ML12115A101

RAI on SAMA for the Review of the Grand Gulf Nuclear Station, Unit 1, LRA Er

ML12115A101
Person / Time
Site:	Grand Gulf
Issue date:	05/21/2012
From:	David Drucker License Renewal Projects Branch 2
To:	Mike Perito Entergy Operations
Drucker D, 415-6223
References
Download: ML12115A101 (10)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 May 21,2012 Mr. Michael Perito Vice President, Site Grand Gulf Nuclear Station Entergy Operations, Inc.

P.O. Box 756 Port Gibson, MS 39150 SUBJECT REQUEST FOR ADDITIONAL INFORMATION ON SEVERE ACCIDENT MITIGATION ALTERNATIVES FOR THE REVIEW OF THE GRAND GULF NUCLEAR STATION, UNIT 1, LICENSE RENEWAL APPLICATION

Dear Mr. Perito:

By letter dated October 28, 2011, Entergy Operations, Inc. (Entergy), submitted an application pursuant to Title 10 of the Code of Federal Regulations Part 54 (10 CFR Part 54), to renew Operating License NPF-29 for Grand Gulf Nuclear Station, Unit 1, for review by the U.S.

Nuclear Regulatory Commission (NRC or staff). The NRC is reviewing the information contained in the license renewal application and the associated Environmental Report. The staff has identified areas where additional information is needed to complete the review in the attached enclosure. Additional requests for additional information may be issued in the future.

As discussed with Mr. Rick Buckley of your staff, we request that you provide your responses no later than 60 days from the date of this letter. If you have any questions, please contact me at 301-415-6223 or bye-mail at david.drucker@nrc.gov.

Sincerely, David Drucker, Sr. Project Manager Projects Branch 2 Division of License Renewal Office of Nuclear Reactor Regulation Docket No. 50-416

Enclosure:

As stated cc w/encl: Listserv

Requests for Additional Information on the Grand Gulf Nuclear Station Analysis of Severe Accident Mitigation Alternatives 1, Provide the following information regarding the Probabilistic Risk Assessment (PRA) used for the Severe Accident Mitigation Alternative (SAMA) analysis. References to Section E are to Section E of the Environmental Report (ER).

a. Section E.1.1 indicates there have been no major plant changes since August 2006 that would have a significant impact on the results of the SAMA analysis. Define "significant" and how this determination was made.

b. Section E.1,4 provides a summary of the Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) from Grand Gulf Nuclear Station (GGNS) probabilistic safety analysis modeling between 1992-2010. Section E.1.4.2 indicates that the update included plant changes through refueling outage 11, but does not specifically list these changes. Identify the major changes with the greatest influence on the SAMA analysis,

c. Section E.1.4.3 indicates the last plant data update covers the period through August 2006. Provide assurance that there are no equipment reliability degradation issues since this update that would adversely impact the SAMA analysis.

d. On page 1-23, the ER indicates that the ratio of the 95 th percentile to the mean is about 2.38. Since point estimates of the CDF and release category frequencies were used rather than mean values, provide the 95 th

_, 50 th

_, and 5 th -percentile CDF results of the uncertainty analysis as well as the point estimate CDF of the model and truncation used for the uncertainty analysis.

e. Differences exist within the license renewal application among quantitative results for CDF, release category frequencies, and Risk Reduction Worth (RRW). The total CDF was presented as 2.05E-06 per year, from the sum of contributions by initiator (Table E.1-1) and sum of the release frequencies (Table E.1-8), and 2.92E-06 per year from the sum of the accident classes (Table 1-7), The applicant's submittal states that the 2.9E-06 value is higher than the others due to non-minimal cutsets, which result from quantifying at the sequence level. Although some difference is expected, the difference of approximately 40% appears to be unusually large for this cause. Further, the sum of the release category frequencies would be expected to be higher since it is also the result of a sequence by sequence quantification, The CDF contribution from various failures implied by RRW values in Table E.1-2 are also significantly different in some cases from those given in Table E.1-1 or Table E.2-2. For example:

Table 1-1 showed the CDF initiated by loss of offsite power (LOSP) as 14% of the total CDF, yet Table E.1-2 indicated a RRW value of 1.6289 for LOSP, which corresponds to a 38,6% contribution.

