ML15034A114

STP Risk- Informed Approach to GSI - 191 Roverd 2015 Meeting Blue 1 29 15

ML15034A114
Person / Time
Site:	South Texas
Issue date:	02/04/2015
From:	South Texas
To:	Plant Licensing Branch IV
Regner L
References
GSI-191
Download: ML15034A114 (38)

Text

STP Risk-Informed Approach to GSI-191 NRC Meeting February 4, 2015

STP Agenda

• Introduction

• Purpose and Desired Outcome

• Risk over Deterministic (RoverD) Assessment

• Technical Specification Concept

• Operability Considerations

• Expected Content of Application Supplement

• Areas for Clarification

• Conclusions 2

Purpose and Desired Outcome

Purpose:

Present to the NRC staff two changes, RoverD and a Technical Specification concept, that are expected to simplify review and resolve issues

• Desired Outcomes

- NRC staff understand proposed changes

- Identification of any issues with the changes and a path to resolution 3

STP Risk over Deterministic (RoverD):

Test-Based Debris Risk Assessment 4

RoverD motivation 1 Reduce reliance on analysis I Correlations may have epistemic uncertainty that is difficult to quantify I Complexities in the engineering analysis may make results less transparent 2 Reduce scope of review I Deterministic test data used to screen out many scenarios I Risk-based review scope limited to fewer scenarios I Use of test data consistent with (for example) fuel testing approach by establishing a limit for loading 3 Add confidence to conclusions regarding risk significance I Relegates ALL failures above the deterministic threshold to failure I Deterministic test produces a conservatively high threshold 5

Summary of RoverD elements 1 Obtain deterministic fiber loading test data I ECCS strainer loading and fiber penetration I Fuel assembly loading 2 Perform supporting analyses I LOCA scenario analysis for break size I Strainer performance criteria for NPSH, flashing, gas voiding, mechanical strength I Fiber generation, transport, erosion, latent fiber quantity I In-vessel analyses F In-vessel fiber limit analysis (blockage analyses for HLB and CLB)

F Boric acid precipitation analysis F Fuel limits (LOCADM for PWRs) 3 Regulatory Guide 1.174 risk assessment I RG 1.174: CDF , CDF , LERF , LERF I RG 1.174: Defense-in-depth, safety margin 6

RoverD flow charts 7

RoverD flow charts 8

RoverD method overview 1 Use deterministic strainer test data I Coatings failure, chemical effects head loss, fiber loading head loss consistent with deterministic approaches I Note amount of fine debris from break, latent fiber, and erosion 2 Use deterministic core fiber loading data I Coatings failure, chemical effects head loss, fiber loading head loss consistent with deterministic approaches I Determine the amount of fiber (based on the amount available from above) bypassed to the core I Ensure the amount bypassed and collected on the core is less than the acceptable tested amount 3 Using CASA Grande generation and transport methodology, find the smallest break size (by sampling) at each weld that produces more fine fiber in the sump than in the strainer test and relegate all larger breaks to failure 4 Derive a total failure frequency from NUREG 1829 to assign to CDF and ensure the total CDF is in Region III of RG 1.174 I Ensure LERF (using the PRA with the CDF) is in Region III of RG 1.174 I Ensure defense in depth and safety margin requirements of RG 1.174 are met 9

ECCS strainer test data analysis 1 Obtain deterministic strainer test data at some fiber loading (coatings failure, chemical precipitate loading, bed configuration, etc.)

I The amount of fiber fines should be representative of how much could arrive on the strainer in the actual plant including latent fiber and 30-day erosion I Examine scenarios at each weld location in the plant for break sizes and orientations from smallest break size to the largest possible I For each weld location, record the smallest break size (Dismallest ),

i = 1, . . . , N, for the scenario that would result in fiber fines more than the amount used in the acceptable strainer performance test (note that some welds may not have a scenario exceeding the tested fiber fines) 2 Preserve NUREG 1829 total frequency by deriving weights, wi , and cumulative scenario frequencies, fi , for each Dismallest 10

STP ECCS strainer test parameters 1 LDFG fine (191.78 lbm) and small (380.35 lbm) fibers I 24.96 lbm latent fine fiber I 166.82 lbm insulation fine fiber I 380.35 lbm smalls (with fines removed) 2 Particulates, Microtherm R and Marinite R board particulates, latent dust and dirt I 33 lbm Microtherm R powder I 182.7 lbm powdered Marinite R board I 141.1 lbm dust and dirt 3 Chemical precipitates representing 30 days of containment spray operation (1,934 lbm chemical precipitates)

