ML23277A133

NRR E-mail Capture - ECCS Strainer Risk Informed Licensing Amendment - Audit Questions

ML23277A133
Person / Time
Site:	Fermi
Issue date:	10/03/2023
From:	Shilpa Arora NRC/NRR/DORL/LPL3
To:	Frank E DTE Electric Company
References
L-2023-LLA-0092
Download: ML23277A133 (12)

Text

From:

Surinder Arora Sent:

Tuesday, October 3, 2023 4:20 PM To:

Eric Frank Cc:

Roxanne Vonhabsburg; Derek C Corrin; Steve Smith-DSS

Subject:

ECCS Strainer Risk Informed Licensing Amendment - Audit Questions Attachments:

Audit Discussion Topics Fermi ECCS Risk Informed LAR.docx Importance:

High Hi Eric, Attached is the first batch of questions that our audit team has prepared and would like to discuss with your team, based on the review of the uploaded documents in the ePortal. Your staff may review these questions after which you can let me know when it would be feasible for us to arrange a Teams meeting with the audit team. I will talk to you more on this subject in our biweekly status meeting tomorrow. If your staff can address these questions in the meeting with the audit team, it will cut down substantially on the number of requests for additional information (RAIs). In these discussion meetings we will also let you know which additional documents the staff would like to review on the portal or on the docket.

Thanks, Surinder Surinder Arora, P. E.

Project Manager, Fermi 2 and Dresden 2 & 3 NRR/DORL/LPL3 surinder.arora@nrc.gov 301-415-1421

Hearing Identifier:

NRR_DRMA Email Number:

2261 Mail Envelope Properties (PH0PR09MB82361D3D7F19255DE3EF309C94C4A)

Subject:

ECCS Strainer Risk Informed Licensing Amendment - Audit Questions Sent Date:

10/3/2023 4:19:40 PM Received Date:

10/3/2023 4:19:00 PM From:

Surinder Arora Created By:

Surinder.Arora@nrc.gov Recipients:

"Roxanne Vonhabsburg" <roxanne.vonhabsburg@dteenergy.com>

Tracking Status: None "Derek C Corrin" <derek.corrin@dteenergy.com>

Tracking Status: None "Steve Smith-DSS" <Stephen.Smith@nrc.gov>

Tracking Status: None "Eric Frank" <eric.frank@dteenergy.com>

Tracking Status: None Post Office:

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Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 1 Tech. Spec. Branch (STSB) Questions

1) The exemption request appears to be incorrect.

a. Precedent for all similar exemptions is to exempt 10 CFR 50.46(a)(1) which points to other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated. The NRC considers the deterministic evaluation of sump performance to be one of the other properties.

A quote from a previously approved exemption - The NRC staff interprets the section 50.46(a)(1) requirement to calculate ECCS performance for other properties as requiring licensees to consider the impacts of debris generation and transport in containment.

b. It is not correct to exempt 50.46(d). 50.46(d) states that the requirements of this section (50.46) are in addition to other any other requirements applicable to ECCS set forth in this part (part 50). The requirement to perform a deterministic evaluation of sump performance is a requirement of 10 CFR 50.46 which is the section referred to in 50.46(d). The requirement to do a deterministic evaluation of sump performance is within section 50.46. 50.46(d) applies only to requirements outside 50.46, but within part 50 (10 CFR 50). It is incorrect to exempt 50.46(d) for any requirement that is contained in 50.46 which includes the sump evaluation. (See submittal page 1 of 8 of Attachment 2-2 (pg. 48) that states that the deterministic evaluation for the sump is a requirement 10 CFR 50.46.)

c. On Attachment 2-2, page 6 of 8 (pg. 53), the submittal states that the GDCs use a deterministic calculational method for demonstrating strainer performance. This is incorrect. The GDC provide high level guidance, acceptance criteria, and assumptions that are to be used in system design. There is no GDC deterministic requirement listed for strainer performance.

d. GDC, for this purpose, do not require an exemption because of relatively recent OGC determination on GDC. This was discussed with the licensee during the presubmittal meeting.

e. GDC-35 does not discuss debris or sump performance.

f. The exemption did not discuss whether the licensee had considered testing or further deterministic analysis as a potential way to resolve the issue instead of using the exemption process. This should be considered when evaluating special circumstances.

