Text

Lr - Draft RAIs for the DCPP SAMA Review
	ML15281A312
Person / Time
Site:	Diablo Canyon
Issue date:	10/08/2015
From:	; Office of Nuclear Reactor Regulation
To:	;
References
	Download: ML15281A312 (16)
	v • d • e

DiabloCanyonNPEm Resource From: Wentzel, Michael Sent: Thursday, October 08, 2015 12:17 PM To: Terrence Grebel (TLG1@pge.com)

Subject:

Draft RAIs for the DCPP SAMA Review Attachments: Requests for Additional Information Related to the Diablo Canyon LRA Environmental Review

- SAMA.docx

Terry, Attached is a draft of the SAMA RAI letter. Once you had a chance to review, please let me know if you would like to have a phone call to clarify.

Thanks, Mike Michael Wentzel Project Manager NRR/DLR/RPB2 (301) 415-6459 michael.wentzel@nrc.gov 1

Hearing Identifier: DiabloCanyon_LicenseRenewal_NonPublic Email Number: 3175 Mail Envelope Properties (a9253d08b430402fae58913bb90a1574)

Subject:

Draft RAIs for the DCPP SAMA Review Sent Date: 10/8/2015 12:17:04 PM Received Date: 10/8/2015 12:17:05 PM From: Wentzel, Michael Created By: Michael.Wentzel@nrc.gov Recipients:

"Terrence Grebel (TLG1@pge.com)" <TLG1@pge.com>

Tracking Status: None Post Office: HQPWMSMRS03.nrc.gov Files Size Date & Time MESSAGE 339 10/8/2015 12:17:05 PM Requests for Additional Information Related to the Diablo Canyon LRA Environmental Review -

SAMA.docx 89683 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received:

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 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:

REQUESTS FOR ADDITIONAL INFORMATION RELATED TO THE ENVIRONMENTAL REVIEW OF THE DIABLO CANYON POWER PLANT, UNITS 1 AND 2 LICENSE RENEWAL APPLICATION - SEVERE ACCIDENT MITIGATION ALTERNATIVES (TAC NOS. MF4019 AND MF4020)

Dear Mr. Halpin:

On November 23, 2009, Pacific Gas & Electric Company (PG&E) submitted an application pursuant to Title 10 of the Code of Federal Regulations (CFR) Part 54 to the U.S. Nuclear Regulatory Commission (NRC) for renewal of operating licenses DPR-80 and DPR-82 for Diablo Canyon Power Plant (DCPP), Units 1 and 2. In accordance with 10 CFR Part 51, PG&E submitted an environmental report as an appendix to the license renewal application for DCPP.

On December 22, 2014, and February 25, 2015, PG&E amended its environmental report to incorporate additional information necessary for the NRC staff to complete its review of the DCPP license renewal application. The staff is reviewing the information contained in the environmental report, as amended, and has identified in the enclosure, areas where additional information is needed to complete the review.

These requests for additional information were discussed with Terry Grebel and a mutually agreeable date to respond is within 30 days from the date of this letter. If you have any questions, please contact me at (301) 415-6459, or by e-mail at michael.wentzel@nrc.gov.

Sincerely, Michael J. Wentzel, Project Manager Projects Branch 2 Division of License Renewal Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

As stated cc w/encl: Listserv

concurrence via email OFFICE LA:DLR* PM:RPB2:DLR BC:RPB2:DLR PM:RPB2:DLR NAME MWentzel JDanna MWentzel DATE Letter from M. Wentzel to E. Halpin dated XXXX

SUBJECT:

REQUESTS FOR ADDITIONAL INFORMATION RELATED TO THE ENVIRONMENTAL REVIEW OF THE DIABLO CANYON POWER PLANT, UNITS 1 AND 2 LICENSE RENEWAL APPLICATION - SEVERE ACCIDENT MITIGATION ALTERNATIVES (TAC NOS. MF4019 AND MF4020)

DISTRIBUTION:

HARD COPY:

DLR RF E-MAIL:

PUBLIC RidsNrrDlr Resource RidsNrrDlrRpb1 Resource RidsNrrDlrRpb2 Resource RidsNrrDlrRerb Resource RidsNrrDlrRarb Resource RidsNrrDlrRasb Resource RidsNrrDlrRsrg Resource RidsOgcMailCenter Resource RidsNrrPMDiabloCanyon Resource MWentzel JDanna RPlasse YDiaz-Sanabria SLingam CKanatas, OGC JLindell, OGC THipschman, SRI JReynoso, RI GMiller, RIV DMcIntyre, OPA LUselding, OPA WMaier, RIV AMoreno, OCA