I 1,575 lbm AlOOH, (1,432 lbm NaAlSI3 O8 , 143 lbm AlOOH)

I 359 lbm CaPO4 4 Coatings, zinc, epoxy, polyamid primer, alkyds, baked enamel I 1,368 lbm zinc powder I 582 lbm acrylic powder 11 I 106 lbm acrylic chips (1/64 - 1/4)

Plant CDF analysis (strainer) 1 Use wi and fi to derive a plant strainer CDF as follows:

XN CDF = fi wi (1) i=1 2 IF the CDF from (1) is in Region III of RG 1.174, AND other criteria for strainer performance that are related to pressure drop (for example, NPSHA, gas evolution, flashing, etc.)

meet the acceptance criteria required by design, THEN the risk associated with LERF should be checked for acceptability, ELSE the risk is unacceptable and further analysis may be indicated 12

Plant LERF analysis (strainer) 1 The STP RCFCs are capable of maintaining containment cooling without dependency on ECCS 2 Independence of containment failure from the concerns raised in GSI-191 allow an accurate estimate of LERF based on CDF from (1):  

CDF LERF = LERFMOR (2)

CDFMOR where values of CDFMOR and LERFMOR are the average values obtained from the PRA model of record 3 IF LERF is in Region III of RG 1.174, THEN the (strainer) risk related to LERF is acceptable 13

CDF analysis (in-vessel) 1 The risk due to core loading effects needs to be assessed against strainer penetration test data I Cooling effectiveness for fiber blockage I Boron precipitation for blockage from the lower plenum 2 IF thermal-hydraulic analysis shows adequate cooling for hot-leg breaks, AND The plant boric acid precipitation design analysis is compatible with the debris analysis, AND The total amount of the fiber used in the strainer test that penetrates the strainer and arrives in-vessel (for STP) on the bottom of the fuel in cold leg breaks is less than 15 gm/FA (WCAP-16793).

Note that amounts of fines greater than that added in the strainer test are relegated to failure already, THEN CDF from in-vessel effects is insignificant and the plant risk due to the concerns raised in GSI-191 is acceptable ELSE further analysis may be required to determine risk acceptability 14

Preliminary RoverD analysis results 1 No scenarios relegated to failure (due to strainer loading) exceed the core fiber limit I Boron precipitation without lower plenum mixing analysis is in progress I All other in-vessel analyses have been completed satisfactorily 2 There are 45 welds (scenarios) in the risk-informed category 3 The maximum frequency (smallest break size) is a DEGB of the 16 inch surge line (Slide 17) 4 All other strainer performance metrics are met in the strainer deterministic analysis 15

RoverD Regulatory approach Submit RoverD description in near-term to permit early NRC staff review and support ACRS Subcommittee meeting

• Describe purpose of RoverD as the primary basis for the STP application

• Provide assumptions and their bases, including basis for acceptability of 2008 test

• Describe expected impact on STP application 16

Preliminary weld list - Fines mass, Weld ID, Dismallest Fiber Mass (lbm) Location Diameter 207.16 16-RC-1412-NSS-8 12.814 191.83 29-RC-1101-NSS-RSG-1A-IN-SE 13.924 191.99 29-RC-1101-NSS-5.1 13.941 196.04 29-RC-1301-RSG-1C-IN-SE 14.368 192.09 29-RC-1401-NSS-RSG-1D-IN-SE 14.404 198.66 29-RC-1201-NSS-5.1 14.428 192.41 29-RC-1401-NSS-4.1 14.428 197.18 29-RC-1301-NSS-5.1 14.434 201.08 29-RC-1201-RSG-1B-IN-SE 14.542 201.07 29-RC-1101-NSS-4 15.052 195.29 29-RC-1201-NSS-4 15.087 197.42 29-RC-1401-NSS-3 15.294 205.18 29-RC-1301-NSS-4 15.496 192.19 31-RC-1102-NSS-2 16.408 200.29 31-RC-1202-NSS-2 16.777 197.21 31-RC-1202-NSS-RSG-1B-ON-SE 16.928 197.81 31-RC-1202-NSS-1.1 16.981 17

