RS-25-103, License Amendment Request for Proposed Change to the USAR to Approve Alternate Method of Verifying MSIV Closure Reactor Protection System Response Time

License Amendment Request for Proposed Change to the USAR to Approve Alternate Method of Verifying MSIV Closure Reactor Protection System Response Time

ML25177C292
Person / Time
Site:	Clinton
Issue date:	06/26/2025
From:	Humphrey M AmerGen Energy Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RS-25-103
Download: ML25177C292 (1)

Text

4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office RS-25-103 10 CFR 50.90 June 26, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461

Subject:

License Amendment Request for Proposed Change to the USAR to Approve Alternate Method of Verifying MSIV Closure Reactor Protection System Response Time

Reference:

Letter from K. Stoedter (U.S. Nuclear Regulatory Commission) to D. Rhoades (Constellation Energy Group, LLC), "Clinton Power Station - Comprehensive Engineering Team Inspection Report 05000461/2025010," dated May 8, 2025 In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," and 10 CFR 50.59, "Changes, tests, and experiments, Constellation Energy Generation, LLC (CEG) requests approval for a change to the Updated Safety Analysis Report (USAR) for Clinton Power Station, Unit 1 (CPS). The proposed change requests approval of an alternate method of verifying Reactor Protection System Response Time (RPSRT) for Main Steam Isolation Valve (MSIV) Closure as an NRC-approved methodology.

The Reference documents a Green Finding with an associated Non-Cited Violation (NCV) from the CPS Comprehensive Engineering Team Inspection (CETI) that was issued by the NRC on May 8, 2025. This violation was cited against 10 CFR 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings, for a failure to have procedures appropriate to the circumstance for performing response time testing of the reactor protection system main steam isolation valve closure function, an activity affecting quality. The violation stated that this failure has led to CPS not meeting Technical Specification (TS) Surveillance Requirement (SR) 3.3.1.1.17, which requires the measurement of the RPS Response Time for Function 6 (Main Steam Isolation Valve - Closure).

The intent of this request is to restore CPS to compliance. Attachment 1 provides an evaluation of the proposed changes. Attachment 2 provides proposed mark-ups of the affected CPS USAR. The mark-up does not include the Amendment number (currently shown as XXX on the mark-up) as that number will EHissued upon approval of this request.

June 26, 2025 U.S. Nuclear Regulatory Commission Page 2 The proposed changes have been reviewed by the CPS Plant Operations Review Committee in accordance with the requirements of the CEG Quality Assurance Program.

CEG requests approval of the proposed license amendment prior to the next CPS refueling outage, which beings on September 8, 2025. The proposed changes will be implemented within 7 days of the issuance of the amendment.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), CEG is notifying the State of Illinois of this application for license amendment by transmitting a copy of this letter and its attachments to the designated State Official.

A regulatory commitment is included in this letter and is discussed in Attachment 3. Should you have any questions concerning this letter, please contact Nick Lien at (779) 231-6283.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 26th day of June 2025.

Respectfully, Mark D. Humphrey Senior Manager - Licensing Constellation Energy Generation, LLC Attachments:

1) Evaluation of Proposed Changes

2) Proposed Updated Safety Analysis Report (USAR) Changes (Mark-Up) -

Clinton Power Station, Unit 1

3) Summary of Regulatory Commitments cc:

NRC Regional Administrator, Region III NRC Senior Resident Inspector, Clinton Power Station Illinois Emergency Management Agency and Office of Homeland Security - Division of Nuclear Safety Humphre y, Mark D.

Digitally signed by Humphrey, Mark D.

Date: 2025.06.26 12:29:28 -05'00'

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 1 of 8

Subject:

License Amendment Request for Proposed Change to the USAR to Approve Alternate Method of Verifying MSIV Closure Reactor Protection System Response Time 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements / Criteria 4.2 Precedents 4.3 No Significant Hazards Consideration 4.4 Conclusions

6.0 REFERENCES

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 2 of 8 1.0

SUMMARY

DESCRIPTION In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," and 10 CFR 50.59, "Changes, tests, and experiments,"Constellation Energy Generation, LLC (CEG) requests approval for a change to the Updated Safety Analysis Report (USAR) for Clinton Power Station, Unit 1 (CPS). The proposed change requests approval of an alternate method of verifying Main Steam Isolation Valve (MSIV) Closure Reactor Protection System Response Time (RPSRT) as an NRC-approved methodology.