2) The FSAR markup does not describe how the risk-informed analysis was performed.

3) The FSAR markup does not specify the key aspects of the risk-informed analysis that are methods that cannot be changed without NRC prior approval.

4) The FSAR markup does not define the 50.46 ECCS acceptance criteria for the effects of debris on strainer performance. When are the strainers operable? What conditions require reporting? (Risk beyond R-III?) What are the design basis requirements? What are the deterministic limits beyond which risk analysis is required? What debris is evaluated by the risk-informed analysis? How is additional discovered debris addressed? Is only the currently identified debris covered by the licensing basis?

5) The FSAR markup, Insert 2 (pg. 35), last sentence wording is misleading. It should not be change in risk that has to meet the 5 attributes. It is the risk-informed analysis that

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 2 has to meet the 5 Key Principles of RG 1.174. Small change in risk is attribute or Key Principle number 4.

6) Provide a basis for the 1/8-inch bed thickness criteria. Strainer acceptance criteria should be based on the plant specific debris loads for Fermi. For example, describe how the design basis testing and analysis that was used to qualify the strainer demonstrates that a fibrous debris amount of 1/8 inch is acceptable. See page 16 of 26 of Attachment 1-1 (PDF pg. 19) that states that breaks that exceed 1/8 inch are already included in the design basis. See page 5 of 94 of the Serco calculation (pg 77) that makes a similar finding. An explanation of these statements may provide the necessary detail. Page 55 of 94 (pg. 127) of the Serco calculation makes the statement that without a fiber bed there is no substrate to capture particulates on the strainer. The staff has observed strainer testing with only microporous insulation, and also vertical loop testing with Cal-Sil, that resulted in high headlosses. No fiber, beyond that in the microporous insulation types was included in these tests. In addition, references in the submittal provide information regarding Min-K headloss with no fiber. See EFA-11-16-004 and DC-5979 which establishes a maximum Min-K load per strainer of 10 lbm. regardless of fiber load.

These references are both based on test results. On Page 57 of 94 (pg. 129) the Serco calculation discusses breaks smaller than the design basis maximum that generate and transport debris in the range of 1/8 inch. On page 65 of 94 of the Serco calculation (pg.

137) it is stated that the risk analysis verifies that debris types and quantities are within the design basis limits. Clear explanation of these statements may help the NRC staff with understanding the acceptability of the 1/8-inch acceptance criterion. What is the bed thickness at the design basis fiber limit? If it is less than 1/8 inch, why is it considered an acceptable criterion since the design basis is based on testing and associated analysis?

Also discussed on page 79 of 94 (pg. 151).

7) Starting on Serco calculation page 22 of 94 (pg. 94) identify the material types of the non-RMI insulation shown as blue spheres in the figures. Based on review of reference 11 it appears that blue is associated with Nukon, but the staff could not confirm this from the submittal. Clarify whether this material is accounted for in the existing deterministic debris loads or if this material is newly discovered. Identify the material of the vertical red lines in the torus in figure 2-5. Define the material types shown in the blue spheres.

Figure 2-6 refers to non-RMI Nukon and Min-K on the right-side illustration and it appears that all of the locations are denoted with blue.

8) Page 28 of 94 of the Serco calculation (pg. 100) states that check valves that are closed and holding reactor pressure are excluded from the failure analysis because in-service failure of these valves is unlikely. How is it determined that each valve is holding pressure? Page 25 of 94 of the Serco calculation states that the MS drain valves are shut and verified shut. How is this accomplished?

9) On page 36 of 94 of the Serco calculation (pg. 108), it appears that Table 2-3 has the above and below grating transport fractions reversed from the URG guidance. Clarify whether this is a typo and whether the correct values were used in the analysis.

10) On page 37 of 94 of the Serco calculation (pg. 109), the stated overlap for miscellaneous debris is 50%. Clarify whether this should be 25% and what was used in the analysis.

The calculations that are presented in the text appear to correctly use 25%.

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 3

11) Describe the current design basis for area occluded by miscellaneous debris, and the updated design basis from additional miscellaneous debris from more recent discovery.

