ML14206A008
| ML14206A008 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/31/2014 |
| From: | Peter Bamford Plant Licensing Branch IV |
| To: | Halpin E Pacific Gas & Electric Co |
| Bamford P | |
| References | |
| TAC MF2333, TAC MF2334 | |
| Download: ML14206A008 (32) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 July 31, 2014 Mr. Edward D. Halpin Senior Vice President and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424
SUBJECT:
DIABLO CANYON POWER PLANT, UNITS 1 AND 2- REQUEST FOR ADDITIONAL INFORMATION RE: LICENSE AMENDMENT REQUEST TO ADOPT NATIONAL FIRE PROTECTION ASSOCIATION STANDARD 805 (TAC NOS. MF2333 AND MF2334)
Dear Mr. Halpin:
By letter dated June 26, 2013, as supplemented October 3, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML13196A139 and ML13277A457, respectively), Pacific Gas and Electric Company (PG&E, the licensee), submitted a license amendment request (LAR) for Diablo Canyon Power Plant, Units 1 and 2 (DCPP). The proposed amendment would enable PG&E to adopt a new fire protection licensing basis for DCPP, which complies with the requirements in paragraphs 50.48(a) and (c) of Title 10 of the Code of Federal Regulations (10 CFR). Specifically, DCPP would transition the fire protection program to one based on the National Fire Protection Association Standard 805 (NFPA 805)
Performance-Based Standard for Fire Protection For Light Water Reactor Generating Plants (2001 Edition) (ADAMS Accession No. ML010800360).
The Nuclear Regulatory Commission staff has been reviewing the submittal and has determined that additional information is needed to complete its review. The specific questions are found in the enclosed request for additional information (RAI). The questions were discussed, in draft form, in a teleconference with your staff on July 8, 2014, as well as during an audit performed at the DCPP site during the week of July 14-18, 2014. It was agreed that a response to this RAI would be submitted as follows:
Response Times (from RAI Number date of this letter)
Safe Shutdown Analysis (SSA) RAI 1, 2, 3, 4, and 5 Fire Protection Engineering (FPE) RAI 4 and 6 60 Days Fire Modeling (FM) RAI 5 Probabilistic Risk Assessment (PRA) RA16, 9, 10, 12, 16, 17, 18, 19, and 20 SSA RAI 6 and 7 FPE RAI1, 2, 3, 5, 7, and 8 90 Days FM RAI2 and 3 PRA RAI2, 4, 7, 11, and 13 FM RAI1, 4, and 6 120 Days PRA RA11, 3, 5, 8, 14, 15, 21, and 22
E. Halpin If you have any questions, please contact me at 301-415-2833 or via e-mail at Peter.Bamford@nrc.gov.
Sincerely, Peter J. Bamford, Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323
Enclosure:
Request for Additional Information cc w/encl: Distribution via Listserv
REQUEST FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST TO ADOPT NATIONAL FIRE PROTECTION ASSOCIATION STANDARD 805 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON POWER PLANT. UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323 By letter dated June 26, 2013 (Agencywide Documents Access and Management System Accession No. ML13196A139), supplemented by letter dated October 3, 2013 (ADAMS Accession No. ML13277A457), Pacific Gas and Electric Company (PG&E, the licensee),
submitted a license amendment request (LAR) for Diablo Canyon Power Plant, Units 1 and 2.
The LAR would modify Facility Operating License Nos. DPR-80 and DPR-82, to incorporate a transition to National Fire Protection Association Standard 805, "Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants," 2001 Edition (NFPA 805). In order for the U.S. Nuclear Regulatory Commission (NRC) staff to complete its review of the LAR, a response to the following request for additional information (RAI) is requested.
Safe Shutdown Analysis (SSA} RAI 01 The LAR, Section 4.2.1.2, addresses the minimum safe and stable condition as hot standby (Mode 3). Please provide the following additional information relating to this plant condition:
a) The LAR states that Mode 3 applicability for the nuclear safety capability assessment (NSCA) is defined as being up to the point at which the motor control center (MCC) breakers for the residual heat removal (RHR) pump suction valves are unlocked and closed, at which point spurious operation of these valves can occur. Please describe the impacts on maintaining safe and stable conditions if spurious operation of these RHR valves occurs. Describe whether there are feasible recovery actions identified in the NSCA to mitigate this spurious operation.
b) The LAR describes water supplies for: decay heat removal, reactor inventory makeup, reactivity control, and fuel supplies for emergency diesel generators (EDG). However, the LAR does not address the nuclear safety performance criteria (NSPC) of primary system pressure control including decay heat removal and any system limitations. Please provide additional information regarding the methods for meeting the NSCA for removing decay heat (e.g., main steam safety valves or power-operated relief valves/atmospheric steam dumps) and maintaining reactor coolant system pressure. Include a description of system capacity limitations and/or time-critical actions for supporting systems (e.g.,
nitrogen/air supply to accumulators for valve operations).
Enclosure
c) Section 4.2.1.2 of the LAR states, in part, that For the most limiting fire scenarios, the NSCA documents the availability of long term decay heat removal provided by operation of the Residual Heat Removal (RHR) system.
- i. Please provide confirmation that the RHR system is considered necessary to maintain safe and stable conditions and describe the timing for needing RHR in service under these scenarios.
ii. On the basis of these scenarios and the NFPA 805 requirement to maintain safe and stable conditions, please describe any necessary actions to recover the RHR system. Describe whether these actions are included in the feasibility analysis.
SSA RAI 02 The disposition of variance from deterministic requirement (VFDR) 2-583-008 in LAR Attachment C states that the VFDR was dispositioned with "no further action required."
However, LAR Attachment G, Table G-1 includes a recovery action for Fire Area 5-8-3 associated with this VFDR. Please confirm if the recovery action described in Attachment G is credited in the disposition of VFDR 2-583-008, for Fire Area 5-8-3. If the associated recovery action in Attachment G is credited in the disposition of VFDR 2-583-008, confirm that the delta-risk value reported in LAR Attachment W, Table W-5, includes the risk of this recovery action. If not, provide the revision toLAR Attachment W, Table W-5 accordingly.
SSA RAI 03 Please provide the following information pertaining to the non-power operations (NPO) discussions provided in LAR Section 4.3 and LAR Attachment D:
a) Provide a description of any operator actions being credited to minimize the impact of fire-induced spurious actuations on power-operated valves (e.g., air-operated valves (AOVs) and motor-operated valves (MOVs) during NPO (e.g.,
pre-fire rack-out, actuation of pinning valves, and isolation of air supplies).
b) The description of the NPO review in LAR Attachment D states that resolutions to pinch-points include recovery actions. Identify the recovery actions relied upon in NPO. Include in the description how these actions will be factored into operator procedures.
SSA RAI 04 In LAR AttachmentS, Table S-2, "Plant Modifications Committed," Modification S-2.4 describes that incipient detection is to be installed in Fire Areas 7-A and 7-B (Cable Spreading Rooms) and Fire Areas 8-G and 8-H (Safeguards Rooms) but this does not provide sufficient information for the NRC staff to complete its review. Please provide the following additional information:
a) Describe if and how this proposed detection system is credited to initiate any operator/recovery actions for safe shutdown.
b) Describe the expected operator/plant staff response to an Alert/Alarm of the proposed detection system in all fire areas that the proposed detection system will be installed.
c) In Attachment C, fire areas 8-G and 8-H are referred as Safeguards Rooms and in Attachment S the same fire areas are referred as Solid State Protection Rooms. Clarify the inconsistency in the LAR.
SSA RAI 05 The LAR identifies recovery actions requiring the cross-tie of Unit 1 and Unit 2 systems (i.e., Auxiliary Saltwater Pumps (ASW)) to achieve the NSPC. Please provide the following additional information:
a) Describe whether these cross-connecting recovery actions require staff from both units. If so, describe how the feasibility analysis reflects the Unit 1 and Unit 2 staffing, communication, and operational interface.
b) Describe the operational impacts (by fire), if any, on the unaffected unit created by cross-tying these systems. Describe whether Technical Specification 3.0.3 is entered once the cross-tie with the opposite unit had been completed for fire safe shutdown.
c) Describe whether there are any other Unit 1 and Unit 2 safe shutdown systems that may be shared/cross-tied and, if so, also provide the information requested in items a) and b) above.
