO OSSY FONT * * *

This report is being made under CFR 50.72 (b)(2)(iv)(B) for an automatic reactor scram due to loss of offsite power due to high winds. In addition, this report is being made under CFR 50.72 (b)(3)(iv)(A) and (B) due to PCIS ((Primary Containment Isolation System)) Groups 1, 2, 3, 4 and 5 (activating) due to loss of offsite power. All isolations went to completion. RCIC injecting for level control. All rods fully inserted during the scram. The plant electrical line up is both SBDGs (Standby Diesel Generators) are running. Decay heat is being removed via SRVs (Safety Relief Valves) to the torus. Progress towards shutdown cooling. NRC Senior Resident (Inspector) notified at 1448. Notified R3DO (Pelke).

At 0934 CDT, while appropriately removed from service for pre-planned testing, the High Pressure Coolant Injection (HPCI) inboard steam isolation valve, MO-2238, valve position indication was found to be inadequate. As a result, MO-2238 was declared inoperable in accordance with Technical Specification (TS) 3.6.1.3. This resulted in a condition that caused the HPCI system to be inoperable. The cause of the inadequate valve position indication is currently being investigated. This report is being made pursuant to 10 CFR 50.72(b)(3)(v)(D). The NRC Resident Inspector has been informed.

• * * RETRACTION ON 09/11/17 AT 1144 EDT FROM BOB MURRELL TO BETHANY CECERE * * *

The purpose of this notification is to retract a previous report made on 8/1/17 at 1700 (EDT) (EN 52881). NRC notification was initially made as a result of the High Pressure Coolant Injection (HPCI) inboard steam isolation valve, MO-2238, valve position found to be inadequate. Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the condition observed on 8/1/17 for MO-2238 did not exist prior to removing the system from service for pre-planned testing, but was observed during post maintenance testing. Consequently, the failure does not meet the reporting requirements of 10 CFR 50.72 or 10 CFR 50.73. The NRC Resident Inspector has been notified. Notified the R3DO (Riemer).

On April 12, at 1235 CDT, Duane Arnold Energy Center contacted officials with the State of Iowa (Bureau of Radiological Health and Department of Natural Resources) and Linn County Public Health Department in accordance with the nuclear industry voluntary reporting criteria contained in NEI 07-07 'Industry Ground Water Protection Initiative'. The site contacted the agencies as courtesy to notify them about the identification of low levels of tritium found within the site's protected area from a potential new source. Samples were taken, and no regulatory limits were exceeded. The site team is working with industry experts on pinpointing the cause and installing an extraction well to remediate the situation. This report is being made in accordance with 10 CFR 50.72(b)(2)(xi), as a result of notification to offsite agencies.

The Licensee has notified the NRC Resident Inspectors. There is no risk to plant employees, the public or drinking water.

At 1050 (CDT) on 4/23/2015, an equipment malfunction resulted in DAEC (Duane Arnold Energy Center) declaring the Division 1 Essential Electrical Bus inoperable. The LPCI ( Low Pressure Coolant Injection) system was inoperable but available as part of a planned evolution at the time of the malfunction. Declaring the Essential Electrical Bus inoperable caused the 'A' Core Spray System to be considered inoperable. LPCI and 'A' Core Spray being inoperable simultaneously constituted a loss of safety function. The 'B' Core Spray system remained operable and available. The equipment malfunction was resolved promptly, allowing the Division 1 Essential Electrical Bus to be returned to an operable status. The notification is being made pursuant to 10 CFR 50.72(b)(3)(v)(D). The (NRC) Resident Inspector has been notified. The licensee entered and exited TS LCO 3.5.1 condition B.

• * * RETRACTION FROM BOB MURRELL TO DONALD NORWOOD AT 0835 EDT ON 5/8/2015 * * *

The purpose of this notification is to retract a previous report made on 4/23/15 at 1851 EDT (EN 51006). Notification to the NRC was initially made as a result of an event or condition that could prevent the fulfillment of the safety function of Emergency Core Cooling System (ECCS) due to an equipment malfunction associated with the Division 1 Essential Electrical Bus Breaker 1A306. Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the Division 1 Essential Electrical Bus was fully capable of performing its intended safety function with the malfunction on Bus Breaker 1A306. Therefore, this event is not considered a Safety System Functional Failure and is not reportable to the NRC as a Licensee Event Report (LER) per 10 CFR 50.73. The NRC Resident Inspector has been notified. Notified R3DO (Skokowski).

