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On May 27, 2017, an attempt to start the red train High Pressure Injection (HPI) pump (BJ) in accordance with normal operating procedures was initiated. Control Room operators received an annunciator, HPI PUMP TRIP, and observed no indication of the pump starting.

During investigative walk downs with the relay department, personnel discovered the HPI breaker was not fully racked up (trip pedal still in a tripped (down) condition and roller not free to roll). Operations personnel performed manual breaker operations to rack the 4160 V breaker (EB) further in the up direction. The pump was successfully started and declared operable.

The condition was the result of an inadequate risk evaluation.

The associated Operations Directive has been revised to require Operations management approval when waiving start-checks of vital 4160 VAC components following racking up of the respective breaker. The revision is expected to ensure appropriate personnel are involved when determining the risk associated with not testing components for functionality/operability following racking up evolutions of an associated breaker.

On April 26, 2017, ANO-2 was in day 28 of a refueling outage with the core completely off loaded to the spent fuel pool (SFP). Power to ANO-2 plant equipment was supplied from Start Up Transformer 2 (SU2) while SU3 was out of service for planned maintenance. 500kV and 161kV offsite power lines were in service. The area around the plant was experiencing severe weather from thunderstorms and tornado warnings had been issued from the National Weather Service for the four county area. Switchyard work was ceased.

At approximately 1002 CST switchyard breakers for 500kV lines opened on fault current. High winds had damaged the transmission towers approximately 16 miles away from ANO and caused phase to ground faults. This resulted in a loss of all offsite power lines to the 500 kV bus. The autotransformer also locked out, as designed, when the 500 kV transmission lines faulted.

When the 500kV bus tripped, the 4.16kV bus that feeds a vital 480 volt bus was subjected to a voltage transient; subsequently; the #1 emergency diesel generator (EDG) auto started. The EDG output breaker never closed due to the fact that voltage was restored to normal almost immediately. This EDG was secured due to running unloaded.

Both SFP cooling pumps were out of service after the transient. A SFP cooling pump was restarted at 1020 CST.

The temperature of the SFP did not change during this event.

On September 29, 2016, at Arkansas Nuclear One, Unit 1 (ANO-1), during refueling outage 1R26 with both trains of Decay Heat Removal (DHR) in service, a 0.125 gpm leak was identified in the DHR system at a one-inch drain line.

This leak was on a section of cross-connect piping shared by both trains of the DHR system. The consequence of the leak was that both trains of the DHR system were declared inoperable.

The leakage was due to a fatigue crack caused by vibration of the drain line due to a pipe support that was not designed for system vibration.

Other systems and components in ANO-1 and ANO, Unit 2 (ANO-2) exposed to elevated system vibration were evaluated with respect to this condition. As a result of this evaluation, socket welds on other drains and vents in the ANO-1 DHR system were cut out and replaced, and pipe supports were modified where needed to withstand system vibration.

On August 24, September 11, and September 15, 2016, during performance of an extent of condition evaluation related to the protection of Technical Specification (TS) equipment from external flood hazards, Arkansas Nuclear One, Unit 1 (ANO-1), identified non-conforming plant design conditions such that specific ANO-1 TS equipment was considered to not be adequately protected from tornado missiles. These are legacy design issues.

On August 24, 2016, at 0945, September 11, 2016, at 1504, and September 15, 2016, at 0958, Operations declared the affected components inoperable, implemented Enforcement Guidance Memorandum (EGM) 15-002, "Enforcement Discretion for Tornado-Generated Missile Protection Noncompliance", along with necessary compensatory measures, and subsequently declared the affected equipment operable but non-conforming.

The cause of this issue was unclear and changing regulatory requirements during original plant licensing that led to an inadequate understanding of the regulatory guidance with respect to tornado missile protection design requirements.

Interim corrective actions include implementation of compensatory strategies. Plant modifications and license basis changes are being evaluated to resolve outstanding issues.