SSA RAI 06 In LAR Attachment G, there are numerous recovery actions to provide portable fans for temporary cooling of the vital 480 V switchgear rooms, the battery rooms, and the inverter/battery charger rooms for fire areas 34 (U2), 3-BB, 3-CC, 5-A-1, 5-A-3, 5-A-4, 5-B-1, 5-B-3, 5-B-4, 6-B-5, and TB-7. The NRC staff noted that portable generators are used to provide electrical power for these recovery actions. Please provide the following additional information:
a) Describe the location(s) of the portable generators when in use for these recovery actions and the location of NSCA structures, systems, and components (SSCs), if any, in the vicinity of these location(s). Describe the installation of temporary power cables, the connections to distribution panels during the recovery actions, and any disruptions to fire area boundaries. Provide justification for the configuration of the equipment manipulated by these recovery actions.
b) Describe the type of fuel and quantity associated with the generator and the availability and the location(s) of sufficient fuel sources to support maintaining safe and stable conditions for the time period required.
c) Provide justification that refueling the generators does not present a fire exposure hazard to NSCA SSCs.
d) LAR Attachment B, Table B-2, Element 3.1.2.6.3 states in the Alignment Basis that heating, ventilation, and air conditioning (HVAC) is required for the ASW pump rooms, the 4 kiloVolt (kV) switchgear rooms, and the direct current (DC) and 480 Volt (V) switchgear rooms. The staff noted that portable ventilation is also utilized in the event of fire-induced failure of the required systems. LAR Attachment G does not include recovery actions for portable ventilation in the ASW pump rooms and 4kV switchgear rooms. Clarify this discrepancy.
e) In the current Appendix R licensing basis, there are recovery actions for temporary restoration of Main Control Room (MCR) ventilation following a loss of MCR ventilation; however, in the NFPA 805 LAR, there are no recovery actions for temporary restoration of MCR ventilation. Provide a justification for the lack of these recovery actions.
SSA RAI 07 LAR Attachment C describes the fire suppression effects on NSPC on a fire area basis as required by NFPA 805, Section 2.4.2.4. Please provide the following additional information:
a) The "Fire Suppression Effects on Nuclear Safety Performance Criteria," section of the fire area states one of the following statements for several fire areas (Examples include: 3-Q-1, 3-T-1, 4-A-1, 4-A-2, 4-A (U1), 4-B-1, 4-B-2, 4-B (U1/U2) and 6-A-4) (Also include any other fire areas that did not provide
sufficient information for the NRC staff to complete its review in addition to the examples cited):
There is no suppression effect concern for this Fire Area because there is no NSCA credited electrical equipment in this Fire Area.
or, There is no suppression effect concern for this Fire Area because there are no fire suppression systems or NSCA credited equipment in the Fire Area.
The NRC staff notes that the fire areas are performance-based areas that contain VFDRs and have been assessed for risk. Explain the conclusion that there is no NSCA equipment in the fire area. In addition, explain why manual suppression effects are not addressed in these fire areas.
b) Similar to a) above, several deterministic-based areas also contain the same statements (Examples include: 3-P-1, 3-P-5, 4-A (U2), 7-C, 11-D, etc.) (Also include any other fire areas that did not provide sufficient information for the NRC staff to complete its review in addition to the examples cited): Confirm that these deterministic areas do not contain NSCA-credited equipment.
c) For certain fire areas, the LAR states "no fire suppression systems in the fire area," but the defense-in-depth (DID) section states under Echelon 2 that the area is provided with an automatic suppression system (e.g., 3-B-1, 3-B-2, 3-D-1, and 3-D-2). (Also include any other fire areas that did not provide sufficient information for the staff to complete its review in addition to the examples cited):
Clarify the discrepancies.
d) Fire areas AB-2 and TB-13 state there are "no fire suppression systems in the fire areas," but the required systems table for the fire areas indicates a wet pipe fire suppression system is required. Clarify this discrepancy.
e) The NRC staff notes that fire area 4-A (U2) is a deterministic fire area and that the LAR states, "There is no suppression effect concern for this fire area because there is no NSCA credited equipment in this fire area." Fire area 4-A (U2) is associated with licensing action #2 in LAR Attachment K, that is being transitioned and is associated with a VFDR from 10 CFR 50, Appendix R, Section III.G.2(c). Explain the conclusion that no NSCA credited equipment is in this fire area in light of the need to transition the subject licensing action.
Fire Protection Engineering (FPE) RAI 01 NFPA 805, Section 3.3.5.3, provides the requirement that electrical cable construction shall comply with a flame propagation test acceptable to the authority having jurisdiction (AHJ) (i.e.,
the NRC). NFPA 805, Section 3.3.5.3 includes an exception that is not endorsed by the NRC,
as described in paragraph 50.48(c)(2)(v) of Title 10 of the Code of Federal Regulations (10 CFR). In the compliance basis statement in LAR Attachment A, for Element 3.3.5.3, the licensee states that, "Therefore, Category 4 cables are permitted to remain as is per the exception to this section." Please provide further justification for the acceptability of the Category 4 cable and wiring to meet the requirements of NFPA 805 Section 3.3.5.3 that does not rely on the exception.
FPE RAI 02 NFPA 805 Section 3.4.1 (c) requires that the fire brigade leader and at least two brigade members have sufficient training and knowledge of nuclear safety systems to understand the effects of fire and fire suppressants on NSPC. The licensee stated it complies with this requirement with exception of a noted change to correct a procedure to properly reflect plant practice. The NRC staff noted that the fire brigade organization includes an operations responder assigned to the fire brigade to act as the knowledgeable individual on safe shutdown and also be the liaison with the control room (CR) during the event. Based on the NRC staff's review of the LAR, the LAR does not provide sufficient information for the staff to determine whether the operations responder or the brigade leader qualifications demonstrate the competence to assess the potential safety consequences of a fire and advise control room personnel. Please provide the following:
a) Clarification of compliance with NFPA 805, Section 3.4.1 (c), or the exception to that section that allows sufficient training and knowledge to be provided by an operations advisor dedicated to the fire brigade.
b) If not relying on an operations advisor, describe how the fire brigade leader and members have sufficient training and knowledge of nuclear safety systems and understand the effects of fire and fire suppression on nuclear safety performance criteria.
c) Describe how the operations responder has sufficient training and knowledge of nuclear safety systems and understands the effects of fire and fire suppression on NSPC.
d) If the operations responder is considered an "operations advisor" per the exception to NFPA 805, Section 3.4.1 (c), describe whether this position is dedicated to fire brigade support and if so; whether the position is responsible for other actions related to the event and what those other responsibilities entail.
e) Describe the interaction and means of communication between the brigade leader, operations responder, and CR. Describe whether the brigade leader and operations responder are in the fire location. Describe whether all responders wear turn-out gear. Describe how communication effected with regard to suppression effects on nuclear safety between the brigade members directly applying suppression, the brigade leader, and the operations responder.
FPE RAI 03 Numerous attributes in NFPA 805 Chapter 3 define the Power Block. LAR Attachment I provides a listing of power block structures and the associated fire areas, but does not specifically list a "Yard" fire area other than the transformer yard. Fire Areas 2, 26, and 27 A-C are included in LAR Attachment C but not in LAR Attachment I. Risk values (Core Damage Frequency (CDF) and Large Early Release Frequency (LERF)) are provided for Fire Areas 2 and 26 in LAR Attachment W. LAR Attachment E includes evaluation of radioactive release from fire areas 2, 26, and 27 A-C. Nuclear Energy Institute (NEI) 04-02, "Guidance for Implementing a Risk-Informed, Performance Based Fire Protection Program Under 10 CFR 50.48(c)," Revision 2 (ADAMS Accession No. ML081130188), Appendix K, Section K.2, includes structures for radioactive waste as being in the power block.
a) Please provide confirmation that fire areas 2, 26, 27 A, B and C, are properly described along with an appropriate basis for the determination.
b) Confirm there are no other SSCs that would be considered in the yard area outside the primary structures listed in LAR Attachment I. Include a discussion of the Raw Water Storage Reservoir.
FPE RAI 04 LAR Attachment L, Approval Request 3, requests NRC approval of a performance-based approach to compliance with NFPA 805 Section 3.3.5.2 regarding non-metallic electric raceways. The approval request describes PVC [polyvinyl chloride]-coated rigid iron conduit in the intake structure as deviating from the NFPA 805 requirement but does not provide a basis for acceptability of this configuration in the "Basis for Request." Please provide additional basis for the acceptability of the application and configuration of the PVC coated conduit in the intake structure. Additionally, describe any other locations where PVC-coated metallic conduit is used.