DIABLO CANYON POWER PLANT, UNITS 1 AND 2 LICENSE RENEWAL APPLICATION ENVIRONMENTAL REVIEW REQUESTS FOR ADDITIONAL INFORMATION SEVERE ACCIDENT MITIGATION ALTERNATIVES

1. Provide the following information regarding the Level 1 Probabilistic Risk Assessment (PRA) used for the Severe Accident Mitigation Alternative (SAMA) analysis. Basis: Applicants for license renewal are required by Title 10 of the Code of Federal Regulations (10 CFR) 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the Diablo Canyon Power Plant (DCPP) SAMA analysis, the U.S. Nuclear Regulatory Commission (NRC) staff is evaluating Pacific Gas and Electrics (PG&Es) treatment of internal events and calculation of core damage frequency (CDF) in the Level 1 Probabilistic Risk Assessment (PRA) model. The requested information is needed in order for the NRC staff to reach a conclusion on the sufficiency of PG&Es Level 1 PRA model for supporting the SAMA evaluation.

a. Environmental Report (ER), Amendment 2, Section F.2 (p. F-12) states The CDF values for the models presented in Section F.2.1 are all point estimate values.

The evaluation of base case benefits was based on point estimate values.

The CDF values given for a number of the PRA models in subsequent subsections (F.2.1.6, p. F-23; F/.2.1.7, p. F-26; F.2.1.8, p. F-29; F.2.1.9, p. F-32; and F.2.1.10, p. F-

36) are indicated to be mean values. Please clarify.

b. Section F.2.1 of the ER describes the shared systems and/or the systems that can be cross-tied between Units 1 and 2. Discuss the treatment of the unavailability of Unit 2 components due to test, maintenance and refueling in the Unit 1 model. Discuss the potential for and the modeling of initiating events that can impact both Units 1 and 2.

c. Section F.2.1.10 of the ER indicates that the DC03 Fire PRA includes the Westinghouse low leakage shutdown seals and an upgrade of the hot shutdown panel that are to be implemented in the future. Table 4 of PG&E Letter DCL 080 (p. 34) indicates that while the fire portion of the DC03SA model, and some steam generator tube rupture (SGTR) scenarios, include credit for the planned installation of the shutdown seals at DCPP, the seals are not credited in the DC03SA internal events model. Provide the status of the hot shutdown panel in all of the DC03SA models and of the low leakage seals in the internal flooding and seismic models, particularly with respect to the SGTR scenarios. Describe the differences between the current and new seals and the features of the hot shutdown panel upgrade and their qualitative impact on the PRA models, the identification and scope of relevant potential SAMAs, and the SAMA cost-benefit analysis.

d. The original 2009 SAMA analysis submittal and responses to NRC staff request for additional information (RAIs) were based on PRA models DC01A and DC01B. These two models are not described in Section F.2.1 of the ER, but the seismic initiating event ENCLOSURE

frequencies are cited in the discussion of the DC03 interim model. Briefly discuss these models. Also, clarify any differences between the descriptions and/or results provided in the 2009/2010 submittals and the current models, such as the statement in the 2009 ER Section F.2.1.9 that the charging pumps were replaced with centrifugal pumps, which is not mentioned in the current submittal.

e. The initiating event contributors to the internal events CDF shown in Figure F.2-1 do not include loss of offsite power (LOOP). Provide the CDF due to LOOP initiators. If included in the "others" category (which would appear to indicate that LOOP contributes less than 2% to the total internal events CDF), explain why it is so low. Note that the 2010 SAMA analysis indicated that the CDF due to grid-related LOOP was 8.9E-07/year which corresponds to 8% of the current internal events CDF (excluding internal flooding).

f. Provide the station blackout (SBO) and anticipated transient without scram (ATWS) contributions to the internal events and internal flooding CDFs for the DCPP PRA used for the SAMA analysis

g. Provide the freeze date or the date which corresponds to the DCPP design and operation incorporated into the DCPP PRA used for the SAMA analysis. Identify any design or operational (including fuel cycle) changes that have or, are planned, since this freeze date that might impact the SAMA analysis.

h. The discussion in Section F.2.3.1 (p. F-47) of the ER regarding the PRA maintenance and update procedures states:

"These procedures delineate the responsibilities and guidelines for updating the full power internal events PRA models at the Diablo Canyon Power Plant."