Preliminary weld list - Fines mass, Weld ID, Dismallest Fiber Mass (lbm) Location Diameter 200.54 31-RC-1102-NSS-1.1 17.071 202.54 31-RC-1102-NSS-RSG-1A-ON-SE 17.200 195.30 31-RC-1202-NSS-3 17.240 194.34 31-RC-1302-NSS-2 17.345 194.85 31-RC-1102-NSS-3 17.374 193.02 31-RC-1302-NSS-1.1 17.636 195.21 31-RC-1202-NSS-4 17.843 196.75 31-RC-1302-NSS-3 17.919 198.32 31-RC-1302-NSS-RSG-1C-ON-SE 18.108 197.07 31-RC-1402-NSS-1.1 18.137 197.35 31-RC-1102-NSS-4 18.179 197.95 31-RC-1402-NSS-RSG-1D-ON-SE 18.198 193.08 31-RC-1402-NSS-2 18.311 191.90 31-RC-1302-NSS-4 18.343 191.86 31-RC-1202-NSS-8 19.235 192.96 31-RC-1402-NSS-3 19.247 192.04 27.5-RC-1103-NSS-1 19.461 18

Preliminary weld list - Fines mass, Weld ID, Dismallest Fiber Mass (lbm) Location Diameter 191.92 27.5-RC-1203-NSS-1 19.566 193.04 31-RC-1102-NSS-8 19.617 192.37 31-RC-1402-NSS-4 20.236 192.03 31-RC-1302-NSS-8 20.350 192.45 27.5-RC-1303-NSS-1 21.053 192.11 31-RC-1202-NSS-9 21.116 192.34 31-RC-1102-NSS-9 21.278 191.96 27.5-RC-1403-NSS-1 22.047 192.16 31-RC-1402-NSS-8 22.174 193.18 31-RC-1302-NSS-9 23.169 192.46 31-RC-1402-NSS-9 25.335 19

RoverD RAI impact - APLAB RAI Description RoverD elimi-nates?

APLA-XI-1 Project Quality Assurance No APLA-XI-2 Treatment of Unanalyzed Plant Conditions Yes APLA-XI-3 Human Reliability Analysis Yes APLA-XI-4 Key Assumptions/Key Sources of Uncer- No tainty DEGB APLA-XI-5 Validity of Assumption on Pump Configura- Yes tions APLA-XI-6 Clarification on Response to APLA-IV-5 Yes APLA-XI-7 Fidelity between RELAP simulations and Yes CASA Grande APLA-XI-8 State-of-Knowledge Correlation Yes APLA-XI-9 Mean Values No APLA-XI-10 Selection of Johnson Parameters No 20

RoverD RAI impact - SSIB RAI Description RoverD eliminates?

F SSIB-RAI-2 Size distributions within the postu- No lated ZOIs F SSIB-RAI-4 Verify methodology results in over- No all realistic or conservative transport fractions considering LDFG conges-tion F SSIB-RAI-6a Justify the debris capture metrics No used in the evaluation are realistic F SSIB-RAI-7b Justify the washdown values from a No 30 minute test are applicable to the STP condition F SSIB-RAI-14 Confidence in the head loss correla- Yes tion used to perform the sensitivity study F SSIB-RAI 15- Use of head loss correlations will meet Yes 18,21,22 the established staff position 21

RoverD RAI impact - SSIB RAI Description RoverD eliminates?

F SSIB-RAI-27 CSHL Yes F SSIB-RAI-28 Individual and aggregate uncertainties Yes F SSIB-RAI-31 Void collection within the strainer Yes F SSIB-RAI-33 Sump water level evaluation Yes F SSIB-RAI-34 Basis for using random flow rates No F SSIB-RAI-41c Credit for strainer backwash No SSIB-RAI-43 Head loss bump up factor Yes SSIB-RAI-44 Bed compression Yes SSIB-RAI-45a Assumptions and modeling techniques re- No garding debris arrival timing and filtration SSIB-RAI-45b Dependency on arrival timing No SSIB-RAI-45c Bypass test result uncertainties No SSIB-RAI-45d Time step sensitivity No SSIB-RAI-45e mtest value No SSIB-RAI-45f Comparisons of filtration efficiencies and No shedding rates 22

RoverD RAI impact - SSIB RAI Description RoverD eliminates?

SSIB-RAI-46 Certain break sizes are not predicted or are No much less likely to occur than would be ex-pected SSIB-RAI-47 Appendix B used for CAD No SSIB-RAI-48 Mass of fiber No SSIB-RAI-49 Damage from a reflected jet No SSIB-RAI-50 Small and fine debris treated as if they have Yes the same properties SSIB-RAI-51 Flashing evaluation Yes SSIB-RAI-52 1/16 bed formation Yes SSIB-RAI-53 Variability in head loss calculations Yes SSIB-RAI-54 Safety margin evaluation Yes SSIB-RAI-55 RCS for hot leg switchover timing No 23

RoverD RAI impact - SNPB RAI Description RoverD eliminates?

