IR 05000346/2022040

95001 Supplemental Inspection Report 05000346/2022040 and Follow-Up Assessment Letter

ML22314A225
Person / Time
Site:	Davis Besse
Issue date:	11/10/2022
From:	Richard Skokowski NRC/RGN-III/DORS/EB2
To:	Tony Brown Energy Harbor Nuclear Corp
References
IR 2022040
Download: ML22314A225 (14)

Text

SUBJECT:

DAVIS-BESSE NUCLEAR POWER STATION - 95001 SUPPLEMENTAL INSPECTION SUPPLEMENTAL REPORT 05000346/2022040 AND FOLLOW-UP ASSESSMENT LETTER

Dear Terry Brown:

On September 27, 2022, the U.S. Nuclear Regulatory Commission (NRC) completed a supplemental inspection using Inspection Procedure 95001, "Supplemental Inspection Response to Action Matrix Column 2 (Regulatory Response) Inputs, and discussed the results of this inspection with you and other members of your staff. The NRC discussed the implementation of your corrective actions with you and other members of your staff. The results of this inspection are documented in the enclosed report.

The NRC performed this inspection to review your stations actions in response to a White finding in the Mitigating Systems cornerstone which was documented and finalized in NRC Inspection Report 05000346/2021092. On June 22, 2022, you informed the NRC that your station was ready for the supplemental inspection.

The NRC determined that your staffs evaluation identified the cause of the White finding.

Specifically, your staff determined that the root cause of Davis-Besses failing to select a speed switch which was suitable for operation within the safety-related Emergency Diesel Generators (EDGs), which resulted in the unavailability and inoperability of the Division 2 EDG when it was being relied upon for plant safety, was less than adequate incorporation, internalization, and anchoring of operating and in-house experiences as it pertains to the unique design vulnerabilities in the direct current (DC) distribution system.

The inspectors concluded the corrective actions to preclude repetition of the root of the White performance issue were effective and adequately prioritized considering safety significance and regulatory compliance. In addition, the inspectors determined evaluations were documented at a sufficient level of detail, included relevant operating experience, and identified the root causes, extent of conditions, and extent of causes of the performance issue. Based on the results of the inspection, the inspectors concluded the objectives of the Inspection Procedure (IP) were met.November 10, 2022 The NRC determined that completed or planned corrective actions were sufficient to address the performance issue that led to the White finding. Therefore, the performance issue will not be considered as an Action Matrix input after the end of the third quarter of 2022. Nonetheless, because of the existing security-related greater-than-green finding, Davis-Besse will remain in Action Matrix Column 2 (Regulatory Response).

No findings or violations of more than minor significance were identified during this inspection.

Although, two corrective actions to prevent recurrence were documented and will be tracked for subsequent NRC inspection follow-up.

This letter, its enclosure, and your response (if any) will be made available for public inspection and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document Room in accordance with Title 10 of the Code of Federal Regulations 2.390, Public Inspections, Exemptions, Requests for Withholding.

Sincerely, Richard A. Skokowski, Chief Engineering Branch 2 Division of Operating Reactor Safety Docket No. 05000346 License No. NPF-3

Enclosure:

As stated

Inspection Report

Docket Number: 05000346

License Number: NPF-3

Report Number: 05000346/2022040

Licensee: Energy Harbor Nuclear Corp.

Facility: Davis-Besse Nuclear Power Station

Location: Oak Harbor, OH

Inspection Dates: August 29, 2022 to September 27, 2022

Inspectors: I. Hafeez, Senior Reactor Inspector

Approved By: Richard A. Skokowski, Chief Engineering Branch 2 Division of Operating Reactor Safety

Enclosure

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting a 95001 supplemental inspection at Davis-Besse Nuclear Power Station, in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs program for overseeing the safe operation of commercial nuclear power reactors.

Refer to https://www.nrc.gov/reactors/operating/oversight.html for more information.

List of Findings and Violations

No findings or violations of more than minor significance were identified.