Although guidelines for full power, internal and external events are mentioned, it is not clear whether these are included in the cited procedures or other documentation. Clarify the applicability of the cited procedures to other than internal events PRA models and if not applicable, identify the procedures that are applicable.

i. Section F.3.2.2 (p. F-48) lists the dates of the peer reviews of the various DCPP PRAs.

Identify the specific model revisions listed in Section 2.1 reviewed by each of the peer reviews, the scope of each review and the number of findings and Facts and Observations (F&Os) for each peer review. If the PRA model reviewed is not described in Section 2.1, provide the CDF and large early release frequency (LERF) for the model reviewed and how the model differs from the prior model.

j. Confirm that no changes have been made to the DCPP PRA model used in the SAMA analysis since the Peer Reviews that would constitute an upgrade as defined by ASME/ANS RA-Sa-2009, as endorsed by Regulatory Guide (RG) 1.200, Revision 2.

k. Section F.2.3.5 of the ER, Conclusion Regarding PRA Capability for SAMA Identification and Evaluation, discusses and concludes that the DCPP PRA Model DC03 results are suitable for use as a resource in the SAMA identification process. Clarify why the discussion and conclusions does not address the suitability for the SAMA cost-benefit evaluation process.

l. With regard to ER, Amendment 2, Addendum 1:

i. For the first item Internal flooding -NRC IN 98-31 ISER 3-98, A0468801 confirm that this has not been closed in the DC02 update of internal flooding and if not provide more information on the basis for the conclusion that no direct impact on the current model is anticipated.

ii. For the fourth item, Address anchorage of relay panels in cable spreading rooms, confirm that the requested analysis has been performed or otherwise justify that this is only a documentation issue.

iii. For the fifth item, Address potential for d/g lockout from cardox, provide the basis for the conclusion that the impact of this issue is expected to be minor.

m. The figures in ER Amendment 2 presenting the contributors to the internal fire and internal flood CDF and LERF (Figures F.2-5 through F.2-8) indicate that the contributions are by initiating event. Confirm that the contributions are by initiating event rather than fire or flood zone or if not, provide the correct description. Also, note that in Figure F.2-5, the contribution from 3BB115, while included in the figure itself, it is not included in the description table. Please add this to the table.

2. Provide the following information relative to the Level 2 PRA analysis. Basis: Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, the NRC staff is evaluating PG&Es treatment of accident propagation and radionuclide release in the Level 2 PRA model. The requested information is needed in order for the NRC staff to reach a conclusion on the adequacy of PG&Es Level 2 PRA model for supporting the SAMA evaluation.

a. Section F.2.2 of the ER describes the Level 1 to Level 2 mapping and the need for plant damage states (PDSs) and key plant damage states (KPDSs). Is the transfer of information from Level 1 to Level 2 transferred directly in the logic models or are the numerical PDS frequency results of the Level 1 analysis added and input into the Level 2 analysis (the containment event trees (CETs)) as a frequency?

b. Section F.2.2.3 of the ER discusses the development of the KPDSs and Table F.2-3.

This table presents the ranking of PDSs based on PRA model DCPRA-1991and states that the relative ranking of PDSs and therefore the definition of KPDSs is not expected to change significantly from DCPRA-1991 to DC03. Provide further support for the final statement and discuss the role of relative ranking in the definition of KPDSs. Discuss if all plant damage states (PDSs) that result from the Level 1 analysis are assigned to a KPDS or if some are grouped together as a remainder group and if so how is the remainder considered in the Level 2 analysis.

c. The discussion of release category binning in Section F.2.2.4.1 of the ER includes the statement:

For early-small containment failures, the medium pressure sequences are binned with the high pressure sequences because containment pressures may be greater later in the event and high RCS retention then becomes a liability.