SNPB-1 2 inch cold leg break BAP No SNPB-2 One assembly unblocked BAP No SNPB-3 Boric acid density treatment in RELAP5 No SNPB-4 Advection in RELAP5 No SNPB-6 Switchover timing variability No (should be 5) 24

RoverD RAI impact - ESGB RAI Description RoverD eliminates?

ESGB-23 RAI questions that may not be relevant (Yes)

ESGB-24a Detailed description of the chemical head Yes loss model ESGB-24b Bin selections allow the staff to discriminate Yes different outcomes ESGB-24c L* method independence from head loss Yes ESGB-24d Chemical model uncertainties Yes ESGB-25a Further model development Yes ESGB-25b Plausible range of head loss for test Yes ESGB-25c Calculation of scaled head loss value Yes ESGB-25d Basis for scaling equation/limitations Yes ESGB-26a Copy of the Reference 17 (CHLE-SNC-005 Yes Bench Test)

ESGB-26B Orange line in Figure 25 Yes ESGB-26c Aluminum release model prediction Yes 25

RoverD RAI impact- ESGB RAI Description RoverD eliminates?

ESGB-27 Scaffolding corrosion behavior Yes ESGB-28 Range of postulated plant temperature Yes profiles relative to CHLE MBLOCA and LBLOCA profiles ESGB-29 Provide the quantity of zinc that is included No in the particulate source ESGB-30 Which release equations will be used Yes ESGB-31 How model accounts for greater chemical Yes loading for less than three trains ESGB-32 Provide a modified response to ESGB RAI Yes

1. 14a ESGB-33 CRUD mass No ESGB-34 Differing fiber amounts in tables Yes 26

RoverD RAI impact - ESGB RAI Description RoverD eliminates?

Ct-ESGB-8 Revised analysis for the unqualified epoxy Yes coatings Ct-ESGB-9 Revised analysis for the ZOI of inorganic zinc Yes coatings Ct-ESGB-10 Revised analysis for the unqualified coatings Yes in upper containment 27

RoverD RAI impact - STSB RAI Description RoverD elimi-nates?

STSB-1 Assumptions listed in page 30 of 35 used for No operability determination STSB-2a Description demonstrating the relationship No between probability and operability STSB-2b Explain probability of occurrence of the as- No sumptions listed in page 30 of 35 change to improve or degrade the impact on contain-ment sump performance 28

RoverD RAI impact - SCVB RAI Description RoverD eliminates?

SCVB-10a Description of revised licensing basis analysis No of the containment heat removal (GDC-38)

SCVB-10b Description of revised Iodine removal (GDC- No 41)

SCVB-10c Description of revised licensing basis analysis No for ECCS (GDC-35)

SCVB-12,1 a,b Full or partial exemption from GDC-38 heat No removal SCVB-12,2 a,b Full or partial exemption from GDC-38 fol- No lowing any LOCA SCVB-12, 3 a,b Full or partial exemption from GDC-38 No LOOP SCVB-12, 4 a,b Full or partial exemption from GDC-38 Single No failure SCVB-13 Operation of the CSS for fission product re- No moval 29

RoverD RAI impact - SCVB RAI Description RoverD eliminates?

SCVB-14, 1 a,b Full or partial exemption from GDC-41 with No hydrogen and oxygen and other substances SCVB-14, 2 a,b Full or partial exemption from GDC-41 pos- No tulated accidents SCVB-14, 3 a,b Full or partial exemption from GDC-41 Leak No detection and isolation SCVB-14, 4 a,b Full or partial exemption from GDC-41 No LOOP SCVB-14, 5 a,b Full or partial exemption from GDC-41 Single No failure SCVB-15 Associated SSCs, procedures and activities No supporting operation of ECCS 30

RoverD RAI impact - SCVB RAI Description RoverD eliminates?

