ML20266G343

Issuance of Amendment No. 235 Regarding Operation of the Emergency Auxiliary Reserve Transformer Load Tap Changer

ML20266G343
Person / Time
Site:	Clinton
Issue date:	10/14/2020
From:	Joel Wiebe Plant Licensing Branch III
To:	Bryan Hanson Exelon Generation Co
Wiebe J
References
EPID L-2020-LLA-0006
Download: ML20266G343 (13)

Text

October 14, 2020 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)

Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

CLINTON POWER STATION, UNIT NO. 1 - ISSUANCE OF AMENDMENT NO. 235 REGARDING OPERATION OF THE EMERGENCY RESERVE AUXILIARY TRANSFORMER LOAD TAP CHANGER (EPID L-2020-LLA-0006)

Dear Mr. Hanson:

The U.S. Nuclear Regulatory Commission (the Commission) has issued the enclosed Amendment No. 235 to Facility Operating License No. NPF-62 for the Clinton Power Station, Unit No. 1. The amendment is in response to your application dated January 14, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20014E719), as supplemented by letter dated June 29, 2020 (Accession No. ML20181A267).

The amendment revises the license to allow operation of the emergency reserve auxiliary transformer load tap changer in the automatic mode.

A copy of the Safety Evaluation is also enclosed. The Notice of Issuance will be included in the Commissions next biweekly Federal Register notice.

Sincerely,

/RA/

Joel S. Wiebe, Senior Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-461

Enclosures:

1. Amendment No. 235 to NPF-62

2. Safety Evaluation cc: Listserv

ML20266G343 *via e-mail **via memo OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DEX/EEOB/BC OGC NAME JWiebe SRohrer BTitus* KGamin NLO DATE 9/25/20 9/ 24 /20 7/21/2020 10/13/20 OFFICE NRR/DORL/LPL3/BC NRR/DORL/LPL3/PM NAME NSalgado JWiebe DATE 10/14/20 10/14/20 EXELON GENERATION COMPANY, LLC DOCKET NO. 50-461 CLINTON POWER STATION, UNIT NO. 1 AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 235 License No. NPF-62

1. The U.S. Nuclear Regulatory Commission (the Commission) has found that:

A. The application for amendment by Exelon Generation Company, LLC (the licensee), dated January 14, 2020, as supplemented by letter dated June 29, 2020, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B. The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C. There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commissions regulations; D. The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E. The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

2. Accordingly, by Amendment No. 235, the license is amended to authorize revision to the Updated Safety Analysis Report (USAR), as set forth in the application dated January 14, 2020. The licensee shall update the USAR to incorporate the automatic operation of the Emergency Reserve Auxiliary Transformer load tap changer as described in the licensees application dated January 14, 2020, and the NRC staffs safety evaluation attached to this amendment, and shall submit the revised description authorized by this amendment with the next update of the USAR.

4. This license amendment is effective as of its date of issuance and shall be implemented within 60 days from the date of issuance. The USAR changes shall be implemented in the next periodic update to the USAR in accordance with 10 CFR 50.71(e).

FOR THE NUCLEAR REGULATORY COMMISSION Digitally signed by Nancy Nancy L. L. Salgado Date: 2020.10.14 16:14:14 Salgado -04'00' Nancy L Salgado, Chief Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Date of Issuance: October 14, 2020

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 235 TO FACILITY OPERATING LICENSE NO. NPF-62 EXELON GENERATION COMPANY, LLC CLINTON POWER STATION, UNIT NO. 1 DOCKET NO. 50-461

1.0 INTRODUCTION

By application dated January 14, 2020 (Agencywide -Documents Access and Management System (ADAMS) Accession No. ML20014E719), as supplemented by letter dated June 29, 2020 (ADAMS Accession No. ML20181A267), Exelon Generation Company, LLC (the licensee) requested a license amendment (LAR) to revise the Clinton Power Station, Unit 1, (CPS)

Updated Safety Analysis Report (USAR) to allow the use of the automatic function of the load tap changer (LTC) for the emergency reserve auxiliary transformer (ERAT). The ERAT provides offsite power to CPS.

The supplement dated June 29, 2020, provided additional information that clarified the application, did not expand the scope of the application as originally noticed, and did not change the U.S. Nuclear Regulatory Commission (NRC or the Commission) staffs original proposed no significant hazards consideration determination as published in the Federal Register on March 24, 2020 (85 FR 16683).

