NLS2024023, Request for Notice of Enforcement Discretion for Technical Specifications 3.3.1.1, Reactor Protection System (RPS) Instrumentation

Request for Notice of Enforcement Discretion for Technical Specifications 3.3.1.1, Reactor Protection System (RPS) Instrumentation

ML24091A003
Person / Time
Site:	Cooper
Issue date:	03/31/2024
From:	Dia K Nebraska Public Power District (NPPD)
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NLS2024023
Download: ML24091A003 (1)

Text

NLS2024023 March 31, 2024 H

Nebraska Public Power District "Always there when you need us" Attention: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

Subject:

Request for Notice of Enforcement Discretion for Technical Specifications 3.3.1.1, "Reactor Protection System (RPS) Instrumentation" Cooper Nuclear Station, Docket No. 50-298, Renewed License No. DPR-46

Dear Sir or Madam:

On March 29, 2024, Nebraska Public Power District (NPPD) verbally requested a Notice of Enforcement Discretion (NOED) associated with Technical Specification (TS) Limiting Condition of Operation (LCO) 3.3.1.1, "Reactor Protection (RPS) Instrumentation," for Cooper Nuclear Station (CNS). The following information was discussed with representatives of the U.S. Nuclear Regulatory Commission (NRC) on March 29, 2024, at 1700 Central Daylight Time (CDT), with subsequent approval being verbally granted by the NRC on March 29, 2024, at 1804 CDT. The enforcement discretion expires on April 5, 2024, at 2037 CDT for TS LCO 3.3.1.1 Condition B, and at 023 7 CDT on April 6, 2024, for TS LCO 3.3.1.1 Condition A.

Enforcement discretion is needed because of a design concern regarding channel independence for the Turbine Stop Valves that cannot be resolved within the TS completion time. There is no indication that this design configuration has been changed since initial plant startup and original licensing, and there are no equipment failures currently identified. A detailed justification for the NOED is provided in the attachment.

An NOED was requested in accordance with NRC Enforcement Manual, Appendix F, Notices of Enforcement Discretion, based on the potential for an unnecessary reduction in power without a corresponding health and safety benefit. The determination of this criterion's applicability is based on CNS being in a 6-hour and 12-hour action statement to TS 3.3.1.1, for Table 3.3.1.1-1, Function 8, "Turbine Stop Valve - Closure (:S 10% closed)," with a subsequent reduction in power required. The additional time requested by the NOED will allow for the preparation, review and submittal of an Emergency License Amendment Request (LAR).

As discussed in the teleconference, compensatory measures have been implemented to protect equipment with elevated potential for initiating a turbine trip and to avoid work activities that increase the chances of a turbine trip or result in a yellow or higher Probabilistic Risk Assessment risk window during the duration of the NOED.

COOPER NUCLEAR STATION 72676 648A Ave/ P.O. Box 98 / Brownville, NE 68321 http://www.nppd.com

NLS2024023 Page 2 of2 The Station Operations Review Committee has reviewed this NOED request and determined that operation of CNS in accordance with the discretion granted will not endanger the health and safety of the public.

This letter fulfills the requirement to submit a written enforcement discretion request within two working days after NRC verbal approval is granted and provides the justification discussed with theNRC.

There are no regulatory commitments made in this submittal. If you should have any questions regarding this submittal, please contact Linda Dewhirst, Regulatory Affairs and Compliance Manager, at (402) 825-5416.

Sincerely, Khalil Dia Site Vice President

/mu

Attachment:

Request for Enforcement Discretion for Technical Specification 3.3.1.1, "Reactor Protection (RPS) Instrumentation" cc:

Regional Administrator w/ attachment USNRC - Region IV Cooper Project Manager w/ attachment USNRC - NRR Plant Licensing Branch IV Senior Resident Inspector w/ attachment USNRC-CNS NPG Distribution w/ attachment CNS Records w/ attachment

NLS2024023 Attachment Page 1 of 6 Attachment Request for Notice of Enforcement Discretion for Technical Specifications 3.3.1.1, "Reactor Protection (RPS) Instrumentation" Nebraska Public Power District (NPPD) is requesting a Notice of Enforcement Discretion (NOED) regarding completion of the required actions for Technical Specification (TS) Limiting Condition of Operation (LCO) 3.3.1.1, "Reactor Protection System (RPS) Instrumentation,"

Conditions A and B, for Table 3.3.1.1-1, Function 8, Turbine Stop Valve - Closure, related to a concern regarding channel independence.