FPE RAI 05 LAR Attachment L, Approval Request 3, contains the following statement regarding safety margin:
The use of these materials has been defined by the limitations of the analytical methods used in the development of the Fire Probabilistic Risk Assessment (FPRA). Therefore, the inherent safety margin and conservatisms in these methods remain unchanged.
Please provide the following:
a) A description of how the use of these materials has been defined by the limitations of the analytical methods of the PRA.
b) A description of the meaning of "inherent safety margin and conservatisms in these methods."
FPE RAI 06 LAR Attachment L, Approval Request 4, requests approval of a performance-based approach to compliance with NFPA 805, Section 3.3.7.2 regarding the placement of outdoor high-pressure flammable gas storage such that the tank axis is not pointed at buildings. The approval request describes that hydrogen storage tanks are located in a separate building with the tank axis pointed at power block structures. Please describe the building containing the hydrogen storage tanks and whether it is considered outdoor storage as described in NFPA 805, Section 3.3.7.2. In addition, provide the justification for how this configuration meets the rule.
FPE RAI 07 LAR Attachment L, Approval Request 5, requests approval of a performance-based approach to compliance with NFPA 805 Section 3.3.8 regarding the installation of an automatic-closing, heat-actuated valve on the EDG day tank withdrawal connection as required by NFPA Standard 30 "Flammable and Combustible Liquids Code." Please address the following:
a) In the basis for request, the LAR describes a number of valves in the fill lines to the day tank and the fuel supply lines to the EDG and indicates manual actions can be taken by operators to close the valves and minimize fuel leakage.
Describe the location and configuration of the valves in the lines to and from the EDG day tank, including the location of the valves relative to the EDG tank and the potential fire location. For example, state whether these valves would remain accessible during a fire in the EDG day tank area.
b) In the basis for request, the LAR states that credible fires of sufficient size and intensity to damage the EDG day tanks are not anticipated, in-part, because an EDG day tank spill will be directed from the EDG room by floor drains to the turbine building sump. Provide further explanation describing the potential, or lack thereof, for a fuel fire in the EDG room to propagate to the turbine building via the floor drains to the turbine building sump.
c) In the discussion of safety margin, the LAR states, "Due to the presence of redundant and adequately separated EDG systems, the inherent safety margin and conservatisms in these methods remain unchanged." Explain what is meant by the "inherent safety margin and conservatisms in these methods" relative to the lead-in to the statement that redundancy and separation exists in the design of the EDG systems. Discuss the safety margin in the context of the associated criteria described in LAR Section 4.5.2.2.
FPE RAI 08 LAR Table 4-3 identifies radiant energy shields and electrical raceway fire barrier systems (ERFBS) as required features in several fire areas. LAR Attachment A, Element 3.11.5, states that ERFBS credited for NFPA 805, Chapter 4 complies with Element 3.11.5 through the use of existing engineering equivalency evaluations (EEEEs). The references for this element in LAR
Attachment A indicates that Pyrocrete and 3M lnteram wrap are used. There is no specific compliance basis discussion with regard to the requirements of Generic Letter 86-10, Supplement 1, "Fire Endurance Test Acceptance Criteria for Fire Barrier Systems Used to Separate Safe Shutdown Trains within the Same Fire Area," dated March 25, 1994 (ADAMS Accession No. ML031130661).
a) Please provide additional discussion regarding compliance with element 3.11.5, including the exceptions, if applicable.
b) The reference for 3M lnteram wrap, MIP C-13.0, appears to be an installation procedure. Please describe the basis for compliance (see Item a) above.
c) Please state whether other ERFBS materials, other than Pyrocrete and 3M lnteram wrap, are credited in the NFPA 805 Chapter 4 analyses. If so, describe the location and the associated compliance basis for any such materials.
Fire Modeling RAI 01 NFPA 805 Section 2.4.3.3 states that the PRA approach, methods, and data shall be acceptable to the NRC. The NRC staff noted that fire modeling comprised the following:
- The algebraic equations implemented in FDT5 [Fire Dynamics Tools] and Fire Induced Vulnerability Evaluation, Rev. 1 (FIVE) were used to characterize flame radiation (heat flux), flame height, plume temperature, ceiling jet temperature, hot gas layer (HGL) temperature, sprinkler activation and smoke detector actuation.
- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays.
- The Consolidated Model of Fire and Smoke Transport (CFAST) was used in the temperature sensitive equipment HGL study, in HGL calculations for various compartments and the control room abandonment calculation.
- Fire Dynamics Simulator (FDS) was used in the plume/HGL interaction and temperature sensitive equipment zone of influence (ZOI) studies, as well as an additional study as part of the MCR abandonment calculation and analysis in Fire Zone 8-G.
LAR Section 4.5.1.2, "Fire PRA" states that fire modeling was performed as part of the Fire PRA (FPRA) development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V," for a discussion of the acceptability of the fire models that were used.
Regarding the acceptability of the FPRA approach, methods, and data:
a) Please identify whether any fire modeling tools and methods have been used in the development of the LAR that are not discussed in LAR Attachment J (e.g.,
using FDS in the MCR abandonment calculation, Fire Zone 8-G, or using CFAST in a specific analysis for Fire Zone 14-D).
b) Please describe how non-cable intervening combustibles were identified and accounted for in the fire modeling analyses.
c) It appears that, for fire areas that have mixed amounts of thermoplastic and thermoset cables, a sliding scale was used to determine the assumed heat release rate (HRR) and flame spread rate of the cable tray in a fire propagation analysis. Please provide the technical justification for this methodology.
d) The HRR of electrical cabinets throughout the plant appears to be based on the assumption that they are either Case 3 (fire limited to a single bundle of unqualified cable) or Case 4 (closed doors and fire involving multiple bundles of unqualified cable) as described in Table E-1 of NUREG/CR-6850, "EPRI [Electric Power Research lnstitute]/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Volume 2: Detailed Methodology," September 2005 (ADAMS Accession No. ML052580118). The NRC staff notes that typically, during maintenance or measurement activities in the plant, electrical cabinet doors remain open for a certain period of time. Please describe whether there are any administrative controls in place to minimize the likelihood of fires involving such a cabinet, and describe how cabinets with temporarily open doors were treated in the fire modeling analysis.
e) Please explain how the model assumptions in terms of location and HRR of transient combustibles in a fire area or zone will not be violated during and post-transition. Provide the technical justification for the assumption that in specific scenarios, the HRR of transient fires is 69 kilowatts (kW) (e.g., fire zone 8-G).
f) Specifically regarding the use of the algebraic models:
- i. Please describe how horizontal vents and vents at or near the ceiling of the compartment were treated in the Method of McCaffrey, Quintiere, and Harkleroad (MQH) calculations; and ii. Please describe how the time to sprinkler activation and the time to heat and smoke detector actuation was calculated.
g) Please describe how high energy arcing fault (HEAF) initiated fires were addressed, including in the HGL calculation, and provide the technical justification for the approach that was used to calculate HGL development timing.
h) Specifically regarding the CFAST analysis in Fire Zone 14-D, please describe the input parameters for the fire modeling and detailed results of this assessment.
i) Specifically regarding the use of CFAST and FDS in the MCR abandonment calculations:
- i. It appears that only one set of MCR calculations were performed and the results were applied to both units. Please provide the technical justification for applying results from one unit to the other unit. In addition, describe the MCR configurations for both units and compare the similarities and differences.
ii. Please clarify whether the volumes of the main control boards (MCBs),
electrical panels, raised platforms or other obstructions were excluded from the effective volume used for calculating the MCR abandonment time. If these volumes were not included, provide a technical justification for this assumption.
iii. It appears that the growth time for transient fires was assumed to be 10 minutes. Please provide the technical justification for the use of this 10-minute growth time based on the transient combustibles expected to be present in the MCR or provide a sensitivity study to evaluate how growth times would affect the MCR abandonment time.
iv. The analysis does not appear to consider fire spread to adjacent cabinets. NUREG/CR-6850 Appendix S indicates that fires may spread to the adjacent cabinet in 10 minutes if the cabinets are separated by a single wall and will not spread if the cabinets are separated by a double wall with an air gap. Please provide a technical justification for not considering propagating panel fires to adjacent cabinets, or perform a sensitivity study to evaluate how propagating panel fires would affect the abandonment time.
