SVPLTR 20-0037, Response to Apparent Violation in NRC Inspection Report 05000237/2020012 and 05000249/2020012; EA-20-053

Response to Apparent Violation in NRC Inspection Report 05000237/2020012 and 05000249/2020012; EA-20-053

ML20184A260
Person / Time
Site:	Dresden
Issue date:	07/02/2020
From:	Karaba P Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EA-20-053, IR 2020012, SVPLTR 20-0037
Download: ML20184A260 (19)

Text

Exelon Generation Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450 July 2, 2020 SVPLTR: #20-0037 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249

Subject:

Response to Apparent Violation in NRC Inspection Report 05000237/2020012 And 05000249/2020012; EA-20-053

Reference:

Letter from D. Curtis (NRC) to B. Hanson (EGC), "DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3 - NRC INSPECTION REPORT 05000237/2020012 AND 05000249/2020012 AND APPARENT VIOLATION,"

dated May 19, 2020 In the referenced letter, the Nuclear Regulatory Commission (NRC) notified Exelon Generation Company, LLC (EGC) of an Apparent Violation (AV) of 10 CFR 50.59 at Dresden Nuclear Power Station (DNPS). The AV is being considered for escalated enforcement consistent with the NRC Enforcement Policy. The AV is associated with a 50.59 evaluation for a change to the DNPS Updated Final Safety Analysis Report (UFSAR) Section 9.2.5.3.1, identified during the NRC Ultimate Heat Sink (UHS) Inspection completed April 24, 2020.

The deficiency identified in the 50.59 evaluation was entered into the EGC Corrective Action Program (CAP) and a Corrective Action Program Evaluation (CAPE) was performed. Based on this evaluation and the referenced letter, the enclosure to this letter contains the response which includes: (1) restatement of the Apparent Violation, (2) reasons for the Apparent Violation, (3) corrective steps taken and results achieved, (4) corrective steps that will be taken, (5) the date when full compliance was achieved, and (6) additional information for consideration.

July 2, 2020 U.S. Nuclear Regulatory Commission Page 2 With respect to the severity level of the Apparent Violation , EGC advocates that the proper characterization is Severity Level IV. The basis supporting this position is discussed in the enclosure.

A revised 50.59 Evaluation has been provided to the NRC.

No regulatory commitments are contained in this letter. If there are any questions concerning this letter, please contact Ryan Sprengel, Regulatory Assurance Manager, at (815) 416-2800.

Respectfully,

~-

Peter J. Karaba Site Vice President, Dresden Nuclear Power Station cc: NRC Regional Administrator, Region Ill NRC Project Manager, NRR - Dresden Nuclear Power Station NRC Senior Resident Inspector, Dresden Nuclear Power Station K. Stoedter, NRC Branch Chief

Enclosure:

Response to Apparent Violation Described in NRC Inspection Report 0500023712020012 and 05000249/2020012

Enclosure Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25

Response to Apparent Violation Described in NRC Inspection Report 05000237/202001 2 and 05000249/2020012 Restatement of the Apparent Violation As stated in Inspection Report 2020-012 (Reference 2):

The inspectors identified an Apparent Violation (AV) of 10 CFR 50.59, "Changes, Tests, and Experiments," for the licensee's failure to have a written evaluation which provided the bases for determining a change made pursuant to 10 CFR 50.59(c) did not require a license amendment. Specifically, the licensee approved a change to the Updated Final Safety Analysis Report (UFSAR) which reduced the Ultimate Heat Sink (UHS) coping time and capacity from four days to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. This evaluation failed to provide a basis for the determination that the change would not result in more than a minimal increase in the likelihood of occurrence of a malfunction of the DGCW system previously evaluated in the UFSAR.

Reasons for the Apparent Violation As stated above, the Apparent Violation is for a failure to document a technical basis in the written 50.59 evaluation conclusion that the change did not result in more than a minimal increase in the likelihood of a malfunction of a structure, system, or component (SSC) previously evaluated. Exelon Generation Company, LLC (EGC) performed a Corrective Action Program Evaluation (CAPE) to identify why the 50.59 evaluation did not document sufficient technical basis to support the conclusion. It was determined that plant personnel did not translate their extensive knowledge, history, and background of the inputs and considerations into the 50.59 evaluation documentation; high level statements were made without quantitative, in-depth documentation to support the conclusions.

UHS bathymetric assessment results from 2018 and 2019 were viewed from the standpoint that the reduced volume in the UHS was the result of a buildup of sedimentation on the floor of the UHS. Therefore, the height and volume of water above the critical SSC parameters were unchanged and existing calculational margins were thought to be maintained.

