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On April 5, 2017, Wolf Creek Generating Station (WCGS) was in Mode 1 at 100 percent power. During evaluation of protection for safety-related equipment from the damaging effects of tornados, WCGS personnel determined that safety-related fuel oil transfer lines inside the Diesel Generator Building could be damaged if tornado generated missiles struck the non-safety related truck connections to these transfer lines. As these safety-related transfer lines are required to supply fuel to the Emergency Diesel Generators (EDGs) from the fuel oil storage tank, Operations declared both of the EDGs inoperable. On April 5, 2017, at 1632 Central Daylight Time, an 8- hour, non-emergency report to the Nuclear Regulatory Commission (NRC) (reference NRC Event Notification Number 52666) was made in accordance with 10 CFR 50.72. Compensatory measures were implemented consistent with Enforcement Guidance Memorandum (EGM) 15-002, "Enforcement Discretion for Tornado-Generated Missile Protection Noncompliance." The EDGs were then declared operable but non-conforming.

These tornado missile vulnerabilities existed since the original plant construction. Immediate compensatory measures included verification that the severe weather procedures were up-to-date, ensuring that Operations personnel were current on their training to these procedures, and implementing measures to heighten station awareness until the vulnerabilities had been corrected. These vulnerabilities have now been permanently eliminated.

On November 16, 2016, at approximately 2109 Central Standard Time, while in Mode 5, a fault occurred which isolated the East Switchyard Bus from the Train "A" emergency AC plant bus NB01. During Refueling Outage 21, a modification to Transformer #7 allowed the offsite power through Transformer #7 to NB01 to be fed from either the East or West Switchyard Busses through 2 different breakers. After the loss of the East Switchyard Bus, the second breaker unexpectedly tripped which resulted in a loss of offsite power to NB01. An undervoltage condition was detected on NB01, which caused the Train "A" emergency diesel generator to start and to power NB01 as designed. The apparent cause of this event was that wiring in the Transformer #7 primary differential protective relay was landed on the incorrect termination point.

The wiring error on the primary differential protective relay was corrected and its functionality was verified.

The secondary differential protective relay wiring was verified to be correct. The East Switchyard Bus, Transformer #7, and its differential relays were all restored to service.

On May 5, 2015, it was discovered that the motive force (air supply) was not removed for two containment shutdown purge valves as required by Technical Specification 3.6.3, "Containment Isolation Valves." The motive force was restored to allow the performance of procedure STS KJ-001A, "Integrated Diesel Generator and Safeguards Actuation Test - Train A," on April 26, 2015. After performance of procedure STS KJ-001A, the motive force was not removed for the two containment shutdown purge valves. The plant entered Mode 4 on April 28, 2015 at 0144 Central Daylight Time (CDT).

Upon discovery, the air supply valves for the two containment shutdown purge valves were locked closed, removing the motive force. The cause of the event was the decision to only track components listed in the manual Locked Component Log during plant start-up, allowed a mode change with components out of position.

The safety significance of the event was low as each penetration flow path had a redundant valve that was closed with the motive force removed.

On May 3, 2015 at 1021 Central Daylight Time (CDT), Wolf Creek Generating Station (WCGS) was at approximately 25% power during startup from Refueling Outage 20. The 'C' steam generator received a Hi-Hi level signal while the Reactor Operator was manually transferring feedwater control from the Main Feedwater Regulating Valve (MFRV) bypass valves to the MFRVs. This resulted in a main turbine trip, feedwater isolation, and auxiliary feedwater actuation. A manual reactor trip was initiated at 1022 CDT. The root cause was the lack of a reliable and consistent standardization between the operating crews to control the transfer of the steam generator feedwater flow between the MFRV bypass valves and MFRVs and a sense of urgency by the control room operators.

The event is bounded by analyses as reported in the Wolf Creek Generating Station (WCGS) Updated Safety Analysis Report (USAR) Section 15.2.7, "Loss of Normal Feedwater Flow.

On October 18, 2013 at 1141 Central Daylight Time (CDT), the Class 1E electrical equipment air conditioning unit, SGKO5A, was declared nonfunctional due to low lube oil pressure on the SGKO5A compressor. As a result, Technical Specification (TS) Limiting Condition for Operation (LCO) 3.0.3 was entered and a plant shutdown was commenced. Mode 3 was entered on October 18, 2013 at 1735 CDT.