Reference 1 documents a Green Non-Cited Violation (NCV) from the CPS Comprehensive Engineering Team Inspection (CETI) that was issued by the NRC on May 8, 2025. This violation was cited against 10 CFR 50, Appendix B, Criterion V, "Instructions, Procedures, and Drawings", for "failure to have procedures appropriate to the circumstance for performing response time testing of the reactor protection system main steam isolation valve closure function, an activity affecting quality." The violation stated that this failure has led to CPS not meeting Technical Specification Surveillance Requirement 3.3.1.1.17, which measures RPS Response Time.

The CPS TS Definition of RPS RESPONSE TIME reads, "The RPS RESPONSE TIME shall be that time interval from when the monitored parameter exceeds its RPS trip setpoint at the channel sensor until de-energization of the scram pilot valve solenoids. The response time may be measured by means of any series of sequential, overlapping, or total steps so that the entire response time is measured. In lieu of measurement, response time may be verified for selected components provided that the components and methodology for verification has been previously reviewed and approved by the NRC."

Currently, CPS performs SR 3.3.1.1.17 for MSIV Closure (Function 6) by generating the trip signal via a test switch in the main control room. This test switch replaces the MSIV Closure sensor contact and associated wiring to the associated MSIV. The NRCs position is that this does not meet the criteria of "at the channel sensor" nor has the component and methodology been NRC-approved.

CPS is requesting approval of an alternate method of generating an open trip signal via a test switch in the main control room as an NRC-approved methodology. The technical justification for this request is included in section 3.0 of this attachment.

2.0 DETAILED DESCRIPTION CPS is proposing to include in its USAR under Section 1.8 "Conformance to NRC Regulatory Guides", under Regulatory Guide 1.118, Rev 2 (June 1978), a description of the verification methodology used to measure MSIV Closure RPSRT. This testing is performed per procedure CPS 9431.20 "RPS Main Steam Isolation Valve (MSIV) Response Time Test". This procedure verifies response time of RPS to a MSIV Closure signal. This signal is generated by breaking (opening) the circuit via a temporary test switch in the Main Control Room (MCR) that replaced the MSIV Closure sensor contact and associated wiring between the MCR and the associated

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 3 of 8 MSIV. The model of this test switch is a generic single pole test switch. The model of the MSIV limit switch is NAMCO EA740-50100.

The requested description in the USAR is shown in Attachment 2 of this document.

Approval of this change will allow CPS to comply with the TS RPSRT definition by verifying an approved component (the MSIV limit switch) with an approved methodology.

The violation from the 2025 CETI stated that CPS failed to have procedures appropriate to the circumstance for performing response time testing of the reactor protection system main steam isolation valve closure function, an activity affecting quality. Specifically, the surveillance procedure used, CPS 9431.20, failed to include steps to ensure the time interval from when the RPS MSIV closure limit switches exceeded their RPS trip setpoint at the channel sensor until de-energization of the scram pilot valve solenoids was measured. As such, TS 3.3.1.1.17 has not been met.

3.0 TECHNICAL EVALUATION

MSIV closure results in loss of the main turbine and the condenser as a heat sink for the Nuclear Steam Supply System and indicates a need to shut down the reactor to reduce heat generation. Therefore, a reactor scram is initiated on a Main Steam Isolation Valve-Closure signal before the MSIVs are completely closed in anticipation of the complete loss of the normal heat sink and subsequent overpressurization transient.

MSIV closure signals are initiated from limit switches located on each of the eight MSIVs. Each MSIV has one position switch. The logic for the Main Steam Isolation Valve-Closure Function is arranged such that either the inboard or outboard valve on two or more of the main steam lines (MSLs) must close in order for a scram to occur.

RPS is de-energize to actuate, meaning that a loss of power to the circuit will initiate a scram signal. The MSIV-Closure RPS trip signal is created by a limit switch opening its sensor contact, thus breaking the circuit.

The Main Steam Isolation Valve-Closure Allowable Value is the maximum amount of valve closure specified to ensure that a scram occurs prior to a significant reduction in steam flow, thereby reducing the severity of the subsequent pressure transient.