Table F.2-5 indicates that for small early release categories, the medium pressure sequences are binned with the low pressure sequences. In addition, Table F.3-11 of the ER describes the Modular Accident Analysis Program (MAAP) case RC16U as low pressure core melt while the description of the small early release category in Section F.2.2.4.2 states Other cases within this release category group would either have medium to low RCS pressure... Explain this binning and the selection of the representative MAAP case for the small early release category.

d. Table F.3-11 of the ER identifies the representative MAAP case for ST3 as RC10 and describes it to include CS OK. RC10 is indicated in Table F.2-5 to not have containment sprays available. The Section F.2.2.4.2 description of ST3 indicates that containment fails due to prolonged core-concrete interaction, while RC10 is indicated to have coolable debris. Please clarify.

e. Section F.2.2.4.2 of the ER provides a discussion of assigning non-isolated steam generator tube rupture (SGTRN) with Auxiliary Feedwater (AFW) success to the interfacing system loss of cooling accident (ISLOCA) release category. Provide a further discussion of these sequences and the basis for this assignment. The discussion includes the statement RC18 was reviewed to see if there are any sequences with AFW successful that should be allocated to the Containment Bypass group. None were found. Since RC18 is composed of ISLOCAs it is not clear why AFW availability is relevant. Explain.

f. Table F.2-7 of the ER gives the frequency of RC17 as 3.59E-06/year and the frequency of RC18 as 1.28E-08/year. Fifty percent of RC17 yields 1.79E-06/year for the frequency of ST4, in agreement with the frequency for ST4 in Table F.3-13. Fifty percent of RC17 added to the above value for RC18 yields 1.8E-06/year which is different from the value for ST5 given in Table F.3-13 of 2.97E-06/year. Explain this difference and describe the basis for the 50 percent value.

g. Provide an updated version of Table F.2-7 of the ER based on the results of the DC03SA PRA.

h. Table F.3-11 of the ER provides the MAAP run times for each of the release category source term cases. Justify that the source term release fractions from these run durations represents the maximum release whenever the run end time is less than 48 hours5.555556e-4 days 0.0133 hours 7.936508e-5 weeks 1.8264e-5 months after the declaration of general emergency.

i. It is noted that the sum of DC03 model release categories ST1 and ST5, both leading to a large early release, is 1.02E-05 per year while the quoted value for LERF for unit 1 is 1.20E-05 per year. Explain the reasons for the difference. If this is due to Level 2 model changes compared to a LERF only model, describe the changes from the peer reviewed LERF model to the current full Level 2 model.

j. Provide a discussion of the development of the Level 2 model, particularly the CETs, the basis for the CET split fractions, and updates since the Individual Plant Examination (IPE) to represent the current state of the art.

3. Provide the following information with regard to the treatment and inclusion of external events in the SAMA analysis. Basis: Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, the NRC staff is evaluating PG&Es treatment of external events in the PRA models. The requested information is needed in order for the NRC staff to reach a conclusion on the sufficiency of PG&Es PRA models for supporting the SAMA evaluation.

a. Provide the total seismic CDF and LERF for the DC03SA model and the contribution to the seismic CDF by initiating event. Include the contribution from the new initiating event for ground motion accelerations greater than 4.0g for both the DC03 as well as DC03SA models.

b. Section F.2.3.2 of the ER indicates that a peer review of the seismic events model was conducted in January 2013 and states:

The update of the seismic fragilities of PRA SSCs is currently in progress. Once the update is completed in 2015, the seismic F&Os will be resolved followed by the update of the Seismic model.

Page 1 of the PG&E Letter DCL-15-080 submittal states "The DC03SA model uses the same fragilities as the DC03 model. The Long Term Seismic Program (LTSP) fragility curves are acceptable for use in DC03SA because no scaling is necessary for use with the updated hazard spectral information from the March 2015 50.54(f) response."

i. The first statement indicates that changes to seismic fragilities were being made subsequent to the DC03 (interim) model, yet the second statement indicates that no changes were made from those used in the LTSP. Explain.

ii. The first statement implies that the only seismic F&Os unresolved involve the seismic fragilities. Confirm that all the findings from the 2013 peer review have been resolved.

iii. Page 1 of the PG&E Letter DCL-15-080 submittal provides a comparison of the LTSP uniform hazard spectrum with the updated spectral information indicating that in one frequency range the shapes may differ by plus or minus 14%. Provide an additional discussion of this comparison and of the potential impact of a 14%

difference in spectral shapes on seismic risk in general and the SAMA analysis in particular.

iv. The PG&E Letter DCL-15-080 discussion indicates that at other hazard levels relevant to the PRA model (1E-03 to 1E-05) the shape does not differ significantly

from the shape at 1E-04 hazard level. Since the new (greater than 4.0 g) seismic initiating event has a frequency on the order of 1E-06, are the conclusions in the ER concerning the spectral shape at this lower hazard level?

