ML102930180

Lr - SAMA Clarifications

ML102930180
Person / Time
Site:	Diablo Canyon
Issue date:	10/20/2010
From:	Office of Nuclear Reactor Regulation
To:	Division of License Renewal
References
Download: ML102930180 (7)

Text

1 DiabloCanyonNPEm Resource From:

Stuyvenberg, Andrew Sent:

Wednesday, October 20, 2010 11:01 AM To:

Grebel, Terence Cc:

Tan, Miranda; DiabloCanyonNPEm Resource

Subject:

SAMA Clarifications Attachments:

Draft Diablo Canyon Clarifications to SAMA RAI Responses_ALS.docx Terry, Miranda -

Attached are the SAMA clarifications that I received from our reviewers. Once you have an opportunity to review them with your staff, I would like our staff to discuss them with your staff via a teleconference to determine which of them will require formal responses and to be sure that the requests themselves are clear.

Our staff is unavailable next week, though its possible that I may be able to find some availability yet this week. Our staff should be available the week following next.

Best, Drew DrewStuyvenberg U.S.NuclearRegulatoryCommission 3014154006 Andrew.Stuyvenberg@nrc.gov

Hearing Identifier:

DiabloCanyon_LicenseRenewal_NonPublic Email Number:

2002 Mail Envelope Properties (AF843158D8D87443918BD3AA953ABF7819C7767CE2)

Subject:

SAMA Clarifications Sent Date:

10/20/2010 11:01:17 AM Received Date:

10/20/2010 11:01:20 AM From:

Stuyvenberg, Andrew Created By:

Andrew.Stuyvenberg@nrc.gov Recipients:

"Tan, Miranda" <M1TF@pge.com>

Tracking Status: None "DiabloCanyonNPEm Resource" <DiabloCanyonNPEm.Resource@nrc.gov>

Tracking Status: None "Grebel, Terence" <TLG1@pge.com>

Tracking Status: None Post Office:

HQCLSTR02.nrc.gov Files Size Date & Time MESSAGE 688 10/20/2010 11:01:20 AM Draft Diablo Canyon Clarifications to SAMA RAI Responses_ALS.docx 24162 Options Priority:

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1 REQUEST FOR CLARIFICATION REGARDING PG&E RESPONSES TO DIABLO CANYON POWER PLANT (DCPP)

SAMA RAIs

1. RAI 1.e The response to this RAI states that SBO due to LOOP initiating events accounts for 6%

of the CDF. What is the contribution from consequential LOOPs for other initiating events?

2. RAI 1.f

a. Confirm that the modeling of Unit 2 systems in the Unit 1 PRA takes into account the operational and maintenance status of Unit 2.

b. The response to this RAI does not include mention of a two unit LOOP. This would impact the availability of the Unit 2 EDGs. Discuss this and any other two unit initiating events

3. RAI 1.g The response to this RAI (Some important component variables that increased in failure rate include the emergency diesel generator ) implies that there are other important component failure rates that have increased. If this is true identify other important variables that have increased and their potential impact on the SAMA analysis.

4. RAI 1.i The response to this RAI indicates that the DC00 stage 1 model reviewed in the PWROG peer review is different than the DC00 model described in Section F.2.1.6 of the ER.

Identify the most significant changes made to the prior model to obtain the DC00 stage 1 model and the most significant changes made in the DC00 stage 1 model to obtain the DC00 model. Also provide the internal events, fire and seismic contributions to the total CDF.

5. RAI 1.k The response to this RAI states Given that the PRA impact of each of the open items is small, their resolution is not expected to change the conclusions of the SAMA analysis.

