ML23334A091

NRR E-mail Capture - Diablo Canyon 1 and 2 - Audit Questions for License Amendment Associated with TSTF-505, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b

ML23334A091
Person / Time
Site:	Diablo Canyon
Issue date:	11/30/2023
From:	Siva Lingam NRC/NRR/DORL/LPL4
To:	Richardson M, Schrader K Pacific Gas & Electric Co
References
L-2023-LLA-0100
Download: ML23334A091 (17)

Text

From:

Siva Lingam Sent:

Thursday, November 30, 2023 10:54 AM To:

Richardson, Michael; Schrader, Kenneth Cc:

Jennifer Dixon-Herrity; Jennie Rankin; Samson Lee; Malcolm Patterson

Subject:

Diablo Canyon 1 and 2 - Audit Questions for License Amendment Associated with TSTF-505, Provide Risk-Informed Extended Completion Times-RITSTF Initiative 4b (EPID L-2023-LLA-0100)

Attachments:

Diablo Canyon TSTF-505 Audit Questions.docx Attached please find the official audit questions for the subject license amendment.

Siva P. Lingam U.S. Nuclear Regulatory Commission Project Manager Palo Verde Nuclear Generating Station, Units 1, 2, and 3 Grand Gulf Nuclear Station Entergy Fleet Location: O-9E22; Mail Stop: O-9E03 Telephone: 301-415-1564 E-mail address: Siva.Lingam@nrc.gov

Hearing Identifier:

NRR_DRMA Email Number:

2320 Mail Envelope Properties (SJ0PR09MB6109BB008A8012CE370A4527F682A)

Subject:

Diablo Canyon 1 and 2 - Audit Questions for License Amendment Associated with TSTF-505, Provide Risk-Informed Extended Completion Times-RITSTF Initiative 4b (EPID L-2023-LLA-0100)

Sent Date:

11/30/2023 10:53:53 AM Received Date:

11/30/2023 10:53:00 AM From:

Siva Lingam Created By:

Siva.Lingam@nrc.gov Recipients:

"Jennifer Dixon-Herrity" <Jennifer.Dixon-Herrity@nrc.gov>

Tracking Status: None "Jennie Rankin" <Jennivine.Rankin@nrc.gov>

Tracking Status: None "Samson Lee" <Samson.Lee@nrc.gov>

Tracking Status: None "Malcolm Patterson" <Malcolm.Patterson@nrc.gov>

Tracking Status: None "Richardson, Michael" <MJRm@pge.com>

Tracking Status: None "Schrader, Kenneth" <KJSe@pge.com>

Tracking Status: None Post Office:

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Regulatory Audit Questions in Support of License Amendment Request to Revise Technical Specifications to Adopt Risk-Informed Completion Times Pacific Gas and Electric Company Diablo Canyon Nuclear Power Plant, Units 1 and 2 Docket Nos. 50275 and 50323 By letter dated July 13, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23194A228), Pacific Gas and Electric Company (the licensee) submitted a license amendment request (LAR) for Diablo Canyon Nuclear Power Plant, Units 1 and 2, to adopt Technical Specifications Task Force (TSTF) Traveler 505 (TSTF505),

Revision 2, Provide Risk-informed Extended Completion TimesRITSTF [Risk-Informed TSTF]

Initiative 4b (ML18183A493), to permit the use of risk-informed technical specification completion times for certain actions required when limiting conditions for operation are not met.

The U.S. Nuclear Regulatory Commission staff is conducting a virtual regulatory audit to support its review of the LAR. A regulatory audit is a planned activity that includes the examination and evaluation of information that is not docketed. The audit is conducted to increase the NRC staffs understanding of the LAR and identify information that may require docketing to support the NRC staffs regulatory findings. The NRC staff issued the audit plan on September 21, 2023 (ML23264A001).

The NRC staff plans to hold virtual audit meetings on December 11 to 13, 2023. The audit plan states: At the [audit] meetings, the licensee is to discuss information needs and questions arising from the NRCs review of the application and other material reviewed during the audit.

The NRC staff has formulated initial audit discussion questions below, identified by members of the Office of Nuclear Reactor Regulation; Division of Engineering and External Hazards (DEX),

Division of Risk Assessment (DRA), and Division of Safety Systems (DSS). If time allows, prepare responses to these questions in advance. It would facilitate the audit discussions, especially if responses can be posted in the online portal as they become available.

