ML25010A151
| ML25010A151 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 02/07/2025 |
| From: | Robert Kuntz NRC/NRR/DORL/LPL3 |
| To: | Rhoades D Constellation Energy Generation |
| Klett, AL | |
| References | |
| EPID L-2022-LLA-0140 | |
| Download: ML25010A151 (1) | |
Text
February 7, 2025 David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
LIMERICK GENERATION STATION, UNITS 1 AND 2 - REGULATORY AUDIT REPORT FOR REVIEW OF HUMAN FACTORS ENGINEERING PORTION OF LIMERICK DIGITAL INSTRUMENTATION AND CONTROLS LICENSE AMENDMENT REQUEST (EPID L-2022-LLA-0140)
Dear David Rhoades:
By non-public letter dated September 26, 2022, as supplemented by letters dated August 12, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22224A149), and November 29, 2022 (ML22333A817), Constellation Energy Generation, LLC (Constellation, licensee), submitted license amendment requests (LAR) for Limerick Generation Station, Units 1 and 2 (Limerick). The proposed amendment requests would change both the design and technical specifications to permit the use of a new single digital instrumentation and controls system to replace analog instrumentation of reactor protection system, analog nuclear steam supply shutoff system, emergency core cooling system, reactor core isolation cooling system, and end-of-cycle recirculation pump trip at Limerick. In addition, the proposed amendments would change the classification of the redundant reactivity control system from safety-related to non-safety-related, eliminate the automatic redundant reactivity control system feedwater runback function, eliminate the automatic isolation function for the turbine enclosure main steam line tunnel temperature high indication, eliminate several surveillance requirements, and allow the use of automated operator aids (or automated controls) from the main control room.
To assist in its review of the Limerick digital instrumentation and controls LAR, the U.S.
Nuclear Regulatory Commission staff conducted a regulatory audit on the equipment consistent with the audit plan issued February 6, 2023 (ML23032A244). A summary of the activities completed during this audit are in the enclosed audit report.
If you have any questions, please contact me by telephone at 301-415-3733 or by email to robert.kuntz@nrc.gov.
Sincerely,
/RA/
Robert F. Kuntz, Senior Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-352 and50-353
Enclosure:
Audit Report cc: Listserv
Enclosure REGULATORY AUDIT
SUMMARY
TO SUPPORT THE HUMAN FACTORS REVIEW OF THE LICENSE AMENDMENT REQUEST TO SUPPORT THE DIGITAL INSTRUMENTATION AND CONTROL UPGRADE FOR LIMERICK GENERATING STATION, UNITS 1 AND 2 EPID L 2022 LLA 0140 DOCKET NOS. 50-352 AND 50-353
1.0 BACKGROUND
This audit was conducted with the intent to: (1) examine the preliminary validation approach in the design phase, (2) gain familiarity with the testbed used to complete the preliminary validation process, (3) observe the scenarios used for the preliminary validation and (4) identify any information that may require docketing to support the U.S. Nuclear Regulatory Commission (NRC, the Commission) staffs regulatory finding.
By non-public letter dated September26, 2022, as supplemented by letters dated August12,2022 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML22224A149), and November 29, 2022 (ML22333A817), Constellation Energy Generation, LLC (Constellation, the licensee), submitted license amendment request (LAR) for Limerick Generation Station, Units 1 and 2 (Limerick). The proposed amendment request would change both the design and technical specifications to permit the use of a new single digital instrumentation and controls (I&C) system to replace analog instrumentation of the reactor protection system, analog nuclear steam supply shutoff system, emergency core cooling system, reactor core isolation cooling system, and end-of-cycle recirculation pump trip at Limerick.
The NRC staff performed a preliminary review of the LAR and determined that a regulatory audit would assist in reviewing the licensees LAR and timely completion of the review. The regulatory audit was performed consistent with NRC Office of Nuclear Reactor Regulation Office Instruction LIC-111, Revision 1, Regulatory Audits, dated October 31, 2019 (ML19226A274).
2.0 AUDIT ACTIVITIES The NRC staff conducted an on-site audit and walkdown of the testbed configuration to support the LAR on February 2123, 2023. An audit plan was provided to the licensee by letter February 6, 2023 (ML23032A244), which specified the subject matter area of focus, provided the purpose and scope and requested the necessary information and other material for the audit.