c. Provide a further description of the development of the fire PRA used for the SAMA analysis, including its relationship to the Individual Plant Examination - External Events (IPEEE) model and the model revision(s) that incorporated the guidance of NUREG/CR-6850.

d. Discuss the inclusion in the fire PRA used in the SAMA analysis of the changes resulting from and/or required by the NRC review of transition to NFPA 805 application. If not included, provide the CDF and LERF results by hazard class from PG&E's response to the NFPA 805 transition integrated analysis RAI and discuss the reasons for any differences in results between the models and their impact on the SAMA analysis.

e. PG&E's flood hazard evaluation of March 11, 2015 in response to the 10 CFR 50.54(f) request includes in Section 3.6.4.2 the statement "Based on the above assumptions, the probability of a large marine vessel arriving at the DCPP breakwater and impacting the intake structure was determined to be 3.1E-05 events per year."

Provide support for the continued use of the IPEEE ship impact CDF considering the 3.1E-05 events per year value given in the flood hazards report and/or an updated value of CDF that is appropriate for the conditions associated with flood hazard impact frequency. Discuss the effect of any changes in the ship impact CDF value on the results of the SAMA analysis.

4. Provide the following information relative to the Level 3 PRA analysis. Basis: Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, the NRC staff is evaluating PG&Es analysis of consequences in the Level 3 PRA model.

The requested information is needed in order for the NRC staff to reach a conclusion on the acceptability of PG&Es Level 3 PRA model for supporting the SAMA evaluation.

a. In Section F.3.1 of the ER, it is stated that The MACCS2 code is being used in a slightly updated fashion ... Clarify what is meant by updated fashion.

b. In Section F.3.1 of the ER, uncertainty is discussed. Briefly describe/expand why the mean consequence is expected to be minor (e.g., there are no single contributing effects that could significantly impact the mean).

c. In Section F.3.2 of the ER, it is stated that Individual growth rates were calculated for each grid element based on the county growth rate and the proportion of land in each grid element associated with the applicable counties. Clarify that this is the county population averaged over the county area, and the population is then partitioned to the spatial elements by the land fraction? Also, address whether there were any high

population density regions near the edges of a spatial element that could distort the spatial assessment.

d. In Section F.3.2 of the ER, it is stated that projected populations were obtained from the California Department of Finance. Identify the date the data was accessed. Also, confirm that the population projections were taken directly from the California Department of Finance projections and not separately estimated by PG&E.

e. In Section F.3.3 of the ER, clarify what is the year 2012 CPI?

f. In Sections F.3.5 and F.4.5 of the ER, the original SAMA analysis used an electrical net power output of 1138 megawatt electric (MWe) and thermal output of 3411 megawatt thermal (MWt). The current SAMA analysis uses an electrical net power output of 1180 MWe and thermal output of 3411 MWt. Discuss why the thermal power is not increased with the increased electrical output. If the thermal power should be increased, address the potential impact on the core inventory and the SAMA analysis results.

g. In Section F.3.6 of the ER, it is stated that An additional 15 minutes is added to the ETE evacuation times to account for processing time by offsite officials. Briefly describe the processing required by offsite officials.

5. Provide the following information with regard to the selection and screening of Phase I SAMA candidates. Basis: Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, NRC staff is evaluating PG&Es basis for the selection and screening Phase I SAMA candidates. The requested information is needed in order for the NRC staff to reach a conclusion on the adequacy of PG&Es Phase I SAMA selection and screening process for the SAMA evaluation.

a. Section F.5.1.2 of the ER indicates that the types of strategies called for in the DCPP Severe Accident Mitigation Guidelines to mitigate and recover from severe accidents are not included as SAMAs because they are already implemented at the site. Discuss if credit for these strategies is included in the current DCPP PRA model (DC03SA).

b. Review of Importance analysis

i. In a number of the discussions of potential SAMAs from review of importance lists, phrases such as In most of the scenarios..., "The significant sequences... or Some of the larger contributors... are used. Discuss in general terms what is meant by these phrases and the possibility of identifying potential SAMAs from the portion of the event impact that is not included in most of the scenarios, the significant sequences or some of the larger contributors.