DRA, PRA Licensing Branch A (APLA)

Audit Question APLA01 (Success criteria)

The NRC staffs final safety evaluation (ML071200238) to Nuclear Energy Institute (NEI) 0609 (ML122860402) specifies that the LAR should identify the technical specification limiting conditions for operation (LCOs) and action statements for which risk-informed completion times (RICTs) are proposed. The LAR should compare the functions of structures, systems, and components (SSCs) subject to those technical specifications with functions of those SSCs

modeled in the probabilistic risk assessment (PRA). For functions that are modeled, the LAR should justify that the scope of the PRA model is consistent with the licensing basis assumptions. The LAR should address any differences and explain how they will be handled, for example, by programmatic restrictions.

The safety evaluation for NEI 06-09 also states that when the licensee determines that risk sources may be excluded from PRA models because they are not significant to the calculation of risk, the LAR should discuss conservative or bounding analysis to be applied to the calculation of RICT when those sources are not addressed in the PRA models.

Table E11 in Enclosure 1 of the LAR identifies each LCO proposed for inclusion in the RICT program. For each LCO, the table identifies whether the associated SSCs are modeled in the PRA. For certain LCOs, the table explains that the associated SSCs are not modeled in the PRAs but will be conservatively represented using a surrogate event. The description in the LAR did not allow the NRC staff to conclude that the modeling of surrogate events bounds the risk or conservatively represents the identified SSCs.

a. For TS 3.4.11, Pressurizer Power Operated Relief Valves (PORVs), the LAR states that the PRA success criteria are in some cases more restrictive when the PORVs are credited to mitigate some beyond-design-basis scenarios. Clarify and justify the PRA success criteria used, including the scenarios where success criteria differ from the design basis.

b. For TS 3.5.2, ECCS [emergency core cooling system] - Operating, the LAR states that the PRA does not credit mitigation for main steamline break events. It also states that the PRA success criteria are based on plant-specific analyses. Justify the proposed modeling does not have an impact on RICT estimates.

c. For TS 3.6.6, Containment Spray [CS] and Cooling Systems, Note 4 to LAR Table E11 states that neither the CS system nor the containment fan cooling units (CFCUs) are credited in the fire PRA. The NRC staff observes that choosing not to model a system in the PRA may produce a nonconservative calculation of RICT. Justify the proposed modeling does not have an impact on the RICT estimates.

d. For TS 3.8.1, AC [Alternating Current] Sources - Operating, Note 8 to LAR Table E11 states that the 500 kV offsite circuits are only credited for the mitigation of internal events.

Discuss the role of the 500kV system and justify why crediting the system only in the mitigation of internal events results in an acceptable RICT estimate.

Audit Question APLA02 (Process for reviewing key assumptions and sources of uncertainty)

Regulatory Guide (RG) 1.174, Revision 3, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (ADAMS Accession No. ML17317A256), describes an approach that is acceptable to the NRC staff for developing risk-informed applications for a licensing basis change that considers engineering issues and applies risk insights. It provides general guidance concerning analysis of the risk associated with the proposed changes in plant design and operation. Section C.4.

Documentation to Support a Regulatory Submittal, of RG 1.200, Revision 2, An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed

Activities (ADAMS Accession No. ML090410014), provides guidance regarding documentation of the acceptability of the PRA to support a regulatory submittal.

Further, Section 2.5 of RG 1.174 states that the impact of PRA uncertainties should be considered, including uncertainties that are explicitly accounted for in the results and those that are not, and cites NUREG1855, Revision 1, Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed DecisionMaking (ADAMS Accession No. ML17062A466), provides acceptable guidance for the treatment of uncertainties in risk-informed decision-making.

NUREG1855 describes how the impact of PRA uncertainties should be assessed and documented. It states, "Additional qualitative screening criteria may be identified as applicable for specific applications. The bases for any criteria used to qualitatively eliminate missing scope and level-of-detail items from a PRA must be documented," as well as, "At a minimum, assumptions made in lieu of data, operational experience or design detail should be well documented with the basis for the assumptions clearly explained." of LAR describes the process used for reviewing the PRA assumptions and sources of uncertainty. The LAR explained that the list of assumptions and sources of uncertainty were reviewed to identify those that would be significant for the evaluation of configuration-specific changes in risk in the RICT Program.

