ML072820416

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2007/01/18-Oyster Creek September 2007 Evidentiary Hearing - Applicant Exhibit 40, Amergen'S Oyster Creek Generating Station License Renewal ACRS Presentation
ML072820416
Person / Time
Site: Oyster Creek
Issue date: 01/18/2007
From:
AmerGen Energy Co
To:
Office of Nuclear Reactor Regulation, NRC/SECY
SECY RAS
References
50-219-LR, AmerGen-Applicant-40, FOIA/PA-2009-0070, RAS 14254
Download: ML072820416 (137)
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R14-5 / 41,ý2 g 4 APPLICANT'S EXHIBIT 40 M A SM Mn Ixelon Compwimy Oyster Creek License Renewal Presentation to ACRS Subcommittee U January 18, 2007 os wmom DOCKETED USNRC October 1,2007 (10:45pm)OFFICE OF SECRETARY RULEMAKINGS AND ADJUDICATIONS STAFF S, NUUL REGULATORY COMMISSION by pIt"e -n intervenor NRf St9),{ ttjr tn: AD ITT / EJECTED WITHDRAWN-- ------1jely)p late Y-6ýqlg-g>EC y- 0.;-

M Amereensm An Exelon Compaqy AmerGen Representatives

  • Fred Polaski" John O'Rourke" Howie Ray" Pete Tamburro* Dr. Hardayal Mehta" Barry Gordon" Jon Cavallo" Ahmed Ouaou 2 VIM. Aý6 Amenr G.epým Agenda Ani I-eldn Compiry* Drywell Shell Corrosion-Physical Overview-Cause and Corrective Actions-Drywell Shell Thickness Analysis-Sand Bed Region-Embedded Portions of the Drywell Shell-Upper Shell 3 Smer%;er M Exeionl Company Drywell Shell Corrosion Cause and Corrective Actions 4 AmerGen Mti kd[Xi~ Uompiiiýn SEE DETAIL 'A'SEE DETAIL 'B'SEE DETAIL "C'I V 5 n._ Aer en, Alrl , oI~ir I.~I Pl A(,' (*C"AVJYE~; IiNiN. F ~ ~ IL Li I \ I -\U C: 0 N c- R? Fýý L ý- L; 1,. 1 A I L " H " J.It .-(2 Q AC 1 II -i DRYWELL AND REACTOR CAVITY SECTION DETAIL "A" 6 AmerGen An xeloti DRYWELL TO REACTOR CAVITY SEAL DETAIL DETAIL 'B'OBSERVED DAMAGE AT LUP OF TROUGH CORRECTED IN 1988 TOP PLATE iU PROTECTIVE SHIELDING

--LEAKAGE~--STAINLES8 GUSSET 7 -REFUELING I DRYWELL t3ASKET -INIiBR 15LSIE/ TERIAL BOTTOM PLATE/ / / N FOR a TROUGH (2')/ / I(3>i {DRAIN FOR CONCRETE TROUGH Z2)V GOAP i PATH,\STEEL LINER IELLOWS 7 AmerGen, LOWER DRYWELL/SANDBED REGION DETAIL C/7 SANL)L&D R 'ON A/P Q// r/ /LLAKAGE IPAlH EROM O 4 ItiN U~qYWLLL.

IC)2 iUblI, 4 KANI)HI 1) ý;l ItI I n11 o" LWE I 2ýu kýý'N 4'S.Ili. lom 1 K 1" -di ~ANi)Iii 0 --4 4 4 4 4 44 944 4 4 4 4 44 4 4 5 ~ d 4 *-~ --4 N--K'U0rýYW[L ViN. ~I N 4 ,#4 4 4 4 44 4 4 4 44 4 44 L.4 4, 44e 4 4 5 4 4 4 4 4 44 4 44-L 4'. nPFAIN P Pr', 44 44////8 AmerGen REACTOR BUILDING, DRYWELL SUPPORT STRUCTURE CONTAINMENT SHELL--'--_

SANDBED REGION /&REACTOR VESSEL CURB URYWELR FLOOR " EL L , ' 0 ' -,.5 "2 " M N A TORUS o -/_JDRA NACE%!~ tC FI ," -A A 7" , I " ' i' /EDESTAM ,./-" "\ -- -7 i f. , ... .7-- ; ---: Fo OF MAT --GRADE EL. 23'-6"-WATER STOP IT ALL IAROUND)-REGLET 5D-U" LIMII UýMEMBRANIE i L .E 4' 6" WATFRPROOFING (TYP ALL AR(WATER STOP (1 ALL AROUND)-5 GALLON POXY BOTTLE 7.Z_ -MEMBRANE WAT ERPROOFING AI LRPRO) NG OUND)ry -ý)__..................

...........

.... LFVE[LING S[AB 1 9 DRYWELL AmerGen,1.e(lor brlo!paq~t I[. ti /'-~ "-)Ij ý: A9IN("", IN M S I~A EL. 51-10' PTHK 722" 1 EL, 0 2 UT READINGS IN tf T-K .770 IHLSL ARLAS ( (THK .770" 13011 GM C> SAN )HI)U ~ P SUPPORT SKIRT-(SLL DEIAIL 1)UT READINGS IN THIS AREA-I--L_LL. 60"-0" UT READINGS IN THIS AREA/ 71./ !10 (01 ANIit I)FTIK1.154"--FTHK .676"-2'.5 " 10 An Ixelln Company Cause and Corrective Actions* Water accumulation in the sand bed region resulted in corrosion of the exterior surface of the drywell shell* Corrective actions were completed in 1992-Prevented water intrusion into the sand bed region-Eliminated corrosive environment by removing the sand-Coated the drywell shell with epoxy in the sand bed region 11 S~erGen-S Verification and Monitoring In 2006 refueling outage-Leakage from the reactor cavity liner, estimated at about 1 gpm, was captured by the drainage system-UT measurements of the drywell at 19 monitoring locations for the sand bed region showed no change in thickness-100% visual inspection of the epoxy coating showed it to be in good condition-There was no water in the sand bed region 12 A eroer , An [xe1ori Comnpany Verification and Monitoring In 2006 refueling outage-106 UT measurements at locations measured in 1992, before epoxy coating applied, showed the drywell shell exceeds design thickness requirements