Further it is stated that the exercise in re-evaluating the SAMAs using the 95th percentile more than bounds the impact of PRA open items found in Addendum 1. While the evaluation of the open items in Addendum 1 concludes for most of the items that the impact of the PRA is insignificant or that the results are conservative. This is not the stated conclusion for all the items. For some items, the acceptability of the current model is stated to be that a SAMA has been identified that addresses the stated impact of the model deficiency. While this may partially justify the adequacy of the model for the

2 SAMA identification process, it does not justify the adequacy of the model for the cost-benefit analysis. Further, the assessment at the 95th percentile is intended to provide insights associated with the uncertainty in input parameters not in the best estimate model. Provide further justification for those open items for which the conclusion of no impact on the SAMA identification process described in Addendum 1 is not necessarily applicable to the SAMA cost benefit analysis. In the response, specifically address SAMAs 727 (p. F-277), 289 (p. F-309), 419 (p. F-315), 420 (p. F-315), and 431 (p. F-317),

6. RAIs 2.b and 2.c The response to RAI 2.c indicated that ST4 is made up solely of RC17 while ST 5 is made up solely of RC18. The frequencies for these RCs provide in response to RAI 2.b are different from those provided for ST4 and ST5 in Table F.3-7 of the ER as shown below.

Freq. In Table F.3-7 Freq. In RAI 2.b Response ST4 RC17 1.23E-06 1.34E-06 ST5 RC18 2.88E-07 1.82E-07 It appears from the response to RAI 2.e that a portion of the SGTR events (RC17) is allocated to ST5. Clarify the derivation of these ST frequencies.

7. RAI 2.c The response to this RAI indicates that the grouping of the 37 release categories into 6 source term categories was performed in a manner similar to that described in IPE Section 4.8. The IPE release category groups were stated to be for the purposes of gaining insights. In the SAMA analysis the Source Term categories function to provide a representation of radioactive release that can be used in the level 3 analysis to provide a reasonable estimate of the consequences. The IPE release category groups termed small and large are based on containment break size and not amount of fission products released. The appropriateness of the release category grouping for providing source terms that yield a reasonable consequence analysis is not clear. Provide further justification for the appropriateness of the release categories assigned to the source term categories and of the resulting consequence analysis.

8. RAI 2.d and 2.e The response to RAI 2.d indicates that the representative MAAP case chosen for each source term category for the consequence analysis was based on their contribution to the total RC (ST) frequency. This approach does not account for release categories of lower frequency but higher release fractions.

The response to RAI 2.e indicates that for small early releases (ST2) the release category selected (RC14) represents over 50% of the RC frequency and would tend to represent

3 the highest consequence conditions. RC16U makes up 36 % of the ST2 category and appears to be similar except that the debris is uncoolable.

Provide further support for the selection of representative cases for each ST category and specifically confirm that use of RC16U release fractions would not result in a higher dose-risk or OECR.

Also clarify the use of the term release category versus source term category in the response to this RAI. For example, in the above discussion and the discussion of containment bypass.

9. RAI 2.h The response to this RAI indicates that no post core damage recoveries are included in the L2 model (except, for limited cases, containment isolation). Is recovery of AC power post core damage credited?

10. RAI 2.j

a. The response to this RAI notes that the individual fission product release shows a stable condition at the end of the simulation except for the noble gas release for ST2 and ST6 which does increase beyond the 50 hour5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> analysis cut off, but that the sensitivity analyses described in the ER bound the potential impact on the SAMA analysis. However, the release fractions reported in Table F.3-6 are in many cases appreciably less than those reported in Table F.2-8. For example, the total release fraction for ST2 noble gases is shown to be 0.36 in Table F.3-6 and 0.89 in Table F.2-8 (similar results are shown for other source terms), suggesting that the dose-risk could potentially be double that reported in the ER for ST2. Provide further justification for the conclusion in the RAI response that the simulation time cut off does not impact the results of the SAMA analysis

b. The response to this RAI also notes the potential for onsite or offsite mitigation measures for releases that extend beyond the simulation time.

Provide a discussion of these mitigation measures and clarify the reason for why these measures were not considered as SAMAs.

