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 Report dateSiteEvent description
05000331/LER-2017-00127 March 2017Duane Arnold

On January 25, 2017, at 1800 CST, while operating at 100% power, during planned surveillance testing, Drywell Vent Inboard Isolation Valve, CV4302 (System Code JM), was found to exceed its Leakage Integrity Test limits and was declared inoperable. The initial observed conditions indicated that CV4302 was the likely source of leakage and was the focus of repair efforts. After completion of repairs to CV4302, post maintenance testing showed that the Drywell Vent Line Outboard Isolation valve, CV4303, was exceeding its valve leakage limits, and therefore, was declared inoperable at 0300 CST on January 26, 2017. This resulted in a containment penetration flow path not within purge valve leakage limits and was reported in accordance with 10 CFR 50.72(b)(3)(v)(C) (reference EN#52511). Repairs were completed on CV4303 and both primary containment valves were declared operable at 1007 CST on January 26, 2017.

The cause of this event was determined to be inadequate work instructions and maintenance procedures.

This event was of low safety significance and had no impact on public health or safety. This event is reportable pursuant to 10CFR50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

05000331/LER-2016-0036 December 2016Duane ArnoldOn October 18, 2016, with the unit shutdown for a planned refueling outage (Mode 5, Refueling, 0% power), an evaluation of data from the scheduled Main Steam Line Isolation Valve (MSIV) (System Code SB) and Main Steam Line Drain valve penetration Local Leak Rate Testing (LLRT) determined the 'as found' maximum pathway leakage for the 'B' Inboard MSIV, CV-4415, and the Outboard Main Steam Line Drain valve, MO-4424, was in excess of the Technical Specification (TS) 3.6.1.3 leakage limit of 100 scfh for a single MSIV and 5 200 scfh for combined pathway leakage. The cause was determined to be a failure to perform periodic internal inspections of the MSIVs and a non-optimal valve design for the steam line drain application. Corrective actions included reworking CV-4415 to restore its leakage limit to below TS limits. Corrective actions are planned to replace MO-4424 with an optimal valve design. This event was of low safety significance had no impact on public health or safety. This event is reportable pursuant to 10CFR50.73(a)(2)(i)(B).
05000331/LER-2016-0026 December 2016Duane ArnoldOn April 28, 2016, at 1055, while operating at 100% power, with no structures, systems, or components inoperable that contributed to this event, during the performance of Surveillance Test Procedure (STP) 3.3.6.1-28, Reactor Core Isolation Cooling (RCIC) System Steam Line Flow - High Channel Functional Test, the RCIC turbine received an unplanned trip signal and subsequent turbine stop valve closure. The cause of the event was a human performance error associated with verifying the correct installation location of the relay block. The turbine trip resulted in the unplanned inoperability of RCIC, therefore, this condition meets the reporting requirements of 10CFR50.73(a)(2)(v)(D). At 1353 on April 28, 2016, the RCIC turbine was reset and RCIC was declared available. The safety significance of this event was low since all Emergency Core Cooling Systems were operable during the time the RCIC turbine was tripped.
05000331/LER-2016-00118 August 2016Duane Arnold

On June 19, 2016, while operating at 82% power, two secondary containment access airlock doors were briefly opened simultaneously during a surveillance test. This event was a momentary inoperability of secondary containment integrity, which is an 8 hour reportable event. The Resident Inspector was notified, and an Event Notification made pursuant to 10 CFR 50.72(b)(3)(v)(C). (Reference EN#52022). Following the event, the door controls were adjusted and verified to function properly. On June 29, 2016, at 100% power, workers opened two doors concurrently when entering a secondary containment access airlock. The individuals promptly closed their respective doors. The event was a brief inoperability of secondary containment integrity as above, notifications were made, and repairs completed. (Reference EN#52053) The root causes were determined to be inadequate procedural guidance and equipment design not being able to prevent the simultaneous opening of an inner and outer door at all times, under all possible conditions. Corrective actions include modification of the interlock tests, and replacement of key door interlock components.

These events did not result in a safety system functional failure. There were no radiological releases associated with these events.