-UT measurements at 13 locations in the upper elevations of the drywell show only 1 location with minimal ongoing corrosion (meets minimum required through 2029 with margin)t3 AmerGer,,, Drywell Shell Current Condition An xeleon Company Nominal Minimum Minimum Minimum Drywell Design Measured Required Available Region Thickness, Thickness, Thickness, Thickness mils mils mils Margin, mils Cylindrical 640 604 452 152 Knuckle 2,625 2,530 2260 270 Upper 722 676 518 158 Sphere Middle Sphere 770 678 541 137 Sphere Lower Sphere 1154 1160 629 531 Sand Bed 1154 800 736 64 14 AmerGen, A/n ml on Coupany Drywell Thickness Analysis Hardayal S .Mehta, Ph.D P.E.m I General Electric 15 Drywell Analysis A eoe~kns Exedn ornlCpa~ly" Analysis completed in early 1990s-Without sand in the sand bed* Modeling of the drywell-Loads and Load Combinations" Buckling analysis-Controls the required drywell shell thickness in the sand bed region-Uniform drywell shell thickness of 736 mils over the entire sand bed region was used in the analysis" ASME Section VIII stress analysis based on 62 psi" Drywell pressure design basis change from 62 psi to 44 psi-Stress analysis of the drywell shell based on 44 psi 16 kn Edon Compafl Modeling of the Drywell 17 Drywell Configuration Oyster Creek Drywell Geometry ki 1Lxel11C O.fpaly-It is 105'-6" high-Drywell head is 33' in diameter-Spherical section has an inside diameter of 70'-Ten vent pipes, 6'-6" in diameter, are equally spaced around the circumference to connect the drywell to the vent header inside the pressure suppression chamber-Drywell interior filled with concrete to elevation 10'-3" to provide a level floor-Base of the drywell is supported on a concrete pedestal conforming to the curvature of the vessel-Shell thicknesses vary* Drywell shell, i.e., the sphere, cylinder, dome and transitions, was constructed from SA-212, Grade B Steel ordered to SA-300 spec.18 SmerGen, Finite Element Models Used Conypaq" Axisymmetric, Beam and Pie Slice models used" Axisymmetric drywell model used to evaluate-Unflooded and flooded seismic inertia loading-Thermal loading during postulated accident condition" Beam drywell model used to evaluate stresses due to seismic relative support displacement" Pie slice drywell model used for the Code and buckling evaluations

-Vent lines included in the model" No sand stiffness considered in any of the models 19 AmerGenr Aii [xeloii Compaqy Pie Slice Model and Load Application Taking advantage of symmetry of the drywell with 10 vent lines, a 36 degree section was modeled-The model included the drywell shell from base of the sand bed region to the top of the elliptical head and the vent and vent header-Drywell shell thickness in the sand bed region: 736 mils uniform 20 AmerGen An xkvluii ", 01 Pie Slice model I AN'IVU A,.%VIC~ 4 19*0@71.,u : 14 A%3Awr6,-L IAHALý0.13 t," VAND.21 AmerGer , Applied Loads A Ixelo Corn" Gravity loading consists of dead weight loads, penetration loads, live loads" Design pressure of 62 psi pressure (at 1750F)-Note 62 psi criterion was later changed to 44 psi per Tech.Spec. Amendment

  1. 165 (SER dated September 13, 1993)" Seismic Loads-Inertia loads-Relative support displacement (Drywell and Reactor Building)22 SmerGep,M Seismic Load Definition Ali AIxvi0ilCompaq" Axisymmetric finite element model used to determine inertia loading-Drywelt is constrained at the "reactor building/drywell/

star truss" interface at elevation 82'-6" and at its base" Spectra at two locations:

At the mat foundation and at the upper constraint" Envelope spectrum used in ANSYS analysis 23 AmerGeni Am [xelu Coryaq Load Combinations and Constituent Loads Load Combination Constituent Loads Normal Operating Gravity loads+ Pressure (2 psi external)

+ Seismic (2 x DBE)Condition Refueling Gravity loads + Pressure (2 psi external)

+ Water load Condition

+Seismic (2 x DBE)Accident Gravity loads + Pressure (62 psi @ 175 deg. F or 35 psi @Condition 281 deg.F) + Seismic (2 x DBE)Post-Accident Gravity loads + Water Load to El. 74' 6" + Seismic (2 x Condition DBE)24 Ah1 Lxdon Compafny Buckling Analysis 25 An [:xeUlon Con 1 ny Buckling Analysis Conclusion The buckling analysis was conducted using a uniform drywell shell thickness in the sand bed region of 736 mils." Stress limits and safety factors are in accordance with the Code requirements.

  • The analysis shows that the drywell shell meets ASME Code Case N-284 requirements considering all design basis loads and load combinations." A locally thinned 12"x 12" area down to 536 mils was evaluated and determined not to have significant impact on buckling.* The drywell shell thickness will be monitored using 736 mils as acceptance criteria for the minimum required general thickness and 536 mils as the minimum required local thickness.

26 Buckling Analysis Details 4m Lxec~hi [xelv iConyt-lqll

  • Basic approach used in buckling evaluation followed the methodology outlined in ASME Code Case N-284 Allowable Compressive Stress = Yliaioie/FS

-FS is factor of safety (equal to 2.0 for refueling condition and 1.67 for post accident condition)

  • Boundary conditions for buckling analysis-Symmetric at both edges (sym-sym)-Symmetric at one edge and asymmetric at the other edge (sym-asym)

-Asymmetric at both the edges (asym-asym)

-This captures all possible buckling mode shapes" A uniform drywell shell thickness in the sand bed region of 736 mils was used in the buckling analysis 27 n AmerGep,,, Ali kdoll Compaq Buckling Analysis Details Center ,of.Orywell Sphere/ \ R~- Planes of< Symmetry 3 e \/ 3O \/'N N Unbucked Shape Vent Budded Shape (Radal DMsp(acement No Rotation)Symmetric Buckling of Drywe!f 28

_-AmerGem, A ýxdon ComPaq Buckling Analysis Details Center of Drywel spoews Planes of Symmetry U"udked, Shape&ickWe Shape R(otaton No Radal Disp .)Vent Asymmetric Buckling of Drywell 29 merGer,, AnI [v'io Com~paq~Buckling Analysis Details Limiting load combination is the refueling condition Loads during refueling condition are-Gravity loads including weight of refueling water-External pressure of 2 psig-Seismic inertia and deflection loads for unflooded condition 30 A,4merGen,'

Buckling Analysis Details s/ "" OCT 21 1912 FAWC7-8141 LiN~ a 0 OL03AL DM)( -oi.a3193 5169 -~) ~n .Ot1441 Xv -I 11 1% *ftT-I]10243