The cause of the SGKO5A failure was a loss of lube oil pressure sensing to the pressure switch of the SGKO5A compressor. Contaminates in the system caused the loss of lube oil pressure sensing to the pressure switch. An inadequate flush and restoration of the system in May 2013 allowed contaminates to remain in the system.

SGKO5A was returned to a functional status on October 21, 2013 at 1915 CDT. Wolf Creek Generating Station returned to Mode 1 on October 27, 2013 at 2007 CDT.

On June 17, 2013 at 1111 Central Daylight Time (CDT), the Class 1 E electrical equipment air conditioning unit, SGKO5A, was declared nonfunctional due to an analysis of an oil sample that showed elevated levels of aluminum. As a result, Technical Specification (TS) Limiting Condition for Operation (LCO) 3.0.3 was entered and a plant shutdown was commenced.

On June 17, 2013, enforcement discretion was sought to permit noncompliance with TS 3.8.4, TS 3.8.7, TS 3.8.9, as well as LCO 3.0.3, to permit additional time to complete repairs and restoration of SGKO5A before a plant shutdown would be required. An additional 168 hours was requested to restore SGKO5A to a functional status such that the Completion Time of LCO 3.0.3 would expire at 1111 CDT on June 24, 2013. The Nuclear Regulatory Commission granted approval of the requested enforcement discretion on June 17, 2013. The replacement of the SGKO5A compressor and testing to restore functionality was completed at 2220 CDT on June 21, 2013.

On May 6, 2013 at 1733 Central Daylight Time (CDT), the Class 1 E electrical equipment air conditioning unit, SGKO5A, was declared nonfunctional due to an increasing temperature trend in the 'A' train safety related electrical equipment room. As a result, Technical Specification Limiting Condition for Operation 3.0.3 was entered and a plant shutdown was commenced.

Wolf Creek Generating Station (WCGS) entered Mode 3 on May 7, 2013 at 0009 CDT.

Damage to the liquid line filter drier assembly was caused by over tightening of the wing screw that holds the assembly together. This caused the partial blockage of the thermostatic expansion valves feeding the SGKO5A evaporator coils resulting in the temperature increase in the 'A' train safety related electrical equipment room.

The thermostatic expansion valves and filter drier assembly were replaced and WCGS returned to Mode 1 on 5/13/2013 at 0832 CDT.

On 03/08/2013, Wolf Creek Generating Station was in Refueling Outage 19 with the core defueled and no movement of irradiated fuel assemblies. During replacement of the SGKO5A Class lE electrical equipment air conditioning compressor, it was discovered that the compressor terminal box mounting screws were over torqued to 50 inch pounds. A work history review determined that SGKO5B and the SGKO4B control room air conditioning compressor also had over torqued mounting screws. SGKO4A was unaffected as no maintenance had been performed on the compressor terminal box that specified torque requirements for the mounting screws. As a result, it was determined that SGKO5B had been nonfunctional and SGKO4B had been inoperable during the previous cycle. This resulted in a condition prohibited by Technical Specification and a condition that could have prevented the fulfillment of a safety function.

The mounting screws were replaced with safety related screws and torqued to the proper value.

On January 8, 2013, at 0500 hours Central Standard Time (CST), Required Action B.4.1 of Technical Specification (TS) 3.8.1 was entered when the 'B' diesel generator (DG) was declared inoperable for performing voluntary preplanned maintenance activities. During the planned replacement of the o-ring between the cylinder head and valve housing on the number 7 cylinder, maintenance personnel contacted one of the eight cylinder head studs and identified that the stud was loose. The broken stud was removed by hand.

On January 10, 2013, enforcement discretion was sought to permit noncompliance with TS 3.8.1, i.e., to permit additional time to complete repairs and restoration of the 'B' DG before a plant shutdown was required. An additional 96 hours was requested to restore the 'B' DG to operable status such that the Completion Time of Required Action B.4.1 would expire at 0500 hours CST on January 15, 2013. The NRC granted approval of the requested enforcement discretion on January 10, 2013. The replacement of the broken stud and two adjacent studs and testing to restore operability was completed at 2254 hours CST on January 12, 2013.