Idaho National Lab (INL) Light Water Reactor Sustainability R&D Program Technical Integration Office facilitated the Limerick Generating Station Preliminary Validation Workshop (PV). On site at INL were representatives from Constellation, Westinghouse Electric Company (Westinghouse), Department of Energy, Sargent and Lundy, CORYS, and technical experts from INL in the areas of I&C and human factors engineering (HFE). The audit activities were comprised of presentations, discussions with the design team/licensee and observing the performance of demonstrations on the testbed. The presentations and discussions described the process used for the PV development which included collaboration between multiple of subject matter expert teams. The testbed simulated the physical layout of the Limerick control room with functional, modified Human-System Interfaces (HSIs) which support the digital I&C system upgrade.
Presentation content included:
Overview of HFE program for the Digital Upgrade Testbed Limitations Conceptual Validation (CV) teams, method, and results Preliminary Validation Scope The testbed demonstrations were conducted on a partial scope, single unit main control room simulation facility that referenced the Limerick plant design. The testbed was assembled utilizing the INL Human-Systems Simulation Laboratory (HSSL). Operators navigated and dynamically operated the updated HSIs in the HSSL. The demonstrations included scenarios relevant to the HFE aspects of the digital I&C modernization project. These scenarios were used in the development of the conceptual validation and the preliminary validation which each will have reports reviewed by the staff as a part of the LAR. The PV workshop was performed to support the licensees assertion that the documented sequences of manual operator actions are reasonable, realistic, and bounded by the conceptual validation workshop analysis as documented.
3.0 AUDIT TEAM The NRC audit team members:
Brian Green, Team Lead and Senior Human Factors Engineer Kamishan Martin, Human Factors Engineer Jesse Seymour, Senior Reactor Engineer Michael Marshall, Senior Project Manager 4.0 OBSERVATIONS During the site audit, the NRC staff participated in detailed discussions throughout the presentations and observed the testbed performing scenarios relevant to the HFE aspects of the Limerick digital I&C upgrade. The staff did not identify any issues with the methodology presented by the subject matter experts nor did the staff observe any substantial issues with the HSSL functioning as a testbed during the PV workshop. Participants who operated the testbed did provide feedback on their experience and developmental issues. Staff observed the exchange between participants and the design team regarding these details, which are expected to contribute to further refinement of HSI design and the associated procedures. The staff confirmed with the Limerick HFE team that the plant modification tracking system is adequate for tracking issues and will continue throughout the validation process.
During the audit, the licensee presented an overview of the modification plans with a focus on how the HSIs will be upgraded and how existing systems (Reactor Protection System, Nuclear Steam Supply Shutoff System, Emergency Core Cooling System, and Plant Protection System) will be combined into one system. The presentations detailed extensive changes to the control room design including some updates which will yield digital mimics of the current HSI in place while other HSI would change in arrangement, design, and presentation. The automation which supports the integration of operations from the combined systems into a single operating system was also included in the presentations.
The NRC staff engaged in discussions regarding the proposed changes and the iterative process used to develop the HSI design changes to the control room. This iterative practice laid the groundwork for the verification and validation (V&V) process for the modernization project.
Following the presentations, the staff conducted a walkthrough of the testbed and observed scenarios. These scenarios demonstrated operator actions, with post scenario feedback being given to the design team that contributed both to the iterative process of design development and to the identification and tracking of issues. In total, staff observed the completion of nine operational scenarios which included initial monitoring and conducting Emergency Operating Procedures (EOPs) to test a range of important human actions. The scenarios evolved from information gathered from the functional requirements analysis and function allocation (FRA&FA) and task analysis (TA) results. This was described to the staff during the presentations as an iterative process used to not only identify the tasks but also to develop the HSIs and refine the testbed. The details of the FRA&FA and TA were provided in the LAR for staffs review. The scenarios and associated simulator exercise guides (SEG) were used in the CV workshop and subsequently used in the PV as well with minor adjustments. Each scenario required operators to manage one or more events in which necessary tasks were grouped in a specific manner. The tasks were grouped in a logical manner to ensure the proper context was considered for clear observation. The staff was given SEGs during the scenarios to examine and follow along in real time. The SEGs detail the events, personnel roles, tasks to manage events, directions for the simulator driver, and instructions for the simulator operator to follow during each scenario. Staff observed that the SEGs used for these scenarios appropriately identified critical tasks that needed to be completed by the operators and provided reasonable measures and criteria to evaluate whether the tasks were successfully performed.