Additional Tracking Items

Type Issue Number Title Report Status Section NOV 05000346/2021050-05 Failure to Install Emergency 95001 Closed Diesel Generator Parts that were Suitable to the Application LER 05000346/2021-001-00 LER 2021-001-00 for 95001 Discussed Davis-Besse Nuclear Power Station, Unit 1, Emergency Diesel Generator Speed Switch Failure due to Direct Current System Ground

INSPECTION SCOPES

Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with their attached revision histories are located on the public website at http://www.nrc.gov/reading-rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared complete when the IP requirements most appropriate to the inspection activity were met consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection Program - Operations Phase. The inspectors reviewed selected procedures and records, observed activities, and interviewed personnel to assess licensee performance and compliance with Commission rules and regulations, license conditions, site procedures, and standards.

OTHER ACTIVITIES

- TEMPORARY INSTRUCTIONS, INFREQUENT AND ABNORMAL

===95001 - Supplemental Inspection Response to Action Matrix Column 2 (Regulatory Response) Inputs

The inspectors reviewed and selectively challenged aspects of Davis-Besses problem identification, causal analysis, and corrective actions in response to a White finding and related violation to comply with Title 10 of the Code of Federal Regulations Part 50, Appendix B, Criterion III, Design Control. Notification of the NRCs updated assessments were documented in Inspection Reports 05000346/2021050, 05000346/2021090, and 050003446/2021092 (ADAMS Accession Nos. ML21321A365, ML21340A221, and ML21356A058).

Supplemental Inspection Response to Action Matrix Column 2 (Regulatory Response) Inputs

=

(1) From August 29 to September 27, 2022, the inspectors conducted onsite and in-office reviews review to verify all aspects of the Inspection Procedure were met.

This performance issue was previously documented in the inspection reports listed above.

INSPECTION RESULTS

Assessment 95001 1. Problem Identification

a.

Identification. The finding involved the failure to select a replacement for the emergency diesel generator (EDG) speed switch that was suitable to the application.

The issue was self-revealed on September 4, 2020, when Division 2 EDG (EDG 2)failed to start during a scheduled monthly surveillance test. This issue was documented in the licensees corrective action program in Condition Report (CR) -2020-06947.

The direct current (DC) system at Davis-Besse is designed as an ungrounded system. When a component on the DC system fails, it is possible that the failed component will short to ground. The design of the system as ungrounded permits the system to continue to operate correctly even in the presence of a short to ground.

The speed switch design was not compatible with the stations 125/250 Volts direct current (Vdc) battery system. The speed switch design contained a subcomponent that was rated for 170 Vdc but was exposed to a voltage potential in excess of its rating (approximately 201 Vdc). The long-term exposure to this voltage potential degraded this subcomponent and contributed to its failure. When another component on the 125/250 Vdc system grounded, the result was a failure of the subcomponent and speed switch to which it was integral. The failure of the speed switch resulted in the failure of the EDG to start during testing on September 4, 2020. The failed speed switch was identified and replaced on September 7, 2020, restoring the EDG to an operable status.

b.

Exposure Time. Following a review of recorded data, the speed switch was reasonably known to be in a failed condition from early August 29, 2020, until September 7, 2020. During this window, EDG 2 was unavailable; an exposure time of 9 days.

c.

Identification Opportunities. In general, Davis-Besse appropriately considered site and industry operating experience. In this instance, they identified a missed opportunity from 2010 involving the DC system voltages when grounds are present.

As discussed below, under a specific set of circumstances, the floating ground DC system can see elevated voltages when grounds occur.

In 2010, during the investigation of a failure of the Auxiliary Feedwater System (AFW)

Target Rock position control boards Davis-Besse found that multiple grounds on the 250 Vdc floating ground DC system could apply up to 280 Vdc across components and grounded components should be rated for the full potential voltage. The extent of condition evaluation at that time determined that only the AFW Target Rock position control boards were susceptible to this issue. The root cause evaluation (RCE)determined the design was adequate, and the preventive actions focused on improving prioritization of resolving DC grounds. As such, no revisions were made to any design documents concerning potential voltage across DC components as a result of the 2010 event. The corrective actions for CR-G201-2010-81205, and the associated condition report CR-G201-2010-81273, were focused on eliminating the latent design issues associated with identified position controllers and understanding the extent of vulnerability once the latent issue had been identified. Corrective actions for CR-G201-2010-81273 (SR) were focused on promptly eliminating DC grounds.