11. RAI 3.c

a. A portion of the response to this RAI discusses the evaluation of SAMA 18 and that credit could not be taken for seismic events larger than 1.75g because most of the Class I equipment needed for safe shutdown is only seismically qualified up to that level. While this may be true, is it possible that sufficient equipment needed for safe shutdown may have a realistic capacity above 1.75g so that all the modification included in SAMA 26 is not needed. Discuss this potential.

4

b. Updated results are provided for SAMAs 5, 9 and 18. Relative to these SAMAs provide the following:

i. Given that the change in results is substantial for each SAMA, it appears that the Assumptions and the PRA Model Changes Made to Model SAMA descriptions in the ER may have changed for these SAMAs. Provide updated Assumptions and PRA Model Changes Made to Model SAMA for each of these SAMAs.

ii. The revised evaluations of SAMAs 5 and 18 did not include the revised quantification method provided in response to RAI 6.o even though the change in dose-risk and OECR was greater than the change in internal event CDF. Provide an updated evaluation of SAMAs 5 and 18 for both the DC01A and DC01B models that uses the revised quantification method described in the response to RAI 6.o.

iii. Table 3.C-3 indicates that SAMA 9, evaluated using the DC01B model, is potentially cost-beneficial. Provide the detailed cost-benefit results for the DC01A model. Also, describe PG&Es plans regarding further evaluation of this SAMA and any other SAMAs determined to be cost-beneficial in response to RAIs.

c. Table 3.C-3 provides the change in averted cost-risk due to the change in seismic hazard modeled in DC01B and other non-seismic related changes made to other SAMAs in response to RAI 3.c and RAI 6.o. However, the averted cost-risk was reported to have changed for all SAMAs, even those that were not impacted by RAI responses (e.g., SAMAs 2, 7, 8, and 12-17).

Describe the significant changes made to PRA Model DC01A to develop PRA Model DC01B.

12. RAI 3.d The third highest seismic CDF sequence is described as involving seismic failure of the auxiliary feedwater system. A review of the importance analysis provided in response to RAI 3.c includes important events (OB1SE and AW1S) that are described to include AFW failure due to operator error. Clarify the cause of AFW failure for this sequence.

13. RAI 3.e The response to this RAI attributes the changes in FS type fire scenario results to routine changes in the internal events models that are used in evaluating the FS fire scenarios as opposed to relatively minor changes in the CSR1/CSR2 fire scenarios that utilize their own simplified event trees that have not had as many changes. The reason for the reduction in the VB1 fire scenario CDF contribution from the IPEEE is not discussed. As the IPEEE notes, this control room fire scenario utilizes its own special event tree and not

5 the internal events event tree. Discuss the reasons for the reduction in the VB1 fire scenario CDF from that given in the IPEEE.

14. RAI 5.b The response to this RAI discusses the potential for a specific cost beneficial SAMA (strengthening a block wall) that focuses on one of the contributors to a split fraction rather than a SAMA that addresses the overall function represented by the split fraction.

While this particular SAMA may not be cost beneficial, it does illustrate that there are potential SAMAs that can be identified from a review of the individual contributors to a split fraction. It is stated that basic event level results are often reviewed during the sequence analysis to determine what the dominant contributors to a split fraction may be, but that the process is not documented. Provide further assurance that a review of the basic event contributors to the important split fractions will not yield additional SAMAs that may be cost beneficial.

15. RAI 6.e The response to this RAI indicates that there is a 2% reduction in the seismic CDF for SAMA 3 and that the cost benefit analysis results are provided in response to SAMA RAI 3.c. Table 3.C-2 indicates that there is no change in seismic CDF for SAMA 3. Clarify and provide complete CDF results and the C/B evaluation for SAMA 3 for the DC01A and DC01B models. Also update the response to RAI 6.o for SAMA 3.

16. RAI 7 The response to this RAI dismisses the feasibility of using a gagging device for closing a SG SV based on the challenging work environment. Expand on this rationale particularly if gagging is implemented for a SGTR prior to the onset of core damage. If considered feasible in this situation, provide an assessment of the cost-benefit of using such a device.