Additionally, there was a general position that the existing calculations demonstrated adequate margin . Assumptions of the impacts on heat capacity and temperature from volume changes due to silting, and the resulting effect on pump performance were not adequately documented. The failure to document these aspects with technical rigor within the 50.59 evaluation resulted in the conclusions of the 50.59 not being adequately supported.

Corrective steps taken and results achieved Based on assumptions made and the subsequent failure to adequately document a sufficient supporting basis in the 50.59 evaluation, EGC has performed a comprehensive reanalysis of the UHS capacity calculation, the critical SSC parameters impacting performance, and the associated licensing basis. Additionally, enhancements were added to the station procedure used to replenish the UHS following a failure of the Dresden Lock and Dam. The details of this reanalysis and procedure revisions are provided below in the Additional Information for Consideration section.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 This comprehensive reanalysis was then used to revise the 50.59 evaluation. As discussed below, the revised 50.59 evaluation concluded that these changes can be made without prior NRC approval. This revised 50.59 evaluation corrects the documentation of the technical basis deficiency identified in the Apparent Violation.

Corrective steps that will be taken In addition to the comprehensive reanalysis of the UHS and the revised 50.59 evaluation, several additional actions were identified in the CAPE. Additional actions that will be completed are not corrective actions directly related to restoring compliance for the Apparent Violation; these actions are enhancements that ensure organizational learning from this event.

• Reinforce the use of Appendix 7.9 of LS-AA-104-1000, 50.59 Checklist, with applicable DNPS personnel.

• Submit Training Request to DNPS Training Review Committee on 50.59 Training.

• Add the lessons learned as Operating Experience into the EGC 50.59 fleet training material.

• Communicate lessons learned to EGC Design Engineering Manager Lead Peer Group on this event.

• Communicate lessons learned to qualified DNPS Plant Operations Review Committee (PORC) Members.

Date when full compliance will be achieved Full compliance was achieved on June 29, 2020. The 10 CFR 50.59 Evaluation 2020-02-001, Revision 1 has been approved. The revision was supported by the comprehensive UHS reanalysis and provided the documented technical basis.

This included the determination that there was not more than a minimal increase in the likelihood of occurrence of a malfunction of the Diesel Generator Cooling Water (DGCW) system. The 50.59 evaluation concluded that prior NRC approval is not required for implementation of the changes evaluated. The details supporting this conclusion are provided below.

Additional Information for Consideration In order to provide context for the answers in the above responses, EGC is including further information to discuss an overview, timeline of events, licensing basis review, event scenario, and station response, all of which support full compliance being achieved on June 29, 2020.

Overview In February of 2020, the NRC Triennial UHS Inspection of DNPS began. During this inspection, the NRC raised concerns with 50.59 Screening 2019-134 as impact to the UHS design function was not marked as adverse. EGC reviewed this concern and agreed with the NRC. 50.59 Evaluation 2020-02-001 Revision 0 was completed and determined the proposed change did not require prior NRC approval. The NRC reviewed the 50.59 evaluation and issued an Apparent Violation (Reference 2).

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 EGC accepts the Apparent Violation and agrees that 50.59 Evaluation 2020-02-001 Revision 0 did not include adequate documentation of technical justification to support the conclusion. In addition, the change assessed using one million gallons of water within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> which as-written, could be interpreted as changing the coping time from approximately four days to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. This was not the intent; 50.59 Evaluation 2020-02-001 Revision O documented UHS bathymetric surveys showing more than 1.8 million gallons of water available. 50.59 Evaluation 2020-02-001 Revision 1 specifically states that with a credited UHS volume of 1.8 million gallons results in a coping time of 3.7 days prior to river make-up.

With this information, analysis, and additional documented technical justification, the same conclusion was reached that the proposed change did not require prior NRC approval.

50.59 Evaluation 2020-02-001 was revised per CAPE 4343358, using a quantitative rather than qualitative assessment. In addition, a separate CAPE 4323025 was performed for the design control violation issued in Inspection Report 2020-012 (Reference 2). The corrective actions from CAPE 4323025 were to revise Calculation DRE16-0011, "Required Ultimate Heat Sink (UHS) Capacity," Calculation DRE03-0026, "Analysis of the Intake Canal, CCSW Heat Exchanger, and Temporary Pumps following a Dam Failure and 1 inch LOCA," and UFSAR Section 9.2.5 "Ultimate Heat Sink," to remove inconsistences, ensure alignment to station response in DNPS Procedure DOA 0010-01, "Dresden Lock and Dam Failure," and address design aspects such as vortexing.

To support the UFSAR revision, a thorough licensing basis review was performed and is summarized in Appendix 1. UFSAR Section 9.2.5.3.1 "Dam Failure During Normal Plant Operation," has been revised to accurately describe the scenario associated with the catastrophic structural failure of the Dresden Lock and Dam with offsite power available and no seismic activity. DOA 0010-01 has been revised with enhanced procedural steps, refined implementation milestones, and location of mud mats which are now staged onsite.