Opportunities to capture lessons learned from the susceptibility of grounded components (i.e., surge protection and filters) having higher than normal DC voltage and updating design documents (Specifications, System Descriptions, or the Design Criteria Manual) to identify the maximum voltage on the DC bus were missed.

Corrective actions associate with the speed switch failure are expected to address this previously missed opportunity. (CA-2022-0079-001)

d.

Risk and Compliance. The RCE documented that the risks associated with the unknown internal configuration of the speed switches (e.g., internal metal-oxide varistors motor-operated valves (MOVs) which were grounded) were never evaluated during the generation of the Part/Component Equivalent Replacement Package. The RCE also documented the corrective actions encompassing the safety culture aspects of design margins, documentation, training, challenging the unknown and operating experience. Based on their review, the inspectors concluded the RCE demonstrated an understanding of the significant plant consequences and compliance concerns associated with the event and the White performance issue.

The NRCs risk evaluation of Davis-Besses White performance issue was documented in prior inspection report(s) most recently Inspection Report(s)05000346/2021090.

NRC Assessment: The inspectors determined that the licensee appropriately evaluated and documented problem identification, including adequate considerations of identification credit, how long the condition had existed, missed opportunities for self-identification, and risk insights. The inspectors had the following observations:

As identified in the licensees missed opportunity write-up and in their causal factor analysis, when multiple grounds are present in the DC system and depending on the location of the grounds, components installed on the 125 Vdc buses can be exposed to voltages as high as 280 Vdc. The licensee concluded that, because this performance characteristic was not documented or well known, it contributed to this event. The inspectors agreed with the licensees assessment.

As identified in the licensees causal factor analysis, following the 2010 event, no design documents were updated to include information about DC system performance when grounds are present in the system. The licensee concluded that the failure to add this information to the design documents following the event in 2010 contributed to this event. The inspectors agreed with the licensees assessment.

As identified in the licensees causal factor analysis, the design of the internal components of the speed switch were unknown to engineering staff when they concluded that the component was acceptable as a replacement for the previous speed switch. The licensee concluded that engineering staff did not sufficiently evaluate the EDG speed switch component design to ensure it was appropriate. The inspectors agreed with the licensees assessment.

As identified in the licensees causal factor analysis, the unique design of the DC system being a 250 Vdc floating ground system with a normally energized DC ground detection system was not fully understood by the Engineers. On this point the inspectors accepted the licensees assessment and recognized the planned training needs analysis as a reasonable first step for exploring, defining, and closing a gap in knowledge.

General Weakness - Problem Identification, Section 1.a: The inspectors determined that, engineering staff missed or misunderstood the function of the ground connection in the speed switch. The original speed switch had a ground connection that only supported the function of personnel protection (e.g., chassis ground). The replacement speed switch had a ground connection, but this ground connection supported a surge suppression function. This function caused the new speed switch to behave differently than the previous model when grounds, potentially even a single ground, were present on the 125 Vdc system and this aspect of the speed switch design contributed to the failure.

Assessment 95001

2. Causal Analysis

a.

Methodology. The root cause evaluation (RCE) employed systematic, evidence-based methodologies including TapRoot methodology along with Event &

Causal Factors Charting, Organizational Effectiveness Evaluation, Performance Gap Analysis, and Barrier

Analysis.

Root

Cause:

The final version captured one Root Cause and four Causal Factors.

The licensee determined that the Root Cause of Davis-Besse failing to select a speed switch which was suitable for operation within the safety-related Emergency Diesel Generators (EDG) which resulted in the unavailability and inoperability of the Division 2 EDG when it was relied upon for plant safety was less than adequate incorporation, internalization, and anchoring of operating and in-house experiences as it pertains to the unique design vulnerabilities in the direct current (DC) distribution system. Causal Factors were discussed in the NRC Assessment as documented in the previous section of this report.

b.