2.0 REGULATORY EVALUATION

2.1 Description of the CPS Power Distribution System A 345 kiloVolt (kV) switchyard and a 138 kV transmission line from the transmission network supplies offsite power to CPS. The 345 kV switchyard provides alternating current (AC) power to the plant via three reserve auxiliary transformers (RATs) A, B, C. According to the USAR, Section 8.3.1 (ADAMS Accession No. ML20105A259), RAT A provides power to the 6900 Volt (V) switchgear buses and is sized to provide the startup load of the unit from these buses. RAT B provides power to the 4.16 kV Class 1E engineered safety feature (ESF) safety-related buses 1A1, 1B1, and 1C1 and a 4.16 kV non-Class 1E Bus 1A. RAT B is sized to provide the startup and running load for these buses as well as the total coincidental loss-of-coolant accident (LOCA) load for the unit. RAT C provides power to the 4.16 kV non-Class 1E Bus 1B and is sized to carry the startup and running load of this bus.

Enclosure 2

In Attachment 1 to its letter dated January 14, 2020, the licensee states that the second source of offsite power to the 4.16 kV ESF buses is provided by the ERAT powered by the 138 kV transmission line. In addition, each ESF bus can be fed by a dedicated onsite emergency diesel generator (EDG). The ESF systems of any two of the three load divisions (powered by the three 4.16 kV ESF buses) can provide the minimum safety functions necessary to shut down the unit and maintain it in a safe shutdown condition.

The ERAT has onload tap changing capability, which means the tap setting can be varied while the transformer is in service. The number of effective primary windings can be varied over a range of 1.06 per unit (pu) to 0.81 pu by an LTC mounted on the ERAT to provide a consistent 4.16 kV output. Currently, the LTC is only operated manually. In the manual mode, an operator can make tap changes locally at the ERAT with the transformer in service.

According to USAR, Section 8.3.1, the RAT B winding taps can be varied over a range of 1.04 pu to 0.77 pu with an LTC mounted on RAT B to provide a consistent secondary voltage output.

The LTC is operated manually. In the manual mode, an operator can make tap changes locally at RAT B with the transformer in service.

The loss of power (LOP) instrumentation monitors the 4.16 kV ESF bus voltages. Offsite power is the preferred source of power for the 4.16 kV ESF buses. If the voltage monitors (relays) determine that bus voltages are insufficient, the buses are disconnected from the offsite power sources, and connected to the onsite diesel generator power sources.

According to the LAR, Attachment 1, the ERAT and RAT B are provided with a permanently installed static Volt-Ampere-Reactive compensator (SVC) which can be connected to the secondary side of these transformers. The ERAT SVC and RAT B SVC provide steady state, dynamic, and transient voltage support to ensure that the Class 1E loads will operate as required during anticipated or postulated events. The SVC voltage support to the offsite power sources is required depending on the offsite grid conditions.

2.2 Reason for the Proposed License Amendment In the LAR, Attachment 1, the licensee states that the SVCs at CPS are unique to the nuclear industry and obsolete due to their age. Specifically, the SVC's control system is obsolete and replacement parts are not readily available. As a result, alternative methods of providing voltage support are being pursued by the licensee to replace the SVCs.

In the LAR, Attachment 1, the licensee also states that its current plan is to eliminate use of the SVCs for both the RAT and ERAT. As an alternative, a new control system for mechanically switched capacitor banks will be installed, in conjunction with the automatic LTC, and over-voltage protection features, to regulate the voltage at the safety-related buses during transient conditions. However, based on current estimates, parts necessary to install this alternative solution will not be available until fourth quarter 2020.

In order to minimize the impact of an unforeseen failure of either the ERAT SVC or the RAT SVC (i.e., prior to installation of the new mechanically switched capacitor banks), the licensee states that an interim solution has been developed that could be used to regulate the voltage at the safety-related buses. This interim solution involves operation of the ERAT LTC in the automatic mode. The interim solution will be implemented in the event of an unforeseen failure of either the ERAT SVC or RAT SVC; and would only remain in place until the alternative

solution involving switched capacitor banks is installed. The interim solution is explained as follows:

In the event of an unforeseen ERAT SVC failure that cannot be promptly remedied with the existing spare parts, the ERAT SVC will be decommissioned and the ERAT LTC will be placed into the automatic mode of operation. In this situation, one of the qualified circuits [fed by ERAT] required by Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.8.1, "AC Sources - Operating," would be inoperable. Condition A of LCO 3.8.1 would be entered for one offsite circuit inoperable, with a Required Action to restore the offsite circuit to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The ERAT circuit would remain inoperable until ERAT LTC is placed in automatic mode.