50.59 Evaluation 2020-02-001 Revision 0 relied on procedural guidance in DOA 0010-01 Revision 36 which directed operators to establish make-up within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Revision 37 of DOA 0010-01 has bolstered EGC's confidence of completing actions to establish river make-up in as little as 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> following the event. The operator action time to establish river make-up compared to the analyzed coping time provides days of margin. As further defense in depth, operators will take actions to manage onsite water. Substantial volumes of water are not credited in the coping time of 3. 7 days, but the water could be used if needed and provide additional coping margin.

Timeline of Events A Regulatory Commitment was made in support of License Renewal, requiring DNPS to perform annual soundings to ensure adequate volume of water is available to support the function of the UHS. In 2018, DNPS conducted a bathymetric survey of the intake and discharge canals which concluded the acceptance criteria of two million gallons in the intake canal above the Diesel Generator Cooling Water Pump (DGCWP) suction was not met.

Action Request (AR) 4206439 was generated to document inconsistencies between calculation DRE16-0011, Revision 0 and the UFSAR.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 As a result, DRE16-0011 and the UFSAR were revised, documenting that approximately one million gallons of UHS capacity would be used in the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post lock and dam failure. The associated 50.59 Screening 2019-134, "Licensing Basis of the Ultimate Heat Sink (UHS) Credited Volume and UFSAR Update," acknowledged that although use of one million gallons was considered to last for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, based on the bathymetric survey results, additional water beyond one million gallons was available to provide margin for a coping time in excess of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

In February of 2020, the NRC conducted a UHS inspection at DNPS. During this time, the NRC raised a concern with 50.59 Screening 2019-134. This screening reviewed changes made to UFSAR Section 9.2.5.3.1, "Dam Failure During Normal Plant Operation," to reflect consumption of up to one million gallons UHS volume for the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following dam failure and establishment of intake canal replenishment from the Kankakee River within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in accordance with DOA 0010-01 Revision 36.

During the inspection, the NRC challenged the adequacy of the screening as captured in the NRC Inspection Report (Reference 2), "because reducing the UHS required capacity also reduced the coping time for which the UHS could be credited to maintain the safe shutdown condition from four days to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, an adverse impact to the UHS design function." In discussions with the NRC, EGC stated that the screening was based on improvements made to plant equipment and procedures. EGC re-reviewed the screening considering the NRC's concerns and documented the issue in CAP under AR 4318708.

The parameter in question was the volume of the UHS, specifically the volume above the DGCWP suction and below the lip of the intake canal at the inlet from the river. UHS volume is verified annually in Procedure DTS 4450-04, "Dresden Credited Ultimate Heat Sink Bathymetric Surveillance for Intake and Discharge Canals." The DTS 4450-04 acceptance criterion was incorrectly changed to one million gallons under Engineering Change (EC) 629625 and has been corrected as part of the revision to 50.59 Evaluation 2020-02-001.

50.59 Evaluation 2020-02-001, Revision 0, was performed by two highly experienced engineers with significant plant and 50.59 experience. To support completion during the inspection, additional oversight and reviews were performed. It was concluded, following a failure of the Dresden Lock and Dam, that the available UHS volume ensured plant systems could perform their required functions. Therefore, it was determined that the change may be performed in accordance with 10 CFR 50.59 without prior NRC approval.

The 50.59 evaluation was then presented to the PORC. PORC members had various challenges during the meeting and verbal discussion supplemented the product. The PORC members also had plant knowledge of the UHS, its history, procedure actions, and bathymetric survey results.

The 50.59 evaluation was provided to the NRC. The NRC reviewed the 50.59 evaluation and disagreed with the conclusion as stated in the Apparent Violation discussion above. As a result of this Apparent Violation, EGC initiated CAPE 4343358 to evaluate the cause of the failure to document a basis for the 50.59 evaluation.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 During the UHS inspection, EGC discussed various calculations, evaluations, drawings, ARs, and the silting mechanism with the NRC. As part of the NRC's review, there were concerns related to the 50.59 evaluation. This evaluation utilized the results of existing UHS calculations to determine the UHS volume necessary to support the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post dam failure. These UHS calculations did not consider equipment impacts from:

(1) Net Positive Suction Head (NPSH),

(2) UHS temperature, and (3) minimum submergence to prohibit vortexing.

While analytical margins and equipment impacts were considered during challenges and discussions, the conclusions were not clearly documented and appropriately translated into 50.59 Evaluation 2020-02-001, Revision 0. EGC was inappropriately focused on adding clarifying information to address the concern identified by the NRC to 50.59 Screening 2019-134.