On March 19, 2016, two block-out penetrations separating the Arkansas Nuclear One, Unit 1 (ANO-1) Turbine Building from the Auxiliary Building were determined to be non-functional. The penetrations are located in the floor of Turbine Building elevation 354 ft. Below the penetrations is the Auxiliary Building, housing safety related equipment.

On March 17, 2016, it was identified that two penetration seals did not match approved fire penetration or approved flood seal details. Further investigation, completed on March 19, 2016, revealed that the two block-out penetrations were not grouted and represented a previously unknown vulnerability in a credited external flood barrier.

The apparent cause of this event was less than adequate project management control for the size and scope of the External Flood Mitigation Project associated with post Fukushima Dai-ichi resolutions and requirements set forth by the NRC.

Mitigating strategies and extent of condition reviews have been implemented for the identified conditions. Permanent repair of the deficient flood barriers is complete minus cure time. Actions to correct programmatic aspects of this condition are in progress.

On October 26, 2015, the Containment Purge and Exhaust Isolation Process Monitor was discovered to be inoperable due to not having its required sample pump in operation. The Containment Building Purge Radiation Monitor Sample Pump provides flow to the Containment Purge and Exhaust Isolation Process Monitor. Technical Specification 3.3.3.1, Table 3.3-6, requires the Containment Purge and Exhaust Isolation was in Mode 6 with refueling operations in progress while the Containment Purge and Exhaust Isolation Process Monitor was inoperable.

The apparent cause of this event was a a human performance error associated with the failure to restart the Containment Building Purge Radiation Monitor Sample Pump following manual transfer to its alternate power supply.

On April 3, 2014, at approximately 1300 CST, Arkansas Nuclear One Unit 2 (ANO-2) tripped from 100% power due to a fault in 161kV Russellville East Line. The fault caused a momentary degraded voltage state on the 161kV and 500kV grid at ANO and an undervoltage condition for ANO-2 Startup #3 Transformer (SU3). This under voltage condition caused SU3 undervoltage relays to initiate a fast transfer of ANO-2 4160V bus (2A-1) and 6900V bus (2H-1), to Startup Transformer #2 (SU2). Buses ANO-2 6900V (2H-2) and 4160V (2A-2) were not allowed to fast transfer to SU2 because of operational restraints per design. The removal of power to 2A-2 caused an auto start of the ANO-2 Emergency Diesel Generator (2K-4B) due to under voltage on safety bus 2A-4 which is normally fed from 2A-2.

Bus 2A-2 slow transferred back to SU3. 2K-4B did not tie to 4160V safety bus (2A-4) as voltage had recovered prior to the diesel reaching rated speed and voltage. Bus 2H-2 was de-energized causing the loss of two Reactor Coolant Pumps (RCPs) which led to a reactor trip on low RCP speed and the actuation of the Emergency Feedwater System (EFW) on low Steam Generator Level. It was determined that a lighting strike caused a three phase fault on the 161kV Russellville East Line causing the ANO-2 trip. The corrective action is for Entergy Arkansas to review the adequacy of 161kV Russellville East Transmission Line Lightning Protection System.

On March 31, 2013, at approximately 0750 CDT, during lifting and removal of the Arkansas Nuclear One Unit 1 (ANO-1) original Main Generator Stator (Stator), the temporary lift assembly collapsed due to failure of one of the structural columns, resulting in the Stator falling onto the turbine deck (386' elevation) and rolling down into the ANO-1 train bay (354' elevation) adjacent to Arkansas Nuclear One Unit 2 (ANO-2).

The event resulted in one fatality, multiple injuries, structural damage to the ANO-1 and ANO-2 turbine buildings, and damage to non-vital systems and electrical equipment. At the time of the event, ANO-1 was in MODE 6 and ANO-2 was in MODE 1 at approximately 100 percent power. The event resulted in a loss of offsite power for ANO-1, with both Emergency Diesel Generators (EDGs) starting to supply safety loads.