This condition is reported in accordance with 10 CFR 50.72(b)(3)(v). On 3/12/15, during surveillance testing on LPCI (Low Pressure Coolant Injection) Loop Select Instrumentation, a degraded component was discovered. At 1230 CDT on 3/13/15, LPCI was declared INOPERABLE in accordance with Technical Specification requirements. All remaining ECCS systems remain available and operable. The NRC Resident Inspector has been informed.

• * * UPDATE AT 0210 EDT ON 03/14/15 FROM SCOTT AREBAUGH TO S. SANDIN * * *

At 0105 CDT on 3/14/15, the subject component has been replaced and retested with satisfactory results. LPCI INOPERABLE condition was exited at 0105 CDT and the LPCI System is OPERABLE. The licensee informed the NRC Resident Inspector. Notified R3DO (Orth).

• * * RETRACTION AT 1737 EDT ON 04/23/15 FROM BOB MURRELL TO DONG PARK * * *

The purpose of this notification is to retract a previous report made on 3/13/15 at 1859 EDT. Notification of the event to the NRC was initially made as a result of an event where Low Pressure Coolant Injection (LPCI) was declared inoperable due to the discovery of a degraded LPCI Loop Select timing relay. Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the LPCI Loop Select timing relay was tested in a configuration that affected time delay measurements. This testing configuration was revised in 2012 following a modification to the LPCI Loop Select Logic, STP 3.3.5.1-29. The inadequate testing configuration adversely affected the time delay when the test equipment was installed. A revision to STP 3.3.5.1-29 was completed to resolve the inadequate testing configuration. Subsequent bench testing, performed to mimic plant installed configuration, of the affected relay, was completed. This testing demonstrated that the relay could be tested in a manner that provided acceptable results, and it has been concluded that the relay would have performed its required safety function up to when it was tested on 3/13/15. Therefore, this event is not considered a Safety System Functional Failure and is not reportable to the NRC as a Licensee Event Report (LER) per 10 CFR 50.73. The NRC Resident Inspector has been notified. Notified R3DO (Valos).

At 0107 CDT on October 23rd, 2014, both doors in one of the Secondary Containment airlocks were momentarily open concurrently. This occurred during vessel drain down following refueling activities, an Operation with the Potential to Drain the Reactor Vessel (OPDRV), which required Secondary Containment to be operable. The doors being open at the same time resulted in the momentary inoperability of Secondary Containment. One of the doors was immediately closed, and Secondary Containment was restored to an operable status. The station (Duane Arnold) has now completed the OPDRV associated with vessel drain down, and Secondary Containment is no longer required to be operable. The Resident Inspector has been notified.

• * * RETRACTION FROM BOB MURRELL TO JOHN SHOEMAKER AT 1232 EST ON 12/17/14 * * *

The purpose of this notification is to retract a previous report made on 10/23/2014, at 0948 (EDT) (EN 50560). Notification of the event to the NRC was initially made as a result of an event where both doors in one of the Secondary Containment airlocks were momentarily open concurrently. This occurred during vessel drain down following refueling activities, an Operation with the Potential to Drain the Reactor Vessel (OPDRV), which required Secondary Containment to be operable. The doors being open at the same time resulted in the momentary inoperability of Secondary Containment. One of the doors was immediately closed, and Secondary Containment was restored to an operable status. Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the doors in question were not mechanically degraded such that they were incapable of being closed. A momentary condition of having both secondary containment airlock doors open for a matter of seconds is not an event or condition that could have prevented the fulfillment of a safety. Furthermore, the conduct of OPDRVs during a momentary opening of both secondary containment doors that is immediately rectified does not constitute a condition prohibited by TS. Therefore, this event is not considered a Safety System Functional Failure or a Condition Prohibited by TS and is not reportable to the NRC as a Licensee Event Report (LER) per 10 CFR 50.73. The NRC Senior Resident Inspector has been notified. Notified the R3DO (McCraw). .