One aspect of the 50.59 evaluation that was missing was the way silting affects UHS volume during the annual bathymetric survey. DNPS understood the silting mechanism and system interrelations which result in UHS volume fluctuation year to year rather than a fixed downward trend. The UHS is comprised of a long intake canal which starts with a lip of 494.2' and slopes towards a forebay directly in front of the crib house. This topography above the DGCWP suction represents the credited UHS volume. The volume of the forebay below the suction pipe is not credited. Any silt that enters and initially settles in the intake canal or walls of the forebay about the suction pipe results in a decrease in volume. Based on velocities of the water, this silt has been shown to be carried to the lower elevation of the forebay or swept out of the UHS, which results in an increase in volume (from previous bathymetric survey results).

The details described above were not translated into the 50.59 evaluation documentation.

The assigned engineers focused on adding clarifying information around the 50.59 Screening 2019-134 to address the concern identified by the NRC.

In response to this Apparent Violation and the Green Finding and associated NCV for 10 CFR 50 Appendix B, Criterion Ill, "Design Control," EGC performed the following:

• Reviewed the licensing basis history of the UHS and revised UFSAR Section 9.2.5.

• Revised the UHS calculation DRE16-0011 to incorporate appropriate inputs, assumptions, and conditions. This included the impact of volume changes on NPSH, temperature, and vortexing.

• Revised the DNPS procedure, DOA 0010-01 to enhance guidance. This included added information on the location of newly purchased mud mats, instead of the previous reliance on procuring materials post event.

• Revised 50.59 Evaluation 2020-02-001, accounting for the UHS calculation, UFSAR, and procedural changes above.

EGC concluded in 50.59 Evaluation 2020-02-001, Revision 1 that the revised UHS calculation now provides the necessary documentation to support the conclusion that prior NRC approval is not required to change the UHS volume from 2 million gallons to 1.8 million 5

Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 gallons, which results in a coping time of 3.7 days. This conclusion is based on the fact that the reduction of 200,000 gallons does not significantly change the margin between the time the UHS volume can maintain safe shutdown of both units and the time to establish UHS make-up. The details informing this conclusion are provided in the remainder of this Enclosure.

Licensing Basis Review Following the UHS inspection documented in NRC Inspection Report 2020-012 (Reference 2), an in-depth review of DNPS licensing basis documents and correspondence was completed, as summarized in Appendix 1. A critical part of the review was analyzing references related to the available UHS volume and coping strategies for the failure of the Dresden Lock and Dam. Prior to 2019, the most recent docketed correspondence of a change to the UHS credited volume was in support of the DNPS Extended Power Uprate (EPU) request in 2001 (Reference 1). EGC provided additional information supporting the EPU request which credited the volume of the intake canal of approximately two million gallons above the suction to the DGCWPs. This volume was determined to last approximately four days, during which time, make-up to the intake canal can be provided. In 2001, the Abnormal Operating Procedure for Dresden Lock and Dam failure, DOA 0010-01, Revision 13 specified that make-up water would be supplied from the river using pumps sourced from surrounding company facilities or procured from local rental pump suppliers following the event.

The NRC Safety Evaluation (SE) for EPU (Reference 3), dated December 2001, stated the following (emphasis added):

Before depletion of water in the intake canal, the licensee noted that makeup can be provided from the Kankakee River using portable, low head, high volume, engine-driven pumps, which can be readily obtained from other stations or purchase or rental. The licensee noted that at least four days are available before this replenishment is required under EPU conditions. Therefore, the basis for the conclusion reached during the SEP, that several days to a week would be available to obtain portable pumps for UHS replenishment, is unaffected by EPU.

Both DNPS units can be simultaneously brought to hot shutdown and maintained in that condition for 30 days using the IC following EPU. The sources of makeup water are not seismically qualified but, considering the redundancy and diversity of the sources, there is a high confidence that at least one source will be available following a design basis event, including seismic events that could cause dam failure. Based on the review of the licensee's rationale and evaluation, the staff agrees with the licensee's conclusion that the ability of the DNPS UHS to support operations at the proposed EPU conditions is acceptable.

The UHS was originally reviewed by the NRC as part of original plant licensing and again reviewed by the NRC for the Systematic Evaluation Program (SEP). SEP concluded the UHS has sufficient capacity due to several days of coping time and the ability to effectively replenish. Historically, the DNPS licensing basis scenarios and conditions for failure of Dresden Lock and Dam were not well defined. This question was one of the primary issues 6

Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 addressed in Task Interface Agreement (TIA)98-009 (Reference 4) and Unresolved Item (URI) 97021-01 closed in 2004 NRC Inspection Report 2004010 (Reference 5).