ii. For events PRB1A and PRC1A (PG&E Letter DCL-15-080, Table 4, pp. 10 and 19), both involving fire induced loss of cooling accidents (LOCAs), would additional fire barriers be a feasible SAMA to limit the impact of the relevant fires?

iii. For event RF3Z (PG&E Letter DCL-15-080, Table 4, p. 12), Fire: switchover to recirculation after SLOCA degraded instrumentation, SAMA 7 to automate the swap is proposed. Discuss if the fire procedures provide guidance specific to these fires and if they do not, the potential for developing these procedures as a viable alternative SAMA.

iv. SAMA 9, identified to mitigate event AW4, support for both motor-driven (MD) pumps unavailable (PG&E Letter DCL-15-080, Table 4, p. 14), includes spray barriers to protect the turbine-driven (TD) AFW pump as well as MD pumps that can operate submerged. Discuss the potential and effectiveness for a SAMA that would only include the TD pump spray barriers.

v. SAMA 11, to install a swing Residual Heat Removal (RHR) pump, is proposed to mitigate events LA1 and LB2 (PG&E Letter DCL-15-080, Table 4, pp. 15 and 16),

involving failure of RHR pumps to start and run which results in loss of recirculation capability and containment heat removal. Consider improvements in the feed and bleed capability and other, less expensive means for providing containment heat removal capability.

vi. SAMAs 2 and 18, both involving engine driven pumps, are identified to mitigate fire induced failures of 4 kV Bus F (event AZAF3, PG&E Letter DCL-15-080, Table 4,

p. 16). Discuss the potential for SAMAs to directly impact the causes or severity of the relevant fires.

vii. For event AWFZ (PG&E Letter DCL-15-080, Table 4, p. 18), no support for AFWP2, AFWP3 and fire impacts AFWP1, discuss the potential for additional fire barriers as a SAMA to limit the impact of the relevant fires.

viii. For events SDS1, reactor coolant pump (RCP) shutdown seals fail to actuate (PG&E Letter DCL 080, Table 4, p.23), SAMA 18, consisting of engine driven high pressure RCS and steam generator (SG) injection pumps is evaluated. For event SPCET3 (PG&E Letter DCL-15-080, Table 5, p. 35), RCP seal cooling unavailable, SAMA 2, an engine driven SG injection pump is evaluated. Consider a SAMA that provides only alternative seal cooling for mitigating both of these events.

ix. Event OR1 (PG&E Letter DCL-15-080, Table 4, p.23), operator cooldown and depressurize RCS, indicated to be associated with SGTRs combined with failure to isolate the ruptured SG, and Event OX1 (Table 5, p. 36), operator decides to isolate the ruptured SG, are both mitigated by SAMA 19 to install primary side SG isolation valves. Consider a SAMA for improving the procedures and training or automating the ruptured SG isolation function.

x. The top contributor to Event CD1FL (PG&E Letter DCL-15-080, Table 4, p. 31) is described as a flood sequence from reactor water storage tanks (RWST) breaks in the fuel handling building. SAMA 18, portable engine driven high-pressure RCS and SG injection pumps, is identified to mitigate this event. Consider the potential for alternative SAMAs involving use of flood barriers and alternate supplies to make up for the loss of RWST.

xi. The top contributors to Event GXH (PG&E Letter DCL-15-080, Table 5, p. 48) are described as flooding events in the AFW rooms. Consider the potential for flood barriers to mitigate these floods.

c. The discussion in Section F.5.1.3.7 of Grand Gulf SAMA 59 indicates that, except for the third non-safety centrifugal charging pump, high head injection and low pressure pumps are dependent on the component cooling water (CCW) system. Also Figure F.2-1 indicates that loss of the CCW leads to 13 percent of the internal events CDF. Consider a SAMA similar to Grand Gulf's SAMA 59, Increase operator training for alternating operation of the injection and low pressure pumps for loss of CCW scenarios in addition to the alternate means described for DCPP.

d. For SAMA 10, provide an alternate DC generator, discuss the availability of such a generator as part of other programs such as B.5.b and Diverse and Flexible Coping Capability (FLEX).

e. For a number of the Phase I SAMAs included in Table F.5-3, the statement "This SAMA is addressed by elements of the DCPP FLEX strategy." Discuss the implications of this relative to the inclusion of credit for this in the DCPP PRA, the cost of and further consideration of the associated SAMAs.

f. The table in Section F.5.1.7 (page F-91) uses the term site in the column headings.