The NRC staff reviewed the Diablo Canyon documents provided on the audit portal and was unable to identify a document demonstrating this review of PRA assumptions and sources of uncertainty for impact on the RICT Program.

Confirm that the review of plant-specific PRA assumptions and sources of uncertainties was documented for use in the RICT program.

Audit Question APLA03 (Key assumptions and sources of uncertainty)

The NRC staffs safety evaluation to NEI 0609 specifies that the LAR should provide a discussion of how the key assumptions and sources of uncertainty were identified. Table E91 in of the LAR discusses and presents the disposition for each identified key assumption or source of uncertainty.

a. Dual unit trips are not considered in the single-unit model (except for seismic events). The LAR further identifies that this approach is nonconservative because the plant equipment credited may be required by the second unit and be unavailable for crosstie. The LAR disposition to this uncertainty item states that shared systems and equipment between the units will be identified in procedures for RICT Program implementation so that consideration of additional risk management actions will be made.

Identify the shared systems and equipment.

i.

Explain how the RICT program procedures will capture the unavailability of shared SSCs.

ii.

Describe the process that will be used for identifying and selecting additional risk management actions.

b. Charging and safety injection (SI) pumps are credited for inventory makeup for a medium loss of coolant accident, and it is assumed that two of the four high-pressure injection pumps are required for success. The LAR states that this was conservatively modeled as 1 out of 2 charging pumps and 2 out of 2 SI pumps. The LAR further states that this is modeled conservatively, and the model is further adjusted by an assumed recovery factor to offset this conservatism when all support for the function is available.

However, the LAR states that this assumption is not conservative whenever a charging pump is unavailable and the safety injection system fails.... Accordingly, the emergency core cooling system charging pump recovery factor will not be credited in the RICT Program whenever an emergency core cooling system charging pump is made unavailable.

Explain how the proposed model adjustment will be handled in the configuration risk management program (CRMP) tool when pumps become inoperable and justify this treatment for the RICT estimates.

c. A 6-hour mission time was assumed for the emergency diesel generators (EDGs) and the fuel oil transfer pumps. The LAR states that this assumption does not have a significant impact on the baseline PRA model. It further states, Whenever the 230 kV offsite power system is unavailable and cannot reasonably be recovered within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, the 6-hour mission time is nonconservative.

The LAR therefore proposed the 24-hour mission time will be applied to the EDGs and fuel oil transfer pumps in the RICT Program whenever the offsite power 230 kV system is made unavailable.

Explain how the proposed adjustment will be addressed in the RICT program.

d. Vacuum breakers cannot fail in a manner to impact the Auxiliary Salt Water (ASW) function within the 24-hour mission time. The LAR explains that There are two vacuum relief valves per ASW header. The LAR further states that the RICT Program will assume inoperability of the ASW train if one or more vacuum breakers are nonfunctional.

Explain how this proposed adjustment will be handled in the CRMP tool.

e. The LAR states that certain systems and components are always assumed failed in the fire PRA and the seismic PRA models (and that they are assumed always successful in the baseline PRA model). The LAR concludes that the resulting RICT is conservatively bounded.

Describe how this is modeled and identify the systems treated in this way.

i.

Describe the systems affected.

ii.

Describe what is meant by stating that these systems are assumed always successful in the baseline PRA model. Clarify how this treatment applies to the fire and seismic PRAs.

iii.

Provide further justification to demonstrate that the RICT estimates are conservative.

f. The LAR describes a model simplification for the auxiliary feedwater (AFW) system that applies to sequences involving depressurization of multiple steam generators.

The LAR states that Pump runout protection is only modeled for Auxiliary Feedwater Pump 1-2 and is always successful for pump 1-3.

Further justify (1) the effect of this simplification on other sequences (e.g., those involving AFW pumps or main steam isolation valves), (2) the expression of risk (expressed here as a fraction of core damage frequency (CDF), and (3) impact on the RICT estimate.

Audit Question APLA04 (Procedures)

The NRC staffs safety evaluation to NEI 0609 specifies that the LAR should include discussion of the licensees programs and procedures which assure the PRA models that support the risk managed technical specifications (RMTS) are maintained consistent with the asbuilt, asoperated plant.

a. The LAR states, Plant changes that meet the criteria defined in the PRA Configuration Control Program (including consideration of the cumulative impact of other pending changes) will be incorporated into the applicable PRA model(s) as an interim update, consistent with the NEI 06-09-A guidance.

i.