05000331/LER-2015-00618 February 2016Duane Arnold

On July 23, 2015, while operating at 100% power, with no structures, systems, or components inoperable that contributed to this event, during the performance of Surveillance Test Procedure (STP) 3.5.3-05, RCIC/HPCI Suction Transfer Interlock, the Condensate Storage Tank (CST) Low Level HPCI and RCIC Suction Swap Relay, E41A-K059, as-found time to trip was 19.86 seconds. This was outside the relay design band of 0.0-5.0 seconds. This condition resulted in the HPCl/RCIC CST suction swap function being inoperable. Technical Specification (TS) require HPCI and RCIC to be declared inoperable within 1 hour from the discovery of the inoperable support feature. HPCI and RCIC were not declared inoperable and therefore, this

  • condition meets the reporting requirements of 10CFR50.73(a)(2)(i)(B) and 10CFR50.73(a)(2)(v)(A) and (D).
05000331/LER-2015-00228 January 2016Duane ArnoldOn March 31, 2015, while operating at 100% power, with no structures, systems, or components inoperable, an unanalyzed condition regarding the primary containment suppression pool coating was identified. Specifically, during an inspection of suppression pool (torus) during the October 2014 refueling outage, degradation of the torus coating was discovered. Some of the coating had become delaminated. NextEra Energy Duane Arnold took immediate action to restore the coating to within design parameters during the refueling outage and the degraded condition no longer exists. Extensive analysis was performed to determine effect of the delaminated material. Upon completion of this investigation, it was determined that an unanalyzed condition, a condition prohibited by Technical Specifications, an event or condition that could have prevented fulfillment of a safety function and common cause inoperability existed and is reporting the condition under various sections of 10 CFR 50.73. The root causes of this event were less than adequate coating application specification and work instructions and less than adequate project oversight and control.
05000331/LER-2015-00516 December 2015Duane Arnold

On October 20, 2015 at 1800, while operating at 100% power, a voltage transient due to a lightning strike resulted in an automatic start of both of the site's Emergency Diesel Generators (EDGs) (IEE Code EK).

Neither EDG loaded onto its respective essential bus, as offsite power remained available. The 'A' EDG was secured at 1930 on October 20, 2015. The 'B' EDG was secured at 1947 on October 20, 2015. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 51484 was made pursuant to 10 CFR 50.72(b)(3)(iv)(A) due to a valid system actuation.

The apparent cause of the starting of both EDGs was a storm-induced voltage dip (fault). This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2015-00125 June 2015Duane Arnold

On March 21, 2015, while operating at 100% power, workers opened doors concurrently when entering a secondary containment access airlock. The individuals involved each closed their respective doors upon encountering this unexpected condition; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and an Event Notification was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function (Reference EN#50914).

Following the event, the doors were verified to be functioning properly and no deficiencies were noted on either door.

A Root Cause Evaluation was conducted and determined the root cause of this event is that the airlock door interlock is not designed to prevent more than one airlock door from opening under all possible conditions.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2014-0069 December 2014Duane ArnoldOn October 12, 2014, while in Mode 5 for a refueling outage and prior to commencing certain planned activities, Duane Arnold Energy Center (DAEC) implemented the guidance of NRC EGM 11-003, R2, "Enforcement Guidance Memorandum 11-003, Revision 2, Dispositioning Boiling Water Reactor Licensee Noncompliance with Technical Specification Containment Requirements during Operations with a Potential for Draining the Reactor Vessel" (OPDRV). Throughout the planned OPDRV activities that continued, DAEC implemented interim actions per EGM 11-003 as an alternative to maintaining Secondary Containment operability as required by Technical Specification (TS) 3.6.4.1. While the NRC's enforcement guidance provides allowance for these actions, the OPDRV activities without Secondary Containment are still considered reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a Condition Prohibited by Technical Specifications. The implementation of EGM 11-003, Revision 2 was a planned activity and did not require a cause evaluation. Consistent with the guidance in the EGM, Duane Arnold Energy Center will submit a license amendment request (LAR) within twelve months after issuance of a notice of availability regarding a generic resolution of the issues surrounding the need for the EGM.
05000331/LER-2014-00529 August 2014Duane Arnold

On June 30, 2014, at 1913, while operating at 98% power, a grid disturbance resulted in an automatic start of both of the site's Emergency Diesel Generators (EDGs) (IEE Code EK). Neither EDG loaded onto its respective essential bus. The cause of the EDG starts was a momentary (approximately 13 cycles) dip in essential bus voltage to 62%. A review of the system design showed that since the EDGs started on an automatic start signal of essential bus voltage less than 65% for greater than 12 cycles, the EDGs operated as designed. Both EDGs were secured and returned to their normal standby readiness condition at 2116 on June 30, 2014. This event resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 50246 was made pursuant to 10 CFR 50.72(b)(3)(iv)(A) due to a valid system actuation.