ANO-1 decay heat removal was lost for approximately four minutes. ANO-2 automatically tripped off-line after the vibration from the dropped Stator resulted in the actuation of relays in the ANO-2 switchgear located adjacent to the train bay, subsequently tripping a reactor coolant pump motor breaker. After the reactor trip, emergency feedwater was manually initiated by ANO-2 Control Room Operators. As debris fell into the train bay, an 8-inch firewater pipe was ruptured and the Alternate AC Diesel Generator electrical tie to ANO-1 was severed. At 0923 CDT that same day, water intrusion from the ruptured firewater piping into a 4160 volt breaker resulted in an ANO-2 Startup Transformer lockout, de-energizing a safety bus. An EDG automatically started as designed and supplied the affected safety bus. An ANO-2 Notification of Unusual Event was declared at 1033 CDT due to fire or explosion from an electrical fault in the 4160 volt switchgear with indications of bus damage. After damage assessment and repairs, ANO-2 returned to power operation on April 28, 2013. ANO-1 returned to power operation on August 7, 2013.

On January 02, 2013 at 1308 CST, Arkansas Nuclear One Unit-2 (ANO-2) experienced an invalid Safety Injection Actuation Signal (SIAS), Containment Isolation Actuation Signal (CIAS), and Containment Cooling Actuation Signal (CCAS) while technicians were performing Plant Protection System (PPS) matrix testing, resulting in the auto start of the Emergency Diesel Generators, High Pressure Safety Injection (HPSI) Pumps and Low Pressure Safety Injection (LPSI) Pumps in the standby mode, and the re-positioning of numerous safety related components to their actuated state. The operating crew appropriately entered the Abnormal Operating Procedures (AOP) for inadvertent SIAS and inadvertent CIAS. In accordance with the inadvertent SIAS AOP, the operating crew restored Auxiliary Cooling Water flow from the Service Water (SW) System and restored SW flow to the Component Cooling Water (CCW) System by overriding the SIAS to the respective flow path valves. HPSI and LPSI Pumps were placed in pull-to-lock to prevent pump overheating, as procedurally directed. In accordance with the inadvertent CIAS AOP, the operating crew overrode the CIAS to CCW isolation valves to restore CCW flow to the Reactor Coolant Pumps. The SIAS initially aligned boric acid injection into the Reactor Coolant System as designed, and resulted in a reactor power decrease to approximately 87%. The invalid actuation signals were reset and HPSI/LPSI pumps were restored within one hour of actuation. ANO-2 returned to full power operation the same day.

A failure modes analysis determined that the direct cause of the event was the degradation of a PPS matrix test switch, with the Root Cause determined to be failure to implement a preventative maintenance strategy for the switch during a 1986 modification.

• 20.2203(a)(2)(vi) 0

• 50.73(a)(2)(i)(B) 0

• 50.73(a)(2)(v)(D)

• 20.2203(a)(2)(vi) 0 @ 50.73(a)(2)(i)(B) 0

• 50.73(a)(2)(v)(D)

• 20.2203(a)(2)(vi) 0

• 50.73(a)(2)(i)(B) 0

• 50.73(a)(2)(v)(D)

• 20.2203(a)(2)(vi) D 0 50.73(a)(2)(i)(B) D

• 50.73(a)(2)(v)(D)

On April 7, 2008, at approximately 1345 CST, with the plant shutdown in Mode 3, and with all Control Element Assemblies (CEAs) withdrawn two steps in preparation for CEA drop time testing, the Control Room was informed that the software verification for the Control Element Assembly Calculators (CEACs) had not been verified and that the CEACS should be considered inoperable. The Shift Manager (SM) was told by Reactor Engineering (RE) personnel that the raw CEA inputs to the CEACs could not be used to verify CEA position.

Although the CEACs were not required to be operable in Mode 3, at least one position indicator is required to be operable for each CEA not fully inserted. At 1350, the Shift Manager directed that the reactor trip breakers be opened to comply with the associated technical specifications action statement. The cause of this event was inadequate communication between the SM and RE personnel which led to the incorrect conclusion that the CEA position indicators were inoperable. A "Lessons Learned" document regarding this event was prepared by the involved SM and was distributed to the SMs of both ANO units.