ML17292A136
| ML17292A136 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 10/19/2017 |
| From: | Brett Titus Japan Lessons-Learned Division |
| To: | Euten Mr Southern Nuclear Operating Co |
| References | |
| Download: ML17292A136 (2) | |
Text
NRR-PMDA-ECapture Resource
Subject:
Vogtle SPRA Clarification Question Call.
Location: OWFN-8B4 Start: Thu 07/06/2017 3:00 PM End: Thu 07/06/2017 5:30 PM Show Time As: Tentative Recurrence: (none)
Meeting Status: Not yet responded Organizer: Titus, Brett Required Attendees: Euten, Matthew R.; Biswajit Dasgupta; Osvaldo Pensado; Lyons, Sara; Vasavada, Shilp; Pettis, Robert; NRR_JLD_JHMB Resource; Bridgeline Resource Optional Attendees: Heeszel, David; De Messieres , Candace; Reisi Fard, Mehdi Addressees, The NRCs review of the Vogtle SPRA submittal is progressing well. In order to continue the momentum and efficiency of the review, we are holding a conference call with the Southern Nuclear team to assist us in obtaining a clear understanding of some information in the submittal. We are not requesting any documentation or ePortal information to support this effort; this is simply an opportunity for our technical reviewers to have a discussion with Southerns technical folks to facilitate the ongoing review.
The attached file contains the clarification questions and topics we wish to cover. It is being provided to facilitate clear communication and to ensure that the appropriate staff are available to answer questions in various technical areas. Again, we are not requesting any documentation or written responses at this time.
Please let me know if you have any questions.
- Thanks, Brett Titus 1
Fragility Clarifications
- 1. F&O 14-5: It is stated in the response that differential settlements were computed between structures which resulted in no significant impact to the SPRA results or conclusions.
- a. Please clarify whether the conclusion is based on the magnitude of the calculated settlement of the buildings alone, or whether the evaluation considered system- or component-specific susceptibility to the calculated settlements on a case-by-case basis.
- b. Please clarify whether the evaluation only considered differential settlement between structures and equipment and components spanning the gap between the structures, or whether the evaluation also considered settlement of a structure relative to the surrounding soil and equipment and components (e.g., piping) at the interface.
- 2. F&O 14-7: The fragility evaluation of the Containment Polar Crane was updated to include uncertainty in the fundamental frequency and contribution of higher order modes to the response under seismic conditions. Please confirm whether the fundamental mode shape and frequency including higher order modes (2nd order bending, torsion etc.) were included in the fragility evaluation.
- 3. F&O 14-8: The resolution of this F&O stated that relay fragilities were updated. Please clarify whether the updated median capacities of these relays were above or below the screening level.
- 4. F&O 14-9: Fragility of these components were updated as a result of peer review findings: (a) piping interaction, (b) anchorage configuration of the inverters; (c) interaction with the overhead heater, (d) consideration of valve operator height and weight that were outside EPRI guidelines, and (e) Diesel Generator exhaust silencer anchorage. Please clarify whether the updated median capacities of these components were above or below the screening level.
- 5. F&O 14-10: The response stated that CCW and ACW heat exchanger capacities were updated.
- a. Please clarify whether the median fragilities for the Battery Rack and Turbine Driven Auxiliary Feedwater Pump were also updated.
- b. Please clarify whether the updated median capacities of these components were above or below the screening level.
- 6. F&O 14-14: Please clarify which failure modes for sloshing induced failure of NSCW pumps and discharge MOVs were included in the fragility evaluation and the basis for the conclusion that there was no significant impact on the fragilities.
- 7. F&O 14-17: Please clarify if the fragilities of the NSSS components were recalculated. If so, please briefly describe the impact on the screening and SPRA model.
- 9. F&O 16-2 identified inconsistent use of seismic hazard information, where the fragility estimation was based on a 2012 seismic hazard analysis and the SPRA evaluation was based on 2014 seismic hazard analysis. In response to this finding, it was stated that the fragilities have been recalculated based on the 2014 seismic hazard analysis, and the new values were incorporated into SPRA quantification. Please clarify whether the recalculation resulted in significant changes in the fragilities and screening of SSCs.
- 10. The Peer Review summary on page 69 of 124 states that the screening level was established at 2.5g median capacity. Section 4.4.1 states that the screening level was adjusted to 3g because some capacities of components at screening level 2.5g contributed significantly to the SCDF.
Clarify how the components between 2.5 g and 3 g median capacity were considered to be screened out on a system response basis.
- 11. Because the peer review of fragility of SSCs was based on the 2012 seismic hazard analysis and a 2.5g screening level, please confirm whether pertinent peer review comments, such as conservatism in median capacity, clipping of spectra for in-structure components, and contribution of higher modes to failure, were addressed during reevaluation of fragility of all SSCs with the 2014 seismic hazard analysis and a 3g screening level.
- 12. F&O 14-20: The response stated that seismically-induced-fire and flood interactions were evaluated by walkdown, and the methodology, screening, and results were documented in the quantification report. Section 4.2 identified three seismic-induced flood scenarios that were included in the system model. Please clarify whether the evaluation involved estimation of the fragility of components in these scenarios.