- v. In the analysis, it is assumed that the external doors to the MCR open at 10 minutes is based on an estimated fire brigade arrival time. Please provide a technical justification for the assumption that the fire brigade will arrive 10 minutes after the start of a fire event based on historic drill records or demonstrate that this assumption is conservative.
j) Specifically regarding the multi-compartment analysis (MCA):
- i. Please describe the criteria that were used to screen multi-compartment scenarios based on the size of the exposing and exposed compartments.
ii. Please explain how the size of the vents in the exposing compartments used in the MQH HGL calculations was determined, and to what extent these vent sizes are representative of conditions in the plant.
FM RAI 02 ASME/ANS [American Society of Mechanical Engineers/American Nuclear Society] Standard RA-Sa-2009, "Standard for Levei1/Large Early Release Frequency Probabilistic Risk Assessments for Nuclear Power Plant Applications," Part 4, requires damage thresholds be established to support the FPRA. Thermal impact(s) must be considered in determining the potential for thermal damage of SSCs and appropriate temperature and critical heat flux criteria must be used in the analysis.
a) Please describe how the installed cabling in the power block was characterized, specifically with regard to the critical damage threshold temperatures and critical heat fluxes for thermoset and thermoplastic cables as described in NUREG/CR-6850.
b) Please describe how cable tray covers, fire-resistive wraps, and conduits affect the damage thresholds that were characterized, e.g., with regard to damage criteria, fire propagation, etc., in the fire modeling analyses. In addition, explain how holes in cable tray covers were treated in this respect.
c) Please provide the technical justification for the method used to establish the damage thresholds for temperature sensitive equipment and address any limitations of the method that were considered in the determination of damage conditions.
FM RAI 03 NFPA 805, Section 2. 7.3.2, states that each calculational model or numerical method used shall be verified and validated through comparison to test results or comparison to other acceptable models.
LAR Section 4.5.1.2 states that fire modeling was performed as part of the FPRA development (NFPA 805, Section 4.2.4.2). Reference is made toLAR Attachment J, for a discussion of the verification and validation (V&V) of the fire models that were used. Furthermore, LAR Section 4.7.3 states that "calculational models and numerical methods used in support of compliance with10 CFR 50.48(c) were verified and validated as required by Section 2.7.3.2 of NFPA 805."
Regarding the V&V of fire models:
a) LAR Attachment J states that the smoke detection actuation correlation (Method of Heskestad and Delichatsios) has been applied within the validated range reported in NUREG-1824, "Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications." However, the latter reports a validation range only for Alpert's ceiling jet temperatures correlation. Please provide technical details to demonstrate that the temperature to smoke density correlation has been applied within the validated range, or to justify the application of the correlation outside the validated range reported in the V&V basis documents.
b) For any tool or method identified in the response to FM RAI 01(a) above, please provide the V&V basis if not already explicitly provided in the LAR (for example in LAR Attachment J).
FM RAJ 04 NFPA 805, Section 2.7.3.3, states that acceptable engineering methods and numerical models shall only be used for applications to the extent these methods have been subject to V&V.
These engineering methods shall only be applied within the scope, limitations, and assumptions prescribed for that method.
LAR Section 4.7.3 states that engineering methods and numerical models used in support of compliance with 10 CFR 50.48(c) are used and were applied appropriately as required by Section 2.7.3.3 of NFPA 805.
Regarding the limitations of use:
a) The NRC staff notes that algebraic models cannot be used outside the range of conditions covered by the experiments on which the model is based.
NUREG-1805, "Fire Dynamics Tools (FDTs): Quantitative Fire Hazard Analysis Methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program," December 2004 (ADAMS Accession No. ML043290075), includes a section on assumptions and limitations that provides guidance to the user in terms of proper and improper use for each FDT. It appears that the licensee has provided a general discussion of the limitations of use for the algebraic equations that were utilized for hand calculations. It is not clear, however, how these limitations were applied for the individual fire areas or for the MCA. Please provide a description of how the limit of applicability was determined for each fire area.
b) Please identify uses, if any, of CFAST outside the limits of applicability of the model and explain how the use of CFAST was justified.
c) Please identify uses, if any, of FDS outside the limits of applicability of the model and explain how the use of FDS was justified.
FM RAJ 05 LAR Section 4.5.1.2 states that fire modeling was performed as part of the FPRA development (NFPA 805, Section 4.2.4.2). The NRC staff notes that this requires that qualified fire modeling and PRA personnel work together. Furthermore, LAR Section 4.7.3 states that post transition, for personnel performing fire modeling or FPRA development and evaluation, PG&E will develop and maintain qualification requirements for individuals assigned various tasks.
Position-specific guides will be developed to identify and document required training and mentoring to ensure individuals are appropriately qualified per the requirements of NFPA 805 Section 2.7.3.4 to perform assigned work.
Regarding qualifications of users of engineering analyses and numerical models (i.e., fire modeling techniques):
a) Please describe the requirements to qualify personnel for performing fire modeling calculations in the NFPA 805 transition.
b) Please describe the process for ensuring that fire modeling personnel have the appropriate qualifications, not only before the transition but also during and following the transition.
c) When fire modeling is performed in support of the FPRA, please describe how proper communication between the fire modeling and FPRA personnel is ensured.
FM RAI 06 LAR Section 4.7.3, states that uncertainty analyses were performed as required by Section 2.7.3.5 of NFPA 805 and the results were considered in the context of the application.
This is of particular interest in fire modeling and FPRA development.
Regarding the uncertainty analysis for fire modeling:
a) Please describe how the uncertainty associated with the fire model input parameters (compartment geometry, radiative fraction, thermophysical properties, etc.) was addressed and accounted for in the analyses.
b) Please describe how the "model" and "completeness" uncertainties were accounted for in the fire modeling analyses.
Probabilistic Risk Assessment (PRA) RAI 01- FPRA Facts and Observations (F&Os)
Section 2.4.3.3 of NFPA 805 states that the probabilistic safety assessment (PSA) (PSA is also referred to as PRA) approach, methods, and data shall be acceptable to the AHJ, which is the NRC. Regulatory Guide (RG) 1.205, "Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants," Revision 1 (ADAMS Accession No. ML092730314),
identifies NUREG/CR-6850 as documenting a methodology for conducting an FPRA and endorses, with exceptions and clarifications, NEI 04-02, "Guidance for Implementing a Risk-Informed, Performance-Based Fire Protection Program Under 10 CFR 50.48(c)," Revision 2 (ADAMS Accession No. ML081130188), as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. RG 1.200, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities," Revision 2 (ADAMS Accession No. ML090410014), describes a peer review process utilizing an associated ASME/ANS standard (currently ASME/ANS-RA-Sa-2009) as one acceptable approach for determining the technical adequacy of the PRA once acceptable consensus approaches or models have been established for evaluations that could
influence the regulatory decision. The primary result of a peer review are the F&Os recorded by the peer review and the subsequent resolution of these F&Os.
Please clarify the following dispositions to fire F&Os and Supporting Requirement (SR) assessment identified in LAR Attachment V that have the potential to impact the FPRA results and do not appear to be fully resolved:
a) ES-81-01-2008. ES-81-02-2008, and CS-A11-01-2008 (Lack of cable routing)
These F&Os observe that a number of plant systems were not modeled (i.e., were assumed failed) due to lack of cable routing information. The analysis identifies eight systems not credited (i.e., 500kV back-feed, 12kV non-essential power, Anticipated Transient Without Scram Mitigating System Actuation Circuitry (AMSAC), Instrument Air, Feedwater and condensate systems, containment fan coolers, containment spray, and make up to refueling water storage tank from the fuel pool). The disposition to this F&O explains that exclusion of these systems is justified because of their low significance to the Internal Events PRA (lEPRA), and due to the results of a sensitivity analysis. The results of the sensitivity analysis shows that the impact of modeling these excluded systems is an increase of 6 percent(%) in core damage frequency (CDF). The sensitivity study does not present the impact on the delta (~) CDF and ~LERF of modeling these systems.