The Main Steam Isolation Valve-Closure (MSIV-Closure) RPS trip is verified by the following Surveillance Requirements (SR), all of which are controlled in accordance with the Surveillance Frequency Control Program (SFCP):

x SR 3.3.1.1.9 (Channel Functional Test), currently performed at least every 24 months.

x SR 3.3.1.1.13 (Channel Calibration), currently performed at least every 48 months.

x SR 3.3.1.1.15 (Logic System Functional Test), currently performed at least every 48 months and, x

SR 3.3.1.1.17 (RPS Response Time verification), currently performed at least every 24 months on a STAGGERED TEST BASIS (i.e., each division once per 96 months).

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 4 of 8 Channel Functional Test (SR 3.3.1.1.9): This test verifies that MSIV position will cause an RPS trip signal. This is verified by performing a slow closure of an MSIV, using a test pushbutton, until it generates a trip signal. When the trip signal is generated, the MSIV is returned to its full open position by releasing the pushbutton.

Channel Calibration Test (SR 3.3.1.1.13): This test verifies that a trip signal occurs within the TS Allowable Value of 13% closed (from the open position). This is verified by taking a physical measurement of stem travel distance from the full open position to full closed position, locally at the MSIV, and comparing it to a physical measurement of stem travel distance required to open the limit switch which drives the RPS trip signal. This test can reveal possible deterioration of the limit switch, such as sluggish behavior (ex. slow movement or sticking) of the limit switch, which would preclude a trip within the TS 3.3.1.1-1 allowable limits. Moreover, the channel calibration ensures sufficient overlap in circuit diagnostics to identify degradation in the parts of the channel not actively monitored by the current SR 3.3.1.1.17 methodology, and it currently achieves this at an equal or higher frequency compared to SR 3.3.1.1.17.

The Logic System Functional Test (SR 3.3.1.1.15): This test verifies that the appropriate system actuations occur upon receipt of an RPS trip signal from the MSIV limit switch(es). This requirement is satisfied by the overlap of multiple tests (as permitted by the TS definition of RPS Response Time).

RPS Response Time Verification (SR 3.3.1.1.17) - (described below).

To meet the definition of RPS Response Time, the test must be done at the channel sensor (i.e.,

the MSIV limit switch) by either manually toggling the switch or closing the MSIV. Alternately, the definition allows for response time verification for selected components provided that the components and methods for verification have been previously reviewed and approved by the NRC.

CEG is requesting the latter due to the impracticality of timing events in the millisecond range at remote location in the plant and the MCR. Performing this at the sensor would require connecting a high-speed chart at the MSIV limit switch to the MCR at the output of the high-voltage level input digital signal conditioner where it inputs to the solid-state RPS logic.

Furthermore, plant conditions during refueling outages do not always allow for MSIVs to be cycled open or closed to support testing needs. A closed MSIV would prevent the ability to toggle the limit switch manually. Cycling the MSIVs would cause unnecessary wear and tear.

Approval of this testing methodology will allow greater flexibility in scheduling and performing the required testing during an outage and prevent undue wear on the MSIVs.

Additionally, savings are realized by not having personnel at the MSIV limit switch for this testing. Inboard MSIVs are located in the drywell. Outboard MSIVs are located in the Auxiliary Building Steam Tunnel. The dose estimates for the channel calibrations for MSL A Channel Cal 9431.10A, RPS MAIN STEAMLINE ISOLATION VALVE B21-F022A CHANNEL

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 5 of 8 CALIBRATION and MSL D Channel Cal 9431.10D, RPS MAIN STEAMLINE ISOLATION VALVE B21-F022D CHANNEL CALIBRATION are 46 mR and 69 mR respectively. This is representative of average dose accumulated per Main Steam Line for RPS RTT. Performing this test from the control room instead of locally will save an average of 115 mR per outage.

Importantly, stroking the MSIVs to measure RPSRT is not warranted if there is no mechanism by which valve position could become uncoupled from limit switch actuation. In other words, limit switch actuation is what indicates valve position, specifically, that MSIV position has reached the RPS Setpoint. The physical setting of the limit switch is verified on a more frequent bases by calibration checks, therefore stroking the valve to actuate the limit switch is not required for response time purposes and introduces unnecessary wear to these components.

The current RPS Response Time Verification (SR 3.3.1.1.17) testing is performed for each MSIV as follows with a figure below:

1)

Leads are lifted in the MCR for the associated outboard MSIV limit switch circuit.

2)

A test switch is installed across the terminal points from which the leads were lifted.

3)

A high-speed chart recorder (ASTRO-Med Dash 10 or equivalent) is connected across those terminal points.