Through review of these documents, EGC concluded that a structural failure of the Dresden Lock and Dam, alone, is the scenario that must demonstrate both units can be simultaneously brought to hot shutdown. The coping strategy for this event could utilize both Class I and Class 11 systems and shows that adequate coping time is available while taking action to implement procedurally driven UHS make-up capability. The scenario for failure of the Dresden Lock and Dam does not require consideration for concurrent or simultaneous occurrences of a LOCA, a loss of offsite power, or a seismic event.

Dam Failure During Normal Operation Appendix 1 provides a summary of the licensing basis documents reviewed. As a result of the licensing basis review, portions of DNPS UFSAR Section 9.2.5, "Ultimate Heat Sink,"

have been revised to clarify the coping strategy and ensure alignment with procedures and analysis.

UFSAR Section 9.2.5.3.1, "Dam Failure During Normal Operation," describes a coping scenario following a catastrophic structural failure of the Dresden Lock and Dam with offsite power available and no seismic activity. A substantial amount of onsite cooling water is available from the intake canal, discharge canal, tanks, main condenser intake piping, and the cooling lake.

In response to the event, operators will commence shut down of all operating units and initiate closed cycle cooling. Intake canal level will be maintained at 494.2' to prevent water spilling out into the river. Operators will establish a compartment dedicated for Containment Cooling Service Water (CCSW) suction, run hoses from the DGCWP to the Isolation Condenser tie-in, and establish river make-up.

The Isolation Condenser would be used to reduce Reactor pressure using water from onsite tanks and then would be aligned to draw from the UHS via the DGCWP. Water trapped as part of the intake canal inventory above the suction of the DGCWP is considered available from the UHS. Make-up to the UHS from the river will be provided by on-site portable pumps.

Operator Response to Lock and Dam Failure DNPS Procedure DOA 0010-01, "Dresden Lock and Dam Failure," directs operators to take action to establish make-up flow from the river within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Beyond the make-up from the river, operators are also directed to close off the flow diverter gates to maintain water in the discharge canal at elevations not to exceed 508' and to close the lake spillover gate to maintain lake level. Water from the discharge canal and lake is then released into the intake canal in a controlled manner to not exceed 494.2'.

DOA 0010-01 has been reviewed and updated to Revision 37. An operator aid has been added which lays out a 17-hour sequence of key actions to establish make-up from the river.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 Procedural steps are aligned with both UFSAR Section 9.2.5 and DRE16-0011 Revision 1.

Enhancements made to DOA 0010-01 Revision 37 included the following:

1. Importance of maintaining Isolation Condenser level band

2. Actions for providing a flow path from Main Condenser intake piping to forebay

3. Specified onsite storage location of mud mats (used to aid in accessing river water with portable pumps)

4. Refined time durations for procedural milestones Analysis As discussed above, 50.59 Evaluation 2002-02-001, Revision 0 did not document assessments of silting mechanisms, net positive suction head (NPSH}, and equipment impacts from increased temperature. Interviews conducted in support of the CAPE 4343358 found that silting, NPSH, and other impacts were considered, but were not translated into the final document.

The UHS is comprised of a long intake canal connected to a forebay preceding the crib house. The bathymetric surveys the canal and determines a volume that includes water from the lip at 494.2' at the intake flume down to the DGCWP suction in the forebay. A historical review of bathymetric surveys showed that the topography of both the intake canal and forebay fluctuate annually. Additionally, DNPS reviews raw water impacts to plant equipment in accordance with NRC Generic Letter (GL) 89-13, "Service Water System Problems Affecting Safety-Related Equipment," and system monitoring; no silting issues are currently known to be affecting DNPS, Units 2 and 3.

The maximum temperature of the UHS occurs during the beginning of the analyzed scenario. At the end of the analyzed scenario, the height of water above DGCWP suction is at its minimum value. Temperature and water height are parameters that affect NPSH, now evaluated continuously in DRE 16-0011 Revision 1. This revision determined that there is a minimum of 20 feet of margin between the required NPSH (NPSHr) and available NPSH (NPSHa) over the analyzed period. The conclusion made in 50.59 Evaluation 2020-02-001, Revision 0 has since been confirmed in DRE 16-0011, Revision 1.

Another parameter that was assessed but not documented in 50.59 Evaluation 2020-02-001, Revision 0 was temperature impacts to plant equipment. In DRE03-0026, the bulk temperature of the UHS is shown to decrease through evaporation and initial water transfer from the main condenser to discharge canal. After 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, this temperature continues to decrease and is bounded by the conservative model in DRE03-0026 which considers CCSW heat inputs which are not applicable in a normal shutdown scenario.

50.59 Evaluation 2020-02-001, Revision 0 did not document the specific equipment impact as it was thought to have minimal impact.