Explain whether conservative modeling of the compliant plant underestimates the risk contribution to ~CDF or ~LERF. If so, remove this conservatism as part of the integrated analysis performed in response to PRA RAI 3.
b) CS-A6-01-2008 (Inadequate circuit protection on non-safety buses D and E)
The disposition to this F&O states that cable protection was found to be inadequate for non-safety related buses D and E (in both Units), and so modeling impacts of those circuits was reviewed. The analysis presents the results of a sensitivity study demonstrating that the risk associated with these circuits is small (i.e., the increase in CDF was shown to be 1.8E-7/year for Unit 1 and 1.3E-7/year for Unit 2), and as a result, these scenarios were excluded from the FPRA. Describe the method that will be put in place to ensure that the failures associated with these common enclosure related circuits will be modeled in the FPRA before using the FPRA for self-approval as requested in PRA RAI 3.b.
c) CS-A7-01-2008 and CF-A1-03-2008 (3-phase hot short)
The disposition to F&O CS-A7-01 (2008) states that valves 8701 and 8702 are considered "High Consequence" components and so hot short analysis was performed. The response to F&O CF-A 1-03 (2008) clarifies that modeling failures induced from 3-phase hot shorts for valves 8701 and 8702 are excluded from the FPRA based on low frequency of occurrence. Section 9.5.2.2 of NUREG/CR-6850 explains that the likelihood of a grounded 3-phase proper polarity hot short is low and can be screened from the FPRA as less than 1E-7/year, per Section 2.5.6 of NUREG/CR-6850. However, this same guidance also states this failure mode on an ungrounded system cannot be screened as being less than 1E-7/year. Explain whether the electrical circuits for valves 8701 and 8702 are part of a grounded or ungrounded system. If they are part of an
ungrounded system, provide justification for screening these failures and explain whether other such fire-induced failures on ungrounded systems were excluded from the FPRA.
d) CS-A8-01-2008 (Thermoset versus thermoplastic cable)
The disposition to F&O CS-A8-01 states that fire modeling of all fire areas containing thermoplastic cables was updated since the peer review to incorporate guidance from NUREG/CR-6850 related to material properties for thermoset and thermoplastic cables. The extent of thermoplastic cables was estimated in the analysis and used to update treatment of cables as FPRA targets, secondary combustibles, and ignition sources. It is not clear from the disposition to this F&O whether a distinction was made in the circuit failure analysis between thermoset and thermoplastic cables. Describe what update was made to the FPRA related to cable type since the peer review and whether it is consistent with guidance in NUREG/CR-6850 or other NRC guidance. Include in the description any changes made to the way circuit failures probabilities were determined.
e) PRM-C1-01-2010 (Modification credit)
This F&O observes that at the time of the 2010 peer review there was no description of modifications credited in the FPRA. LAR AttachmentS, Table S-2, lists five modifications and indicates that all five are credited in the FPRA for "medium" or "high" contribution to risk reduction. Confirm what modifications are credited in the FPRA, and indicate which are associated with resolving a VFDR and which are non-VFDR modifications that reduce risk.
f) PRM-C1-02-2010 (RCP seal modification)
This F&O observes that installation of high temperature reactor coolant pump (RCP) seals does not exclude the possibility that RCP seals will fail, and that modeling of RCP seal failure and operator actions to trip the RCPs should be added to the FPRA model. LAR AttachmentS, Table S-2 indicates that risk reduction credit is taken in the FPRA for "RCP seal cooling modification," but does not indicate what type of seal will be installed. The disposition to this F&O explains that the seal modeling was modified based on guidance in WCAP-17100-P, Supplement 1 (PRA Model for the Westinghouse Shut Down Seal (SDS)), and WCAP-17541-P (Implementation Guide for the Westinghouse Reactor Coolant Pump SHIELD Passive Thermal SDS). This implies that the new seals will be the Westinghouse RCP SHIELD Passive Thermal Shutdown Seals (SDSs). Given recent concerns about the operation of new Westinghouse RCP shutdown seals during post-service testing (see Westinghouse letter, LTR-NRC-13-52, from James Gresham to NRC dated July 26, 2013, "Notification of Potential Existence of Defects Pursuant to 10 CFR Part 21"; ADAMS Accession No. ML13211A168), the risk reduction credit shown in LAR Attachment W, Tables W-4 and W-5 for upgraded RCP seals may be optimistic. Describe the RCP seal modification that will be performed, discuss the credit taken in the FPRA for the modification, and the technical basis for that credit (e.g., technical report submitted to or approved by the NRC) in the response to PRA RAI 3. If a technical report is the basis, compare the
seal modification and credit taken with the seal addressed in the report and the associated modeling guidance.
g) FSS-A 1-01-2010 (Electric distribution panels)
This F&O observes that the electrical distribution panels were "typically" excluded from fire modeling because fires in these panels are not expected to propagate beyond the ignition source. Guidance in Section 6.5.6 of NUREG/CR-6850 indicates that electrical cabinets with circuits less than 440 volts meeting the definition of a "well-sealed' cabinet, or simple wall-mounted panels housing less than four switches can be excluded from the counting process. Explain whether the electrical distribution panels that were excluded meet one of the above criteria. If electrical distribution panels were excluded that do not meet these criteria, explain whether fire propagation could lead to further target damage than is currently addressed by the FPRA. If further target damage is possible, estimate the impact of this damage on CDF, LERF, ~CDF, and ~LERF and include this impact in the integrated analysis performed in response to PRA RAI3.
h) FSS-81-01-2008 (MCR abandonment scenario)
The disposition to this F&O explains that based on their significance to the overall fire risk, the MCR abandonment scenarios were screened. The analysis indicates, though it does not seem to be directly stated, that credit for MCR abandonment is considered only for loss of habitability (i.e., is not credited in non-habitability scenarios in which fire-induced failures lead to loss of control from the MCR). The analysis also present the basis for screening the abandonment scenario on low frequency and shows that even if the conditional core damage probability (CCDP) associated with failure to successfully perform shutdown from the Hot Shutdown Panel (HSDP) is conservatively set to "1.0" that the CDF associated with MCR abandonment is only 5.98E-8/year. The staff noted that a factor in this determination is the assumption that the unavailability of the smoke purge system is "approximately 1E-3" for scenarios outside the MCB, which seems low. The staff also noted that the basis for this assumption is not provided, and it is not clear whether this assumption considers out-of-service time for test, maintenance, or repair. Another factor presented in the analysis is that probability of abandonment for transient fires is zero. Though the basis may be explained elsewhere, the reason that transient fires do not contribute to MCR abandonment does not seem to be explained in this report. Provide the basis for the assumptions made about the smoke purge system, and explain whether transient fires were modelled in the MCR and whether they lead to MCR abandonment. If abandonment due to loss of habitability is credited, describe and justify the approach.
i) FSS-C8-01-2008 (Credit for fire wrap)
The disposition to this F&O states that fire wrap is credited in the FPRA which is consistent with LAR Table 4-3 that indicates ERFBS are credited in a number of fire areas for risk reduction. The disposition to this F&O does not provide technical justification for the fire wrap qualification as requested by the F&O.
Provide technical justification of the qualification for fire wrap credited in the FPRA for risk reduction.
j) FSS-07 2010 and FSS-E2-01-201 0 (Detection and suppression system availability)
F&Os FSS-07-01 and FSS-E2-01 ask about the basis for the unavailability assumed for fire detection and suppression systems. The dispositions to these F&Os explain that review of plant-specific test and maintenance data did not reveal outlier behavior for the Cable Spreading Room (CSR) fire detection or fire suppression system. It is not clear that data limited to the CSR can be generalized to the balance of the plant. As requested by F&O FSS-07 -01, provide the results of review of plant-specific maintenance and testing data for fire suppression and detection systems credited in the FPRA that characterize the unavailability's of these systems and confirm there are no outliers.
k) FSS-E3-01-2008 (State of Knowledge Correlation)
This F&O cites the lack of qualitative or quantitative uncertainty analysis associated with fire modeling and accident sequence analysis. The F&O disposition explains that since the 2008 peer review, the analysis has been completed that provides qualitative and quantitative characterization of uncertainty and that the analysis discusses the state of knowledge correlation (SOKC) and indicates that SOKC needs to be considered for fire ignition frequencies. The analysis also states that the SOKC was taken into account for fire ignition frequencies and also indicates that the uncertainty of internal events component failure probabilities, circuit failure likelihood, and non-suppression probabilities were treated quantitatively, but does not indicate that SOKC was taken into consideration. If SOKC for these parameters was not accounted for in the FPRA quantification, then address SOKC for these parameters in the integrated analysis performed in response to PRA RAI 3.