The licensee presented on the limitations of the testbed, including describing the systems in the testbed which are currently functioning, and which are planned to be operational when the integrated system validation (ISV) is performed. The descriptions included a primer on how the testbed simulates the behavior of the new design via simulated annunciators, audio cues, simulated lighting, and mock controls. The staff challenged the presenters on how the limitations may affect the validity of PV results regarding timing. The licensee explained the spatial elements of the testbed were developed from 3-D modeling to contribute to accuracy and then described how the limitation in functionality provides a negative time bias in the execution of control actions. The operation of the testbed was observed by the staff during the walkthrough portion of the audit.
INL presented the process for HFE V&V of the modified control room design and the associated timeline. The process described involves an iterative practice involving early testing activities at multiple points in the timeline. As detailed in the LAR, this includes the task support verification and the CV workshop. The iterative process entails thorough and efficient feedback and communications between the design team and the operators. The staff discussed the development of training and procedures associated with the modernization project. The licensee acknowledged that, due to the digital upgrade, the procedures will either need to be changed or the digital controls will need to conform to the steps in the current procedures. During the discussions, INL communicated that automated operator aids will be introduced with the updated design. INL also stated that the process will allow the distinction between issues with the HSI, issues with procedural development to address the changes and issues requiring an update to training materials.
The scope of the plant protection system (PPS) modification also includes upgrading the Redundant Reactivity Control System (RRCS) with the Westinghouse Ovation programmable logic controller (PLC) platform. The PPS provides relevant plant/system data on the HSIs and additionally interfaces with the non-safety Distributed Control System (DCS) to provide various information including annunciation signals. Constellation selected Westinghouse to provide the new digital system which, is based on the NRC-approved Westinghouse Common QTM platform.
The NRC staff also confirmed during the PV workshop that the DCS will be operational during the ISV.
Testbed Walkthrough The staff observed the representation of the proposed updated control room in the testbed -
including annunciators, heads-up display screens which mimics the current annunciators (which will not change) and proposed modifications. The testbed represented the spatial elements of control room changes with components which mimic changes to the operator workstations and the new video display units (VDUs) introduced by the modernization. The updated operator workstations (ovation) demonstrate that anthropometric considerations in HSI design development are consistent with the current control room design. This testbed facility used a combination of dynamic and static HSIs that were grouped in a manner that approximated the configuration and spatial orientation of the intended, modified control room design. Both the safety (Common Q) and non-safety (Ovation) portions of the system are emulated.
The staff selected certain portions of the Common Q and Ovation HSIs for a detailed examination and further questioning of the licensee, vendor, and laboratory staff. The portions sampled reflected systems and operations that are of high safety significance for the design.
Specifically, this included the Common Q interface for operation of the Automatic Depressurization System (ADS) and Safety Relief Valves (SRVs), as well as the Ovation interface for the DCS to be used in the event of a common cause failure of Common Q channels.
While observing multiple scenarios with the scenario guides in the testbed, the licensee explained the platform used for the simulations is Ovation. The staff observed where the reactor operator (RO), Plant RO, Senior RO, and the Shift Technical Advisor interacts with the HSI on the specific workstations represented in the testbed as described by the licensee during the walkthrough. Through various scenarios, the staff perceived the overall intent of the enhancements to the control room design as eliminating distractions for the operator which resulted in some automated tasks, some actions previously requiring local plant operations to a simplified task in the control room and a decrease in the time necessary for monitoring and task completion. This includes the performance of EOPs to address emergencies much faster than when an auxiliary operator had to be dispatched or when valves needed to be manually operated. The digital upgrade introduces new automation that helps integrated operations and increases crew efficiency by facilitating certain actions being done in seconds from the control room, thereby reducing workload and secondary transients.
The staff observed firsthand the testbed components as described in the PV results summary report via scenarios selected to showcase the operator actions and how the testbed simulates the control room. This includes upgraded annunciator panels which reflect the new single system - PPS, the ovation DCS VDUs, updated reactor operator workstations with five new VDUs (four Common Q PPS VDUs and one Ovation DCS VDU) and the existing benchboard indicators and controls adjacent to the new HSI. The staff did not observe any deviations from the overview of the method to perform conceptual verification referenced in, or from the execution of scenarios described by, the PV report.