4)

A high-speed chart recorder is connected at the output of the high-voltage level input digital signal conditioner where it inputs to the solid-state RPS logic.

5)

The chart recorder is started then the test switch for the associated MSIV is opened.

6)

Response time data is recorded.

7)

The associated MSIV limit switch circuits are restored to their pre-test configurations.

8)

Total Response Time is determined for a given division by using the slower response time of the inboard and outboard MSIV and adding the Self-Test System response time (8.25 milliseconds) of the Logic/Load Driver. This overall value is verified to be 40 milliseconds. This is the MSIV Closure response time listed in the Operational Requirements Manual (ORM) Attachment 2, Table 13.

Figure showing test for A Outboard MSIV:

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 6 of 8 The testing method requested is electrically equivalent to physically actuating the limit switch to break the logic circuit. The impact of the length of wiring between the MSIV limit switch in the field and the MCR is insignificant with respect to the measured RPS RESPONSE TIME. The speed of electricity in a wire is in ranges estimated at 50-99% of the speed of light, depending on the transmitting material. The speed of light is 9.836e8 feet per second (ft/s). Approximating the speed of electricity as 50% lightspeed, then, is 4.918e8 ft/s, or 491800 ft/ms. To contribute 1 ms of delay to the sensing circuit, the interconnected wiring would have to have a length greater than 93 miles (491800 ft/ms /5280 ft). Assuming a significantly conservative bounding value that 10 miles of wiring are installed in the MSIV RPS logic paths, the physical wiring in an RPS circuit can contribute no more than 0.1 ms delay to the RPS signal (10 mi

• 5280 ft /

491800 ft/ms). Even with a significantly conservative estimate, the impact of wiring on RPS signal response time from the MSIV limit switches to the MCR is negligible, and any de-energization of the RPS input is equivalent to opening the circuit at the MSIV.

Degradation of the response time of the sensor (NAMCO Limit Switch), can be detected by monitoring for sluggish response of the snap-acting limit switch during calibrations. In addition, the as-found setpoint of the limit switch can be trended for degradation. A commitment has been made (see Attachment 3) to revise the Channel Calibration procedures to perform both of those actions.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements / Criteria The following applicable regulations and regulatory requirements were reviewed in development of this submittal:

10 CFR 50, Appendix A, "General Design Criteria for Nuclear Power Plants," Criterion 13, "Instrumentation and control," requires that instrumentation shall be provided to monitor variables and systems over their anticipated ranges for normal operation, for anticipated operational occurrences, and for accident conditions as appropriate to assure adequate safety, including those variables and systems that can affect the fission process, the integrity of the reactor core, the reactor coolant pressure boundary, and the containment and its associated systems. Appropriate controls shall be provided to maintain these variables and systems within prescribed operating ranges.

10 CFR 50.36, Technical Specifications, paragraph (c)(3), states that surveillance requirements are requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation will be met.

4.2 Precedents There are no precedents to this request.

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 7 of 8 4.3 No Significant Hazards Consideration CEG has evaluated the proposed changes, using the criteria in 10 CFR 50.92, "Issuance of amendment," and has determined that the proposed changes do not involve a significant hazards consideration. The following information is provided to support a finding of no significant hazards consideration.

In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," and 10 CFR 50.59, "Changes, tests, and experiments, Constellation Energy Generation, LLC (CEG) requests approval for a change to the Updated Safety Analysis Report (USAR) for Clinton Power Station, Unit 1 (CPS).

This request would revise the CPS USAR to describe a methodology for performance of RPS Response Time verification for the Main Steam Isolation Valve - Closure function so that the testing is in compliance with the CPS TS definition of RPS Response Time.

1. Do the proposed changes involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No The proposed changes would allow for a testing methodology that meets the definition of RPS Response Time. RPS Response Time testing for this function would still be performed to ensure that the full system response would occur to mitigate the consequences of inadvertent MSIV closure as described in USAR section 15.2.4 MSLIV Closures. The proposed changes do not involve a significant increase in the probability of an accident previously evaluated because the changes involve no change to the plant or its modes of operation.

2. Do the proposed changes create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No The proposed change does not change the design, configuration, or method of operation of the plant. The proposed change does not involve a physical alteration of the plant (i.e., no new or different kind of equipment will be installed). This request allows for a verification methodology that meets the definition of RPS Response Time

3. Do the proposed changes involve a significant reduction in a margin of safety?

Response: No There is no change in safety margin because Technical Specification-required RPS Response Time testing requirements, including total response time, remain unchanged.