The apparent cause of the event was determined to be a valid start of the EDGs per design. This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2014-00425 July 2014Duane Arnold

On May 30, 2014, at 1043, while operating at 100% power, during the performance of a routine Technical Specification (TS) required Surveillance Test Procedure (STP), the 'A' side High Pressure Coolant Injection (HPCI) (BG) isolation logic was activated. The logic activation occurred while attempting to block open contacts of HGA relay E41A-K43, HPCI Auto Isolation Logic Steam Line High Differential Pressure.

The root cause of this event was the design of the HGA relay makes the act of installing relay blocks very difficult and prone to inadvertent actuation. The Resident Inspector was notified, and Event Notification Number 50154 was made pursuant to 10 CFR 50.72(b)(3)(v)(D) due to a condition at the time of discovery that prevented the fulfillment of the HPCI safety function. On May 30, 2014, at 1209, HPCI was returned to operable status after resetting the isolation logic and returning the system to standby readiness condition.

This event did result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2014-00325 July 2014Duane Arnold

On May 30, 2014, while operating at 100% power, workers opened doors concurrently when entering a secondary containment access airlock. The individuals involved each closed their respective doors upon encountering this unexpected condition; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 50153 was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function.

The apparent cause of the event was determined to be excess strength of a permanent magnet on one of the doors. The monthly surveillance test will be revised to address the lag between the interlock lights turning off and the door latching, to document maintenance actions to allow trending and to quantify the gap between the interlock light turning off and the door latching.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2013-00614 July 2014Duane Arnold

On December 18, 2013, while operating at 100% power, two workers opened doors concurrently when entering a secondary containment access airlock. Both individuals realized that this was not allowed and closed their respective door; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 49657 was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function.

The apparent cause of the event was determined to be excess strength of a permanent magnet on one of the doors. The monthly surveillance test will be revised to check the permanent magnet for proper adjustment and to adjust it as needed.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2014-00130 April 2014Duane Arnold

On January 17, 2014, while operating at 100% power, Standby Transformer 1X4 Undervoltage Relay 127/SB2 failed to meet requirements of Surveillance Test Procedure (STP) 3.3.8.1-05B, 1A4 4KV Emergency Transformer Supply Undervoltage Calibration. Two relay trip circuit contacts were found to be incorrectly configured such that the relay could not perform the intended function to actuate on loss-of-voltage to trip the Standby Transformer supply breaker. A past operability review determined that the relay had been inoperable for 120 days, 8 hours and 5 minutes. The relay is required to be operable in Modes 1, 2, and 3, and when the associated "B" Emergency Diesel Generator is required to be operable by Limiting Condition for Operation (LCO) 3.8.2, AC Sources-Shutdown. The event resulted in a condition prohibited by Technical Specifications and is reportable pursuant to 10CFR50.73(a)(2)(i)(B). The safety significance is minimized due to the fact that degraded voltage relays perform a similar function and would trip the Standby Transformer supply breaker to allow the "B" Emergency Diesel Generator to carry essential loads during a Loss-of-Offsite-Power.

The root cause of this event was inadequate procedural guidance for both preplanned maintenance and post maintenance testing. This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

05000331/LER-2014-00217 April 2014Duane Arnold

On February 18, 2014, while operating at 100% power, workers opened doors concurrently when entering a secondary containment access airlock. The individuals involved each closed their respective doors upon encountering this unexpected condition; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 49838 was made pursuant to 10 CFR 50.72(b)(3)(v)(.C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function.

The apparent cause of the event was determined to be excess strength of a permanent magnet on one of the doors. The monthly surveillance test has been revised to check the permanent magnet for proper adjustment and to adjust it as needed.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.