Identify the criteria that will be used to assess impact on the RICT Program.

ii.

Confirm that an appropriate reference will be included in the configuration control program procedure to cite RMTS guidance.

b. The industry guidance NEI 06-09 also states that the purpose of this tracking is to demonstrate the risk accumulated as a result of SSC inoperability beyond the front-stop completion time is appropriately managed.

An example of tracking is presented in the industry guidance. The accumulated risk is monitored on entering such plant configurations, that is, when the front-stop completion time is exceeded. An alternative presented is to maintain a 52-week rolling average CDF, updated weekly. In contrast, Enclosure 11 to the LAR states that the calculation of cumulative impact will be required every refueling cycle.

Justify the calculation of cumulative impact only once per refueling cycle and explain how this will be adequate to manage risk in accordance with the risk-informed principles in RG 1.174.

Audit Question APLA05 (Risk management actions) 2 to the LAR presents examples of risk management actions and explains the basis for calculating a risk management action time (RMAT). Clarify the limits proposed for incremental core damage probability, large early release probability, instantaneous CDF, and instantaneous large early release frequency.

Audit Question APLA06 (CRMP model)

Regulatory Position 2.3.3 of RG 1.174, Revision 3, states that the level of detail in the PRA should be sufficient to model the impact of the proposed licensing basis change. The characterization of the problem should include establishing a cause-effect relationship to identify portions of the PRA affected by the issue being evaluated. Full-scale applications of the PRA should reflect this cause-effect relationship in a quantification of the impact of the proposed licensing basis change on the PRA elements.

Section 4.2 of NEI 06-09, Revision 0A, describes attributes of the CRMP. A few of these attributes are listed below:

Initiating events accurately model external conditions and effects of out-of-service equipment.

Model translation from the PRA to a separate CRMP tool is appropriate; CRMP fault trees are traceable to the PRA. Appropriate benchmarking of the CRMP tool against the PRA model shall be performed to demonstrate consistency.

Each CRMP application tool is verified to adequately reflect the asbuilt, asoperated plant, including risk contributors which vary by time of year or time in fuel cycle or otherwise demonstrated to be conservative or bounding.

Application specific risk important uncertainties contained in the CRMP model (that are identified via PRA model to CRMP took benchmarking) are identified and evaluated prior to use of the CRMP tool for RMTS applications.

CRMP application tools and software are accepted and maintained by and appropriate quality program.

The CRMP tool shall be maintained and updated in accordance with approved station procedures to ensure it accurately reflects the asbuilt, asoperated plant. of the LAR describes the attributes of the CRMP model for use in RICT calculations. The LAR also describes several changes made to the baseline PRA models to support calculation of configuration-specific risk and mentions approaches for ensuring the fidelity of the CRMP tool. Table E81 provides a list of CRMP model changes for configuration-specific risk. Clarify the following:

a. (Table E81 first item) Clarify how the plant availability factor is addressed in the CRMP tool. The LAR states that the initiating events frequencies are adjusted to per critical year

for the CRMP tool, as opposed to per calendar year, however this appears to contradict the remainder of the text.

b. (Table E81 fourth item) The LAR states the PRA model includes conservative success criteria for room cooling. Summarize the criteria and explain how they are conservative.

c. (Table E81 seventh item) The LAR states that the baseline PRA model includes credit for a backup portable fuel oil pump. It further states this is not credited for the CRMP model when a diesel fuel oil transfer system pump is out of service.

Further explain how the credit for backup portable fuel oil pump is removed from the CRMP model.

Audit Question APLA07 (Open Phase Condition)

Section C.1.4 of RG 1.200 states the base PRA is to represent the asbuilt, asoperated plant to the extent needed to support the application. The licensee is to have a process that identifies updated plant information that necessitate changes to the base PRA model.