In the event of an unforeseen RAT SVC failure that cannot be promptly remedied with existing spare parts, the ERAT SVC will be decommissioned and the ERAT LTC will be placed into the automatic mode of operation. Parts from the decommissioned ERAT SVC would then be used to restore the RAT SVC to operable status. In this situation, initially the Condition A of LCO 3.8.1 would be entered for one offsite circuit inoperable

[fed by RAT]. Efforts to decommission the ERAT SVC and commission the ERAT automatic LTC would commence, requiring entry into Condition C of LCO 3.8.1 for two offsite circuits inoperable [fed by RAT and ERAT], with a Required Action to restore one of the offsite circuits to operable status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The ERAT would be restored to operable status following placing the ERAT LTC in automation operation; and then the RAT would be restored to operable status by repairing the RAT SVC with parts from the decommissioned ERAT SVC. Condition C of LCO 3.8.1 would be exited when either the ERAT or RAT is restored to operable status. However, Condition A would continue to apply until the second offsite circuit is also restored to operable status.

In the LAR, Attachment 1, the licensee states that operating the ERAT LTC in the automatic mode, has the potential to cause a failure involving an over-voltage condition on the Class 1E 4.16 kV buses that is not bounded by the over-voltage condition previously identified in USAR Section 8.3.1.1.2, "Unit Class 1E A-C Power System." The USAR state in Section 8.3.1.1.2 that the maximum steady state Class 1E bus voltage is 4300 V, and operation above 4300 V but less than 4454 V is allowed for 30 minutes. A failure of the LTC to control voltage could result in the voltage exceeding the analyzed high voltage condition of 4454 V. Therefore, operating the ERAT LTC in the automatic mode creates the possibility of a malfunction of a Structure, System or Component (SSC) important to safety with a different result than any previously evaluated in the USAR. The licensee determined that operation of the LTC in automatic mode, with the SVC secured, requires NRC approval in accordance with 10 CFR 50.59, since automatic LTC operation creates a possibility for a malfunction of an SSC important to safety with a different result than any previously evaluated in the USAR.

2.3 Proposed USAR Change In the LAR, Attachment 1, the licensee states that the ERAT LTC will be operated only in the manual mode (which does not require prior NRC approval) until the requested change is approved. Once the proposed change is approved, operation of the LTC in automatic mode will be allowed, and the USAR description of the offsite power sources will be revised by the licensee to describe the automatic LTC operation.

In the LAR, Attachment 2, the licensee submitted a proposed markup of USAR, page 8.3-6.

The licensee proposed to revise the description of LTC operation of the ERAT as follows (the proposed changes are shown below in BOLD):

For the ERAT, the number of effective primary windings can be varied over a range of 1.06 pu to 0.81 pu by a load tap changer (LTC) mounted on the ERAT to provide a consistent 4160-V output. The ERAT LTC can be operated in a manual or automatic mode.

In the manual mode, an operator can make tap changes locally at the ERAT, and the changes may be made with the ERAT in service.

In the automatic mode, a controller in the ERAT LTC raises or lowers the tap setting in response to grid voltage. A backup controller provides oversight of the primary controller, preventing tap movement above or below prescribed setpoints.

2.4 Regulatory Requirements The NRC staff applied the following regulations for review of the LAR:

Title 10 of Code of Federal Regulations (10 CFR) Part 50, Appendix A, "General Design Criteria (GDC) for Nuclear Power Plants," Criterion 17, "Electric power systems," requires, in part, that offsite power be available to the facility to ensure that specified fuel design limits and the design conditions of the reactor coolant pressure boundary are not exceeded.

According to CPS, USAR, Section 8.2.2.1, offsite AC power is supplied to the CPS switchyard from the Ameren Illinois grid system and meets the requirements of GDC 17 of Appendix A to 10 CFR 50. To satisfy GDC 17, the voltages provided by offsite power to the safety-related equipment must be adequate (within certain design limits) for satisfactory functioning of equipment.

