NRC-24-0064, Supplement to License Amendment Request for a Risk Informed Approach to ECCS Strainer Performance

Supplement to License Amendment Request for a Risk Informed Approach to ECCS Strainer Performance

ML24305A147
Person / Time
Site:	Fermi
Issue date:	10/31/2024
From:	Domingos C DTE Electric Company
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NRC-24-0064
Download: ML24305A147 (1)

Text

Christopher P. Domingos Site Vice President DTE Electric Company 6400 N. Dixie Highway, Newport, MI 48166 Tel: 734.586.5025 Fax: 734.586.5295 Email: christopher.domingos@dteenergy.com October 31, 2024 10 CFR 50.90 NRC-24-0064 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Fermi 2 Power Plant NRC Docket No. 50-341 NRC License No. NPF-43

Subject:

Supplement to License Amendment Request for a Risk Informed Approach to ECCS Strainer Performance

References:

1) DTE Letter NRC-23-0020, License Amendment Request for a Risk Informed Approach to ECCS Strainer Performance, dated June 13, 2023 (ML23164A232)

2) NRC E-mail Capture, Fermi 2 - Request for Additional Information for License Amendment Request Regarding Risk-Informed ECCS Strainer Performance Evaluation (L-2023-LLA-0092)", dated March 20, 2024 (ML24080A391)

3) DTE Letter NRC-24-0027, Partial Response to Request for Additional Information for License Amendment Request Regarding Risk Informed Approach to Performance ECCS Strainer Performance dated April 24, 2024 (ML24115A095)

4) DTE Letter NRC-24-0033, Final Response to Request for Additional Information for License Amendment Request Regarding Risk Informed Approach to Performance ECCS Strainer Performance dated May 30, 2024 (ML24151A173)

5) DTE Letter NRC-24-0040, Verification of No Significant Hazards Considerations for License Amendment Request for a Risk Informed Approach to ECCS Strainer Performance Supplement provided in NRC-24-0033, dated June 6, 2024 (ML24158A009)

DTE

USNRC NRC-24-0064 Page 2 In Reference 1, DTE Electric Company (DTE) submitted a License Amendment Request (LAR) for a Risk Informed Approach to ECCS Strainer Performance. In Reference 2, an email from Mr. Surinder Arora to Mr. Eric Frank dated March 20, 2024, the NRC sent DTE a Request for Additional Information (RAI) regarding the LAR. In Reference 3, a partial response to the RAI was provided. Reference 4 provided responses to the RAIs that were not provided in Reference

3. In Reference 5, it was documented that the information provided in Reference 4 did not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the reference information provided in the Reference 4 letter did not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

In Reference 6, the NRC requested further information was needed on the docket. Enclosure 1 provides responses to NRC audit questions on the Category 2 items requiring additional information on the docket. Attachment 1 provides revised UFSAR page mark-ups. Attachment 2 provides revised pages for Requests for Exemptions for DTE Fermi Risk-Informed ECCS Evaluations 2 General, 2 Request for Exemption from 10CFR50.46(a)(1), 2 Request for Exemption from General Design Criterion (GDC)-35 and 2 Request for Exemption from GDC-38. There were no changes impacting Attachment 3 therefore, it was not included in in this supplement. Attachment 4 provides revised pages to the technical supplement. The changes in this supplemental letter supersede previously submitted information in References 1 through 5.

DTE has determined that the information provided in this supplement does not alter the conclusions reached in the 10 CFR 50.92 no significant hazards determination previously submitted. In addition, the information provided in this submittal does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

In accordance with 10 CFR 50.91(b)(1), a copy of this application, with the enclosure, is being provided to the designated State of Michigan official.

No new commitments are being made in this submittal.

Should you have any questions or require additional information, please contact Mr. Eric Frank at (734) 586-4772.

6) NRC Letter, Fermi 2 Power Plant - Audit Summary for License Amendment Request and Regulatory Exemptions for a Risk-Informed Approach to Address Emergency Core Cooling System (ECCS) Strainer Performance (EPID L-2023-LLA-0092), dated October 1, 2024 (ML24268A099)

SNRC NRC-24-0064 Page 3 J declare under penalty of pe~jury that the foregoing is true and con:i~et.

xecuted on ctober 31 2024

Enclosure:

~

~-w---_)

Christop er P. Domingos Site Vice President

1. Responses to C

uction Strainer Audit Questions Attachments: 1. License Amendment Request for DTE Fermi Risk Informed ECCS Evaluation (Revised) 1-2 UFSAR Page Markups (For Information)

2. Requests for Exemptions for DTE enni Risk-In armed ECC Evaluation (Revised) 2-1 General 2-2 Request for Exemption from 10CFR50.46(a}(l) 2-3 Request for Exemption from GDC-35 2-4 Request for Exemption from GDC-38

4. LAR Attachment 4 Technical Supplement (Re ised) cc; NRC Project Manager NRC Resident Office Regional Administrator, Region ID Michigan Department of Environment, Great Lakes, and Energy

to NRC-24-0064 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Responses to ECCS Suction Strainer Audit Questions to NRC-24-0064 Page 1 FERMI 2 ECCS SUCTION STRAINER AMENDMENT REQUEST (EPID L-2023-LLA-0092)

Fermi Responses to Audit Questions Audit Question P2-1: Page 10 of Enclosure 1 states that the design allows some margin for emergent issues. It also states that the 100 ft2 provides a new design basis for miscellaneous debris. The FSAR markup states that the LAR only applies to the current condition. Provide clarification for this apparent discrepancy. The risk analysis in the amendment applies to the present condition, i.e., the amendment is not intended to allow accommodation of additional debris in the future. The risk analysis does not apply to the design debris loads, (defined in Fermi Calculation DC-5979 Rev-B) that are successfully addressed using the methodology defined in NEDO-32721P-A. It appears that the 100 ft2 is a new design basis, but it is unclear as to whether it provides margin for future conditions. Should the FSAR markup be clarified to state that the 100 ft2 is the new design basis value that contains margin in case additional miscellaneous debris is discovered in the future.

DTE Response: (Response to Request for Additional Information) to DTE letter NRC-24-0027, ML24115A095 (Partial Response to Request for Additional Information for License Amendment Request Regarding Risk Informed Approach to ECCS Strainer Performance) dated April 24, 2024 states on Page 10 in the subsection Plant Implementation of the response to Question STSB-RAI-9, the baseline assumption bounds the sum of the total design basis and the newly identified debris in both the overlapped and non-overlapped configurations, and allows some margin for unexpected emergent issues. The baseline assumption discussed in this response is 100 ft2 of total strainer area obstructed by overlapped miscellaneous debris.

(LAR NRC-23-0020 Attachment Mark-ups) to DTE letter NRC-24-0027, ML24115A095 (Partial Response to Request for Additional Information for License Amendment Request Regarding Risk Informed Approach to ECCS Strainer Performance) dated April 24, 2024 states on Pages 2 and 3 in the subsection INSERT TWO, The risk analysis in the amendment applies to the present condition, i.e., the amendment is not intended to allow accommodation of additional debris in the future.

To clarify, note that the present condition is defined as the plant configuration that exists at the time NRC accepts/approves the Fermi LAR. The present condition, or plant configuration, includes all materials that are known to exist in containment at the time the risk analysis was performed. The present condition does not include intentional future introduction of materials known to adversely affect strainer performance, for example, application of new nonconforming paper/plastic tags or tape.

The 100 ft2 of total obstructed strainer area provides the (new) design basis for miscellaneous debris that bounds the sum of the original strainer design basis and the legacy inventory of nonconforming tags and labels characterized by best available containment walkdown information.

The 100 ft2 design basis analyzed by the risk assessment intentionally includes margin, so that any increase in identified amounts of miscellaneous debris, up to but not exceeding 100 ft2, will be accommodated by the new design basis without increasing risk analyzed and approved to NRC-24-0064 Page 2 under the LAR. Possible reasons (emergent conditions) that identify increased amounts of miscellaneous debris might include: 1) improved walkdown procedures or measurement methods, 2) discovery of additional labels or materials not previously identified in walkdown inventories, 3) discovery of a miscellaneous debris source unintentionally left in containment during an outage.

To resolve the noted discrepancy, the cited UFSAR statement will be revised to read:

The risk analysis in the amendment applies to the plant present condition existing at the time of License Amendment XXX approval, i.e., the amendment is not intended to allow intentional introduction accommodation of additional miscellaneous or Min-K debris sources in the future.

The risk analysis accommodates up to 100 ft2 of total obstructed strainer surface area caused by overlapping miscellaneous debris arriving at the strainers from all identified sources.

Audit Question P2-2: Should the FSAR include the amendment number to clearly define the current condition?

DTE Response:

LAR amendment number NRC-23-0020, ML23164A232 is included above (see response to Audit Question P2-1) in a proposed revised UFSAR markup. The text XXX will be replaced with the amendment number when it is assigned.

Audit Question F1-1: In the Exemption markups, the three key elements of the exemption are listed. It is unclear whether these key elements should all be considered necessary limits together (and) or whether each separately provides an element that alone allows use of the exemption (or).

DTE Response:

LAR Attachment 2, Requests for Exemptions for DTE Fermi Risk-Informed ECCS Evaluation, contains the following language:

The key elements of the exemption request are:

1. It applies only to the effects of debris as described in Attachment 3.

2. It applies only for LOCA breaks that can generate and transport fiber debris that is not bounded by the DTE strainer failure criteria established in Attachment 3.

3. It applies to any LOCA break that can generate and transport fiber debris that is not bounded by strainer failure criteria, provided that the cumulative CDF and LERF associated with these breaks remain in Region III of RG 1.174.

The intent of the above is that all three elements must be satisfied (and) for the condition to be addressed by the exemption request.

to NRC-24-0064 Page 3 Audit Question F1-2: Items 2 and 3 both limit the exemption to fiber debris. It is unclear whether Min-K is included in the key elements since it is microporous debris. This applies to the 50.46 and both GDC exemptions. (On Attachment 2-2, Page 2 (PDF 35) for 50.46.)

DTE Response:

Fermi LAR Attachment 1 states in Section 2.3, Description of the Proposed Change, that DTE proposes to amend the licensing basis to document reliance on the RG 1.174 risk-based methodology for evaluating ECCS performance for these additional containment label and drywell penetration Min-K debris sources while retaining the RG 1.82/URG based deterministic methods for those debris sources already considered in the current ECCS strainer design.

It is Fermis intent to include drywell penetration Min-K debris and legacy tags/labels in the key elements of each exemption request. Fermi will edit all occurrences of the three elements to read:

1. It applies only to the effects of penetration Min-K and nonconforming containment label debris as described in Attachment 3.

2. It applies only for LOCA breaks that can generate and transport fiber debris that is not bounded by the DTE strainer failure criteria established in Attachment 3.

3. It applies to any LOCA break that can generate and transport fiber debris that is not bounded by strainer failure criteria, provided that the cumulative CDF and LERF associated with these breaks remain in Region III of RG 1.174.

Audit Question F2-1: The exemptions refer to the risk-informed analysis evaluating the full spectrum of breaks; however, the analysis evaluated only DEGBs (e.g., Attachment 2-2, Page 6, as well as GDC exemptions). Wording in the exemptions should be consistent with the scope of the analysis.

DTE Response:

Fermis intent was to convey that exemptions refer to the risk-informed analysis evaluating all DEGB breaks, All occurrences in Attachment 2 of the text full spectrum of breaks (or similar) will be revised to read all DEGB breaks (or similar)

Audit Question F3-1: The exemptions, Attachment 2-2, Page 9 (PDF 42) (similar for GDC exemptions) request approval within 1 year of the LAR submittal. This is unlikely to be met due to delays in the review including delayed RAI responses.

DTE Response:

Fermi rescinds its request for approval within 1 year of the LAR submittal. All occurrences of a request for an approval timeline will be deleted.

to NRC-24-0064 Page 4 Audit Question F6-1: How many breaks exceed the fibrous debris bed limit (1/8 inch) in the baseline scenario?

DTE Response:

Please, refer to the description of Table 6-1. In the baseline scenario, 65 + 103 = 168 breaks can exceed the 1/8-inch fiber thickness criterion.

Table 6-1. Baseline risk and weld count for two strainer failure metrics.

Failure Metric Risk contribution (1/yr)

1. welds exceeding metric 1/8 Thickness Exceedance Alone 3.10E-07 65 Thickness AND Min-K Exceedance 5.46E-07 103 Min-K Exceedance Alone 2.34E-06 30 NonIsolable Break Risk 3.19E-06 198 Audit Question F7-1: NRC-24-0033 (ML24151A173), Attachment 4, page 10 (PDF 69),

discusses a single break that contributes significantly to risk for some scenarios and states that mitigation of this condition could reduce the risk. Are the actions listed that could reduce the risk being taken by Fermi?

DTE Response:

Fermi currently has no plans to implement specific mitigation measures for the risk dominant break(s) near penetration X-10. The DTE response to audit question F5b-4 provides physical justification for analytically reducing or even eliminating penetration Min-K damage at penetration X-10. Pending the outcome of the RAI process, Fermi may revisit the risk mitigation options listed in Attachment 4, page 10.

Audit Question F8-1: NRC-24-0033 (ML24151A173), Attachment 4, Page 11 (PDF 70) discusses the necessity to have a minimum amount of fiber to establish a filtering bed that would allow Min-K to create a substantial headloss. There is additional discussion on, page 13, Item 3. The discussion is not consistent with NRC staff observations of a test that included only particulate debris and Min-K yet resulted in substantial headloss.

Refer to ML102160226 for a summary of the test. The NRC is not aware of other tests that have included Min-K without any fibrous debris added. Justify the conclusions in the discussion in light of the test observations or revise it to be consistent with the empirical observations.

DTE Response:

Fermi has reviewed the insights provided in ML102160226 and on that basis had modified the discussion on Page 11 of Attachment 4 as indicated below:

The two failure metrics serve separate complementary purposes.

to NRC-24-0064 Page 5

1.

The fiber thickness failure criterion is intended to establish a minimum fiber load that is well within the current licensing basis and provides a measure of strainer performance that is sensitive to miscellaneous debris obstruction. A fiber thickness of 1/8th-inch has traditionally been used as a threshold for testing whether a strainer having complex geometry can form a contiguous layer of fiber capable of filtering particulate (a thin bed). In recognition of concerns that Min-K, a microporous material, can aid in formation of a thin bed with less than 1/8th-inch of equivalent fiber thickness, a sensitivity case was evaluated using a 1/16th-inch failure limit (see Section 4 below). Risk contributions from bed thickness failure increase by 10% to 40% depending on the flow history examined, but do not equal risk contributions from exceeding the DB Min-K limit. Recall that the entire Min-K debris volume is counted as fiber against the fiber thickness limit.

2.

The DB debris limits are intended to confirm that all scenarios recorded as successful strainer performance have debris loads that do not exceed any of the debris constituent quantities they are qualified for, and thus, do not pose new risks that contribute to CDF. No cases are found that exceed DB fiber loads, but exceedance of DB Min-K limits is now the dominant risk contributor.

Fermi has modified the discussion on Page 13 of Attachment 4 as indicated below:

Comparison of the Table 5 row labeled DB Exceedance Risk (alone) to the Table 5 row titled Total Risk (1/yr) serves to emphasize that exceedance of the DB Min-K limit is dominating total calculated risk. It is also important to understand that all break scenarios contributing risk in this row have less than 1/8th-in. of equivalent bed thickness. Given the importance of the DB Min-K failure criterion, it is prudent to examine the potential effect that source term uncertainty may introduce to the risk quantification.

Audit Question F9-1: In the baseline and sensitivity parameter values table, NRC-24-0033 (ML24151A173), Table 4, on Attachment 4, page 12, the double asterisk note states that additional capacity for Min-K arises from a change in Min-K density. The RHR and CS baseline values appear to be the RHR strainer limit based on a total suppression pool load of 5.9 lb. (CSS and RHR loads total to 5.9 lb at a density of 11.4 lb./ft3.) The original density assumption was 16 lb./ft3. The NRC staff understands that the qualified load for the strainers (suppression pool limit) is 9.5 lbm. of Min-K based on mass. It appears that the sensitivity case a is based on 9.5 lbm of Min-K (0.833 ft3 at a density of 11.4 lbm./ft3. How does the change in density result in the values in the Min-K amounts for sensitivity case 5a? Page 18 of (item 5) also discusses this sensitivity case and indicates that a change in Min-K density is involved in the debris volume change. Note that these values are discussed in SERCO REP DTE 22929 02 Rev 0, on Page 14 and 15.

DTE Response:

All quantitative observations made in the question statement are accurate. References made, in the double asterisk note and in later discussion, to the density change were only intended to imply that a safety margin resulted from changing Min-K density from the original incorrect value of 16 lbm/ft3 to the correct value of 11.4 lbm/ft3. The benefit is an artifact of the controls to NRC-24-0064 Page 6 that were adopted for Min-K and not a direct result of the density value applied to the 9.5 lbm mass limit.

The historical progression of Min-K limits and the density correction follows:

1.

Strainer DB calculations analyzed 9.5 lbm of total Min-K debris to establish the qualified load for RHR and CS strainers, individually, based on their respective DB flow rates.

2.

Using the original (incorrect) density of 16 lbm/ft3, the qualified total debris mass implies a qualified total debris volume of 9.5 16

=0.59 ft3.

3.

Applying the new (correct) density of 11.4 lbm/ft3 to this volume gives a mass of 0.59x11.4=6.76 lbm, which appears in TSR-36828 as the qualified mass load.

4.

Fermi established a lower administrative limit of 5.9 lbm, which appears in Design Calculation DC-5979 Rev. A and B as the monitored control limit. The total Min-K debris limit of 5.9 lbm is partitioned to one RHR and one CS strainer based on their DB flows to establish an RHR strainer limit of 5.9x 11,000 17,100

=3.8 lbm (0.334 ft3 with correct density 11.4 lbm/ft3) and a CS strainer limit of 5.9x 6,100 17,100

=2.1 lbm (0.186 ft3 with correct density 11.4 lbm/ft3).These limits are enforced for each strainer for all risk calculations, except sensitivity Case 5a.

The strainer design basis qualified the strainers for a total quantity of Min-K debris up to 9.5 lbm, based on GE test correlations. Fermi currently applies a Min-K debris mass limit of 5.9 lbm, leaving a safety margin of 3.6 lbm. Fermi does not plan to apply this margin for risk reduction at this time, so it qualifies as safety margin embedded in the analysis. Sensitivity Case 5a attempts to quantify the benefit of the embedded safety margin.

Debris volume limits applied in Sensitivity Case 5a for each strainer are determined as follows:

RHR strainer 9.5 lbmx 11,000 17,100 ÷11.4 lbm ft3 =0.536 ft3 CS strainer 9.5 lbmx 6,100 17,100 ÷11.4 lbm ft3 =0.297 ft3 The strainer limits are more directly useful when stated in terms of volume, because debris generation models calculate volumes of damaged insulation.

Audit Question F10-1: The risk computation considers two pump configurations to represent a two-division and one-division system, assigned 90% and 10% probabilities. The one-division system, the baseline system, is based on Case 2A. The two-division system risk values were computed based on Case 3A. Why was Case 3A considered for a two-division system, and not Cases 1A or 2B that have active flows through all the strainers?

DTE Response:

Case studies that distribute debris over more active strainers minimize the opportunity to exceed either a design basis debris limit or the baseline thin-bed limit, on a per strainer basis, so Cases 1A and 2B, though specific to two-division response, could be considered non conservative.

to NRC-24-0064 Page 7 Selection of a flow condition to represent the two-division system response poses a contradiction because, although all strainer/pump combinations are functional, operators act quickly to secure or throttle pumps that are not needed to maintain core level and temperature.

For example, Case 4A presents a hypothetical progression that operators might follow that creates a relatively high risk if operators fail to monitor pump status and bring functional assets back on-line if needed.