  • VF -1.3~82* -a 312,431 AN32- -10 0. &0 7k -0 IiC317F-03 0,8162E-03 O) UUL 441 FigIure 3 18 Syrn Symi Bucklingj Mode Shaipe -Refueling Case OVSIER CRi4K ORYWiLL ANALYSIS" OWRIFk SVM-SVN' (NU~ SAND), REFUE.LLU) 31 AmerGen.Buckling Analysis Details I ANSYS 4.4A D GLOBAL mtDI SImb68-23 WX = :-y =-8z:'*2F =1 j.983-00201 00~061a* r C -/~.-~..-4-t~t figure 3419 Sym-Asyni fluckling Mtode Shapo Refueling CaseýOYSTFR CREEK DRYWFIJ -ASYM -SYMI , NO SAND, REFUELING 32 Buckling Analysis Details berGen Summary of Buckling Analysis Results -Refueling Case.Paramenter Val.ue Theoretical Elastic Instability Stress, (ie (ksl) 46.59 Capacity Reduction Factor, 4i 0.207 Circumferential Stress, 0c (ksi) 4.51 Equivalent Pressure, p (psi) 15.81"X" Parameter 0.087 AC 0.072 Modified Capacity Reduction Factor, 1lmod 0.326 Elastic Buckling Stress, ae N i,mod tle (ksi) 15.18 Proportional Limit Ratio, A Ile/ 0, 0.40 Plasticity Reduction Factor, ni 1.00 Inelastic Duckling Stress, 01 = ni le (ksl) 15.18 Code Factor of Safety, FS 2.0 Allowable Compressive Stress, a all =1 i/FS (ksl) 7.59 Applied Compressive Merldional Stress, IT (ksi) 7.59 33 M[ Eelon Evaluation of Local Thinning on Buckling Analysis -Sensitivity Study A locally 12"x1 2" thin area was modeled in the sand bed region drywell shell in the highest stress area, to determine the impact of local thinning on buckling stress-Establish minimum required local thickness down to 536 mils Note: UT thickness measurements taken through 2006 show that locally thinned areas of the drywell shell are not coincident with high stress areas. The locally thinned areas are typically scattered below and near the vent headers. These areas are not highly stressed because of the additional stiffness provided by the vent header.34 merGern, Buckling Analysis Conclusion The buckling analysis was conducted using a uniform drywell shell thickness in the sand bed region of 736 mils.* Stress limits and safety factors are in accordance with the Code requirements." The analysis shows that the drywell shell meets ASME Code Case N-284 requirements considering all design basis loads and load combinations." A locally thinned 12"x 12" area down to 536 mils was evaluated and determined not to have significant impact on buckling.° The drywell shell thickness will be monitored using 736 mils as acceptance criteria for the minimum required general thickness and 536 mils as the minimum required local thickness.

35 kAmer~eeph Af)I~r X010i Compaqd ASME Section VIII Stress Analysis 36 AmerGe , ,, ASME Section Vill Stress Analysis Conclusion Stress analysis of the drywell shell was conducted in accordance with ASME Code and SRP 3.8.2 using reduced thicknesses due to corrosion.

  • Stress limits and safety factors are in accordance with the ASME Code requirements.
  • The analysis shows that the drywell shell meets ASME Code Stress requirements considering all design basis loads and load combinations.
  • To regain margin, a plant specific analysis was conducted that reduced drywell design basis pressure from 62 psi to 44 psi (Tech Spec Amendment
  1. 165)* The reduction in pressure resulted in a stress reduction of up to 5200 psi* The minimum required general and local drywell shell thicknesses were calculated in accordance with ASME Code based on 44 psi pressure." The drywell shell thickness will be monitored for corrosion using the calculated minimum required general and local thicknesses as acceptance criteria.

37 AmerGen, , Codes and Standards" The Oyster Creek drywell vessel was designed, fabricated and erected in accordance with the 1962 Edition of ASME Code,Section VIII and Code Cases 1270N-5, 1271N and 1272N-5" Original Code of record and Code Cases do not provide specific guidance in two areas" For the size of the region of increased membrane stress, guidance sought from Subsection NE of Section III" For the Post-accident stress limits Standard Review Plan Section 3.8.2 was used as guidance 38 zmerGen,, Drywell -Section Vill Allowable Stresses Drywell Allowable Stresses Afi Ixelon Cumý),i!ýý Stress Allowable Stress Values (psi)Category All Conditions Except Post-Accident Post-Accident Condition*

General Primary 19300 38000 Membrane General Primary 29000 57000 Membrane Plus Bending Primary Plus Secondary 52500 70000* Allowable values based on Standard Review Plan Section 3.8.2, Steel Containment 39 Code Stress Evaluation Results.erGern A (ixelon Comllpil (based on 62 psi, 1993)Primary Stress Evaluation Drywell Calculated Allowable Region Stress Category Stress Stress Percent Magnitude (psi) s Margin Cylinder Primary 19850 21200* 6 (t=0.619 in.) Membrane Primary 20970 29000 28 Memb.+Bending Upper Primary 20360 21200* 4 Sphere Membrane (t=0.677 in.) Primary 28100 29000 3 Memb.+Bending Middle Primary 19660 21200* 7 Sphere Membrane (t=0.723 in.) Primary 24610 29000 15 Memb.+Bending Lower Primary 13940 21200* 34 Sphere Membrane (t=l.154 in.) Primary 17640 29000 39 Memb.+Bending Sand Bed Primary 16540 21200* 22 (t=0.736 in.) Membrane Primary 23130 29000 20 Memb.+Bending

-,1 .4 .- /.n .a = i iI Ii I. i t I_ --I ------... ... .. --... .---.. ...REF" I nis is 4 I .lXi9UU) an(a is ine inresnold 3213.10 Tor Iocal primary membrane stress per tNE-40 Regain Margin through , , Licensing Basis Change* The drywell pressure of 62 psi was very conservative

  • Analysis was conducted in early 1990's to establish Oyster Creek specific drywell design pressure.-Design pressure changed from 62 psi to 44 psi.44 psi is based on conservatively calculated peak drywell pressure of 38.1 psi plus an added 15% allowance.

-The change was approved by NRC per Technical Specification Amendment No. 165 (SER dated September 13, 1993).-The reduction in pressure resulted in a pressure stress reduction of up to 5200 psi* Recalculated the required drywell shell thicknesses based on 44 psi to regain thickness margin.41 AmerOet, An Primary Membrane Stress Comparison 62 psi vs.44 psi As-analyzed Calculated Allowable Stress Drywell Time Thickness Stress Stress Stress Margin Region Frame (mils) Category (psi) (psi) (%)1993 619 Primary 19,850 21,200 6 Cylinder Membrane 2006 604 Primary 14,446 19,300 25 Membrane 1993 677 Primary 20,360 21,200 4 Upper Membrane 23 Sphere 2006 676 Primary 14,796 19,300 23 Membrane 1993 723 Primary 19,660 21,200 7 Middle Membrane Sphere 2006 678 Primary 15,499 19,300 20.. .. ...._ Membrane 1993 1154 Primary 13,940 21,200 34 Lower Membrane Sphere 2006 1154 Primary 10,660 19,300 45"_ Membrane 1 Primary 16,540 21,200 22 Sand 1993 736 Membrane Bed 2006 736 Primary 11,404 19,300 41 Bed_ 2006 736 Membrane 42 AmerGen,m, Minimum Required Al [xeloi Co°nydl)" Drywell Shell Thickness Minimum required general thickness for 44 psi-Calculated based on primary membrane stresses for 62 psi, adjusted for pressure reduction (62 psi to 44 psi)Minimum required local thickness for 44 psi-Calculated based on ASME Section III provisions which allow increase in allowable local primary membrane stress from 1.0 Smc to 1.5 Smc-Local thickness criteria is applicable to an area of 2.5" in diameter and less consistent with ASME Section III, Subsection NE-3332.1-Extent of Locally thinned areas is evaluated per ASME Section III, Subsection NE-3213.10, NE-3332.2, and NE-3335.1 43 AmerGem, Minimum Required Thicknesses Based on 44 psi pressure Avk~oi Nelu uip~1r1 Drywell Design Minimum Minimum Minimum Region Nominal Measured Required Required Local Thickness, General General Thickness, mils mils Thickness Thru Thickness, mils 2006, mils Cylinder 640 604 452 301 Upper 722 676 518 345 Sphere Middle 770 678 541 360 Sphere Lower 1154 1160 629 419 Sphere Sand Bed 1154 800 479(1) 319(2)(1)(2)The minimum required general drywell shell thickness in the sand bed region is 736 mils, controlled by buckling.Acceptance criteria for evaluating locally thinned areas of the drywell shell in the sand bed region is conservatively based on 490 mils instead of 319 mils 44 ASME Section Vill erGeI Stress Analysis Conclusion" Stress analysis of the drywell shell was conducted in accordance with ASME Code and SRP 3.8.2 using reduced thicknesses due to corrosion.