3.0 TECHNICAL EVALUATION

3.1 Automatic Operation of the ERAT LTC In the LAR, Attachment 1, page 6, the licensee explained the operation of ERAT LTC. The licensee states that the tap changer mechanism for the LTC is located in a separate enclosure attached to the transformer. A drive motor rotates the tap changer to increase or decrease the number of transformer windings in service. The LTC has two modes of operation: automatic and manual. In the automatic mode, the LTC is controlled by a primary voltage controller (VRR) and a backup voltage controller (VBR). The function of the VRR and VBR is to control the ERAT's secondary voltage by adjusting the tap position on the primary winding. The VRR and VBR get their voltage feedback signal from a potential transformer (PT) on the ERAT secondary winding. The VRR and VBR require user input setpoints for their voltage control point (i.e.,

Bandcenter), and tolerance around that voltage control point (i.e., Bandwidth). The feedback signal from the PT is compared to the Bandcenter and Bandwidth, and based on the comparison, the VRR and VBR control circuitry sends appropriate commands to the LTC to change taps as necessary to maintain the sensed voltage within the voltage Bandwidth.

In its supplement dated June 29, 2020, the licensee provided additional details on the Bandcenter and Bandwidth of the VRR as follows:

Bandcenter setpoint = 121.9 V [Adjustable from 100 V to 135 V in 0.1 V increments]

Bandwidth = 3.0 V [Adjustable from 1 V to 10 V in 0.1 V increments]

Based on the above information, the NRC staff determines that the VRR is set to control the voltage within +/- 1.25 percent with the Bandcenter set at approximately 101.6 percent (based on nominal 120 V).

In the LAR, Attachment 1, page 7, the licensee states that the VRR is designed to regulate the 4.16 kV bus voltages under both normal and accident conditions. In the event the VRR fails, and the voltage rises or falls outside its operating voltage band, the VBR will take over automatic operation of the LTC. The VBR utilizes a redundant relaying scheme to ensure the LTC does not raise or lower the voltage beyond the limits set within the VBR. With the use of this redundant relaying scheme, a single relay failure cannot cause the LTC to operate outside the operating range of the VBR. In the LAR, Attachment 1, page 8, the licensee states that the VBR will also lower the voltage if the regulated voltage remains above the upper voltage limit past its time delay setpoint.

In its supplement dated June 29, 2020, the licensee provided additional details on the Bandcenter and Bandwidth of the VBR controller as follows:

Bandcenter setpoint = 121.5 V [Adjustable from 100 V to 140 V]

Bandwidth = 8.0 V [Adjustable from 6 V to 24 V for 120 V]

Time Delay = 5.0 second [Adjustable from 1 second to 30 second]

Based on the above information, the NRC staff determines that the VBR controller is set to control the voltage within +/- 3.33 percent with the Bandcenter set at approximately 101.2 percent (based on nominal 120 V). The combination of the VRR and VBR would control the ERAT LTC such that voltage at the 4160 V ESF bus would remain close to nominal voltage.

In the LAR, Attachment 1, page 7, the licensee further states that no LTC control or tap position indication is available in the control room (CR). The CR operators, however, do have both high and low voltage alarms for the buses that are fed by the ERAT. Actual bus voltages can be obtained from voltmeters on the CR panels or through computer points via the plant's process computer. In addition, the VRR, and VBR initiate CR and local panel alarms should their microcontrollers or power supplies fail. The LTC has sufficient range to respond to the expected 138 kV system range of 0.94 pu to 1.05 pu of nominal. By providing automatic adjustment of the voltage to the CPS auxiliary power system, the ERAT LTC will be able to compensate for a wide range of 138 kV system operating voltages.

In the LAR, Attachment 1, page 7, the licensee states that the regulating relays controlling the LTC are set with an initial delay of one second. The voltage must be out of band for one second before the controls initiate a tap change. Once given a signal to change taps, either manually or automatically, the tap changer will complete a tap change in three seconds. If multiple taps are needed, the initial one second delay will occur only once (i.e., one second + three seconds for the first tap + three seconds for each subsequent tap, if required).

