05000305/LER-2012-008
| Docket | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3052012008R00 - NRC Website | |
Event Description
At 1400, CDT, on September 13, 2012, while in Mode 1, Technical Specification (TS) Limiting Condition for Operation (LCO) 3.4.14, RCS Pressure Isolation Valve (PIV) [ISV] Leakage, was discovered not met for the Residual Heat Removal (RHR) [BP] System interlock function. This was due to the setpoint for the RHR System Interlock [IEL] set such that the RHR inlet valves could be opened when Reactor Coolant System (RCS) [AB] pressure is greater than 450 psig.
The Kewaunee Power Station (KPS) RHR System is designed to remove residual and sensible heat from the core and reduce the temperature of the RCS during the second phase of plant cooldown, when the pressure and temperature of the RCS are the RHR System is used to transfer refueling water between the Refueling Water Storage Tank (RWST) [TK] and the refueling cavity at the beginning and end of refueling operations. In addition, portions of the system are utilized as parts of the Emergency Core Cooling System [BQ] and the Containment Spray System [BE].
To prevent overpressurizing the RHR System from the RCS, redundant, remotely operated valves in the RHR System inlet lines are provided to isolate the RHR system from the RCS. Two valves in series (RHR 1A/2A, and RHR-1B/2B) are provided, with each valve interlocked (RHR System Interlock) to prevent opening unless the RCS pressure is below the RHR System design pressure.
KPS TS 3.4.14, "RCS Pressure Isolation Valve (PIV) Leakage," in part requires that the RHR System interlock function shall be OPERABLE. TS 3.4.14 contains a surveillance requirement (SR), SR 3.4.14.2, which requires verification that the RHR System interlock prevents the valves (i.e., RHR-1A, -2A, -1B, and 2B) from being opened with a simulated or actual RCS pressure signal 450 psig. The KPS TS Bases for this SR state, "Verifying that the RHR interlock is OPERABLE ensures that RCS pressure will not pressurize the RHR System beyond its design pressure of 600 psig at the pump discharge. The interlock setpoint that prevents the valves from being opened is set so the actual RCS pressure must be 450 psig to open the valves." Ensuring the RHR System interlock function that prevents the valves from being opened is OPERABLE, ensures that RCS pressure will not pressurize the RHR System beyond its design pressure at the pump discharge.
On September 13, KPS staff identified that KPS TS SR 3.4.14.2 was not being met because the calibration procedure that calibrated the interlock bistable contained an improper setpoint of 450 psig (+/- 15 psi) decreasing pressure; and a reset of 480 psig (+/- 15 psi) increasing pressure. Because the proceduralized bistable setting did not ensure the valves could not be opened when RCS pressure is greater than 450 psig, the RHR System interlock function was declared INOPERABLE as not meeting the requirements of SR 3.4.14.2 and therefore, LCO 3.4.14, RCS Pressure Isolation Valve (PIV) Leakage, was not met. This resulted in an entry into LCO 3.4.14, Condition C, RHR System interlock function inoperable.
TS 3.4.14, Required Action C.1 requires isolating each of the affected lines by use of one closed manual or deactivated automatic valve within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Operations personnel completed this Required Action by verifying each of the affected lines is isolated by use of one closed manual or deactivated automatic valve.
Condition C contains no other Required Actions and with Required Action C.1 completed, TS 3.4.14 allows continued plant operation. The normal at-power lineup of the RHR System has these isolation valves closed and deactivated.