I) HRA-C1-01-2010 (Minimum joint Human Error Probability The disposition to this F&O explains that since the 2010 peer review, an updated human reliability analysis (HRA) dependency analysis was completed. The NRC staff noted that the analysis does not indicate that a minimum joint Human Error Probability (HEP) was applied to the dependency analysis. Per guidance in NUREG -1921, "EPRI/NRC-RES Fire Human Reliability Analysis Guidelines Final Report," the Human Failure Event (HFE) dependency analysis should consider the minimum joint value (i.e., floor) for multiple HFEs occurring in the same cutset. Explain whether a "floor" was applied in the HFE dependency analysis, and if so, identify the floor used and justify any value used less than 1E-5. If a "floor was not used, apply a floor to the HFE dependency analysis as part of the integrated analysis performed in response to PRA RAI 3, and justify the value used.
m) MU-A1-01-2008 and MU-A2-01-2008 (Procedure improvement completion)
F&O MU-A 1-01 (2008) observes that the PRA administrative procedure focuses on internal events, and therefore needs to be updated to address the FPRA per the guidance in the PRA Standard. F&O MU-A2-01 (2008) observes that the
licensee's procedure does not require monitoring changes in PRA technology and industry experience. The disposition to these F&Os explains that "DCPP Procedures AWP E-028 and TS3.NR1 will provide the overall program of the PRA model maintenance and upgrade." Though implementation Item S-3.26 of the LAR commits to new plant administrative procedure AWP E-028 for scheduling updates and controlling associated models and files, there does not appear to be a process for updating the applicable administrative procedures. It is not clear whether improvements to the applicable administrative procedures have been performed yet. Explain whether the cited improvements to the administrative procedures have already been performed or are included in an existing implementation item listed in LAR Attachment S, Table S-3. If the cited improvements have not yet been made and are not described in an existing implementation item, then discuss the method to ensure that the cited improvements in FPRA procedure TS3.NR1 will be made before it is used as a basis in self-approval of post-transition changes.
PRA RAI 02 - Internal Events PRA F&Os Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. RG 1.205 identifies NUREG/CR-6850 as documenting a methodology for conducting an FPRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. RG 1.200 describes a peer review process utilizing an associated ASME/ANS standard (currently ASME/ANS-RA-Sa-2009) as one acceptable approach for determining the technical adequacy of the PRA once acceptable consensus approaches or models have been established. The primary results of a peer review are the F&Os recorded by the peer review and the subsequent resolution of these F&Os.
Please clarify the following dispositions to Internal Events F&Os and SR assessment identified in LAR Attachment U that have the potential to impact the FPRA results and do not appear to be fully resolved:
a) SC-A5-01: (Modeling actions needed to reach stable plant condition in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />)
F&O SC-AS-01 observes that for sequences that do not achieve stable plant conditions in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, system recovery or operator actions needed to attain a stable state should be modeled in the PRA. The disposition to this F&O explains that the FPRA was updated to include supplemental water supply to auxiliary feedwater (AFW) for non-loss-of-coolant accident (LOCA) scenarios. Though not explicitly stated, the F&O disposition implies that accident sequences were reviewed to ensure that they reach a stable state in a 24-hour mission time.
Explain whether the FPRA accident sequences were reviewed to ensure that the actions needed to reach a stable state in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> were modeled. If modeling of these actions was not incorporated, then provide justification or incorporate this excluded modeling into the integrated analysis performed in response to PRA RA13.
b) SY-A16-01, SY-815-01, HR-A1-01, HR-A3-01, HR-C3-01, and 03-01: (Pre-initiators)
Regarding the lack of complete treatment of pre-initiator modeling, the dispositions to F&Os SY-A16-01, SY-815-01, HR-A1-01, HR-A3-01, HR-C3-01, and 03-01 explain that a sensitivity study was performed for the FPRA indicating that the risk increase associated with complete treatment of pre-initiators is less than 1% of the FPRA CDF and LERF. Provide a method to ensure that that the excluded pre-initiators will be incorporated into the FPRA model before using the model for self-approval of post-transition changes as requested in PRA RAI 3.b.
c) SY -810-01: (Actuation logic permissives and interlocks)
The disposition to this F&O indicates that actuation logic permissives and interlocks were not directly modeled but were included as part of the FPRA circuit analysis. The NRC staff notes that this seems to indicate that fire-induced failures of permissives and interlocks were modeled but random failures were not modeled and that the impact of this modeling treatment on the risk estimates is not clear. Explain how the actuation logic permissives and interlocks were modeled in the FPRA. Include a discussion of failures (e.g., random failures) that were excluded as a result of not directly modeling actuation logic permissives and interlocks and their impact on the risk estimates. If the current treatment impacts the risk estimates, then incorporate direct modeling of actuation logic permissives and interlocks in the integrated analysis performed in response to PRA RA13.
d) SY-C2-01 and SY-88-01: (HVAC dependency)
F&Os SY-C2-01 and SY-88-01 observe that room heat-up and HVAC dependency discussions are absent from the system notebooks. The analysis does not present room heat-up calculation results or system success dependency on HVAC but does state: "room heat-up calculations are used throughout the DCPP PRA either as a basis for operator timing or to demonstrate that loss of cooling would not impact modelled SSCs." The NRC staff notes that this statement appears to imply that HVAC may not have been modeled in the PRA, and based on the above, the dependency of system success on HVAC is not clear. Clarify whether HVAC is modeled in the lEPRA and FPRA and how system success dependency on HVAC is determined.
e) DA-04-01: (Errors in the Bayesian update)
The disposition to this F&O does not confirm that a Bayesian update was performed addressing the specific concerns defined in the F&O. Clarify whether the five specific concerns defined in the F&O were addressed and if not, provide justification.
f) IF SO-A 1-01 through IFPP-A5-01: (Fire-induced flooding or sprays)
The dispositions to all14 Internal Flooding F&Os (five Suggestions and nine Findings) include the following statement as part of the rational for why the F&Os could not impact the FPRA: "During the development of the FPRA, no fire-induced flood scenario was identified." Clarify whether any fire event can result
in internal flooding or a spray effect that contributes to fire risk. In the response, include discussion of interfacing system LOCA (ISLOCA) sequences and fire suppression actuation. If a fire event can result in internal flooding or a spray effect that contributes to fire risk, include these impacts into the integrated analysis provided in response to PRA RAI 3.
PRA RAI 03 - Integrated Analysis Section 2.4.4.1 of NFPA-805 states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," provides quantitative guidelines on core damage frequency, large early release frequency, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified additional information that is required to fully characterize the risk estimates.
The PRA methods currently under review in the LAR include:
- PRA RAI 2.a regarding systems or actions needed for safe and stable state at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />
- FM RAI 1.i regarding calculation of time to abandonment Please provide the following:
a) Results of an aggregate analysis that provides the integrated impact on the fire risk (i.e., the total transition CDF, LERF, ~CDF, ~LERF) of replacing specific methods identified above with alternative methods which are acceptable to the NRC. In this aggregate analysis, for those cases where the individual issues have a synergistic impact on the results, a simultaneous analysis must be performed. For those cases where no synergy exists, a one-at-a-time analysis may be done. For those cases that have a negligible impact, a qualitative evaluation may be done. It should be noted that this list may expand depending on NRC's review of the responses to other RAis in this document.
b) For each method (i.e., each bullet) above, explain how the issue will be addressed in 1) the final aggregate analysis results provided in support of the LAR, and 2) the PRA that will be used at the beginning of the self-approval of post-transition changes. In addition, provide a method to ensure that all changes will be made, that a focused-scope peer review will be performed on changes that are PRA upgrades as defined in the PRA standard, and that any findings will be resolved before self-approval of post-transition changes.
c) In the response, explain how the RG 1.205 risk acceptance guidelines are satisfied for the aggregate analysis. If applicable include a description of any new modifications or operator actions being credited to reduce delta risk as well as a discussion of the associated impacts to the fire protection program.
d) If any unacceptable methods or weaknesses will be retained in the PRA that will be used to estimate the change in risk of post-transition changes to support self-approval, explain how the quantification results for each future change will account for the use of these unacceptable methods or weaknesses.
PRA RAI 04- Sensitive Electronics (Related to FM RAI 02.c)
In regard to modeling fire damage to sensitive electronics, the analysis states that studies show that using a steel housing for temperature sensitive electronics is effective in reducing damaging heat fluxes and maintaining the internal equipment to below damage thresholds. The analysis also presents fire event trees showing end-states involving damage to temperature limited
equipment, but does not specifically discuss modeling related damage to sensitive electronics.
Though the treatment of sensitive electronics may be consistent with recent guidance on modeling sensitive electronics, neither Appendix H of the LAR or the licensee's procedures refer to use of Frequently Asked Question (FAQ) 13-0004, "Clarifications on Treatment of Sensitive Electronics," dated December 3, 2013 (ADAMS Accession No. ML13322A085).