Level of Detail. The inspectors determined the RCE, in aggregate, was performed in a manner commensurate with the safety significance and complexity of the performance issue and was of sufficient detail to identify the root and contributing causes, extent of conditions, and extent of causes.

The RCE teams utilized a formal cause analysis process to identify the problems and determine corrective actions. The RCEs were performed by individuals in the licensees organization with varying levels of experience and backgrounds.

c.

Operating Experience. The inspectors determined that, as a result of this event, Davis-Besses efforts to identify operating experience appropriately considered prior speed switch failures, DC system design issues, industry and agency operating experience.

d.

Extent of Condition and

Cause.

The inspectors determined that Davis-Besse appropriately identified the extent of condition and extent of cause. In general, to accomplish the extent of condition review, Davis-Besse conducted an evaluation to assess many reliability concerns, including Title 10 of the Code of Federal Regulations Part 21 Notices related to the EDG speed switch (EDG Reliability Evaluation Report, CR-2021-04529-ATA-19105). A portion of that report included an independent review of the subject by MPR (Enclosure to MPR letter dated August 20, 2021, 0200-0212-LTR-002 Rev 0). This review focused on safety-related components on the 125 Vdc buses and concluded that system components would not experience degradation and/or failure due to voltage conditions to ground which may be as high as 280 Vdc.

In general, to accomplish the extent of cause, Davis-Besse conducted a search of corrective action documents across the Energy Harbor fleet that were characterized as either an Apparent Cause or Root Cause and that contained the characterization of industry or in-house experience relating to a current problem existed previous to the problem but was not assimilated by the organization. For instance, a similar characterization as the root cause for the failed speed switch. The licensee concluded that issues rising to the level of root causes resulting from failure to incorporate industry or in-house operating experience is not a common occurrence within the Energy Harbor fleet nor is it common to any one specific site. The extent of cause is negligible with corrective actions generated to address the root cause, failure to incorporate, internalize and anchor operating experiences and the direct cause of internal components being subject to voltages greater than design.

e.

Safety Culture. The inspectors determined the safety culture components referenced in NUREG-2165, Safety Culture Common Language, were appropriately considered during the licensees evaluations of the root cause, extent of condition, and extent of cause.

NRC Assessment: The inspectors review concluded Davis-Besses RCE contained two general weaknesses. First weakness was in Problem Identification and second was in Level of Detail. For more details, see Sections 1.a and 3.a respectively.

Generally, the evaluation contained the appropriate level of detail, relevant operating experience, root causes, contributing causes (causal factors), extent of conditions, and extent of causes for the White performance issue. Additionally, the inspectors determined the licensees RCE appropriately considered the safety culture aspects related to the failure of the EDG speed switch.

Assessment 95001

3. Corrective Actions

a. Corrective Actions

to Preclude Repetition. The inspectors concluded that corrective actions planned or taken to preclude repetition of the Davis-Besse White performance issue were appropriate, timely, and commensurate with the safety significance of the issue. The inspectors noted the following seven corrective actions while reviewing Davis-Besses root cause evaluation (RCE).

(1) Completed

(a) Davis-Besse took the following corrective actions following failure of the Emergency Diesel Generator (EDG) speed switch.

1. ODMI 21-04 was issued with guidance to maintain EDGs on normal control power while recognizing the vulnerability of the installed speed switches. This guidance was in place while corrective actions were underdevelopment and during implementation.

2. The work order 200629726 replaced the original speed switch with a new design according to the Part/Component Equivalent Replacement Package (PERP) process. This work was completed on October 2, 2019.

3. Work Order 200861035: Replaced speed switch ST6221 on EDG 1-1.

This model uses 24 VDC input power, requires the addition of an external power supply, and is capable of withstanding full voltage within the direct current (DC) ground detection system. This work was completed on January 7, 2022.

4. Work Order 200861036: Replaced speed switch ST6231 on EDG 1-2.

This model uses 24 VDC input power requires the addition of an external power supply and is capable of withstanding full voltage within the DC ground detection system. This work was completed on January 20, 2022.

(b) Davis-Besse identified the following corrective actions to preclude repetition of the speed switch failure.