• Case 1 was evaluated by eliminating all cutsets for station blackout (SBO), and the CDF is stated to be reduced by 13.6%. Table 1-1 indicates that SBO contributes to 36.6% of the CDF. Based on the values of RRW, the elimination ENCLOSURE

2 of basic events "ZSBO" and "ZT1 B" cited for Case 1 supports a 36.3% reduction in CDF.

• Case 22 on improved availability of the diesel generator system through heating, ventilation, and air conditioning (HVAC) improvements was stated to be evaluated by eliminating HVAC failure in diesel generator rooms which results in a 9.2% reduction of CDF. Basic event X77-FF-CFSTARTU, "X77 common cause start failures," has a RRWof 1.2754, which corresponds to a 21.6% reduction in CDF.

SAMA Number 63 cited for basic event E51-043-G, "Lube oil cooling line hardware failure," in Table E.1-2 is evaluated by Case 46. The CDF reduction given in Table E.2-2 was 4.7%. The RRW given for this basic event is 1.0839, which corresponds to a CDF reduction of 7.7%.

In light of these differences among results, further support for the validity of the model quantification (i.e., CDF, release category frequencies, and RRW) in the SAMA analysis is needed. Provide reasons for these differences and more details on how the quantification was performed for each situation, including examples related to this request. Describe specific contributions to the approximate 40% difference in CDF, such as some of the non-minimal cutsets or other reasons. Justify use of the lower CDF, rather than the higher CDF, for determining cost risk in the SAM A analysis.

f.

Section 1.4.5 indicates that all of the 'B' priority comments have been addressed except for one documentation item related to the internal flood modeling. If any facts and observations (F&Os) were addressed by internal reviews that concluded that changes to the model were not needed or the F&O was incorrect, identify and discuss these F&Os and confirm their disposition remains applicable to the PRA used for the SAMA analysis.

g. Discuss the process and procedures for assuring technical quality of PRA updates since the peer review.

h. Section E.1.4 includes an unnumbered table of changes in contribution to CDF per initiator group for each model revision beginning on page 1-70 titled, "Contribution to CDF Changes in PRA Models." The percentage contributions shown for R3 EPU (Revision 3, Extended Power Uprate version of the PRA model) are Significantly different from those shown in Table E.1-1. Explain the basis for the unnumbered table in Section E.1.4 and the reasons for the differences from Table 1-1.

2. Provide the following information relative to the Level 2 analysis:

a. Provide a brief history of the Level 2 Probabilistic Safety Assessment and key modeling changes that may have influenced the release category frequencies. Identify steps taken to assure technical adequacy.

b. Section E.2.2.6 provides a summary of how a value for each release-to-environment mass fraction was obtained from the representative Modular Accident Analysis Program (MAAP) calculation per Containment Event Tree (CET) sequence. Table E.1-8

- 3 results of the CET quantification and identifies total annual release frequency per Level 2 release category. Provide further information on:

i.

Criteria used for assignment of release categories to each CET endpoint ii.

Process to determine the representative sequence for quantifying the release fractions for each release category iii. How the weighting of release fractions discussed on page evaluation of benefit for potential SAMAs 1-54 affects the

c.

