ML060380676
| ML060380676 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/09/2004 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| GL-88-020, TAC MC5729 CDQ1 999 2004 0156, Rev 0 | |
| Download: ML060380676 (18) | |
Text
ENCLOSURE 4 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION INDIVIDUAL PLANT EXAMINATION FOR EXTERNAL EVENTS TVA CALCULATION NO. CDQ1 999 2004 0156,"HCLPF CALCULATIONS OF MCC ANCHORAGE FOR SEISMIC IPEEE PROGRAM," REV. 0, JUNE 9, 2004.(SEE ATTACHED) 1(QA Record TVAN CALCULATION COVERSHEET/CCRIS UPDATE Pages 1 of 2 Page I REV 0 EDMStRIMS NO. EOMS TYPE: EDMS ACCESSION NO (WA for REV. 0).78 04. 06 2 4 O1 0 Calcuations(nuclear)
WA CaloTide:
HCLPF CALCULATIONS OF MCC ANCHORAGE FOR SEISMIC IPEEE PROGRAM CALC ID ORO PLANT BRANCH NUMBER CUR REV NE ;CURRENT CN NUC BFN CEB REVISION NEW CN NUC BFN CEB CDQ1 999 2004 0156 000 Entire cage C3 No CCRIS Changes 0 ACTION NEW l DELETE 0 SUPERSEDE 0 CCRIS UPDATE ONLY Q (For calc revision, CCRIS REVISION El RENAME 0l DUPLICATE 0 (VerifIer Approval Signatures Not been reviewed and no Required)
CCRIS changes required)UNITS SYSTEMS UNIDS 001 999 I N/A DCN.EDC.NA APPLICABLE DESIGN DOCUMENfi CLASSIFICATION
_N/A INtA E _QAALITY SAFETY RELATED? UNVEIF SPECIAL REQUIREMENTS DESIGN OUTPUT SAR/TS AFFECTED RLATED? (If yes, OR yea) ASUMPTION AN/OR LIMITINt ONDITIONS?
ATTACHMENT yeaIN No El yes la No yes Y No Yes ElNo CNfO Yes A No 1 Yes A No 1T PREPARER ID PREPARER PHONE NO l PEPARING )RG (BRANCH) VERIFICATIONMETHOD NW METH OD OF ANALYSIS Farld Elsabee -(256) 729-7000 x18023 CEB Design Review I Yes l No PREPARER<99NATUO DATE CHECKER TURE DATE Farid Elsabee 6124/04 _512=Eder 6125/04 VERrI S1tN~Ut DATE APPAP SjN~ DATE J.O. Dizon 6/26104 DeGj STATEMENT OF PROBLEM, ACT* This calculation docunents the High Confidence Low Probability of Failure (HCLPF) values for the MCC's at BFN Unit 1.MICROFICHE/EFICHE Yes 3 No E FiCHE NUMBER(S)0 LOAD INTO EDMS AND DESTROY 1 LOAD INTO EDMS AND RETURN CALCULATION TO CALCULATION LIBRARY. ADDRESS: BFN CalculatIon LUbrary El LOAD INTO EDMS AND RETURN CALCULATION TO: TVA 40632 [07-20011 Page 1 of 2 NEOP-2-1 (07-09-20011 TVAN CALCULATION COVERSHEET/CCRIS UPDATE Psige 2 of 2 Page iA CALC ID IYPE I ORO I PLANT I BRANCH NUMBER R FEV NEW I N IN IBFNI CEB CDQ1 999 2004 0156 000 ALTERNATE CALCULATION IDENTIFICATION fOOM I ELEV COORD/AIM EIRM print Rport Yes 01 WNA N/A WA Bechtel CATEGORIES F06 KEY NOU NS(A-add, "selete)ACTION KEY NOUN AI_ EYNU____ aANCHORAGE SEISMIC QUALIF SEISMIC DESIGN_ _ _ U f e -. .__ _ _CROSS-REFERENCES (A-add, C-change, delete)ACTION XREF XREF XREF XREF XREF XREF (A/OlD) CODE __kf _.&=BRANCH NUMBER REV P CN BFN CEB CDQI 999 2003 2570 P CN BFN CEB CDQ1 251 2003 2569 P CN BFN CEB CDQl 999 2003 0654 P ON BFN CEB CDQ0 000 94 0339 OCRIS ONLY UPDATES, Following are required only when makIng keyword/cross ref ererlocisCFIu atee andp ea f form NEDP-2-1 Isnot Included: PREPARER SIGNATURE 1 DATE CHECKER SIGNATURE DATE PREPARER PHONE NO. EDMS ACCESSION NO. V 0 4 fl 6 2 4 0 1 0 TA 403 [.-01 ... o EP- 0-0-01 TVA 40532 [07-2001)Page 2 of 2 NEDP 2-1 07-09-2001]