It appears that the 6 ft2 of sacrificial circumscribed area is equivalent to 69.1 ft2 of strainer area based on the ratio of these surface areas. The newly identified material appears to equate to 65.25 ft2 of sacrificial flow area based on the 25% overlap allowance. The total obstructed area would then be 134.35 ft2. Page 38 of 94 of the Serco calculation (pg. 110) states that the baseline risk analysis assumes 100 ft2 of lost strainer area. What is the basis for using this value? Is does not appear to be acceptable to apply the 0.75 overlap multiplier to the circumscribed area from the original design basis. If 100 ft2 is the assumption in the analysis provide the basis. Also see Serco calculation page 71 of 94 (pg. 143). Clearly state the design basis value of occluded (sacrificial) area and provide its basis. Provide the additional sacrificial area assigned to account for the newly discovered tags and labels and its basis. Describe any values used in the risk-informed analysis, how they are used, and the basis for using the values.

12) How is the effect of the newly evaluated miscellaneous debris (tags and labels) on the areal density of non-fibrous debris types (other than Nukon or LDFG) that may collect on the strainer evaluated by the risk-informed analysis? Is the change in the areal density of the other debris types bounded by the design basis analysis? As stated above, the NRC has observed strainer testing that included only microporous debris and particulate debris, with no added fiber, that resulted in high headlosses. This was also observed during vertical loop testing with Cal-Sil. The test observations are in contrast to the implicit assumption regarding the need for a 1/8-inch fiber bed to filter substantial amounts of particulate debris (page 16 of 26 of Attachment 1-1 or pg. 19). As strainer area is reduced due to additional miscellaneous debris, describe how any increased bed thickness and velocity though the debris bed is considered in the evaluation. For example, Page 66 of 94 (pg. 138) of the Serco calculation Table 5-1 provides the maximum transportable fiber and Min-K from non-isolable breaks. How is the additional sacrificial area from the newly identified tags and labels accounted for in the analysis for the debris types? Is it valid to simply compare the masses or volumes of each debris type?

13) On page 14 of 16 of attachment 1-1 (Pg 17), it is stated that deterministic goals applied to the original strainer design bound all debris loads generated by LOCAs for all inboard non-isolable locations. On page 79 of 94 (pg. 151) the safety margin discussion states that the Fermi strainers are designed to meet the design basis loads with sufficient margins. In addition, it states that the current debris generation estimates for non-isolable breaks are lower than the design basis inventories. Explain these statements. If the new estimates are to become the design basis, it sounds like there is margin over the old analysis that establishes the strainer allowable loads. If this is the case, there would be no need to perform a risk analysis for the non-isolable breaks. However, the additional miscellaneous debris may cause the updated debris loading per area to be higher than the current design basis. Maybe newly discovered tags and microporous debris are not covered by these statements? Discuss whether the updated debris loading is bounded by the current licensing basis debris loads and the resulting impact on the need to assess risk impact for non-isolable welds.

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 4

14) On Page 56 of 94 (pg. 128) the Serco calculation states that the strainer failure criterion for the baseline risk evaluation is 1/8-inch of fiber on any operating strainer. Are there any other scenarios that would result in a failure? Other statements in the submittal state that no scenarios exceed the design basis except for Min-K. This implies that greater than 1/8-inch of fiber cannot occur. Failure should occur at any time that the design basis load for any debris type (per strainer area) is exceeded.

15) Page 41 of 94 (Pg. 113) of the Serco calculation describes the LPCI runout case as the most challenging for LPSI runout and states that the critical parameter in NPSH. How is this case evaluated in the analysis? Are all cases that do not result in scenario failures bounded for headloss or NPSH margin by the design basis debris loads and flows (considering blocked strainer area)?