In the LAR, Attachment 1, pages 7 and 8, the licensee further states that, in the event of a voltage dip, a race condition will be created between the LTC and degraded voltage relay. If a LOCA were to occur at full power operation and the switchyard voltage were to stay within the voltage limits analyzed for the ERAT LTC operation, then for the worst-case, the ERAT

LTC will correct the voltage in a maximum duration of 13 seconds. The second-level degraded voltage relays are bounded by the Division 3 nominal time delay which is set at 13.2 seconds (i.e., the degraded voltage time delays for Divisions 1 and 2 are longer than 13.2 seconds). If the voltage does not recover before 13.2 seconds have elapsed, the safety buses will be disconnected from offsite power and will align to the EDGs. The allowable value for the Division 3 degraded voltage time delay specified in TS 3.3.8.1 is >

13.2 seconds and < 16.8 seconds. Therefore, because the LTC will correct the voltage within 13 seconds, it will be successful in preventing a trip of the degraded voltage relays in the event of a voltage dip, precluding unnecessary disconnection of the safety buses from offsite power.

In the LAR, Attachment 1, page 4, the licensee states that an engineering evaluation has been performed to determine the acceptability of using the ERAT LTC in automatic mode without the ERAT SVC.

In its supplement dated June 29, 2020, the licensee provided minimum voltage and maximum voltage values at the 4.16 kV ESF buses, with the ERAT LTC in automatic mode, without SVC, and 138 kV switchyard voltage expected within the range of 0.94 pu and 1.06 pu.

The NRC staff finds that the minimum voltage calculated as 4150 V is above the TS 3.3.8.1 Degraded Voltage Relay reset value of 4109.3 V and is therefore acceptable. The maximum voltage is calculated as 4217.4 V which is less than the maximum 4300 V considered in the USAR, Section 8.3.1.1.2, and is therefore acceptable.

The NRC staff reviewed the proposed operation of the ERAT LTC as explained in the LAR and supplement dated June 29, 2020. The staff finds that the functioning of the ERAT LTC in automatic mode would maintain voltages at the ESF 4160 V safety buses within the desired range (4109.3 V as specified in TS 3.3.8.1 and 4300 V as specified in the USAR), thus continuing to assure adequate voltages to safety-related loads and meeting the intent of GDC 17.

3.2 Failure Mode Analysis of the ERAT LTC in Automatic Mode In the LAR, Attachment 1, page 8, the licensee states that the most severe potential malfunction would be a failure of the VRR that causes transformer output voltage to rapidly increase or decrease. The backup controller (i.e., VBR) prevents a defective LTC tap changer VRR from running the voltage outside established upper and lower limits by blocking the raise and lower logic of the tap changer. The VBR will also lower the voltage if the regulated voltage remains above the upper voltage limit past its time delay setpoint. The design also allows the operators to override both LTC controllers, taking local manual control if necessary.

In the LAR, Attachment 1, page 9, the licensee states that the failure probability of the ERAT LTC to spuriously operate or to have a failure of both controllers due to a failure common to both controllers was calculated to be 9.77E-07. Therefore, although automatic LTC operation can create a possibility for a malfunction of an SSC important to safety with a different result than any previously evaluated in the USAR, the likelihood of such a malfunction involving simultaneous failures of both controllers, or a failure of the LTC motor, is very low.

In its supplement dated June 29, 2020, the licensee provided a brief summary of the calculation showing the derivation of cumulative failure probability of the ERAT LTC as

9.77E-07. The licensee considered the probability of the LTC motor to spuriously operate similar to a motor operated valve (MOV). The data for an MOV to spuriously operate is provided in the NRC website (https://nrcoe.inl.gov/resultsdb/AvgPerf/). The licensee states that VRR and VBR controller failure rates are based on vendor data of LTC.

Based on the data provided on the NRC website, the NRC staff finds that the data considered for calculation of probability of the ERAT LTC to spuriously operate or to have a failure of both controllers due to a common mode failure is reasonable. The NRC staff finds that the overall calculated cumulative failure probability calculated as 9.77E-07 is very low and is therefore acceptable.

In the LAR, Attachment 1, the licensee explained the impact of various failure modes, which are briefly summarized as follows:

Failure Mode that Increases Voltage In this failure mode, the LTC drive mechanism fails to stop changing taps after initiation of a raise voltage signal by the microcontroller. This failure mode can be caused by LTC controller malfunction, or a runaway motor that continues to change taps without stopping until the end of the LTC tap range.