1. Added DC system voltage to ground configuration of the DC electrical distribution system to the Design Criteria Manual. Include verbiage from IEEE 946-2004 guidance; for ungrounded 250 Vdc split bus systems, including surge and filter protection, components should be rated for the full system voltage to ground (280 Vdc during equalizing charge).

(CA-2022-00079-001)

2. Added DC System voltage to ground to appropriate DC system specifications. Include verbiage from IEEE 946-2004 guidance; for ungrounded 250 Vdc split bus systems, including surge and filter protection, components should be rated for the full system voltage to ground (280 Vdc during equalizing charge). (CA-2022-00079-002)

3. Added a discussion to applicable system descriptions to document typical DC System Voltages to Ground. Include verbiage from IEEE 946-2004 guidance; for ungrounded 250 Vdc split bus systems, including surge and filter protection, components should be rated for the full system voltage to ground (280 Vdc during equalizing charge). (CA-2022-00079-003)

(c) Effectiveness Review. The inspectors determined that effectiveness reviews were not completed for the corresponding completed corrective actions to preclude repetition at the time of the supplemental inspection. The inspectors determined that an effectiveness review for completed actions could be reviewed during the effectiveness reviews for planned corrective actions discussed below.

(2) Planned

(a) Upon completion of CA-2022-00079-001, -002, & -003; the licensee plans to generate a training need analysis to analyze the need for Work Group Specific training on the 125/250V and 120 Vdc System and the Ground Detection System following the revision of the base engineering documents.

This is a potential Corrective action review board (CARB) review action so the CARB can evaluate the results of the training needs analysis and direct appropriate follow-up actions. (CA-2022-00079-004)

(b) Effectiveness Review. The inspectors determined that the effectiveness review actions established by Davis-Besse for planned corrective actions were appropriate. The inspectors concluded the actions, owners, and due dates were appropriate and commensurate with the corresponding corrective action to preclude repetition. (ER-2022-00079-1)

NRC Assessment: The inspectors concluded the dates for implementation and completion of the planned root and contributing cause corrective actions were reasonable, effective, and prioritized with consideration for risk significance and regulatory compliance. The inspectors also concluded the licensee established reasonable measures of success to evaluate the effectiveness of the corrective actions.

When complete, the NRC plans to inspect and assess the planned corrective action to prevent recurrence identified in Section 3(2)(a).

General Weakness - Level of Detail, Section 3.a: The inspectors determined the previous planned corrective actions were narrowly tailored. The licensees planned approach was to modify the DC system description and ground busting procedures.

Specifically, programmatic aspects, like guidance associated with maintenance and test procedures or personnel protection requirements, due to the potential for the 125 Vdc system to have voltages as high as 280 Vdc were not identified as needing review.

Subsequently, the licensee created two corrective actions documents to review procedures to ensure that they contain appropriate guidance. The procedure improvements will be reviewed during a future inspection (CA-2022-00079-004).

Upon the completion of the RCE review, the inspectors concluded that, in general, the dates for implementation and completion of the planned root cause corrective actions were reasonable, effective, and prioritized with consideration for risk significance and regulatory compliance. The inspectors also concluded the licensee established reasonable measures of success to evaluate the effectiveness of the corrective actions.

Additionally, the inspectors informed Davis-Besse that the NRC has plans to inspect and assess the planned corrective action to preclude repetitions upon their completion. These planned corrective actions are annotated below and summarized previously in the planned corrective actions to preclude repetition, Section 3.(2)(a) of this report. The NRC is tracking these as open items in an NRC internal reactor program system database which is used for inspections, inspection scheduling, and reporting:

CA-2022-00079-004, for the needs assessment and any subsequent actions associated with the results of the needs analysis.

ER-2022-00079-1, for the effectiveness review of corrective actions planned or taken.

Assessment 95001 4. Conclusion

The inspectors concluded the corrective actions to preclude repetition of the root and contributing causes (causal factors) of the White performance issue were effective and adequately prioritized considering safety significance and regulatory compliance. In addition, the inspectors determined evaluations were documented at a sufficient level of detail, included relevant operating experience, and identified the root causes, extent of conditions, and extent of causes of the performance issue. Based on the results of the inspections, the inspectors concluded the objectives of the IP were met.