A planned maintenance evolution at the Duane Arnold Energy Center (DAEC) will remove the emergency power supply to the TSC from service. The TSC would be rendered non-functional with the loss of normal power. The repair to the power supply is expected to last 1 day. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures. Maintenance will be expedited to restore the emergency power supply to service. This notification is being made in accordance with 10 CFR 50.72(b)(3)(xiii) due to the loss of an Emergency Response Facility (ERF). An update will be provided once the TSC emergency power supply has been restored to normal operation. The NRC Resident Inspector has been notified.

• * * UPDATE FROM TERRY BRANDT TO DONG PARK AT 1653 EDT ON 11/19/13 * * *

The emergency power has been returned to service to the TSC.

 The licensee has notified the NRC Resident Inspector.

Notified R3DO (Hills).

A planned maintenance evolution at the Duane Arnold Energy Center (DAEC) will de-energize the Meteorological Data Tower. No other indications or annunciators will be unavailable during this maintenance to affect the plant's ability to assess or monitor an accident or transient in progress. National Weather Service data is expected to be available throughout the duration of the planned maintenance. A follow up notification will be provided when power to the Meteorological Data Tower has been restored. The NRC Resident Inspector has been notified.

• * * UPDATE AT 1718 EDT ON 10/07/13 FROM TERRY BRANDT TO HUFFMAN * * *

Maintenance activities on the Meteorological Data Tower is complete and the tower has been returned to service. The licensee has notified the NRC Resident Inspector. R3DO (Skokowski) notified.

A planned maintenance evolution at the Duane Arnold Energy Center (DAEC) will remove the emergency power supply to the TSC from service. The TSC would be rendered non-functional with the loss of emergency power. The repair to the power supply is expected to last 2 hours. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures. Maintenance will be expedited to restore the emergency power supply to service. This notification is being made in accordance with 10CFR50.72(b)(3)(xiii) due to the loss of an Emergency Response Facility (ERF). An update will be provided once the TSC emergency power supply has been restored to normal operation. NRC Resident Inspector has been notified.

• * * UPDATE FROM TIM ERGER TO HOWIE CROUCH AT 1325 EDT ON 9/22/13 * * *

The TSC EDG remains unavailable due to emergent work. The licensee has notified the NRC Resident Inspector. Notified R3DO (Riemer).

• * * UPDATE FROM MIKE STROPE TO DANIEL MILLS AT 1237 EDT ON 9/25/13 * * *

The TSC EDG has returned to functional status. The licensee notified the NRC Resident Inspector. Notified R3DO (Dickson).

A planned maintenance evolution at the Duane Arnold Energy Center (DAEC) has removed the emergency power supply to the TSC from service as of 0900 EDT. If a loss of the normal power supply to the TSC were to occur during this period, the TSC would be rendered non-functional. The repair to the power supply is expected to last 6 hours. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures. Maintenance will be expedited to restore the emergency power supply to service. This notification is being made in accordance with 10 CFR 50.72(b)(3)(xiii) due to the loss of an Emergency Response Facility (ERF). An update will be provided once the TSC emergency power supply has been restored to normal operation. The licensee has notified the NRC Resident Inspector.

• * * UPDATE ON 6/6/13 AT 1614 EDT FROM STEPHEN SPEIRS TO DANIEL MILLS * * *

The TSC diesel generator has been returned to functional status. The NRC Resident Inspector has been notified R3DO (Lipa) has been notified.

At 0930 (CST) on January 03, 2013 NextEra Energy Duane Arnold discovered that the Emergency Response Data System (ERDS) was no longer capable of transmitting plant data to the NRC. The loss of ERDS is reportable per 50.72(b)(3)(xiii). At 1151 (CST) on January 03, 2013 Information Management personnel restored ERDS to working status. The NRC Resident (Inspector) has been notified. The licensee has the cause under investigation.