The referenced section of the Nuclear Regulatory Commission (NRC) Enforcement Manual -

Appendix F, Notices of Enforcement Discretion, provides guidance on the information to be included in a request for enforcement discretion. The sections below are arranged to correspond to that guidance.

1. Explain why a licensing process is not appropriate to address the issue and why the need for a NOED could not reasonably have been avoided. If applicable, this explanation shall address previous instances of the issue and decisions to pursue licensing solutions in the past.

On March 29, 2024, at 1437 CDT, Cooper Nuclear Station (CNS) entered a 12-hour action statement under TS 3.3.1.1 Condition A, and a 6-hour action statement under TS LCO 3.3.1.1 Condition B, related to TS Table 3.3.1.1-1, Function 8, "Turbine Stop Valve

- Closure (:S 10% closed)," as a result of a concern with how the RPS function for the Main Turbine Stop Valve Limit Switches meet channel independence criteria in its current design configuration. The configuration consists of two Turbine Stop Valves with two RPS Limit Switches actuated by each stop valve. A linkage on each stop valve transmits stop valve movement to contact the limit switch arm of the upper limit switch.

The upper limit switch arm is attached by another linkage to the lower limit switch arm.

This arrangement ensures simultaneous rotation of both limit switches' splined shafts.

There is no indication that this design configuration has been changed since initial plant startup and original licensing. There are no equipment failures currently identified.

Resolution of the design concern cannot be accomplished within the completion time of the TS LCO Action Conditions.

Consequently, NPPD reviewed NRC Enforcement Manual, Appendix F, "Notices of Enforcement Discretion," and determined that this request satisfies Section 1.3 -

Applicability, as the time to process an Exigent or Emergency License Amendment Request (LAR) is not feasible due to the completion time associated with the action statement.

The Enforcement Manual Notice of Enforcement Discretion criterion applies to a plant in power operation to avoid an unnecessary reduction in power as a result of compliance with the TS or a license condition, without a corresponding health and safety benefit. As noted above, the TS completion time does not support the time required to process an Exigent or Emergency LAR, which provides the justification for enforcement discretion.

NPPD will be submitting an Emergency License Amendment.

NLS2024023 Attachment Page 2 of6

2. Provide a description of the TSs or other License Conditions that will be violated. This description shall include the time the condition was entered and when the completion time will expire.

Enforcement discretion was requested to delay taking the required actions for TS LCO 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Conditions A and B, for Table 3.3.1.1-1, Function 8, Turbine Stop Valve - Closure. TS LCO 3.3.1.1, Conditions A and B were entered at 1437 CDT on March 29, 2024, and would have expired at 0237 CDT on March 30, 2024, if the NOED had not been granted at 1804 CDT on March 29, 2024.

3. Provide sufficient information to demonstrate that the cause of the situation is well understood including extent of condition on other related SSCs ( e.g., common cause).

The Turbine Stop Valve Limit Switches are mechanically connected to actuate together on Turbine Stop Valve closure. TS LCO 3.3.1.1, Table 3.3.1.1-1, Function 8, requires two channels per trip system. The configuration of the mechanical trip input to the Turbine Stop Valve Limit Switches does not meet channel independence criteria. This configuration is unique to the Turbine Stop Valves. Therefore, there is no extent of condition beyond the two Turbine Stop Valves.

4. Provide an evaluation of all safety and security concerns associated with operating outside of the TS or license condition that demonstrates that the non-compliance will not create undue risk to the public health and safety or involve adverse consequences to the environment. This should include as appropriate a description of the condition and operational status of the plant, equipment that is out of service, inoperable, or degraded, that may have risk significance, may increase the probability of a plant transient, may complicate the recovery from a transient, or may be used to mitigate the condition. This evaluation shall include potential changes to off site and on site power sources and forecasted weather conditions.

The RPS function for the Main Turbine Stop Valve Limit Switches does not meet channel independence criterion. There is no known current degradation with the Turbine Stop Valve Limit Switches.