Identify and describe the representative sequences for each release category. If the representative sequence for each release category is the one with the highest frequency but is not the one with the highest source term, justify this selection for determining the benefit of potential SAMAs, particularly for impacts to the sequences with higher source terms that may be greater than the impact to the representative sequence.

d. Section 1.2 defines release category (RC) based on the magnitude of Csi (Cesium iodide) release with High (H) being> 10%, Medium (M) being between 1% and 10 %,

etc. The release fractions given in Table E.1-9 are not necessarily consistent with these definitions. For example, the RC High/Early (H/E) frequency is given as the LERF yet the Cs release fraction is less than 10%. Provide the rationale for the release fraction selection and discuss its impact on the validity of the SAMA benefit analysis.

e. Figure E.1-1 indicates that negligible releases (NCE or NCF for no containment failure) account for 44% of the total CDF. Identify the CET end states that comprise this release category and how the frequency for this release category was determined.

f.

In Table E.1-9 (Sheet 1 of 2), some release timings do not agree with the Release Mode timing categories. For example, the start of release minus the warning time is 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> for Release Mode Medium/Early (M/E), but the timing for an early (E) release is defined to be less than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The start of release minus the warning time is 12 minutes for Release Modes Low/Intermediate (LlI) and Low-Low/Intermediate (LLlI), but the timing for an intermediate (I) release is defined to be between 4 and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Discuss the reasons for this lack of agreement, including the plant damage states and CET end states that contribute to these Release Modes, and the impact on the SAMA assessment.

g. Table E.1-9 (Sheet 2 of 2) does not include source terms for the NCF release category, and it is not included in the consequence analysis. For this category, Table E.1-5 indicates a release fraction of 0 for cesium iodide and describes it as negligible. With a frequency for NCF many times higher than the other categories, design basis leakage without containment failure might lead to atmospheric releases similar to or even higher than those given for Low-Low/Early (LLlE) and Low-Lowllntermediate (LLlI) release categories in Table 1-9. Provide further support for exclusion of the I\\JCF release category from the consequence analysis and confirm that design basis leakage is considered in developing the source terms for the LLIE and LLII release categories.

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h. At the time of the Grand Gulf extended power uprate submittal, there was a peer review comment related to failure to model vacuum breakers, low suppression pool level, and personnel hatch seal, which had not been addressed in the Level 2 model. Provide the resolution status of this peer review comment If not treated in the current Level 2 model for license renewal, justify the current modeling with respect to this issue and describe its impact on the SAMA assessment

3. Provide the following information with regard to the treatment and inclusion of external events in the SAMA analysis:

a. Section E.1.3.2 states that Table E.1-1 0 presents the results of the current GGNS Individual Plant Examinations for External Events (IPEEE) fire analysis. Explain what is meant by "current" as it relates to IPEEE. If the IPEEE analysis has been revised or new fire analyses performed, describe the revision and present its results.

b. Section 4.21.5.4 indicates that seismic risk is negligible in the estimation of external events multiplier. The August 2010 report, "Generic Issue 199 (GI-199), entitled Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants, shows a decrease in the GGNS seismic CDF when the 2008 United States Geological Survey (USGS) seismic hazards curve is used compared to the seismic CDF resulting from the 1994 Lawrence Livermore National Laboratory hazard curves but an increase compared to the seismic CDF based on the Electric Power Research Institute (EPRI) hazard curves. For the simplified approach to estimate the CDF from a seismic margins analysis using the latest published USGS seismic hazards information, GGNS seismic CDF may be about or slightly less than 10-5/year.

Discuss the impact of the aforementioned considerations on the SAMA analysis.

c. Section 3.2.1 discusses conservatisms in the GGNS IPEEE fire analysis. Recent research and guidance reported in NUREG/CR-6850, specifically in the areas of hot short probabilities, fire ignition frequencies, and non-suppression probabilities, indicate that the fire analysis methodologies utilized for the Individual Plant Examinations (I PEs) may underestimate fire risk. Provide assurance that consideration of this information is not expected to impact the selection of cost beneficial SAMAs for GGNS. Discuss the impact on the evaluation of potential SAMAs for fire risk contributors in addition to the use of the external events multiplier.

d. For SAMAs 240-244, Table E.2-1 states:

The IPEEE showed the risk from external flooding at GGNS is minor.