Finally, Design Control Violation 2020012-01 (Reference 2) documented that DRE16-0011, Revision 0 did not account for minimum submergence to prevent vortexing or air ingestion in the DGCWPs. The condition could impact the equipment performance. This potential phenomenon was not considered in DRE16-011, Revision O and was not discussed in 50.59 Evaluation 2020-02-001, Revision 0.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 DRE16-0011, Revision 1 incorporates revisions to UFSAR 9.2.5.3.1 and DOA 0010-01, evaluating that the DGCW system would be able to perform its safety function at the UHS temperature, elevation, and volume extremes expected following a failure of the lock and dam. The changes included:

(1) No Emergency Diesel Generators in operation (i.e., offsite power remains available},

(2) Use of water inventory contained in onsite tanks, (3) Use of trapped Main Condenser intake piping water, and (4) Carryover fraction that correlates to isolation condenser level.

DRE16-0011, Revision 1 also analyzed NPSHa and NPSHr as a function of temperature instead of in a separate calculation. Additionally, DRE16-0011, Revision 1 calculated the minimum submergence required for the DGCWP to prevent vortexing. Operators maintain Isolation Condenser level between 4 and 4.8 feet in order to conserve water inventory. Due to restrictions on Isolation Condenser level per DOA 0010-01, the flow would be throttled near minimum pump flow requirements or non-continuous operations, which would tend to disrupt vortex formation.

DRE16-0011, Revision 1 concluded that DNPS can maintain hot shutdown without make-up for 3.7 days with an initial UHS volume of 1.8 million gallons. Two sensitivity runs were included in DRE16-0011 Revision 1, using an initial UHS volume of 1.6 million gallons and 1.074 million gallons. An initial UHS volume of 1.6 million gallons resulted in a coping time of 3.3 days. A coping time of 2 days would be available with an initial UHS volume of 1.074 million gallons. All simulations of DRE16-0011, Revision 1 only account for water inventory contained in: onsite tanks, Main Condenser intake piping, and UHS volume.

Defense in Depth Over decades of plant operation, DNPS has increased the reliability of equipment, and improved operator guidance for failure of Dresden Lock and Dam coping strategy through assessments and modifications:

(1) Seismic Qualification User Group (SQUG) Assessments in Individual Plant Examination of External Events {IPEEE},

(2) Seismic Calculations of Isolation Condensers, (3) Modification to use DGCWP make-up to isolation condensers, (4) Modifications of onsite equipment in accordance with Diverse and Flexible Coping Strategies (FLEX) Implementation Guidelines, (5) In-depth procedure guidance in DOA 0010-01, and (6) Combination of lake Procedure EPIP 0200-09 into DOA 0010-01.

DRE 16-0011, Revision 1 results do not credit the substantial amount of onsite cooling water available in the cooling lake, discharge canal above elevation 495', well water system, and river make-up. Beyond establishing river make-up within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, DOA 0010-01, Revision 37 directs operators to ensure water is trapped in the lake, water level is maintained in the discharge canal, and water from the lake or discharge canal is utilized to 9

Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 replenish the intake canal without spillover to the river. Between the cooling lake and discharge canal, millions of gallons of water will be available.

In response to the failure of the Dresden Lock and Dam, the Isolation Condenser initially uses water inventory from onsite tanks including the clean demineralizer tank. Per DOA 0010-01, operators will refill the clean demineralizer tank from well water through a demineralizer trailer. The well water tank is 200,000 gallons and is automatically refilled.

Based on the above, a considerable volume of onsite water is available which provides significant margin beyond the coping time calculated in DRE16-0011 Revision 1.

50.59 Evaluation 2020-02-001 Revision 50.59 Evaluation 2020-02-001, Revision 0 was rewritten to Revision 1, documenting the basis for concluding that the activity does not require prior NRC approval. The UHS provides adequate coping for 3. 7 days without crediting river make-up. This coping time includes consideration of the minimum submergence of the DGCWP suction line to prevent air ingestion and ensure the DGCW system will be able to perform its required function.

Consistent with the licensing basis, the UHS continues to provide several days of coping time prior to requiring make-up.

EGC confirmed the conclusion of not more than a minimal increase in the likelihood of a malfunction of the UHS and the DGCW system based on 50.59 Evaluation 2020-02-001, Revision 1 and results in DRE16-0011, Revision 1, which quantified NPSH, temperature, and vortexing effects.

DRE16-0011, Revision 1 included a sensitivity case with a calculated amount of UHS water for two days of coping time. This volume was found to be 1.074 million gallons which supports the estimation in 50.59 Evaluation 2020-02-001, Revision 0.

Severity Level of Apparent Violation With respect to the severity level of the Apparent Violation, EGC advocates that the proper characterization is Severity Level IV. The basis supporting this position is as follows:

• There is not a loss of UHS function associated with this Apparent Violation.