LER LER 2021-001-00 for Davis-Besse Nuclear Power Station, 95001 (Discussed) Unit 1, Emergency Diesel Generator Speed Switch Failure due to Direct Current System Ground LER 05000346/2021-001-00

Description:

The inspectors reviewed aspects of Licensee Event Report (LER) 2021-001, Emergency Diesel Generator Speed Switch Failure due to Direct Current System Ground.

LER 2021- (ADAMS Accession Number ML21105A489). This review was insufficient to close the LER. The results of this inspection should be considered during subsequent reviews and closure of the LER. This LER remains Open.

EXIT MEETINGS AND DEBRIEFS

The inspectors verified no proprietary information was retained or documented in this report.

On September 27, 2022, the inspectors presented the 95001 supplemental inspection results to Terry Brown, Site Vice President and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection Type Designation Description or Title Revision or

Procedure Date

95001 Calculations C-EE-002.01-013 125/250 VDC Distribution System Ground Detection 0

Corrective Action CR-2020-06691 Bus 2 DC Sys GRND 1097 in Alarm 08/25/2020

Documents CR-2020-06856 Abnormal DC MCC2 Ground Indication 09/01/2020

CR-2020-06947 Lockout of EDG#2 during Monthly Test 09/04/2020

CR-2021-00920 EDG2 Speed Switch Failure from 9/4/2020 Past Operability 02/12/2021

CR-2021-04070 CFAM Elevation: Emergency Diesel Generator Reliability 06/28/2021

CR-2021-04520 Negative Trend in EDG Reliability during Cycle 22 06/08/2021

CR-2021-05173 NRC Identified Concern Regarding Potentially Inadequate 07/07/2021

Part 21s Leading to EDG Failures

CR-2021-05657 2021 EDG Reliability Evaluation: Speed Switch Design 07/26/2021

Concern for Application in DC System

CR-2021-06400 2021 INPO AFI: ER.2 Reliability of the Emergency Diesel 08/24/2021

Generator(EDG) Safety System

CR-2022-00079 NRC Apparent Violation: Failure to Install EDG Speed Switch 01/05/2022

that Was Suitable to the Application

Corrective Action CR-2022-06750 NRC 2022 EDG Inspection: Potential Failure Mechanism for 09/01/2022

Documents EDG Speed switches not Identified for EDG Speed Switch

Resulting from Failure

Inspection CR-2022-07124 Response to NRC 95001 Speed Switch Evaluation Comment 09/20/2022

CR-2022-07126 Remaining NRC Concerns for 95001 EDG Speed Switch 09/20/2022

Inspection

Drawings B15702501 Schematic Diagram Engine Control for Emergency Diesel T22

Generator 1-1

B157F02504 Full Line Wiring Diagram-Engine Control Sub-Panel 17

E-542 SH. 2A Connection Diagram 125/250 VDC & 120V Instrument AC 5

Power Source & Dist. Equip. (Channels 2 & B)

E-6 SH.4 125/250 V.D.C. MCC No.2 (Essential) Single Line Diagram 34

E-7 125/250 DC and Instrumentation AC One Line Diagram 54

Miscellaneous M-180-00093 Vender Manual Synchro-Start Electronic Speed Switches 07/24/1973

and Mini-Gen Signal Generator

Procedures DB-OP-06322 Locating Grounds on the Station 250/125VDC System 10

NOBP-CC-7007 Part Interchangeability Evaluation 2

Inspection Type Designation Description or Title Revision or

Procedure Date

NOBP-ER-3015 License Renewal Implementation Guidelines 3

NOP-CC-2003 Engineering Changes 27

NOP-CC-2007 Part/Component Equivalent Replacement Packages 03

NOP-CC-7002 Procurement Engineering 14

Work Orders 200629727 200629727 11/12/2020

200859702 FunctionalLocationDescription: 08/04/2021

DG1-1SPEEDTRANSMITTER

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