Emergency Operating Procedures (EOP)s guide operators to bring the long-term flow configuration to something that looks very much like a single-division response. Case 3A was selected to represent the two-division risk, because of its similarity in flow assignments to Case 4A after 2 minutes, and because the Case 3A risk (3.41E-06/yr) is between Cases 1A/1B (two-division flow) and Case 4A (hypothetical two-division flow).

to NRC-24-0064 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 License Amendment Request for DTE Fermi Risk Informed ECCS Evaluation (Revised) 1-2 UFSAR Page Markups (For Information)

-2 UFSAR Page Markups

FERMI 2 UFSAR A-64 REV 24 11/22 operability and reliability. An alternate to CTG 11-1 is CTG 11-2, 11-3, or 11-4 which can be started with the standby diesel generator.

d.

Procedures and training have been established for operator actions necessary to cope with a station blackout event.

e.

Quality assurance activities have been implemented as applicable for the non-safety systems and equipment required to support responses to a station blackout event. Further discussion of Station Blackout is provided in Section 8.4, Station Blackout (SBO).

A.1.160 REGULATORY GUIDE 1.160 (JANUARY 1995), MONITORING THE EFFECTIVENESS OF MAINTENANCE AT NUCLEAR POWER PLANTS The Fermi 2 plant is in compliance with Regulatory Guide 1.160. Regulatory Guide 1.160 endorses the use of NUMARC 93-01 as acceptable guidance for implementing the Maintenance Rule (10 CFR 50.65). Regulatory Guide 1.160 states that methods other than those expressed in NUMARC 93-01 may be used to implement the Maintenance Rule.

However, the NRC will determine the acceptability of other methods on a case by case basis.

Fermi 2 has utilized NUMARC 93-01 as the base document for implementing the Maintenance Rule. However, after appropriate justification, exceptions were taken. Most of these exceptions were improvements to NUMARC 93-01 guidance.

A.1.163 REGULATORY GUIDE 1.163 (SEPTEMBER 1995), PERFORMANCE-BASED CONTAINMENT LEAK-TEST PROGRAM By License Amendment 108, the Fermi 2 Plant has implemented the approach as described in Regulatory Guide 1.163 Performance Based Containment Leak Test Program. This program allows the testing periodicity to be extended from the present two year limit for Type B and C tests up to 120 months for Type B test and up to 60 months for Type C tests.

Also, the periodicity for Type A test has been extended from 3 every 10 years to once per 10 years. Regulatory Guide 1.163 approves Nuclear Energy Institute (NEI) 94-01, Revision 0, which provides methods acceptable to the NRC staff for complying with provisions of Option B in Appendix J to 10 CFR 50, subject to four exceptions listed in Regulatory Guide 1.163. By License Amendment No. 153, a one-time extension of the Type A test interval to 15 years was implemented. By License Amendment 205, the program was revised for the permanent extension of the Type A test interval to once every 15 years and extension of the Type C test interval up to 75 months. The program is in accordance with NEI 94-01 Revision 3-A, dated July 2012, and the limitations and conditions specified in NEI 94-01 Revision 2-A, dated October 2008.

A.1.181 REGULATORY GUIDE 1.181 (SEPTEMBER 1999), CONTENT OF THE UPDATED FINAL SAFETY ANALYSIS REPORT IN ACCORDANCE WITH 10 CFR 50.71 (e)

Fermi 2 complies with the general intent of this regulatory guide. Regulatory Guide 1.181 endorses the use of NEI 98-03, Guidelines for Updating Final Safety Analysis Reports, Add Insert 1 from the following page -2 NRC-24-0064 Page 1 of 6

-2 NRC-24-0064 Page 2 of 6 The scope of marked-up pages of the FERMI 2 UFSAR is limited to discussion of Regulatory Guide 1.174 and Regulatory Guide 1.82.

The following new entry in the UFSAR is proposed to address the implementation of Regulatory Guide 1.174, Rev. 3.

• License Amendment number will be listed when it is assigned with NRC approval.

INSERT 1 A.1.174 REGULATORY GUIDE 1.174, REV. 3, AN APPROACH FOR USING PROBABILISTIC RISK ASSESSMENT IN RISK-INFORMED DECISION ON PLANT-SPECIFIC CHANGES TO THE LICENSING BASIS

By License Amendment *XXX, Fermi 2 has implemented the approach as described in Regulatory Guide 1.174. Fermi 2s implementation of Regulatory Guide 1.174 is limited to application of a risk-based approach for dispositioning the effects on ECCS sump strainer performance of quantities of Min-K insulation and miscellaneous debris greater than that which is addressed deterministically in the plant design basis. Using the guidance in Regulatory Guide 1.174, risk-informed analysis of the effects of quantities of Min-K and miscellaneous debris greater than that which is deterministically addressed in the plant design basis is shown to result in a CDF that lies in Region III, i.e., very small change" in risk, as defined in the Regulatory Guide.

FERMI 2 UFSAR A-41 REV 24 11/22 Chemical Quantity Location Distance From Control Center (ft)

Liquid nitrogen 6000 gal West wall of Reactor building 170 In general, Fermi 2 is in compliance with Regulatory Guide 1.78, Revision 1. However, there are shipments of hazardous chemicals by rail and road routes within a 5-mile radius of the plant. The closest transportation line lies about 3.5 miles from the plant. As discussed in Section 6.4.3.4, at this distance, a release of a hazardous chemical is not considered a threat to Fermi 2 control room habitability.

A.1.79 REGULATORY GUIDE 1.79 (September 1975, Revision 1),

PREOPERATIONAL TESTING OF EMERGENCY CORE COOLING SYSTEMS FOR PRESSURIZED WATER REACTORS This guide is not applicable to Fermi 2, which is a BWR.

A.1.80 REGULATORY GUIDE 1.80 (June 1974), PREOPERATIONAL TESTING OF INSTRUMENT AIR SYSTEMS Preoperational testing of the control air system was in accordance with this guide.

A.1.81 REGULATORY GUIDE 1.81 (January 1975, Revision 1), SHARED EMERGENCY AND SHUTDOWN ELECTRIC SYSTEMS FOR MULTI-UNIT NUCLEAR POWER PLANTS This guide is not applicable to Fermi 2 because the current design incorporates only a single nuclear generating unit.

A.1.82 REGULATORY GUIDE 1.82 (May, 1996, Revision 2), WATER SOURCES FOR LONG TERM RECIRCULATION COOLING FOLLOWING A LOSS-OF-COOLANT ACCIDENT Consistent with Section D, the Detroit Edison response to NRC Bulletin 96-03 committed to replace the original RHR and CS suction strainers with new, larger passive strainers designed to meet the sizing criteria of Revision 2 of this regulatory guide. The new strainers, which were designed and installed in RF06, are of the GE optimized stacked-disk [OSD] design.

Whereas the original design sizing was predicated on the deterministic assumption of 50%

plugging, the new OSD strainers were designed under the commitment to satisfy the mechanistic design methodology described in Revision 2 of the Regulatory Guide. In their closure of the Fermi response to Bulletin 96-03, the NRC expressed their understanding that the design of the Fermi OSD strainers was performed in accordance with the method provided in NEDO-32686, BWROG Utility Resolution Guidance. The NRC SER that approved the URGs did not accept its proposed analytical methodology for calculating debris head loss and instead stipulated that the calculation of debris head loss were based on vendor supplied analytical correlations developed from tested performance. This requirement is satisfied by utilizing the debris head loss methodology in the NRC-approved GE Licensing -2 NRC-24-0064 Page 3 of 6

FERMI 2 UFSAR A-42 REV 24 11/22 Topical Report NEDO-32721P-A, except as modified to correct elements of the method affected by errors identified in GE Safety Communication 08-02.

A.1.83 REGULATORY GUIDE 1.83 (July 1975, Revision 1), INSERVICE INSPECTION OF PRESSURIZED WATER REACTOR STEAM GENERATOR TUBES This guide is not applicable to Fermi 2, which is a BWR.

A.1.84 REGULATORY GUIDE 1.84 (September 1983, Revision 21), DESIGN AND FABRICATION CODE CASE ACCEPTABILITY--ASME SECTION III, DIVISION 1 The Fermi 2 plant is in compliance with Regulatory Guide 1.84.

To ensure integrity of the RCPB commensurate with its important safety function, Fermi 2 has applied the code cases of the ASME Boiler and Pressure Vessel Code Section III, to design, fabrication, erection, and testing of Class 1 components within the limitations set forth in 10 CFR 50, Section 50.55(a).

For specific identification of the code cases used, refer to Table 5.2-3.

A.1.85 REGULATORY GUIDE 1.85 (September 1983, Revision 21), MATERIALS CODE CASE ACCEPTABILITY--ASME SECTION III, DIVISION 1 To ensure integrity of the RCPB commensurate with its important safety function, Fermi 2 has applied the code cases of the ASME Boiler and Pressure Vessel Code Section III, to design, fabrication, erection, and testing of Class 1 components within the limitations set forth in 10 CFR 50.55(a) and Regulatory Guide 1.85. Thus the Fermi 2 RCPB is in compliance with the positions of this guide.

For specific identification of the code cases used, refer to Table 5.2-3.

A.1.86 REGULATORY GUIDE 1.86 (June 1974), TERMINATION OF OPERATING LICENSES FOR NUCLEAR REACTORS This guide is not presently applicable to Fermi 2. At the time of decommissioning and dismantlement of the Fermi 2 plant, Edison intends to follow procedures in compliance with this guide.

A.1.87 REGULATORY GUIDE 1.87 (June 1975, Revision 1), GUIDANCE FOR CONSTRUCTION OF CLASS 1 COMPONENTS IN ELEVATED TEMPERATURE REACTORS (SUPPLEMENT TO ASME SECTION III CODE CASES 1592, 1593, 1594, 1595, and 1596)

This guide is not applicable to the Fermi 2 BWR. -2 NRC-24-0064 Page 4 of 6 delete period

, (hereafter referred to as "NEDO-32721P-A", with the understanding that "NEDO-32721P-A" includes the corrections in GE Safety Communication 08-02).

Add Insert 2 from the following page as a continuation of A.1.82

-2 NRC-24-0064 Page 5 of 6 INSERT 2 DTE has amended its ECCS suction strainer licensing basis consistent with the U.S. Nuclear Regulatory Commissions Policy Statement on probabilistic risk assessment (PRA). The methodology employed is identified as a risk over deterministic approach. The basic principle of the risk over deterministic analysis is that operational risks posed by accident scenarios, debris sources, and assumptions considered during original ECCS strainer design are addressed by the deterministic design basis (shown to be acceptable using NEDO-32721P-A). Operational risks posed by newly identified failure modes and debris sources, such as tags/labels and from Min-K insulation applied in containment penetrations, are addressed by risks over or beyond the deterministic design basis and are quantified based on the extent to which they impact incremental changes to core damage frequency (CDF) and large early release frequency (LERF).

The risk analysis is described in detail in Attachment 3 of License Amendment Request for DTE Fermi Risk Informed ECCS Evaluation (SERCO-REP-DTE-22609-02 R1). At a high level, transported post-LOCA debris quantities from postulated pipe breaks at each Class 1 weld location were computed and compared to deterministic limits based on NEDO-32721P-A. In addition, fiber debris thickness accumulated on active strainers during each break scenario was compared to an assumed 1/8th-inch strainer failure criterion. CDF and LERF contributions for each break where deterministic limits or 1/8th-inch debris thickness were exceeded were summed and the total CDF and LERF from all break cases were compared to the risk region definitions in US NRC Reg Guide 1.174. Consequently, the conditions under which strainers are evaluated must include review of (1) the quantities of debris, other than those attributable to tags/labels type materials and from Min-K insulation applied in containment penetrations are within limits in DC-5979 Vol I for determinist basis, and (2) the total CDF and LERF from all break cases, including the effects of tags/labels type material and from Min-K insulation applied in containment penetrations are within the bounds of the Risk-Informed analysis. These two conditions comprise the acceptance criteria that would need to be satisfied if new potential debris is discovered.

The risk analysis and the amended ECCS suction strainer licensing basis apply only to use of a risk-informed methodology to address potential debris quantities arising from tags/labels type material and from Min-K insulation applied in containment penetrations exceeding those currently evaluated in the deterministic licensing methodology. The risk analysis in the amendment applies to the plant condition existing at the time of License Amendment XXX* approval, i.e., the amendment is not intended to allow intentional introduction of additional miscellaneous or Min-K debris sources in the future. The risk analysis accommodates up to 100 ft2 of total obstructed strainer surface area caused by overlapping miscellaneous debris arriving at the strainers from all identified sources. The risk

-2 NRC-24-0064 Page 6 of 6 analysis does not apply to the design debris loads, (initially defined in Fermi Calculation DC-5979 Rev-B at the time of amendment) that are successfully addressed using the methodology defined in NEDO-32721P-A.

The scope of the amendment does not apply to any existing configuration controls, containment cleanliness programs, or containment inventory monitoring practices. These are not being modified or relaxed by the amendment. Existing controls include equipment labeling procedures and engineering review of all changes to containment insulation and other potential debris sources. Fermi does not anticipate any new procedural changes arising from the LAR. Fermi intends to observe all existing material controls with emphasis on labels, Min-K insulation, and fiber insulation.

DTE has demonstrated that the risk significance of potential additional debris loads posed by tags/labels type material and Min-K in containment penetrations is very-low as defined by Region III of RG 1.174 in terms of incremental change to core damage frequency (CDF) and incremental changes to large early release frequency (LERF). Regulatory Guide 1.174 permits consideration of accident scenario frequency in combination with accident scenario magnitude provided that the risk-informed analysis (1) meets current regulation, or is accompanied by requested exemptions; (2) is consistent with the defense-in-depth philosophy; (3) maintains adequate safety margin; (4) is small and consistent with the NRC Safety Goal policy; and (5) is monitored by performance measurement strategies that are discussed in Attachment 3 to the Fermi LAR.

Key aspects of the analysis supporting the amendment that cannot be changed without NRC prior approval are: (1) baseline risks must remain in RG 1.174 Risk Region III as computed using the approved assumption of 100 ft2 of total obstruction caused by overlapped miscellaneous debris (tags/labels) transported to the clean strainer area of all active strainers; (2) the definition of strainer success/failure accepted by NRC (i.e., 1/8th inch of fiber on any single strainer causing core damage); and (3) observance of all existing material controls with emphasis on labels, Min-K insulation, and fiber insulation.

• Amendment number will be changed to the number provided at the time the license amendment is approved.

to NRC-24-0064 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Requests for Exemptions for DTE Fermi Risk-Informed ECCS Evaluation (Revised) 2-1 General 2-2 Request for Exemption from 10CFR50.46(a)(1) 2-3 Request for Exemption from GDC-35 2-4 Request for Exemption from GDC-38

-1 NRC-24-0064 Page 1 of 10 2-1 General Introduction In support of the DTE Electric Company (DTE) risk-informed approach to addressing the impact of isolated debris sources on the Emergency Core Cooling System (ECCS) suppression pool strainer performance at Fermi Unit 2 (Fermi 2), Attachment 2 Sections 2-2 through 2-4 provide DTE requests for exemptions under 10CFR50.12 from certain requirements in 10CFR50.46 and 10CFR50 Appendix A, General Design Criteria (GDC). The exemption requests complement a proposed license amendment request (LAR) provided in Attachment 1 to this letter, proposing methodology changes that will be incorporated in the Fermi 2 Updated Final Safety Analysis Report (UFSAR) based on NRC acceptance of the risk-informed method and results. No changes are requested for the Technical Specifications under this proposed LAR. Note that acronyms used in this Attachment are defined in Attachment 1.

Specifically, "the proposed change addressed by the LAR and the accompanying exemptions is to apply a risk-informed method rather than a strictly deterministic method to quantify the risk associated with additional debris sources identified in Attachment 1 and to establish a high probability of success for performance of ECCS based on guidance in Regulatory Guide (RG) 1.174.

It may be inferred by regulatory precedent that licensees are required to demonstrate compliance with the regulations cited below using a bounding calculation or other deterministic method.

DTE requests, in Attachment 1, relief from a solely deterministic method in order to enable the use of the risk-informed method to demonstrate acceptable ECCS and containment heat removal performance with regard to the effects of LOCA generated debris. While demonstrating very low risk, as defined by applicable guidance, the risk-informed analysis does not strictly satisfy all elements of the cited regulations, e.g., 10 CFR 50.46(a)(1)(i), because the NRC has interpreted these regulations as requiring a deterministic approach and bounding calculation to show compliance with ECCS and CSS performance criteria. Thus, the exemptions are deemed necessary to implement the risk-informed analysis method in the Fermi 2 licensing basis.

The exemptions from regulation are requested only for the scope of debris effects that exceed the quantities that have been shown to be acceptable using deterministic design basis analysis, which documents successful ECCS performance on a deterministic basis. Note that in the balance of this document, debris quantities that exceed those shown to be acceptable based on deterministic analysis are referred to as debris effects, additional debris, or similar.

Specific exemption requests, pertaining to requirements that concern the Emergency Core Cooling System (ECCS) and the containment cooling mode of the ECCS function for core cooling and containment heat removal following a postulated loss of cooling accident (LOCA),

are provided as follows:

-1 NRC-24-0064 Page 2 of 10 Attachment 2-2, Request for Exemption from 10CFR50.46(a)(1)

Attachment 2-3, Request for Exemption from GDC 35 Attachment 2-4, Request for Exemption from GDC 38 Approval of the exemptions will allow use of a risk-informed method accounting for the probabilities and uncertainties associated with mitigation of the effects of debris following postulated LOCAs. The method evaluates the effects on strainer blockage and RHR/CS pump NPSH resulting from post-LOCA debris. In order to confirm acceptable performance, the risk associated with additional debris sources is evaluated to include the failure mechanisms associated with loss of core cooling and strainer blockage.

Each separate Attachment 2-2 through 2-4 identifies the applicable rule from which exemption is requested, the regulatory requirements involved, the purpose of the request, and the technical basis and justification for the exemption request, including the presence of special circumstances pursuant to 10CFR50.12(a). The requested exemptions are part of a risk-informed approach to address the impact of retaining the additional debris sources in the licensing basis. The risk-informed approach is designed to be consistent with the guidance in Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis."

The scope of the exemptions applies for the limited debris effects addressed in the risk-informed element of the Fermi RoverD methodology as described in Attachment 3 (SERCO-REP-DTE-22609-02, Fermi-2 Risk Informed ECCS Strainer Performance Evaluation) that was used to respond to a series of corrective actions regarding identified debris sources exceeding the existing Fermi strainer design basis. Fermi 2 retains the deterministic methodology in the current design basis for the existing debris loads but modifies the license to accept the identified debris sources exceeding the current design basis using a risk informed methodology following the guidance in RG 1.174.

The DTE risk-informed approach addresses the five key principles in RG 1.174 for risk-informed decision-making. The resulting risk metrics, i.e. changes in Core Damage Frequency (CDF) and Large Early Release Frequency (LERF), associated with these debris source concerns are used to determine whether plant modifications are warranted to ensure acceptable strainer performance. The requested exemptions support this approach.

The DTE risk approach is similar in method to the STP pilot study (ML17038A223) that suggests additional debris loads, or variations in debris loads, identified at Fermi 2 may be dispositioned by demonstrating low or very-low risk significance, as defined by RG 1.174 in terms of incremental change to core damage frequency (CDF) and incremental change to large early release frequency (LERF).

-1 NRC-24-0064 Page 3 of 10 Based on the results of analyses for Fermi 2, documented in Attachment 3, the risk from the effects of additional debris is within Region III, "Very Small Changes," of RG 1.174. Thus, no additional physical changes to the facility or changes to the operation of the facility are proposed.

Background and Overview Fermi LAR Attachment 1 is "License Amendment Request for DTE Fermi Risk Informed ECCS Evaluation". Attachment 1 is designated as Attachment 1-1.

Fermi LAR Attachment 1 has an Attachment 1-2, "UFSAR Page Markups", designated as "Attachment 1-2".

Fermi LAR Attachment 2 (this document) is "Requests for Exemptions for DTE Fermi Risk-Informed ECCS Evaluation". Attachment 2 is designated as "Attachment 2-1".