• The conclusion of the revised 50.59 evaluation is that prior NRC approval is not required to implement the changes; the same conclusion as the initial 50.59 evaluation.

• 50.59 evaluation conclusion is unchanged, there was no impact on the ability of the NRC to perform its regulatory oversight function.

Considering the above, in light of the examples contained in the NRC Enforcement Policy, the NRC Enforcement Manual guidance, and previous NRC issued 50.59 traditional enforcement actions, the Apparent Violation issued to EGC associated with 50.59 documentation quality warrants no greater than an assignment of Severity Level IV.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 Conclusion The Corrective Action Program has been used to drive Corrective Actions to update the 50.59 evaluation, calculations, procedures, and the UFSAR. EGC has taken action to ensure alignment and consistency between the station procedures, licensing basis descriptions, and analyses.

EGC has restored compliance through 50.59 Evaluation 2020-02-001 Revision 1. The revised 50.59 evaluation, considering a UHS volume of 1.8 million gallons with a coping time of 3.7 days, provides the basis for determining the change does not require prior NRC approval. Sensitivity studies in DRE16-0011 Revision 1 provided the quantitative results to support the original 50.59 evaluation conclusion .

The DNPS response to the failure of the Dresden Lock and Dam scenario, as documented in Station Procedures, will be performed well in advance of the analyzed coping time. The coping time of 3.7 days does not account for significant amount of onsite water available, with procedural guidance to retain available water available for use in response the event.

Therefore, DNPS continues to maintain significant available margin in calculated coping time relative to the time to establish make-up.

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Response to Apparent Violation Described in NRC Inspection Report 05000237/2020012 and 05000249/2020012 References

1. Letter from EGC to U.S. NRC, Additional Information Supporting the License Amendment Request to Permit Uprated Power Operation at Dresden Nuclear Power Station, dated 09/26/2001 (ML012760060)

2. NRC Inspection Report, Dresden Nuclear Power Station, Units 2 and 3 - NRC Inspection Report 05000237/2020012 and 05000249/2020012 and Apparent Violation, dated 05/29/2020 (ML20140A181)

3. NRC Safety Evaluation, Related to Amendment No. 191 To Facility Operating License No. DPR-19 and Amendment No. 185 To Facility Operating License No. DPR-25, Related to Extended Power Uprate (EPU), dated 12/21/2001 (ML013540187)

4. Memorandum from S. C. Black (NRR) to J. A Grobe (NRC Region Ill), Task Interface Agreement (TIA)98-009 - Low Ultimate Heat Sink Level Safe Shutdown Issues -

Dresden Nuclear Power Station, Units 2 and 3 (TAC NOS. MA2427 AND MA2428),

dated 11/30/1999 (ML993410430)

5. NRC Inspection Report, Dresden Nuclear Power Station, Units 2 and 3 - NRC Integrated Inspection Report 05000237/2004010; 05000249/2004010, dated 10/27/2004 (M L043020589) 12

Appendix 1: Dresden UHS Licensing Basis History Date Document Relevant Information 2/28/1969 Answer to AEC Questions, DNPS FSAR Discussed response to a catastrophic failure of the Dresden Lock and Dam.

Amendment No. 9, and Amendment No. 10 1/4/1982 Letter from T. J. Rausch (ComEd) to NRC, Calculated approximately 2.5 million gallons per unit required to remove decay heat Additional information for SEP Topics 11-3.A, produced by one Unit/reactor for 30 days.

11-3.B, 11-3.B.1 & 111-3.C, per NRC request dated 10/29/1981 06/21/1982 Safety Evaluation of SEP Topics 11-3.A, II- The NRC accepted a less-than 30-day supply as adequate because, provided that 3.B, 11.3.B.1 & 11-3.C, with Enclosure 2, adequate emergency procedures were in place, equipment available to DNPS Technical Evaluation Report - Dresden Unit 2 Units 2 and 3 assured that the water supply could be replenished to ensure the

- Hydrological Considerations SEP Prep by continuous capability of the UHS to perform its safety functions.

Franklin Research Center dated 5/7/1982 "Because the amount of water available in the intake canal is large, it can be expected that a significant period of time would pass before make-up would be required. It can be conservatively estimated to be several days to a week or more .. . it can be reasonably concluded that replenishment can be effected to ensure the continuous capability of the sink to perform its safety function .. ."

12/30/1997 Letter from J. M. Heffley (ComEd) to NRC, Generic Letter 88-20, "Individual Plant Examination for Severe Accident Final Report Vols I, II & Ill , "IPEEE for Vulnerabilities," requested each plant to perform an Individual Plant Examination of Seismic Fire High Winds/Tornadoes External External Events (IPEEE) in order to identify potential vulnerabilities that were Floods Transportation Accidents," per GL previously not known. The approach involved evaluation of three separate areas:

88-20. seismic concerns, fire concerns, and other external events.