16) Starting on page 38 of 94 of the Serco calculation (pg. 110) the strainer flow configuration is described. This is also discussed in other sections, e.g., starting on page 54 of 94. It appears that the configuration assumed for the analysis (single train runout) is an unlikely configuration that may result in earlier scenario failure, but also result in lower risk values than the more likely single train suppression pool cooling case. It is also stated that the suppression pool cooling case is the design basis case. Further discussion of the strainer flow rates is provided on page 73 of 94 (page 144), and 80 and 81 (pg. 152 and 153) of the Serco calculation. The submittal states that the Suppression Pool Cooling (SPC) mode (1 RHR strainer and 1 CS strainer) results in higher risk than the baseline.

a. Provide the methodology for determining the limiting strainer alignment and flow conditions that result in the fastest failure times.

b. Discuss how a three strainer case results in reaching the failure criterion faster than a two strainer case.

c. Provide the basis for the choice of using the runout case for the baseline for the risk-informed analysis instead of the more likely suppression pool cooling (SPC) mode.

d. In several places in the submittal it is stated that the runout case is used to reduce time for defense-in-depth (DID) operator actions, but these actions are still credited as DID without further analysis. Discuss difference in failure time and how this affects DID actions.

e. Provide a basis for selecting a baseline configuration that is less likely and results in lower risk than the SPC pump alignment.

f. Explain why failure timing was chosen as a more critical parameter than change in risk to select the baseline configuration.

17) In the description of the torus cooling mode on page 39 of 94 of the Serco calculation (pg. 111) it is stated that the flow rate is 10,000 gpm rated. Explain what rated means in this case. Is this an actual, realistic, calculated, or assumed flow rate? What flow rates for torus cooling mode are considered in design basis analyses?

18) On page 82 of 94 (pg. 154) the submittal discusses the assumptions for RHR strainers in service. It states that the loads are calculated assuming one RHR strainer and one CS strainer in SPC mode. Bringing the idle strainer back into service is discussed. The discussion does not appear to be consistent with the baseline evaluation that assumes

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 5 two RHR pumps in runout and one CS strainer operating. Clarify the referenced discussion.

19) Page 43 of 94 (pg. 115) of the Serco calculation includes Table 2-5 which provides a history of the design basis suppression pool debris loads over time. Provide a description of the evolution of each debris type and what the values in the columns represent. For example, are these the design basis limits for suppression pool debris at different times? Are they debris amounts that are predicted to reach the suppression pool by different analyses? Is column 5 the proposed qualified suppression pool limits going forward or is it simply an updated transport analysis? Provides the design basis maximum for each debris type entering the suppression pool and the bases for each value. Compare these values to the design basis limits for the strainers for the evaluated system response scenarios. Discuss how these changes were related to or accounted for the strainer issues associated with the strainer correlation (2009), discovery of Min-K and Nukon improperly identified (2010), incorrect assumptions regarding Min-K debris characterization and transport (2011), RMI headloss (2011), additional tags and labels discovered (2015), and additional Min-K discovered in penetrations (2016).

20) Provide a description of non-RMI insulation installed in the plant at locations other than the penetrations. Page 18 of 94 of the Serco calculation (pg. 90) states that DC-5797 identifies that both Nukon and Min-K are installed at whip restraints. On page 25 of 48 of Ref. 3 (and 49) of the Serco calculation (DC-5979, Rev. 0) Min-K on pipe whip restraints is described. On page 9 of Ref. 41 of the Serco calculation (EFA-E11-16-004) Min-K on the main steam drain lines is described.

a. On Page 61 of 94 (pg. 133) of the Serco calculation modeling of whip-restraint insulation is described. How were the materials and associated volumes of insulation at these locations determined?

b. Has all Min-K that was installed in the primary containment been removed from all locations except for the penetrations and few locations in Reference 11, Table 7-2? It appears that some of the whip restraints have or had up to 40 lbm of Min-K installed based on older referenced calculations. Reference 11 indicates that the Min-K source term has been reduced.

c. For Min-K that was removed, what was used as a replacement, if applicable?

d. Is Min-K still installed on the MSL drains? If so, is it listed in Reference 11, Table 7-2?

e. Provide all locations where Min-K remains installed outside of that installed at penetrations or confirm that all of these installations are identified appropriately in Reference 11, Table 7-2. If there are there locations where non-penetration Min-K is installed other than those listed in Reference 11, Table 7-2 provide those locations and potential debris amounts.

f. Provide a discussion of how the sources of Min-K are accounted for in the calculations that are listed in Table 2-5 of the Serco calculation on 43 of 94 (pg.