Fermi LAR Attachment 2 (this document) includes Attachments 2-2, 2-3, and 2-4 that address the deterministic requirements in 10CFR50.46, GDC 35 and 38 for which exemptions are proposed. Specifically:

• -2, Request for Exemption from 10CFR50.46(a)(1)

• -3, Request for Exemption from GDC 35

• -4, Request for Exemption from GDC 38 is SERCO-REP-DTE-22609-02, R0, SERCO-REP-DTE-22609-02, Fermi-2 Risk Informed ECCS Strainer Performance Evaluation.

Special Circumstances Common to Proposed Exemptions to 10CFR50.46(a)(1), GDC 35 and GDC 38 10CFR50.12(a)(2)(ii) applies:

Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.

An objective of each of the regulations (10CFR50.46(a)(1), GDC 35 and GDC 38) for which an exemption is proposed is to maintain low risk to the public health and safety through functions that are supported by the ECCS, including the suppression pool as a water source. By regulatory precedent, licensees are required to demonstrate this capability by the use of a bounding calculation or other deterministic method. The supporting analysis demonstrates that a risk-informed approach to ECCS performance is consistent with the Commission's Safety Goals for nuclear power plants and supports operation of those functions with a high degree of reliability.

-1 NRC-24-0064 Page 4 of 10 Consequently, the special circumstances described in 10CFR50.12(a)(2)(ii) apply to each of the exemptions proposed by DTE.

10CFR50.12(a)(2)(iii) applies:

Compliance would result in undue hardship or other costs that are significantly in excess of those contemplated when the regulation was adopted or that are significantly in excess of those incurred by others similarly situated.

In order to meet a deterministic strainer design limit for debris loading, Min-K insulation in the penetrations at Fermi 2 would need to be removed and replaced. In terms of potential radiation expose to personnel, the affected penetrations are in very challenging drywell locations that would require significant time and personnel protections to access. The total dose estimated to be expended for Fermi 2 in support of insulation replacement in the penetrations is expected to be well in excess of industry norms and would not be consistent with plant ALARA objectives.

Any materials removed from containment must be disposed of as potentially contaminated waste. If a suitable insulation could be found for replacing Min-K in very small gaps, that material would also be treated as waste at the end of plant life, thus, doubling the amount of penetration-specific waste to achieve a very small risk reduction (as defined by RG 1.174).

The dose considerations discussed above demonstrate that compliance would result in substantial personnel exposure that is not commensurate with the expected safety benefit based on the results showing that the risk associated with the potential debris concerns is in Region III in RG 1.174. Consequently, the special circumstances described in 10CFR50.12(a)(2)(iii) apply to each of the exemptions proposed by DTE.

Environmental Consideration Pursuant to the requirements of 10CFR51.41 and 10CFR51.21, "Criteria for and identification of licensing and regulatory actions requiring environmental assessments," the discussion in the sections beginning with Identification of the Proposed Action, below, is provided. As demonstrated in the discussion below, the requested exemptions qualify for a categorical exclusion of 10CFR51.22. However, if the NRC determines that an environmental assessment is necessary, the information that follows will support a finding of no significant impact. The assessment applies to all of the proposed exemptions.

Identification of the Proposed Action The proposed exemptions allow for use of a risk-informed approach to evaluate the residual risk associated with potential debris sources greater than those currently evaluated within the strainer design basis, i.e., those concerns that have not been fully addressed using deterministic methods.

The proposed exemptions are for the purpose of amending the license basis for acceptable mitigation of the effects of debris during low-pressure or containment cooling modes of the

-1 NRC-24-0064 Page 5 of 10 ECCS following postulated LOCAs. Approval of the proposed exemptions would complement approval of the methodology addition to be incorporated in the UFSAR, as provided in to this letter, for implementation of the risk-informed method at DTE Fermi 2.

Need for the Proposed Action In the Commission's Policy Statement on "Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities", the Commission stated that "the use of PRA technology in NRG regulatory activities should be increased to the extent supported by the state-of-the-art in PRA methods and data and in a manner that complements the NRC's deterministic approach" and that is consistent with traditional defense-in-depth concepts.

The intent of the Commission's Policy Statement is to use the PRA to further understand the risk associated with a proposed change for the purpose of removing unnecessary conservatism associated with regulatory requirements in order to focus attention and allocation of resources to areas of true safety significance.

To implement the Commission Policy Statement, the NRC issued RG 1.174 to provide guidance on an acceptable approach to risk-informed decision-making, based on a set of five key principles. The proposed action (approval of stated exemptions) is needed to allow DTE to use a risk-informed method to address the potential for insulation and other debris generated in the event of a postulated LOCA within the containment to impact acceptable operation for ECCS and challenge the ability of ECCS to provide adequate long-term core cooling. The proposed exemptions are consistent with the key principle in RG 1.174 requiring the proposed change to meet current regulations unless explicitly related to a requested exemption.

Environmental Impacts Consideration The proposed exemptions have been evaluated and determined to result in no significant radiological environmental impacts associated with the implementation of the change. This conclusion is based on the following:

The proposed exemptions allow a risk-informed method for demonstrating that the design and licensing bases for the ECCS are not significantly impacted by debris effects. No physical modifications or changes to operating requirements are proposed for the site or facility, including any systems, structures and components relied upon to mitigate the consequences of a LOCA.

The intent of the proposed change is to quantify the risk associated with identified potential debris sources. This quantification, provided in the form of risk metrics using the guidance in RG 1.174, demonstrates that the risk is in Region III, "Very Small Changes," in RG 1.174.

Therefore, the proposed exemptions support a change that represents a very small increase in Large Early Release Frequency (LERF) that corresponds to an insignificant impact on the environment.

-1 NRC-24-0064 Page 6 of 10 Based on the results of the risk-informed method demonstrating that the increases in risk are very small, the proposed exemptions have a negligible effect on accident probability, and adequate assurance of public health and safety is maintained. The proposed exemption does not involve any changes to the facility or facility operations that could create a new or significantly affect a previously analyzed accident or release path, and therefore would result in no significant changes in the types or quantities of radiological effluents that may be released offsite. The proposed change does not affect the generation of any radioactive effluents and does not affect any of the permitted effluent release paths.

The proposed exemptions have no impact on requirements related to the integrity of the reactor coolant system piping or any other aspect related to the initiation of a LOCA. No physical modifications or changes to operating requirements are proposed for the facility, including any systems, structures and components relied upon to mitigate the consequences of a LOCA.

Therefore, the proposed exemption does not affect the probability of an accident initiator.

The proposed exemptions do not significantly impact a release of radiological effluents during and following a postulated LOCA. The design-basis LOCA radiological consequence analysis in the current licensing basis is a deterministic evaluation based on the assumption of a major rupture of the reactor coolant system piping and a significant amount of core damage as specified in RG 1.183. The current licensing basis analysis shows the resulting doses to the public and to control room and technical support center personnel are acceptable. The proposed change validates and does not change the input parameter values used in the radiological analysis.

Therefore, the proposed exemption does not affect the amount of radiation exposure resulting from a postulated LOCA.

The proposed exemptions do not involve any changes to the site property, physical changes to the facility, or changes to the operation of the facility. Therefore, there are no irreversible and irretrievable commitments of resources which would be involved in the proposed action should it be implemented. The risk-informed method requires a determination that the risk associated with the proposed change meets the Commission's safety goals. Therefore, the proposed action would not result in a significant increase in any radiological hazard beyond those events previously analyzed in the UFSAR. There will be no change to radioactive effluents that affect radiation exposures to plant workers and members of the public. Therefore, no significant changes or different types of radiological impacts are expected as a result of the proposed action. The proposed exemptions do not change the input parameter value used in the radiological analysis.

Therefore, the proposed change would not significantly increase the probability or consequences of an accident, and there will be no significant offsite impact to the public from approval of the proposed exemptions.

No additional physical modifications or changes to operating requirements are proposed for the facility, including any systems, structures and components relied upon to mitigate the

-1 NRC-24-0064 Page 7 of 10 consequences of a LOCA. Therefore, the proposed exemptions do not result in a significant increase in individual or cumulative occupational radiation exposure and will not cause radiological exposure in excess of the dose criteria for restricted and unrestricted access specified in 10 CFR Part 20.

The proposed exemptions do not involve any changes to non-radiological plant effluents or any activities that would adversely affect the environment. The proposed exemptions do not affect any procedures used to operate the facility, or any physical characteristics of the facility, systems, structures, and components. The proposed change only pertains to the licensing basis for components located within the restricted area of the facility, to which access is limited to authorized personnel. Therefore, the proposed exemptions do not create any significant non-radiological impacts on the environment in the vicinity of the plant.

Since implementation of the exemption requests, if approved, would result in no physical changes to the facility, there is no possibility of irreversible or irretrievable commitments of resources. Similarly, the proposed exemptions do not involve the use of any resources not previously considered by the NRC in its past environmental statements for issuance of the facility operating licenses or other licensing actions for the facility. As a result, the proposed exemptions do not involve any unresolved conflicts concerning alternative uses of available resources.

Alternatives The alternative to approval of these exemptions is compliance with the existing provisions in 10CFR50.46(a)(1) and the relevant GDCs. Compliance with 10CFR50.46(a)(1) and the relevant GDCs would entail removal and disposal of significant amounts of insulation and installation of new insulation less likely to impact strainer performance in the event of a LOCA. As discussed below, the alternative would not be environmentally preferable, or cost justified.

The exemptions entail a very small risk, and correspondingly, an environmental impact which is so small that it is remote and speculative for environmental assessment purposes.

Removal and reinstallation of insulation would entail significant appreciable radiation exposures to workers. This option results in extensive modifications to the facility and significant occupational dose. Under the alternative action (strict compliance with applicable regulation),

replacement of insulation in penetrations would double the volume of radiologically contaminated waste associated with these reactor locations, because the waste would be handled first in compliance with regulation and then a second time during decommissioning. As such, the alternative is not environmentally preferable. Additionally, the anticipated very high cost of the installation replacement is not justified in light of the very small risk associated with the risk-informed exemptions.

-1 NRC-24-0064 Page 8 of 10 Categorical Exclusion Consideration DTE has evaluated the proposed exemptions against the criteria for identification of licensing and regulatory actions requiring environmental assessments in accordance with 10CFR51.21 and determined that the proposed exemptions meet the criteria and is eligible for categorical exclusion as set forth in 10CFR51.22, "Criterion for categorical exclusion; identification of licensing and regulatory actions eligible for categorical exclusion or otherwise not requiring environmental review," paragraph (c)(9).

This determination is based on the fact that these exemption requests arise from requirements under 10CFR50 with respect to the installation or use of a facility component located within the restricted area, as defined in 10CFR20, specifically, to authorize a change to the licensing basis for the ECCS as it relates to acceptable suppression pool strainer performance following a postulated LOCA. The proposed exemptions have been evaluated to meet the following criteria under 10CFR51.22(c)(9).

(i) The exemption involves no significant hazards consideration.

An evaluation of the three criteria set forth in 10CFR50.92(c) as applied to the exemptions is provided below. The evaluation is consistent with the no significant hazards consideration determination provided in Attachment 1 in support of the LAR.

(1)

The proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

Approval of the proposed exemptions and accompanying license amendment request would allow the results of a risk-informed evaluation to be included in the UFSAR that concludes the ECCS will operate with a high probability following a LOCA when considering the impacts and effects of debris accumulation on the ECCS strainers following loss of coolant accidents (LOCAs).

The proposed change does not implement any physical changes to the facility or any structures, systems and components (SSCs), and does not implement any changes in plant operation. The proposed change confirms that required SSCs supported by the ECCS suction strainers will perform their safety functions with a high probability, and does not alter or prevent the ability of SSCs to perform their intended function to mitigate the consequences of an accident previously evaluated within the acceptance limits. The safety analysis acceptance criteria in the UFSAR continue to be met for the proposed change. The proposed change does not affect initiating events because it addresses existing initiating events, i.e., loss of coolant accidents. The proposed change does not significantly affect the operation of the containment systems to ensure that there is a large margin between the temperature and pressure conditions reached in the containment

-1 NRC-24-0064 Page 9 of 10 and those that would lead to failure so that there is a high degree of confidence that damage of the containment cannot occur.

The calculated risk associated with the proposed change is very small and in Region III as defined by RG 1.174, for both CDF and LERF. As required in the guidance of RG 1.174, there is substantial safety margin and defense in depth that provide additional confidence that the design basis functions are maintained.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of any accident previously evaluated in the UFSAR.

(2)

The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.

The proposed change is a risk-informed analysis of debris effects from accidents that are already evaluated in the DTE UFSAR; no new or different kind of accident is being evaluated. The change neither installs nor removes any plant equipment, nor alters the design, physical configuration, or mode of operation of any plant structure, system, or component. The proposed change does not introduce any new failure mechanisms or malfunctions that can initiate an accident. The proposed change does not introduce failure modes, accident initiators, or equipment malfunctions that would cause a new or different kind of accident.

Therefore, the proposed change does not create the possibility for a new or different kind of accident from any accident previously evaluated.

(3)

The proposed change does not involve a significant reduction in a margin of safety.

The proposed change does not involve a change in any functional requirements, the configuration, or method of performing functions of plant SSCs. The effects from all double-ended guillotine breaks for all piping sizes up to and including the largest pipe in the reactor coolant system, are analyzed. Appropriate redundancy and consideration of loss of offsite power and worst-case single failure are retained, such that defense-in-depth is maintained.

Application of the risk-informed methodology showed that the increase in risk from the contribution of debris effects is very small as defined by RG 1.174 and that there is adequate defense in depth and safety margin. Consequently, DTE determined that the suppression pool ECCS strainers will continue to support the ability of safety related components to perform their design functions when the effects of debris are considered. The proposed change does not alter the manner in which safety limits are determined or deterministic acceptance criteria associated with a safety limit are fulfilled. The proposed change does not implement any changes to plant operation and does not significantly affect SSCs that respond to safely shutdown the plant and to maintain the plant in a safe shutdown condition. The proposed change does not significantly

-1 NRC-24-0064 Page 10 of 10 affect the existing safety margins in the barriers for the release of radioactivity. There are no changes to any of the safety analyses in the UFSAR. Therefore, the proposed change does not involve a significant reduction in a margin of safety.

(ii)

The proposed exemptions involve no significant change in the types or significant increase in the amounts of any effluents that may be released offsite.

No physical modifications or changes to operating requirements are proposed for the facility, including any systems, structures and components relied upon to mitigate the consequences of a LOCA. Approval of the exemptions requires the calculated risk associated with debris effects to meet the acceptance guidelines in RG 1.174, thereby maintaining public health and safety.

Therefore, there is no significant change in the types or significant increase in the amounts of any effluents that may be released offsite.

(iii)

The proposed exemptions involve no significant increase in individual or cumulative occupational radiation exposure.

No physical modifications or changes to operating requirements are proposed for the facility, including any systems, structures and components relied upon to mitigate the consequences of a LOCA. Therefore, with respect to installation or use of a facility component located within the restricted area there is no significant increase in individual or cumulative occupational radiation exposure as a result of granting the exemption requests. Approval of the exemption requests avoids significant occupational dose exposure and other occupational hazards associated with insulation removal, disposal, and replacement that would be performed to achieve compliance with existing regulations.

Based on the above, DTE concludes that the proposed exemptions meet the eligibility criteria for categorical exclusion set forth in 10CFR51.22(c)(9). Additional technical justification for this conclusion is provided on the basis that the guidance and acceptance criteria provided in RG 1.174 are satisfied as described in Attachment 3.

-2 Request for Exemption from 10CFR50.46(a)(1)

-2 NRC-24-0064 Page 1 of 8 Request for Exemption from Certain Requirements of 10CFR50.46(a)(1)

1.

Exemption Request Pursuant to 10CFR50.12, DTE Electric Company (DTE) is submitting, this request for exemption from certain requirements of 10CFR50.46(a)(1), "..other requirements," as it relates to using specific deterministic methodology to evaluate the effects of debris on long-term core cooling.

A portion of 10 CFR 50.46(a)(1) is shown below with the "other properties" portion (for which exemption is requested) in bold italics.

(a)(1)(i) Each boiling or pressurized light-water nuclear power reactor fueled with uranium oxide pellets within cylindrical zircaloy or ZIRLO cladding must be provided with an emergency core cooling system (ECCS) that must be designed so that its calculated cooling performance following postulated loss-of-coolant accidents conforms to the criteria set forth in paragraph (b) of this section. ECCS cooling performance must be calculated in accordance with an acceptable evaluation model and must be calculated for a number of postulated loss-of-coolant accidents of different sizes, locations, and other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated. Except as provided in paragraph (a)(1)(ii) of this section, the evaluation model must include sufficient supporting justification to show that the analytical technique realistically describes the behavior of the reactor system during a loss-of-coolant accident. Comparisons to applicable experimental data must be made and uncertainties in the analysis method and inputs must be identified and assessed so that the uncertainty in the calculated results can be estimated. This uncertainty must be accounted for, so that, when the calculated ECCS cooling performance is compared to the criteria set forth in paragraph (b) of this section, there is a high level of probability that the criteria would not be exceeded. Appendix K, Part II Required Documentation, sets forth the documentation requirements for each evaluation model. This section does not apply to a nuclear power reactor facility for which the certifications required under §50.82(a)(1) have been submitted.

The DTE risk-informed approach to addressing potential debris sources and adequate ECCS NPSH is consistent with the NRC staff safety evaluation of NEI 04-07 that discussed the modeling of strainer performance as follows:

While not a component of the 10CFR50.46 ECCS evaluation model, the calculation of sump (strainer) performance is necessary to determine if the sump and the residual heat removal system are configured properly to provide enough flow to ensure long-term cooling, which is an acceptance criterion of 10CFR50.46. Therefore, the staff considers the modeling of sump performance as the validation of assumptions made in the ECCS evaluation model. Since the modeling of sump performance is a boundary calculation for the ECCS evaluation model, and acceptable sump performance is necessary for

-2 NRC-24-0064 Page 2 of 8 demonstrating long-term core cooling capability (10CFR50.46(b)(5)), the requirements of 10CFR50.46 are applicable.

The scope of the requested exemption applies for limited debris effects addressed in the DTE RoverD methodology described in Attachment 3 that was used to respond to a corrective action associated with Min-K found in the drywell penetrations at Fermi 2. The LOCA break sizes and locations potentially generating an amount of Min-K debris exceeding the quantity established by the DTE original design basis testing and analysis are described in Attachment 3.

The key elements of the exemption request are:

1.

It applies only to the effects of penetration Min-K and non-conforming containment label debris as described in Attachment 3.

2.

It applies only for LOCA breaks that can generate and transport debris that is not bounded by the DTE strainer failure criteria established in Attachment 3.

3.

It applies to any LOCA break that can generate and transport debris that is not bounded by strainer failure criteria and provided that the CDF and LERF associated with the break size remain in Region III of RG 1.174.

This exemption request is complemented by the accompanying License Amendment Request (LAR) (Attachment 1) seeking NRC approval of the changes to the Fermi 2 Updated Final Safety Analysis Report (UFSAR), to amend the licensing basis based on acceptable design of the ECCS suction strainers. The risk-informed method provides high probability assurance that, as calculated in the ECCS evaluation model (Attachment 3), ECCS operation, including strainer performance and debris mitigation, will be acceptable.

2.

Regulatory Requirements Involved By regulatory precedent, licensees are required to demonstrate compliance with the relevant regulations by the use of a bounding calculation or other deterministic method. DTE seeks exemption to the extent that 10CFR50.46(a)(1) requires deterministic-only calculations or other analyses to address the debris concerns related to acceptable plant performance during core and containment cooling modes following a LOCA. The proposed changes to the licensing basis, submitted for NRC approval with Attachment 1, address the additional debris loads at the ECCS strainers for Fermi 2 on the basis that the associated risk is shown to meet the acceptance guidelines in Regulatory Guide (RG) 1.174 and that, in conjunction with the existing licensing basis, adequate safety is demonstrated.