Please describe the treatment of sensitive electronics for the FPRA and explain whether it is consistent with the guidance in FAQ 13-0004, including the caveats about configurations that can invalidate the approach (i.e., sensitive electronic mounted on the surface of cabinets and the presence of louver or vents). If the approach is not consistent with FAQ 13-0004, justify the approach or replace the current approach with an acceptable approach into the integrated analysis performed in response to PRA RAI 3.
PRA RAI 05- Transient Heat Release Rate (Related to FM RAI 01.e)
Though not specifically acknowledged in the LAR, it appears that reductions below the 98 1h percentile NUREG/CR-6850 HRR of 317 kW for transient fires are credited in the FPRA (e.g., the analysis shows that a 98th-percentile HRR of 142 kW was used for fire area 6-A-3).
Please identify the fire areas for which reduced HRRs are credited and discuss the key factors used to justify the reduced rate below 317 kW per the guidance provided in the June 21, 2012, memorandum from Joseph Giitter to Biff Bradley ("Recent Fire PRA Methods review Panel Decisions and EPRI 1022993, 'Evaluation of Peak Heat Release Rates in Electrical Cabinets Fires'," ADAMS Accession No. ML12171A583). Include in this discussion:
a) Identification of any other fire compartments for where reduced HRR transient fires are credited.
b) For each location where a reduced HRR is credited, a description of the administrative controls that justify the reduced HRR including how location-specific attributes and considerations are addressed. Provide a discussion of required maintenance for ignition sources in each location, and types/quantities of combustibles needed to perform that maintenance. Also discuss the personnel traffic that would be expected through each location.
c) The results of a review of records related to violations of the transient combustible and hot work controls.
d) The impact of assuming reduced HRRs on the fire risk estimates. Note that if a reduced HRR cannot be justified using these guidance criteria, then use the transient fire HRR values from Table G-1 of NUREG/CR-6850 in the integrated analysis performed in response to PRA RAI 3.
PRA RAI 06 - Use of Unacceptable Methods LAR Attachment V states that the "DCPP Fire PRA model includes no deviations from NRC Accepted Fire PRA Methods, and contains no unreviewed analysis methods (UAMs)." LAR Attachment V did not define the licensee's understanding of what constitutes "NRC Accepted
Fire PRA Methods." Therefore, though UAMs, as evaluated by the EPRI/NRC panel were not used, please indicate if any other methods were employed that deviate from guidance in NUREG/CR-6850 or other acceptable guidance (e.g., FAQs or interim guidance documents). If so, justify any deviations from NRC guidance, or replace those methods with another method and submit that method to the NRC for review. Also, determine the impact on Fire CDF, LERF, 1.\CDF, and LlLERF by including any new approaches as part of the integrated analysis performed in response to PRA RAI 3.
PRA RAI 07- Transient Fire Placement at Pinch Points In the analysis, there appears to be no description of how "pinch points" were modeled for transient fires. Per the guidance provided in NUREG/CR-6850, Section 11.5.1.6, transient fires should at a minimum be placed in locations within the plant physical analysis units (PAUs) where CCDPs are highest for that PAU (i.e., at "pinch points"). The NRC staff notes that pinch points include locations of redundant trains or the vicinity of other potentially risk-relevant equipment. The NRC staff notes that hot work should be assumed to occur in locations where hot work is a possibility, even if improbable. Please provide the following:
a) Clarification of how "pinch points" were identified and modeled for transient fires.
b) A description of how transient and hot work fires are distributed within the PAUs.
In particular, identify the criteria used to determine where such ignition sources are placed within the PAUs.
PRA RAI 08 - Main Control Board (MCB) Fire Modeling and Fire Ignition Frequency a) The analysis provides a description of how MCB fires are modeled for the FPRA and includes an explanation that the probability of damage to a target set on the MCB is performed in accordance with the method described in Appendix L of NUREG/CR-6850. The analysis also explains that the MCB for each unit is comprised offive adjoining vertical boards (i.e., VB1 to VB5) arranged in an L-shape and three smaller Control Console sections (i.e., CC1, CC2, and CC3).
The analysis also presents probabilities of MCB fire scenarios for different so-called Functional Target Sets (FTSs) based on the distance "d" between targets and that the distance "d" appears to be limited to targets contained within a vertical board (or the Control Console) and ranges from about 6" to 30." If targets are constrained to a single vertical board, please provide a discussion of the barrier between vertical sections which limits propagation. Otherwise, extend the target set across the vertical boards.
b) The licensee's analysis indicates that the total adjusted fire ignition frequency is 1.65E-03/year for the two units. The analysis indicates that the MCB ignition frequency was divided between MCB sections according to the ratio of the section surface area to the total MCB surface area, but also shows that for MCR abandonment the whole MCB fire ignition frequency was used. Please explain this inconsistency and the correct ignition frequency that was used. If the MCB ignition frequency is divided by factoring in the MCB surface area, the NRC staff
cannot complete its review. In this case, replace this treatment in the integrated analysis provided in response to PRA RAI 3, and provide an explanation of the approach used and the results in sufficient detail so the staff can make a conclusion regarding the use of the approach.
c) During the audit, the licensee indicated that supplemental analysis beyond NUREG/CR-6850, Appendix L, was developed to evaluate the risk due to horizontal raceways in the MCB. Please describe and justify the approach including the various aspects of the analysis and assumptions.
PRA RAI 09- Use of Incipient Detection LAR Section 4.8.2.1 and LAR Attachment S, Table S-3, state that incipient detection will be installed in the CSR and the Solid State Protection System (SSPS) rooms for both Units 1 and 2, and is credited in the FPRA consistent with guidance in FAQ 08-0046, Incipient Fire Detection Systems (ADAMS Accession No. ML093220426). Though not identified in LAR Attachment S, Table S-3, the analysis indicates that incipient detection will also be installed in the MCR and the Safeguards room. It is not clear whether these additional modifications not cited in LAR AttachmentS, Table S-3, have been or will be made, and whether they are credited in the FPRA. Please clarify what locations incipient detection will be installed and how incipient detection is credited for those locations in the FPRA. If incipient detection is credited in the FPRA for very early warning in the MCR or in area-wide applications, or is credited beyond what is described by FAQ 08-0046, then do not include this credit as part of the integrated analysis performed in response to PRA RAI 3.
PRA RAI 10 - PRA Treatment of Dependencies between Units 1 and 2 LAR Attachments C and U discuss cross-ties and systems shared between units (e.g., the Diesel Fuel Oil, and ASW systems). LAR Appendix W shows contribution by fire area of CDF, LERF, ~CDF, and ~LERF, but does not explain how the risk contribution from fires originating in one unit is addressed in the risk for the other unit given the possible physical proximity of fire area and the existence of shared systems and cross ties. LAR Attachment W, Tables W-4 and W-5 indicate that some of the fire areas are common between the two units (i.e., 4-B, 34, CR-1, FB-1, and TB-7). It is not clear how the risk is reported for these common areas and whether fire impacts in these areas are fully considered for both units. In light of these considerations, please address the following:
a) Explain how the risk contribution of fires in one unit is addressed for the other unit due to the physical layout of the units and shared systems. Include identification of locations where fire in one unit can affect components in the other unit, and a description of the extent to which systems are shared. If the contribution of fires originating in one unit is not addressed for the other unit, perform this assessment and include it as part of the integrated analysis requested for PRA RAI 3.
b) Explain how the risk contribution for common areas (e.g., 4-B, 34, CR-1, FB-1, and TB-7) was assessed and is reported. Explain whether fire impacts in these
areas are fully considered for both units. If the impact is not fully addressed, then address this risk as part of the integrated analysis requested for PRA RAI 3.
PRA RAJ 11 -Screening of Junction Boxes as Non-Damaging Ignition Sources The analysis states "Junction boxes that are robustly secured and well-sealed will be screened as non-damaging ignition sources." The NRC staff notes that unlike electrical cabinets, there is no exclusion of a junction box from the count because it is robustly secured and well-sealed. If the approach to evaluating junction boxes is not consistent with FAQ 13-0006, "Modeling Junction Box Scenarios in a Fire PRA" (ADAMS Accession No. ML133318213), then please explain the method used and justification for using this method instead of FAQ 13-0006.
Perform sensitivities as necessary to justify the approach. If unable to justify the method, then include another method as a part of the response to PRA RAI 03.
PRA RAJ 12 - Smoke Damage The analysis indicates that, although qualitative analyses are performed of smoke damage, no fire modeling for smoke effects is performed. The guidance in Appendix T of NUREG/CR-6850 states that the effects of smoke damage should be quantitatively addressed in the FPRA for certain equipment and configurations. It is not clear how smoke effects were addressed in the FPRA. Please explain how effects of smoke on equipment were evaluated using the guidance provided in Appendix T of NUREG/CR-6850.