The function of other redundant trips or diverse methods of reactor shutdown ( e.g., other automatic RPS trips, alternate rod insertion, or manual reactor trip capacity) remain unaffected by this concern. Therefore, there are no other equipment impacts that may have risk significance, increase the probability of a plant transient, or may complicate the recovery from a transient. Assuming the Turbine Stop Valve Limit Switches are not operable and a SCRAM signal from Turbine Stop Valve position does not occur, the existing plant safety analysis demonstrates that this condition would be mitigated by other RPS trip functions.

SCRAMs based on Turbine Governor Valve Fast Closure and Turbine Stop Valve Fast Closure are anticipatory in nature in order to provide additional margin to over pressurization of the Reactor Coolant System boundary. The High Reactor Vessel Pressure SCRAM, in conjunction with the pressure relief system, is sufficient to maintain

NLS2024023 Attachment Page 3 of 6 Reactor Coolant System boundary pressure below applicable limits. [USAR Section VII-2.4]

The Reactor Coolant System boundary analysis is based on the Main Steam Isolation Valve (MSIV) Closure event with a High Flux SCRAM. This event does not assume a Turbine Stop Valve or Turbine Governor Control Valve Fast Closure SCRAM signal.

Reactor Coolant System boundary pressure values are below applicable limits when evaluating the shortest MSIV Closure time of three seconds. [USAR Section IV-4.9]

The Turbine Stop Valves close via depressurization of the stop valve emergency trip header. Likewise, depressurization of this header will also cause the Turbine Governor (Control) Valve emergency trip header to depressurize [Engineering Change EC-6039700, "Turbine Generator Fluid Stop Valve Emergency Trip Pressure Control," Section 1.1].

This results in a separate SCRAM signal [TS Table 3.3.1.1.-1, Function 9]. This SCRAM signal is the basis for the Turbine Control Valve Fast Closure (generator load rejection event), which is explicitly analyzed. [USAR Section XIV-5.1.1.3]

Fuel damage is avoided by setting the most limiting operating limit Minimum Critical Power Ratio (MCPR, which protects the safety limit MCPR during the event). This is determined based on the most limiting event for the cycle. Turbine trip events are not limiting for this cycle. The limiting pressurization events from the CNS Cycle 33 reload analysis are: Inadvertent HPCI Injection, Generator Load Rejection Without Bypass, and Feedwater Controller Failure [Global Nuclear Fuel Report 006N2092, "Supplemental Reload Licensing Report for Cooper Nuclear Station Reload 32 Cycle 33 (SRLR)",

Section 9 and Appendix G].

There are no potential changes to off site and on site power sources and forecasted weather conditions that are related to this concern.

5. Provide a description of the timeline of the proposed course of action to resolve the situation ( e.g., likely success of the repairs) and explain how the resolution will not result in a different or unnecessary transient. This shall include the time period of the requested discretion and demonstrate a high likelihood of completion within the requested period of enforcement discretion. If the proposed course of action necessitates enforcement discretion greater than 5 days, the licensee shall justify why a longer-term solution ( e.g., emergency amendment) should not be processed within the duration of a 5-day NOED.

NPPD is requesting enforcement discretion to allow sufficient time for the preparation, review, and submittal of an Emergency LAR. NPPD will submit the Emergency LAR no later than 1700 CDT on April 1, 2024, with a request for the NRC to review and approve the LAR by 1700 CDT April 5, 2024, to allow for exiting the TS LCO conditions and subsequent termination of the enforcement discretion.

6. Detail and explain compensatory actions the plant has both taken and will take to reduce risk(s), focusing on both event mitigation and initiating event likelihood.

Describe how each compensatory measure achieves one or more of the following:

a. Reduces the likelihood of initiating events.

NLS2024023 Attachment Page 4 of6

b. Reduces the likelihood of the unavailability of redundant trains during the period of enforcement discretion.

c. Increases the likelihood of successful operator actions in response to initiating events.

To reduce the likelihood of initiating events, compensatory measures as follows will be taken to remove activities during the duration of the NOED that would increase the likelihood of a turbine trip:

1. The work schedule will be reviewed and any work that increases the chances of a turbine trip will be avoided.

2. Actions will be taken to remove any planned work activities from the schedule which result in a Yellow or higher Probabilistic Risk Assessment (PRA) risk window.

3. The Protected Equipment Program will be utilized to drive heightened sensitivity and risk management actions associated with equipment with elevated potential for initiating a Main Turbine trip.