This exemption request is for the purpose of allowing the use of a risk-informed method to demonstrate acceptable mitigation of the effects of debris following postulated loss of coolant accidents (LOCAs). The effects of LOCA debris have been evaluated, using deterministic methods, to meet the current licensing basis assumptions for analyzing the effects of post-LOCA

-2 NRC-24-0064 Page 3 of 8 debris blockage at the suction strainers; however, these evaluations have not been shown to fully address debris effects for the as-built, as-operated plant. The risk informed approach evaluates the risk associated with additional potential debris sources on ECCS strainer performance beyond those currently established in the strainer design basis, which employed deterministic methods. Based on confirmation of acceptable ECCS design as determined by the resulting risk meeting the acceptance guidelines in RG 1.174, the licensing basis for ECCS is amended by approval of this exemption.

2.1 Evaluation of Impacts on the Balance of 10CFR50.46 and Appendix K to 10CFR50 The exemption request is intended to address ECCS cooling performance design as invoked by the need for documentation of other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated in 10 CFR 50.46(a)(1).

For the purposes of demonstrating the balance of the acceptance criteria of 10CFR50.46, the design and licensing basis descriptions of accidents requiring ECCS operation, including analysis methods, assumptions, and results, which are provided in Fermi 2 UFSAR Chapters 6 and 15 remain unchanged. The performance evaluations for accidents requiring ECCS operation described in UFSAR Chapters 6 and 15, based on the Appendix K Large-Break Loss-of-Coolant Accident (LBLOCA) analysis, demonstrate that for breaks up to and including the double-ended severance of a recirculation loop pipe, the ECCS will limit the clad temperature to below the limit specified in 10CFR50.46 and assure that the core will remain in place and substantially intact with its essential heat transfer geometry preserved.

The requirements of 10CFR50.46(a)(1) remain applicable to the model of record that meets the required features of Appendix K. Approval of the requested exemption does not impact the current ECCS evaluation. The current ECCS evaluation model remains the licensing basis for demonstrating that the ECCS calculated cooling performance following postulated LOCAs fulfills the acceptance criteria.

The DTE risk-informed approach uses the break frequencies from NUREG 1829 to quantify the residual risk associated with the additional debris loads for those LOCAs which have not been resolved using deterministic methods and shows that it meets the acceptance guidelines defined in RG 1.174. The exemption request is specific to the requirement for demonstrating ECCS cooling performance design as required by 10 CFR 50.46(a)(1), which has traditionally been interpreted as requiring deterministic-only evaluation. It is not intended to be applicable to other requirements provided in Appendix K to 10CFR50.

As noted above, the NRC staff considers the modeling of strainer performance (pressure drop) as an input to the ECCS evaluation model, and therefore the requirements of 10CFR50.46 are applicable. Consistent with this, the requirements and attributes for the proposed DTE risk-informed method evaluates all postulated, double-ended guillotine breaks up to and including the largest piping in containment.

-2 NRC-24-0064 Page 4 of 8 Engineering analyses and evaluations to address the deterministic scope of the Fermi 2 ECCS performance analysis are consistent with the Utility Resolution Guidance (URG) and related NRC SER for evaluation of strainer performance. The proposed exemption does not affect any of the 10CFR50.46 (a)(1) or Appendix K requirements for an acceptable ECCS evaluation model and does not change the ECCS acceptance criteria in 50.46(b) as it applies to the calculated results. Application of the exemption request allows use of a risk-informed approach to evaluate the effects of LOCA debris beyond a deterministic strainer failure limit. The results of the risk-informed method demonstrate that the risk associated with additional debris sources beyond those deemed acceptable by deterministic means meet the acceptance guidelines of RG 1.174.

The current licensing basis for addressing the adequacy of ECCS to meet the criteria of 10CFR50.46, including the Appendix K Large-Break LOCA analysis and the associated Chapter 15 accident analysis for LOCA, remain in place.

2.2 Evaluation of Impacts on other Regulatory Requirements - Conclusion The proposed exemption does not result in any physical changes to the facility or changes to the operation of the plant and does not change any of the programmatic requirements. In, the ECCS suction strainer design and hence ECCS design are shown to be acceptable using a risk-informed approach, i.e., with an exemption from 10CFR50.46(a)(1) requirements to use of deterministic evaluation methods. Therefore, compliance with other regulatory requirements that rely on acceptable design for these systems and components continue to be met in the current licensing basis.

3.

Basis for the Exemption Request Under 10CFR50.12, a licensee may request and the NRC may grant exemptions from those requirements of 10CFR50 which are authorized by law, will not present an undue risk to the public health and safety, are consistent with the common defense and security, and when special circumstances are present.

The exemption request ensures compliance with a key principle of RG 1.174, which states "The proposed change meets the current regulations unless it is explicitly related to a requested exemption." This exemption request is provided in conjunction with the proposed License Amendment Request in Attachment 1.

3.1 Justification for the Exemption Request As required by 10CFR50.12(a)(2), the Commission will not consider granting an exemption unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable. DTE has evaluated the proposed exemption against the conditions specified in 10CFR50.12(a) and determined that this proposed exemption meets the requirements for granting an exemption from the regulation, and

-2 NRC-24-0064 Page 5 of 8 that special circumstances are present. The information supporting the determination is provided below.

Pursuant to 10CFR50.12, "Specific exemptions," the NRC may grant exemptions from the requirements of this part provided the following three conditions are met as required by 10CFR50.12(a)(1).

The exemption is authorized by law.

The NRC has authority under the Atomic Energy Act of 1954, as amended, to grant exemptions from its regulations if doing so does not violate the requirements of law. This exemption is authorized by law as is provided by 10CFR50.12 which provides the NRC authority to grant exemptions from 10CFR50 requirements with provision of proper justification. Approval of the exemption from applicable parts of 10CFR50.46(a)(1) does not conflict with any provisions of the Atomic Energy Act of 1954, as amended, any of the Commission's regulations, or any other law.

The exemption does not present an undue risk to the public health and safety.

The purpose of 10CFR50.46 is to establish acceptance criteria for ECCS performance, and together with GDC 35, to provide high confidence that the systems will perform their required functions. The proposed exemption does not involve any modifications to the plant that could introduce a new accident precursor or affect the probability of postulated accidents, and therefore the probability of postulated initiating events is not increased. The PRA and engineering analysis demonstrate that the calculated risk is very small and consistent with the intent of the Commission's Safety Goal Policy Statement, which defines an acceptable level of risk that is a small fraction of other risks to which the public is exposed.

As discussed in previous 10CFR50.46 rulemaking, the probability of a large break LOCA is sufficiently low that the application of a risk-informed approach to evaluate the ability of the ECCS to meet 10CFR50.46 and relevant GDCs with high probability and with low uncertainty, rather than using a calculational model using deterministic methods to achieve similar understanding, would have little effect on public risk. This is applicable to evaluating acceptable strainer performance in support of ECCS in both core and containment cooling modes.

The proposed change is to apply a risk-informed method rather than a strictly deterministic method to quantify the risk associated with additional debris sources and to establish a high probability of success for performance of ECCS in accordance with the ECCS cooling performance design addressed in 10CFR50.46. The risk-informed approach involves a complete evaluation of the spectrum of LOCA breaks, including double-ended guillotine breaks, up to and including the largest pipe in the reactor coolant system. The risk-informed approach analyzes LOCAs, regardless of break size, using the same methods, assumptions, and criteria in order to quantify uncertainties and overall risk metrics. This ensures that large break LOCAs with

-2 NRC-24-0064 Page 6 of 8 relatively small contribution to CDF due to the low probability of such a break as well as smaller break LOCAs with higher probabilities of occurrence are considered in the results. Since the design basis requirement for consideration of double-ended guillotine breaks of the largest pipe in the reactor coolant system is retained and since no physical changes to the facility or changes to the operation of the facility are being made, the existing defense-in-depth and safety margin established for the design of the facility is not reduced.

This exemption only affects 10CFR50.46(a)(1) and does not impact the acceptance criteria for cladding performance that is important to maintain adequate safety margins.

The exemption is consistent with the common defense and security.

The exemption involves a change to the licensing basis for the plant that has no relation to the control of licensed material or any security requirements that apply to DTE Fermi 2. Therefore, the exemption is consistent with the common defense and security.

3.2 Special Circumstances This section discusses the presence of special circumstances as related to 10CFR50.12(a).

10CFR50.12(a)(2) states that NRC will not consider granting an exemption to the regulations unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable.

Such special circumstances are present in this instance to warrant exemption from the implicit requirement in 10CFR50.46(a)(1) with respect to use of a deterministic calculational method as the design basis for demonstrating acceptable strainer performance and to validate that the results of the ECCS evaluation model demonstrating long-term cooling criterion is met. Approval of this exemption request would allow the use a risk-informed method to amend the design basis for acceptable performance of the ECCS strainer, for validation of inputs used in the ECCS evaluation model, and to support the existing licensing bases for compliance with all other parts of 10CFR50.46.

Specifically, 10CFR50.12(a)(2)(ii) applies:

Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.

The intent of 10CFR50.46(a)(1) is to ensure ECCS cooling performance design requirements are fulfilled. This exemption request is consistent with that purpose in that use of the proposed risk-informed approach accounts for the effect of debris on the ECCS cooling performance and supports a high probability of successful ECCS performance, based on the risk results meeting the acceptance guidelines of RG 1.174.

-2 NRC-24-0064 Page 7 of 8 As discussed in the Commission's Policy Statement on "Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities", NRC regulations and their implementation are generally based on deterministic approaches that consider a set of challenges to safety and determine how those challenges should be mitigated.

This exemption is requested to align requirements in the regulations for using deterministic methods to demonstrate acceptable design with risk informed regulation guidance that ensure high probability of system performance and acceptable risk. Regulatory requirements are largely based on a deterministic framework, and are established for design basis accidents, such as the LOCA, with specific acceptance criteria that must be satisfied. Licensed facilities must be provided with safety systems capable of preventing and mitigating the consequences of design basis accidents to protect public health and safety. The deterministic regulatory requirements were designed to ensure that these systems are highly reliable. The LOCA analysis and the General Design Criteria (GDC) were established as part of this deterministic regulatory framework.

In comparison, the risk-informed approach considers nuclear safety in a complementary way by examining the likelihood of a broad spectrum of initiating events and potential challenges, considering the frequencies of a wide range of credible events, and assessing the risk based on the reliability of mitigating systems.

An objective of 10CFR50.46 is to maintain low risk to the public health and safety through a reliable ECCS. The supporting analysis demonstrates that a risk-informed approach to strainer performance is consistent with the Commissions Safety Goals for nuclear power plants, including ECCS operation with a high degree of reliability. Consequently, the special circumstances described in 10CFRS0.12(a)(2)(ii) apply.

Specifically, 10CFR50.12(a)(2)(iii) applies:

Compliance would result in undue hardship or other costs that are significantly in excess of those contemplated when the regulation was adopted, or that are significantly in excess of those incurred by others similarly situated.

The specific hardship is the excessive occupational radiological dose that is expected to be incurred for plant modifications to remove and replace insulation. This was discussed in -1, above.

In conclusion, special circumstances in 10CFR50.12(a)(2)(ii) and 10CFR50.12(a)(2)(iii) are present as required by 10CFR50.12(a)(2) for consideration of the request for exemption to applicable parts of 10CFR50.46(a)(1).

-2 NRC-24-0064 Page 8 of 8

4.

Technical Justification for the Exemption Technical justification for the risk-informed method is provided in Attachment 1 and.

The proposed risk-informed approach meets the key principles in RG 1.174 in that it is consistent with the defense-in-depth philosophy, maintains sufficient safety margins, results in small increase in risk, and is monitored using performance measurement strategies that are discussed in. The proposed exemption from 10CFR50.46(a)(1) enables use of the risk-informed method and is consistent with the key principle in RG 1.174 that requires the proposed change to meet current regulations unless explicitly related to a requested exemption.

The results of analyses in Attachment 3 show that risks associated with the additional debris sources are in Region III, "Very Small Changes," of RG 1.174, and therefore are consistent with the Commission's Safety Goals for public health and safety. *

5.

Conclusion Approval of an exemption to allow the use of the risk-informed approach is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security requirements of 10CFR50.12(a)(1). Furthermore, special circumstances required by 10CFR50.12(a)(2) are present for item 10CFR50.12(a)(2)(ii) in that application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule.

Based on the determination that the risk of the exemption meets the acceptance guidelines of RG 1.174; the results demonstrate there is reasonable assurance that the ECCS will function in the recirculation mode and that the public health and safety will be protected.

6.

Implementation DTE requests that this exemption request be approved for implementation concurrently with review and acceptance of Attachment 1, the LAR modifying the licensing basis of ECCS strainers for select debris from a deterministic basis to a risk-informed basis.

-3 Request for Exemption from General Design Criterion 35

-3 NRC-24-0064 Page 1 of 7 Request for Exemption from Certain Requirements of General Design Criterion 35

1.

Exemption Request Pursuant to 10CFR50.12, DTE is submitting this request for exemption from certain requirements of 10CFR50 Appendix A, General Design Criterion (GDC) 35, which states:

Criterion 35 - Emergency core cooling. A system to provide abundant emergency core cooling shall be provided. The system safety function shall be to transfer heat from the reactor core following any loss of reactor coolant at a rate such that (1) fuel and clad damage that could interfere with continued effective core cooling is prevented and (2) clad metal-water reaction is limited to negligible amounts.

Suitable redundancy in components and features, and suitable interconnections, leak detection, isolation, and containment capabilities shall be provided to assure that for onsite electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming onsite power is not available) the system safety function can be accomplished, assuming a single failure.

By regulatory precedent, licensees are required to demonstrate this capability by the use of a bounding calculation or other deterministic method. DTE requests an exemption from the need to use only deterministic methods, in order to enable the use of a risk-informed method to demonstrate acceptable strainer design and ECCS performance with regard to the effects of LOCA debris.

Approval of this exemption will allow use of a risk-informed method to account for the probabilities and uncertainties associated with mitigation of the effects of debris following postulated LOCAs. The method evaluates the effects on strainer blockage resulting from debris concerns identified within the DTE corrective action program. In order to confirm acceptable ECCS strainer design, the risk associated with post-LOCA debris sources are evaluated to include the failure mechanisms associated with loss of core cooling and strainer blockage.

The scope of the exemption applies for limited debris effects addressed in the DTE RoverD methodology described in Attachment 3 that was used to respond to a corrective action associated with Min-K found in the drywell penetrations at Fermi 2 and unqualified tags/labels found throughout containment. The LOCA break sizes and locations that potentially generate an amount of Min-K that exceeds the quantity established in DTE original design basis testing and analysis are described in Attachment 3. The key elements of the exemption request are:

1. It applies only to the effects of penetration Min-K and non-conforming containment debris as described in Attachment 3.

2. It applies only for LOCA breaks that can generate and transport debris that is not bounded by the DTE strainer failure criteria established in Attachment 3.

-3 NRC-24-0064 Page 2 of 7

3. It applies to any LOCA break that can generate and transport debris that is not bounded by strainer failure criteria, provided that the cumulative CDF and LERF associated with these breaks remain in Region III of RG 1.174.

This exemption request is complemented by the accompanying License Amendment Request (LAR) (Attachment 1), which seeks NRC approval to change the licensing basis in the Fermi 2 Updated Final Safety Analysis Report (UFSAR) to allow the use of a risk-informed approach for demonstrating acceptable design of the ECCS suction strainers. The risk-informed method provides high probability assurance that, as calculated in the ECCS evaluation model (Attachment 3), ECCS operation, including strainer performance and debris mitigation, will be acceptable.

2.

Regulatory Requirements Involved DTE seeks exemption to the extent that GDC 35 requires deterministic calculations or other deterministic analyses to address the debris concerns related to acceptable plant performance during core and containment cooling mode following a LOCA. The proposed changes to the licensing basis, submitted for NRC approval with Attachment 1, address the additional debris loads at the ECCS strainers for Fermi 2 on the basis that the associated risk is shown to meet the acceptance guidelines in Regulatory Guide (RG) 1.174 and that, in conjunction with the existing licensing basis, adequate safety is demonstrated.

This exemption request is for the purpose of allowing the use of a risk-informed method to demonstrate acceptable mitigation of the effects of debris following postulated loss of coolant accidents (LOCAs). The effects of LOCA debris have been evaluated, using deterministic methods, to meet the current licensing basis assumptions for analyzing the effects of post-LOCA debris blockage at the suction strainers; however, these evaluations have not been shown to fully address debris effects for the as-built, as-operated plant. The risk informed approach evaluates the risk associated with additional potential debris sources on ECCS strainer performance beyond those currently established in the strainer design basis, which employed deterministic methods. Based on confirmation of acceptable ECCS design as determined by the resulting risk meeting the acceptance guidelines in RG 1.174, the licensing basis for ECCS compliance with GDC 35 expectation of solely deterministic evaluations will be changed to permit use of a complementary risk-informed methodology.

2.1 Evaluation of Impacts on other Regulatory Requirements - Conclusion The proposed exemption does not result in any physical changes to the facility or changes to the operation of the plant and does not change any of the programmatic requirements. In Attachment 3, the ECCS suction strainer design and hence ECCS design are shown to be acceptable using a risk-informed approach, i.e., with an exemption from GDC 35 requirements to use only deterministic evaluation methods. Therefore, compliance with other regulatory requirements that

-3 NRC-24-0064 Page 3 of 7 rely on acceptable design for these systems and components continue to be met in the current licensing basis.

3.

Basis for the Exemption Request Under 10CFR50.12, a licensee may request and the NRC may grant exemptions from those requirements of 10CFR50 that are authorized for exemption by law, will not present an undue risk to the public health and safety, are consistent with the common defense and security, and when special circumstances are present.

The exemption request meets a key principle of RG 1.174 that states "The proposed change meets the current regulations unless it is explicitly related to a requested exemption." This exemption request is provided in support of the proposed change provided in the License Amendment Request provide in Attachment 1.

3.1 Justification for the Exemption Request As required by 10CFR50.12(a)(2), the Commission will not consider granting an exemption unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable. DTE has evaluated the proposed exemption against the conditions specified in 10CFR50.12(a) and determined that this proposed exemption meets the requirements for granting an exemption from the regulation, and that special circumstances are present. The information supporting the determination is provided below.

Pursuant to 10CFR50.12, "Specific exemptions," the NRC may grant exemptions from the requirements of this part provided the following three conditions are met as required by 10CFR50.12(a)(1):

The exemption is authorized by law.

The NRC has authority under the Atomic Energy Act of 1954, as amended, to grant exemptions from its regulations if doing so does not violate the requirements of law. This exemption is authorized by law as is provided by 10CFR50.12, which provides the NRC authority to grant exemptions from 10CFR50 requirements with provision of proper justification. Approval of the exemption does not conflict with any provisions of the Atomic Energy Act of 1954, as amended, the Commission's regulations, or any other law.

The exemption does not present an undue risk to the public health and safety.

The proposed change is to apply a risk-informed method rather than a strictly traditional deterministic method in order to quantify the residual risk associated with additional debris loads and to establish a high confidence of acceptable ECCS design. The purpose of GDC 35 is to establish an acceptable design for the ECCS, and together with the acceptance criteria of

-3 NRC-24-0064 Page 4 of 7 10CFR50.46, to provide high probability that the systems will perform the required functions.

The proposed exemption does not involve any modifications to the plant that could introduce a new accident precursor or affect the probability of postulated accidents, and therefore, the probability of postulated initiating events is not increased. The PRA and engineering analysis demonstrate that the calculated risk is very small and consistent with the intent of the Commission's Safety Goal Policy Statement, which defines an acceptable level of risk that is a small fraction of other risks to which the public is exposed As discussed in previous 10CFR50.46 rulemaking, the probability of a large break LOCA is sufficiently low that application of a risk-informed approach to evaluate the ability of the ECCS to meet its design requirements with high probability and with low uncertainty, rather than using a calculational model using deterministic methods to achieve similar understanding, would have little effect on public risk. This is applicable to evaluating the effects of debris on the acceptability of ECCS design during the recirculation modes.

The risk-informed approach involves a complete evaluation of the spectrum of LOCA breaks, including double-ended guillotine breaks, up to and including the largest pipe in the reactor coolant system. The risk-informed approach analyzes LOCAs, regardless of break size, using the same methods, assumptions, and criteria in order to quantify uncertainties and overall risk metrics. This ensures that large break LOCAs with relatively small contribution to CDF due to the low probability of such a break as well as smaller break LOCAs with higher probabilities of occurrence are considered in the results. Since the design basis requirement for consideration of a double-ended guillotine break of the largest pipe in the reactor coolant system is retained and since no physical changes to the facility or changes to the operation of the facility are being made, the existing defense-in-depth and safety margin established for the design of the facility is not reduced.

The exemption is consistent with the common defense and security.

The exemption involves a change to the licensing basis for the plant that has no relation to the possession of licensed material or any security requirements that apply to DTE Fermi 2.

Therefore, the exemption is consistent with the common defense and security.

3.2 Special Circumstances This section discusses the presence of special circumstances as related to 10CFR50.12(a).

10CFR50.12(a)(2) states that NRC will not consider granting an exemption to the regulations unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable.

Such special circumstances are present in this instance to warrant exemption from the implicit requirement in GDC 35 to use a deterministic method to demonstrate acceptable ECCS suction

-3 NRC-24-0064 Page 5 of 7 strainer performance. Approval of the exemption request would allow use of a risk-informed method to amend the licensing basis for acceptable ECCS strainer design to demonstrate ECCS design compliance with GDC 35. Specifically, 10CFR50.12(a)(2)(ii) applies:

Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.

The intent of GDC 35 is to ensure ECCS design provides abundant core cooling to mitigate fuel and clad damage and clad metal-water reaction following any loss of reactor coolant. GDC 35 sets forth the general ECCS cooling performance design requirements, which are in addition to the requirements of 10CFR50.46. This exemption request is consistent with the stated purpose in that use of the proposed risk-informed approach demonstrates a high probability of successful ECCS performance, which includes realistically available long-term cooling, based on the risk results meeting the acceptance guidelines of RG 1.174. The risk-informed approach assesses ECCS design for all double-ended guillotine breaks and assesses equipment failures that include loss of offsite power and worst-case single failure, consistent with the GDC 35 requirements.

Since the proposed exemption does not involve any physical changes to the plant, there is no effect on the GDC 35 requirements for ECCS design for redundancy in components and features, interconnections, leak detection, isolation, and containment capabilities. The current licensing basis evaluations for ECCS compliance with GDC 35 for these aspects continue to be met.

As discussed in the Commission's Policy Statement on "Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities", NRC regulations and their implementation are generally based on deterministic approaches that consider a set of challenges to safety and determine how those challenges should be mitigated.

This request does not seek exemption from any explicit language in the regulatory requirements.

Rather, the exemption request addresses the implicit requirements in the regulations for using deterministic methods to demonstrate acceptable design. Regulatory requirements are largely based on a deterministic framework, and are established for design basis accidents, such as the LOCA, with specific acceptance criteria that must be satisfied. Licensed facilities must maintain safety systems capable of preventing and mitigating the consequences of design basis accidents to protect public health and safety. The deterministic regulatory requirements were designed to ensure that these systems are highly reliable. The LOCA analysis and the General Design Criteria (GDC) were established as part of this deterministic regulatory framework.

In comparison, the probabilistic approach considers nuclear safety in a complementary way by examining the likelihood of a broad spectrum of initiating events and potential challenges, considering a wide range of credible events, and assessing the risk based on the reliability of mitigating systems.

-3 NRC-24-0064 Page 6 of 7 An objective of GDC 35 is to maintain low risk to the public health and safety through a reliable ECCS. The supporting analysis provided in Attachment 3 demonstrates that a risk-informed approach to suction strainer performance is consistent with the Commissions Safety Goals for nuclear power plants, including ECCS operation with a high degree of reliability. Consequently, the special circumstances described in 10CFR50.12(a)(2)(ii) apply.

Specifically, 10CFR50.12(a)(2)(iii) applies:

Compliance would result in undue hardship or other costs that are significantly in excess of those contemplated when the regulation was adopted, or that are significantly in excess of those incurred by others similarly situated.

The specific hardship is the excessive occupational radiological dose that is expected to be incurred for plant modifications to remove and replace insulation. This was discussed in -1.

In conclusion, special circumstances in 10CFR50:12(a)(2)(ii) and 10CFR50.12(a)(2)(iii) are present as required by 10CFR50.12(a)(2) for consideration of the request for exemption.

4.

Technical Justification for the Exemption Technical justification for the risk-informed method is provided in Attachment 3 and.

The proposed risk-informed approach meets the key principles in RG 1.174 in that it is consistent with the defense-in-depth philosophy, maintains sufficient safety margins, results in small increase in risk, and is monitored using performance measurement strategies that are discussed in. The proposed change to the licensing basis to allow use of the risk-informed method is consistent with the key principle in RG 1.174 that requires the proposed change to meet current regulations unless explicitly related to a requested exemption.

The results of analyses in Attachment 3 show that the risk associated with GSI-191 concerns is in Region III, "Very Small Changes," of RG 1.174, and therefore are consistent with the Commission's Safety Goals for public health and safety.

5.

Conclusion Approval of this exemption that is needed to allow the use of the risk-informed approach is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security requirements of 10CFR50.12(a)(1). Furthermore, special circumstances required by 10CFR50.12(a)(2) are present for item 10CFR50.12(a)(2)(ii) in that application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule.

-3 NRC-24-0064 Page 7 of 7 Based on the determination that the risk of the exemption meets the acceptance guidelines of RG 1.174, the results demonstrate there is reasonable assurance that the ECCS will function in the recirculation mode and that the public health and safety will be protected.

6.

Implementation DTE requests that this exemption request be approved concurrently with the LAR (Attachment 1).

-4 Request for Exemption from General Design Criterion 38

-4 NRC-24-0064 Page 1 of 7 Request for Exemption from Certain Requirements of General Design Criterion 38

1.

Exemption Request Pursuant to 10CFR50.12, DTE is submitting this request for exemption from certain requirements of 10CFR50 Appendix A, General Design Criterion (GDC) 38, which states:

Criterion 38 - Containment heat removal. A system to remove heat from the reactor containment shall be provided. The system safety function shall be to reduce rapidly, consistent with the functioning of other associated systems, the containment pressure and temperature following any loss-of-coolant accident and maintain them at acceptably low levels.

Suitable redundancy in components and features, and suitable interconnections, leak detection, isolation, and containment capabilities shall be provided to assure that for onsite electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming onsite power is not available) the system safety function can be accomplished, assuming a single failure.

By regulatory precedent, licensees are required to demonstrate this capability by the use of a bounding calculation or other deterministic method. DTE requests an exemption from the need to use only deterministic methods, in order to enable the use of a risk-informed method to demonstrate acceptable strainer design and ECCS performance with regard to the effects of LOCA debris.

Approval of this exemption will allow use of a risk-informed method to account for the probabilities and uncertainties associated with mitigation of the effects of debris following postulated LOCAs. The method evaluates the effects on strainer blockage resulting from debris concerns identified within the DTE corrective action program. In order to confirm acceptable ECCS strainer design, the risk associated with post-LOCA debris sources are evaluated to include the failure mechanisms associated with loss of core cooling and strainer blockage.

The scope of the exemption applies for limited debris effects addressed in the DTE RoverD methodology described in Attachment 3 that was used to respond to a corrective action associated with Min-K found in the drywell penetrations at Fermi 2 and unqualified tags/labels found throughout containment. The LOCA break sizes and locations that potentially generate an amount of Min-K that exceeds the quantity established in DTE original design basis testing and analysis are described in Attachment 3. The key elements of the exemption request are:

1.

It applies only to the effects of penetration Min-K and non-conforming containment debris as described in Attachment 3.

2.

It applies only for LOCA breaks that can generate and transport debris that is not bounded by the DTE strainer failure criteria established in Attachment 3.

-4 NRC-24-0064 Page 2 of 7

3.

It applies to any LOCA break that can generate and transport debris that is not bounded by strainer failure criteria, provided that the cumulative CDF and LERF associated with these breaks remain in Region III of RG 1.174.

This exemption request is complemented by the accompanying License Amendment Request (LAR) (Attachment 1), which seeks NRC approval to change the licensing basis in the Fermi 2 Updated Final Safety Analysis Report (UFSAR) to allow the use of a risk-informed approach for demonstrating acceptable design of the ECCS suction strainers The risk-informed method provides high probability assurance that, as calculated in the ECCS evaluation model (Attachment 3), ECCS operation, including strainer performance and debris mitigation, will be acceptable.

2.

Regulatory Requirements Involved DTE seeks exemption to the extent that GDC 38 requires deterministic calculations or other deterministic analyses to address the debris concerns related to acceptable plant performance during core and containment cooling modes following a LOCA. The proposed changes to the licensing basis, submitted for NRC approval with Attachment 1, address the additional debris loads at the ECCS strainers for Fermi 2 on the basis that the associated risk is shown to meet the acceptance guidelines in Regulatory Guide (RG) 1.174 and that, in conjunction with the existing licensing basis, adequate safety is demonstrated.

This exemption is needed for the purpose of allowing the use of a risk-informed method to demonstrate acceptable mitigation of the effects of debris following postulated loss of coolant accidents (LOCAs). The effects of LOCA debris have been evaluated, using deterministic methods, to meet the current licensing basis assumptions for analyzing the effects of post-LOCA debris blockage at the suction strainers; however, these evaluations have not been shown to fully address debris effects for the as-built, as-operated plant. The risk informed approach evaluates the risk associated with additional potential debris sources on ECCS strainer performance beyond those currently established in the strainer design basis. Based on confirmation of acceptable ECCS design as determined by the resulting risk meeting the acceptance guidelines in RG 1.174 and approval of this exemption, the licensing basis for ECCS compliance with GDC 38 requirements requiring use of deterministic methods will be amended to a risk-informed methodology.

2.1 Evaluation of Impacts on other Regulatory Requirements - Conclusion The proposed exemption does not result in any physical changes to the facility or changes to the operation of the plant and does not change any of the programmatic requirements. In Attachment 3, the ECCS suction strainer design and hence ECCS design are shown to be acceptable using a risk-informed approach, (with an exemption from GDC 38 requirements to use deterministic evaluation methods). Therefore, compliance with other regulatory requirements that rely on

-4 NRC-24-0064 Page 3 of 7 acceptable design for these systems and components continue to be met in the current licensing basis.

3.

Basis for the Exemption Request Under 10CFR50.12, a licensee may request and the NRC may grant exemptions from those requirements of 10CFR50 for which exemptions are authorized by law, will not present an undue risk to the public health and safety, are consistent with the common defense and security, and when special circumstances are present.

The exemption request meets a key principle of RG 1.174, which states "The proposed change meets the current regulations unless it is explicitly related to a requested exemption." This exemption request is provided in support of the proposed change provided in the License Amendment Request provided in Attachment 3.

3.1 Justification for the Exemption Request As required by 10CFR50.12(a)(2), the Commission will not consider granting an exemption unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable. DTE has evaluated the proposed exemption against the conditions specified in 10CFR50.12(a) and determined that this proposed exemption meets the requirements for granting an exemption from the regulation, and that special circumstances are present. The information supporting the determination is provided below.

Pursuant to 10CFR50.12, "Specific exemptions," the NRC may grant exemptions from the requirements of this part provided the following three conditions are met as required by 10CFR50.12(a)(1):

The exemption is authorized by law.

The NRC has authority under the Atomic Energy Act of 1954, as amended, to grant exemptions from its regulations if doing so does not violate the requirements of law. This exemption is authorized by law as is provided by 10CFR50.12 which provides the NRC authority to grant exemptions from 10CFR50 requirements with provision of proper justification. Approval of the exemption does not conflict with any provisions of the Atomic Energy Act of 1954, as amended, the Commission's regulations, or any other law.

The exemption does not present an undue risk to the public health and safety.

The proposed change is to apply a risk-informed method rather than a strictly traditional deterministic method in order to quantify the residual risk associated with the additional debris loads and to establish a high confidence of acceptable ECCS design. The purpose of GDC 38 is to establish acceptable design for containment heat removal, which includes the heat removal

-4 NRC-24-0064 Page 4 of 7 functions of the ECCS, together provide high probability that the systems will perform the required functions. The proposed exemption does not involve any modifications to the plant that could introduce a new accident precursor or affect the probability of postulated accidents, and therefore the probability of postulated initiating events is not increased. The PRA and engineering analysis demonstrate that the calculated risk is very small and consistent with the intent of the Commission's Safety Goal Policy Statement, which defines an acceptable level of risk that is a small fraction of other risks to which the public is exposed As discussed in previous 10CFR50.46 rulemaking, the probability of a large break LOCA is sufficiently low that the application of a risk-informed approach to evaluate the ability of the ECCS to meet its design requirements with high probability and with low uncertainty, rather than using a calculational model using deterministic methods to achieve similar understanding, would have little effect on public risk. This conclusion is consistent with evaluation of the effects of debris on the acceptability of ECCS design during the recirculation modes provided in.

The risk-informed approach involves a complete evaluation of the spectrum of LOCA breaks, including double-ended guillotine breaks, up to and including the largest pipe in the reactor coolant system. The risk-informed approach analyzes LOCAs, regardless of break size, using the same methods, assumptions, and criteria in order to quantify uncertainties and overall risk metrics. This ensures that large break LOCAs with relatively small contribution to CDF due to the low probability of such a break as well as smaller break LOCAs with higher probabilities of occurrence are considered in the results. Since the design basis requirement for consideration of a double-ended guillotine break of the largest pipe in the reactor coolant system is retained and since no physical changes to the facility or changes to the operation of the facility are being made, the existing defense-in-depth and safety margin established for the design of the facility is not reduced.

The exemption is consistent with the common defense and security.

The exemption involves a change to the licensing basis for the plant that has no relation to the possession of licensed material or any security requirements that apply to DTE Fermi 2.

Therefore, the exemption is consistent with the common defense and security.

3.2 Special Circumstances This section discusses the presence of special circumstances as related to 10CFR50.12(a).

10CFR50.12(a)(2) states that NRC will not consider granting an exemption to the regulations unless special circumstances are present. Special circumstances are present whenever one of the listed items (i) through (vi) under 10CFR50.12(a)(2) are applicable.

-4 NRC-24-0064 Page 5 of 7 Such special circumstances are present in this instance to warrant exemption from the implicit requirement in GDC 38 to use a deterministic method to demonstrate acceptable ECCS suction strainer design. Approval of the exemption request would allow use of a risk-informed method to amend the licensing basis for acceptable ECCS strainer performance to demonstrate compliance with GDC 38. Specifically, 10CFR50.12(a)(2)(ii) applies:

Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule.

The intent of GDC 38 is to ensure the ECCS design provides abundant containment cooling to rapidly reduce containment pressure and temperature following any LOCA and maintain them at acceptably low levels. This exemption request is consistent with that purpose in that use of the proposed risk-informed approach demonstrates a high probability of successful ECCS performance, which includes realistically available long-term containment cooling and suppression pool cooling, based on the risk results meeting the acceptance guidelines of RG 1.174. The risk-informed approach assesses ECCS design for all double-ended guillotine breaks and assesses equipment failures that include loss of offsite power and worst-case single failure, consistent with the GDC 38 requirements.

Since the proposed exemption does not involve any physical changes to the plant, there is no effect on the GDC 38 requirements for ECCS design for redundancy in components and features, interconnections, leak detection, isolation, and containment capabilities. The current licensing basis evaluations for containment heat removal with GDC 38 for these aspects continue to be met.

As discussed in the Commission's Policy Statement on "Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities", NRC regulations and their implementation are generally based on deterministic approaches that consider a set of challenges to safety and determine how those challenges should be mitigated.

This request does not seek exemption from any explicit language in the regulatory requirements.

Rather, the exemption request addresses the implicit requirements in the regulations for using deterministic methods to demonstrate acceptable design. Regulatory requirements are largely based on a deterministic framework, and are established for design basis accidents, such as the LOCA, with specific acceptance criteria that must be satisfied. Licensed facilities must have safety systems capable of preventing and mitigating the consequences of design basis accidents to protect public health and safety. The deterministic regulatory requirements were designed to ensure that these systems are highly reliable. The LOCA analysis and the General Design Criteria (GDC) were established as part of this deterministic regulatory framework.

In comparison, the probabilistic approach considers nuclear safety in a complementary way by examining the likelihood of a broad spectrum of initiating events and potential challenges,

-4 NRC-24-0064 Page 6 of 7 considering a wide range of credible events, and assessing the risk based on the reliability of mitigating systems.

An objective of GDC 38 is to maintain low risk to the public health and safety through a reliable ECCS. The supporting analysis provided in Attachment 3 demonstrates that a risk-informed approach to strainer performance is consistent with the Commission's Safety Goals for nuclear power plants, including ECCS operation with a high degree of reliability. Consequently, the special circumstances described in 10CFR50.12(a)(2)(ii) apply.

Specifically, 10CFR50.12(a)(2)(iii) applies:

Compliance would result in undue hardship or other costs that are significantly in excess of those contemplated when the regulation was adopted, or that are significantly in excess of those incurred by others similarly situated.

The specific hardship is the excessive occupational radiological dose that is expected to be incurred for plant modifications to remove and replace insulation. This was discussed in -1.

In conclusion, special circumstances in 10CFR50:12(a)(2)(ii) and 10CFR50.12(a)(2)(iii) are present as required by 10CFR50.12(a)(2) for consideration of the request for exemption.

4.

Technical Justification for the Exemption Technical justification for the risk-informed method is provided in Attachment 3 and in the LAR (Attachment 1).

The proposed risk-informed approach meets the key principles in RG 1.174 in that it is consistent with the defense-in-depth philosophy, maintains sufficient safety margins, results in small increase in risk, and is monitored using performance measurement strategies that are discussed in. The proposed exemption is needed to allow use of the risk-informed method in a manner consistent with the key principle in RG 1.174 that requires the proposed change to meet current regulations unless explicitly related to a requested exemption.

The results of analyses in Attachment 3 show that the risks associated with additional debris concerns is in Region III, "Very Small Changes," of RG 1.174, and therefore are consistent with the Commission's Safety Goals for public health and safety.

5.

Conclusion Approval of an exemption that is needed to allow the use of the risk-informed approach is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security requirements of 10CFR50.12(a)(1). Furthermore, special circumstances required by 10CFR50.12(a)(2) are present for item 10CFR50.12(a)(2)(ii) in that

-4 NRC-24-0064 Page 7 of 7 application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule.

Based on the determination that the risk of the proposed change to a RI methodology meets the acceptance guidelines of RG 1.174, the results demonstrate there is reasonable assurance that the ECCS will function in the recirculation mode and that the public health and safety will be protected

6.

Implementation DTE requests that this exemption request be approved concurrently with the LAR (Attachment 1).

to NRC-24-0064 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 LAR Attachment 4 - Technical Supplement (Revised) to NRC-24-0064 Page 1 of 26

1. Introduction to LAR Attachment 4 - Technical Supplement (Revised)

Various audit topics and RAIs question the amount, treatment, and risk implications of Min-K insulation present in containment penetrations. LAR Att-1 and Att-3 (DTE Letter NRC-23-0020, (ML23164A232)), consistent with the strainer design basis (DB), do not include penetration Min-K as a potential debris source for non-isolable breaks occurring between the reactor vessel and the isolation valves. To provide a technical basis for responding to these topics related to penetration Min-K, this supplement (Att-4) 1) explains how the CAD model Min-K inventory was changed, 2) explains how penetration Min-K can be damaged to form debris, and 3) presents revised baseline risk with penetration Min-K included as a debris source for non-isolable breaks. These changes do not affect risk contributions from isolable breaks that occur between isolation valves and potentially inside of a penetration. As stated in the LAR (Att-1 Table 3-1, and Att-3 Table 7-1), baseline risk contributed from isolable breaks is 2.12E-07/yr.