  • Stress limits and safety factors are in accordance with the ASME Code requirements.
  • The analysis shows that the drywell shell meets ASME Code Stress requirements considering all design basis loads and load combinations." To regain margin, a plant specific analysis was conducted that reduced drywell design basis pressure from 62 psi to 44 psi (Tech Spec Amendment
  1. 165)* The reduction in pressure resulted in a stress reduction of up to 5200 psi" The minimum required general and local drywell shell thicknesses were calculated in accordance with ASME Code based on 44 psi pressure." The drywell shell thickness will be monitored for corrosion using the calculated minimum required general and local thicknesses as acceptance criteria.45 Zak'A mrft r s m An Exelon Company Sand Bed Region 46 Amer en M An Explon ComplaqHy Sand Bed Region Conclusions" Corrosion on the outside of the dry shell in the sand bed region has bE arrested" The coating shows no degradation" There is sufficient margin to the minimum thickness requirement (6 mils margin above code required average thickness of 736 mils)well.en 4 47 AmerGen, , Background and History An Sand Bed Internal UTs 1983 to 1986 corrosion data 360 at elev.11'3"-When thin locations were identified, UT measurements were taken horizontally and vertically to locate the thinnest locations-UT grid measurements were taken at the thinnest locations-19 locations were selected for corrosion monitoring based on over 500 initial data points measured-At least one grid is located in each of the 10 bays 48 H fl' -EL 87 'NfIkIAGM UHAIII WNI 1.NNTION WAIDI AmerGen M i KEY PLAN 49 AmerGen VIEW FROM INSIDE DRYWELL An kdon Cumýjýinv UPPER CURB -EL. 12'-30 TOP OF SANDBED/I 41 A EJEJEJEJ I/A<1 ,4 LOWER CURB 11'-0o A A In A1 DRYWELL FLOOR -EL. 10'-3" 50 AmerGen DRYWEL L WALL TOP O SANDBED EL, 12'-'" & UKPPR CURB-LOWER CURB FL. 11'-0" FLOOR F-4.4 4 A\10'- 3" L L. 8'-9" REGION A 414 EXCAVATION IN 2006 4 4 ,t'I J~. A 441 ~ -~.4 4 BAYý 5 -TRENCH 4 4 4 4 4 4.A 4. 4 qA A 4 4 4*4 A 4 A ,A e 4 4.4.d 4 4 51 AmerGen FLO(EL_. 9'-- 3-TO~ OF SANDBED EL. 12 -3" & UFPER CL LOWER CURB F.... 11'-O'-DR FL. 1O'-3" 4 44 4 ~, 4 4 4 4--- .4- ...~4... 4 4 1 ....4 4 4 44 4 4 .4 4 4 ~. 4 4 4 4 4 4 4 4 4 4 4 4 4 7 4 44 4 4 4 4~ 44 4 44 4 4.~ .4 4 -a DRYWELL WALL 4 4 4. 4 4 4 43 S4 4-ANDBED 4 RECION V I -4 a 1 4 4 4 4 4 4 4 ,0 6 41~ 4 4 4 4 44 744 4 4 4 4 44 BAY 17-TRENCH 4 4 44 4 44 I 4 4 44 4 4 4 4 44 I4I44 4 4 4 44 4 44 4 4 441 4 52 Sand Bed Region Background and History Trenches in bays 5 and 17 were excavated in 1986 to determine corrosion in sand bed at elevations below the drywell interior floor-Bays 5 and 17 were selected because UT measurements indicated these bays had the least and the most corrosion, respectively

-The trenches extend to about the elevation of the bottom of the sand bed-UT measurements taken in the trenches confirmed that the corrosion below elev. 11' 3" was bounded by the monitoring at elev. 11' 3" 53 AMer etm A~n !'xduii Crrydn 2006 Inspection Data General Thickness (mils)Bay 5 Bay 17 17/19 Grid 5D 17A Top 17A Bottom 17D 17/19 Top Bottom Grid Elev. 11'3" Above Lower 1185 1122 935 818 964 972 Curb Trench Lower Curb to Sand Bed 1074 986 Floor Trench Below Sand Bed Floor 54 AmerGep,, Sand Bed Region t\I*xCntv Background and History* Sand was removed in 1992 and the shell was cleaned* External UT measurements were taken in all bays at thinned local areas (as determined by visual inspection)

  • The shell was coated with epoxy coating SLUT grid measurements were taken at the 19 monitored locations at elev. 11 '3" as a baseline for the new condition 55 An Nxelon Condition of the Drywell Shell in the Sand Bed Region After Sand Removal 56 AmerGen Sand Bed Region 1992 Drywell Shell Corrosion product on drywell vessel 57 AmerGen Sand Bed Region 1992 Drywell Shell As found condition of floor bed 58 A& reGeni An C011'Iqn~~Ij Condition of the Drywell Shell in the Sand Bed Region After Application of Epoxy Coating 59 AmerGen,, Sand Bed Region 1992 Alr 1 x l Shell Sandbed Floor Bay 5 before shell coating 60 Sand Bed Region 1 992 ArnerGen,.

Shell 4'Floor v J~1 ft Shell and floor undergoing coating and repairs 61 Sand Bed Region 1992 AmerGen,, Shell Caulk Seal-Sandbed Floor A -Finished floor, vessel with two top coats -caulking material applied 62 merGern Sand Bed Region A lon Compaq Background and History DEVOE Epoxy coating system (3 part)-Designed for application on corroded surfaces-One coat DEVOE 167 Rust Penetrating Sealer e Penetrates rusty surfaces* ,Reinforces rusty steel substrates 9 Ensures adhesion of Devran 184 epoxy coating 63 AmrenM Sand Bed Region Background and History* DEVOE Epoxy coating system-Two coats Devran 184 epoxy coating" Designed for tank bottoms, including water tanks, fuel tanks, selected chemical tanks" Coating application was tested in a mock-up for coating thickness and absence of holidays or pinholes" Two coats used to minimize any chance of pinholes or holidays" The two coats are different colors 64 SerGenSM An Exon Use of Coatings to Prevent Corrosion Jon R. Cavallo, PE, PCS Vice President Corrosion Control Consultants and Labs, Inc.65 S~erGenm Background and History The OCNGS Protective Coatings Monitoring and Maintenance Program aging management program is consistent with NUREG 1801, Rev. 1 (the GALL Report), Appendix XI.S8-NUREG 1801, Appendix Xl.S8 only covers Coating Service Level I coatings* In addition, the OCNGS Coating Monitoring and Maintenance Program includes the Coating Service Level II coatings applied to exterior of drywell in Sand Bed region 66 Background and History An belon corrlparýInspection and evaluation of OCNGS external coated drywell Sand Bed region surfaces (Coating Service Level II Coatings) is conducted in accordance with ASME Section XI, Subsection IWE by qualified VT inspectors.

-Areas shall be examined (as a minimum) for flaking, blistering, peeling, discoloration and other signs of distress.The premise of ASME Section Xl, Subsection IWE is that degradation of a steel substrate will be indicated by the presence of visual anomalies in the attendant protective coatings 67 A ero'ep,[xelon Company How Barrier Coating Systems Prevent Corrosion* Barrier coating systems separate the electrolyte from the anodes, cathodes and conductors" A barrier coating system has been applied to the steel substrate in the OCGS Sand Bed region 68 Technical Review of Ari [xelni Compaqy OCGS Sa nd Bed Region ig System Coatir° The OCGS Sand Bed region system consists of: barrier coating-Devoe Pre-Prime 167 penetrating sealer-Devoe Devran 184 mid- and top-coat-Devoe Devmat 124S caulk and is appropriate for the intended service 69 Technical Review of OCGS _________Sand Bed Region Coating System Ak xelon Compainy" With periodic condition assessment and maintenance (if required), the OCNGS Sand Bed region coating system will continue to prevent corrosion of the steel substrate for the period of extended operation" Oyster Creek inspected 100% of the Sand Bed region coating in 2006 and will inspect at least three bays every other outage, with all 10 inspected every 10 years" The 10 year inspection periodicity cycle is appropriate and commensurate with the Sand Bed Region environment and industry experience

-EPRI 1003102, "Guideline on Nuclear Safety-Related Coatings" 70 h[Ielon Comnp~ny UT Thickn ess Measurements I n the Sa nd Bed Pete Tamburro Oyster Creek Engineering 71 Amer Gepw Background and History Sand Bed Region° UT grid measurements were taken at the 19 monitored locations at elev. 11 An [-Xeinon [onpalny as a baseline for the new condition in 1 992* In1 992, thinnest grid average thickness 800 mils vs. criterion of 736 mils*Inl1 992, thinnest local reading 618 mils vs. criterion of 490 mils 72 Background and History Ani E[xeIoit Company Sand Bed Region 0 19 grids repeated in 1994 and 1996-Statistically, no changes in thickness were observed-Basis for corrosion "arrested" in the sand bed region, on outer surface of the drywell-Basis for NRC SER concluding that further UT measurements are not needed and visual inspection of the coating is sufficient

  • The 2006 UT measurements confirmed that corrosion has been arrested 73 Amer O r UT Measurements of 6"x6" G rid An [elon Company Sand Bed Region* Measurement locations are marked inside of the drywell shell on the* Use a stainless steel template with 49 holes to align the UT probe* UT probe placed perpendicular to the surface to consistently obtain lowest reading* A protective grease is applied to the 6"x6" grid during operation, and removed to take UT measurements 74 AmerGen Statistical Methodology 49 UT readings are recorded over a 6" by 6" area.Diameter of each hole between 9/16" and 5/8".1" (Typ.)1/16" by 1/4" slit centered on middle row or column/1i (Typ.)A stainless steel template is used to ensure that the readings are recorded consistently and in same location (+/- 1/16") every time.For each location, the mean and standard error and the thinnest of the 49 readings are calculated after each inspection.

75 6" (Typ.) 1" (Typ Statistical Methodologya

  • Because of roughness of the exterior surface of the drywell shell in the sand bed, there is uncertainty in the mean thickness calculated for each grid location* The major contributor to the uncertainty in the means is the variance from point to point due to the rough surface and not inaccuracy or repeatability of the UT Instrumentation 76 Statistical Methodology Ame rxe0,nComm For each location the means and thinnest points are trended over time Today 0 0.Thickness Time 77 Statistical Methodology___
1) A curve fit based on the regression model is then developed.
2) The Corrosion "F" Test is performed to determine if the data meet the curve fit with 95% confidence.

4ni lxelon Cnmpdny"F" Test of Curve to 95%Confidence Thickness Curve Fit KEY* -mean value H- standard error Time 78 Projection Based on Successful Corrosion F tests All b~elofl col.ý,paflý eFit Projected Margin in 2029 with 95%Confidence Thickness Time 79 Ma Amerwersm 2006 Sand Bed Data Summary 1992 2006 1996 In th, sand 1994 there insp(with betw Nmils Then insp, Minimum Corr Required 95%Thickness,.

An lxeln Con-ipanýe case of the 2006 bed inspections, are only 4)ctions per location most standard errors een +/- 8 and +/-16 e are not enough)ctions to satisfy the osion Test F test with confidence.

KEY 0 -mean value D- standard error 80 Time Smeroen, M Afl klon y Statistical Methodology We then employed a conservative statistical analysis based on a "Monte Carlo" type simulation to determine a minimum statistically observable corrosion rate for the purpose of ensuring adequate inspection frequency 81 imeroepsht Given only 4 inspections and the standard errors, simulation was required to determine the minimum observable rate with 95% confidence.

This is not an hn Nyc) Coiiipxin actual rate!1994 1992 1996 2006 Thickness-4-i The simulation answered the question:

What is the minimum rate that passes the F Test with 95% confidence given four inspections and most standard errors between 8 and 16 mils Time 82 The simulation used a random number generator based on the normal distribution AmerGen,, An Ixt,1(, n , 1 Input Mean Standard Error -49 Normal Distribution Random Number Generator Output 0000000 0000000 0000000 0000000 0000000 0000000ýAn array with 49 randomly generated values. The array is normally distributed with a resulting simulated mean and a resulting simulated standard error.83 Simulation

-Minimum Observable Corrosion Rate AmeroenstA Chose a rate and performed 100 Iterations (Steps 1 through 6)1) Simulated mean for 1992 based on 49 generated random values.Input to the generator is the grid 19A, 1992 mean and standard error.k I'vion 2) Simulated mean for 1994 based on 49 random generated values. Input to the generator is: the 19A, 1992 mean minus the selected rate times 2 (1994-1992);

and standard error./3) Simulated mean for 1996 based on 49 random generated ,,,-"values.

Input to the generator is: the 19A, 1992 mean minus the selected rate times 4 (1996-1992) and standard error.mpy Thickness I I I a I a 5) Determine the curve fit based on the 4 simulated means and perform the Corrosion"F" Test.4) Simulated mean for 2006 based on 49 random generated values. Input to the generator is: the 19A, 1992 mean minus the selected rate times 14 (2006-1992) and standard error.6) If the curve fit passes the "F" test than this iterations counts as a successful iterations.

84 1992 1994 1996 1992I I99t6 /1UO Simulation

-Minimum Observable Corrosion Rate AmerGens The minimum rate which consistently passes the Corrosion "F" Tests 95 out of 100 times is the Minimum Observable Corrosion Rate.1992 2006 1996 1994 Repeat each 100 iteration simulation with increasing rates.Thickness 6.7m 8 mp Rate Number Successful"F" Test -19A 2mpy 27 3.5 mpy 55 5mpy 80 Smpy 92 9 mpy 96.2 97 y 98 Average -100 Iterations were repeated 10 times Time 85 Next Required Inspection Based on the Minimum Observable Rate 4o1:d ( Ck ii( V i 1994 Based on this statistical approach, the next inspection shall be performed prior to this date Based on this statistical approach the most limiting locations are 19A and 17D with required inspection dates prior to 2016.Thickness Minimum Required Thickness Time 86 A eroer s AnI Exeloii Coirijxlny Results of the Statistical Simulation" The most limiting locations are 19A and 17D, with required inspections prior to 2016" Therefore, the next inspection scheduled for 2010 is appropriate" Analysis after future inspections will be used to determine the appropriate inspection frequency 87 anM Aiih AmerGensm 2006 Inspections Sand Bed Region Ani Ielon (ofnpip-ny

  • Visual inspection of coating in (external) all 10 bays* UT measurements of 19 grids at elev.(internal) 11'3"* UT measurements 106 locally thinned single point locations (external) 88 Atn Exeon Con'pilny 2006 Inspection Results Sand Bed Region° Visual inspection of External Shell Coating -no degradation 89 Sand Bed Region 2006 AmerGen"M Al Ixowiu Shell -Caulk Floor External UT Inspection locations Bay 7 -Drywell shell, caulking, sand bed floor 90 Sand Bed Region 2006 AmerGen Reference for-locating inspection points External UT Inspection location Bay 13 Drywell shell 91 Sand Bed Region 2006 AnerGen, An! [ xl'on C u)!'T,mvl~

ShellCaulk Floor Bily 19 caulking Drywell Shell Bay 19 92

.-A/5zN Amer P"OPSM An 1'xdn Companý2006 Inspection Results Sand Bed Region* UT measurements at 19 internal grid locations-No ongoing corrosion 93 General Thickness at 19 Grid Locations AmerGen Location Pre- May Sept. 1992 1994 1996 2006 Min. Nominal Margin 1992 1992 Req'd Thick.Thick Std Error Thick Std Error Thick Std Error Thick Std Error 1D 1115 1101 110U0 1151 '13.6 1122 18.4 365 3D 1178 1184 +/-49 1175 17.5 1180 +/-5.7 439 5D 1174 1168 -'2.6 1173 i2.2 1185 L2 432 7D 1135 1136 +/-4.3 1138 +/-5.9 1133 +/-6.5 397 9A 1155 1157 '4.5 1155 +/-4,8 1154 +/-4.2 418 90 992 1000 1004 110.0 992 +/-10.4 1008 +/-10.6 993 -11.2 256 11A 833 842 825 L8,2 820 +/-7,7 830 +/-8.7 822 +/-8&0 84 11C Bot 856 882 859 +/-64 850 A4.5 883 +/-7.4 855 +/-4.5 114 Top 952 1010 970 12318 982 +/-23.4 1042 +/-21.4 958 +/-24.7 216 13A 849 865 858 +/-9.6 837 -7.8 853 +/-8.8 846 +/-8.2 101 13D Bot 900 931 906 +/-9.0 895 +/-8.2 933 +/-9.6 904 L8.9 159 Top 1048 1088 1055 114.1 1037 +/-13.6 1059 +/-11.2 1047 +/-13.7 736 1154 301 13C 1149 +/-1.9 1140 13.8 1154 A3.2 1142 '3.1 404 15A 1120 1114 i16.3 1127 -10.8 1121 +/-16.6 378 15D 1042 1065 1058 +/-8.7 1053 +/-9.0 1066 +/-8.5 1053 18.9 306 17A Bot 933 948 941 +/-11.8 934 i10.7 997 +/-10.7 935 +/-10.5 197 Top 999 1125 1125 +/-7.2 1129 +/-6.8 1144 +/-11.1 1122 +/-7.2 263 17D 822 823 817 L9.2 810 +/-9.5 848 +/-8.9 818 +/-9.5 74 17/19 Top 954 972 976 +/-4.8 963 +/-4.9 967 +/-6.0 964 14.8 218 Frame Bot 955 990 989 +/-6.3 975 +/-7.8 991 +/-6.2 972 +/-5.9 219 19A 803 809 800 18.4 806 19.9 815 +/-9.6 807 +/-8.9 64 19B 826 847 840 +/-8.7 824 +/-7.8 837 +/-9.5 848 +/-8.6 88 190 822 832 819 +/-11.0 820 +/-10.5 854 +/-11.8 824 +/-11ý3 83 94 Note: Shaded cells indicate thickness value used to conservatively calculate the margin merGepsm Minimum Available Al xlon Company Thickn ess Margins Bay No. 1 3 5 7 9 11 13 15 17 19 Minimum Available 365 439 432 397 256 84 101 306 74 64 Margin, mils 95 Figure 21 Sandbed Bay # 19A 1154 Mil Nominal Shell Plate Thickness 1200 -U)4)Q 1000-*-1+- 8.4 m ils +/- 9.9 m ils + -9.6 m ils-15 M'~s/y noI+1- 8.9 mils 800 Margin = 64 Mils 736 Mil General Required Shell Thickness 61Drain Lines Cleaned 00 Start Sar Remova:i--Strippable Coating Complete Sand Added to Rx Cavity Removal and apply Epoxy Coating Strippable Coating Strippable Added to Rx Cavity CotiUe Not Used i I--.1 Source: Raw Data -Amergen Calculation C-1 302-187-5300-021, C-1 302-187-5300-028, C-1 302-187-8610-030 96 Figure 1. Sandbed Bay# ID 1154 Mil Nominal Shell Plate Thickness 1200 U a N +/- 13.6 mils+/- 10 mils L+/- 8.4 mils 1 000~4)C-U go-Margin = 365 Mils 736 Mil General Required Shell Thickness--_..

a-600 Drain Lines Cleaned Start Sand Removal Strippable Coating Complete Sand Added to Rx Cavity Removal and apply Epoxy Coating Strippable Coating Strippable N ei Added to RxCavity Coating -I Not Used: 0 0 0 BlBW is BW f Bpi 19 Buy7 iWo KayP~ui Buy Source Raw Data -AmerGen Calculation C-i 302-187-5300-021, C-1 302-187-5300-028, C-1302-187-8610-97 Smerole'PS 2006 Inspection Results Ao Exel(onCompily External Sand Bed UTs* 106 individual UT measurements were taken externally in the sand bed region 0 It was verified that all 106 measurements meet the local thickness requirements (both buckling and membrane stresses)0 The 2006 measurements are not directly comparable to the 1992 results because of differences in measurement techniques 98 Inside Drywell AmerGen Concave Curvature Effects 1992 vs. 2006 External UT Data (106) Sand Bed Readings Uncoated 1992 Traditional pulse echo technique Coating 99 A~n 111on Comaqrp External UT Inspection Result-s Location 1992 UT Measurements 2006 UT Measurements No. of No. of UTs Thickness in Thickness in No. of No. of UTs Thickness in Thickness in UTs <736 mils mils <736 mils >736 UTs <736 mils mils <736 mils >736 Bay 1 23 9 680 to 726 760 to 1156 23 10 665 to 731 738 to 1160 Bay 3 8 0 780 to 1000 8 0 764 to 999 Bay 5 8 0 890 to 1060 7 0 880to1007 Bay 7 7 0 920 to 1045 5 0 964 to 1040 Bay 9 10 0 791 to 1020 10 0 781 to 1016 Bayl1 8 1 705 755 to 850 8 1 700 751 to 830 Bay 13 29 9 618 to 728 807 to 941 15 6 602 to 708 741 to 923 Bay!5 11 1 722 770 to 932 11 0 749 to 935 Bay17 11 1 720 760to1150 10 1 681 822 to 970 Bay 19 10 0 776 to 969 9 0 738 to 932 Total 125 21 1061 18-mI~m'The locally thinned areas prepared for UT measurements in 1992 were measured in 2006.However, the inspection team was able to locate only 106 points instead of 125.100 AmerGen 2006 Measurement Locations In the Sandbed Region Color Code for thileleo Oresn -UT Messurem gnts b 736 Mile Yellow- UT Measurements Betveen 638 and 736 Mils Red -UT Measurem ants Betyeen S36 and 836 Mils Location Il wje of UT uarjrmlt A External Point UT Measurements I.- internal Grid UT Meaiurements n Internal Point UT Measurements A iAA 11' -O0................

A BAY 8 A A A SAY1 SAY'13 A A I,'-I I--I i£i 10' -1.1,' -., 11 -I" I,. -1t" I.f by Lontin (Day t4.nbikr)i ""am Ii)I Im 1Mi in=1m iiib. wqW, minmsirn~

I. .%fill SiMFMM~ 13 Mid .61 Its IndM"~ ill" A eroenoc Sand Bed Region Conclusions

  • Corrosion on the outside of the drywell shell in the sand bed region has been arrested* The coating shows no degradation
  • There is sufficient margin to the minimum thickness requirement (maintain 64 mils margin above code required average thickness of 736 mils)102 SmerGen,,, Future Inspections in Ao![vi Con-y(-!q the Sand Bed Region* Visual inspection of exterior coating in three bays every other outage, inspecting all 10 bays once every 10 years" UT measurements at 19 grid locations at elev. 11'3" in 2010, then every 10 years thereafter" Repeat UT at 106 locally thinned locations from the exterior in 2008 outage-In future outages, perform UT in 2 bays every outage 103 An Exelon Compafiy Embedded Portions of the Drywell Shell 104 A[n klon Comnla Embedded Shell Conclusions" Corrosion on the embedded surfaces of the drywell shell, both interior and exterior, is not significant

-The environment of embedded steel in concrete prevents significant corrosion* Estimated at <1 mil / year" Drywell shell meets design basis requirements, with margin to 2029 105 AmerGen,,,, LOWER DRYWELL-M ý vloii (wýl[)L-lq SANDBED, TRENCH& SUMP RFACTOR PFDFST4---EL. 8' 1 1 SAND BED RýEGION IL SUB-PIL r ROOM...R O U G -LP EL. 10'--9'-A EL. 10' 0" -HP EL. 1t'-i1 SUMP 7L, "0 DRYWELL E-. 10'-3"SKIRT'11"3 A I3 A A N 4 ELEVATION LOOKING WEST 106 AnierGen Aw x(lioll kvwl'my REACTOR BUILDING, DRYWELL SUPPORT STRUCTURE CONTAINMENI SHELL -LL 23-6" A SANDBLD REGION.;GRADE EL. 23'-6" I IREATOR ESSE CUR-RL. (-)C-N'1 L_. -U LIMIt Ul-MEMBRANE WATERPROOFINO

'4 1 lo'! o" I /CIANNEL 44 E_ 4'-6" UORUS ROOM-MEMBRANL WAILRPROOF ING (TYP ALL AROUND)IONCP7D El PE DESTAL.4-4* 4. 4 ICONCRE-E MATI 4 WAlFR STOP (IYD)ALL AROUND)----------

' " .--_ A ]EL 4 9'I _Z2 -l _ _ 43'-G6"_- I FVFI INC SI ARMEMBRANE WAfERPROOFING 107 AAmerGen,, I\ \-C-UtSUEL FLAIL SAND BED AREA Ol () " 11 OW E-D 'A 10H 01Y A-;P V NI i l (it O

  • Ail"'F~IM USi -1'4' zl /I PM1" 1! 1< PLAiL,

,"IMAIM 1'll 4; DR1Mk TWol 1/)" ldAlt FT ,, I ý ): ' I " SECTIONAL VIEW OF SAND AT VENT PIPE BED AREA 108 EL. 87' 5" (13)AmerGen, An L[don o wofli 1 lq7 270" IA PA2ý ýKEY PLAN 109 Ame~fr Gm Embedded Shell -Exterior Surface* Any corrosion of the drywell exterior embedded surface occurred because of water leakage into the sand bed region* Corrective actions for the sand bed region arrested corrosion of the drywell exterior embedded shell-Water leakage into the sand bed region was prevented-The joint between the drywell shell and floor of the sand bed region was sealed to prevent water from contacting the exterior shell 110 merGen ,F Embedded Shell -Interior Surface Water that was identified in the trenches in bays 5 and 17 inside the drywell when the foam filling was removed during the 2006 refueling outage was determined to have originated from equipment leakage inside the drywell (Not from external sources)111 merGen,, M [xdon Company Embedded Shell -Interior Surface* Investigations into the source of the water indicate that there could have been water below the drywell interior floor for an extended period* Additional concrete was removed from the bottom of the bay 5 trench to expose 6 inches of drywell shell that was embedded on both sides for UT thickness measurements of the drywell shell 112 AmerGenrleloi Embedded Shell -Interior Surface Corrective actions during the 2006 refueling outage included-Caulking the joint between the drywell interior floor and the drywell shell-Repairs to the collection trough in the sub-pile room 113 AmerGep, , Corrosion of Steel Embedded in Concrete Barry Gordon Structural Integrity Associates Inc.114 Corrosion of Steel Embedded in Concrete* Drywell shell was constructed first, followed by pouring of concrete both on the inside and the outside of the shell* The high pH (e.g., 12.5 to 14) environment created during hydration of the cement in the concrete results in the formation of a passive, protective film [Fe(OH)2 +Ca(OH)2] on the carbon steel surface that mitigates corrosion in the absence of an aggressive environment 115 A.erGen Exterior Embedded Steel MAel0, Cninp m, Environment