In response to the January 30, 2012, event at the Byron Generating Station initiated by an open-phase condition (OPC), the NRC issued Bulletin 2012-01.1 As part of the initial voluntary industry initiative for mitigation of the potential for the occurrence of an OPC in electrical switchyards,2 licensees have modified their designs to add an open-phase isolation system (OPIS). Per the Staff Requirements Memorandum for SRM-SECY-16-0068,3 the NRC staff was directed to ensure that licensees have appropriately implemented OPIS and that licensing bases have been updated accordingly. From the revised voluntary initiative 4 and resulting industry guidance in NEI 19-02, Guidance for Assessing Open Phase Condition Implementation Using Risk Insights (ADAMS Accession No. ML19122A321), on estimating OPC and OPIS risk, 5 it is understood that the risk impact of an OPC is highly dependent on electrical switchyard configuration and design.

a) For Diablo Canyon, discuss the evaluation of the risk impact associated with OPC events including the likelihood of OPC initiating plant trips and the impact of those trips on PRA-modeled SSCs. Report whether an OPIS has been installed. If such a system has been installed, discuss its function and operation. Include any operator actions needed to activate the system or to respond if it annunciates or actuates automatically.

b) Clarify whether any installed OPIS equipment and associated operator actions are credited in the PRA models that support this application. If OPIS equipment and associated operator actions are credited, then provide the following information:

i.

Describe the OPIS equipment and associated actions that are credited in the PRA models.

ii.

Describe the impact, if any, that this treatment has on key assumptions and sources of uncertainty for the RICT program.

iii.

Discuss human reliability analysis (HRA) methods and assumptions used for crediting OPIS alarm manual response.

iv.

Discuss how OPC-related scenarios are modeled for non-internal event scenarios such as internal floods, fire, and seismic.

v.

Regarding inadvertent OPIS actuation:

Explain whether scenarios regarding inadvertent actuation of the OPIS, if applicable, are included in the PRA models that support the RICT calculations.

If inadvertent OPIS actuation scenarios are not included in the PRA models, then provide justification that the exclusion of this inadvertent actuation does not impact the RICT calculations.

c) If OPC and OPIS are not included in the application PRA models (whether OPIS equipment is installed or not), then provide justification that the exclusion of this failure mode and mitigating system does not impact the RICT calculations.

d) As an alternative to Part (c), propose a mechanism to ensure that OPC-related scenarios are incorporated into the application PRA models prior to implementing the RICT program.

1 U.S. NRC Bulletin 2012-01, Design Vulnerability in Electric Power System (ML12074A115).

2 Anthony R. Pietrangelo to Mark A. Satorius, Ltr re: Industry Initiative on Open Phase Condition -

Functioning of Important-to-Safety Structures, Systems and Components (SSCs), dated October 9, 2013 (ML13333A147).

3 U.S. NRC SRM-SECY-16-0068, Interim Enforcement Policy for Open Phase Conditions in Electric Power Systems for Operating Reactors, dated March 9, 2017 (ML17068A297).

4 Doug True to Ho Nieh, Ltr re: Industry Initiative on Open Phase Condition, Revision 3, dated June 6, 2019 (ML19163A176).

5 Nuclear Energy Institute (NEI) 19-02, Guidance for Assessing Open Phase Condition Implementation Using Risk Insights, Revision 0, April 2019 (ML19122A321).

DRA, PRA Licensing Branch C (APLC)

Audit Question APLC-01 Section 4.0, Item 5 of the final safety evaluation for NEI 0609 states that the LAR will provide a justification for excluding any risk sources determined to be insignificant to the calculation of configuration-specific risk and will provide a discussion of any conservative or bounding analyses to be applied to the calculation of RICTs for sources of risk not addressed by the PRA models. of the LAR discusses the generic methodology used to identify and disposition such risk sources and provides the plant-specific results of the application of the generic methodology for impacts to the RICT program. One of the screening criteria (screening criterion B) used to disposition the risk sources is if the CDF, calculated using a bounding or demonstrably conservative analysis, has a mean frequency of less than 1E6 per year.

Table E4-1 of enclosure 4 of the LAR provides the external hazards evaluated, identifies the applicable screening criteria, summarizes the evaluation, and provides a disposition for the RICT program. This table includes the aircraft impact, extreme wind or tornado, hurricane, and tsunami external hazards, and it screens each of these external hazards using screening criterion B as follows:

For the aircraft impact external hazard, the table states that the CDF from an aircraft crash is estimated to be 7.43E7 per year.