This supplement (Att-4) also provides technical information supporting responses to RAI questions related to sensitivity cases involving suppression pool cooling, 1/8th-inch debris thickness failure criterion, 100 ft2 of strainer obstruction by miscellaneous debris, and other parameter variations.

Three principal revisions provided in the present document (LAR Attachment 4 - Technical Supplement (Revised)) are: 1) additional descriptions of the risk reduction obtained from a 25%

reduction in penetration Min-K debris, including tallies of weld-break scenarios failing multiple strainer performance metrics; 2) a rationale for why relatively high risk obtained for the arithmetic mean break frequency sensitivity is consistent with an overarching conclusion of very low risk, and 3) a change in terminology from modified baseline risk to baseline risk. While the adjective modified was intended to help distinguish the evolution of risk calculation assumptions between LAR Att-3 and LAR Att-4, the more common terminology baseline now denotes all assumptions applied through LAR Att-4. No changes to assumptions, conditions, or methods are introduced as a result of the terminology change.

To aid review and comparison of results, all baseline risk assumptions defined in LAR Att-3 are applied in this supplement (Att-4). Principal baseline risk assumptions defined in Att-3 include:

1) single-division Low Pressure Coolant Injection (LPCI) run-out flow with 2) no quantitative risk reduction for single-division pump-state probability, and 3) Emergency Core Cooling System (ECCS) failure defined by a 1/8th-inch debris thickness accumulation on any single strainer, or, 4) exceedance of any strainer DB debris constituent quantity. (If either condition 3 or 4 is true on any single strainer, the break case is assumed to cause ECCS failure and contributes to risk of core damage). Because the strainer DB includes only small amounts of Min-K debris, exceedance of the DB Min-K quantity can become a significant risk contributor when penetration Min-K is included in the CAD model. This supplement (Att-4) modifies Att-3 baseline risk quantification assumptions by applying three additional conditions: 1) a 10%

single-division pump-state probability, 2) a factor of 0.2 to account for operator failure to diagnose strainer debris accumulation, and 3) a 25% reduction in penetration Min-K debris to credit obstruction of Zones of Influence (ZOI) located outside of containment penetrations by hydraulic pipes inside the penetrations. A necessary component of accounting for single-division to NRC-24-0064 Page 2 of 26 pump-state probability is the addition of risk arising from suppression pool cooling, which is expected to occur with a 90% complement pump-state probability.

Risk results reported here after including penetration Min-K as a debris source, but prior to applying the above three mitigating conditions are referred to as revised Att-3 risks, because penetration Min-K is now treated in a manner fully consistent with Att-3 assumptions. Of particular interest is the revised Att-3 baseline risk that emphasizes the risk increase caused by including penetration Min-K. Final risk tabulations reported in this supplement (Att-4, Section

3) include the three mitigating conditions, and state the final risk tabulation of the Fermi-2 LAR.

This supplement (Att-4) contains five sections: 1) Introduction, 2) CAD Model Revisions, 3)

Revised Att-3 Baseline and Final Baseline Risk With Penetration Min-K, 4) Sensitivity Case Summary, and 5) Strainer Failure Tabulation for 25% Penetration Min-K Reduction. Technical information provided in this supplement (Att-4) and in the cited references supersedes similar technical information provided in LAR Att-1 and Att-3. In particular, previous statements of the numerical baseline total risk (5.95E-07/yr) are now replaced with a final total baseline risk of 6.94E-07/yr that is defined here in Section 3.

Summaries of methods and results presented in this revised supplement (Att-4) are fully developed and explained in the following references.

1. MEMO-9045-AVR-2018-01, Verification of Fermi CAD Model, Rev. 3, March 2024.

2. ALION-CAL-SI-9045-132, DTE Energy Fermi-2 CASA Grande Debris Generation and Risk Quantification, Rev. 2, May 2024.

3. SERCO-REP-DTE-22929-02, Rev. 0, Sensitivity Study of Fermi Unit 2 Risk-Informed Core Damage Frequency, May 2024.

4. DTE Letter NRC-24-0033 to the U.S. Nuclear Regulatory Commission, Final Response to Request for Additional Information for License Amendment Request Regarding Risk Informed Approach to Performance ECCS Strainer Performance, NRC Docket No. 50-341, May 30, 2024.

2. CAD Model Revisions Three changes made to the Fermi-2 CAD model after submittal of LAR Att-3 can affect the risk quantification.

CAD Change 1: Additional whip restraint insulation Table 7-2 in LAR Att-3 Ref. 11 ("Estimation of Debris Sources for ECCS Suction Strainers, DC-5979," Rev A) provides a list of all non-Reflective Metal Insulation (RMI) present in containment that is not located in penetrations. The CAD model used to generate debris supporting the LAR risk quantification was based on LAR Att-3 Ref. 3 (DC-5979, Rev 0) Table to NRC-24-0064 Page 3 of26 6.1 that does not include the last 6 rows of Table 7-2 (DC-5979, Rev A). See excerpt of Table 7-2 provided below in Figure. 1.

After revision (Ref. 1 above) the CAD model now includes the six whip-restraint insulation sources found at the bottom of DC-5979 Rev A, Table 7-2. The new points increase total containment fiber by approximately 4.6 ft3 and total containment Min-K (not including penetrations) by 0.113 ft3.

Additionally, one potentially conservative discrepancy was found in the amount of insulation reported for whip restraint SRlB. DC-5979 Rev O Table 6.1 lists 3.7 ft 3 ofNUKON and DC-5979 Rev A Table 7-2 lists 2.73 ft3 ofNUKON at that location. The CAD model continues to use the larger amount specified in Rev 0.

The additional whip-restraint insulation introduced to the CAD model causes a small increase in revised Att-3 baseline risk because a few additional breaks are able to exceed the baseline failure criterion of 1/8th-in of fiber accumulating on any single active strainer. No risk-informed conclusions are changed as a result of this small increase in containment insulation.

DC-5979 VOL I Rev. A Page 41 of 72 Table 7-2: Insulation Targets Mass and l ocation Pipe Diamond Diamond Volume of Type of AutoCAD AutoCAO Whip Power Vendor Power Insulation Insulation Insulation Insulation Insulation Model Model Restraint System Drawing File #

Piece ID (in)

OD (in)

Length input into CAD Min-K8 or Location Location Mark (590001-Mark (in!

Model(ft'J NUKON8 (x)

!vi xxxJ DRS Main Steam Drains 36C SJJ,2 P3-228 85 2.38 7

11.19 0.22 Min-Ks-544 145 DRS Main Steam Drains 36C SJJ,2 P3-228 7

2.38 7

9.44 0.19 NUKON 8 600 135 DR13 Main Steam 36C SJJ_ l P3-228 20 2.38 7

13 0.26 Min-K6 692 145 Drains Reactor A3C Recircu lation 40C §!J_ l P3-223 A3C 24 30 7

0. 515 NUKON 8 759.75 623.75 Loop A Reactor 63E Recircu lation 40C §!)_2 P3-223 63E 24 30 7

1.031

• NUKON8 471.25 335.25 loop B Reactor B3D Recircu lation 40C §!)_2 P3-223 63D 24 30 7

1.031 NUKON 8 488.25 318.25 loop B Reador B14D Recircu lation 40C§!J_2 P3-223 B14D 24 30 7

1.031 NUKON 8 471.25 606.75 loop B Reactor B14E Recircu lation 40C §!)_2 P3-223 B14E 24 30 7

1.031 NUKON 8 488.25 623.75 loop B G028 Feedwater loop B 4,3C SJJ,2 P3-223 18 20 21.5 8

0.113 M in-Ke-893.4 314.5

• Added by FMR 5-7173 (104]

"Added under EDP-36681 (105]

Figure 1. Excerpt of LAR Att-3 Ref. 11 Table 7.2 (DC-5979, Rev. A) showing the last 6 rows of whip restraint insulation (asterisks).

AutoCAD Model Location (z) 7053 7037 7051

7237u, 7237° 7237**

7237**

7237**

7304*

to NRC-24-0064 Page 4 of 26 CAD Change 2: Whip-restraint insulation x-coordinate reflection The Fermi-2 containment layout is highly symmetric. Visual examinations of the CAD model performed during original placement of whip-restraint insulation confirmed placement points on or near known whip restraint locations for nearly all entries in LAR Att-3 Ref. 11 Table 7-2 (see Figure-1 excerpt). Recent comparisons of whip-restraint labels in Table 7-2 with plant drawings revealed an improper reflection in the CAD model of whip-restraint x-coordinates across the horizontal y-axis midline. Replacement of all whip-restraint insulation x-coordinates in the CAD model by the reflection = produced placements fully consistent with plant drawings.

The coordinate reflection applied to whip-restraint insulation does not change the total amount of pipe-whip restraint insulation present in containment, the pipe centerline location of any ZOI, or the location of any structural barriers.

The coordinate reflection applied to whip-restraint insulation did move a small number of whip-restraint insulation targets into the line-of-sight of existing ZOI, which causes a small increase in revised Att-3 baseline risk because a few additional breaks are able to exceed the baseline failure criterion of 1/8th-in of fiber accumulating on any single active strainer. No risk-informed conclusions are changed as a result of the new target placement.

CAD Change 3: Penetration Min-K LAR Att-3 describes the intended baseline damage to Min-K insulation present inside penetrations by non-isolable LOCA occurring on welds between the reactor vessel and the first isolation valves. The principal statements are: 1) Min-K insulation sleeves not readily found on plant drawings are assumed to extrude 18 inside containment, and 2) Penetration Min-K is damaged by all non-isolable breaks having a line of sight between the ZOI center point and the insulation target. The LAR Att-3 description includes Figure 2-2 (Min-K insulation sleeves (detail) applied in drywell penetrations.) found on Page 93 of 274.

However, results reported in LAR Att-3 for baseline risk are more properly described as a sensitivity case where penetration Min-K is afforded complete protection from external LOCA by mechanical congestion near the containment wall and by the recessed position of Min-K sleeves inside guard pipes. In effect, Min-K sleeves shown in LAR Att-3 Figure 2-2 are not included as debris sources in Att-3 reported baseline risk results. Assumed non-damage of penetration Min-K by non-isolable LOCA is consistent with the design basis of the strainers, but does not meet the full intention of the risk analysis.

To produce risk results that include penetration Min-K as a debris source consistent with stated Att-3 baseline assumptions, two changes were made to the CAD model: 1) precise Min-K insulation geometry was obtained from drawings in consultation with plant design engineering staff, and 2) guard pipes were added to each penetration consistent with plant drawings. Figures 2 and 3 appearing below illustrate penetration Min-K without guard pipes (Figure 2) and with guard pipes (Figure 3), respectively.

to NRC-24-0064 Page 5 of 26 Figure 2. CAD depiction of penetration Min-K sleeves (magenta) without guard pipes.

Figure 3. Revised CAD model including guard pipes on each penetration.

(Containment wall not shown).

Addition of guard pipes that are credited as robust barriers leads to the CAD configuration shown in Figure 3. Although interior hydraulic pipes are shown in Figure 3, they are not credited as robust barriers in the revised baseline analysis. While guard pipes offer some protection from obliquely incident ZOI, penetration Min-K is still vulnerable to direct impingement from ZOI sharing the same guard-pipe centerline. Without credit for shadowing by the hydraulic pipe, or an assumption made to limit the depth of erosion by an external damage zone, Min-K sleeves are damaged in the revised analysis to a depth equal to the full ZOI radius by LOCA sharing the same pipe centerline.

Inside Containment to NRC-24-0064 Page 6 of 26 Figure 3 does not show the containment wall, but it is present in the CAD model, just as illustrated in Figure 2. Application of the containment wall a robust barrier does not affect debris generation, because no exposed insulation targets reside at distances within any ZOI that are also beyond the wall and outside of a guard pipe.

3. Revised Att-3 Baseline and Final Baseline Risk With Penetration Min-K After implementation of CAD Changes 1 and 2, without including penetration Min-K and consistent with risks reported in LAR Att-3, baseline change in Core Damage Frequency (CDF) from non-isolable breaks increases from 3.83E-7/yr to 4.01E-7/yr. In addition, the maximum fiber generated by any single break increases from 17.6 to 17.9 ft3 (counting the full mass of any non-penetration Min-K debris as fiber). The new maximum fiber debris quantity is still less than the strainer design basis fiber limit of 21 ft3. These results confirm that the small increase in containment insulation caused by additional whip restraint locations, and the small increase in insulation debris caused by coordinate reflections do not materially affect risk results.

CAD Change 3, inclusion of guard pipes housing precisely dimensioned Min-K insulation sleeves, permits a significant number of postulated breaks to exceed the DB limit for Min-K.

When Min-K debris volume is counted as fiber, some cases also exceed the 21-ft3 DB limit for fiber, but recall that including Min-K debris in the fiber debris inventory is a safety margin applied to increase the prevalence of bed thickness failures, not a requirement of the DB, which tracks fiber and Min-K as separate debris constituents. Therefore, no break cases have been found that exceed the DB fiber limit. The combined effect of all CAD changes 1 - 3 allows baseline CDF from non-isolable breaks to increase from 3.83E-7/yr to 3.19E-6/yr. This revised result does not include any modifications to baseline assumptions defined in LAR Att-3.

In order to address the additional risk increase caused by penetration Min-K insulation, the following three conditions are applied to the quantification of final baseline risk:

1. Apply a 10% single-division plant-state probability to reduce baseline risk with penetration Min-K by a factor of 10.

a. Add risk contributed by the planned, most likely, condition of suppression pool cooling weighted by the complement 90% plant-state probability.

2. Credit limited damage to penetration Min-K afforded by the presence of hydraulic pipes inside every penetration (25% damage reduction).

One additional condition is applied to risk contributed by suppression pool cooling in order to justify total risk in Risk Region III:

3. Credit operator ability to recognize debris induced pump labor and rotate flow to existing available pumps and strainers (assumed 20% failure rate).

Risk from suppression pool cooling is calculated in the following manner.

to NRC-24-0064 Page 7 of 26 First, it is expected that all pumps will respond at their maximum, injection-limited, flow rates to initial indications of a LOCA. If all pumps in both divisions were allowed to operate at maximum flow, supporting calculations (Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0) show that no strainers would exceed the 1/8th-inch debris thickness criterion for any postulated breaks.

This case demonstrates that it is always beneficial to share debris between as many operating strainers as possible.

Second, ignore the benefit of initial two-division automatic debris accumulation on all active strainers and assume operators quickly diagnose reactor pressure and flood level and elect to turn off all Division-II pumps and establish the suppression pool cooling flow rates defined in Table 1.

Table 1. Assumed Suppression Pool Cooling Flow Rate Assignments.

Suppression Pool Cooling (Strainer Flow Rate (gpm))

Division Pump 0 - 20 min

>20 min I

RHR-A 15540 10500 II RHR-B 0

0 I

RHR-C 14550 10500 II RHR-D 0

0 I

CS-A 6350 6350 I

CS-C II CS-B 0

0 II CS-D Supporting calculations for the Table 1 flow configuration (from Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0, Table 5-1, Case 3A - See Table 5 below) estimate the risk contributions identified in column 2 of Table 2 as Direct Risk, which have not yet been reduced by baseline conditions 2 or 3.

Table 2. Non-Isolable Risk Contributions for Suppression Pool Cooling Before Applying Penetration Min-K Debris Reduction (Condition 2).

Contributor Direct Risk (per year)

Two-Div Plant-State Probability Conditional Risk (per year)

Bed Thickness Exceedance (alone) 3.11E-07 0.9 2.80E-07 Bed Thickness and DB Exceedance (both) 5.53E-07 0.9 4.98E-07 DB Exceedance (alone) 2.34E-06 0.9 2.11E-06 Total Non-Isolable Risk 3.20E-06 0.9 2.88E-06 to NRC-24-0064 Page 8 of 26 Similar results (from Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0, Table 5-1, Case 2A - see Table 5 below) are shown in Table 3 for non-isolable risk contributions for baseline one-division LPCI response.

Table 3. Non-Isolable Risk Contributions for One-Division LPCI response Before Applying Penetration Min-K Debris Reduction (Condition 2).

Contributor Direct Risk (per year)

One-Div Plant-State Probability Conditional Risk (per year)

Bed Thickness Exceedance (alone) 3.10E-07 0.1 3.10E-08 Bed Thickness and DB Exceedance (both) 5.46E-07 0.1 5.46E-08 DB Exceedance (alone) 2.34E-06 0.1 2.34E-07 Total Non-Isolable Risk 3.19E-06 0.1 3.19E-07 Boolean logic used to construct the rows of Tables 2 and 3 avoids double counting any failed weld break scenarios. To find the total risk of exceeding the bed thickness criterion, add rows 2 and 3. To find the total risk of exceeding a DB criterion, add rows 3 and 4. Total risk reported in the bottom row is the sum of the three failure categories. Be aware that weld breaks contributing to row 3 of Tables 2 and 3 exceed both strainer failure criteria, but they must only be counted as a single LOCA-event failure. Additional details provided in Section 5 of this revised Att-4 supplement expand on the number of weld breaks that contribute to each row of Table 2 and 3.

Baseline Condition 2 - Reduced Min-K Damage Supporting calculations (Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0) describe how even a small reduction in assumed penetration Min-K damage can significantly reduce risk from all non-isolable breaks (both One and Two-Division Response). It is evident in Figure 4 that a 25%

reduction in penetration Min-K source terms would induce more than a factor of 2 reduction in risk contributed from DB Min-K violations (the dominant risk contributor) for suppression pool cooling (Case 3A) flow rates. To recreate this observation, first note that each curve in Figure 4 displays an exceedance function of cumulative risk for DB Min-K violations (y axis) as functions of the amount of Min-K delivered to the suppression pool. The upper-right, light-blue function shows the risk exceedance function for zero reduction in penetration Min-K damage consistent with baseline damage assumptions. The vertical dotted line represents the minimum amount of Min-K debris in the pool (0.838 ft3) under suppression pool cooling (Case 3A) flow rates that can exceed the DB Min-K limit on any single strainer (0.334 ft3 for RHR strainers and 0.186 ft3 for CS strainers), which intersects the upper-right light-blue function at a value of 2.89E-06/yr (top black dot). The same DB Min-K limit intersects the orange exceedance function, corresponding to 25% reduction in Min-K damage, at a value of 1.39E-06/yr (second black dot). Thus, a 25% reduction in penetration Min-K damage leads to a risk reduction factor for DB Min-K exceedance of 2.89/1.39 2.

In Figure 4, the minimum Min-K debris volume (0.838 ft3) that can lead to a DB failure (vertical dotted line) is determined by solving time-dependent debris accumulation histories for each strainer for all postulated breaks and sorting the Min-K debris source terms of all scenarios to NRC-24-0064 Page 9 of26 that are found to exceed the limits. The smallest source term capable of causing a DB failure cannot be determined precisely using ratios of strainer flow rates, except in the case where all strainer flow rates are held constant for the duration of the event.

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tii 10-6 "O

Q)

Q)

(.)

X w

.8903e.-06,......, "'"""""'"'""

.. 3899e.-06......................................................

• 0955e.,06. "'"""'"'"'"""""""""'"'"'""""' '"..

-- o

-- 0.25 0.5

-- 0.75

-- 1 10-7 '----~~---~--~~--~~~---...,

10*3 10*2 10-1 100 101 102 Suppression Pool Min-K Volume (ft3)

Figure 4. Suppression Pool Cooling (Case 3A) DB Min-K risk for assumed reductions of penetration Min-K debris source terms.

Section 5 provides additional details regarding the number of weld break cases that fail before and after Min-K debris is reduced. Table 4 shows how risk contributions for suppression pool cooling change after Min-K damage is reduced (compare to Table 2). Table 5 shows how risk contributions for single-division response change after Min-K damage is reduced (compare to Table 3). Risk results for the two operating conditions are nearly identical because the strainer configurations and flow rates are so similar, even though the two states are achieved in different ways.

Table 4. Non-lsolable Risk Contributions for Suppression Pool Cooling After Applying Penetration Min-K Debris Reduction (Condition 2).

Contributor Direct Risk Two-Div Plant-Conditional Risk (per year)

State Probability (per year)

Bed Thickness Exceedance (alone) 3.32E-07 0.9 2.99E-07 Bed Thickness and DB Exceedance 5.17E-07 0.9 4.65E-07 (both)

DB Exceedance (alone) 8.73E-07 0.9 7.86E-07 Total Non-Isolable Risk 1.72E-06 0.9 1.55E-06 to NRC-24-0064 Page 10 of 26 Table 5. Non-Isolable Risk Contributions for One-Division LPCI response After Applying Penetration Min-K Debris Reduction (Condition 2).

Contributor Direct Risk (per year)

One-Div Plant-State Probability Conditional Risk (per year)

Bed Thickness Exceedance (alone) 3.32E-07 0.1 3.32E-08 Bed Thickness and DB Exceedance (both) 5.16E-07 0.1 5.16E-08 DB Exceedance (alone) 8.73E-07 0.1 8.73E-08 Total Non-Isolable Risk 1.72E-06 0.1 1.72E-07 Baseline Condition 3 - Credit Operator Action Direct application of Table 4 Conditional Risks for suppression pool cooling would ignore the fact that two idle RHR strainers and one idle CS strainer are available to draw necessary cooling flow. Operators are trained to recognize symptoms of debris-induced strainer issues, including increasing pump current, loss of level, loss of pressure, and mechanical vibration in association with active backflush procedure 20.000.29 (Fermi, "Plant Mechanical Procedure - Fermi 2 Abnormal Operating Procedure: LPCI Suppression Pool Suction Strainer Clogging, 20.000.29, Rev. 5," November 5, 2019). In addition, operators have great flexibility to reduce flow on any given system and rotate systems as needed to respond to any LOCA scenario. Recognition of debris blockage symptoms does not imply that a backflush will be performed. Operators must only manage flow using common Emergency Operating Procedures (EOP) and equipment available under successful, automatic, two-division LOCA response to avoid ECCS failure under baseline condition 2a.

Given the availability of idle equipment under automatic, two-division response, and operator awareness of potential debris accumulation challenges in suppression pool cooling mode, a strong argument can be made that nearly all of the Table 2 Conditional Risk (last column) represents analytic safety margin. It would be very unusual for the normal two-division response with all pumps operable to contribute more risk (2.88E-06/yr from Table 2) than loss of a full division (3.19E-07/yr from Table 3). Table 2 Conditional Risks are inordinately high because the Table 1 pump flow histories do not acknowledge the ability to rotate flow to idle equipment.

Assume a conservative 1 in 5 chance (20%) that operators do not recognize symptoms of strainer blockage and/or cannot prevent ECCS failure using existing operable resources (i.e., must resort to some form of alternate injection that is presently reserved as defense in depth). A formal Human Reliability Assessment (HRA) could provide additional credit for operator action to further reduce the risk from Two-Division Suppression Pool Cooling scenarios, given that no new accident progressions are added and the fact that operators normally monitor and adjust pump flow rates.

Using information in Tables 4 and 5 the total baseline risk R = 6.94E-07/yr is calculated as follows.

R=(1.72E-06)(0.1)+(1.72E-06)(0.9)(0.2)+(2.12E-07)=6.94E-07/yr (Non-Iso)(One Div) + (Non-Iso)(TwoDiv)(Op fail) + Iso Risk = Total Risk to NRC-24-0064 Page 11 of 26 Note that the baseline risk of 6.94E-07/yr presented in this supplement is lower than the modified baseline risk reported in Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0 because additional risk reduction is applied here for limited Min-K debris generation and operator action. Baseline risk would vary if different reduction factors were chosen for Operator-Failure-to-Diagnose-Debris-Accumulation and Reduced-Penetration-Min-K-Damage. For example, if a detailed HRA demonstrated that operators are much more effective than the assumed 20% failure rate, then either total baseline risk would decrease, or the credit for Reduced-Penetration-Min-K-Damage could be reduced to maintain the same baseline risk (6.94E-07/yr). This example explains the total baseline risk reported in this LAR Attachment 4 - Technical Supplement (Revised) and illustrates the potential tradeoff between two independent analysis assumptions.

Information provided in Section 5 of this revised Att-4 explains how penetration Min-K debris source terms are reduced by 25% to recalculate cumulative risk of exceeding all defined performance metrics.

Risk Analysis Insight Supporting analyses (Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0) also show that a single, relatively small, 3.63-inch diameter (and therefore relatively high-frequency) break contributes 46% of the non-isolable break risk for the suppression pool cooling flow histories defined in Table 1. Proactive monitoring of this weld to substantiate lower break frequency, or removal of Min-K at a whip restraint within its ZOI would result in modified baseline risks well within RG 1.174 Risk Region III.

Comparison of Complementary Strainer Failure Criteria The LAR baseline analysis explains that two strainer failure criteria are applied to debris accumulation for every postulated break. ECCS failure and subsequent core damage are assumed to occur if any single strainer either 1) accumulates 1/8th-inch of fiber debris, or 2) exceeds the DB limit for any debris constituent. LAR Att-3 presents results that do not include penetration Min-K as a debris target, effectively assuming complete protection of the insulation in confined annular gaps from non-isolable breaks occurring outside of the penetrations, so no failures were found that exceed DB strainer limits. These results placed a critical focus on the 1/8th-in. bed thickness limit (first failure criterion) as the only measure of strainer failure and the only means of risk contribution. Revised calculations presented in this Supplement (LAR Att-4), which now include penetration Min-K, show that exceeding strainer DB limits for Min-K (second failure criterion) is the dominant risk contributor.

The two failure metrics serve separate complementary purposes.

1. The fiber thickness failure criterion is intended to establish a minimum fiber load that is well within the current licensing basis and provides a measure of strainer performance that is sensitive to miscellaneous debris obstruction. A fiber thickness of 1/8th-inch has traditionally been used as a threshold for testing whether a strainer having complex geometry can form a contiguous layer of fiber capable of filtering particulate (a thin bed).

to NRC-24-0064 Page 12 of 26 In recognition of concerns that Min-K, a microporous material, can aid in formation of a thin bed with less than 1/8th-inch of equivalent fiber thickness, a sensitivity case was evaluated using a 1/16th-inch failure limit (see Section 4 below). Risk contributions from bed thickness failure increase by 10% to 40% depending on the flow history examined, but do not equal risk contributions from exceeding the DB Min-K limit. Recall that the entire Min-K debris volume is also counted as fiber against the fiber thickness limit.

2. The DB debris limits are intended to confirm that all scenarios recorded as successful strainer performance have debris loads that do not exceed any of the debris constituent quantities they are qualified for, and thus, do not pose new risks that contribute to CDF.

No cases are found that exceed DB fiber loads, but exceedance of DB Min-K limits is now the dominant risk contributor.

4. Sensitivity Case Summary Reference 3 (SERCO-REP-DTE-22929-02, Rev. 0) reproduces the revised baseline risk (with penetration Min-K) from Reference 2 (ALION-CAL-SI-9045-132, Rev. 2) and analyzes a suite of alternate assumptions representing variations to individual baseline parameters. Examination of alternate assumptions provides perspective on the sensitivity of Core Damage Frequency (CDF) to key input choices. All results presented in this section include the CAD model changes and ECCS failure metrics described above, but do not include the additional 3 baseline risk quantification conditions (pump-state probability, reduced Min-K debris, and operator actions),

except where noted in discussions of sensitivity to Arithmetic Mean break frequencies. Seven parameter variations are examined:

1. three choices of total strainer face area obstruction by miscellaneous debris (65 ft2, 100 ft2, and 120 ft2);

2. three fiber failure thicknesses (1/16th in., 1/8th in., and 1 in.);

3. two methods of aggregating expert opinion for break frequency quantification (Arithmetic Mean and Geometric Mean);

4. three debris transport periods (0.1 min, 1 min, and 10 min),

5. two design basis Min-K debris volume limits (0.334 ft3 and 0.536 ft3 on RHR strainers and 0.186 ft3 and 0.297 ft3 on CS strainers),

6. application of 10% single-division and 90% dual-division plant-state probabilities; and

7. eight strainer flow conditions, including dual and single-division suppression pool cooling, applied to every sensitivity case.

Table 6 itemizes all baseline and sensitivity parameter values analyzed.

to NRC-24-0064 Page 13 of 26 Table 6. Baseline and Sensitivity Parameter Values.

1. Parameter Baseline Value Sensitivity Cases a

b 1 Obstructed strainer face area 100 ft2 65 ft2 120 ft2 2 Fiber thickness failure threshold 1/8th inch 1/16th 1 inch*

3 Break frequency aggregation method Geometric Mean (GM)

Arithmetic Mean (AM) 4 Debris introduction time 0.1 min (6 sec) 1 min 10 min 5 Design basis debris limits Min-K on RHR strainers 0.334 ft3 0.536 ft3**

Min-K on CS strainers 0.186 ft3 0.297 ft3**

Fiber on RHR strainers 13.5 ft3 Fiber on CS strainers 7.5 ft3 6 Plant-state probabilities 0.1 Single-Div 0.9 Dual-Div applied as needed 7 Isolable break risk 2.12E-7/yr 4.56E-7***

applied to all except Sensitivity Case #3 applied to Sensitivity Case #3 8 System response One Division, Run-out multiple

• No break exceeds 1-in. of fiber. This case turns off the thickness failure risk criterion.

• • Additional capacity arises from an identified change in Min-K product density.

• • • Isolable break risk for AM break frequencies is (3.26E-04)x(1.4E-03/yr)=4.56E-07/yr Risk results are tabulated by running identical debris accumulation simulations for all 887 non-isolable weld breaks described in the LAR and summing the frequencies for all events that exceed the defined failure criteria. Table 7 reproduces Table 5-1 from Ref. 3 - SERCO-REP-DTE-22929-02, Rev. 0 and presents risk results and times to failure for the baseline assumptions (Case 2A) and for seven alternative pump flow configurations, holding all other baseline parameters constant.

Note that Non-Isolable Break Risk (third row from bottom) equals the sum of 3 separate failure conditions listed in previous rows: 1) Thickness Exceedance Risk (alone) where a break violates ONLY the fixed thickness criterion, 2) Thickness AND Design Basis Exceedance where a break exceeds BOTH the fixed thickness AND the DB limit for either Min-K OR fiber, and 3) DB Exceedance Risk (alone) where a break violates ONLY a DB debris limit. It has been determined that there are no violations of DB fiber limits, so all risks entered in row DB Exceedance Risk (alone) are contributed solely by exceedance of DB Min-K limits. Independently estimated risk from isolable breaks (2.12E-07/yr from Ref. 2) appears as a fixed value in all tables, except for the AM break frequency sensitivity where the corresponding risk from isolable breaks is 4.56E-7/yr.

Also, total risk results exceeding the 1E-06/yr upper limit of RG 1.174 Risk Region III are to NRC-24-0064 Page 14 of 26 highlighted in light red for further discussion. Table 7 results do not include any modifications to or additional conditions placed on baseline assumptions, except for presenting risks for alternate flow rates. Definitions and rationale for each analyzed flow configuration are provided in Table 8, which provides a common set of footnotes for all risk results.

Comparison of the Table 7 row labeled DB Exceedance Risk (alone) to the Table 7 row titled Total Risk (1/yr) serves to emphasize that exceedance of the DB Min-K limit is dominating total calculated risk. It is also important to understand that all break scenarios contributing risk in the row DB Exceedance Risk (alone) have less than 1/8th-in. of equivalent bed thickness. Given the importance of the DB Min-K failure criterion, it is prudent to examine the potential effect that source term uncertainty may introduce to the risk quantification.

Figure 5 illustrates how smaller breaks at Fermi dominate risk of exceeding the single-strainer DB Min-K limit. The top panel shows Min-K debris in the suppression pool (y axis) for every postulated break size (x axis). Lines of stacked points represent breaks having common discrete weld diameters. Marked on the dashed line is the smallest debris source generated that can exceed the DB Min-K limit on at least one strainer. All cases generating Min-K debris equal to or greater than (above) this limit will contribute to DB failure risk, which is shown in the lower panel of Figure 4 as an exceedance function. The first blue dot in the upper center denotes a 3.63-in.

diameter break that causes approximately 50% of the baseline risk caused by DB Min-K limit violations. DEGB on welds larger than 20-in. diameter make up 10% of the total baseline risk caused by Min-K limit violations.

to NRC-24-0064 Page 15 of 26 Table 7. ECCS failure risk for baseline assumptions and alternate flow configurations.

Strainer Flow Rate (epm ) Tim e Hist ory (minutes)

Two Div, Max Flow Two Div, Max Flow One Div, Max Flow One Div, Max Flow with One Div, Pool Cooling

• Hypothetical

• Max RHR Use Hypothetical: Time Step Case, ED required or full depressurization One Div, RHR Runout, Strainer Max Strainer-Flow One Div, Pool Cooling following ODEl0 pump sequence and time critical action to bring up Division Pump (rounded)

(not rounded)

-Baseline*

(All times notional, must have Torus cooling by 20 min)

CS at Min Tech Spec Area(ft2)

(Case IA)

(Case 18)

(Case2A)

Disparity (Case 3A)

(Case3B) torus cooling.

(Case5A)

(Case 28)

(Case4A) 0 - l0min

>l0min 0 - l0min

>l0min 0 - l0min

>l0 min 0 - l0min

>l0mln 0 - 20min

>20mtn 0 - 3min 3 -5min 5 - 20min

>20 min 0

• 2mtn 2 - 5min 5-l0mln 10-20 min

>20 min 0 - l0mln

>l0min I

RHR-A 387.42 15540 15540 15540 15540 15540 15540 15540 15540 15540 10500 15540 15540 15540 15540 15540 15540 0

10500 10500 15540 15540 II RHR*B 387.42 15540 15540 14570 14570 0

0 0

0 0

0 0

0 0

0 14570 0

0 0

0 0

0 I

RHR*C 387.42 15540 15540 14550 14550 15540 15540 14550 14550 14550 10500 14550 14550 0

0 14550 14550 0

0 0

15540 15540 II RHR*D 387.42 15540 15540 14585 14585 0

0 0

0 0

0 0

0 0

0 14585 0

0 0

0 0

0 I

CS-A 387.42 8200 8200 8081 8081 8200 8200 8081 6350 6350 6350 6350 6350 6350 6350 8081 6350 6350 0

0 5725 5725 I

CS-C II CS-B 387.42 8200 8200 8120 II CS-D 8120 0

0 0

0 0

0 0

0 0

0 8120 6350 6350 6350 6450 0

0 min time to first failure (min\\

0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 avg time to first failure (min) 6.2 5.7 42.7 34.8 45.2 40.7 49.2 33.9 max time to first failure (min) 44.3 33.2 95.9 86.5 162.1 179.9 189.0 110.6 Thickness Exceed Risk (alone) 0.OOEi-00 0.OOEi-00 3.l0E-07 3.llE-07 3.llE-07 l.93E*06 5.17E-07 3.18E-07 Thickness AND DB Exceedance 9.40E-08 9.78E-08 5.46E-07 5.53E-07 5.53E-07 l.04E-06 7.13E-07 5.53E-07 DB Exceedance Risk (alone) 6.82E-07 6.78E-07 2.34E-06 2.34E-06 2.34E-06 2.23E-06 2.SOE-06 2.34E*06 Non-lsolable Break Risk 7.76E-07 7.76E-07 3.19E-06 3.20E-06 3.20E-06 5.19E-06 3.73E-06 3.21E-06 lsolable Break Risk 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 Total Risk {1/yr) 9.86E-07 9.86E-07 3.40E-06 3.41E-06 3.41E*06 S.40E-06 3.94E-06 3.42E-06 to NRC-24-0064 Page 16 of 26 Table 8. Flow condition footnotes common to all risk result tables.

Flow Hi'll Ory Oe1aipUon Two Div, Max flow Two Div, Max f low One Div, Max f low One o,v. Max flow with One Div, Pool Coollnc *Hypothetical* Max AHR use H'1)0thetlcaI: Time Step Case, ED re<auired Of full One Div, AHR Runout, (rounded)

(not rounded)

• Sasellne--

Max Stralner*flow One o,v. Pool coonnc

{All times notional, must have TOfus coollnc by 20 min) depressurl:atlon follow,nc OOUO pump seQuenc:e and time CS at Min TKh Sp<<

(C.aselA)

(Case 18)

(tase 1A)

Olspantv (C'ase 3A)

(Case 38) cr,Ucal anion to t>rint: up torus coollnc (Case SA}

(C'ase 28)

(Case 4A) 0

• 10mln I >10mln 0

• 10mln I >10mln 0*10mln I >10mln 0

• 10mln I >10mln 0*20mln I >20mln 0 *3 mln 3-Smln 5

• 20mln

>20m1n O* Smln S*10mln 10-20mln I >20mln 0

• 10mln I >10mln AHR Case UX6-2b AHR case X6-2b Maximum system flows There Is no h','Clraullc Mode G - Tw~Pump lOCAoccurs CS remains 21'dRHR Torus coollnc l s lOCA occurs CS One AHR Torus coollnc must be Non-physic.al to run AHR analy:ed fOf runout of 4 resultlnc ca It'd flows Identified In respemve case run ror l pumps to lPCl lnfealon. TOfuS and all on IOWflOW pump ls now In service.

assumed on min flow to pump or achieved by 20 min, but on OS. bvtCSatMlnTS pumps w/falled loop rather than slncle-pump AHR and CS h','Clraullc broken rec1tc with OS to Coollnc avallable whlle AHR Put on min maximl:e strainer flow lnfectlnc wlll llkely be sooner.

Common power supply selea, max HP, and min maximum analyses.

match 4-pump max tlow.

pumps pumps flow to dlspat1ty, di slon cannot achieve both NPSH.

Hl&hest One-Div flow as GE system l)foc.ess Inject.

makeup assess throttled to exuemes.

cs case 6 Mode G.

This Case applied In described here Is 2*

dlaaram considers tw~

ltveltO t>reakslze assess CS hydraullc model Runout to RPV at O psld Ref. 111 as the t>asellne pump I.Kl to One Div pump LPCI Injection up assess bfeakslze.

calibration to a CS test flow conflauratlon fOf with OS, and low Rx to ~minutes based on bfeak size.

line maximum.

• After 10mlnutes, CS l s rlskanatysls.

Pressure at hiCh water assumed slncte failure One Div throttled per Tjme temperature (AHR Mode of one ECCS division.

AHR on min Slnale*pump max flow Crncal OperatOf Action.

G-6).

Thereafter, the flow to applied to all pumps See M-5981* 1.

operable dlvtslon Is assess consistent with a After 10 minutes, CS Is placed In torus coollnc.

break size.

baseline.

Action desalbed In throttled per Time 23.203CSSOP.

Cfltcal OperatOf Action.

10,5001pm bounds max cs slnile pump tlow In SOC assumed f low of 63501pm used of l03051pm case Ol*X.

ottto throu1hout as a maximize reference level f0<

Considers the strainer throttled flow.

possibllltythat both d1spar1ty diVisions of lPCI are and avoid available and that with PfOlonced two divis,ons available, use in min one d1Y1Slon may be flow operated In lPCI mode This case lllusuates a sequence typlcal of a smaller COfe Spfayflow Is throttled to 6JSO CPffl per SOP 23.201.

bfeak that can be handled by CS. May possibly run with No loss of power fOf Tw~Oiv. optfatlon, so no toss of assets.

one RHR pump lnJe<tlnc (others on min flow). If operatlnc pump labors from debrls. alternate pump on less obstructed strainer will be used (see badtflush lo,oc.edurel.

LPCI TOfUs Coolinc lOWflOW to NRC-24-0064 Page 17 of 26 Figure 5. Baseline distribution of Min-K debris volume (top) and fractional risk contribution (bottom) for all discrete weld break sizes.

Baseline Min-K TM Debris and Risk Fraction 102.---------~-~-~-~~~~~--.-----~-----,

~ 101

i

I g

lj

-~ 100 SmalleslMin,K~-~-.source.10.fail........................ '......................................................... '.............. J.;.....,

..C I

I I Q) 0 "ffi

.. : i I..