PRA RAI13- Multi-Compartment Analysis The analysis presents an MCA, but LAR Attachment W does not explain how the MCA results are incorporated into the risk estimates provided in LAR Attachment W. Please explain whether the CDF, LERF, f1CDF, and f1LERF values reported in LAR Attachment W, Tables W-4 and W-5 include the contribution from MCA or if they are reported separately elsewhere, and whether MCA contribution is considered when comparing total and change in risk results to Regulatory Guide (RG) 1.200 risk guidelines.
PRA RAI14- Calculation ofVFDR ~CDF and ~LERF LAR Attachment W, Section W.2.1 provides a description of how the f1CDF and f1LERF associated with VFDRs is determined. Please supplement the description by:
a) Describing the types of model adjustments that were made to remove different types of VFDRs from the compliant case FPRA. In addition, identify any major changes made to the FPRA models and data for evaluating VFDRs.
b) Describing how VFDR and non-VFDR plant modifications are credited in the compliant and post transition PRA models.
c) Describing of the type of VFDRs identified, and providing justification that any VFDRs identified but not modeled in the FPRA do not impact the risk estimates.
PRA RAI 15 - Large Reduction Credit for Modifications LAR Attachment W, Tables W-4 and W-5 report change-in-risk values for each fire area before crediting "beyond compliance" (i.e., non-VFDR related) modifications, and the total change-in-risk based on the sum of all the fire areas after crediting non-VFDR modifications by use of a "risk offset" value. It is not clear why the risk reduction for just the RCP seal upgrade is so substantial (i.e., 5.35E-05/year for Unit 1 and 6.58E-05/year for Unit 2). Given the significance of the risk reduction and the fact that a conservative calculation of the compliant plant CDF and LERF can lead to a non-conservative calculation of the t:.CDF and t:.LERF, please provide the following:
a) Clarification of what modifications are associated with the risk reduction presented at the bottom of LAR Attachment W, Tables W-4 and W-5, and an explanation of how this risk reduction was determined.
b) A summary of the risk significant scenarios for fire areas in the compliant plant model which are most significantly impacted by the risk offset.
c) A discussion of the contribution of fire-induced failures for those risk significant scenarios.
d) For the risk significant scenarios, a discussion of the impact of any assumptions made that significantly contribute to the variant and the compliant case risk.
PRA RAI 16 - Defense in Depth and Safety Margin LAR Section 4.5.2.2 provides a high-level description of how the impact of transition to NFPA 805 impacts DID and safety margin was reviewed. Please provide further explanation of the method used to determine when a substantial imbalance between DID echelons existed in the Fire Risk Evaluations (FREs), and identify the types of plant improvements made in response to this assessment. Also, provide further discussion of the approach in applying the NEI 04-02, Revision 2 criteria for assessing safety margin in the FREs.
PRA RAI 17 - Implementation Item Impact on Risk Estimates LAR AttachmentS, Implementation item S-3.24 indicates that verification of the validity of the reported change-in-risk will occur upon completion of all LAR Attachment S, Table S-2 modifications. It does not, however, include a method to update the FPRA following completion of other implementation items and does not identify a plan of action if RG 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," Revision 2 (ADAMS Accession No. ML100910006), guidelines are exceeded. This implementation should include the process for updating the FPRA model after all implementation items are complete, and also a process to identify a plan of action if RG 1.174 guidelines are exceeded.
PRA RAI 18 - Internal Events PRA Peer Review LAR Attachment U explains that the lEPRA peer review was performed in December 2012, while LAR Attachment V explains that the second phase of the FPRA peer review was performed 2 years earlier in December 2010. This sequence of peer reviews is counter to the expectation that an internal events model is first peer reviewed and then used as a starting point for the FPRA model. Based on dispositions provided LAR Attachment U, it appears that actions were taken in response to F&Os that in some cases involved improvements to the lEPRA. Given that the FPRA was performed 2 years earlier, it is not clear if or how these same improvements were incorporated into the FPRA, and whether these modifications resulted in the need to reconstitute the FPRA. Please describe the improvements made to the lEPRA as a result of responses to Internal Event F&Os and explain how these improvements were incorporated into the FPRA. For improvements that have not yet been incorporated, then include them in the integrated analysis provided in response to PRA RAI 03.
PRA RAI 19 - FPRA Peer Reviews LAR Attachment V explains that technical adequacy of the FPRA model was evaluated by a two-phase full-scope peer review against the PRA standard. The first phase of the peer review was performed in October 2008, against PRA Standard ANSI/ANS-58.23-2007. LAR Section 4.5.1.3 states that this review was conducted to represent a "trial application of the FPRA review process." LAR Attachment V also explains that not all technical elements of the FPRA were completed at the time of the 2008 peer review. The second phase of the peer review was performed December 2010 against PRA Standard ASME/ANS RA-Sa-2009 as clarified by RG 1.200, Revision 2, but the scope of that review is not defined. It is not clear if the gap assessment addressed all of the changes between the 2007 (ANSI/ANS-58.23-2007) and 2009 (ASME/ANS RA-Sa-2009) versions of the PRA Standard. Please describe the scope of the 2010 peer review and how the differences in SRs between the versions of the PRA Standard used in the peer reviews was addressed. If this difference was not addressed, then provide a gap assessment of those SR differences on the FPRA.
PRA RAI 20- Reduction in Total Plant Risk Due to Non-VFDR Modifications LAR Attachment W, Table W-1 presents total CDFs (i.e., 9.47E-5/year for Unit 1 and 9.06E-5/year for Unit 2) just below the RG 1.174 guideline of 1E-4/year. Please clarify whether these CDFs reflect the risk reduction to the internal events CDF and LERF due to non-VFDR modifications credited in the FPRA identified in LAR AttachmentS, Table S-1 (e.g., RCP seal upgrade).
PRA RAI 21 -Sensitivity Analysis on FAQ 080048 Fire Bin Frequencies LAR Attachment V, Table V-1 presents the results of a sensitivity study on the updated fire ignition bin frequencies provided in NUREG/CR-6850, Supplement 1 (i.e., FAQ 08-0048) using the mean of the fire frequency bins contained in Section 6 of NUREG/CR-6850 for those bins with an alpha value less than or equal to one. It is not clear why the percent increase for LlCDF and LlLERF is higher than the percent increase for the total fire CDF and LERF (e.g., the percent increase in CDF for Unit 2 is 57% while the percent increase in LlCDF for Unit 2 is
74%), given that fire ignition frequencies impact both the compliant and post-transition plant case accident sequences the same, and do not affect CCDP and CLERP values. Please provide the following:
a) An explanation of the anomaly cited above and whether the reported change-in-risk values in LAR Attachment V, Table V-1 are correct.
b) An updated sensitivity study based on the integrated analysis performed in response to PRA RAI 3. Include in the sensitivity study any adjustments needed to correct anomalous results from the initial sensitivity study.
c) An indication of whether the acceptance guidelines of RG 1.174 may be exceeded when this sensitivity study with respect to FAQ 08-0048 is applied to the integrated study of PRA RAI 3. If these guidelines may be exceeded, provide a description of fire protection, or related, measures that can be taken to provide additional defense in depth, as discussed in FAQ 08-0048.
PRA RAI 22- Human Error Probabilities for Control Room Abandonment Scenarios During the audit, the licensee explained that the analysis could better address the timing of the fire scenarios that are supported by thermal-hydraulic analysis and the resulting cues for operator actions. As a result, please evaluate where abandonment due to loss of control is credited and provide an assessment of MCR abandonment through establishing a bounding scenario or a set of representative scenarios. Ensure the potential complexity of fire-induced damage, including spurious operations, are incorporated into these scenarios. Evaluate the timing supported by thermal hydraulics for these scenarios and the effect on the HRA including the effect on cues. Provide a comparison of the results of this analysis with the values from the PRA supporting the LAR, and explain any potential differences.
ML14206A008 *via email OFFICE NRR/DORULPL4-1 /PM NRR/DORULPL4-1/LA NRR/DRA/AFPB/BC*
NAME PBamford JBurkhardt AKiein DATE 7/24/14 7/25/14 7/17/14 OFFICE NRR/DRA/APLA/BC* NRR/DORULPL4-1/BC NRR/DORULPL4-1 /PM NAME HHamzahee EOesterle PBamford DATE 7/17/14 7/31/14 7/31/14