- 13. F&O 14-20 discusses a seismically induced fire evaluation based on walkdowns. Please briefly describe the systematic evaluation performed during and after the plant-specific walkdowns including the following elements in the discussion:
- a. The identification of seismic-fire interaction sources
- b. The systematic screening of the identified sources
- c. Consideration of human actions during the screening
- d. And, any subsequent inclusion in the SPRA (citing any guidance that was followed).
Plant Response
- 1. Please clarify whether the peer review findings associated with the internal events PRA that served as the basis for the seismic PRA are already available on the docket. If so, clarify whether the resolution of those findings was completed as described in the referenced submittal.
- a. Are the internal events findings and their resolutions from Vogtles recent response to GSI-191 (ML17116A096) valid for the internal events model that was used as the foundation for the SPRA submittal in response to the 50.54(f) letter?
- b. Were all the modifications to the internal events PRA model committed to as part of the implementation items for the 50.69 amendment (ML14203A252) presented in the internal events model-of-record used to develop the SPRA?
- 2. According to information on page 74 of 124, certain aspects of FLEX that are permanently installed and operational without operator intervention, i.e., notably improved RCP seals are reflected in internal events and seismic PRA models. However, it is not clear whether other aspects of FLEX are also credited.
- a. Clarify which aspects of FLEX are credited in the seismic PRA model and whether those modeling aspects have been the subject of a peer review (internal events or seismic).
please clarify:
- i. How the low leakage RCP seals were modeled (i.e., failure probabilities for each failure mode considered, common cause considerations, associated human error probabilities and consideration of seismic effects on those HEPs, and how any
potential seismic effects on the performance of the RCP seals were accounted for),
ii. Whether the low leakage RCP seals were included and peer-reviewed in the internal events PRA model that was used as the foundation for the SPRA, and iii. The basis for not considering the inclusion of the low leakage RCP seals as a PRA upgrade if they were not peer-reviewed as part of the internal events PRA model.
- 3. Table 5.4-1 (on page 40 of 124) carries a foot note that states that a plant availability factor basic event (not included) is also part of the quantification. However, several sequences in the table include the identifier PLL which, according to Table 5.4-1a, represents fraction of time above power level specified in ATWS model. Please clarify:
- a. The difference between the plant availability factor basic event (not included) and PLL,
- b. Whether the availability factor is being applied multiple times for any sequence including the ATWT sequences,
- c. Whether the availability factor or PLL is being applied again during the SLERF calculations since Table 5.5-1 (on page 49 of 124) also carries such a foot note.
- 4. Section 5.7.1 on page 53 of 124 discusses how the truncation was carried out for the base model but is silent on any sensitivity calculations. Clarify whether sensitivity calculations were performed to determine the impact of the truncation choice.
- 5. Section 5.7.5 on page 55 of 124 discusses the sensitivities performed related to the HEPs. One of the cases that was investigated increased the HEPs to 1.0 beyond 0.8 g. Please clarify:
- b. The rationale for selection of 0.8 g as the critical breaking point beyond which all HEPs are 1.0.
- 6. F&O 16-18 indicates that the licensees unique approach for screening out small-small Loss-of-Coolant Accidents (SSLOCAs) is based on plant walkdowns. The sensitivity study performed in Section 5.7.2 of the submittal demonstrates that the SSLOCA assumption used in the SPRA model has a significant impact on the results and insights. Please briefly describe:
- a. The methodology followed for the systematic evaluation of the sources for SSLOCAs recognizing that guidance documents, including the 2009 ASME/ANS PRA standard, state that [i]t is almost never feasible in a seismic-PRA walkdown to evaluate every small impulse line connected to the primary circuit and breaks in one or a very few such lines cannot always be precluded, given the large number of such lines and their unusual configurations in many cases,
- b. The justification for the evaluation that all the relevant lines have very high capacity such that the initiator can be completely screened out,
- c. The justification for using the small break LOCA (SLOCA) logic, including accident progression, sequence timing, success criteria, and the lack of makeup in the logic model, as a surrogate for small-small LOCAs in the sensitivity study performed in Section 5.7.2 of the submittal,
- d. The justification based on accident progression, sequence timing, success criteria, and relevant seismic bins, for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> available time to restart AFW in case of a SSLOCA, described in Section 5.7.2 of the submittal.
- 7. The resolution of the F&O 16-5 states that the LOCA basis has been reevaluated and updated.
It appears that the surrogate component(s) used to represent the fragility for LOCAs has been changed, subsequent to the peer-review, to that for the Reactor Coolant Pump (RCP) supports.
Representative fragilities for SBLOCAs and MBLOCAs in past SPRAs are much lower than those for the RCP supports. The sensitivity study presented in Section 5.7.2, which uses the SBLOCA sequence and a representative fragility similar to that in available guidance documents, demonstrates the impact of the chosen representative fragility for SBLOCAs on the results and insights. Please briefly describe the technical justification, including the impact of the assumption on SCDF and risk insights, for the currently used surrogate components and fragilities for modeling SBLOCAs and MBLOCAs.
- 8. The resolution of F&O 16-11 states that the dependency analysis has been performed using the EPRI HRA Calculator. The suggested finding resolution states that the licensee plans to transition to a different dependency analysis method based on HRA calculator. Please clarify: