View source for NOC-AE-16003367, Second Set of Responses to April 11, 2016 Requests for Additional Information Regarding Risk-Informed GSI-191 Licensing Application

{{Adams
| number = ML16196A241
| issue date = 06/16/2016
| title = Second Set of Responses to April 11, 2016 Requests for Additional Information Regarding Risk-Informed GSI-191 Licensing Application
| author name = Connolly J
| author affiliation = South Texas Project Nuclear Operating Co
| addressee name = 
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000498, 05000499
| license number = 
| contact person = 
| case reference number = NOC-AE-16003367, TAC MF2400, TAC MF2401
| document type = Letter type:NOC, Response to Request for Additional Information (RAI)
| page count = 59
| project = TAC:MF2400, TAC:MF2401
| stage = Other
}}

=Text=
{{#Wiki_filter:South Tex3S Project E!ectnc Cit:nerating St;Jt/on l?Q 8aY 28~ U'Jdsworth. Teras 77481 June 16', 2016 NOC-AE-16003367 10 CFR 50.12 10 CFR 50.90 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Units 1 & 2 Docket Nos. STN 50-498, STN 50-499 Second Set of Responses to *April 11, 2016 Requests for Additional Information Regarding STP Risk-Informed GSl.,.191 Licensing Application CTAC NOs MF2400 and MF2401)
Referen_ces:
: 1. Letter, G. T. Powell, STPNOC, to NRC Document Control Desk, "Supplement 2 to STP Pilot Submittal and Requests for-Exemptions and License Amendment for a Risk-Informed Approach to Address Generic-Safety Issue (GSl)-191 and Respond to Generic Letter (GL) 2004-02", August 20, 2015, NOC-AE-15003241, ML15246A126
: 2. Letter, Lisa Regner, NRC, to Dennis Koehl, STPNOC, "South Texas Project, Units 1 and 2- Request .for Additional Information.Related to Request for Exemptions and License Amendment for Use of a Risk-Informed. Approach to Resolve the Issue _of Potential Impact of Debris Blockage on*Emergency Recirculation During Design-Basis Accidents at Pressurized-Water Reactors", April 11,-2016, ML16082A507 Reference 2 transmitted RAls on STPNOC'.s application in Reference 1 and divided the RAls into 3 sets to be responded to in 30-day intervals. This submittal responds to the second set of RAls.
There are no commitments in this letter.
STI 34306884
                                                                                       /

NOC-AE-16003367 Page 2 of 3 If there are any questions, please contact Mr. Wayne Harrison at 361-972-877 4.
I declare under penalty of perjury that the foregoing is true and correct.
                                                                            ~t?
1~nolly Os~~e Vice President 0
awh Attachments:
: 1. Response to Follow-up RAls 19, 26, and 37
: 2. Response to SSIB-3-8 and 3-9
: 3. Response to SNPB-3-9 and 3-10
: 4. Definitions and Acronyms
                                                                                        \

NOC-AE-16003367 Page 3 of 3 cc:
(paper copy)                        (electronic copy)
Regional Administrator, Region IV   Morgan. Lewis & Beckius LLP U.S. Nuclear Regulatory Commission  Steven P. Frantz, Esquire 1600 East Lamar Boulevard Arlington, TX 76011-4511            U. S. Nuclear Regulatory Commission Lisa M. Regner Lisa M. Regner Senior Project Manager              NRG South Texas LP U.S. Nuclear Regulatory Commission  Chris O'Hara One White Flint North (08H04)       Jim van Suskil 11555 Rockville Pike                Skip Zahn Rockville, MD 20852 CPS Energy NRC Resident Inspector              Kevin Pollo U. S. Nuclear Regulatory Commission Cris Eugster P. 0. Box 289, Mail Code: MN116     L. D. Blaylock Wadsworth, TX 77 483 Crain Caton & James. P.C.
Peter Nemeth City of Austin Elaina Ball John Wester Texas Dept of State Health Services Helen Watkins Robert Free
                                                        \
I

NOC-AE-16003367 Attachment 1 Attachment 1 Response to Follow-up RAls 19, 26, and 37

NOC-AE-16003367 Attachment 1 Page 1 of 35 Follow-up RAls Follow-up RAI 19- In the December 23, 2009, RAI, the NRC staff asked the licensee to estimate the quantity of fines that could erode from small pieces of fiberglass debris that were assumed to transport to the strainer, but settled during the head loss test. The NRC staff's position is that the small fibrous debris should be accounted for, either as settled in the pool and eroded, or by performing a test that confirms that any fiber that is calculated to transport to the strainer transports to the strainer during the test. The Rovero analysis does not explicitly account for small fibrous debris in that it only uses the fine debris amounts from the July 2008 test as a datum of comparison to the CASA Grande generated, transported, and eroded fine fiber quantities.
Small fiber contributes to the Rovero fiber fines mass through erosion of small fiber retained in structures or settled in the pool. Previous approaches that may have been designed to overestimate the amount of small fiber accumulating on the strainer (in the context of now obsolete head loss computations), would result in underestimates of the amount of fiber fines in the Rovero analysis.
a)       Please provide information on the amounts of small fiber assumed to transport to the strainer and assumed to settle in the pool (and potentially subject to erosion into fiber fines).
b)       Please provide a sensitivity analysis of the Rovero results (e.g., set of critical welds and magnitude of the breaks causing the debris to exceed the tested .amount of fiber fines, and changes on the delta core damage frequency). considering the assumptions and uncertainties on the amount of small fiber settHng and retained on structures and transported to the strainer, as well as adequate values of erosion fraction (e.g., either 7 percent or 1O percent as discussed in the follow-up to RAl-18).
STP Response:
Part A: Provide information on the amounts of small fiber assumed to transport to the strainer and assumed to settle in the pool (and potentially subject to erosion into fiber fines)
The summary of Rovero total small fibrous debris transport was provided in Attachment 1-3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1]
in Table 3 on Page 13. It can be seen from Table 3 that 2.1 % of the total destroyed small piece inventory was calculated to be eroded fines and was included in the Rovero analysis; where 0.4 % was eroded at elevations above the pool floor by sprays and 1.7%
was eroded in the containment pool by recirculation flow, regardless of the actual break location. This total portion of eroded/transported small fibrous piece debris, as pointed out by NRC Staff in the above Follow-Up to 2009 question, does not account for the erosion of the total Rovero assumed settled intact small pieces. To explain this further, in the CFO pool transport analysis [2] there is a portion of intact small piece fibrous debris that is calculated to settle in the pool and erode at 7% and there is a portion of intact small piece fibrous debris that transports to the strainer. In the July 2008 test [3] all intact small piece fibrous debris was visually observed not to transport to the strainer. The Rovero evaluation in the August 2015 submittal [1] used both the transport analysis of record [2]
and the test observations [3] to define transport of small piece fibrous debris. However,

NOC-AE-16003367 Attachment 1 Page 2 of 35 when combining the no small piece fiber transport assumption from the test with the transport evaluation, the portion of the small piece fibrous debris calculated to transport directly to the strainer in the transport evaluation [2] was assumed settled due to test observation [3] but it was not analyzed to erode.
The zero percent transport fraction assume.d for intact small piece fibrous debris in the pool is based on the July 2008 test where small piece fibrous debris was not observed to transport to the strainer when exposed to flume conditions that bound STP ~trainer flow conditions. To be consistent wjth test observations, intact SIJlall pieces were not transported in the computational Rovero assessment that compared each postulated break to the strainer flume test fiber limit. It is recognized that not considering erosion from a portion of the intact small pieces of fiber (as described in the previous paragraph) that are treated as settled in the Rovero evaluation based on test observation is a discrepancy in the analysis and the impact of this is assessed in the response to the second part (Part 2) of this (Follow-Up to 2009 RAl-19) RAI response which contains a sensitivity study on the total amount of small piece fiber transport. The sensitivity analysis addresses this evaluation discrepancy by assuming 100% settling of all small fibrous debris that reaches the pool and then subjecting the total settled small piece fibrous debris to 7% erosion.
Part B: Provide a sensitivity analysis of the Rovero results (e.g., set of critical welds and magnitude of the breaks causing the debris to exceed the tested amount of fiber fines, and changes on the delta core damage frequency) considering the assumptions and uncertainties on the amount of small fiber settling and retained on struCtures and transported to the strainer, as well as adequate values of erosion fraction (e.g., either 7%
or 10% as discus~ed in the follow up to RAI 18)
To investigate the sensitivity of Rovero risk and the critical weld list to variance in the amount of small fibrous debris Galculated to transport, due to settling and erosion discussed in part one of this RAI, two cases including one sensitivity study were run in CASA Grande. The sensitivity analysis represents changes to the Rovero risk-informed debris generation/transport analysis while the Rovero deterministic fiber threshold from the July 2008 test is held constant. The goal of this sensitivity analysis is to assess what effect settling all small piece fibrous debris that is transported to the pool, as was observed in the July 2008 test, combined with erosion of this total settled small piece fibrous debris has on calculated risk using the Rovero method. Case descriptions of the CASA Grande analyses performed are provided in the numbered case definitions list below.
Case 0:      Baseline run BLR-CRO is the baseline CASA Grande run representing the analysis currently described in Attachment 1-3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1].
Case 1:      Sensitivity run SR-HALLSE7P was designed to investigate the effect of settling all intact small fibrous debris pieces that reach the containment pool, as was visually observed in the July 2008 test, and subjecting them to ?-
percent erosion. Note th?t the basis for ?-percent erosion has been explained in Follow-Up to 2009 RAl-18 (2016).

NOC-AE-16003367 Attachment 1 Page 3 of 35 A summary table of the sensitivity case definitions is provided in Table 1 for convenience.
Table 1: Summary of Rovero Sensitivity Case Definitions Sensitivity     Sensitivity Case        Erosion % of Debris          Transport % of Case#                Name                 Settled in Pool         Smalls (Non-Fines}
7% erosion of transport calculation settled portion, 0 % erosion of 0               BLR-CRO           debris settled due to                  0%
observation in test but transported in transport calculation [2]
1            SR-HALLSE7P          7%                                     0%
The sensitivity analysis and associated risk calculations were performed _with CASA Grande release version 1. 7 .2. The sensitivity study (Case 1) was analyzed considering two separate plant states, two and one trains operable, as described in Section 4.2 of -3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl~191 closure [1]. The success frequencies are defined as the yearly frequencies with,.which the STP PRA would see a combination of trains, associated with a given plant~ 'state, go through recirculation successfully. The success frequencies for the two and;_one train operable plant states are 4.16E-06 and 1.55E-09 yearly occurrences respectively.
T_he sensitivity case was evaluated with the continuum model, where the continuum model allows break sizes up to the max break size (inner diameter) of the pipe. Frequencies of breaks occurring for a given pipe rupture size were taken from NUREG-1829 and change in core damage frequency (~CDF) results were computed for both the Geometric and Arithmetic means of the expert elicitation process [4]. The statistical methodology implemented in Rovero is explained in detail in Attachment 1-3 of Supplement 2 to the STP licensing submittal [1].                                                        -
Case 0 Results: BLR-CRO The baseline run of the Rovero analysis, also described in Attachment 1-3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1], was rerun for completeness with CASA Grande release version 1.7.2. The failure frequency calculation in Attachment 1-3 was performed with the RUFF software which has an identical methodology to the Rovero routines in CASA Grande release version 1. 7 .2. This baseline analysis however is based on slightly different geometry inputs than were used for the analysis supporting the August 2015 submittal [1]. Slight changes to geometry inputs defining concrete and steel structures were made to support responses to NRC Staff RAls about coatings destruction in this (2016) RAI set. Due to refinements in concrete structures for coatings, that also define robust barriers for debris destruction, small differences were observed in oismau which have been evaluated to have a negligible impact on calculated
~CDF, which is essentially identical to the ~CDF calculated for the August 2015 submittal
[1 J.                                                                -

NOC-AE-16003367 Attachment 1 Page 4 of 35 A summary of t.CDF results are given in Table 2. Note that the columns labeled '2-Train '
and '1-Train' are the t.CDF estimates for both for the 2-train and 1-train operable plant states respectively, and the column label t.CDF is the combined total core damage frequency considering each plant state's success frequency; 4.16E-06 and 1.55E-09 yearly occurrences respectively. The methodology for combining calculated t.CDF from the 2-train and 1-train frequencies is described in detail by Equation 5, Section 4.2 of Attachment 1-3 in Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1]. All t.CDF estimates summarized in Table 2 have been evaluated at the 5th, 5oth, Mean, and 95th percentiles to highlight values in the standard range of uncertainty.
Note that the t.CDF estimates, considering the 5th , 5oth, Mean, and 95th percentiles, are in Region-3 of Regulatory Guide 1.17 4 [5] for the baseline (BLR-CRO) when using geometric averages, and the geometric method of aggregation should be considered the most appropriate estimator of LOCA frequency.
Table 2: BLR-CRO Continuum Break Model Results Summary Continuum Break Model - NUREG-1829 Geometric Means                           Arithmetic Means Quantile                                   Delta                                 Delta 2-Train          1-Train       CDF          2-Train     1-Train     CDF 5th     2.73E-10 4.67E-09 2.75E-10 6.59E-09 2.83E-08 6.60E-09 5oth     7.78E-09 1.05E-07 7.82E-09 1.71E-07 5.79E-07 1.71E-07 Mean      1.23E-07 6.18E-07 1.23E-07 1.59E-06 4.54E-06 1.59E-06 95th     3.59E-07 2.26E-06 3.59E-07 4.86E-06 1.44E-05 4.86E-06 The critical weld list, as defined in the Rovero methodology [1 ], is a collection of welds that have a break occurrence that can generate and transport enough fibrous debris to exceed the amount of fibrous debris that reached the stra iner in the July 2008 strainer flume test [3] . The critical weld list for plant state one, with two trains operable, is given in Table 3 below. Columns two , three, four, and five provide the break location , smallest break size to fail o isma11 , the amount of fiber transported for the smallest break to fail , and the difference between the transported fiber amount and the amount of fine fibe r transported in the test (191 .78 lbm).
Table 3: BLR-CRO Critical Weld List Train Operation o ismall    Fiber Transported at   Difference from
#               Break Location                                 Smallest Break Size       Threshold (inches)
(lbm)                (lbm) 1    16-RC-1412-NSS-8                             12.814              213.296              21.516 2    29-RC-1401-NSS-3                             14.390              191.845               0.065 3    29-RC-1101-NSS-4                             14.590              191.817               0.037 4    29-RC-1201 -NSS-4                            14.900              191 .847              0.067 5    29-RC-1301-NSS-4                             14.910              191 .848              0.067 6    31-RC-1302-NSS-RSG-1 C-ON-SE                 15.410              191.900               0.119 7    29-RC-110 1-NSS-RSG-1A-IN-SE                 15.620              191.823               0.043 8    29-RC-1101-NSS-5.1                           15.630              191.849               0.069

NOC-AE-16003367 Attachment 1 Page 5 of 35 o ismall Fiber Transported at  Difference from
 #           Break Location                Smallest Break Size      Threshold (inches)
(lbm)               (lbm) 9 29-RC-1401-NSS-RSG-1 D-IN-SE  15.640          191.783              0.003 10 29-RC-1401-NSS-4.1            15.650          191 .962             0.182 11 29-RC-1201-NSS-5.1            15.930          191 .796             0.016 12 29-RC-1201-RSG-1 B-IN-SE      15.930          191 .986             0.206 13 29-RC-1301-RSG-1 C-1 N-SE     15.940          191 .800             0.020 14 29-RC-1301-NSS-5.1            15.950          191 .884             0.104 15 31-RC-1102-NSS-1 .1           16.030          191 .792             0.012 16 31-RC-1102-NSS-RSG-1A-ON-SE   16.030          191 .806             0.026 17 31-RC-1202-NSS-4              16.070          191 .818             0.038 18 31-RC-1102-NSS-4              16.190          191.790              0.010 19 31-RC-1202-NSS-1 .1           16.230          191.815              0.035 20 31-RC-1202-NSS-RSG-1 B-ON-SE  16.230          191 .817             0.037 21 31-RC-1202-NSS-2              16.290          191 .819             0.039 22 31-RC-1302-NSS-2              16.360          191 .838             0.058 23 31-RC-1102-NSS-2              16.420          191 .940             0.160 24 31-RC-1302-NSS-4              16.500          191 .821             0.041 25 31-RC-1302-NSS-1 .1           16.650          191 .851             0.071 26 31-RC-1402-NSS-2              16.800          191 .854             0.074 27 27 .5-RC-1203-NSS-1           17.240          191 .825             0.045 28 27.5-RC-1303-NSS-1            17.260          191 .826             0.046 29 27.5-RC-1103-NSS-1            17.280          191 .873             0.093 30 31-RC-1402-NSS-1 .1           17.330          191.836              0.056 31 31-RC-1402-NSS-RSG-1 D-ON-SE  17.330          191.889              0.108 32 31-RC-1202-NSS-8              17.500          191 .813             0.033 33 31-RC-1102-NSS-8              17.810          191 .792             0.012 34 31-RC-1402-NSS-4              18.080          191 .797             0.017 35 31-RC-1302-NSS-8              18.440          191 .795             0.015 36 31-RC-1102-NSS-3              18.780          191 .782             0.002 37 31 -RC-1102-NSS-9             18.800          191 .810             0.030 38 31-RC-1202-NSS-9              18.830          191 .818             0.038 39 27.5-RC-1403-NSS-1            18.850          191.782              0.002 40 31-RC-1202-NSS-3              18.880          191.808              0.028 41 31-RC-1302-NSS-3              19.020          191.794              0.014 42 31-RC-1302-NSS-9              19.270          191 .808             0.028 43 31 -RC-1402-NSS-3             19.700          191 .810             0.030 44 31 -RC-1402-NSS-8             20.280          191.822              0.042 45 31-RC-1402-NSS-9              21 .190         191.888              0.107

NOC-AE-16003367 Attachment 1 Page 6 of 35 The critical weld list for plant state two , with one train operable, is given in Table 4 below.
Columns two , three , four, and five provide the break location , smallest break size to fail 11 o isma , the amount of fiber transported for the smallest break to fa il, and the difference between the transported fiber amount and the amount of fine fiber transported in the test scaled to one train operable (95.89 lbm).
Table 4: BLR-CRO Critical Weld List-1-Train Operation Fiber Transported o ismall                         Difference from
 #                Break Location                                at Smallest Break (inches)                          Threshold (lbm)
Size (lbm) 1     16-RC-1412-NSS-8                               9.550           95.892                 0.002 2     31-RC-1102-NSS-1 .1                            9.890           95.947                 0.057 3     31-RC-1102-NSS-RSG-1 A-ON-SE                   9.890           95.890                 0.000 4     31-RC-1202-NSS-1.1                             9.960           95.925                 0.035 5     31-RC-1202-NSS-RSG-18-0N-SE                    9.960           95.918                 0.028 6     31-RC-1302-NSS-RSG-1 C-ON-SE                   9.980           95.960                 0.070 7     12-RC-1221-BB1-9                              10.016           95.910                 0.020 8     12-RC-1221-BB1-11                             10.016           95.932                 0.042 9     12-RC-1125-BB1-9                              10.036           95.896                 0.006 10     29-RC-1301 -NSS-4                             10.110           95.912                 0.022 11     29-RC-1401-NSS-3                              10.120           95.924                 0.034 12     12-RC-1112-BB1-1                              10.126           97.467                 1.577 13     12-RC-1125-BB1-8                              10.126           97.070                 1.180 14     12-RC-1125-BB 1-10                            10.126          130.232                34.342 15     12-RC-1125-BB1-11                             10.126          131 .521               35.631 16     12-RC-1125-BB1-12                             10.126          125.681                29.791 17     12-RC-1125-BB 1-13                            10.126          101.131                 5.241 18     12-RC-1221-BB1-10                             10.126          130.729                34.839 19     12-RC-1221-BB1 -12                            10.126          130.616                34.726 20     12-RC-1221-B81-13                             10.126          124.218                28.328 21     12-RC-1221 -B81 -14                           10.126           97.943                 2.053 22     12-RC-1322-BB 1-1                             10.126          132.724                36.834 23     12-RC-1322-BB 1-1 A                           10.126          132.267                36.377 24     12-RC-1322-BB 1-2                             10.126          127.727                31.837 25     12-RC-1322-BB 1-3                             10.126          122.891                27.001 26     12-RC-1322-B81-4                              10.126           98.582                 2.692 27     12-Sl-1315-BB1-7                              10.126          102.462                 6.572 28     12-Sl-1315-BB1-8                              10.126          114.529                18.639 29     12-Sl-1315-BB1-9                              10.126          118.890                23.000 30     12-Sl-1315-B81-10                             10.126          123.075                27.185 31     29-RC-1101-NSS-3                              10.126          98.873                  2.983 32     29-RC-1201-NSS-3                              10.126          96.848                  0.958

NOC-AE-16003367 Attachment 1 Page 7 of 35 Fiber Transported o ismall                     Difference from
 #            Break Location               at Smallest Break (inches)                       Threshold (lbm)
Size (lbm) 33 29-RC-1301-NSS-3              10.126          96.839             0.949 34 29-RC-1101-NSS-4              10.160          95.936             0.046 35 29-RC-1101 -NSS-RSG-1A-IN-SE  10.170          95.979             0.089 36 29-RC-1101 -NSS-5.1           10.180          96.006             0.116 37 29-RC- 1201 -NSS-4            10.190          95.913             0.023 38 31-RC-1302-NSS-1.1            10.210          95.969             0.079 39 29-RC-1301-RSG-1 C-IN-SE      10.220          95.912             0.022 40 29-RC-1301-NSS-5.1            10.230          95.904             0.014 41 29-RC-1201-RSG-1 B-IN-SE      10.290          95.942             0.052 42 31-RC-1202-NSS-2              10.290          95.999             0.109 43 29-RC-1201-NSS-5.1            10.300          95.988             0.098 44 31-RC-1102-NSS-2              10.340          95.964             0.074 45 29-RC-1401-NSS-RSG-1 D-IN-SE  10.390          95.912             0.022 46 31-RC-1302-NSS-2              10.390          95.955             0.065 47 29-RC-1401-NSS-4.1            10.400          95.975             0.085 48 31-RC-1402-NSS-1 .1           10.580          95.900             0.010 49 31-RC-1402-NSS-RSG-1 D-ON-SE  10.580          95.906             0.016 50 16-RC-1412-NSS-7              10.740          95.977             0.087 51 31-RC-1402-NSS-2              10.830          95.900             0.010 52 16-RC-1412-NSS-9              10.970          95.891             0.001 53 29-RC-140 1-NSS-2             10.980          95.916             0.026 54 16-RC-1412-NSS-6              11 .040         95.896             0.006 55 27. 5-RC-1203-NSS-1           11 .180         95.916             0.026 56 27.5-RC-1303-NSS-1            11.180          95.895             0.005 57 31-RC-1202-NSS-4              11 .220         95.921             0.031 58 27.5-RC- 1103-NSS-1           11.270          95.912             0.022 59 31-RC-1202-NSS-8              11 .330         95.935             0.045 60 31-RC-1102-NSS-4              11.340          95.959             0.069 61 31-RC-1302-NSS-4              11.400          95.942             0.052 62 31-RC-1102-NSS-8              11.530          95.901             0.011 63 31-RC-1202-NSS-3              11 .570         95.908             0.017 64 31-RC-1302-NSS-3              11.610          95.957             0.067 65 31-RC-1102-NSS-3              11.640          95.941             0.050 66 31-RC-1302-NSS-8              11 .750         95.935             0.045 67 31-RC-11 02-NSS-9             11.980          95.929             0.039 68 31-RC-1202-NSS-9              12.000          95.893             0.003 69 31-RC-1302-NSS-9              12.170          95.895             0.005 70 16-RC-1412-NSS-5              12.330          95.890             0.000 71 27.5-RC-1403-NSS-1            12.410          95.898             0.008

NOC-AE-16003367 Attachment 1 Page 8 of 35 Fiber Transported o ismall                         Difference from
#                  Break Location                                at Smallest Break (inches)                           Threshold (lbm )
Size (lbm) 72    31-RC-1402-NSS-3                               12.540            95.924                0.034 73    31-RC-1402-NSS-4                               12.620            96.028                0.138 74    31-RC-1402-NSS-8                               13.460            95.938                0.048 75    31-RC-1402-NSS-9                               14.180            95.900                0.010 76    27.5-RC-1103-NSS-RPV1 -N2ASE                   23.780            95 .906               0.016 77    27.5-RC-1203-NSS-5                             23.830            95.894                0.004 78    27.5-RC-1203-NSS-RPV1-N2BSE                    23.930            95.890                0.000 79    29-RC-1401-NSS-1                               24.460            95.909                0.019 80    29-RC-1401-NSS-RPV1-N1 DSE                     24.490            95.898                0.008 81    29-RC-1101-NSS-1                               24.540            95.926                0.036 82    29-RC-1301-NSS-1                               24.620            95.919                0.029 83    29-RC-1301-RPV1-N1 CSE                         24.670            95.923                0.033 84    29-RC-1101-NSS-RPV1-N1ASE                      24.780            95.900                0.010 85    29-RC-1201-NSS-1                               25.010            95.930                0.040 86    29-RC-1201-RPV1-N1 BSE                         25.100            95.897                0.007 87    27 .5-RC-1203-NSS-4                            26.640            95.892                0.002 88    27.5-RC- 1103-NSS-6                            27.000            95.892                0.002 89    27.5-RC-1103-NSS-7                             27.500           142.343               46.453 90    27 .5-RC-1303-NSS-5                            27.500           124.279               28.389 91    27.5-RC-1303-NSS-6                             27.500           128.099               32 .209 92    27 .5-RC-1303-NSS-RPV1-N2CSE                   27.500           128.746               32 .856 93    27 .5-RC-1403-NSS-5                            27.500           118.646               22 .756 94    27 .5-RC-1403-NSS-6                            27.500           124. 614              28.724 95    27 .5-RC-1403-NSS-RPV1-N2DSE                   27.500           125.859               29.969 Case 1 Results: SR-HALLSE7P The sensitivity evaluated for the RAI response was designed to investigate the effect of settling all intact small fibrous debris pieces that reach the conta inment pool based on observations from the July 2008 test [3]. Th is case demonstrates the impact of add itionally generated fibrous fi nes from add itional (including the total) small piece debris that would settle out of the pool rather than transport to the strainers; as mentioned before the total portion of transported small fibrous piece debris accounted for in Attachment 1-3 of the STP Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1]
analysis, as pointed out by NRC Staff in the above Follow-Up to 2009 question , does not account fo r erosion from the portion of debris calculated in the debris transport evaluation to tra nsport directly to the strainer as intact small fi brous pieces. Th is case has a greater amount of fi ber fi nes produced from erosion fo rces in the pool as compared to the same quantity in the basel ine (Attachment 1-3 analysis [1]) case because it includes erosion from the assumed settling of all small piece fibrous debris based on July 2008 strainer flume test observations [3] . The erosion fraction fo r this sensitivity study was chosen to

NOC-AE-16003367 Attachment 1 Page 9 of 35 be ?-percent during recirculation for fiber settled in the pool which is bounded by Alion erosion testing [6) .
A summary of .0.CDF results for the continuum break model is given in Table 5. Note that the columns labeled '2-Train' and '1-Train' are the .0.CDF estimates for both for the 2-train and 1-train operable plant states respectively, and the column labeled .0.CDF is the combined total core damage frequency considering each plant state's success frequency; 4.16E-06 and 1.55E-09 yearly occurrences respectively. The methodology for combining calculated .0.CDF from the 2-train and 1-train frequencies is described in detail by Equation 5 Section 4.2 of Attachment 1-3 in Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1]. All .0.CDF estimates summarized in Table 5 have been evaluated at the 5th, 5oth, Mean, and 95th percentiles to highlight values in the standard range of uncertainty. Note that the .0.CDF estimates, considering the 5th, 50th, Mean , and 95th percentiles, are in Region-3 of Regulatory Guide 1.17 4 [5] for the baseline (SR-HALLSE7P) when using geometric averages, and the geometric method of aggregation should be considered the most appropriate estimator of LOCA frequency.
Table 5: SR-HALLSE7P Continuum Break Model Results Summary Continuum Break Model - NUREG-1829 Geometric Means                                 Arithmetic Means Quantile 1--2  ---T-ra
_i_n--1--T   -r-a-in-~D-e-lt_a_C_D_ F -+--2
                                                                    ---T-ra
_i_n--1---T-ra_i_n-....-
D-e-lt_a_C_D_F----i 5th        2.84E-10         4.38E-09     2.85E-10          6.?OE-09        2.66E-08       6.71 E-09 50th        8.09E-09         9.86E-08     8.13E-09          1.74E-07        5.43E-07       1.74E-07 Mean         1.27E-07         5.80E-07     1.28E-07          1.61 E-06       4.26E-06       1.62E-06 95th        3.73E-07         2.12E-06     3.73E-07          4.91 E-06       1.35E-05       4.92E-06 The critical weld list, as defined in the Rovero methodology [1 ], is a collection of welds that have a break occurrence that can generate and transport enough fibrous debris to exceed the amount of fibrous debris that reached the strainer in the July 2008 strainer flume test [3] . The critical weld list for plant state one, with two trains operable, is given in Table 6 below. Columns two , three , four, and five provide the break location, smallest break size to fail o isma 11 , the amount of fiber transported for the smallest break to fail, and the difference between the transported fiber amount and the amount of fine fiber transported in the test (191 .78 lbm).
Table 6: SR-HALLSE7P Critical Weld List- 2-Train Operation o ismall      Fiber Transported Difference from
#                 Break Location                                       at Smallest Break (inches)                                Threshold (lbm)
Size (lbm) 1    16-RC-1412-NSS-8                                   12.814               226.647                34.867 2    29-RC-1401-NSS-3                                   13.980               191.895                 0.114 3    29-RC-1101-NSS-4                                   14.170               191.912                 0.132 4    29-RC-1201-NSS-4                                   14.400               191 .834                0.054 5    29-RC-1301-NSS-4                                   14.410               191 .780                0.000 6    31-RC-1302-NSS-RSG-1 C-ON-SE                       14.780               191 .853                0.073 7    29-RC-1101-NSS-RSG-1A-IN-SE                        15.070               191.924                 0.144

NOC-AE-16003367 Attachment 1 Page 10 of 35 Fiber Transported o ismall                    Difference from
 #           Break Location                at Smallest Break (inches)                      Threshold (lbm)
Size (lbm) 8 29-RC-1101-NSS-5.1            15.080         191 .864           0.084 9 29-RC-1401-NSS-RSG-1 D-IN-SE  15.100         191 .793           0.013 10 29-RC-1401-NSS-4.1            15.110         191 .813           0.033 11 31-RC-1102-NSS-1 .1           15.240         191 .813           0.033 12 31-RC-1102-NSS-RSG-1 A-ON-SE  15.240         191.840            0.059 13 29-RC-1201-RSG-1 B-IN-SE      15.330         191.831            0.051 14 29-RC-1201-NSS-5.1            15.350         191.972            0.192 15 29-RC-1301-RSG-1 C-IN-SE      15.350         191.939            0.159 16 31-RC-1202-NSS-1.1            15.350         191.796            0.016 17 31-RC-1202-NSS-RSG-1 B-ON-SE  15.350         191 .840           0.060 18 29-RC-1301-NSS-5.1            15.360         191 .946           0.166 19 31-RC-1202-NSS-4              15.540         191 .785           0.005 20 31-RC-1202-NSS-2              15.580         191.836            0.056 21 31-RC-1102-NSS-2              15.630         191 .897           0.117 22 31-RC-1302-NSS-2              15.630         191.811            0.031 23 31-RC-1302-NSS-1.1            15.700         191.804            0.024 24 31-RC-1102-NSS-4              15.710         191 .792           0.012 25 31-RC-1302-NSS-4              15.920         191.780            0.000 26 31-RC-1402-NSS-2              15.990         191 .788           0.008 27 31-RC-1402-NSS-RSG-1 D-ON-SE  16.490         191.784            0.004 28 31-RC-1402-NSS-1.1            16.500         191.802            0.022 29 27.5-RC-1203-NSS-1            16.620         191.870            0.089 30 27.5-RC-1303-NSS-1            16.620         191.921            0.141 31 27.5-RC-1103-NSS-1            16.650         191 .861           0.081 32 31-RC-1202-NSS-8              16.840         191 .803           0.023 33 31-RC-1102-NSS-8              17.130         191.789            0.009 34 31-RC-1402-NSS-4              17.480         191 .819           0.039 35 31 -RC-1302-NSS-8             17.750         191 .797           0.017 36 31-RC-1102-NSS-3              17.760          191 .83            0.05 37 31-RC-1202-NSS-3              17.820         191 .921           0.141 38 31 -RC-1102-NSS-9             18.100         191.794            0.014 39 31-RC-1202-NSS-9              18.110         191.883            0.103 40 31-RC-1302-NSS-3              18.140         191.833            0.053 41 27.5-RC-1403-NSS-1            18.150         191.785            0.005 42 31-RC-1302-NSS-9              18.570         191 .818           0.038 43 31-RC-1402-NSS-3              19.020         191 .877           0.097 44 31-RC-1402-NSS-8              19.690         191 .826           0.046 45 31 -RC-1402-NSS-9             20.500         191 .923           0.143

NOC-AE-16003367 Attachment 1 Page 11 of 35 The critical weld list for plant state two , with one train operable , is given in Table 7 below for Case SR-HALLSE7P. Columns two, three, four, and five provide the break location ,
smallest break size to fa il o isma 11 , the amount of fiber transported for the smallest break to fail , and the difference between the transported fiber amount and the amount of fine fiber transported in the test scaled to one train operable (95.89 lbm).
Table 7: SR-HALLSE7P Critical Weld List-1-Train Operation Fiber Transported at o ismall                           Difference from
#                 Break Location                                Smallest Break Size Threshold (lbm)
(inches)
(lbm) 1    16-RC-1412-NSS-8                               9.340             95.950                0.060 2    31-RC-1102-NSS-1 .1                            9.560             95.951                0.061 3    31-RC-1102-NSS-RSG-1A-ON-SE                    9.560             95.904                0.014 4    31-RC-1202-NSS-1.1                             9.650             95.900                0.010 5    31-RC-1202-NSS-RSG-18-0N-SE                    9.650             95.901                0.011 6    31-RC-1302-NSS-RSG-1 C-ON-SE                   9.700             95.968                 0.078 7     12-RC-1221-B81-9                              9.720             96.009                 0.119 8     12-RC-1221-B81-11                             9.720             95.906                 0.016 9     12-RC-1125-B81-9                              9.750             95.892                 0.002 10    29-RC-1101-NSS-RSG-1A-IN-SE                    9.760             95.895                 0.004 11    29-RC-1101-NSS-5.1                             9.780             95.997                 0.106 12    29-RC-1401-NSS-3                               9.810             95.902                 0.012 13     12-Sl-1315-BB1 -8                             9.840             95.968                 0.078 14    29-RC-1301-NSS-4                               9.840             95.929                 0.039 15     12-RC-1322-881-1                              9.900             95.893                 0.003 16    29-RC-1101-NSS-4                               9.900             96.009                 0.119 17     31-RC-1302-NSS-1.1                            9.900             95.982                 0.092 18    29-RC-1301-NSS-5.1                             9.920             95.925                 0.035 19    29-RC-1301-RSG-1 C-IN-SE                       9.920             95.945                 0.055 20     12-RC-1322-B81-1 A                            9.930             95.921                 0.031 21     12-RC-1125-B81-11                             9.940             95 .911                0.021 22    29-RC-1201-NSS-4                               9.940             95.931                 0.041 23     29-RC-1201-NSS-5 .1                           9.990             95.914                 0.024 24     29-RC-1201-RSG-18-IN-SE                       9.990             95.964                 0.074 25     31-RC-1202-NSS-2                              9.990             95.890                 0.000 26     12-RC-1125-B81-10                            10.006             95.967                 0.077 27     12-RC-1221-B81-12                            10.016             95.915                 0.025 28     29-RC-1401-NSS-RSG-1 D-1 N-SE                10.030             95.969                 0.079 29     29-RC- 1401-NSS-4.1                          10.040             95.921                 0.031 30     12-RC-1322-B81-2                             10.066             95.893                 0.002 31     31-RC-1102-NSS-2                             10.070             95.964                 0.074 32     12-RC-1221-B81-10                            10.106             95.933                 0.043

NOC-AE-16003367 Attachment 1 Page 12 of 35 o ismall Fiber Transported at Difference from
 #           Break Location                Smallest Break Size (inches)                         Threshold {lbm)
{lbm) 33 12-RC-1112-BB1-1              10.126          102.659               6.769 34 12-RC-1125-BB1-8              10.126          102.699               6.809 35 12-RC-1125-BB1-12             10.126          132.401              36.511 36 12-RC-1125-BB1 -13            10.126          105.968              10.078 37 12-RC-1212-BB1-1              10.126           97.000               1.110 38 12-RC-1221-BB1-8              10.126           97.830               1.940 39 12-RC-1221-BB1-13             10.126          130.840              34.950 40 12-RC-1221-BB1-14             10.126          102.462               6.572 41 12-RC-1312-BB1-1              10.126           97.760               1.870 42 12-RC-1312-BB1-8              10.126           96.047               0.157 43 12-RC-1322-BB 1-3             10.126          129.669              33.779 44 12-RC-1322-BB 1-4             10.126          103.194               7.304 45 12-Sl-1315-BB1-7              10.126          108.774              12.884 46 12-Sl-1315-BB1-9              10.126          125.120              29.230 47 12-Sl-1315-BB1-10             10.126          129.673              33.783 48 29-RC-1101-NSS-3              10.126          104.133               8.243 49 29-RC-1201-NSS-3              10.126          101 .944              6.054 50 29-RC-1301-NSS-3              10.126          102.019               6.129 51 31-RC-1302-NSS-2              10.140           95 .946              0.056 52 31 -RC-1402-NSS-1 .1          10.220           95.963               0.073 53 31-RC-1402-NSS-RSG-1 D-ON-SE  10.220           95.980               0.090 54 16-RC-1412-NSS-7              10.410           95.912               0.022 55 31 -RC-1402-NSS-2             10.540           95.894               0.004 56 16-RC-1412-NSS-9              10.690           95.894               0.004 57 29-RC-1401-NSS-2              10.700           95.892               0.002 58 16-RC-1412-NSS-6              10.740           95.978               0.088 59 31-RC-1202-NSS-8              10.880           95.891               0.001 60 27. 5-RC-1303-NSS-1           10.910           95.916               0.026 61 27. 5-RC-1203-NSS-1           10.930           95.947               0.057 62 27.5-RC-1103-NSS-1            10.990           96.007               0.117 63 31-RC-1202-NSS-4              11 .000          95.915              0.025 64 31-RC-1102-NSS-8              11.090           95.906              0.016 65 31-RC-1102-NSS-4              11 .100          95.999              0.109 66 31-RC-1302-NSS-4              11 .170          95.915              0.025 67 31 -RC-1302-NSS-8             11 .280          95.971              0.081 68 31 -RC-1202-NSS-3             11.310           95.921              0.031 69 31-RC-1102-NSS-3              11 .370          95.895              0.005 70 31-RC-1302-NSS-3              11 .380          96.013              0.123 71 31 -RC-1202-NSS-9             11.480           95.909              0.019

NOC-AE-16003367 Attachment 1 Page 13 of 35 O ;small    Fiber Transported at Difference from
  #                Break Location                            Smallest Break Size (inches)                            Threshold (lbm)
(lbm) 72     31-RC-1102-NSS-9                        11.490              95.929                0.039 73     31 -RC-1302-NSS-9                       11.670              95.912                0.022 74     16-RC-1412-NSS-5                        11 .960             95.919                0.029 75     27 .5-RC-1403-NSS-1                     12.070              95.904                0.014 76     31-RC-1402-NSS-3                        12.210              95.945                0.055 77     31 -RC-1402-NSS-4                       12.350              95.984                0.094 78     16-RC-1412-NSS-1                        12.814             100.521                4.631 79     16-RC-1412-NSS-PRZ-1-N1-SE              12.814             101.594                5.704 80     31-RC-1402-NSS-8                        13.010              95.990                0.100 81     31-RC-1402-NSS-9                        13.700              95.891                0.001 82     27.5-RC-1103-NSS-RPV1-N2ASE             22.570              95.899                0.009 83     27 .5-RC-1203-NSS-5                     22.610              95.904                0.014 84     27 .5-RC-1203-NSS-RPV1 -N2BSE           22.680              95.894                0.004 85     29-RC-1401-NSS-1                        23.260              95.954                0.064 86     29-RC-1301-NSS-1                        23.290              95.921                0.031 87     29-RC-1401-NSS-RPV1-N1 DSE              23.290              95.961                0.071 88     29-RC-1301-RPV1-N1 CSE                  23.320              95.919                0.029 89     29-RC-1101-NSS-1                        23.510              95.901                0.011 90     29-RC-1101 -NSS-RPV1-N1ASE              23.670              95.905                0.015 91     29-RC-1201-NSS-1                        23.830              95.892                0.002 92     29-RC-1201-RPV1-N 1BSE                  23.850              95.926                0.036 93     27 .5-RC-1203-NSS-4                     24.650              95.937                0.047 94     27 .5-RC-1103-NSS-6                     24.940              95 .897               0.007 95     27.5-RC-1103-NSS-7                      25.410              95.891                0.001 96     27 .5-RC-1303-NSS-RPV1-N2CSE            26.780              95.911                0.021 97     27.5-RC-1303-NSS-6                      26 .820             95.891                0.001 98      27.5-RC-1303-NSS-5                      27.500             133.504               37.614 99      27.5-RC-1403-NSS-5                      27.500             127.450               31.560 100     27.5-RC-1403-NSS-6                      27.500             133.732               37.842 101     27.5-RC-1403-NSS-RPV1-N2DSE             27.500             135.049               39.159 Summary and Conclusion Analysis was performed to explore the sensitivity of calculated risk (~ CDF) , using the Rove ro method, to changes in the amount of small fibrous piece debris that is settled in the pool, eroded, and tra nsported to the strainer. The ca se definition for the sensitivity study is summarized below in Table 8. Of the two Cases: Case 0 represents the Augu st 2015 submittal baseline evaluation (Attachment 1-3 analysis [1]) with minor modifications to CASA Grande geometry inputs as noted in the "Case 0 Resu lts: BLR-CRO" section of th is RAI , and Case 1 represents individual effects of increased eroded small piece fibrous debris.

NOC-AE-16003367 Attachment 1 Page 14 of 35 Table 8: Summary of Rovero Sensitivity Case Definitions Sensitivity            Sensitivity         Erosion % of Debris         Transport % of Smalls Case#               Case Name                Settled in Pool                 (Non-Fines) 7% erosion of transport calculation settled portion, 0
                                       % erosion of debris settled 0             BLR-CRO                                                          0%
due to observation in test but transported in transport calculation [2]
1             SR-HALLSE7P         7%                                           0%
Results were produced for the sensitivity case including NUREG-1829 uncertainty aggregation [4], for both the Geometric and Arithmetic aggregation methods. Mean ~ CDF results for the sensitivity case considering both of the uncertainty aggregation methods have been provided in Table 9 for ease of comparison. Analyzing Table 9, considering the Regulatory Guide 1.174 thresholds for region three and two respectively of <1E-6 and
 <1 E-5 occurrences per year, it is seen that the geometric mean for the baseline (Attachment 1-3 analysis [1]) and sensitivity case fall within Region 3; and the geometric method of aggregation is considered the most appropriate estimator of LOCA frequency.
The arithmetic mean for the baseline and the sensitivity case fall within Region 2 considering the Regulatory Guide 1.17 4 thresholds.
Table 9: Mean Delta CDF Results Summary Geometric     Arithmetic Case Case Name            Means          Means Cont          Cont 0     BLR-CRO               1.23E-07     1.59E-06 1     SR-HALLSE7P           1.28E-07     1.62E-06 Placement of the baseline and sensitivity case results on the Reg ulatory Guide 1.174 risk region map have been provided in Figure 1 and Figure 2 fo r ease of visua lization . In Figure 1 and Figure 2 the varying colors of 'x' marks identify the case stud ies as defined in the right of the figure . The green, yellow and red filled areas of the plot illustrate risk Region-3, Region-2 , and Region-1 of the Regulatory Guide 1.174 risk regions respectively. It is seen in Figure 1 below that the continuum model geometric mean ~ CDF values for the baseline and the sensitivity case fa ll with in risk Region-3 .

NOC-AE-16003367 Attachment 1 Page 15 of 35 Risk Regions - STP -Sensitivity Ana lysis - Continuum Model - GM 1.0E                                                  ~
REGION I u:-
0                                                                                            REGIO N II u      1.0E-05
* I
()'                                                                                         REGION Ill c
  <lJ
  ~    1.0E-06
* u..                                                                                       )(  BLR-CRO
  <lJ QD 8E     1.0E-07 X   NBR-HALLSE7P
  <lJ u
0                                                                                     -     STPCurve c
  <ll  1.0E-08 QD c
..c u
1.0E-09                                                                   -
1.0E-06                 1.0E-05                    1.0E-04           1.0E-03 Core Damage Frequency (CDF)
Figure 1: Sensitivity Analysis Summary of Continuum Model Risk Regions - Geometric Mean

NOC-AE-16003367 Attachment 1 Page 16 of 35 The results for the August 2015 submittal baseline [1] and the sensitivity considering the continuum break model and arithmetic uncertainty aggregation are illustrated below in Figure 2. The calculated mean t.CDF values for the baseline and the sensitivity case were calculated to be in Region-2.
Risk Regions - STP - Sensitivity Analysis - Continuum Model - AM 1.0E-04 "'
                                               ~
REGION I u:-
0                                                                                           REGION II u    1.0E-05 s.
u c
OJ
::l O"
 ~
u.
OJ QI) 1.0 E-06 I                                                 I REGIONlll X BLR-CRO E
1.0E-07 X  NBR-HALLSE7P 0"'
OJ u
0                                                                                      -    STPCurve c
OJ 1.0E-08 QI) c J::
u 1.0E-09                                                     -
1.0E-06                 1.0E-05                    1.0E-04            1.0E-03 Core Damage Frequency (CDF)
Figure 2: Sensitivity Analysis Summary of Continuum Model Risk Regions - Arithmetic Mean Analysis of resultant figures from the geometric aggregation model shows that increased transport of small fibrous pieces, through increased erosion of settled debris, does not significantly affect the location of the results as compared to the baseline Risk-Region (Region-3) calculated in Attachment 1-3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [1] . This conclusion is supported by Figure 1 which shows that the calculated geometric means of t.CDF for the baseline (Attachment 1-3 analysis [1]) and sensitivity case lie within Region-3 and visually lie on top of each other in the figure. Further this conclusion is supported by the sensitivity results for the 5th, 50 1h, mean, and 95th percentiles in Table 5, which show that all analyzed quantiles lie within risk Region 3; where the 95th percentile value is a reasonably bounding estimate of t.CDF.
Considering the results of the sensitivity study and all former discussion it is concluded that varying the amounts of transported small piece fibrous debris to account for increased settling and erosion as discussed by the NRC Staff in the RAI statement;, will not move STP's geometric average calculated t.CDF out of Regulatory Guide 1.174 Risk Region-3 .
Increased settling and erosion as discussed does not significantly change the results from the baseline reported in the August 2015 submittal for either the geometric or arithmetic aggregation methods.

NOC-AE-16003367 Attachment 1 Page 17 of 35 References
[1] ML15246A126, "Attachment 1-1 STP Piloted Risk-Informed Approach to Closure for GSl-191through1-4 Defense in Depth and Safety Margin," 8/20/2015.
[2] ALION-CAL-STP-8511-08 Rev. 3, "Risk-Informed GSl-191 Debris Transport Calculation, " 2014.
[3] 66-9088089, "South Texas Project Test Report for ECCS Strainer Testing ," July, 2008.
[4] NUREG-1829, "Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process," April, 2008.
[5] Regulatory Guide 1.17 4, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions On Plant-Specific Changes to the Licensing Basis," May 2011 .
[6] ALION-REP-ALION-1006-04, "Erosion Testing of Small Pieces of Low Density Fiberglass Debris - Test Report, Rev. 1," November, 2011.

NOC-AE-16003367 Attachment 1 Page 18 of 35 Follow-up RAI 26 - RAI 26 questioned the effects of the addition of 25 percent of the latent fiber to the test flume prior to starting the recirculation pump. The response to the question provided in the August 20, 2015, submittal references sinking metrics for stagnant water. The sump pool is not stagnant, but is significantly turbulent during pool fill-up. NRC staff disagrees with the statement that fiber would have mixed with particulate debris resulting in trapping or sediment of the fiber. Existing guidance states that all fine fiber should be considered to transport to the strainer. In addition, the 2008 head loss test is used to determine an acceptable fiber limit for comparison. The comparison amount from the test should reflect the amount of fine fiber that was on the strainer at the test completion . Please provide a justification that placing 25 percent of the latent fiber into the test flume prior to starting the pump would result in the transportation of the fiber, or that the amount of fiber under consideration is insignificant.
STP Response:
The NRC Staff's disagreement with the statements made regarding the fiber-particulate mixing and concern about the effect of early fiber introduction's effect on the Rovero fine fiber limit is acknowledged, but the amount of debris which was added to the test flume prior to activation of the pump is insignificant. This response is written to detail the negligible impact discrediting 25% (6.24 lbm) of the latent fiber load , recorded in the July 2008 test report [1 ], from the Rovero fine fiber limit established in Attachment 1-3 of Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure (August 2015 submittal) [2] has on calculated core damage frequency.
The goal of these sensitivities is to see what affect subtracting 25% (6.24 lbm) of the July 2008 test [1] latent debris load (early introduced and possibly settled) from the deterministic August 2015 [2] established Rovero fiber fine limit has on calculated risk and the critical weld list. Two sensitivities have been performed in this evaluation: 1) a variation against the August 2015 subm ittal baseline analysis BLR-CRO and 2) a variation against the follow-up to 2009 RAl-19 sensitivity analysis HALLSE?P. Both of these sensitivity studies represent changes to the deterministic Rovero fiber fine limit, which is the limit that risk-informed CASA Grande calculated debris generation amounts are compared to.
No CASA Grande debris generation input changes were made to perform these sensitivity studies. Case definitions for the August 2015 submittal baseline, the follow-up to 2009 RAl-19 HALLSE?P (2016) case and the two sensitivity studies are provided in the numbered list below. Note that detailed case descriptions and results for the BLR-CRO and HALLSE?P cases are provided in the response to follow-up to 2009 RAl-19 (2016),
and are not transcribed here.
It is important to note that the baseline analysis incorporated slightly different geometry inputs than were used for the analysis supporting the August 2015 submittal [1 ]. Minor changes to geometry inputs defining concrete and steel structures were made to support responses to NRC Staff RAls about coatings destruction in this (2016) RAI set. Due to refinements in concrete structures for coatings, that also define robust barriers for debris destruction, small differences were observed in o isman which have been evaluated to negligibly impact calculated t.CDF, which is essentially identical to the t.CDF calculated

NOC-AE-16003367 Attachment 1 Page 19 of 35 for the August 2015 submittal [1 ]. All sensitivities were performed on the updated geometry input baseline case, BLR-CRO.
Case 01: Baseline run BLR-CRO is the baseline CASA Grande run representing the analysis currently described in the August 2015 submittal [1 ].
Case 02: Sensitivity run SR-HALLSE?P was designed to investigate the effect of settling all intact small fibrous piece debris that reaches the containment pool , as was visually observed in the July 2008 test, and subjecting them to ?-percent erosion. Note that the basis for ?-percent erosion has been explained in Follow-Up to 2009 RAl-18. In this follow-up to 2009 RAI analysis the SR-HALLSE?P case is considered a baseline for variance performed in Case 2, SR-HALLSE7P-ML25P.
Case 1:   Sensitivity run SR-CRO-ML25P was designed to investigate the effect of discrediting the 25% of latent fiber fines which were added to the July 2008 test flume [1] prior to activation of the pump from the deterministic Rovero fine fiber limit. The Rovero fine fiber failure threshold was reduced by 6.24 lbm, and 3.12 lbm for two and one trains operable plant states respectively, to discredit the latent fiber which was added early to the test flume.
Case 2:   Sensitivity run SR-HALLSE7P-ML25P was designed to investigate the exact same effect as that of Case 1 using a previously run sensitivity, SR-HALLSE?P, as a baseline. The SR-HALLSE?P sensitivity case models settling and erosion of all small piece fibrous debris transported to the containment pool and is explained in more detail in Follow-Up to 2009 RAl-19 (2016). The Rovero fine fiber failure threshold was reduced to discred it the latent fiber which was added early to the test flume .
All sensitivities and associated risk calculations were performed with CASA Grande release version 1.7 .2. Each sensitivity study was analyzed considering two separate plant states, two and one trains operable, as described in Section 4.2 of Attachment 1-3 in the August 2015 submittal [2] . The success frequencies are defined as the yearly frequencies with which the STP PRA would see a combination of trains, associated with a given plant state, go through recirculation successfully. The success frequencies for the two and one train operable plant states are 4.16E-06 and 1.55E-09 yearly occurrences respectively.
All sensitivity cases were evaluated with the continuum model; where the continuum model allows break sizes up to the maximum possible break size of the pipe inner diameter. Frequencies of breaks occurring at a given pipe rupture size were taken from NUREG-1829 and change in core damage frequency (t.COF) results were computed for both the Geometric and Arithmetic means of the expert elicitation process [3]. The statistical methodology implemented in Rovero is explained in detail in Attachment 1-3 of the August 2015 submittal [2] .

NOC-AE-16003367 Attachment 1 Page 20 of 35 Case 01 and Case 02 Results: BLR-CRO and SR-HALLSE7P Definition and results for both the BLR-CRO and SR-HALLSE7P cases have been provided in follow-up to 2009 RAl-19 (2016) response and are not transcribed in this response .
Case 1 Results: SR-CRO-ML25P The first sensitivity case of the response was designed to investigate the effect of subtracting 25% of the July 2008 test [1] latent fiber amount from the baseline (BLR-CRO)
Rovero fine fiber threshold. This subtraction directly discredits 6.24 lbm and 3.12 lbm, for two and one trains operable respectively, from the Rovero fine fiber threshold for each weld in the plant. For the two trains operable plant state the baseline (BLR-CRO) fine fiber limit of 191 .78 lbm was reduced to a value of 185.54 lbm in this sensitivity study. Similarly, for the one train operable plant state, the fine fiber threshold was reduced from 95.89 lbm to 92.77 lbm.
A summary of i'.lCDF results for the continuum break model are given in Table 1. Note that the columns labeled '2-Train ' and '1-Train' are the i'.lCDF estimates for both for the 2-train and 1-train operable plant states respectively, and the column label i'.lCDF is the combined total core damage frequency considering each plant states success frequency; 4.16E-06 and 1.55E-09 yearly occurrences respectively. The methodology for combining calculated i'.lCDF from the 2-train and 1-train frequencies is described in detail by Equation 5 Section 4.2 of Attachment 1-3 in Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [2] . All i'.lCDF estimates summarized in Table 1 have been evaluated at the 5th, 50th, Mean, and 95th percentiles to highlight values in the standard range of uncertainty. Note that the i'.lCDF estimates, considering the 5th, 50th, Mean, and 95th percentiles, are in Region-3 of Regulatory Guide 1.174 [4] for the sensitivity (SR-CRO-ML25P) when using geometric averages, and the geometric method of aggregation should be considered the most appropriate estimator of LOCA frequency.
Table I: SR-CRO-ML25P Continuum Break Model Results Summary Continuum Break Model - NUREG-1829 Geometric Means                    Arithmetic Means Quantile 2-Train     1-Train   Delta CDF    2-Train       1-Train  Delta CDF 5th       2.78E-10    4.36E-09   2.80E-10    6.65E-09      2.65E-08  6.65E-09 SOth       7.94E-09    9.80E-08   7.97E-09    1.73E-07      5.43E-07  1.73E-07 Mean       l .25E-07   5.78E-07   1.25E-07    1.60E-06      4.27E-06  1.60E-06 95th       3.66E-07    2.llE-06   3.66E-07    4.89E-06      1.35E-05  4.89E-06

NOC-AE-16003367 Attachment 1 Page 21 of 35 The critical weld list, as defined in the Rovero methodology [1 ], is a collection of welds that have a break occurrence that can generate and transport enough fibrous debris to exceed the amount of fibrous debris that reached the strainer in the July 2008 strainer flume test [3]. The debris amount which reached the strainer is used as a limit in Rovero methodology and is reduced in this sensitivity to discredit the amount of latent fiber which was added early to the test flume. The critical weld list for plant state one, with two trains operable, is given in Table 2 below. Columns two, three, four, and five provide the break location, smallest break size to fail oisma 11 , the amount of fiber transported for the smallest break to fail, and the difference between the transported fiber amount and the Rovero adjusted (for this sensitivity study) fine fiber threshold (185.54 lbm).
Table 2: SR-CRO-ML2SP Critical Weld List- 2-Train Operation Fiber Transported at     Difference from
#                 Break Location           O;small  (inches)
Smallest Break Size (lbm)  Threshold (lbm) 1     16-RC-1412-NSS-8                         12.814                213.296                27.756 2     29-RC-1401-NSS-3                         14.130                185.605                 0.065 3     29-RC-1101-NSS-4                         14.350                185.697                 0.157 4      29-RC-1201-NSS-4                         14.620                185.573                 0.033 5     29-RC-1301-NSS-4                         14.630                185.679                 0.139 6     31-RC-1302-NSS-RSG-lC-O N-SE             15.080                185.584                 0.044 7     29-RC-1101-NSS-RSG-lA-IN-SE              15.320                185.710                 0.170 8     29-RC-1101-NSS-5.1                       15.330                185.689                 0.149 9     29-RC-1401-NSS-RSG-lD-IN-SE              15.330                185.767                 0.227 10     29-RC-1401-NSS-4.1                       15.340                185.783                 0.243 11     29-RC-1201-RSG-lB-I N-SE                 15.580                185.664                 0.124 12     29-RC-1201-NSS-5.1                       15.590                185.618                 0.078 13     29-RC-1301-NSS-5.1                       15.610                185.617                 0.077 14     29-RC-1301-RSG-lC-IN-SE                  15.610                185.567                 0.027 15     31-RC-1102-NSS-RSG-lA-ON-SE              15.630                185.552                 0.012 16     31-RC-1102-NSS-1.1                       15.640                185.643                 0.103 17     31-RC-1202-NSS-4                         15.750                185.548                 0.008 18     31-RC-1202-NSS-RSG-18-0N-SE              15.810                185.550                 0.010 19     31-RC-1202-NSS-1.1                       15.820                185.656                 0.116 20     31-RC-1102-NSS-4                         15.900                185.558                 0.018 21     31-RC-1202-NSS-2                         15.910                185.638                 0.098 22     31-RC-1302-NSS-2                         15.980                185.577                 0.037 23     31-RC-1102-NSS-2                         16.030                185.679                 0.139 24     31-RC-1302-NSS-4                         16.180                185.588                 0.048 25     31-RC-1302-NSS-1.1                      16.200                 185.653                0.113 26     31-RC-1402-NSS-2                         16.360                185.548                 0.008 27     27 .5-RC-1203-NSS-1                     16.910                 185.542                0.002 28     27.5-RC-1303-NSS-1                      16.910                 185.546                0.006

NOC-AE-16003367 Attachment 1 Page 22 of 35 Fiber Transported at    Difference from
#                 Break Location           D;small (inches)
Smallest Break Size (lbm)  Threshold (lbm) 29     31-RC-1402-NSS-1.1                      16.940                 185.591                0.051 30     31-RC-1402-NSS-RSG-lD-ON-SE             16.940                 185.604                0.064 31     27. 5-RC-1103-NSS-1                     16.950                 185.591                0.051 32     31-RC-1202-NSS-8                        17.150                 185.619                0.079 33     31-RC-1102-NSS-8                        17.440                 185.623                0.083 34     31-RC-1402-NSS-4                         17.720                185.550                0.010 35     31-RC-1302-NSS-8                        18.080                 185.583                0.043 36     31-RC-1102-NSS-3                         18.350                185.569                0.029 37     31-RC-1202-NSS-3                        18.400                 185.590                0.050 38     31-RC-1102-NSS-9                        18.430                 185.548                0.008 39     31-RC-1202-NSS-9                         18.440                185.585                0.045 40     27 .5-RC-1403-NSS-1                     18.500                 185.541                0.001 41     31-RC-1302-NSS-3                        18.600                 185.569                0.029 42     31-RC-1302-NSS-9                         18.910                185.543                0.003 43     31-RC-1402-NSS-3                         19.390                185.689                0.149 44     31-RC-1402-NSS-8                        19.960                 185.576                0.036 45     31-RC-1402-NSS-9                         20.800                185.594                0.054 The critical weld list for plant state two, with one train operable, is given in Table 3 below for the SR-CRO-ML25P case. Columns two, three, four, and five provide the break location, smallest break size to fail oisma 11 , the amount of fiber transported for the smallest break to fail, and the difference between the transported fiber amount and the amount of fine fiber transported in the test adjusted for early latent fiber addition scaled to one train operable (92.77 lbm).
Table 3: SR-CRO-ML25P Critical Weld List - I-Train Operation D;small      Fiber Transported at    Difference from
 #                Break Location (inches)    Smallest Break Size (lbm)  Threshold (lbm) 1     16-RC-1412-NSS-8                           9.380                92.814                0.044 2     31-RC-1102-NSS-l.1                         9.660                92.816                0.046 3     31-RC-1102-NSS-RSG-lA-ON-SE                9.660                92.830                0.060 4     31-RC-1202-NSS-1.l                         9.740                92.777                0.007 5     31-RC-1202-NSS-RSG-lB-ON-SE                9.740                92.793                0.023 6     31-RC-1302-NSS-RSG-lC-ON-SE                9.780                92.789                0.019 7     12-RC-1221-BBl-9                           9.790                92.808                0.038 8     12-RC-1221-BBl-11                          9.810                92.802                0.032 9     12-RC-1125-BB 1-9                          9.820                92.779                0.009

NOC-AE-16003367 Attachment 1 Page 23 of 35 D;small   Fiber Transported at     Difference from
#             Break Location (inches)  Smallest Break Size (lbm)  Threshold (lbm) 10  29-RC-1101-NSS-RSG-lA-I N-S E   9.890            92.811                  0.041 11  29-RC-1101-NSS-5.l             -9.900            92.785                  0.015 12  12-Sl-1315-BBl-8                9.910            92.793                  0.023 13  29-RC-1301-NSS-4                9.930            92.797                  0.027 14  29-RC-1401-NSS-3                9.930            92.872                  0.102 15  29-RC-1101-NSS-4                9.970            92.901                  0.131 16  12-RC-1322-BBl-lA               9.986             92.900                 0.130 17  31-RC-1302-NSS-l.1              9.990            92.779                  0.009 18  12-RC-1322-BBl-1                9.996             92.795                 0.025 19  12-RC-1125-BBl-11              10.016            92.836                  0.066 20  29-RC-1201-NSS-4               10.020             92.812                 0.042 21  29-RC-1301-NSS-5.1             10.030             92.862                 0.092 22  29-RC-1301-RSG-lC-IN-SE        10.030            92.850                  0.080 23  12-RC-1221-BBl-12              10.086             92.823  '              0.053 24  29-RC-1201-NSS-5.1             10.090            92.774                  0.004 25  29-RC-1201-RSG-lB-IN-SE        10.090            92.872                  0:102 26  31-RC-1202-NSS-2               10.090             92.799                 0.029 27  12-RC-1112-BBl-1               10.126            97.467                  4.697 28  12-RC-1125-BBl-8               10.126             97.070                 4.300 29  12-RC-1125-BBl-10              10.126            130.232                37.462 30  12-RC-1125-BBl-12              10.126            125.681                32.911 31  12-RC-1125-BBl-13              10.126            101.131                 8.361 32  12-RC-1221-BBl-10              10.126            130.729                37.959 33  12-RC-1221-BBl-13              10.126            124.218                31.448 34  12-RC-1221-BBl-14              10.126             97.943                 5.173 35  12-RC-1312-BBl-1               10.126             92.926                 0.156 36  12-RC-1322-BBl-2               10.126            127.727                34.957 37  12-RC-1322-BBl-3               10.126            122.891                30.121 38  12-RC-1322-BBl-4               10.126             98.582                 5.812 39  12-Sl-1315-BBl-7               10.126            102.462                 9.692 40  12-Sl-1315-BBl-9               10.126            118.890                26.120 41  12-Sl-1315-BBl-10              10.126            123.075                30.305 42  29-RC-1101-NSS-3               10.126             98.873                 6.103 43  29-RC-1201-NSS-3               10.126             96.848                 4.078 44  29-RC-1301-NSS-3               10.126             96.839                 4.069
: 45. 31-RC-1102-NSS-2               10.160            92.830                  0.060 46  29-RC-1401-NSS-4.l             10.170             92.803                 0.033 47  29-RC-1401-NSS-RSG-1 D-1 N-SE  10.170             92.771                 0.001 48  31-RC-1302-NSS-2               10.220            92.836                  0.066

NOC-AE-16003367 Attachment 1 Page 24 of 35 D;small   Fiber Transported at     Difference from
 #            Break Location (inches)  Smallest Break Size (lbm)  Threshold (lbm) 49 31-RC-1402-NSS-1.1             10.330            92.775                 0.005 so 31-RC-1402-NSS-RSG-lD-ON-SE    10.330            92.787                 0.017 51 16-RC-1412-NSS-7               10.520            92.793                  0.023 52 31-RC-1402-NSS-2               10.620            92.779                 0.009 53 16-RC-1412-NSS-9               10.780            92.789                 0.019 54 29-RC-1401-NSS-2               10.780            92.784                  0.014 55 16-RC-1412-NSS-6               10.820            92.823                 0.053 56 27 .5-RC-1203-NSS-1            10.990            92.775                  0.005 57 27 .5-RC-1303-NSS-1            10.990            92.838                 0.068 58 27 .5-RC-1103-NSS-1            11.050            92.848                 0.078 59 31-RC-1202-NSS-4               11.050            92.784                 0.014 60 31-RC-1202-NSS-8               11.050            92.775                 0.005 61 31-RC-1102-NSS-4               11.150            92.783                 0.013 62 31-RC-1302-NSS-4               11.230            92.817                 0.047 63 31-RC-1102-NSS-8               11.240            92.775                 0.005 64 31-RC-1202-NSS-3               11.380            92.777                 0.007 65 31-RC-1302-NSS-8               11.430            92.781                 0.011 66 31-RC-1302-NSS-3               11.440            92.901                 0.131 67 31-RC-1102-NSS-3               11.450            92.829                 0.059 68 31-RC-1202-NSS-9               11.680            92.778                 0.008 69 31-RC-1102-NSS-9               11.700            92.817                 0.047 70 31-RC-1302-NSS-9               11.860            92.792                 0.022 71 16-RC-1412-NSS-5               12.070            92.771                 0.001 72 27.5-RC-1403-NSS-1             12.140            92.816                 0.046 73 31-RC-1402-NSS-3               12.300            92.776                 0.005 74 31-RC-1402-NSS-4               12.410            92.883                 0.113 75 16-RC-1412-NSS-1               12.814            94.726                 1.956 76 16-RC-1412-NSS-PRZ-1-Nl-SE     12.814            95.688                  2.918 77 31-RC-1402-NSS-8               13.190            92.819                 0.049 78 31-RC-1402-NSS-9               13.880            92.773                 0.003 79 27 .S-RC-1103-NSS-RPVl-N 2ASE  23.050            92.772                 0.002 80 27 .S-RC-1203-NSS-5            23.050            92.780                 0.010 81 27.5-RC-1203-NSS-RPV1-N2BSE    23.110            92.776                 0.006 82 29-RC-1401-NSS-1               23.660            92.794                 0.023 83 29-RC-1401-NSS-RPVl-NlDSE      23.680            92.782                 0.011 84 29-RC-1301-NSS-1               23.750            92.775                 0.005 85 29-RC-1301-RPVl-NlCSE          23.820            92.804                 0.034 86 29-RC-1101-NSS-1               23.910            92.774                 0.004 87 29-RC-1101-NSS-RPVl-NlASE      24.160            92.782                 0.012

NOC-AE-16003367 Attachment 1 Page 25 of 35 O;small      Fiber Transported at    Difference from
#                 Break Location (inches)    Smallest Break Size (lbm)  Threshold (lbm) 88     29-RC-1201-NSS-1                       24.190                92.791                0.021 89     29-RC-1201-RPVl-N lBSE                 24.220                92.784               0.014 90     27 .5-RC-1203-NSS-4                    25.370                92.777                0.007 91     27.5-RC-1103-NSS-6                     25.700                92.777                0.007 92     27 .5-RC-1103-NSS-7                    26.350                92.798               0.028 93     27 .5-RC-1303-NSS-5                    27.500               124.279               31.509 94     27 .5-RC-1303-NSS-6                    27.500               128.099               35.329 95     27.5-RC-1303-NSS-RPV1-N2CSE            27.500               128.746               35.976 96     27 .5-RC-1403-NSS-5                    27.500               118.646               25.876 97     27 .5-RC-1403-NSS-6                    27.500               124.614               31.844 98     27.5-RC-1403-NSS-RPV1-N2DSE            27.500               125.859               33.089 Case 2 Results: SR-HALLSE7P-ML25P The second sensitivity case of the response was designed to investigate the effect that discrediting the July 2008 test [1] early introduced portion of latent fine fiber*has when evaluating against the follow-up to 2009 RAl-19 (2016) SR-HALLSE7P case as a baseline.
This case is presented as additional support of the licensee's position that the quantity of latent fine fiber added early to the July 2008 test [1] is insignificant. The sensitivity case, SR-HALLSE7P, was designed in the follow-up to 2009 RAl-19 response to demonstrate
 - the impact of additionally generated fibrous fines from additional (including the total) small piece debris that would settle out of the pool rather than transport to the strainers and erode. The Rovero fine fiber threshold in SR-HALLSE7P, as discussed in follow up to 2009 RAl-19, was unchanged from the baseline BLR-CRO. Instead, transport characteristics of small piece LOFG were adjusted to reflect 2008 test observations [5]
that no small piece LFOG transported. Additionally the follow-up to 2009 RAl-19 response SR-HALLSE7P sensitivity case eroded and transported 7% of the total settled small fibrous debris, which bounds erosion reported in the Alion testing. Case 2 of this RAI response, SR-HALLSE7P-ML25P expands upon the follow-up to 2009 RAl-19 sensitivity study, SR-HALLSE7P, by reducing the Rovero fine fiber threshold to a value of 185.54 lbm and 92. 77 lbm for 2-train and 1-train operable plant states respectively.
A summary of .6.COF results for the continuum break model are given in Table 4. Note that the columns labeled '2-Train' and '1-Train' are the .6.COF estimates for both forthe 2-train and 1-train operable plant states respectively, and the column label .6.CDF is the combined total core damage frequency considering each plant states success frequency; 4.16E-06 and 1.55E-09 yearly occurrences respectively. The methodology for combining calculated
   .6.CDF from the 2-train and 1-train frequencies is described in detail by Equation 5 Section 4.2 of Attachment 1-3 in Supplement 2 to the STP licensing submittal for Risk-Informed GSl-191 closure [2]. All .6.COF estimates summarized in Table 4 have been evaluated at the 5th, 501h, Mean, and 95th percentiles to highlight values in the standard range of

NOC-AE-16003367 Attachment 1 Page 26 of 35 uncertainty. Note that the t.COF estimates, considering the 5th, 50 1h, Mean, and 95th percentiles, are in Region-3 of Regulatory Guide 1.174 [4] for the sensitivity (SR-HALLSE7P-ML25P) when using geometric averages, and the geometric method of aggregation should be considered the most appropriate estimator of LOCA frequency.
Table 4: SR-HALLSE7P-ML25P Continuum Break Model Results Summary Continuum Break Model - NUREG-1829 Geometric Means                       Arithmetic Means Quantile 2-Train      1-Train   Delta CDF      2-Train       1-Train   Delta CDF 5th     2. 98 E-10   4.45E-09   3.00E-10      6.92E-09      2.67E-08    6.93E-09 SOth     8.46E-09     l.OOE-07   8.49E-09      l.80E-07      5.45E-07    l.80E-07 Mean     l.31E-07     5.85E-07   l.32E-07      l.66E-06     4.26E-06     1.66E-06 95th     3.85E-07     2.14E-06   3.86E-07      5.07E-06      l.34E-05    5.07 E-06 The critical weld list, as defined in the Rovero methodology [2] , is a collection of welds that have a break occurrence that can generate and transport enough fibrous debris to exceed the amount of fibrous debris that reached the strainer in the July 2008 strainer flume test [1] reduced to discredit the amount of latent fiber which was added early. The critical weld list for plant state one, with two trains operable, is given in Table 5 below.
Columns two, three, four, and five provide the break location , smallest break size to fail o isma 11 , the amount of fiber transported for the smallest break to fa il, and the difference between the transported fiber amount and the Rovero adjusted fine fiber threshold (185.54 lbm).
Table 5: SR-HALLSE7P-ML25P Critical Weld List- 2-Train Operation Fiber Transported at        Difference from
#                   Break Location             D;small (inches)
Smallest Break Size (lbm)     Threshold (lbm) 1      16-RC-1412-NSS-8                            12.814                   226.647                 41. 107 2      29-RC-1401-NSS-3                            13.790                   185.646                  0.106 3      29-RC-1101-NSS-4                            13.930                   185.695                  0.155 4       29-RC-1201-NSS-4                            14.120                   185.561                  0.020 5       29-RC-1301-NSS-4                            14.150                   185.671                  0.131 6      31-RC-1302-NSS-RSG-lC-ON-SE                 14.450                   185.568                  0.028 7      29-RC-1101-NSS-RSG-lA-IN-SE                 14.800                   185.551                  0.011 8       29-RC-1101-NSS-5.l                          14.820                   185.645                  0.105 9       31-RC-1102-NSS-l. 1                         14.850                   185.624                  0.084 10      31-RC-1102-NSS-RSG-lA-ON-SE                 14.850                   185.622                  0. 082 11      29-RC-1401-NSS-RSG-1 0 -1N-SE               14.860                   185. 738                 0.198

NOC-AE-16003367 Attachment 1 Page 27 of 35 Fiber Transported at      Difference from
 #                Break Location            D;small (inches)
Smallest Break Size (lbm)  Threshold (lbm) 12     29-RC-1401-NSS-4. l                      14.870               185.585                  0.045 13     31-RC-1202-NSS-l.1                       14.990               185.605                  0.065 14     31-RC-1202-NSS-RSG-lB-ON-SE              14.990               185.595                  0.055 15     29-RC-1301-NSS-5. l                      15.050               185.557                  0.017 16     29-RC-1301-RSG-lC-IN-SE                  15.050               185.754                  0.214 17     29-RC-1201-RSG-lB-IN-SE                  15.060               185.612                  0.072 18     29-RC-1201-NSS-5.1                       15.070               185.712                 0.172 19     31-RC-1202-NSS-4                         15.260               185.652                  0.112 20     31-RC-1102-NSS-2                         15.270               185.572                  0.032 21     31-RC-1202-NSS-2                         15.270               185.679                 0.139 22     31-RC-1302-NSS-l.1                       15.280               185.588                 0.048 23     31-RC-1302-NSS-2                         15.300               185.542                 0.002 24     31-RC-1102-NSS-4                         15.460               185.553                 0.013 25     31-RC-1302-NSS-4                         15.610               185.631                 0.091 26     31-RC-1402-NSS-2                         15.650               185.556                 0.016 27     31-RC-1402-NSS-l.1                       16.100               185.679                 0.139 28     31-RC-1402-NSS-RSG-lD-ON-SE              16.100               185.675                 0.135 29     27 .5-RC-1303-NSS-1                      16.310               185.602                 0.062 30     27 .5-RC-1203-NSS-1                      16.340               185.576                 0.036 31     27 .5-RC-1103-NSS-1                      16.350               185.726                 0.186 32     31-RC-1202-NSS-8                         16.500               185.562                 0.022 33     31-RC-1102-NSS-8                         16.770               185.541                 0.001 34     31-RC-1402-NSS-4                         17.180               185.695                 0.155 35     31-RC-1102-NSS-3                         17.310               185.565                 0.025 36     31-RC-1202-NSS-3                         17.350               185.557                 0.017 37     31-RC-1302-NSS-8                         17.380               185.578                 0.038 38     31-RC-1302-NSS-3                         17.670               185.570                 0.030 39     31-RC-1202-NSS-9                         17.710               185.562                 0.022 40     31-RC-1102-NSS-9                         17.730               185.623                 0.083 41     27 .5-RC-1403-NSS-1                      17.810               185.550                 0.010 42     31-RC-1302-NSS-9                         18.210               185.568                 0.028 43     31-RC-1402-NSS-3                         18.640               185.591                 0.051 44     31-RC-1402-NSS-8                         19.360               185.544                 0.004 45     31-RC-1402-NSS-9                         20.130               185.582                 0.042 46     29-RC-1201-RPVl-N lBSE                   29.000               185.694                 0.154 The critical weld list for plant state two, with one train operable, is given in Table 6 below for the SR-HALLSE7P-ML25P case. Columns two, three, four, and five provide the break location, smallest break size to fail Disma11 , the amount of fiber transported for the smallest break to fail, and the difference between the transported fiber amount and the amount of

NOC-AE-16003367 Attachment 1 Page 28 of 35 fine fiber transported in the test adjusted for early latent fiber addition scaled to one train operable (92.77 lbm).
Table 6: SR-HALLSE7P-ML25P Critical Weld List - I-Train Operation D;small       Fiber Transported at      Difference from
#               Break Location (inches)      Smallest Break Size (lbm)   Threshold (lbm) 1     16-RC-1412-NSS-8                        9.190                92.782                   0.012 2     31-RC-1102-NSS-1.1                      9.360                92.802                   0.032 3     31-RC-1102-NSS-RSG-lA-ON-SE             9.360                92.797                   0.027 4     31-RC-1202-NSS-1.1                      9.450                92.786                   0.016 5     31-RC-1202-NSS-RSG-lB-ON-SE             9.450                92.786                   0.016 6     12-RC-1221-BBl-9                        9.490                92.858                   0.088 7     31-RC-1302-NSS-RSG-lC-ON-SE             9.510                92.828                   0.058 8     12-RC-1125-BBl-9                        9.540                92.789                   0.019 9     29-RC-1101-NSS-5.1                      9.540                92.818                   0.048 10    29-RC-1101-NSS-RSG-lA-IN-SE             9.540                92.882                   0.112 11    12-RC-1221-BBl-11                       9.550                92.771          J        0.001 12    12-51-1315-BBl-8                        9.620                92.802                   0.032 13    29-RC-1401-NSS-3                        9.620                92.795                   0.025 14    29-RC-1301-NSS-4                        9.650                92.798                   0.028 15    31-RC-1302-NSS-1.1                      9.680                92.856                   0.086 16    29-RC-1301-RSG-lC-I N-SE                9.690                92.775                   0.005 17    29-RC-1101-NSS-4                        9.700                92.786                   0.016 18    29-RC-1301-NSS-5.1                      9.700                92.853                   0.083 19    12-RC-1322-BBl-1                        9.720                92.870                   0.100 20    12-RC-1125-BBl-11                       9.740                92.867                   0.097 21    12-RC-1322-BBl-lA                       9.740                92.771                   0.001 22    29-RC-1201-NSS-4                        9.750                92.815                   0.045 23    29-RC-1201-RSG-lB-IN-SE                 9.770                92.813                   0.043 24    29-RC-1401-NSS-RSG-lD-IN-SE             9.780                92.823                   0.053 25    31-RC-1202-NSS-2                        9.780                92.816                   0.046 26    29-RC-1201-NSS-5.1                      9.790                92.773                   0.003 27    12-RC-1221-BBl-12                       9.800                92.785                   0.015 28    29-RC-1401-NSS-4.1                      9.800                92.814                   0.044 29    12-RC-1125-BBl-10                       9.810                92.806                   0.036 30    12-RC-1221-BBl-13                       9.860                92.780                   0.010 31    12-RC-1322-BBl-2                        9.860                92.793                   0.023 32    31-RC-1102-NSS-2                        9.870                92.852                   0.082 33    12-RC-1221-BBl-10                       9.900                92.791                   0.021 34    12-RC-1125-BBl-12                       9.920                92.844                   0.074 35    31-RC-1302-NSS-2                        9.940                92.793                   0.023

NOC-AE-16003367 Attachment 1 Page 29 of 35 D;small   Fiber Transported at     Difference from
#             Break Location (inches)  Smallest Break Size (lbm)  Threshold (lbm) 36 12-RC-1322-BBl-3              9.980            92.784                  0.014 37 31-RC-1402-NSS-1.1            9.980            92.850                  0.080 38 31-RC-1402-NSS-RSG-lD-ON-SE   9.980            92.890                  0.120 39 12-51-1315-BBl-10            10.096            92.811                  0.041 40 12-RC-1112-BBl-1             10.126            102.659                 9.889 41 12-RC-1125-BBl-8             10.126            102.699                 9.929 42 12-RC-1125-BBl-13            10.126            105.968                13.198 43 12-RC-1212-BBl-1             10.126             97.000                 4.230 44 12-RC-1221-BBl-8             10.126             97.830                 5.060 45 12-RC-1221-BBl-14            10.126            102.462                 9.692 46 12-RC-1312-BBl-1             10.126             97.760                 4.990 47 12-RC-1312-BBl-8             10.126             96.047                 3.277 48 12-RC-1322-BBl-4             10.126            103.194                10.424 49 12-51-1315-BBl-7             10.126            108.774                16.004 so 12-51-1315-BBl-9             10.126            125.120                32.350 51 27 .5-RC-1303-N55-3          10.126             92.823                 0.053 52 29-RC-1101-N55-3             10.126            104.133                11.363 53 29-RC-1201-N5S-3             10.126            101.944                 9.174 54 29-RC-1301-N55-3             10.126            102.019                 9.249 55 16-RC-1412-NS5-7             10.190             92.771                 0.001 56 31-RC-1402-N5S-2             10.350             92.801                 0.031 57 16-RC-1412-N55-9             10.500             92.791                 0.021 58 16-RC-1412-N55-6             10.520             92.771                 0.001 59 29-RC-1401-N55-2             10.520             92.781                 0.011 60 31-RC-1202-N55-8             10.550             92.810                 0.040 61 27 .5-RC-1303-N5S-1          10.730             92.772                 0.002 62 27 .5-RC-1203-N5S-1          10.750             92.784                 0.014 63 31-RC-1102-N55-8             10.760             92.802                 0.032 64 27.5-RC-1103-N5S-1           10.810             92.804                 0.034 65 31-RC-1202-N55-4             10.850             92.815                 0.044 66 31-RC-1102-N55-4             10.920             92.771                 0.001 67 31-RC-1302-NS5-8             10.950             92.807                 0.037 68 31-RC-1302-NS5-4             11.010             92.808                 0.038 69 31-RC-1202-N55-3             11.080             92.776                 0.005 70 31-RC-1102-N55-3             11.160             92.801                 0.031 71 31-RC-1202-N55-9             11.180             92.784                 0.014 72 31-RC-1302-N55-3             11.180             92.775                 0.005 73 31-RC-1102-N55-9             11.210             92.804                 0.034 74 31-RC-1302-N55-9             11.400             92.790                 0.020

NOC-AE-16003367 Attachment 1 Page 30 of 35 O;small       Fiber Transported at     Difference from
 #                Break Location (inches)     Smallest Break Size {lbm)   Threshold (lbm) 75    16-RC-1412-NSS-5                     11.710                 92.818                 0.048 76    27 .5-RC-1403-NSS-1                  11.810                 92.801                 0.031 77    31-RC-1402-NSS-3                     12.000                 92.792                 0.022 78    31-RC-1402-NSS-4                     12.130                 92.871                 0.101 79    31-RC-1402-NSS-8                     12.750                 92.832                 0.062 80    16-RC-1412-NSS-1                     12.814                100.521                 7.751 81    16-RC-1412-NSS-PRZ-1-N 1-SE          12.814                101.594                 8.824 82    31-RC-1402-NSS-9                     13.420                 92.827                 0.057 83    27.5-RC-1103-NSS-RPV1-N2ASE          21.850                 92.774                 0.004 84    27.5-RC-1203-NSS-5                   21.880                 92.788                 0.018 85    27.5-RC-1203-NSS-RPV1-N2BSE          21.960                 92.782                 0.012 86    29-RC-1401-NSS-1                     22.480                 92.785                 0.014 87    29-RC-1401-NSS-RPVl-N 1DSE           22.560                 92.810                 0.040 88    29-RC-1301-NSS-1                     22.690                 92.785                 0.015 89    29-RC-1301-RPV1-N1CSE                22.740                 92.785                 0.015 90    29-RC-1101-NSS-1                     22.800                 92.775                 0.005 91    29-RC-1101-NSS-RPV1-N1ASE            22.840                 92.772                 0.002 92    29-RC-1201-NSS-1                     23.210                 92.798                 0.028 93    29-RC-1201-RPV1-N1BSE                23.210                92.780                  0.010 94    27.5-RC-1203-NSS-4                   23.730                92.807        *-        0.037 95     27.5-RC-1103-NSS-6                   23.940                92.771                  0.001 96     27 .5-RC-1103-NSS-7                  24.350                 92.780                 0.010 97     27 .5-RC-1303-NSS-6                  24.730                 92.770                 0.000 98    27 .5-RC-1303-NSS-RPV1-N2CSE         24.820                 92.804                 0.034 99    27.5-RC-1403-NSS-RPV1-N2DSE          27.390                92.807                  0.037 100    27.5-RC-1303-NSS-5                   27.500                133.504                40.734 101    27 .5-RC-1403-NSS-5                  27.500                127.450                34.680 102    27 .5-RC-1403-NSS-6                  27.500                133.732                40.962 Summary and Conclusion Analyses were performed to explore the sensitivity of calculated risk (6.COF), using the Rovero method, to a reduction in the deterministic fine fiber threshold. This reduction was equal to 25% of the total test report specified latent fiber fines debris load of 10.4 ft3 or 24.96 lbm [1 ]. Changes to the Rovero fine fiber threshold in the sensitivity analyses were implemented directly to CASA Grande inputs with reductions of 6.24 lbm and 3.12 lbm for 2-train and 1-train operable plant states respectively. These reductions were applied as changes to both the August 2015 submittal baseline case [2], BLR-CRO, and the follow-up to 2009 RAl-19 (2016) sensitivity study case, SR-HALLSE?P. Both the BLR-CRO case and the SR-HALLSE?P case treated small piece LOFG as 100% settled out of recirculation in accordance with observations from July 2008 flume testing [1]; the SR-

NOC-AE-16003367 Attachment 1 Page 31 of 35 HALLSE7P case however fixes a small discrepancy from previous analysis and calculates the total amount of settled small piece fibrous debris to be eroded. More detail about the difference between the follow-up to RAl-19 sensitivity study, SR-HALLSE7P, and the baseline study, BLR-CRO, is available in follow-up to 2009 RAl-19 (2016). The case definitions for the August 2015 submittal baseline BLR-CRO [2], the follow-up to 2009 RAl-19 sensitivity SR-HALLSE7P, and the sensitivities studies are summarized below in Table
: 7. Of the four Cases: Case 01 represents the baseline (Attachment 1-3 analysis [2]), Case 02 represents the follow-up to 2009 RAl-19 sensitivity SR-HALLSE7P, Case 1 represents the effect on the baseline of discrediting the portion of latent fiber fines added early in the July 2008 test while Case 2 represents the same effect on the follow-up to 2009 RAl-19 erosion sensitivity, SR-HALLSE7P.
Table 7: Summary of Rovero Sensitivity Case Definitions Erosion % of Debris   2-Train/1-Train Rovero Fine Sensitivity Case #  Sensitivity Case Name Settled in Pool           Fiber Threshold 7% erosion of transport calculation settled portion, 0 % erosion of 01                  BLR-CRO        debris settled due to        191.78 lbm/95.86 lbm observation in test but transported in transport calculation [S]
02               SR-HALLSE7P      7%                           191.78 lbm/95.86 lbm 7% erosion of transport calculation settled portion, 0 % erosion of 1              SR-CRO-ML25P      debris settled due to        185.54 lbm/92.77 lbm observation in test but transported in transport calculation [5]
2           SR-HALLSE7P-ML25P    7%                           185.54 lbm/92.77 lbm Results were produced for the sensitivity case including NUREG-1829 uncertainty aggregation [3], for both the Geometric and Arithmetic aggregation methods. Mean ~CDF results for the sensitivity case, considering both of the uncertainty aggregation methods, have been provided in Table 8 for ease of comparison. Analyzing Table 8, considering the Regulatory Guide 1.174 thresholds for region three and two respectively of <1 E-6 and
<1 E-5 occurrences per year, it is seen that the geometric mean for the BLR-CRO baseline (Attachment 1-3 analysis [2]), the follow-up to 2009 RAl-19 (2016) SR-HALLSE7P case, and all sensitivity cases fall within Region 3; and the geometric method of aggregation is considered the most appropriate estimator of LOCA frequency. The        ' arithmetic mean for all cases falls within Region 2 considering the Regulatory Guide 1.174 thresholds.

NOC-AE-16003367 Attachment 1 Page 32 of 35 Table 8: Mean Delta CDF Results Summary Geometric     Arithmetic Case#          Case Name Means         Means 01              BLR-CRO              1.23E-07     1.59E-06 02           SR-HALLSE7P             1.28E-07     1.62E-06 1          SR-CRO-ML25P             1.25E-07     l.60E-06 2       SR-HALLSE7P-ML2SP           1.3 2E-07    1.66E-06 Placement of the baseline and sensitivity results on the Regulatory Guide 1.174 risk region map have been provided in Figure 1 and Figure 2 for ease of visualization. In Figure 1 and Figure 2 the varying colors of 'x' marks identify the case studies as defined in the right of the figure. The green, yellow and red filled areas of the plot illustrate risk Region-3 , Region-2, and Region-1 of Regulatory Guide 1.174 respectively. It is seen in Figure 1 below that the continuum model geometric mean L1CDF values for the baseline BLCRO case, the follow-up to 2009 RAl-19 HALLSE7P case, and all sensitivity cases fall within risk Region-3.
The maximum L'.1CDF , considering the continuum break model and geometric uncertainty aggregation, was realized in sensitivity Case 2 (SR-HALLSE7P-ML25P). The SR-HALLSE7P-ML25P sensitivity applied the reduction of fine fiber threshold to the SR-HALLSE7P sensitivity case from follow-up to 2009 RAl-19 (2016), which itself has already been shown to increase L'.1 CDF values only marginally. The combined effect on L'.1CDF shown from the SR-HALLSE7P-ML25P case is nearly indistinguishable from the SR-HALLSE7P and BLR-CRO cases shown in Figure 1.
Risk Regions - STP - Sensitivity Analysis - Continuum Model - GM 1.0E-04    ..
                                                    ~
REGION I Li:'
a                                                                                             REGION II u       1.0E-05
  ~
u c:
   '1J O'
   ~
LI..
   '1J 1.0E-06 I                                                I REGION Ill X  BLR-CRO QD E                                      *
                                                                                              )( SR-HALLSE7P a"'     1.0E-07
   '1J                                                                                        X SR-CRO-ML25P u
0 c:
   '1J    l.OE-08                                                                             X SR-HALLSE7P-QD c:                                                                                            M L25P u"'
  .s::
                                                                                             -STPCurve l.OE-09 1.0E-06                  1.0E-05                    1.0E-04           1.0E-03 Core Damage Frequency (CD F)
Figure I: Sensitivity Analysis Summary of Continuum Model Risk Regions - Geometric Mean

NOC-AE-16003367 Attachment 1 Page 33 of 35 The results for the baseline and both sensitivities considering the continuum break model and arithmetic uncertainty aggregation are illustrated below in Figure 2. The calculated mean tlC OF values for the baseline and all sensitivity cases were calculated to be in Region-2.
Risk Regions - STP - Sensitivity Analysis - Continuum Model -AM 1.0E-04 REGION I u::-                                                                                         REGION II 0
u        l.OE-05 u
c:
I REGION Ill I CIJ
::J er      1.0E-06                                                                           X  BLR-CRO
    ~
u..
CIJ E
X  SR-HALLSE7P 0"'
CIJ 1.0E-07 X SR-&#xa3;RO-ML25P u
0 c:
SR-HALLSE7P-CIJ    1.0E-08
    ""c:                                                                                        M L25P u"'
  ~
                                                                                           -    STPCurve 1.0E-09 1.0E-06                 1.0E-05                    1.0E-04         1.0E-03 Core Damage Frequency (CDF)
Figure 2: Sensitivity Analysis Summary of Continuum Model Risk Regions - Arithmetic Mean Analysis of resultant figures from the geometric aggregation model shows that discrediting the portion of latent fine fiber which was added early in the July 2008 test [1] negligibly affects the value of the results in the general Risk-Region (Region-3) calculated in Attachment 1-3 of the August 2015 submittal [2]. This conclusion is supported by Figure 1 and Figure 2 which show that all calculated geometric means of tlCOF for the baseline (Attachment 1-3 analysis [2]), the follow-to 2009 RAl-19 (2016) SR-HALLSE7P case and all sensitivity cases lie within Region-3, with points visually on top of each other in the risk region plot. Further this conclusion is supported by the sensitivity results for the 5th, 501h, mean , and 95th percentiles in Tables 1 and 4, which show that all analyzed quantiles lie within risk Region 3; where the 95th percentile value is a reasonably bounding estimate of tlCOF.
Considering the results of the sensitivity studies and all former discussion it is concluded that a reduction in the Rovero fine fiber threshold by 25% of the latent fiber fines which were added early to the 2008 flume test has a negligible impact on STP's calculated tlCOF. Therefore the portion of latent fiber fines which were added early to the July 2008 test is considered insignificant to Rovero risk evaluation .

NOC-AE-16003367 Attachment 1 Page 34 of 35 References
[1] 66-9088089, "South Texas Project Test Report for ECCS Strainer Testing," July, 2008.
[2] ML15246A126, "Attachment 1-1 STP Piloted Risk-Informed Approach to Closure for GSl-191 through 1-4 Defense in Depth and Safety Margin," 8/20/2015.
[3] NUREG-1829, "Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process," April, 2008.
[4] Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions On Plant-Specific Changes to the Licensing Basis," May 2011.
[5] ALION-CAL-STP-8511-08 Rev. 03, "Risk-Informed GSl-191 Debris Transport Calculation," 2014.

NOC-AE-16003367 Attachment 1 Page 35 of 35 Net Positive Suction Head Follow-up RAI 37 - In the December 23, 2009, RAI, the NRG staff asked the licensee to provide net positive suction head (NPSH) margin results for low head safety injection (LHSI), high head safety injection (HHSI), and core spray (CS) pumps, for the LBLOCA and SBLOCA cases, under conditions of hot-leg recirculation. The licensee provided the NPSH margin for the LBLOCA for LHSI, HHSI, and CS. The licensee stated that its SBLOCA scenario will have little to no debris on the strainer to contribute to head loss. The licensee concluded that there is only clean strainer head loss for the SBLOCA case, which is much less than LBLOCA total strainer head loss. The lower flow for the SBLOCA would reduce clean strainer head loss compared to LBLOCA and the NPSH available would be slightly higher for SBLOCA since piping friction loss is less due to lower flow. Therefore, for SBLOCA compared to LBLOCA, NPSH margin would increase somewhat and total strainer head loss would be much less. Please provide additional detail for the basis that near-zero debris head loss is justified for the SBLOCA case.
STP Response:
As discussed in Attachment 1-2 of NOC-AE-15003241 of August 20, 2015, the amount of fiber fines from the 2008 July strainer head loss test was 191. 78 lbm. This amount and the other debris items yielded a strainer head loss that was acceptable with respect to NPSH considerations. The fiber bed was less than 1/8 inch thick. SBLOCA would generate much less debris. As shown in Table 17 of Attachment 1-3 of NOC-AE-15003241 of August 20, 2015, the amount of fiber fines for small breaks (e.g. for 0. 75 inch pipe; 1.0 inch pipe; 2.0 inch pipe) is approximately 30 lbm. By comparison to the 1/8 inch thick debris bed for the tested amount of 191. 78 lbm., the small breaks are not expected to yield formation of a debris bed on the sump strainers. There would be open area on the sump strainers resulting in no head loss due to debris. Thus the SBLOCA case would have only clean strainer head loss to consider.

NOC-AE-16003367 Attachment 2 Attachment 2 Response to SSIB-3-8 and 3-9

NOC-AE-16003367 Attachment 2 Page 1of3 SSIB-3-8 FSAR NPSH Values Tables 6.3-1 and 6.2.2-4 of Attachment 3-4 show UFSAR changes for ECCS component parameters and CSS pump NPSH parameters specifically for required and available NPSH.
The changes in Table 6.3-1 are as follows:
High Head Safety Injection Pump Currently          For approval in Parameter                            approved                  the LAR Required NPSH at max. flow rate, ft (max)                  16.1                      1.1 Available NPSH, ft (From RWST [refueling water storage tank)                                               55.8                     41.1 Available NPSH, ft (From RCB [reactor coolant building] Emergency Sump)                                 > 17.8                     7.4 Low Head Safety Injection Pump Currently          For approval in Parameter                            approved                  the LA~
Required NPSH at max. flow rate, ft (max)                  16.5              .... 1.5 Available NPSH, ft (From RWST)                              55.1                     40.8 Available NPSH, ft (From RCB Emergency Sump)                                                     > 18.0                     7.5 The changes in Table 6.2.2-4 are as follows:
CSS Pump                                        ..
Currently          For approval in Parameter                            approved                  the LAR Required NPSH at max. flow rate, ft (max)                  16.4                      1.4       -
Available NPSH, ft (From RWST)                              56.1                     41.4 Available NPSH, ft (From RCB Emergency Sump)                                                     > 17.6                     7.2 Please confirm that the UFSAR changes for the above parameters are not a result of changes to the NPSH licensing basis calculations, but instead a change in the reference point for the calculated values. Define what the reference point is for the currently approved values, for the values for approval in the LAR, and where this definition is described in licensing basis documents.

NOC-AE-16003367 Attachment 2 Page 2 of 3 STP Response:
The parameter values changed from the original plant design with sump screens primarily for these reasons:
* a different treatment of the strainer debris load in response to GL 2004-02 that was based on testing rather than the treatment called for in the original plant licensing basis per RG 1.82, proposed Revision 1, May 1983 that was based on a calculation
* a change in the reference point for NPSH
* a refinement of the containment water level calculation which had a small impact on NPSH Available
* a redefinition of NPSH Available to exclude the debris head loss and the clean strainer head loss The reference point for the NPSH values listed in the above table as "currently approved" is the elevation of the center line of the first stage impeller. As stated on Page 11 of -4 of NOC-AE-15003241 of August 20, 2015, the reference point for the values listed as "for approval in the LAR" is the elevation of the center line of the pump suction nozzle.

NOC-AE-16003367 Attachment 2 Page 3 of 3 SSIB-3-9 The UFSAR markup in the Rovero submittal does not provide a clear value for NPSH margin. The acronym TSHL is not defined in the markup. It is not clear in the tables whether margin includes the strainer losses. Since TSHL changes with temperature, the listing of a single value can be misleading, especially when it is not the limiting value. Consider including a more robust description of TSHL and how it affects NPSH margins under varying conditions.
STP Response:
The acronym TSHL is defined on Page 11 of Attachment 3-4 of NOC-AE-15003241 of August 20, 2015. A new UFSAR markup is planned to be provided for information only after the last round of RAI responses is submitted. Additional cases for various conditions will be considered for inclusion in the UFSAR to show the effects on NPSH margin. This information was previously provided in tables starting on Page 62 of Attachment 1-2 of NOC-AE-15003241 of August 20, 2015.

NOC-AE-16003367 Attachment 3 Attachment 3 Response to SNPB-3-9 and 3-10

NOC-AE-16003367 Attachment 3 Page 1 of 5 SNPB-3-9 Reference and Limits of Closure Relationships Please demonstrate that each closure relationship is associated with an appropriate reference providing its limits of applicability.
Criterion         2.3     Reference      SRP, lll.3a STP Response:
Reference and limits of closure relationships Demonstrate that each closure relationship is associated with an appropriate reference providing its limits of applicability.
        *~
Crlterfon           2.3 Leve,}9f 3                                                            3 Concern Overall Moderate
* Si nificance The RELAP5 series of codes has been developed at the Idaho National Laboratory (INL) under sponsorship of the U.S. Department of Energy, the U.S. Nuclear Regulatory Commission, members of the International Code Assessment and Applications Program (ICAP), members of the Code Applications and Maintenance Program (CAMP), and members of the International RELAP5 Users Group (IRUG). Specific applications of the code have included simulations of transients in light water reactor (LWR) systems such as loss of coolant, anticipated transients without scram (ATWS), and operational transients such as loss of feedwater, loss of offsite power, station blackout, and turbine trip.
RELAP5-3D is the latest in the series of RELAP5 codes which has included all the capabilities of the RELAP5 family in simulating the behavior of a reactor coolant system during transients such as LOCA scenarios. The mission of the RELAP5-3D development program was to develop a code version suitable for the analysis of all transients and postulated accidents in LWR systems, including both large- and small-break loss-of-coolant accidents (LOCAs) [1] .
The RELAP5 code has been widely used for analysis of LOCA scenarios of different break size including large and small breaks. The use of the code has been extended from the initial phases of the accident to the long term core cooling [2].
The development of the models and code versions that constitute RELAP5-3D has spanned more than two decades from the early stages of RELAP5-3D numerical scheme development (circa 1976) to the present. RELAP5-3D represents the aggregate accumulation of experience in modeling core behavior during accidents, two-phase flow process, and LWR systems (3] . The code includes many generic component models from which general systems can be simulated.
The component models include pumps, valves, pipes, heat releasing or absorbing structures,

NOC-AE-16003367 Attachment 3 Page 2 of 5 reactor point kinetics, separators, annuli, pressurizers, accumulators, and control system components. In addition, special process models are included for effects such as form loss, flow at an abrupt area change, branching, counter-current flow, and choked flow.
The code development has benefitted from extensive application and comparison to experimental data in the LOFT, PBF, Semiscale, ACRR, NRU, and other experimental programs.
Volume IV contains a detailed discussion of the models and correlations used in RELAP5-3D [3]
and their applicability. Scaling considerations and assessment are also included. The document is a revised and expanded version of the RELAP5/MOD2 models and correlations report [4], and includes discussion of the correlations and implementation assumptions necessary for an understanding of the model.
A detailed description of the content of Volume IV is provided below:
Section 2 - Field Equations This section lists the finite difference form of the basic field equations used in the two-fluid calculation. Field equations are derived and described in detail in Volume I.
Section 3 - Flow Regime Maps This section describes the models for defining flow regimes and flow-regime-related models for interphase friction, wall friction, wall heat transfer, and interphase heat and mass transfer. Heat transfer regimes are defined and used for wall heat transfer. In particular, Section 3. 1 describes the horizontal volume flow regime map Section 3.2 provides details of the flow regime map applied to vertical volumes Section 3.3 includes a description of the flow regime map used in high-mixing volumes such as pumps Sections 3.5 describes the junction flow regime maps.
Section 4 - Closure Relations for the Fluid Energy Equations This section of the volume is entirely dedicated to the description of the closure relationships used in the RELAP-30 for fluid energy equations. The section is divided into different sub-sections as described below:
Section 4. 1 provides a description of the bulk interfacial heat transfer correlations based on the different possible flow regimes. Modifications of these correlations for specific conditions (noncondensable gases, vertical stratified flow) are also described in this section.
Section 4.2 describes the correlations and methods used to obtain the information necessary for the walls to exchange energy with the fluid where reflood is not activated. This section describes the logic for the selection of the of the heat transfer modes. Table 4.2-1 of Volume IV describes the heat transfer modes included in RELAP5-3D. Table 4.2-3 lists all available RELAP5-3D wall heat transfer correlations. Geometry-specific correlations and limits of applicability of these correlations are included in this section.

NOC-AE-16003367 Attachment 3 Page 3 of 5 Section 4.3 includes a description of a new set of CHF correlations available in RELAP5-3D Section 4.4 describes the modifications to the wall heat transfer coefficients, the lnterfacial heat transfer, and interfacial drag when reflood is active.
Section 5 - Closure Relations Required by Fluid Mass Conservation Equations This section points to Section 4. 7 for the description of the mass conservation closure relations.
Section 6 - Momentum Equation Closure Relations This section discusses the interphase friction and wall drag relations necessary for closure in the momentum equation.
lnterphase friction is described in Section 6.1.
Wall drag is described in Section 6.2.
Section 6.3 provides a detail description of the entrainment correlations available and their applicability.
Section 7 - Flow Process Models RELAP5-3D includes correlations to model special process and effects such as form loss, flow at an abrupt area change, branching, counter-current flow, and choked flow, their applicability and assessment.
Section 7. 1 described the correlations for used for modeling abrupt expansions and contractions in single- and two-phase flow conditions.
Sections 7.2 and 7.3 are entirely dedicated to the models adopted to choked or critical flow. These correlations are designed to handle single phase liquid subcooled choked flow, two-phase choked flow (one-component and two-component), and single phase vapor/gas (one-component and two component) choked flow.
Section 7.4 described the countercurrent flow limitation model, its implementation and the assessment.
Section 7. 5 provides a description of the stratification entrainment/pullthrough model for horizontal and vertical volumes.
Section 8 - Special Component Models This section describes the modes adopted to simulate special components such as pumps, and separators/dryers.
Section 9 - Heat Structure Process Models This includes the heat conduction, the reflood heat conduction, gap conductance, and the point reactor kinetics.
The description of the decay power models available is also included in this section.

NOC-AE-16003367 Attachment 3 Page 4 of 5

==References:==

[1]. Thomas K.S. Liang, Huan-Jen Hung, Chin-Jang Chang, Lance Wang, "Development of LOCA Calculation Capability with RELAP5-3D in Accordance with the Evaluation Model Methodology'', lcone-9, 2001.
[2]. NUREG/CR-6770 LA-UR-01-5561, "GSl-191: Thermal-Hydraulic Response of PWR Reactor Coolant System and Containments to Selected Accident Sequences," Los Alamos National Laboratory, August 2002.
[3]. RELAP5-3D Code Manual, Vol. IV "Models and Correlations". INEEL-EXT-98-00834, Revision 4.1, September 2013.
[4]. R. A. Dimenna et al., RELAP5/MOD2 Models and Correlations, NUREG/CR-5194, EGG-2531, Idaho National Engineering Laboratory, August 1988.
Other References not listed Thomas K.S. Liang, Huan-Jen Hung, Chin-Jang Chang, Lance Wang, "Development of LOCA Calculation Capability with RELAP5-3D in Accordance with the Evaluation Model Methodology",
lcone-9, 2001.
Thomas K. S. Liang, Development of an Appendix K Version of RELAP5-3D and Associated Deterministic-Realistic     Hybrid    Methodology    for    LOCA       Licensing      Analysis, http://www.intechopen.com/
I. Parzer, B. Mavko, Analysis of RELAP5/MOD3.3 Prediction of 2-lnch Loss-of-Coolant Accident at Krsko Nuclear Power Plant, NUREG/IA-0222.

NOC-AE-16003367 Attachment 3 Page 5 of 5 SNPB-3-10 User Manual Please provide the user manual and/or similar guidance for analysts performing simulations using the L TCC EM.
The user manual should provide (a) detailed instructions about how the computer code is used, (b) a description of how to choose model input parameters and appropriate code options, (c) guidance about code limitations and options that should be avoided for particular accidents, components, or reactor types, and (d) if multiple computer codes are used, documented procedures for ensuring complete and accurate transfer of information between different elements of the EM.
Criterion      2.4    Reference      SRP, lll.3a STP Response:
The attached User Manual provides detailed instructions to the user in order to run the Evaluation Model for the STPNOC Units 1 and 2.

User Manual for GSI-191 RCS Thermal-Hydraulics, Revision 0 June 16, 2016 Abstract The application of RELAP 5-3D&#xa9; to analysis of Hot Leg Break (HLB) and small Cold Leg Break (CLB) is described. Simulations have been developed to be used in Generic Safety Issue 191 - the NRC Generic Safety Issue number 191 (GSI-191) screening analyses of hypothesized core blockage scenarios. Because the simulations are used in deterministic Risk-informed Over Deterministic (RoVERD) applications, they are each defined by an Engineering Calculation per OPGP04-ZA-0307. OPGP04-ZA-0307 procedure use is outside the scope of this document; requires qualification per the STP Nuclear Operating Company (STPNOC) Operations Quality Assurance Pro-gram (OQAP).
1

1     Use of RELAP5-3D&#xa9; Detailed instructions on use of of the RELAP5-3D&#xa9; software are given in INEEL-EXT-98-00834, Revision 4.1, September 2013, RELAP5-3D Code Manual Volume II: User's Guide and Input Requirements and RELAP5-3D Code Manual Volume V: User's Guidelines. The entire code manual set (in-cluding the user manuals) are provided in the STPNOC Software Quality Assurance (SQA) package stored in the STPNOC Records Management Sys-tem (RMS) STI 34280651. In the following, some additional details regarding the specific application to GSI-191 are provided.
The authorized version of RELAP5-3D&#xa9; is found in the STPNOC MSI as
'RELAP5-3D'; the SQA package is in STPNOC RMS under STI 34280651.
This is the only version certified for use in GSI-191 RCS thermal-hydraulic calculations at STPNOC. Prior to use on any particular computing platform, the implementation must be verified on the new platform per the RELAP5-3D&#xa9; SQA Test Plan: "RELAP5-3D Rev 0 Test Plan", STI 34280651, 12/08/2015 (or the most current version of the SQA if revised). The code is validated to be used for Reactor Coolant System (RCS) HLBs and small CLBs as enumerated below.
V.1 16" HLB V.2 6" HLB V.3 2" HLB V.4 2" CLB The authorized version of the model for use with GSI-191 is documented in Engineering Calculation RC09989. This is the steady-state base nodal-ization and verification of the steady state STP parameters. Transients are developed from the steady state base case by using the appropriate input file from the engineering calculation as enumerated below.
: 1. small HLB RC09967 R/O (STI# 34327912).
: 2. medium HLB RC09968 R/O (STI# 34327913).
: 3. large HLB RC09969 R/O (STI# 34327914).
: 4. small CLB RC09970 R/O (STI# 34327919).
2

Sensitivity studies are generated by changing core nodalization methodology.
: 1. Core nodalization
: 2. Break size
: 3. Decay power level with 103 Steam Generator (SG) plugging.
: 4. Axial power shape Any deviations from the input files require a revision or new engineering calculation performed per OPGP04-ZA-0307.
2     Input parameter selection The input parameters and code options (INEEL-EXT-98-00834, Revision 4.1, September 2013, RELAP5-3Ife Code Manual Volume II: User's Guide and Input Requirements) are described in Engineering Calculations for each case simulated. The option selection is defined in each Engineering Calculation for the simulation.
3     Limitations and options This user manual is limited to application of the cases as enumerated in items V.l to V.4 (Section 1). Detailed option selections for the particu-lar models are provided in the applicable Engineering calculation for each RELAP5-3D&#xa9; VOLUME and JUNCTION card.
4     Information transfer This section is intended to guide users to run RELAP5-3D simulations on the designated Ubuntu workstation 1 at the Department of Nuclear Engineer-ing at Texas A&M University. The simulated scenarios are Loss of Coolant Accident (LOCA) plus core blockage, with different break sizes.
1 Workstation: Texas A&M Nuclear Engineering- HASSANGRADll - 6G93JS1 - TEES 205657 3

4.1       Guide Every simulation is identified by an unique "case name". Output, restart and plot files of each case have the same filename (the case name), but different extension (.o, .r, and .plt respectively). The input file (.i file) instead might have a different filename. In particular, steady state cases have input file's filenames which is the case name, restart cases instead have input file's filenames different from the state case.
The methodology to run RELAP5-3D&#xa9; simulations is different in case the user runs a steady state case or a restart case. These differences are explained in Section 4.5 of this document. All the other steps described are equivalent for both steady state and restart cases.
4.2       Run folder content In order to run the simulation properly, the run-folder (/media/vaghetto/Relapl/Relap5-3D_v4.1.3Je_2016-04runs) should contain:
* All the files contained into the folder "relap" of the RELAP5-3D version 4.1.3 installation CD provided by INL (65 files).
* License file "rellic.bin".
If one or more of these files are missing, RELAP5-3D will error-out with either a warning message or with a critical error message depending on the importance of the missing file for the calculation.
4.3       Moving input files into the Run folder Each RELAP 5-3D simulation (case) requires the user to move into the running folder some additional files:
* RELAP5-3D input file (.i extension file).
* The shell script file (runRelap5.sh). This script file contains the actual linux command to run the RELAP5-3D case.
In case the user is running a "restart" case, the run folder has to also contain the RELAP5-3D restart file (.r extension file file) from the restart case (the case user want to restart from).
4

4.4       File settings The files relap5.x and runRelap.sh have to be given rights to be run as a program.
4.5       The shell script file 4.5.1       Steady state cases For steady state RELAP5-3D&#xa9; cases, the runRelap5.sh contains only the command to run the simulation. For an Ubuntu machine this shell script file contains:
     ./relap5.x -i ss_case_name.i -o ss_case_name.o -r ss_case_name.r Where "ss_case_name.i" is the name of the input file (that has to be present in the folder), "ss_case_name.o" is the name of the output file created by RELAP5-3D&#xa9; and "ss_case_name.r" is the name of the restart file that will be created as well by RELAP5-3D&#xa9; . Among the output (.o) and restart
( .r) files, a third file with extension "plt" will be created (plot file). This file will be named "ss_case_name.plt".
Once the simulation finishes, the user shall manually create a folder (result folder) inside the running folder named "ss_case_name" ; and move the files "ss_case_name.i", "ss_case_name.o", "ss_case_name.r", "ss_case_name.plt", and "runRelap5.sh" into it.
These final steps (creating the result folder and moving the files) may be done automatically by adding few lines in the runRelap5.sh script. These lines are:
mkdir -v ./ss_case_name mv :-b ss_case_name.* ./ss_case_name/
cp -b runRelap5.sh ./ss_case_name/
5

4.5.2    Restart cases For restart cases, the runRelap5.sh contains the commands for:
* Copying the restart file from the ss case result-folder "ss_case_name.r" into the run folder (changing the name to "tr_case_name.r").
* Creating the result folder inside the running-folder named "tr_case_name".
* Copying into the result folder the steady state restart file "ss_case_name.r" and of the steady state input file "ss_case_name.i".
* Running the simulation.
* Moving the input file, the output file, the restart file, and the plot file inside the result folder.
* Copying the file runRelap5.sh inside the result folder.
These commands are:
mkdir -v . /tr _case_name cp . / ss_case_name / ss_case_name.r . /tr _case_name.
cp ./ss_case_name/ss_case_name.i ./tr_case_name/
cp ./ss_case_name/ss_case_name.r ./tr_case_name/
   ./relap5.x -i tr_filename.i -o tr_case_name.o -r tr_case_name.r mv -b tr _filename.i ./tr_case_name mv -b tr_case_name.* ./tr_case_name cp runRelap5.sh ./tr_case_name The runRelap5.sh file works only if the steady state result folder is inside the running folder and properly formatted accordingly with Section 4.5.l.
The user must be careful when editing the runRelap5.sh for a specific case; the "find and replace" feature of the user's favorite text editor is strongly recommended.
6

4.6     Running the case To run the Relap5 case, open a terminal window and navigate to the running folder:
cd /media/vaghetto/Relapl/Relap5-3D_v4.l.3_ie_2016-04runs Subsequently type:
runRelap5.sh then press enter to run the simulation.
7

NOC~AE-16003367 Attachment 4 Attachment 4 Definitions and Acronyms

NOC-AE-16003367 Attachment 4 Page 1of2 Definitions and Acronyms ANS  American Nuclear Society            ECWS        Essential Cooling Water ARL  Alden Research Laboratory                       System (also ECW)
ASME American Society of Mechanical Engineers                EM          Evaluation Manual BA   Boric Acid                          EOF         Emergency Operations BAP  Boric Acid Precipitation                        Facility BC   Branch Connection                   EOP         Emergency Operating BEP  Best Efficiency Point                           Procedure(s)
B-F  Bimetallic Welds                     EPRI       Electric Power Research B-J  Single Metal Welds                              Institute BWR  Boiling Water Reactor                EQ         Equipment Qualification CAD  Computer Aided Design                ESF        Engineered Safety Feature CASA Containment Accident                 FA         Fuel Assembly(s)
Stochastic Analysis                  FHB        Fuel Handling Building CCDF Complementary Cum1,..1lative         GDC        General Design Criterion(ia)
Distribution Function or             GL         Generic Letter Conditional Core Damage              GSI        Generic Safety Issue Frequency                            HHSI       High Head Safety Injection ccw  Component Cooling Water                         (ECCS Subsystem) ,,.-':'
CDF  Core Damage Frequency                HLB        Hot Leg Break CET  Core Exit Thermocouple(s)            HTVL       High Temperature Vertical .
CFO  Computational Fluid                             Loop Dynamics                             HLSO       Hot Leg Switchover CHLE Corrosion/Head Loss                  ID         Inside Diameter Experiments                          IGSCC      lntergranular Stress CHRS Containment Heat Removal                        Corrosion Cracking System                               ISi        In-Service Inspection CLB  Cold Leg Break or Current            LAR        License Amendment Licensing Basis                               , Request CRMP Configuration Risk                   LBB        Leak Before Break ..
Management Program                   LBLOCA     Large Break Loss of C.oolant cs   Containment Spray                               Accident CSHL Clean Strainer Head Loss             LCO        Limiting Condition for css  Containment Spray System                        Operability (same as CS)                         LDFG       Low Density Fiberglass eves Chemical Volume Control              LERF       Large Early Release System                                          Frequency OBA  Design Basis Accident                LHS        Latin Hypercube Sampling DBD  Design Basis Document                LHSI       Low Head Safety Injection D&C  Design and Construction                         (ECCS Subsystem)
Defects                              LOCA       Loss of Coolant Accident DEGB Double Ended Guillotine              LOOP/LOSP Loss of Off Site Power Break                                MAAP       Modular Accident Analysis DID  Defense in Depth                                Program OM   Degradation Mechanism                MAB/MEAB Mechanical Auxiliary Building ECC  Emergency Core Cooling                          or Mechanical Electrical (same as ECCS)                                  Auxiliary Building ECCS Emergency Core Cooling               MBLOCA     Medium Break Loss of System                                          Coolant Accident

NOC-AE-16003367 Attachment 4 Page 2 of 2 Definitions and Acronyms NIST   National Institute of                Rovero   Risk over Deterministic Standards and Technology                      Methodology NLHS   Non-uniform Latin Hyperc~be          RVWL     Reactor Vessel Water Level Sampling                             RWST     Refueling Water Storage NPSH   Net Positive Suction Head,                    Tank (NPSHA - available, NPSHR            SBLOCA   Small Break Loss of Coolant
       - required)                                   Accident NRC    Nuclear Regulatory                   SC       Stress Corrosion Commission                           SG       Steam Generator NSSS   Nuclear Steam Supply                 SI/SIS   Safety Injection, Safety System                                        Injection System (same as OBE    Operating Basis Earthquake                    ECCS)
OD     Outer Diameter                       SIR      Safety Injection and OQAP   Operations Quality                            Recirculation Assurance Program                    SR       Surveillance Requirement PCI    Performance Contracting,             SRM      Staff Requirements Inc.                                          Memorandum PCT    Peak Clad Temperature                SSE      Safe Shutdown Earthquake PDF    Probability Density Function         STP      South Texas Project PRA    Probabilistic Risk                   STPEGS   South Texas Project Electric Assessment                                    Generating Station PWR    Pressurized Water Reactor            STPNOC   STP Nuclear Operating PW ROG Pressurized Water Reactor                     Company Owner's Group                        TAMU     Texas A&M University PWSCC  Primary Water Stress                 TF       Thermal Fatigue Corrosion Cracking                   TGSCC    Transgranular Stress QA     Quality Assurance                             Corrosion Cracking QDPS   Qualified Display Processing         TS       Technical Specification( s)
System                               TSB      Technical Specification RAI    Request for Additional                        Bases Information                          TSC      Technical Support Center or RCB    Reactor Containment                           Technical Specification Building                                      Change RCFC   Reactor Containment Fan              TSHL     Total Strainer Head Loss Cooler                               TSP      Trisodium Phosphate RCS    Reactor Coolant System               UFSAR    Updated Final Safety RG     Regulatory Guide                              Analysis Report RHR    Residual Heat Removal                UNM      University of New Mexico RI-ISi Risk-Informed In-Service             USI      Unresolved Safety Issue Inspection                           UT       University of Texas (Austin)
RMI    Reflective Metal Insulation          V&V      Verification and Validation RMS    Records Management                   VF       Vibration Fatigue System                               WCAP     Westinghouse Commercial RMTS   Risk Managed Technical                        Atomic Power Specifications                       ZOI      Zone of Influence}}