10-2.__ _______________ _._ ______..._.,

100 101 Break Diameter (in.)

~5................ -... -...................................

~ 1 o-1 o.:1.................................................................................................................................................... I....... _

I

'+-

0 C

0

()

~

lL 10-2 '----------~---~---'-----~-.,._,

100 101 Break Diameter (in.)

to NRC-24-0064 Page 18 of 26 Results parallel to those described for the baseline evaluation presented in Table 7 were generated for all sensitivity cases defined in Table 6. Sensitivity parameters were varied one at a time, while all other parameters remained fixed at baseline values. Table 9 summarizes raw sensitivity study results without additional baseline conditions (i.e., plant-state probabilities, operator diagnosis of debris accumulation, and reduced penetration Min-K debris). Results are presented as if each flow history and sensitivity combination stands alone as an independent total risk estimate. On this basis, risk from each sensitivity case can be compared to baseline results to help judge the importance of each parameter variation. Summation of select one-division and suppression pool cooling cases is discussed in Section 3 - Revised Att-3 Baseline and Final Baseline Risk with Penetration Min-K to arrive at the total modified baseline risk (6.94E-07/yr).

Trends and comparisons observed between the sensitivity studies are summarized in Ref. 3 -

SERCO-REP-DTE-22929-02, Rev. 0, Section 5.3 - Parameter Sensitivity Studies, p. 31 of 84.

Note that differing flow conditions are denoted by upper case letters (Case 2A, Case 2B, etc.)

and parameter variations are distinguished by lower case letters (Case 2a, Case 3a, etc.). The more important findings include:

1. With exceptions noted for Case 2a (1/16th inch fiber thickness failure) and Case 3a (AM break frequencies), the most important finding in the Table 9 risk sensitivity summary is the fact that risks for Suppression Pool Cooling (SPC) flow histories (Case 3A and 3B) are relatively stable for all sensitivity parameter variations. Risk tabulated for SPC depend on the exact flow histories that are followed, and it is possible that flow combinations like Case 3A and 3B, which are labeled as One-Division flow responses, can be established by operator actions even for Two-Division system response. None of the results in Table 9 credit operator ability to rotate flow across all functional strainer/pump systems.

2. Case 2a risks (1/16th-inch fiber thickness failure criterion) are not dramatically higher than baseline risks, ranging from a 10% to a 39% increase between bold entries in the column labeled Baseline and the column labeled 2a, indicating that the 1/8th-inch baseline failure threshold captures the dominant portion of risk contributed by this failure mode. The Case 2a failure threshold of only 1/16th-inch of fiber is very stringent. It is not realistic to imagine that such a delicate debris layer can form contiguously and simultaneously and induce unacceptably high head loss on six strainers operating at high velocity.

3. Sensitivity Case 2b (1-in. thickness failure) effectively turns off any risk contributions from the fiber thickness failure criterion. Comparison of Non-Isolable break risk between Case 2a (1/16th-inch failure thickness) to Case 2b (1-in failure thickness) shows that risk added by monitoring fiber thickness failure at a very stringent 1/16th-in. thickness (5.27E 2.88E-07 = 2.39E-07/yr) contributes less risk than from exceeding DB Min-K limits (compare 2.39E-07/yr from thickness failure vs. 2.88E-07/yr from DB Min-K exceedance). This is a startling observation. Debris beds formed with only 1/16th-inch of fiber are filmy, tenuous, noncontiguous, do not filter particulates efficiently, and cannot sustain high head loss. Yet, the combined risk of ALL events to NRC-24-0064 Page 19 of 26 delivering more 1/16th-in. or more of fiber on any single strainer is less than the risk of exceeding the DB Min-K limit on any single strainer. This comparison illustrates how stringent the DB Min-K limit is compared to the bed thickness limit, but both conditions are applied as assumed failure modes in all risk calculations.

4. Risks tabulated for Case 1a (65 ft2 of miscellaneous debris) and Case 1b (120 ft2 of miscellaneous debris) are nearly identical to the baseline risk assuming 100 ft2 of miscellaneous debris, showing that total miscellaneous debris area has little effect on risk within the debris area and bed thickness ranges of interest.

5. Sensitivity Case 5a (Alternate DB loads) illustrates a fairly significant reduction of risk from Non-Isolable breaks between baseline DB debris loads that retain identified safety margin and increased DB debris loads that explicitly assign the margin for the purpose of risk reduction (3.19E 1.44E-07 = 1.75E-07/yr, a 55% risk reduction). The identified margin arises because of a reduction in Min-K density from 16 lbm/ft3 to 11.4 lbm/ft3 that effectively reduces Min-K debris mass associated with the qualified Min-K debris volume. Baseline assumptions are not modified to explicitly apply the risk reduction, leaving the safety margin available for use in other plant calculations.

to NRC-24-0064 Page 20 of 26 Table 9. Summary of Sensitivity Parameter Risk Evaluations (before applying additional baseline conditions).

Risk Sensitivity Results (Without Plant State Probability Reduction)

Flow Condition Risk Component la lb 2a 2b 3a 4a 4b Sa Baseline (65 ft2)

(120 ft2)

(1/16th in.)

(1 in.)

(AM)

(1 min)

(10 min)

(incr Min-K)

Non-lsolable 7.76E-07 7.76E-07 7.76E-07 l.12E-06 7.76E-07 2.20E-0S 7.76E-07 7.76E-07 6.39E-07 Case lA lsolable (Two Div) 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 4.SGE-07 2.l0E-07 2.l0E-07 2.l0E-07 Total 9.86E-07 9.86E-07 9.86E-07 1.33E-06 9.86E-07 2.24E-05 9.86E-07 9.86E-07 8.49E-07 Non-lsolable 7.76E-07 7.76E-07 7.76E-07 1.12E-06 7.76E-07 2.20E-0S 7.76E-07 7.76E-07 6.48E-07 Case 18 lsolable (Two Div) 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 4.SGE-07 2.l0E-07 2.l0E-07 2.l0E-07 Total 9.86E-07 9.86E-07 9.86E-07 1.33E-06 9.86E-07 2.24E-05 9.86E-07 9.86E-07 8.SSE-07 Non-lsolable 3.19E-06 3.19E-06 3.19E-06 S.27E-06 2.88E-06 3.83E-0S 3.19E-06 3.19E-06 1.44E-06 Case 2A lsolable (One Div) 2.l0E-07 2.l0E-07 2.l0E-07 2.lOE-07 2.l0E-07 4.SGE-07 2.l0E-07 2.lOE-07 2.l0E-07 Total 3.40E-06 3.40E-06 3.40E-06 5.48E-06 3.09E-06 3.87E-05 3.40E-06 3.40E-06 1.65E-06 Non-lsolable 3.20E-06 3.20E-06 3.21E-06 S.3SE-06 2.89E-06 3.83E-0S 3.20E-06 3.21E-06 1.72E-06 Case 28 lsolable (One Div}

2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 4.SGE-07 2.l0E-07 2.l0E-07 2.l0E-07 Total 3.41E-06 3.41E-06 3.42E-06 5.56E-06 3.l0E-06 3.SSE-05 3.41E-06 3.42E-06 1.93E-06 Non-lsolable 3.20E-06 3.20E-06 3.21E-06 S.33E-06 2.89E-06 3.83E-0S 3.20E-06 3.20E-06 1.72E-06 Case 3A lsolable (One Div}

2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 4.SGE-07 2.l0E-07 2.l0E-07 2.l0E-07 Total 3.41E-06 3.41E-06 3.42E-06 5.54E-06 3.l0E-06 3.SSE-05 3.41E-06 3.41E-06 1.93E-06 Non-lsolable S.19E-06 S.l0E-06 S.39E-06 6.71E-06 3.27E-06 1.04E-04 S.29E-06 S.SlE-06 4.82E-06 Case 38 lsolable (One Div}

2.lOE-07 2.l0E-07 2.l0E-07 2.lOE-07 2.l0E-07 4.SGE-07 2.lOE-07 2.lOE-07 2.lOE-07 Total 5.40E-06 5.31E-06 5.60E-06 6.92E-06 3.48E-06 1.04E-04 5.S0E-06 5.72E-06 5.03E-06 Non-lsolable 3.73E-06 3.73E-06 3.73E-06 S.74E-06 3.21E-06 4.4SE-0S 3.73E-06 4.53E-06 1.93E-06 Case 4A lsolable (Two Div) 2.l0E-07 2.l0E-07 2.l0E-07 2.lOE-07 2.l0E-07 4.SGE-07 2.l0E-07 2.lOE-07 2.l0E-07 Total 3.94E-06 3.94E-06 3.94E-06 5.95E-06 3.42E-06 4.S0E-05 3.94E-06 4.74E-06 2.14E-06 Non-lsolable 3.21E-06 3.20E-06 3.21E-06 S.3SE-06 2.89E-06 3.84E-0S 3.21E-06 3.21E-06 1.72E-06 Case 5 lsolable (One Div) 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 2.l0E-07 4.SGE-07 2.l0E-07 2.l0E-07 2.l0E-07 Total 3.42E-06 3.41E-06 3.42E-06 5.56E-06 3.l0E-06 3.89E-05 3.42E-06 3.42E-06 1.93E-06 to NRC-24-0064 Page 21 of 26 Table 9 sensitivity Case 3a (AM) returns higher risks for all flow conditions because of a procedural difference in how a set of expert opinion information is combined, or aggregated. For Arithmetic Mean (AM) aggregation, a common average of estimated break exceedance frequencies is reported at several pipe break sizes (sum of all estimates divided by number of experts). For Geometric Mean (GM) aggregation, the average of estimated break exceedance frequency logarithms is computed before reporting the composite value at each break size. When estimated break frequencies vary by orders of magnitude, AM aggregation can allow a single conservative estimation to dominate a more widely held consensus opinion. For the sensitivity case presented in Table 9, AM aggregation becomes progressively more conservative as break size increases. For example, the AM average annual frequency of 1.40E-3/yr for all breaks greater than 1/2 in diameter is approximately 2.2 times greater than the geometric-mean average annual frequency of 6.5E-4/yr for all breaks greater than 1/2 in diameter, but for the range of breaks that generate enough debris to exceed the performance criteria, the ratio of non-isolable risk contributions can be as high as (3.83E-05) (3.19E-06)=12

(compare Case 2A row Non-Isolable risk for the sensitivity Case 3a column to the Baseline column).

Risk from the Case 3a AM sensitivity case can be reduced by applying the three additional baseline conditions (pump-state probability, reduced Min-K debris, and credit for operator action. Table 10 reports the One-Div (Case 2A) direct risk contributions using AM break frequencies and reduced Min-K debris.

Table 10. Risk Contributions for One-Div Response After 25%

Penetration Min-K Reduction.

Contributor Direct Risk (per year)

Bed Thickness Exceedance (alone) 1.61E-06 Bed Thickness and DB Exceedance (both) 1.69E-05 DB Exceedance (alone) 1.86E-05 Total Non-Isolable Risk 3.71E-05 Table 11 reports the Suppression Pool Cooling (Case 3A) risk contributions using AM break frequencies and reduced Min-K debris. Risk results from the two flow cases are nearly identical because of similarity between One-Div flow conditions and the assumed SPC flow conditions.

Table 11. Risk Contributions for Suppression Pool Cooling After 25%

Penetration Min-K Reduction.

Contributor Direct Risk (per year)

Bed Thickness Exceedance (alone) 1.61E-06 Bed Thickness and DB Exceedance (both) 1.69E-05 DB Exceedance (alone) 1.86E-05 Total Non-Isolable Risk 3.71E-05 to NRC-24-0064 Page 22 of 26 Applying the complementary plant-state probabilities and credit for operator ability to diagnose strainer obstruction during SPC leads to a total risk of R=(3.71E-05)(0.1)+(3.71E-05)(0.9)(0.2)+(4.56E-07)=1.08E-05/yr (Non-Iso)(One Div) + (Non-Iso)(TwoDiv)(Op fail) + Iso Risk = Total Risk Numerous factors of safety margin are embedded in all of the LAR risk calculations that can be used to argue for an additional factor of 10 reduction in risk associated with the AM sensitivity case:

1) Additional reduction in penetration Min-K debris damage could be defended for risk-dominant breaks to reduce the raw Non-Isolable risk contribution of 3.71E-05/yr.

2) Detailed HRA studies could be performed to reduce the rate of operators failing to diagnose debris accumulation. A reduction in operator failure to diagnose from 0.2 to 0.1 leads to a total risk of 7.5E-06/yr, and the rate of failure to diagnose debris accumulation is likely lower than 0.1, given the standard practice of monitoring and adjusting pump flow rates.

3) Accounting for Min-K debris as fiber against the minimum bed-thickness limit adds conservatism that is not required by the strainer design basis.

4) Crediting debris accumulation on automatic, two-division recirculation prior to operator transition to SPC would reduce the amount of debris available to exceed all strainer performance metrics.

5) Some portion of the identified Min-K density correction could be dedicated to the LAR analysis to effectively reduce the total plant load of Min-K insulation.

Finally, numerous defense-in-depth systems and actions discussed in LAR Att-3 could be used in conjunction with the plant PRA to quantify reduced core damage frequencies. Embedded safety margins itemized above, and defense-in-depth systems/actions apply equally to all sensitivity cases presented in Table 9, but they are especially useful for providing context to the relatively high risk indicated in the AM sensitivity case. Application of AM break frequencies satisfies the requirement of RG 1.174 to examine the effect of alternate methodologies as a potential source of uncertainty.

While the Fermi-2 AM sensitivity case produces relatively high risks compared to the baseline, the root-cause is fully understood to be related to alternate methods of break frequency aggregation. There are no other inherent analysis differences that introduce unexplained uncertainty, new accident progressions, or unanticipated system response challenges. Other risk-informed LAR with similar strainer debris accumulation challenges have successfully argued for a conclusion of very low risk (baseline risk in RG1.174 Region III) despite the apparent outlier to NRC-24-0064 Page 23 of 26 introduced by AM frequency aggregation in all similar analyses. These precedents include South Texas Project (Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment Nos. 212 and 198 to Facility Operating License Nos. NPF-76 and NPF-80, STP Nuclear Operating Company, South Texas Project Units 1 and 2 (ML17019A002)) and Callaway Energy Center (NRC Letter, Callaway Plant, Unit No. 1 - Issuance of Amendment No. 228, October 21, 2022 (ML22220A132), among others. Fermi-2 risk results exhibit a similar range of variability as other studies, including the AM frequency sensitivity. As a well-designed, maintained, and operated power plant, Fermi-2 provides a similarly strong complement of safety margin and robust defense-in-depth strategies to ensure protection of the public and the environment.

5. Strainer Failure Tabulation for 25% Penetration Min-K Debris Reduction This section provides additional details regarding application of the 25% Min-K reduction factor using the suppression pool cooling flow configuration as an example. Application of the Min-K debris reduction factor to the One-Div run-out flow configuration is performed similarly.

Table 2 in this revised supplement (Att-4) states the direct risk contributed under Suppression Pool Cooling mode (Case 3A) by non-isolable LOCA that fail three combinations of non-overlapping strainer performance criteria. Direct risk reported in Table 2 does not include any adjustments for pump-state probability, operator action, or reduced penetration Min-K damage. Direct risk is the sum of break frequencies assigned to postulated non-isolable LOCA that exceed the following performance criteria:

1. Bed Thickness Exceedance (alone) - breaks that accumulate 1/8th inch or more of fiber on any single strainer, but do not exceed the 0.334 ft3 DB RHR strainer Min-K limit.

2. Bed Thickness and DB Exceedance (both) - breaks that accumulate 1/8th inch or more of fiber and 0.334 ft3 or more of Min-K debris on an RHR strainer.

3. DB Exceedance (alone) - breaks that accumulate 0.334 ft3 or more of Min-K debris on an RHR strainer, but do not exceed the 1/8th inch fiber limit on any strainer.

Table 12 below itemizes the number of postulated weld breaks, corresponding to Table 2, that exceed each combination of failure metrics. Time-dependent fiber and Min-K accumulation inventories are monitored on each active strainer to determine if and when each criterion (1 - 3 above) are met or exceeded.

to NRC-24-0064 Page 24 of 26 Table 12. Weld-Break Count Contributing to Risk for Suppression Pool Cooling Before 25% Penetration Min-K Reduction.

Contributor Direct Risk (per year)

Weld Break Count Bed Thickness Exceedance (alone) 3.11E-07 66 Bed Thickness and DB Exceedance (both) 5.53E-07 104 DB Exceedance (alone) 2.34E-06 30 Successful Response 0.00E-00 687 Total Non-Isolable Risk 3.20E-06 200 Debris source terms for each postulated weld break are reported in attachments to Ref. 2. Table 13 provides an excerpt of debris quantities for several break locations and illustrates four debris categories: 1) Total Fiber including penetration Min-K (Col. 4), 2) Total Fiber not including penetration Min-K (Col. 5), 3) Total Min-K including penetration Min-K (Col. 6), and 4) Total low-density fiberglass not including Min-K as fiber. Note that Col. 4 minus Col. 5 equals the amount of penetration Min-K debris generated and transported for each break.

to NRC-24-0064 Page 25 of 26 Table 13. Example debris quantities and debris categories.

Weld Location Weld Size (in.)

MEAN DEGB Freq Total Fiber Transported (ft3)

(w/PenMinK)

Column 4 Total Fiber Transported (ft3)

(wo/PenMinK)

Column 5 Total Min-K Transported (ft3)

(w/PenMinK)

Column 6 Total LDFG Transported (ft3)

(wo MinK)

Column 7 NONISOWELD FW-N21-2336-0W12 17.94 9.30E-08 17.61 4.57 13.47 4.13 NONISOWELD FW-N21-2336-12WF1 17.94 9.30E-08 15.56 5.10 10.90 4.66 NONISOWELD FW-N21-2336-12WF2 17.94 9.30E-08 6.80 5.69 1.35 5.46 NONISOWELD FW-N21-2336-12WF2 (12" x 3.4" S0L) 11.06 5.09E-09 3.23 2.55 0.69 2.54 NONISOWELD FW-N21-2336-12W0 17.94 9.30E-08 6.78 5.69 1.32 5.45 NONISOWELD FW-N21-2336-0W3 17.94 9.30E-08 6.12 5.88 0.25 5.87 NONISOWELD SW-3WB (1) 17.94 9.30E-08 6.11 5.92 0.19 5.92 NONISOWELD SW-3WC 17.94 9.30E-08 6.06 5.88 0.18 5.88 to NRC-24-0064 Page 26 of 26 When assessing cumulative risk of exceeding the strainer DB performance metrics with reduced penetration Min-K debris, the amount of Min-K debris analyzed for each break is calculated as:

Reduced Total MinK=(Col 6)-0.25x(Col 4-Col 5).

Total MinK Reduction x (Penetration Min-K)

Min-K is also counted as fiber contributing to the bed-thickness limit. The amount of fiber analyzed for each break is also reduced as:

Reduced Total Fiber=(Col 4)-0.25x(Col 4-Col 5).

Total Fiber - Reduction x (Penetration Min-K).

It is important to note that the debris reduction factor applies only to debris resulting from damage to Min-K insulation residing inside containment penetrations. The reduction factor does not apply to the much smaller debris amount arising from Min-K insulation applied to whip restraints.

Table 14 reports direct risk and failed break scenario counts for each strainer performance metric for Suppression Pool Cooling (Case 3A) after the 25% reduction in penetration Min-K debris.

Note that the sum of risks reported in rows 3 and 4 (5.17E-07+8.73E-07=1.39E-06/yr) represents the total risk of exceeding the DB Min-K limit.

Table 14. Weld-Break Count Contributing to Risk for Suppression Pool Cooling After 25% Penetration Min-K Debris Reduction.

Contributor Direct Risk (per year)

Weld Break Count Bed Thickness Exceedance (alone) 3.32E-07 74 Bed Thickness and DB Exceedance (both) 5.17E-07 94 DB Exceedance (alone) 8.73E-07 30 Successful Response 0.00E-00 689 Total Non-Isolable Risk 1.72E-06 198