TVAN CALCULATION RECORD OF REVISION Page 1 of I Page II TVAN CALCULATION RECORD OF REVISION CALCULATION IDENTIFIER CDQ1 999 2004 0156 Thle HCLPF CALCULATIONS OF MCC ANCHORAGE FOR SEISMIC IPEEE PROGRAM Revision DESCRIPTION OF REVISION No.I 000 Original Issue This Revision 0, Including TVA calculation cover sheets, contains 17 pages total A 001220]Pe1of1ND--[1.04200 TVA 40709 (12-2000]Fige I of I NEDP-2-2 [12-04-20001 TVAN CALCULATION VERIFICATION FORM Page 1 of 1 Page IIi TVAN CALCULATION VERIFICATION FORM Calculation Identifier CDQ1 999 2004 0156 Revision 000 Method of verification used: 1. Design Review 0 2. Alternate Calculation i3 Verifier 4-'0-DT-Date 5/26/04 3. Qualification Test 0 JchnO. Dizon Comments: Thts revision of the calculation has been reviewed by the Design Review Methodology and has been determined to be technically adequate based on the design input information contained herein using accepted handbook ancidor computer applications, and sound engineering practices and techniques supplemented by applicable industry-standard guidelines.
TVA 053 [07200] Pae 1of NED (0709-001 TVA 40533 [07-20011 Page 1d of1 NEDP-2-4 (07-09-2001]
CALCULATION SHEET HCLPF CALCULATIONS OF MCC ANCHORAGE FOR SEISMIC IPEEE PROGRAM Page 1 of 13 CALCULATION SHEET TABLE OF CONTENTS CALCULATION COVER SHEET ...........................................
i CALCULATION RECORD OF REVISION ................................
II DESIGN VERIFICATION (INDEPENDENT REVIEW) FORM ... Iii Calculation Title Page ....................
1.......................
Table of Contents ...............
............................
2 1.0 Purpose. 3 2.0 Scope. 4 3.0 Definitions
............
5 4.0 References.
9 5.0 Anchorage Evaluation.............................................
10 5.1 General Calculation Method .10 5.2 Anchorage HCLPF Capacity Calculation
.11 6.0 ConclusIon
..13 Page 2 of 13 CALCULATION SHEET 1.0 PURPOSE The purpose of this calculation is to determine the High Confidence Low Probability of Failure (HCLPF) capacities for the Anchorage of MCC's at BFN Unit 1. This calculation Is In support of the seismic portion of the Individual Plant Examination of External Events (IPEEE) program at the BFN Plant which Is required per Generic Letter 88-20 (Reference 4.1). The seismic anchorage evaluations are based on the guidelines provided In the Seismic Margin Assessment (SMA) report by EPRI (Reference 4.2). The In-plant walkdowns were performed using the Walkdown Instruction WI-BFN-0-CEB-04 (Reference 4.5). The procedures used also reflect the methods specified in the SQUG Generic Implementation Procedure (GIP, Reference 4.3).The USI A-46 MCC evaluations determined that the seismic capacity of the MCC's is governed by the capacity of the cabinet anchorage.
Therefore, It follows that the HCLPF capacity is similarly controlled by the cabinet anchorage.
For this reason, It Is sufficient to Investigate only the MCC anchorage to determine their HCLPF capacity.Page 3 of 13 CALCULATION SHEET 2.0 SCOPE This calculation is applicable to the following MCC's, to determine the applicable HCLPF values as part of the seismic portion of the IPEEE program: Identification Number Component NmEr 1 -BDBB-281-0001 A 250V DC RMOV BOARD 1 A 19030 1 -BDBB-281
-0001 B 250V DC RMOV BOARD 1 B 19031 1 -BDBB-281
-0001 C 250V DC RMOV BOARD 1 C 19033 1-BDBB-265-0001B 480V RB VENT BD 1 B 19227 1 -BDBB-268-0001 A 430V RMOV BD 1 A 19423 1 -BDBB-268-0001 B 4130V RMOV BD 1B 19424 In the above table, SSEL refers to the Safe Shutdown Equipment List (SSEL), as documented in Reference 4.4.The above MCC's are located In the Reactor/Control Building, at Elevations 565', 593'and 621'-3".* SSEL No. 19030 will be mOdified to meet the A-46 criteria.
Therefore, Its capacity after the modification should result In a HCLPF capacity > 0.3g.* SSEL No. 19423 was evaluated and modified as part of the BFN Unit 2 A-46 review. Therefore, its capacity after the modification should result In a HCLPF capacity > 0.3g.* SSEL No. 19424 was evaluated and screened out under the BFN Unit 2 IPEEE review. Therefore, its HCLPF capacity is > 0.3g.* SSEL Nos. 19031, 19033 & 19227 are evaluated herein.There are no unverified assumptions In this calculation.
There are no known special requirements and/or limiting conditions In this calculation.
Page 4 of 13 CALCULATION SHEET 3.0 DEFINITIONS
3.1 INDIVIDUAL
PLANT EXAMINATION OF EXTERNAL EVENTS (IPEEE)Supplement 4 to Generic Letter 88-20 (Ref. 4.11) requires that each licensee conducts an IPEEE which addresses:
seismic events, internal fires, high winds, floods and transpoitation/nearby facility accidents.
3.2 SEISMIC
MARGIN ASSESSMENT (SMA)The SMA, which has been chosen for Implementation at the BFN plant, is an acceptable method used to perform the seismic portion of the IPEEE. The SMA is designed to (a) demonstrate sufficient margin over and beyond the Safe Shutdown Earthquake (SSE) to ensure plant safety, and (b) find any"weak links" that might limit the plant shutdown capacity to safely withstand a seismic event larger than the design SSE or lead to seismically induced core damage. The SMA for the BFN plants is performed using the EPRI methodology which Is described In Reference 4.2. BFN also elected to combine the USI A-46 and IPEEE walkdowns which were performed in accordance with the SQUG GIP (see below) with enhancements based on the EPRI report (Ref. 4.2). The walkdowns were documented in SEWS (see below).3.3 SEISMIC MARGIN EARTHQUAKE (SME)The earthquake level against which the plant is evaluated while performing the SMA. The SME is specified in terms of two orthogonal horizontal ground response spectra and one vertical ground response spectrum associated with a specific damping value. This Is not a new design earthquake, but one which Is used to evaluate existing plants under a SMA.3.4 REVIEW LEVEL EARTHQUAKE (RLE)The RLE is synonymous vW1th the SME. The two terms are often used Interchangeably.
The RLE for the BFN plants is defined as an earthquake having a response spectrum that matches the median (50% Non Exceedance Probability
-NEP) CR-0098 spectral shape anchored to a peak ground acceleration of 0.3g.Page 5 of 13 CALCULATION SHEET 3.5 HIGH CONFIDENCE LOW PROBABILITY OF FAILURE (HCLPF)The level of earthquake below which core damage frequency is very unlikely, as determined by a seismic margin study. This level of earthquake is called the high-confidence low-probability-of-fallure capacity of the plant.The value is obtained as the smallest capacity value determined for all components on the affected plant success path (aka safe shutdown path).From a mathematical perspective of a probability distribution of capacity, as developed In seismic probabilistic risk assessment (PRA) calculations, the HCLPF capacity values arna approximately equal to a 95% confidence of not exceeding about a 5% probability of failure. This value is also applied to a SMA to evaluate each component against the SME. The CDFM approach is an acceptable method of determining the HCLPF of a component.
3.6 CONSERVATIVE
DETERMINISTIC FAILURE MARGIN (CDFM)APPROACH The deterministic approach used to calculate a seismic margin capability, for which a HCLPF of the component Is demonstrated, Is with the use of a set of pre-established CDFM criteria and procedures.
The CDFM approach Is developed around the following guidelines: (a) The SME Is conservatively specified; (b) The predicted structural and equipment response to the SME is median-centered; and (c) The assessment of component capacity Is conservative. (For example, for expansion anchor bolts, the CDFM capacity should be defined at about the 98% exceedance probability In order to achieve a HCLPF; and thus, the factor of safety against the mean ultimate capacity should be set at a level consistent with about 2% probability of failure. See Appendix O0o: Ref. 4.2 for specific safety factors to be used.]3.7 SCREENED OUT COMPONENTS For these screened out components, it can only be stated that the HCLPF ground motion level exceeds the SME level. Components which are not screened out require a HCLPF capacity estimate to be determined.
Page 6 of 13 CALCULATION SHEET 3.8 GENERIC IMPLEMENTATION PROCEDURE (GIP)The GIP (Ref. 4.3) provides the detailed technical approach, generic procedures and documentation guidance for use by USI A-46 licensees to verify the seismic adequacy of mechanical and electrical safe shutdown equipment.
In this regard, the GIP serves as the acceptance criteria and also contains all of the activities necessary for the resolution of USI A-46.3.9 SAFE SHUTDOWN EQUIPMENT LIST (SSEL)This list contains all mechanical and electrical equipment within the selected success paths necessary to bring the plant from a normal operation condition to a safe shutdown condition to ensure safety during and following a Safe Shutdown Earthquake (SSE), as defined in Section 3 of the GIP (Ref.4.3) as well as Section 3 of the EPRI SMA report (Ref. 4.2). Equipment Items in the SSEL require screening verification and walkdown to ensure its seismic adequacy with respect to its functionality and structural integrity.
3.10 SEISMIC VERIFICATION WALKDOWN An engineering review to verify the seismic adequacy of the as-installed condition of a specific Rem of equipment or component to determine its acceptance or required further evaluations and/or modifications, based on visual inspection for predetermined engineering attributes.
Seismic verification walkdowns are to be performed by Seismic Review Teams.3.11 SEISMIC REVIEW TEAM (SRT)Seismic Review Team is responsible for the screening verification and walkdown of SSEL equipment items. A minimum of two Seismic Capability Engineers with structural or mechanical engineering background Is required on each team, one of which must be a licensed professional engineer.
SRT may also consist of systems engineers or plant operations personnel, as necessary.
Page 7 of 13 CALCULATION SHEET 3.12 SEISMIC CAPABILITY ENGINEER (SCE)Seismic Capability Engineers are degreed engineers or equivalents, who have completed a SQUG-developed training course on seismic adequacy verification of nuclear power plant equipment.
These engineers should have at least five years of experience in earthquake engineering applicable to nuclear power plants and in structural or mechanical engineering.
Refer to Section 2 of the GIP for specific qualifications and training requirements.
3.13 ENGINEERING ATTRIBUTE Engineering attribute Is a predetermined or known seismic vulnerability condition (such as support anchorage, GIP caveats for various types of equipment, etc.) that warrants verification or engineering evaluation during walkdown to ensure its seismic adequacy as It may potentially affect the seismic performance of an equipment item or component.
3.14 SEISMIC INTERACTION Seismic interaction is the physical interaction of any plant structures, features or equipment with a nearby item of safe shutdown equipment caused by relative motions from an earthquake.
Seismic Interaction effects which are included within tie scope of the GIP or seismic IPEEE are (I)proximity; (ii) structural failure and falling; and (iii) flexibility of attached lines and cables.3.15 SCREENING EVALUATION WORKSHEETS (SEWS)The Screening Evaluation Worksheets (SEWS) provide a convenient summary and checklist for documenting the seismic verification walkdowns performed In accordance to the acceptance criteria provided In the GIP (Ref.4.3) and EPRI NP-6041 -SL. (Ref. 4.2). Appropriate SEWS forms for the various equipment classes and other plant features can be found in Appendix G of the GIP and Appendix F of EPRI NP-6041 -SL.3.16 OUTLIER An outlier is an Item of equipment which does not comply with all of the screening guidelines provided In the respective acceptance criteria.
Outliers Identified during the seismic verification walkdowns for USI A-46 shall be documented in the Outlier Seismic Verification Sheet (OSVS) for further evaluation and resolution (Section 5, GIP).Page 8 of 13 CALCULATION SHEET
4.0 REFERENCES
4.1 USNRC, Generic Letter 88-20, Supplement No. 4, "Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities," Final, April 1991.4.2 Electric Power Research Institute (EPRI) Report NP-6041-SL, "A Methodology for Assessment of Nuclear Power Plant Seismic Margin (Revision 1)," August 1991.4.3 "Generic Implementation Procedure (GIP) for Seismic Verification of Nuclear Plant Equipment", Revision 2A.4.4 CDQ1 -999-2003-0654, 'Composite Safe Shutdown Equipment List (SSEL) for USI A-46 and Seismic IPEEE Programs -Browns Ferry Nuclear Plant, Unit 1," Revision 2.4.5 WI-BFN-0-CEB-04, "Selsmic Verification Walkdown Instruction for USI A-46 and Seismic IPEEE Programs," Revision 0.4.6 CDQO-000-940339, "Calculation of Basic Parameters for A46 and Individual Plant Examination of External Events (IPEEE) Seismic Program," Revision 1.4.7 CDQ1 -281-2003-2569, "Anchorage Evaluation for 250V DC RMOV Board 1 B for USI A-46 Resolution," Revision 0.4.8 CDQ1 -999-2003-2570, "Anchorage Evaluation for 480V RB Vent BD 1 B and 250V DC RMOV BoarJ 1C for USI A-46 Resolution," Revision 0.Page 9 of 13 CALCULATION SHEET HCLPF CALCULATIONS OF SEISMIC IPEEE PROGRAM 5.0 Anchorage Evaluation
5.1 General
Calculation Method The general method used for determining the anchorage HCLPF capacities are based on the guidelines provided In EPRI report NFP-6041 -SL (Reference 4.2).The stress to allowable ratios of the anchorage, previously calculated for the components In support of the resolution of USI A-46, are normally used as the basis for the HCLPF capacity determination.
The ratios are modified to reflect the higher level of the RLE vs the SSE level used for the A-46 review. The conservative scaling factor of 1.88 developed In Reference 4.6 Is first used to scale up the A-46 stress to allowable ratio. Note that when this scaling factor is applied to the previous A-46 calculations, the A-46 SSE values are Increased by 1.88/1.25
= 1.504 only, since the HCLPF calculations do not need the 1.25 factor used in the A-46 calculations to account for the median centered curves being used at BFN plants. Furthermore, the IPEEE scaling factor is applied only to the SSE values and care Is to be taken when the controlling stress ratio is based on the combined effect of SSE and DW where DW subtracts from the SSE effects. For such situations, one conservative approach Is to neglect the DW effect which reduces the SSE loads when the IPEEE scaling is performed.
