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While operating in MODE 1 at 100 percent rated thermal power and placing Excess Letdown in service for Reactor Coolant System (RCS) leak detection, RCS operational leakage exceeded 1 gpm (gallon per minute) unidentified leakage as identified by performing RCS Water Inventory Balance using the Nuclear Plant Information System Computer. This required the entry into Technical Specification (TS) Limiting Condition of Operation (LCO) 3.4.13 Condition B at 0808 (CDT) on 9/2/16. The associated action is to place the unit into Mode 3 in 6 hours. Trending of containment sump level indicates the leakage is inside containment with the exact location within containment unknown. Containment inspection is being performed to try and identify the source of Reactor Coolant System leakage. NRC Resident Inspector has been notified. Re-alignment of the Letdown System back to its normal arrangement has subsequently reduced RCS leak rate to 0.521 gpm at 0652 CDT on 9/2/16. Unusual or Not Understood - Leak Location is not known at this time. Maximum leak rate recorded was 1.358 gpm. The leak was first discovered at 08/31/16 at 1519 CDT. Safety Related Equipment not operational - Reactor Vessel Level Indicating System (TS 3.3.3).

• * * RETRACTION AT 1101 EDT ON 10/21/2016 FROM LARRY HAUTH TO JEFF HERRERA * * *

Wolf Creek Nuclear Operating Corporation is retracting the 10 CFR 50.72(b)(2)(i) notification based on subsequent review of the event. The calculation of unidentified leak rate which triggered entry into the Mode 3 Required Action Statement was performed immediately after placing RCS Excess Letdown in service. An evaluation of the leak rate calculation determined that the leak rate was invalid due to performance of the RCS water inventory balance during non-steady state operating conditions. This was contrary to the requirements of TS Surveillance Requirement 3.4.13.1, as this test was performed while charging and letdown flows were being stabilized following the alignment of excess letdown. A walk down of the Excess Letdown system while in-service determined no leakage. Subsequent RCS water inventory balances performed with Excess Letdown in service under steady state operating conditions while in Mode 3 at normal operating pressure and temperature determined the maximum calculated unidentified leak rate was 0.675 gpm. After the plant entered Mode 3 a non-RCS pressure boundary leak was identified during equipment walk downs on a seal weld from the reactor vessel head core exit thermocouple nozzle assembly 77. The leakage did not impact the ability to shut down the unit. No TS limits were exceeded during this event. Therefore, the plant shutdown to investigate and correct leakage past the seal weld of a threaded connection does not meet the reporting requirements of 10 CFR 50.72. The NRC Resident Inspector has been notified. Notified the R4DO (Kramer).

Wolf Creek has commenced a plant shutdown in accordance with Technical Specifications. The A Train Class 1E Electrical Equipment Air Conditioning unit was declared non-functional due to a possible failed compressor cylinder, as indicated by increased vibration. This failure could prevent the unit from performing its required function over its required mission time, as required by Technical Specifications 3.8.4, 3.8.7, and 3.8.9. The following safety related electrical equipment was declared inoperable: 4.16KV Bus NB01; 480 Volt AC buses NG01 and NG03; 120 Volt Instrument AC inverters and buses NN11, NN13, NN01 and NN03; 125 VDC chargers and buses NK11, NK13, NN01 and NN03. Technical Specification 3.0.3 was entered at 1645 CDT on 9/11/2013 from Technical Specification 3.8.7 due to two out of four 120 VAC inverters (NN11 and NN13) being inoperable. Plant shutdown to Mode 5 commenced at 1731 CDT. The unit is currently at approximately 50% power. All electrical systems listed above remain available but are declared inoperable due to inadequate room cooling capability. No major equipment is out of service. The NRC Resident Inspector has been notified. No switchgear room temperature limits were challenged. See EN #49008 (May 6, 2013) and EN #49126 (June 17, 2013) for similar events.

• * * UPDATE ON 9/12/13 AT 0215 EDT FROM MARCY BLOW TO HUFFMAN * * *

At 00:36 CDT 9/12/13, Wolf Creek had an Auxiliary Feedwater Actuation during a plant shutdown in accordance with Technical Specifications. The plant was in Mode 3, all control rods inserted, with reactor trip breakers closed when low steam generator levels prompted a manual reactor trip. A Valid Auxiliary Feed Actuation signal was received due to low steam generator levels. All Auxiliary Feedwater pumps started and operated as expected. The licensee has informed the NRC Resident Inspector. R4DO (Hay) notified.

At 2240 09/20/2005 an engineering evaluation concluded that the Residual Heat Removal Containment Sump Isolation Valves were inoperable based on their inability to open against a higher differential pressure than had been previously evaluated. Historically Wolf Creek has operated with the Component Cooling Water isolated to the Residual Heat Removal Heat Exchangers. If the pumps started during accident conditions there is a potential that the pump heat generated could cause system pressure to increase to the suction relief valve setting of 450 psig. Testing of the valves has shown that they are capable of opening with 207 psid across the valve. Technical Specification 3.0.3 was entered at 2240 9/20/2005 due to the inoperability of both Residual Heat Removal trains. Power reduction was commenced at 2340. Component Cooling Water was aligned to the Residual Heat Removal Heat Exchangers at 0004 9/21/2005 restoring operability of the Residual Heat Removal trains. At 0017 9/21/2005 actions were commenced to restore power to 100%. This event is reportable under 10 CFR50.72(b)(2)(i) Technical Specification required shut down (4 hour) and 10 CFR50.72(b)(3)(v)(B) Event or Condition that could have prevented fulfillment of a Safety Function (8 hour). The NRC Resident has been contacted.

• • • UPDATE AT 15:39 EST ON 11/08/05 FROM DEES TO KNOKE ***

Evaluation of the Residual Heat Removal Containment Sump Isolation Valves concluded that the valves were operable and the Residual Heat Removal trains were capable of fulfilling their safety function. Therefore, this event is not reportable under 10 CFR 50.72(b)(3)(v)(B). The licensee notified the NRC Resident Inspector. Notified the R4DO (Whitten).