SR 3.4.14.2 existed in a similar form from initial plant licensing (1973) until KPS TS were converted to Improved Standard TS (ITS). The conversion was requested under License Amendment Request (LAR) 249, which was approved by the NRC as License Amendment 207 dated February 2, 2011 and implemented at KPS on February 12, 2011. Before the ITS conversion, the SR stated, "Residual Heat Removal System valve interlocks shall be tested once per operating cycle." The SR previously had no setpoint. License Amendment 207 added a setting to the SR and states, "Verify RHR System interlock prevents the valves from being opened with a simulated or actual RCS pressure signal ?. 450 psig." In addition, License Amendment 207 added a License Condition, (12)(c), that states, "For SRs that existed prior to Amendment No. 207 that have modified acceptance criteria, the first performance subject to the modified acceptance criteria is due at the end of the surveillance interval that began on the date the surveillance was last performed prior to the implementation of that amendment." Therefore, the period between the first performance of the surveillance procedure verifying compliance with SR 3.4.14.2 and the time of discovery of the issue, September 13, was reviewed to determine if KPS TS had been violated.
During the 2012 Refueling Outage, a period existed when LCO 3.4.14 was applicable, SR 3.4.14.2 was not met, the Required Action and associated Completion Time of TS 3.4.14 Condition C was not met, and the Actions required by LCO 3.0.3 were not complied with. Therefore, this condition was prohibited by KPS TS and is reportable under 10CFR50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications except when: (1) The Technical Specification is administrative in nature; (2) The event consisted solely of a case of a late surveillance test where the oversight was corrected, the test was performed, and the equipment was found to be capable of performing its specified safety functions; or (3) The Technical Specification was revised prior to discovery of the event such that the operation or condition was no longer prohibited at the time of discovery of the event.
Event and Safety Consequence Analysis The safety consequences of this event is minimal. At the time of discovery of this condition, the Required Actions associated with the applicable condition were met. At least one of each RHR inlet lines isolation valves were closed and deactivated. During the brief period when TS were not complied with, the unit was in either MODE 4 or MODE 3. During these conditions, RHR is either in service for decay heat removal or to meet LTOP requirements. Once RCS temperature is greater than 356°F the RHR inlet isolation valves are closed and deactivated. Operating Procedures restrict plant operation such that the RHR pumps are not allowed to operate if RCS pressure is greater than 425 psig. The RHR system is protected from overpressurization by two safety valves, one set to relieve at 480 psig the other at 500 psig. Additionally, plant operation is controlled within the limitation of RCS pressure/temperature limitation curves that restrict RHR suction pressure to 425 psig. The interlock setpoint to which the bistables were set, although outside the current TS value, was the same value that had been properly used to provide this protective function under the previously approved TSs.
Cause
The cause of this event was determined to be that ITS Implementation did not establish a link between surveillance procedures that calibrate the RHR System interlock bistable and SR 3.4.14.2.
The RHR System interlock uses two RCS wide range pressure instrument loops [PI] to provide the interlock function, P0419 and P0420. Although LCO 3.4.14 requires the RHR System interlock to be OPERABLE, it does not contain a SR for calibration of these instrument loops. The requirement to calibrate these instrument loops is located in TS LCO 3.3.3, Post-Accident Monitoring (PAM) Instrumentation. TS LCO 3.3.3 requires the PAM instrumentation for each Function in Table 3.3.3-1 to be OPERABLE and SR 3.3.3.3 requires performance of a channel calibration for Functions other than Function 20 every 18 months, this includes P0419 and P0420. The implementation database for the conversion project linked the surveillance requirement for the PAM instruments to the implementing procedures calibrating the RCS Pressure (Wide Range) Instruments but did not link SR 3.4.14.2 to these procedures. Because these were not linked to SR 3.4.14.2, the normal review performed to ensure the actual plant setting bounds the surveillance was not performed.
Corrective Actions
1. The RHR System Interlock was declared inoperable, LCO 3.4.14 Condition C was entered and Required Action C.1, "Isolate each of the affected lines by use of at least one closed manual or deactivated automatic valve," was completed within the allowed Completion Time.
2. A corrective action was initiated to establish new calibration parameters for the RHR System interlock and initiate a revision to the associated surveillance procedures.
3. A corrective action was initiated to provide a link in the associated loop calibration procedures to SR 3.4.14.2 to ensure any future revisions maintain compliance with the SR.
Similar Events A review of Licensee Event Reports covering the last three years did not identify any similar events.