For the extreme wind or tornado external hazard, the table states that a conservative strike frequency of a tornado is 7.0E5 per year, the conditional core damage probability (CCDP) for a loss of offsite power (LOOP) due to severe weather with no recovery is 5.16E4 per year, which results in a conservatively estimated CDF from a tornado event of 3.92E8 per year. The table also states that a conservatively estimated CDF from tornado missile events is 2.05E7 per year.

For the hurricane external hazard, the table states that a conservatively estimated CDF from hurricanes is 5.0E7 per year based on an assumption that a hurricane with wind speeds of 150 mph leads directly to core damage.

For the tsunami external hazard, the table states that the CDF from flooding of the intake structure due to a tsunami is estimated to be 2.2E8 per year.

Table E41 neither provides the basis for these values nor does it describe the assumptions and methodology used to calculate them. The details of these calculations are discussed in Calculation X.1, Revision 1, DCPP Other External Events, which was not provided on the docket as part of the LAR.

The NRC staff reviewed Calculation X.1 during the audit and identified the following issues:

Section X.1.8.1 describes the analysis of tornado-generated missiles using the TORMIS methodology. The calculation identifies the plant targets with a high tornado missile damage probability, which includes targets 100, 126, 99, 109, 31, 6, and 55. The calculation states that it provides a discussion of the risk impact of tornado-generated missiles for each target. The calculation provides a discussion of targets 100, 126, 99, and 31. The NRC staff identified that the calculation does not provide a discussion of targets 109, 6, and 55.

The TORMIS methodology determines the probability of components being struck and disabled by a tornado-generated missile, and it was accepted for use by the NRC in a safety evaluation report (ML080870291). This safety evaluation report contains several items to consider when using the TORMIS methodology. The TORMIS methodology is also discussed in Regulatory Issue Summaries (RISs) RIS 200814, Use of TORMIS Computer Code for Assessment of Tornado Missile Protection (ADAMS Accession No. ML080230578) and RIS 201506, Tornado Missile Protection (ADAMS Accession No. ML15020A419).

Table X.1.8.11 summarizes the results of the analysis of tornado-generated missiles.

This table contains a column labeled Hit and another column labeled Damage (Base).

For many of the plant targets, the values in both columns are the same. However, there are some plant targets with different values in these columns. It is unclear to the NRC staff what information these columns are intended to represent.

Section X.1.9 describes the analysis of hurricanes. The calculation uses data from four recorded tropical storms in the 20th century and a hurricane in the 19th century to fit an extreme value distribution to estimate the probability of hurricane winds exceeding 150 mph. The calculation provides a reliability function (also known as a survival function) of the form (0) = 1 ((0 ))

in one location and (0) = 1 (1) ((0 ))

in another location. The calculation provides the following formulas to estimate the parameters from the extreme value distribution.

= 1.65

= 0.577

In these formulas, and represent estimates of the mean and standard deviation of the extreme value distribution, respectively. Although not stated, it appears that the calculation estimates and using the method of moments estimation technique.

The NRC staff identified two concerns with this calculation. First, the NRC staff identified that the reliability function provided is not correct. The correct reliability function for the extreme value distribution is:

(0) = 1 (((0 )))

Second, it appears that calculation used the formula for the sample standard deviation to obtain the estimates of = 0.117 and = 51.9. The NRC staff identified that the method of moments technique uses the formula for the population standard deviation, which results in different estimates for and.

Address the following:

Summarize the evaluation of the aircraft impact, extreme wind or tornado, hurricane, and tsunami external hazards. For this item, describe the data sources used to determine the frequency of the external events, summarize the assumptions and methodology used to calculate the CDFs, and summarize the results.

For the evaluation of extreme wind or tornado external hazard:

i.

Discuss if the TORMIS methodology is included in the plants licensing basis. If the TORMIS methodology is included in the plants licensing basis, identify and justify any deviations from the methodology in the licensing basis and that used for this application. If TORMIS is not included in the plants licensing basis, justify that the TORMIS methodology was used consistent with the items of consideration in the safety evaluation report that approved its use, RIS 200814, and RIS 201506.

ii.

Describe the risk impact of tornado-generated missiles for targets 109, 6, and 55.

Describe the information the columns labeled Hit and Damage (Base) in table X.1.8.11 are intended to represent and the difference between them.

For the evaluation of hurricane external hazard:

iii.