The proposed change does not affect the inputs or assumptions of any of the analyses that demonstrate the integrity of the fuel cladding, reactor coolant system, or containment during accident conditions.

ATTACHMENT 1 Evaluation of Proposed Changes Attachment 1 - Page 8 of 8 Based on the above evaluation, CEG concludes that the proposed amendment presents no significant hazards consideration under the standards set forth in 10 CFR 50.92, paragraph (c), and accordingly, a finding of "no significant hazards consideration" is justified.

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

5.0 ENVIRONMENTAL CONSIDERATION

CEG has determined that the proposed changes would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20 or would change an inspection or surveillance requirement.

However, the proposed changes do not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed changes meet the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed changes.

6.0 REFERENCES

1. Letter from K. Stoedter (U.S. Nuclear Regulatory Commission) to D. Rhoades (Constellation Energy Group, LLC), "Clinton Power Station - Comprehensive Engineering Team Inspection Report 05000461/2025010," dated May 8, 2025

ATTACHMENT 2 Proposed Updated Safety Analysis Report (USAR) Changes (Mark-Up) -

Clinton Power Station, Unit 1

CPS/USAR CHAPTER 01 1.8-56 REV. 11, JANUARY 2005 Regulatory Guide 1.117, Rev. 1 (April, 1978)

Tornado Design Classification Project Position - The project complies with the requirements of Regulatory Guide 1.117 with the following clarifications:

The discussion contained in Regulatory Guide 1.117 states that protection of designated structures, systems, and components may generally be accomplished by designing protective barriers to preclude tornado damage, and if protective barriers are not installed, the structures and components themselves should designed to withstand the effects of the tornado, including tornado missile strikes.

Important systems and components (as discussed in Regulatory Guide 1.117) are generally protected. The limited amount of unprotected portions of important systems and components are analyzed using a probabilistic missile strike analysis consistent with the acceptance criteria in Standard Review Plan 3.5.1.4, Missiles Generated By Natural Phenomena.

USAR Subsection - 3.5.1.4, 3.5.2.4, and 3.5.2.5 Regulatory Guide 1.118, Rev. 2 (June 1978)

Periodic Testing of Electric Power and Protection Systems Project Position - The Project complies with NRC Regulatory Guide 1.118 with the following clarifications:

1)

Reference:

Paragraph C.6 - Trip of an associated protective channel or actuation of an associated Class 1E Load Group is required on removal of fuses or opening of a breaker only for the purpose of deactivating instrumentation or control circuitry.

2)

Reference:

Paragraph C.8.a - Appropriate state-of-the art technology will be implemented to periodically assure that the sensor (beginning at the sensor input), trip unit, logic, and actuator response times have not deteriorated so as to compromise the respective system design requirements.

3)

Reference:

Paragraph C.8.b - Test intervals, both initial and revised, should be such that significant changes in failure rates can be detected.

The Nuclear System Protection System has been designed to support the requirements of this guide.

USAR Chapters - 7 and 8 4)

Reference:

Paragraph C.3 - For RPS Time Response Testing for MSIV Closure, the substitute test creates an RPS trip signal by use of a test switch in the control room instead of at the sensor at the MSIV. This test switch replaces the MSIV Closure sensor contact and associated wiring from the associated MSIV to the control room. While this removes the wiring to and from the MSIV to the control room, this is negligible on overall response time due to the speed at which wiring de-energizes. Degradation of this sensor is assessed by periodic channel calibrations. Description and approval of this method is found in the Safety Evaluation of Amendment No XXX

ATTACHMENT 3 Summary of Regulatory Commitments The following table identifies commitments made in this document. (Any other actions discussed in the submittal represent intended or planned actions. They are described to the NRC for the NRCs information and are not regulatory commitments.)

Commitment Committed Date Commitment Type One-Time Action (Yes/No)

Programmatic (Yes/No)

Revise CPS procedures 9431.10 (A through H) for RPS Main Steamline Isolation Valve Channel Calibrations to:

1) include reviewing as-found data from prior two calibrations to determine if there is a trend showing snap-acting limit switch degradation.

2) Verify there is no sluggish response of the snap-acting limit switch.

9/8/2025 No Yes