• * * UPDATE AT 2136 EST ON 01/03/13 FROM STEPHEN SPEIRS TO S. SANDIN * * *

At 1725 (CST) on January 03, 2013 NextEra Energy Duane Arnold experienced a four minute interruption of the Emergency Response Data System (ERDS). During this time, ERDS was not capable of transmitting plant data to the NRC. The loss of ERDS is reportable per 10 CFR 50.72(b)(3)(xiii). The interruption of ERDS is related to a previous problem with the system reported under EN #48648. Troubleshooting of ERDS continues to ensure long-term reliability. Additional interruptions of ERDS are possible during this troubleshooting, and a follow-up notification will be made when ERDS reliability is assured. The licensee informed the NRC Resident Inspector. Notified R3DO (Skokowski), ERDS Group and CAT Group via email.

• * * UPDATE FROM ROB SPADING TO CHARLES TEAL ON 1/28/13 AT 1436 EST * * *

Maintenance is complete on the ERDS system. It was tested satisfactorily on 01/15/13 at 1130 CST and returned to fully functional status. The NRC Resident Inspector has been informed. Notified R3DO (Stone), ERDS Group and CAT Group via email.

A planned maintenance evolution at Duane Arnold Energy Center (DAEC) to replace a hard drive in the plant process computer will result in a loss of all SPDS indication for a duration of less than six hours. There is no planned maintenance affecting Primary Indications or Annunciators in the Control Room which would affect the plant's ability to assess or monitor an accident or transient in progress. This notification is being made pursuant to 10CFR50.72(b)(3)(xiii). The licensee will notify the NRC Resident Inspector.

• * * UPDATE AT 1433 EST ON 11/16/12 FROM MANKIN TO HUFFMAN * * *

The planned maintenance has been completed and SPDS returned to service at 1431 EST. The licensee has notified the NRC Resident Inspector. R3DO(Kunowski) notified.

A planned maintenance evolution at the Duane Arnold Energy Center (DAEC) will remove the TSC (Technical Support Center) ventilation system from service. The TSC would be rendered non-functional with the loss of ventilation. The repair to the TSC ventilation is expected to last 3 days. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures. Maintenance will be expedited to restore ventilation to the TSC. This notification is being made in accordance with 10CR50.72(b)(3)(xiii) due to the loss of an Emergency Response Facility (ERF). An update will be provided once the TSC ventilation system has been restored to normal operation. The licensee notified the NRC Resident Inspector

• * * UPDATE FROM MIKE STROPE TO CHARLES TEAL ON 9/12/12 AT 1157 EDT * * *

The TSC maintenance has been completed. The TSC has been restored to service. The NRC Resident Inspector has been informed. Notified R3DO (Kunowski).

On 8-20-2012 during scheduled surveillance testing, the Reactor Water Cleanup (RWCU) System Isolation Differential Flow - High function was discovered to be inoperable at 1520 CDT. The high differential flow signal is provided to detect a break in the RWCU system when area or differential temperature would not provide detection (i.e. cold leg break). This instrumentation provides isolation signals to both inboard and outboard isolation valves and its loss is being reported pursuant to 10CFR50.72(b)(3)(v)(C). The NRC Resident Inspector was notified.

• * * RETRACTION AT 1513 EDT ON 9/27/2012 FROM BOB MURRELL TO MARK ABRAMOVITZ * * *

Subsequent to the initial report, NextEra Energy Duane Arnold (NextEra) has determined that the RWCU Differential Flow High instrument loop was, at all times, capable of performing its TS function. Specifically an engineering analysis of the impact of the instrument as-found and as-left values on the overall instrument loop setting was performed. The analysis determined that the instrument in question was set at a value which would have isolated the RWCU Primary Containment Isolation Valves prior to reaching the Technical Specification (TS) allowable value and therefore the instrument loop remained capable at all times of performing its TS function. This event is not considered a Safety System Functional Failure or a Condition Prohibited by TS and is not reportable to the NRC as a Licensee Event Report (LER) per 10CFR50.73. The NRC Senior Resident Inspector has been notified. Notified the R3DO (Lipa).