Consider the following:
A-46 calculation contains:
Tsse/Tall
-TDv/Tall < 1 When scaling for IPEEE, use: 1 .504*Tsse/Tall
< 1 or 1 .504TsserTall
-TDw/Tall < 1 Whichever is simpler to Implement If the resulting stress ratio, after scaling the SSE effects, remains below 1.0, the component Is screened out and the HCLPF capacity level is greater than 0.3g. When the stress ratio exceeds 1.0, a more detailed calculation of the HCLPF capacity level is needed.The detailed calculation will either use a more refined value for the RLE scaling factor or will reduce some of the conservatism which may have been used in the A-46 calculations while still meeting the requirements of References 4.2 and 4.3. If the stress ratio cannot be kept below 1.0, a new HCLPF capacity value (below the 0.3g level) will be calculated for the component of concem.Page 10 of 13 CALCULATION SHEET 5.2 Anchorage HCLPF Capacitv Calculaltion 1 -BDBB-281
-0001 B 250V DC RMOV BOARD 1 B 19031 MCC boted to sill channel 1 -BDBB-281
-0001 0 250V DC FIMOV BOARD 1C 19033 MOC welded to sill channel 1 -BDBB-265-0001 B 480V RB VENT BD 1 B 19227 MCC welded to sill channel 1-BDBB-281-0001 B: Per Reference 4.7, the controlling component is the Y'" bolt connection between the MCC base and the sill channel. Since the stress ratio to allowable in tension for the bolt Is 0.95, the IPEEE scaling factor will definitely result In a stress ratio greater than 1.0.Therefore a detailed HCLPF capacity calculation is needed.Based on Reference 4.7 and using the scaling factor of 1.88, the demand level for the RLE Is: SaEw = 2*0.6722g*1
.88 = 2.53g PGA&4 = 2*0.155g*1.88
= 0.564g PGAVERr = 2*0.089*1.88
= 0.3g VE= 2.53*3465/32
= 274 IlbS VNS = 0.564*3465/32
= 61.1 lbs V = (2742 + 61.12)1/2
= 281 lbs TEw = (2.53*3465*50)
/ (16*17) = 1611.5 lbs Twin = 0.3*3465 / 32 = 32.5 lbs T = (1611.52 4 32.52)12 -(3465132)
= 1504 Ibs The bolt capacity Is: Using the AISC Part 2 capacities as done in Reference 4.7, except use the gross area of the bolts as required by AISC instead of the conservative approach used In Ref. 4.7: Gross A = 0.049 in 2 fv = 281/0.049
= 5.7 ksl < 1.7*10ksi
= 17ksi Ftall = 1 .7*Ftp u = 1.7*26 -1 .8fv = 44.2 -10.26 = 33.94 ksk 1.7*20=34 ksi Page 11 of 13 CALCIJLATION SHEET Document:
CDQ1 899 2004 0156 1Rev.OO Plant BFN Unit(s): 1
Subject:
HCLPF CALCULATIONS OF MCC ANCHORAGE FOR Prepared:
F. Elsabee Date: 5/24/04 SEISMIC IPEEE PROGRAM Checked: S. J. Eder Date: 5125/04 ft =1504/0.049
= 30.7 ksi ftIFtall=30.7/33.94=0.9
< 1.0 1 OK Therefore the HCLPF capacity is > 0.3g 1-BDBB-281
-0001 C & 1 -BIDBB-265-0001 B: The calculation of Reference
4.8 evaluated
the anchorage of both MOC's by enveloping the conditions of both units. Per the calculation, the controlling components are the concrete anchors along the front and back edge of the MCC line up.The pull out load to allowable ratio was calculated as 0.36. Note that this factor Is based on the GIP criteria for expansion anchor bolts which is much more severe than that allowed by Reference 4.2 for the SMA.Based on the Ref. 4.8 calculation, use the RLE scaling factor of 1.504 to increase the A-46 SSE load only while neglecting the counter effect of DW: T = (5912+232)I
- 1.504 / (2,360*0.56)
= 0.67 < 1.0 0 OK Therefore the two MCC's can be screened out and the HCLPF capacity Is > 0.3g Page 12 of 13 CALCULATION SHEET
Subject:
HCLPF CALCULATIONS OF MCC SEISMIC IPEEE PROGRAM 6.0 Conclusion The following table summarizes the HCLPF anchorage capacities of the MCC's based on the above evaluations ISEL Number Identification Comoonent HCLPF Capacitv Number 19030 1-BDBB-281-OOO1A 250V DC RMOV BOARD IA Anchorage modified._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _H CL P F > 0 .3g 19031 1-BDBB-281-OO1B 250V DC RMOV BOARD 1B CaltPated as >p0.3g 19033 1 -BDBB-281
.0001 C 250V DC RMOV BOARD 1 C HCLPF capacity screened out as > 0.3g 19227 1-BDBB-265-o001B 480V RB VENT BD 1B HCLPF capacity____ ___ ___ _ _ ____ ___ ___ ___ screened out as > 0.3g 19423 1-BDBB-268-0001A 480V RMOV BD IA Anchorage modified.19424 I-DB2_B40ROBD1____
HoLPF > 0.3g 19424 1-IBDB-268-OOlB 480V RMOV BD l B HCLPF caacity I__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ screened ouit as > 0.39 Page 13 of 13