Thus this potential modification is assumed not to be cost beneficial, which follows the same assumption in the NRC safety evaluation report.

- 5 The GGNS I (p. 116) includes the following:

Applying the new criteria, the bulk of the precipitation would occur over a shorter time frame, and markedly higher rainfall intensities would result.

As a result, the GGNS site is not expected to be completely protected against external flooding without making some site modifications.

Evaluation reveals that the following site drainage/flood protection improvements would allow for adequate protection of the site against external flooding due to the revised criteria. However, they are not necessarily the only combination of potential changes for consideration.

Given the small probability of occurrence for the PUTP, as described in the preceding paragraph, the relative cost and benefit for potential improvements will be considered prior to implementation of any physical improvements.

While the staff review of the IPEEE as documented in the IPEEE SER did not require implementation of the items listed as SAM As 240-244, this alone does not imply that they should be eliminated from further consideration. In light of the second sentence from the GGNS IPEEE above, provide a discussion of the cost benefit analysis concerning external flood modifications and its influence on conclusions of the SAMA analysis.

4. Provide the following information relative to the Level 3 analysis:

a. In Section E.1.5.2.1, it was stated that "Louisiana and Mississippi state tourism data was used to calculate a transient to permanent population ratio to increase each county's projected population to account for visitors." Clarify how transient population was used in the SAMA analysis.

b. Section E.1.5.2.6 indicated meteorological data from 2009 were selected for the analysis because they resulted in the highest release quantities. Describe the source of precipitation data, modeling of precipitation events, and precipitation influence on calculated doses. Quantify the amount of missing meteorological data, which were estimated using data substitution.

c. Table E.1-12 lists radionuclides in the GGNS core and provides the core inventory for each radionuclide. Table E.1-9 presents release fraction groups used in the Level 3 analysis for calculating radiological doses. Confirm that all radionuclides in the core inventory were used in the radiological dose calculations or explain any differences.

d. Indicate if any changes in future fuel management practices or fuel design are planned or being considered that would change the core inventory presented in Section 1.5.2.8.

5. Provide the following information with regard to the selection and screening of Phase I SAMA candidates:

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a. Provide the complete Phase I candidate SAMA list as described in Section E.2.1, SAM A List Compilation.

b. Describe basic event B21-FO-HEDEP2-1, "Operator fails to manually depressurize vessel with non-ADS valves," given in Table E.1-2. Comment on the potential for improvements in procedures and training to reduce this event.

c. A number of basic events in Table E.1-2 fail the High Pressure Core Spray (HPCS) or the Reactor Core Isolation Cooling (RCIC) and have relatively high RRWs in particular those involving HPCS valves, E22 F004 and E22 F012-C, and the RCIC steam supply valves. In all but one case, the potential SAMAs cited for these basic events involve costly major modifications. Describe the above cited valves and considerations of lower cost alternatives for reducing the impact of these HPCS or RCIC failures.

d. Basic events N21-FO-HEPCS-G, "Human error: Failure to properly align the PCS for injection," NRC-FO-FWSACT, "Failure to align FPW for long term injection," and P53-FOHECOOLlAS, "Operator fails to align SSWB to lAS compressor upon loss of TBCW," have high failure probabilities (1.0, 0.57, and 1.0, respectively). Discuss the potential for improved procedures and training (or possibly staging necessary equipment) to reduce these failure probabilities.