Industry operating experience, 0E30255 dated December 16, 2009, identified that a design feature of each main feedwater (MFW) pump can provide a status indication that the MFW pump is in service when the MFW pump may not actually be supplying water to the steam generator. In this condition, if the MFW pump in service tripped, the motor driven auxiliary feedwater (AFW) pumps would not receive an auto-start signal from the trip of both MFW pumps as required by technical specifications. The operating experience provided reference to Watts Bar Nuclear Plant licensee event reports for a similar event. Further research identified on August 7, 2008, the Nuclear Regulatory Commission (NRC) issued Watts Bar Nuclear Plant - NRC Integrated Inspection Report 05000390. The inspection report identified that a non-operating MFW pump in the reset condition impacts operability of the AFW auto-start channel due to the false (i.e., invalid) indication of the MFW pump status.

On January 21, 2010, the operating experience was placed into the corrective action program. On February 4, 2010, a review of the operating experience determined that the design and normal operation of the MFW pumps at Wolf Creek Generating Station (WCGS) could result in a condition that does not conform to the WCGS Technical Specification (TS) Table 3.3.2-1, Function 6.g., Trip of All Main Feedwater Pumps. During plant startups, the non-operating MFW pump in the reset condition results in two inoperable AFW auto-start channels. There is no TS Condition for two MFW pump trip channels inoperable. Limiting Condition for Operation (LCO) 3.0.3 specifies that when an associated Action is not provided, action shall be initiated within 1 hour to place the plant in Mode 3 in 7 hours. Action had not previously been taken as required by the TSs.

On March 6, 2004, Wolf Creek Generating Station (WCGS) was operating at 100 percent steady state power. At 9:47 P.M. Central Standard Time, startup transformer neutral ground relays 251N-2T1 and 251N-4T1 tripped which initiated protective lockout and transformer trip relays for the startup transformer, tripping the transformer and resulting in a loss of power to the Engineered Safeguards Feature (ESF) bus NB02. The loss of power to the transformer that normally powers this bus resulted in the automatic start, and subsequent loading of the "B" Emergency Diesel Generator (EDG.) The cause of the transformer trip was due to a cable fault in the cable connected to the stamp transformer's "X" winding "C" phase (X-C) bushing, caused by water that had collected in the cable through connecting lug inspection holes.

The safety significance of this event is low. This event is bounded by the current licensing basis analysis as reported in WCGS Updated Safety Analysis Report (USAR) section 15.2.6 "Loss of Non Emergency AC Power to the Station Auxiliaries." All safety-related equipment operated as expected. There were no adverse effects to the health and safety of the public.

On January 15, 2004, at 8:30 PM, central standard time, containment spray system (EIIS: BE) isolation valve (EIIS: ISV) EN-V025 was found locked in the fully open position. The containment spray system was declared inoperable in accordance with Technical Specification (TS) 3.6.6. Valve EN-V025 was closed and the containment spray system was declared operable at 8:51 PM on January 15, 2004.

This valve was unlocked and opened on December 30, 2003, during the performance of the containment spray pump inservice pump test for train B, which is controlled by procedure STS EN-100B. This procedure requires that after this test has been completed, valve EN-V025 is to be restored to closed and locked, and subsequently verified to be closed and locked.

This condition existed prior to discovery for a period greater than 72 hours, the allowed Completion Time associated with Required Action A.1 of TS 3.6.6. As such, this situation represents a condition prohibited by Technical Specifications, and is reportable per 10 CFR 50.73(a)(2)(i)(B).

The root cause for valve EN-V025 being in the incorrect position is lack of information validation or verification. The two nuclear station operators did not adequately validate information, and did not adequately verify the information (i.e., valve position).

At 1000 on March 25, 2003, the Wolf Creek Generating Station (WCGS) Shift Manager was notified that both "A" and "B" wide range trains of Reactor Vessel Water Level Indicating System (RVLIS) were not functioning as designed. B Both "A" and "B" wide range trains of RVLIS in the Main Control Room were off-scale high (>120%), consistent with the plant computer point indication of 122.8%. Based upon discussion with vendor representatives and industry peers, WCGS concluded that this reading was approximately 12% higher than should be expected. The Shift Manager declared both "A" and "B" trains of RVLIS inoperable and entered Condition C of Technical Specification 3.3.3, Post Accident Monitoring (PAM) Instrumentation.