7. Demonstrate that the NOED condition, including compensatory measures will not result in more than a minimal increase in radiological risk, either in quantitative assessment that the risk will be within the normal work control levels (ICCDP less than or equal to SE-07 and/or ICLERP less than or equal to SE-08) or in a defensible qualitative manner.

In regard to the NOED's Incremental Conditional Core Damage Probability (ICCDP) and Incremental Conditional Large Early Release Probability (ICLERP) thresholds, a delay in completion of required actions is supported by risk insights from the CNS internal events PRA. The resulting ICCDP and ICLERP are bounded at 1.98E-11 and 7.14E-13 respectively, and are acceptably below the NOED ICCDP threshold of SE-07 and ICLERP threshold of SE-08. These are also well below the 1.0E-06 threshold listed for Normal Work Control Levels.

The following are the PRA Insights:

Core Damage Risk The concern with channel independence criteria is that the mechanical linkage used to actuate the Main Turbine Stop Valve SCRAM Position Switches is that they could fail in a way that would render the Turbine Stop Valve SCRAM function unavailable.

PRA risk insights in this case are centered around evaluation of reliability and not unavailability as it is noted that the Turbine Stop Valve SCRAM function remains available. Core Damage Risk and Large Early Release risk were reviewed to evaluate the impact of the channel independence concern through applying a bounding screening value for a duration of one year to address a decrease in reliability. The PRA model of record was used to assess the zero test and maintenance (ZTM), Core Damage Frequency (CDF), and Large Early Release Frequency (LERF). The RPS function associated with the Turbine Stop Valve SCRAM was found to be included in the RPS electrical common cause event RPS-SYS-CF-ELEC. This event represents

NLS2024023 Attachment Page 5 of 6 total failure of the RPS function. Risk can be assessed by adjusting this function with a bounding value to overestimate and capture associated risk. Though it can be judged that the common cause RPS event probability is not increased, this study has increased the probability by an order of magnitude to provide risk insights. These results are summarized below:

ICCDP, Conditional CDF (RPS probability increase of an order of magnitude):

l.98E-l 1/yr ICLERP, Conditional LERF (RPS probability increase of an order of magnitude):

7.14E-13/yr These values are far below the acceptable NOED thresholds of 5.0E-07 for ICCDP and 5.0E-08 for ICLERP.

External Event Risk Review Risk from External Events contribution to both the Core Damage and Large Early Release standpoint is judged to be negligible. This is based on the judgment that the majority of shutdowns that are driven by External Events ( e.g., Fire, Seismic, High Winds, External Floods) are best characterized as procedurally driven Manual SCRAMs. The issue evaluated herein does not impact the reliability/availability of the Manual SCRAM function, which in tum minimizes External Event risk.

It is recognized that External Events may result in turbine trips, and the associated Turbine Stop Valve SCRAM. However, the frequency of these External Event driven turbine trips, within the time frame of this NOED to delay completion of required TS actions, is well below turbine trip frequencies analyzed in the Internal Events PRA.

The Internal Events PRA models turbine trip events as greater than 2.49E-01/yr, and is judged to be well above External Event frequencies. Thus, External Event risk from turbine trip Turbine Stop Valve SCRAMs is judged subsumed by the risk insights from the Internal Event analysis provided above.

External Event risk is also minimized through review of current weather forecasts. It is judged that there is no eminent threat of External Events, including: High Winds, Floods, or Seismic activities.

8. Confirm that the facility organization that normally reviews safety issues has reviewed and approved this request and that a written NOED request will be submitted within 2 days of the NRC staffs decision regarding the NOED.

The Station Operations Review Committee reviewed and approved this request on March 29, 2024.

9. In addition to Items 1 through 8, the licensee must provide the following information for a natural event NOED:

a. List the name, organization, and telephone number of the official in the government or independent entity who made the emergency determination, if applicable.

b. Include details of the basis and nature of the emergency situation, including grid information for a grid instability NOED.

NLS2024023 Attachment Page 6 of 6

c. Identify and discuss the potential consequences of compliance with existing license requirements.

d. Discuss the impact of the emergency on plant safety, including the capability of the UHS.

e. Discuss the potential adverse effects on public health and safety from enforcing compliance with specific license requirements during the emergency.

This is not a Natural Event NOED.