Describe the estimation technique used to obtain the parameter estimates for the extreme value distribution or provide a reference for the basis and formulas used to obtain the parameter estimates.

iv.

Confirm the reliability function for the extreme value distribution.

v.

If any errors are identified in the parameter estimates or reliability function, provide an updated evaluation of the risk from hurricanes.

Audit Question APLC-02 Section 4.0, item 3 of the final safety evaluation for NEI 0609 states that the LAR will provide a discussion of the results of peer reviews and self-assessments conducted for the plant-specific PRA models that support the RMTS, including the resolution or disposition of any deficiencies identified in peer reviews (i.e., facts and observations (F&Os)). This item states that the discussion will include a comparison of the requirements of RG 1.200 using the elements of ASME RASb-2005, Addenda to ASME RA-S-2002: Standard for Probabilistic Risk Assessment for Nuclear Power Plant Applications, for capability Category II for internal events PRA models and for other models for which standards exist that have been endorsed in RG 1.200. This item further states that, if additional standards have been1 endorsed by revision to RG 1.200, the LAR will also provide similar information for those PRA models used to support the RMTS program. of the LAR addresses this requirement by providing information on the technical acceptability of the internal events, internal flood, fire, and seismic PRA models that support the RICT program. The LAR states that this information is consistent with the requirements of section 4.0, item 3 of the final safety evaluation for NEI 0609 and addresses each PRA model for which a PRA standard endorsed by RG 1.200, Revision 2 exists.

The LAR states that the PRA models were peer reviewed and assessed using ASME/ANS RA-Sa-2009, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications, and RG 1.200, Revision 2. For the seismic PRA, however, the LAR states that a full-scope seismic PRA peer review, which also included a review of the seismic hazard and fragility analyses, was conducted in June 2017, and it was performed consistent with RG 1.200, Revision 2, using ASME/ANS RA-Sb-2013, Probabilistic Risk Assessment for Advanced Non-Light Water Reactor Nuclear Power Plants. The LAR states that an independent assessment of the finding-level F&Os was conducted from October-December 2017 and the scope of the assessment included all finding-level F&Os resulting from the peer review. The LAR also states that a focused-scope peer review was conducted in conjunction with the closure review and that all F&Os categorized as findings have been resolved by either a PRA model revision or a documentation update.

The NRC staff notes that RG 1.200, Revision 2, endorses ASME/ANS RA-Sa-2009, but it does not endorse ASME/ANS RA-Sb-2013. Similarly, the NRC staff notes that RG 1.200, Revision 3, does not endorse ASME/ANS RA-Sb-2013. As discussed in RG 1.200, Revision 2, a risk-informed submittal should contain discussions concerning peer review. If the peer review is not performed against the endorsed standards, RG 1.200, Revision 2 states that information needs to be included in the submittal that demonstrates that the different criteria used are consistent with the endorsed standards.

Address the following:

a. Provide a comparison of the criteria in ASME/ANS RASb-2013, which has not been endorsed by the NRC for licensing applications, with the criteria in the endorsed ASME/ANS RASa-2009, including an explanation that demonstrates that the analogous ASME/ANS RASa-2009 supporting requirements have been met for instances where the criteria between the two standards differ.

b. Discuss if any changes were made to the seismic PRA since the peer review was completed. For each such change, identify the change and discuss, with justification, if the change is PRA maintenance or a PRA upgrade per the definition in RG 1.200, Revision 2.

Audit Question APLC-03 APLC staff requests a discussion on quantification of the seismic PRA model for RICT calculations, including any simplifications that were considered or implemented.

DSS, Technical Specifications Branch (STSB)

Audit Question STSB-01 The LAR Table E11, In-Scope TS/LCO Conditions to the Corresponding PRA Functions, lists the technical specification number, but not the specific condition. More than one condition may be associated with a given number. Typically, these conditions are distinguished from one another by a letter, and different RICTs are calculated for each condition.

The NRC staff considers that each row of Table E11 should identify a condition with a proposed risk-informed completion time (RICT). Information provided at the LCO level as currently shown is not sufficient for NRC staff review. Revise Table E11 to provide TS LCO conditions and RICT applicable to each row. Note: The design success criteria (DSC) are the minimum set of remaining credited equipment that can achieve the TS safety function while in the specified TS Condition. For example, a condition with two of two offsite circuits inoperable should not have a DSC of one offsite circuit.