Although WCGS entered the applicable Technical Specification Required Action immediately following recognition of this condition, further evaluation determined that this condition existed for a time longer than permitted by Technical Specifications. As such, this issue represents a condition prohibited by Technical Specifications, and is reportable per 10 CFR 50.73 (a)(2)(i)(B).

Because various other means are available to plant operators to determine reactor vessel level, there is minimal safety significance associated with this issue.

At 0815 on June 7, 2002, the Wolf Creek Generating Station (WCGS) Shift Manager was notified of a postulated fire event that could cause a cable-to-cable hot short. If cable-to-cable hot shorts are assumed to occur, this event has the potential to cause water in the refueling water storage tank (RWST) to drain to the containment recirculation sump. It was discovered that the control cables for two redundant motor operated valves are routed in the same electrical raceway. The two valves are in the same electrical separation group, but are redundant in their function of conserving water inventory in the RWST. Further investigation determined that the control cables for motor operated valves in the opposite electrical separation group have the same configuration. The cause of this condition is that cable-to-cable interactions were not considered in the initial design of the plant.

At 0945 on July 19, 2002, the Shift Manager was notified of conditions where a postulated fire event could lead to the loss of motor control centers that power post-fire safe shutdown equipment in both trains due to inadequate horizontal separation in conjunction with improper breaker coordination.

At 1030 on August 20, 2002, conditions were discovered where a postulated fire could cause the loss of both centrifugal charging pump's (CCP) capability to successfully inject borated water into the reactor.

The safety significance of these events is low.

On April 24, 2002, while in Mode 4, Wolf Creek Nuclear Operating Corporation (WCNOC) personnel completed surveillance procedure STS BB-004, "RCS Water Inventory Balance." A calculational (rounding) error resulted in the conclusion that the Reactor Coolant System (RCS) (EIIS system code AB) unidentified leakage was within the Technical Specification (TS) limit of 1.0 gpm. The unidentified leakage was actually 1.091 gpm, or .091 gpm above the TS limit.

On April 25, 2002, Wolf Creek Generating Station (WCGS) entered Mode 3 from Mode 4 contrary to TS Limiting Condition of Operation (LCO) 3.0.4. This specifies that the plant cannot change modes when an LCO is not met. The calculational error made in STS BB-004 was not recognized until after the mode change. When the error was recognized, TS 3.4.13, "RCS Operational LEAKAGE," Condition A, was entered. The source of the leakage was identified and corrected. On April 26, 2002, the leak rate was 0.31 gpm, and Condition B of TS 3.4.13 was exited.

This event is reportable per 10 CFR 50.73(a)(2)(i)(B) as a violation of the plant's Technical Specifications.

The root cause of this event was inadequate procedural guidance for performing RCS leakage calculations.

No impact on personal, nuclear, or radiological safety resulted from this event.

On November 16, 2001, Wolf Creek Nuclear Operating Corporation (WCNOC) personnel identified an error in an internal flood calculation. The calculation under estimated the input flow rate from a pipe break in two Auxiliary Building rooms and over estimated the drain flow rate from these rooms. As a result of correcting these values in the calculation, the calculation results now predict a flood water level that would submerge safety-related equipment required to switch the suction of the Auxiliary Feedwater (AFW) pumps from the Condensate Storage Tank (CST) to the Essential Service Water (ESW) system. Evaluations of event scenarios indicate that flooding of safety-related AFW equipment could occur and/or the decay heat removal function of AFW would not be accomplished.

The isolation valve for this line has been throttled, thus reducing the input flow rate and the resultant flood water level to ensure components required to fulfill the AFW system safety function are not submerged.

The cause for including these incorrect assumptions in this calculation is indeterminate due to the historical nature of this condition (the calculation was performed by an Architect/Engineer's staff in 1986). Based on a sampling review of other calculations, this issue is believed to be an isolated case.

This condition is considered to be of minimal safety significance.