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

a. For many potential SAMAs, cost is taken from the Cooper Nuclear Station or other SAMA analyses. Although this may be valid for some potential SAMAs such as adding major systems/components, its validity is less certain for modifications to plant electrical or other systems for which the GGNS design may differ from the referenced plant (e.g" SAMA Numbers 4,6,26, 34,47, 54, and 55). Discuss steps taken to assure that the cited cost estimates are either valid for GGNS or underestimate the anticipated cost at GGNS.

b. Provide the release category frequencies for each Phase II SAMA

c. The descriptions for Case 6, Reduce Loss of Off-Site Power During Severe Weather, and Case 10, Reduce Plant-Centered Loss of Off-Site Power, indicate that LOSP initiating event frequencies were multiplied by 19/24 and 9/24 to account for severe weather and plant-centered causes of LOSP, respectively, This appears to imply that severe weather caused 5 of a total of 24 LOSP events while plant centered failures caused 15 of 24 LOSP events. Provide the basis for these values.

d. SAMA Number 14 {Provide a portable EDG [Emergency Diesel Generator] fuel oil transfer pump} was evaluated by Case 8 to eliminate failure of EDGs to run. The list of basic events set to zero does not include P81-FR-DG-G13-C, "DG13 fails to run."

Considering values of RRW, inclusion of this basic event might increase the CDF reduction to 5% and could make this potential SAMA cost beneficial. Discuss why DG13 was not included in the assessment, including its impact on the SAMA analysis.

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e. Explain how eliminating failure of hydrogen igniters in Case 32 leads to a 15.9%

reduction in CDF.

f. The description for Case 41, Trip/Shutdown Risk, indicates that certain initiating event frequencies were reduced by 10%. Table E.2-2 states they were reduced by a factor of 2. Confirm the amount of reduction.

g. With reference to the final paragraph of Section 4.21.5 of the ER, describe briefly the GGNS corrective action process incorporating the condition reports which have been initiated to implement the potentially cost-beneficial SAMAs.

7. Provide the following information with regard to the sensitivity and uncertainty analyses:

As provided in Section E.1.1, an uncertainty multiplier of 3 was applied to the cost-benefit analysis for potential SAMAs as a conservative selection to account for differences in the 95th-percentile CDF to the mean CDF. With uncertainty applied, Table E.2-2 indicates that three potential SAMAs (Numbers 13, 14, and 63) are within $10,000 of the stated cost estimate. Comment on the representativeness of the stated cost estimates compared to actual costs at GGNS and provide estimates of cost margin for these potential SAMAs.

8. For certain SAMAs considered in the GGNS Environmental Report, there may be lower-cost alternatives that could achieve much of the risk reduction. In this regard, provide an evaluation of the following SAMAs:

a. Phase II SAM A Numbers 30, 32, and 33 for adding or enhancing Emergency Diesel Generator (EDG) HVAC hardware were considered for basic events involving EDG HVAC failures. SAMA Numbers 30 and 33 involve expensive hardware modifications.

Evaluate the possibilities of opening doors and use of portable fans and ducts. SAM A Number 32 calls for adding diverse EDG HVAC logic. Consider procedures for operators to manually initiate EDG HVAC if the existing automatic logic fails. If no alarms are expected for any of these failures, procedures for the plant auxiliary operators to check on any automatic start of the EDG could allow HVAC failures to be discovered and might eliminate the need for alarms.

b. For SAMA Number 25 (Install a bypass switch to allow operators to bypass low reactor pressure interlock circuitry), consider providing directions to use jumpers to bypass the interlock.

c. For SAMA Number 35, consider the use of other air compressors (service air) that might be connected to the instrument air system instead of providing new compressors.

d. For Case 39 concerning control room fires, consider improving control room fire detection system response for a limited number of key cabinets.

ML12115A101

• concurred on letter only via e-mal OFFICE LADLR*

PM:RPB2:DLR BC:RPB2:DLR PM:RPB2:DLR NAME IKing DDrucker DWrona DDrucker DATE 4/26/12 5/8112 5/21/12 5/21/12

Letter to M. Perito from D. Drucker dated, May 21, 2012

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION ON SEVERE ACCIDENT MITIGATION ALTERNATIVES FOR THE REVIEW OF THE GRAND GULF NUCLEAR STATION, UNIT 1, LICENSE RENEWAL APPLICATION ENVIRONMENTAL REVIEW DISTRIBUTION:

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