115) and how the values changed over time. Include information regarding debris generation, debris characteristics, and transport in the discussion. Reference 11 shows a volume of Min-K at whip restraints of about 1 ft3.

g. Does this 1 ft3 value represent all non-penetration Min-K installed within containment with the exception of that installed at penetrations?

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 6

21) On Page 59 of 94 (pg. 131) the Serco calculation says that all breaks that occur outside of the penetrations damage Min-K based on line-of-sight. On page 36 of 94 of the Serco calculation it is stated that non-isolable breaks are permitted to damage Min-K in penetrations to the extent that robust barriers do not intervene. Is line-of-sight defined by robust barriers? Verify that all targets within the ZOI are assumed to be damaged unless the ZOI is truncated by a robust barrier. Reference 11 implies that this is the case, but it is not evident from the discussion in the submittal.

22) On Page 64 of 94 (pg. 136) of the Serco calculation 4.3.1.c.iii states that assumed immediate loss of flow upon reaching a 1/8-inch bed has never been observed.

Immediate loss of flow is not a valid metric. NPSH margin, based on head loss should be considered. Loss of flow is influenced by many parameters that may be significantly different between test and plant configurations. Describe why this statement is valid to the analysis.

23) On Page 67 of 94 (pg. 139) of the Serco calculation it is stated that the thickness of the newly determined fiber load would result in a 0.55-inch bed if deposited on a single strainer. Was sacrificial area be accounted for in this example? If not, should it be? The paragraph concludes that having other strainers in service would reduce the debris amounts per strainer. What conclusion can be made with respect to the debris amount per strainer as compared to the design basis debris limit considering the baseline model?

24) On Page 75 of 94 (pg. 147) of the Serco calculation a discussion regarding the defense-in-depth-philosophy is provided. The discussion does not include the information specified in the guidance of RG 1.174. The criteria should be addressed. It may be acceptable to state that the 7 RG 1.174 criteria are not affected by the change because..,

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 7 Vessels and Internals Branch (NVIB) Questions

1) SERCO-REP-DTE-22609-002, Revision 1, page 25, states that 1103 welds were selected as the possible LOCA locations in the risk-informed application of CASA Grande. The licensee further stated that The review further identified a subset of 924 welds that are considered active LOCA locations given the at-power plant configurationA subset of only 921 welds represents potentially active LOCA locationsThe plant configuration provides for auto-isolation of 37 welds that reduce the number of welds to 887 unique locations The licensee further reduced the LOCA location to 884 welds.

a) Discuss how 1103 welds were reduced to 924 welds although the licensee did state that the 924 welds are considered active LOCA locations. Explain why 179 welds (1103-924) were eliminated from consideration. (2) Clarify whether 884 welds or 921 welds are included in the risk analysis. (3) Discuss whether every one of the 884 welds has been ultrasonically examined at least once. (4) Clarify whether 884, 924, 921, or 1103 welds are considered in the scope of the license amendment request (i.e., in-scope welds).

2) Section 6.5, SERCO-REP-DTE-22609-002, Revision 1, page 83, states that All Class I welds at Fermi are either Category A, welds with no known cracks that are made from materials that are considered resistant to IGSCC, or Category B, welds made from material that is considered susceptible to IGSCC but have been mitigated by stress improvement prior to two cycles of operation.

a) Discuss the meaning of prior to two cycles of operation. prior to commercial operation? (2) Discuss whether Category A welds have recorded indications from the ultrasonic examinations performed during inservice inspection (ISI) intervals even though the report states the welds have no known cracks (i.e., difference between an indication and a crack). (3) Discuss any degradation occurred in the Category B welds after mitigation. If degradation was identified, discuss the corrective actions. (4) Discuss whether Class 2 welds in the drywell/containment are considered as in-scope welds (i.e., are they part of the risk analysis). If not, clarify why the Class 2 welds in the containment are not included in the risk analysis.