Testbed Limitations In the testbed, the NRC staff observed 27 vertical large screen displays and other smaller workstations - largely representing the plant as configured. There were spatial limitations in the curvature of some of the panels but the overall effect on the mimic of the control room is minimal. The representation for the analog controls (those controls that are not affected by this LAR) was not physically functional and was represented by digital versions. The operators would point to the representation of the control and indicate what their intended action was for those displays, resulting in a simulation worker manipulating the testbed for the appropriate reaction (this is referred to as the man behind the curtain or wizard of oz technique). For the Ovation platform, controls were operational.
The NRC staff questioned how the limitations of the testbed may affect the timing associated with manual action in the scenario events. INL and Constellation described that times associated with the actions performed in the digital testbed were like the timing of the actions established in the existing analog based control room. Specifically, the staff asked how timing associated with the manual actions under study compares with the timing in the existing analog control room considering the performance with the digital interface in the HSSL. The licensee described that the time necessary to complete the manual actions were similar and in multiple instances less time was necessary even with the HSSL incorporating methods to create a conservative, negative time bias. This was observed during the execution of the scenarios involving the wizard of oz technique, which introduces a delay which resulted in a conservative result when measuring both time to perform and time to implement for manual actions. The timing comparisons of the HSSL to the existing completion times developed from scenario Operational Sequence Diagrams were to be included in the PV report.
The NRC staff also observed small adjustments which deviate from a fully functional simulator such as using commercially purchased palm actuated alarm acknowledge pushbuttons, along with battery powered audio and visual cues being provided to operators in spatially accurate locations relative to associated displays. These were not integrated or physically connected to the testbed alarm system; however, they were easily observed when used by operators. The wizard of oz technique was used to disengage the alarms when the observed crew members pressed the button to acknowledge the alarm. Also, INL staff adjusted the lighting to simulate the environment in the Limerick control room and intervened to supply expected equipment responses using the wizard of oz technique. However, the staff noted that in these instances, the overall flow, sequencing, and timing of crew actions was maintained with a realistic degree of fidelity.
The limitations of the testbed were communicated to the crew to distinguish between things that are not included in the design and what is included but what is currently not simulated. The staff noted that the simulator model has not yet been fully developed by the vendor, which necessitated the use of simulator staff manipulation to facilitate the validation activities.
Licensee representatives informed the staff that simulator model development is expected to be complete prior to the conduct of the ISV.
The staff noted that the ADS and SRVs interface appeared to provide an easily readable and readily usable interface that operators were able to effectively interact with during the scenarios.
However, the staff noted the DCS functionality in Ovation had not yet been fully integrated, such that the crew could not manipulate the full range of functions provided by that interface. The staff confirmed with the licensee that the DCS will be fully integrated and functional prior to the conduct of the ISV.
5.0 AUDIT CONCLUSION The testbed provided the NRC staff an understanding of the process for analyzing the digital I&C upgrades for HFE implications, modifications to the control room as represented in the test bed, the adjustment to the manual actions, the intended improvements of the digital upgrades and the spatial elements of the control room upgrades. The dynamic capability of the testbed was generally adequate to allow for the modified important human actions to be exercised as part of validation scenarios, to include implementation of the associated plant procedures by a representative crew of qualified operators. Thorough and efficient interaction between the design team and the operators for the iterative process was demonstrated through the nine scenarios observed to provide the staff with an understanding of the process of gathering operator input for the HSI development. This was observed at the conclusion of each scenario via rollup that included the completion of workload and situational awareness questionnaires by the validation crew. Additionally, the operators were queried to identify any potential issues with, and desired changes for, the HSI design.
The NRC staff was able to fulfill the following objectives:
Gain a clear understanding of the proposed control room changes, including the differences between the old human system interface and the proposed human system interface.
Gain an understanding of the limitations associated with testbed, including the capabilities of the glasstop simulator, as well as any known deviations from the actual simulator/control room.
Gain an understanding of any early design issues, including any discovered human engineering discrepancies and tracking, prioritization, and resolution of issues.
Observe that adequate validation techniques were used during the workshop in accordance with the NUREG-0711 based Human Factors Engineering Program Plan submitted as part of the LAR.
The NRC staff will continue to review docketed material submitted to supplement the activities observed at the PV workshop and the associated PV results summary report.
The site audit was completed on February 23, 2023.
ML25010A151 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL1/LA NRR/DRO/IOLB/BC NAME RKuntz KEntz JAnderson DATE 1/28/2025 1/28/2025 2/3/2025 OFFICE NRR/DORL/LPL1/BC NRR/DORL/LPL3/PM NAME HGonzález RKuntz DATE 2/7/2025 2/7/2025