Audit Question STSB-02 to the LAR references the Risk-Informed Completion Time Program by stating In accordance with the RICT Program instead of spelling the program name out. This is inconsistent with the Diablo Canyon TS and TSTF-505, Revision 2 where each program reference spells the name out fully except when the acronym for the program is defined on the same page where the acronym is used. Provide justification for this variation.

Audit Question STSB-03 In Attachment 1 to the LAR, the licensee proposes a variation for technical specification (TS)

Condition 3.4.11.F, which provides restoration requirements for PORV Block Valves (i.e., more than one inoperable). The licensees Required Action (RA) F.2 appears to be similar to Standard Technical Specification (STS) RA F.1, which is a loss of function condition. TSTF505 does not

provide a RICT for STS RA F.1. The licensee did not provide a technical justification for applying a RICT to this condition and referred to it as an editorial change. Describe how the proposed TS changes preclude the application of the RICT program for loss of function conditions or modify the proposed TS changes to do so.

Audit Question STSB-04 What is the reason for Condition D in LCO 3.6.6? Typically, a licensee must enter all applicable conditions at the same time. Condition A is for one inoperable Containment Spray System.

Condition C is for one inoperable Containment Fan Cooler Unit (CFCU) system. To help staff, ensure that the RICT program can be appropriately applied, discuss the reasons for a separate Condition D for one inoperable CS and one inoperable CFCU.

DEX, Electrical Engineering Branch (EEEB)

Audit Question EEEB-01 In reference to Table E12: Unit 1/Unit 2 In-Scope TS/LCO Conditions RICT Estimate, clarify the term subsystem for the following considering that Updated Final Safety Analysis Report, Chapter 8 refers to load groups, groups, channels, and trains.

a. TS 3.8.9.AOne AC electrical power distribution subsystem inoperable

b. TS 3.8.9.BOne AC vital bus electrical power distribution subsystem inoperable

c. TS 3.8.4.CDC electrical power subsystem inoperable.

Audit Question EEEB-02 The following statement is from Diablo Canyon FSAR section 8.3.1.1.2.3.2, General Design Criterion 4, 1967Sharing of Systems:

The 12-kV system is designed with crosstie capability to align a single 230 kV / 12 kV standby startup transformer (11 or 21) to provide power to both units via the crosstie breaker. Operation in this configuration is restricted by Technical Specification. The shared portion of the 12-kV system [emphasis added] is designed with sufficient capacity and capability to operate the ESFs for a design basis accident (or unit trip) on one unit, and those systems required for a concurrent safe shutdown of the second unit consistent with the requirements of IEEE 308-1971, Section 8.

a. Explain which TS section restricts the 12 kV crosstie capability to align a single 230 kV /

12 kV standby startup transformer (11 or 21).

b. Under what conditions is this sharing permitted by TSs?

Audit Question EEEB-03 Provide clarification for design success criteria (DSC) in Table E11 corresponding to the following TS conditions like DSC for TS LCO 3.8.1 (2):

a. TS LCO 3.8.1, Condition A - One required offsite circuit inoperable (e.g., 2 of 3 engineered safety feature (ESF) buses)

b. TS LCO 3.8.1, Condition B (One diesel generator (DG) inoperable)

c. TS LCO 3.8.1, Condition C (Two required offsite circuits inoperable)

d. TS LCO 3.8.1, Condition D (One required offsite circuit inoperable AND One DG inoperable)

e. TS LCO 3.8.4, Condition A (One battery charger inoperable)

f. TS LCO 3.8.4, Condition B (One battery inoperable)

g. TS LCO 3.8.4, Condition C (One DC electrical power subsystem inoperable for reasons other than Condition A or B)

h. TS LCO 3.8.9, Condition A (One AC electrical power distribution subsystem inoperable)

i.

TS LCO 3.8.9, Condition B (One 120 VAC vital bus subsystem inoperable)

j.

TS LCO 3.8.9, Condition C (One DC electrical power distribution subsystem inoperable)

Audit Question EEEB-04 In reference to Table E12, provide the reasons why the One AC electrical power distribution subsystems inoperable (TS LCO 3.8.9.A) has a significantly lower RICT estimate (4.8 days) compared to the RICT estimate (20.6 days) for One DC electrical power distribution subsystem inoperable (TS LCO 3.8.9.C).