3/6/1998 Inspection reports 50-237/97-21 & NRC identified concerns that the UFSAR (Section 9.2.5.3.1 and 9.2.5.3.2) did not 50-249/97-21 accurately characterize the plant's design-basis or the plant's capability to respond to a potential Dresden Lock and Dam failure. As a result, the NRC concluded that further review by the licensee and NRC was required. An NRC Unresolved Item (URI) was initiated to document these concerns (URI 50-2371249-97021-01 ).

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Appendix 1 : Dresden UHS Licensing Basis History Date Document Relevant Information 4/14/1998 Inspection Reports 50-237/98-07 & NRC identified several discrepancies in the DNPS UFSAR and questioned several 50-249/98-07 underlying assumptions (e.g., use of 498' for discharge canal elevation) and procedures involving the ability to safely shut down the plant following a failure of the Dresden Lock and Dam. Various scenarios were identified concerning dam failure both with and without a LOCA. Added concerns to previous opened URI (URI 50-237/249-97021-01).

3/31/1998 Letter from J. M. Heffley (Com Ed) to NRC, Com Ed identified that a dam failure coincident with a LOCA was beyond the design "Design Basis Initiative Program DNPS basis. Identified use of DGCW Pumps to provide water to isolation condensers.

Containment Cooling Service Water Failure of Dresden Lock and Dam" 9/9/1998 Letter from J. M. Heffley (ComEd) to NRC, Provided ComEd position that Dresden currently meets the licensing basis "Failure of the Dresden Lock & Dam" requirements for safe shutdown following a dam failure. Informed NRC that a decision concerning satisfying GL 87-02, "Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors (USI A-46)," program requirements and enhancing plant safety using the Seismic Qualification Utility Group (SQUG) methodology will be made as part of the GL 87-02 program. The SQUG program requires that seismically verified or seismically qualified safe shutdown equipment be available to safety shutdown the units following an earthquake.

9/30/1999 Letter from J. M. Heffley (ComEd) to NRC, Identified a conceptual design to provide a seismically-qualified flow path involving "Response to Request for Additional a cross-tie from the DGCW system.

Information Regarding Individual Plant Examination of External Events" 2

Appendix 1: Dresden UHS Licensing Basis History Date Document Relevant Information 9/26/2001 Additional Information Supporting the Provided an evaluation which credited the volume of the intake canal above the License Amendment Request to Permit elevation of the suction to the EOG cooling water pumps (i.e., 2 million gallons).

Uprated Power Operation The water in the discharge canal and the hot and cold canals to the cooling lake is also likely to be available. No additional credit was assumed for the volume of water initially trapped in the discharge canal. Before depletion of water in the intake canal, make-up can be provided from the Kankakee River using portable, low head, high volume, engine-driven pumps, which can be readily obtained from other stations or purchase or rental.

12/21/2001 NRC Safety Evaluation, Amendments 191 & NRC noted that at least four days are available before UHS replenishment is 185 re Extended Power Uprate required under EPU conditions. Therefore, the basis for the conclusion reached during the SEP, that several days to a week would be available to obtain portable pumps for UHS replenishment, is unaffected by EPU.

10/27/2004 Inspection Report 05000237-04-010, Closed URI 50-237/249-97021-01, where these items were referred by Task 05000249-04-010 Interface Agreement (TIA) 98-09 "Low Ultimate Heat Sink Level Safe Shutdown Issues" (ML993410430) for Office of Nuclear Reactor Regulation (NRR) review.

Four concerns were closed, NRC came to the following conclusions:

1) A Dresden Dam failure coincident with a LOCA in one of the units was beyond design basis and no supporting analysis was needed.

2) As discussed in the EPU SE, the licensee did not need to use only class I systems to shut down.

3) As stated in TIA 98-09, the licensee's planned action of using portable engine-driven pumps to pump water from the intake and discharge canals was acceptable to compensate for the reduced UHS inventory assumption since the planned actions were in the emergency procedure. The EPU SE also stated this was acceptable.

4) Service Water Pumps did not need to be credited for shutdown following a failure of the lock and dam.

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Appendix 1: Dresden UHS Licensing Basis History Date Document Relevant Information 6/29/2011 Dresden, Units 2 and 3, Updated Final Safety Update UFSAR to align the licensing basis as described in the EPU submittal.

Analysis Report (UFSAR), Revision 9 6/26/2015 Dresden, Units 2 and 3, Updated Final Safety Updated UFSAR to clarify the event specified in in Section 9.2.5.3.1 that lock and Analysis Report (UFSAR), Revision 11 dam failure is with no seismic activity.

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