SCVB-16, 1 a,b Full or partial exemption from GDC-35 fuel No and clad damage SCVB-16, 2 a,b Full or partial exemption from GDC-35 fol- No lowing any LOCA SCVB-16, 3 a,b Full or partial exemption from GDC-35 leak No detection and isolation SCVB-16, 4 a,b Full or partial exemption from GDC-35 No LOOP SCVB-16, 5 a,b Full or partial exemption from GDC-35 Single No failure SCVB-17 Justify inputs and assumptions are conserva- No tive SCVB-18a M&E Mass subtracted from the pool No SCVB-18b Table of major qualitative differences No SCVB-18c Summary Comparison of Main Parameter No Values SCVB-18d Heat transfer properties of materials No 31

Technical Specification Concept

• 3Q15 supplement to application will include a proposed LAR to change Technical Specifications to specifically address effects of debris

- Adds clarity to where the plant is in TS space for emergent conditions

- Eliminates issue of applying PRA (risk) to determine operability

- Expect a long Completion Time

• Adequate to resolve the condition

• RG 1.174 risk evaluation provides basis for the proposed Completion Time 32

Technical Specification Concept

• New Required Actions to be added to the ECCS and the Containment Spray TS:

Reactor Containment Building emergency sump shall be OPERABLE by limiting the containment debris quantities to be less than or equal to the STP debris analysis assumptions.

With less than the required [ECCS or Containment Spray] Systems OPERABLE due to potential effects of debris, perform the following:

a. immediately initiate action to implement compensatory actions, and

b. within [90 days] restore the affected system(s) to OPERABLE status, OR Be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />, 33

Technical Specification Bases

• Applies to ECCS and Containment Spray

- Only systems that rely on strainers

• Applies only for debris-related conditions

- All applicable TS actions must be entered

• If maintenance is required or concurrent non-debris related condition is identified, the applicable TS action must be entered.

• Debris-related TS will continue to apply

• OPERABILITY is based on deterministic evaluation of characteristics of debris and consistency with STP debris analysis

- Intent is that risk calculation is not needed to make the operability determination

- Recognizes that there is margin and conservatism in the debris assumptions used for the deterministic testing and in the debris generation and transport analysis that can be applied to emergent condition

• Compensatory Action may include:

- Remove the debris or source of debris or take action that would prevent transport of the debris to the emergency sump

- Defer maintenance that would affect availability of the affected systems and strainers

- Increase frequency of RCS leak detection monitoring

- Brief operators on LOCA debris management actions

• Conceptual 90-day required action time is conservative and reasonable

- Based on very low contribution of debris to core damage frequency

- Break frequency of 4E-07/yr for smallest break that results in debris-related failure (pressurizer surge line)

- Operability can be restored by mitigation of the debris or by performing a calculation that shows the Licensing Basis is maintained 34

Operability Considerations

• The Licensing Basis with regard to effects of debris is that there is a high probability that ECCS and CSS can perform their design basis functions based on plant-specific prototypical testing using deterministic NRC-approved assumptions, and that the risk from breaks that could generate debris that is not bounded by the testing is very small in accordance with the criteria of RG 1.174.

• The affected ECCS and CSS are OPERABLE with respect to the effects of debris when the quantity and characteristics of the debris assumed in the plant debris analysis bounds the potential quantity and characteristics of transportable debris present in the Reactor Containment Building.

• Use of debris analysis assumptions in operability determination preserves not applying risk to determine operability

- Shift Manager will have debris-related reference material to assist in making the Immediate Operability Determination and to support requesting a Prompt Operability Determination

• An emergent condition outside the as-analyzed conditions is within the LB if the risk remains in the RG 1.174 criteria and could be considered Operable

- Proposed LCO would require Operator to enter TS action

• Determining that the condition is within the RG 1.174 LB allows exiting TS action or determining that there has not been a TS violation 35

Expected Content of Application Supplement

• Incorporates RoverD as primary basis

- Restructured to separate RoverD scope and supporting analyses from CASA Grande and Volume 2 (PRA)

• Revises requested exemption to 50.46(b) to be request for exemption from 50.46(d)

• Incorporates TS change and clarifies UFSAR markups

• Addresses RAIs 36

Areas for Clarification

• Disposition of RAIs that may be resolved or made non-relevant by use of RoverD (e.g., head loss)

- RoverD submittal should facilitate this

• Role of CASA Grande conditional probabilities and quantification based on correlations

- Include those sections of Vol. 2 & 3 as an Appendix to the Supplement and describe as providing additional confidence in validity of RoverD

• Need for additional testing

- RoverD assessment indicates additional testing is not needed

• Agreement on submittal process and content

• Technical Specification requirements and Operability 37

Conclusions

• RoverD simplifies application and preserves the very small risk per RG 1.174

• Proposed Technical Specification is consistent with the analysis and uncomplicated

• Need to address content of the STP application and RAI responses 38