Explain the use of site in this table.

6. Provide the following information with regard to the Phase II cost-benefit evaluations. Basis:

Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, the NRC staff is evaluating PG&Es cost-benefit analysis of Phase II SAMAs. The requested information is needed in order for the NRC staff to reach a conclusion on the acceptability of PG&Es cost estimations for individual SAMAs and cost-benefit evaluation.

a. Provide further information regarding the RISKMAN software quantification options mentioned on page 4 of PG&E Letter DCL-15-080, including the option originally used for SAMAs 2, 9, 10 and 12 and the option used in the updated results.

b. PG&E Letter DCL-15-080, describes a revised evaluation of the benefit of SAMA 8 "Protect RHR cables in fire areas 6-A-2 and 6-A-3." It is understood that the revised evaluation eliminates credit taken in the original evaluation for preventing damage to equipment not protected by SAMA 8. It is noted that the revised evaluation appears to include additional fire impact deletions from the base case model (changes to ELECPWR and FELECPWR) than the original analysis. This would be expected to increase rather than decrease the averted cost-risk. Provide a further discussion of the revised evaluation including the differences in model changes that lead to the reduced credit.

c. Section F.6.3 of the ER indicates that SAMA 5 reduces the CDF by 0.7 percent. This SAMA is identified in Table F.5-1 (p. F-178) to mitigate Event ZTDPHD which has a risk

reduction worth (RRW) of 1.05. Since this RRW corresponds to a CDF reduction of approximately 5%, SAMA 5 would appear to not be very effective in mitigating this event.

Discuss the reasons for this benefit quantification result and the potential for more effective SAMAs for this event.

d. The evaluation of SAMA 9 in Section F.7.2.1.4 (p. F-119) of the ER indicates that protecting the pumps is simulated by removing the fire initiators from the impacted areas. Discuss how this simulates providing spray barriers and waterproof pumps. If this is due to flooding due to fire protection system initiation in response to a fire, discuss the potential for flooding due to fire protection system ruptures in these areas.

e. Section F.7.4 of the ER states "In order to assess the impact on the Phase 2 screening, the truncated frequency was assumed to be proportional to the CDF, and for each SAMA quantification, the truncated frequency was likewise binned to the ST5 release category." Provide further information on this process including the assumed reduction in ST5 release category frequency caused by a SAMA. Illustrate with a numerical example.

f. As indicated in ER, Amendment 2, Section 4.20, the original SAMA found that when the 95th percentile PRA results were considered, SAMAs 12, 13, 24, and 25 were potentially cost beneficial. These original analysis SAMAs are:

SAMA 12: Improve fire barriers for auxiliary saltwater and component cooling water equipment in the Cable Spreading Room SAMA 13: Improve cable wrap for the power operated relief valves in the Cable Spreading Room SAMA 24: Prevent clearing of reactor coolant system Cold Leg Water Seals

SAMA 25: Fill or maintain filled the Steam Generators to scrub fission products Discuss the current relevance of these SAMAs and their potential for being cost-beneficial in the updated analysis. If appropriate, identify plant or modeling changes that made these SAMAs no longer applicable.

g. Section F.6 of the ER states that plant personnel developed DCPP-specific implementation cost estimates for each of the SAMAs. Address the following:

i. Provide a description of: the process PG&E used to develop the SAMA implementation costs, the level of detail used to develop the cost estimates (e.g.,

general cost categories such as hardware design, procurement, installation, and testing, as well as procedure development, quality assurance and licensing support, etc.), and how the calculations are documented.

ii. Provide the details of the cost estimates for SAMAs 5, 10, 12, and 22.

7. For certain SAMAs considered in the DCPP Environmental Report, there may be lower cost or more effective alternatives that could achieve much of the risk reduction. In this regard,

provide an evaluation of the following SAMAs. Basis: Applicants for license renewal are required by 10 CFR 51.53(c)(3)(ii)(L) to consider SAMAs if not previously considered in an environmental impact assessment, related supplement, or environmental assessment for the plant. As part of its review of the DCPP SAMA analysis, the NRC staff is evaluating additional SAMAs that may be more effective or have lower implementation costs than the SAMAs evaluated by PG&E. The requested information is needed in order for the NRC staff to reach a conclusion on the adequacy of PG&Es determination of cost-beneficial SAMAs.