3) Section 6.5, SERCO-REP-DTE-22609-002, Revision 1, page 83, states that Pressure retaining welds are inspected in accordance with ASME Code Case N-716-1 Alternative Classification and Examination Requirements. This Code Case prioritizes inspection of risk significant welds and welds potentially susceptible to a degradation mechanism, such as Intergranular Stress Corrosion Cracking (IGSCC) or thermal fatigue Ten percent of Class I welds are examined over a ten-year interval...

a) Discuss whether the in-scope welds have been examined per the ASME Code,Section XI. (2) Discuss whether the same ten percent of the Class 1 welds are examined per Code Case N-716-1 during every 10-year ISI interval or different population of welds are examined in different 10-year ISI intervals. (3) Discuss the percent of in-scope welds that have not been inspected and will not be inspected to the end of the license renewal period. (4) For the in-scope welds that will never be inspected, discuss whether the higher probability of failure value was used for these welds than for the inspected welds in the risk analysis.

4) Discuss any in-scope welds that are fabricated with nickel-based Alloy 82/182. (2)

Discuss whether these in-scope welds have been mitigated to reduce their susceptibility to stress corrosion cracking. (3) Discuss whether any in-scope nickel-based Alloy 82/182

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 8 welds that have not been mitigated. (4) For those unmitigated in-scope welds, discuss how they are being inspected to monitor their structural integrity. (5) Discuss whether the failure probability value in the risk analysis is increased to account for the unmitigated nickel-based Alloy 82/182 welds.

5) Discuss the number of austenitic stainless steel welds that are susceptible to intergranular stress corrosion cracking (IGSCC) and are included in the risk analysis. (2)

Discuss whether these in-scope austenitic stainless steel welds have been mitigated to reduce their susceptibility to IGSCC (excluding the improvement in primary system water chemistry). (3) For those in-scope unmitigated austenitic stainless steel welds, discuss the corrective actions (excluding water chemistry improvements). (4) Discuss whether the failure probability value in the risk analysis is increased to account for the unmitigated austenitic stainless steel welds that are susceptible to IGSCC.

6) Discuss the capabilities of the leakage detection systems for the reactor coolant system (RCS). (2) Discuss how the RCS leakage detection systems satisfy the guidance in Regulatory Guide 1.45, Revision 1, Guidance on Monitoring and Responding to Reactor Coolant System Leakage.

7) The NRC staff recognizes that the plant technical specifications have leak rate limits for the reactor coolant system (RCS). However, discuss the administrative RCS leak rate limits and associated actions, if any, to ensure that any potential leak rates do not challenge the technical specification leakage limits.

8) BWR owners have implemented inspection guidance of BWRVIP-75-A, BWR Vessel and Internals Project Technical Basis for Revisions to Generic, Letter 88-01 Inspection Schedules. (1) Discuss whether inspection guidance of BWRVIP-75-A has been implemented for the inservice inspection of in-scope welds at Fermi. (2) If affirmative, discuss how inspections of in-scope welds are carried out per the BWRVIP-75-A. (3) If the topic report is not implemented, discuss the reason.

9) Discuss whether failure of flanges and bolts of a piping system, nozzle penetrations to the reactor vessel such as control rod drive mechanisms and standby liquid control system are considered as potential LOCA locations and included in the risk analysis.

10) SERCO-REP-DTE-22609-002, Revision 1, page 33, Table 2-1 shows the failure probability for feedwater is 1.57E-4. Explain why this failure probability is lower than other piping in the table such as main steam and RWCU.

11) Provide the past inservice inspection results for (1) the 1103 welds that were selected for the possible LOCA locations as stated on page 25 of SERCO-REP-DTE-22609-002, Revision 1. (2) In the inservice inspection results identify those welds (884 welds?) that are included in the risk analysis.

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 9 Division of Risk Assessment (DRA) Questions

1) Confirm that the failure probabilities used in EF2-PRA-010 Rev. 4 Component Data Notebook (see Page G-71) for non-LOCA transients as 106 per challenge.

2) Confirm that the failure probabilities used in EF2-PRA-010 Rev. 4 Component Data Notebook (see Page G-71) for LOCAs as 104 per challenge.