In the LAR, Attachment 1, page 9, the licensee states that the 4.16 kV ESF buses are equipped with a process computer alarm that indicates an over-voltage condition has occurred. The CR computer alarm setpoint will be set conservatively below the 110 percent voltage rating of the safety-related motors fed from the bus, consistent with ANSI/NEMA Standard MG-1-2003, "Motors and Generators."

The licensee concluded that the simultaneous failures of both the VRR and VBR, or a malfunction of the LTC motor, that results in rapidly increasing voltage is deemed not credible based on the very low failure probability calculation. The NRC staff finds that the overall calculated cumulative failure probability calculated as 9.77E-07 is very low and therefore the licensees conclusion is acceptable.

Failure Mode that Decreases Voltage In this failure mode, the LTC drive mechanism fails to stop changing taps after initiation of a lower voltage signal by the microcontroller. This failure mode can be caused by LTC malfunction, or a runaway motor that continues to change taps without stopping until the end of the LTC tap range.

In the LAR, the licensee states that failure to restore the bus voltage would cause the power source for these buses to transfer to the RAT (preferred, if available), or to the EDGs. A loss of offsite power has been analyzed in the USAR. The presence of the VBR makes this decrease in voltage failure extremely unlikely, and a low voltage alarm at 4130 V would alert operators to take procedurally guided action prior to reaching the degraded voltage relay setpoint.

In the LAR, the licensee states that a failure that results in decreasing voltage could initiate the timers on the 4.16 kV bus degraded voltage relays, and if sustained, would automatically connect the buses to the onsite diesel generator power sources. The licensee concludes that this failure mode, although not desirable, would not result in an unsafe condition. The NRC

staff finds that since the automatic connection to the onsite diesel generator sources is analyzed in the USAR and failure probability calculated as 9.77E-07 is very low, the licensees conclusion is acceptable.

Failure Mode That Results in Tap Setting Remains "As Is The licensee identified other LTC failure modes or malfunctions that could result in the tap changer failing to change the tap setting when expected (i.e., the tap setting remains "as is").

This can result from a failure of the controller when the LTC is operating in the automatic mode, or from a failure of the drive motor within the LTC, including a LOP to the drive motor, when the LTC is operating.

In the LAR, the licensee states that failure of the tap changer to change when demanded is less severe than other failures of the LTC, since the over-voltage or under-voltage condition would evolve relatively slowly and the magnitude of the resultant change in voltage would be limited to the effect of the change in grid voltage. There are alarms that alert the operator to abnormal voltage conditions on the 4160 V ESF buses, and procedures instruct the operators to take action to mitigate or correct the condition. Actions can include contacting the transmission system operator and requesting that the voltage be increased or decreased as needed. The operator can also arrange for manual operation of the tap changer to change the tap setting if required. Based on the licensees analysis, the NRC staff finds that this failure mode can be adequately mitigated by the operators.

Failure Modes Conclusion Based on the above, the NRC staff finds that the licensee has adequately evaluated the various failure modes of the LTC in automatic mode. The failure modes either have very low probability, would not result in an unsafe condition, or would be easily managed. Therefore, the staff finds that the implementation of the automatic function of the LTC on the ERAT would not result in unsafe operation or shutdown of the plant and is therefore acceptable.

4.0 TECHNICAL EVALUATION

CONCLUSION Based on the technical evaluation provided in Sections 3.1 and 3.2 above, the NRC staff finds the implementation of the ERAT LTC in automatic operation mode will continue to provide adequate voltages at the safety-related buses, and therefore GDC 17 is met. The licensee has adequately addressed the various failure modes of ERAT LTC. The only failure mode in automatic operation mode that can increase voltage at the safety-related buses above a certain limit not analyzed in USAR, has a very low probability, and therefore is of very low safety significance. Therefore, the NRC staff finds that the operation of the ERAT LTC in automatic mode and the corresponding proposed changes to the USAR are acceptable.

5.0 STATE CONSULTATION

In accordance with the Commissions regulations, the NRC staff notified the Illinois State official on September 21, 2020, of the proposed issuance of the amendments. The State official had no comments.

6.0 ENVIRONMENTAL CONSIDERATION

The amendments change requirements with respect to the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 or change inspections or surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts and no significant change in the types of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding, which was published in the Federal Register on March 24, 2020 (85 FR 16683), that the amendments involve no significant hazards consideration, and there has been no public comment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

7.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) there is reasonable assurance that such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor: V. Goel Date of issuance: October 14, 2020