  • The reactor cavity water that flowed into the embedded region outside the drywell was affected by the sand bed However, the chemistry of the water leachate from moist sand from the sand bed region was measured in 1986 revealed high purity water:-pH >7, <0.045 ppm Cl- <0.032 ppm S0 4 (US Water: 59 ppm CI-, 81 ppm S04=)-This water is not aggressive to the embedded steel in concrete per GALL/EPRI 116 Exterior Embedded An ,x0on Conmip0uq Steel Environment
  • The water in the embedded region would have been the same quality as in the sand bed region, except the pH would have been greater because of the interaction with high pH concrete pore water* Per GALL NUREG-1801 Vol. 2, Rev.1 and EPRI 1002950, no aging effects are expected since pH>5.5, <500 ppm Cl- and <1500 ppm SO 4 (GALL ll.Bi.2-2, II.B1.2-8) 117 biierGen-interior Embedded Anixvontonydný Steel Environment i Chemistry of the drywell Trench #5 water (from equipment leakage) shows high pH, low CI-, low S04= and high Ca:-pH 8.4 to 10.2 (despite C02) (> GALL/EPRI limit)-CI-: 13.6 -14.6 ppm (<< 500 ppm GALL/EPRI limit)-S0 4=: 228 -230 ppm (<<1500 ppm GALL/EPRI limit)-Ca: 83.5 -96.6 ppm (No GALL/EPRI limit)* Water is characterized as good quality "concrete pore water" that mitigates steel corrosion Trench #5 water complies with GALL/EPRI embedded steel guidelines 118 AmerGen Interior Embedded Steel Environment 0 yeHl shell with minor Trench #5 water's high surface corrosiqn 6, Ca indicates that the water slowly migrated through the alkaline concrete* Any subsequent water ingress into the concrete floor will also become high pH concrete pore I water 119
  • erGern.Interior Em bedded An 0e0o Cormipi Steel Environment" Corrosion of the steel shell not wetted by high pH concrete pore water is mitigated by subsequent inerting of the drywell during operation* Any possible subsequent steel corrosion could occur only during brief outages when fresh oxygenated water can contact with the shell" Finally, transport of any oxygenated water through the concrete to the steel is slow, will increase in pH and must displace oxygen depleted water before any possible corrosion can occur 120 Ao Ixelon Company 2006 Outage Inspections Embedded Shell* Visual inspection of the surface in the trenches showed minor corrosion which was easily removed with no visible loss of material or degradation of the surface 121 AmerGen,., 2006 Outage Inspections

'1 kelon Compaq Embedded Shell UT measurements in the trenches measure total corrosion on the inside and outside between 1986 and 2006-Corrosion was occurring on the exterior surface that was not embedded until 1992 when sand was removed-Material loss was consistent with the corrosion rates on the outside of the drywell before the sand was removed 122 A M elr n Compiin 2006 Inspection Results Embedded Shell UT measurements in trenches 5 and 17 1986 1986 Std. 2006 2006 Std.Thickness Error Thickness Error Trench 5 1112 mils +/-2.59 mils 1074 mils +2.66 mils 38 mils Trench 17 1024 mils +/-2.85 mils 986 mils +-4.18 mils 38 mils 123 2006 Inspection Results An 0ml)(Iq Embedded Shell L UT measurements of the 6 inch surface excavated in the bottom of the trench in bay 5 were performed to determine total corrosion, both interior and exterior* Measured thickness is 1113 mils, as compared to a nominal of 1154 mils-A change of 41 mils, approximately 1 mil/yr 124 Amer~en, Aii Lxeon 2006 Outage Inspections Embedded Shell° The 106 individual UT measurements made from the exterior of the sand bed region are a baseline for monitoring corrosion of the interior embedded surface of the drywell in future outages 125 An blonIQ Comptmy 2006 Inspection Results Embedded Shell* The joint sealant between the sand bed floor and the exterior drywell shell was inspected and found to be in good condition* No water was identified in the sand bed region in any of the 10 bays 126 AmerGen,.An [xelon Companiy Embedded Shell Conclusions" Corrosion on the embedded surfaces of the drywell shell, both interior and exterior, is not significant

-The environment of embedded steel in concrete prevents significant corrosion° Estimated at <1 mil /year" Drywell shell meets code thickness requirements, with margin to 2029 127 zImerGen, Future Inspections on the An Fxdon Compaý, Embedded Shell* Repeat UT measurements in both trenches, including the newly excavated 6 inches in 2008-If results indicate no significant changes, then fill the trenches with concrete and restore the curb to original configuration Repeat UT measurements at 106 external points in 2008-Perform external UT measurements in 2 bays every refuel outage starting in 2010-All bays will be inspected every 10 years 128 An Fbtlon ComjiXflY Upper Drywell Shell 129 AmerGer,,, An [xloiu Compa[qIr~y Upper Drywell Shell Conclusions

  • These measurements are the lead indicators of corrosion on the outside of the shell* Corrosion of the upper shell is <1 mil / yr* Upper Drywell shell has a minimum of 137 mils margin* Based on current rates, will have margin through the period of extended operation 130

/merGenA Upper Drywell Shell* Starting in 1983, over 1,000 UT measurements were taken to locate areas of corrosion on the exterior surface of the drywell shell* 13 grid locations have been selected for monitoring e These locations are measured every other refueling outage 131 AnierGen,,, Ain xcflo rn r(m iatloy[E L 5ý b C~ 1 0".(8,)Al iA(h) GRlAPHl OW I\ ICAHICN NUML111 Wi~114? ;ýKEY PLAN 132 Upper Drywell UT Measurements Monitored Location Minimum Average MWasturedt Thickness 1.2 mils Projectud Ilevalion Required Tlhickness in Thickness 202)mils 1987 198X 1989 1990 1991 199 193 194 1996 2000 1200)4 2F06 roils Elevation 541 50' 2" Bay 5- 743 742 747 No Observable D12 745 745 747 741 748 741 743 747 Ongoing 746 749 Corrosion Bay 5-SH 761 755 759 No Observable 761 758 759 754 757 754 756 760 Ongoiog 760 Corrosion Bay 5-51L 706 703 703 No Observable 703 705 702 702 705 7016 701 70)5 Ongoing 7016 C.orrosion Bay 13- 762 760 765 No Obscrvable 31H 779 758 763 759 766 762 758 762 Onlg 765 Corrosion Bay 13- 687 689 685 No Observable 31L 684 679 688 683 690 692 693 678 OngoingCorrosion HBy 15. 758 762 767 23H 764 762 763 758 761) 75i 757 765 Bay 15- 726 726 726 749 720 23L 728 729 724 728 724 729 727 725 133 SerGenr Upper Drywell UT Measurements An ý.Ydoil ColplIq Notes: 1. The average thickness is based on 49 Ultrasonic Testing (UT) measurements performed at each location.2. Multiple inspections were performed in the years 1988, 1990, 1991, and 1992.3. The 1993 elevation 60' 10" Bay 5-22 inspections was performed on January 6, 1993. All other locations were inspected in December 1992.134 AmerGer, Upper Drywell Shell AnIIen comnpaqy 2006 Inspection Results* 12 of the 13 locations show no statistically observable corrosion* The location with the minimum margin (137 mils) has no ongoing corrosion° 1 location shows a corrosion rate of 0.66 mils/year-Projected thickness in 2029 is 720 mils, compared to a minimum required thickness of 541 mils 135

'K.eroensM M IvIon Compq Upper Drywell Shell Conci usions* These measurements are the lead indicators of corrosion on the outside of the shell* Corrosion of the upper shell is <1 mil / yr* Upper Drywell shell has a minimum of 137 mils margin* Based on current rates, will have margin through the period of extended operation 136 AmerGen, Overall Conclusions

[xelon Company* The corrective actions to mitigate drywell shell corrosion have been effective* The drywell shell corrosion has been arrested in the sand bed region and continues to be very low in the upper drywell elevations

  • The corrosion on the embedded portion of the drywell shell is not significant
  • The drywell shell meets code safety margins* We have an effective aging management program to ensure continued safe operation 137
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