3) EF2-PRA-013 Rev. 4 Level 1 and 2 Quantification and Summary Notebook pages 28-30 states: It should be noted that FermiV12 incorporates Fermi 2s FLEX equipment and operating strategies; however, the logic associated is not quantitatively nor qualitatively credited in the model of record analyzed in this document. This statement appears contradictory. Please clarify exactly which of the following alternate RPV makeup sources, which are not dependent on the Suppression Pool, are modelled in the PRA model of record:

a. Condensate Pumps,

b. Standby Feedwater,

c. General Service Water,

d. RHR Service Water,

e. Fire Water,

f. FLEX / B.5.b pump(s).

4) EF2-PRA-002 Rev. 4, Accident Sequence Analysis Notebook page 3, indicates that FLEX equipment is in fact modelled, but only for station blackout (SBO) sequences:

Rev. 4 Updated to reflect FLEX implementation for SBO sequences (WR 1758 1943, 2014). Confirm that FLEX pumps were only modeled for SBO sequences and that it would not have an impact on GSI-191 issues (loss of core/containment cooling). Please clarify the limitations in crediting FLEX pump(s) for scenarios involving suppression pool strainer plugging.

5) EF2-PRA-002 Rev. 4, Accident Sequence Analysis Notebook, Page 96 indicates that there are a number of water injection sources external to the Suppression Pool including: Fire Protection System, B.5.b, Condensate, CRD, or RHRSW - but then states: The Fire Protection System and B.5.b are not currently credited in the PRA model for RPV injection in Level 1 because of a lack of DTE calculations to show success under severe accident conditions. Please clarify the water injection sources external to the Suppression Pool considered in the PRA.

6) For each of the alternate RPV makeup sources, please clarify how these alternate water sources connect to the RPV. Via opening pairs of valves on an existing hard piped connection? Via inserting a spool pieces? Via fire hose connections?

7) Page 98 of EF2-PRA-002 Rev. 4, Accident Sequence Analysis Notebook notes that there are 2 SBFW pumps each of which is capable of RCIC equivalent flow - and apparently with sufficient inventory good for 24 hrs. Do provisions exist for replenishing the CST?

8) Page 587 of EF2-PRA-002 Rev. 4 Accident Sequence Analysis Notebook, indicates that Post Venting, the long-term model considers Fire Water, Condensate Polishing, and SBFW. For Large LOCAs, the documentation is confusing about what injection sources are assumed available after containment venting due to failure of Suppression Pool Cooling. There were previous statements that CRD, SBFW, B.5.b Pump, and Diesel Fire

Audit Discussion Topics - Fermi Strainer Risk Informed LAR (EPID: L-2023-LLA-0092) 10 Pump were not credited as a backup to Cooling, but the logic for the event T-ZZ-VNT-LOCA seems to indicate they were all characterized as Success Paths. See Pages 595, 613.

9) EF2-PRA-003 Success Criteria Notebook Rev. 04 (6/4/2021), clarifies some but not all the available post-LPCI/Core Spray injection sources. Page 112 states that Condensate is credited as a long-term makeup source (after LPCI/Core Spray Injection) for Large LOCAs above the TAF. Fire Protection Water and B.5.b pumps are not credited for long-term makeup. Page 113 states that for Large LOCAs below the TAF neither Condensate, Fire Protection Water, nor B.5.b pumps are credited. Please clarify which injection sources are credited in Large LOCA Event Tree Node QUV.

10) According to page 51 of 94 (PDF page 123) of the SERCO-REP-DTE-22609-02 R1 Fermi Tech Report, the double-ended guillotine break (DEGB) model is represented as the baseline model. Why were partial breaks not considered in the sensitivity analysis of the CDF? Reference 11 discusses hemispherical ZOIs for single sided breaks, but states that all jets are treated as double ended. Provide a justification as to why only the DEGB model was used for the analysis. This maximized debris amounts for each break but may not represent risk accurately as smaller single sided breaks may generate larger debris amounts than the DEGBs evaluated in the analysis.

11) The risk-informed analysis does not seem to consider pump configurations with fewer than 3 active strainers. Justify why pump configurations with fewer than 3 active strainers were not examined in the risk-informed analysis and in sensitivity analyses of the CDF. This is related to an STSB question regarding the pump configuration chosen for the baseline model.