a. For SAMA 1, install a Minimum CCW Cooling Flow Line around the RHR Heat Exchanger Outlet Valve, consider a modification to the outlet valve internals to allow a minimum CCW flow even when the valve is closed.

b. SAMA 2, provide an engine-driven SG makeup pump, is proposed to mitigate event AWR1, Failure to supply water from fire water storage tank or raw water reservoir (non-seismic). This SAMA is screened in Phase I as having a cost well in excess of Maximum Averted Cost-Risk (MACR). Discuss the potential for less expensive SAMAs such as procedure changes, automating the backup water supply or increasing the capacity of the condensate storage tank (CST).

c. SAMA 4, provide a seismically qualified response system, is proposed to mitigate a number of sequences involving seismic Alternating Current (AC) and/or Direct Current (DC) system failures. Consider the potential for strengthening the weakest link in these systems to provide at least one source of AC and/or DC power at a considerably lower cost than SAMA 4.

d. SAMAs 9 and 17, install spray barriers to protect the TD AFW pump and install a waterproof AFW pump, and install flood sensors are proposed to mitigate fire protection system pipe breaks. As a low cost alternative for flooding in general, discuss the potential for using mobile sump pumps (including hose/pipes and power supplies).

DiabloCanyonNPEm Resource From: Wentzel, Michael Sent: Thursday, October 08, 2015 12:17 PM To: Terrence Grebel (TLG1@pge.com)

Subject:

Draft RAIs for the DCPP SAMA Review Attachments: Requests for Additional Information Related to the Diablo Canyon LRA Environmental Review

- SAMA.docx

Terry, Attached is a draft of the SAMA RAI letter. Once you had a chance to review, please let me know if you would like to have a phone call to clarify.

Thanks, Mike Michael Wentzel Project Manager NRR/DLR/RPB2 (301) 415-6459 michael.wentzel@nrc.gov 1

Hearing Identifier: DiabloCanyon_LicenseRenewal_NonPublic Email Number: 3175 Mail Envelope Properties (a9253d08b430402fae58913bb90a1574)

Subject:

Draft RAIs for the DCPP SAMA Review Sent Date: 10/8/2015 12:17:04 PM Received Date: 10/8/2015 12:17:05 PM From: Wentzel, Michael Created By: Michael.Wentzel@nrc.gov Recipients:

"Terrence Grebel (TLG1@pge.com)" <TLG1@pge.com>

Tracking Status: None Post Office: HQPWMSMRS03.nrc.gov Files Size Date & Time MESSAGE 339 10/8/2015 12:17:05 PM Requests for Additional Information Related to the Diablo Canyon LRA Environmental Review -

SAMA.docx 89683 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received:

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 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:

REQUESTS FOR ADDITIONAL INFORMATION RELATED TO THE ENVIRONMENTAL REVIEW OF THE DIABLO CANYON POWER PLANT, UNITS 1 AND 2 LICENSE RENEWAL APPLICATION - SEVERE ACCIDENT MITIGATION ALTERNATIVES (TAC NOS. MF4019 AND MF4020)

Dear Mr. Halpin:

On November 23, 2009, Pacific Gas & Electric Company (PG&E) submitted an application pursuant to Title 10 of the Code of Federal Regulations (CFR) Part 54 to the U.S. Nuclear Regulatory Commission (NRC) for renewal of operating licenses DPR-80 and DPR-82 for Diablo Canyon Power Plant (DCPP), Units 1 and 2. In accordance with 10 CFR Part 51, PG&E submitted an environmental report as an appendix to the license renewal application for DCPP.

On December 22, 2014, and February 25, 2015, PG&E amended its environmental report to incorporate additional information necessary for the NRC staff to complete its review of the DCPP license renewal application. The staff is reviewing the information contained in the environmental report, as amended, and has identified in the enclosure, areas where additional information is needed to complete the review.

These requests for additional information were discussed with Terry Grebel and a mutually agreeable date to respond is within 30 days from the date of this letter. If you have any questions, please contact me at (301) 415-6459, or by e-mail at michael.wentzel@nrc.gov.

Sincerely, Michael J. Wentzel, Project Manager Projects Branch 2 Division of License Renewal Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

As stated cc w/encl: Listserv

concurrence via email OFFICE LA:DLR* PM:RPB2:DLR BC:RPB2:DLR PM:RPB2:DLR NAME MWentzel JDanna MWentzel DATE Letter from M. Wentzel to E. Halpin dated XXXX