ML20236S755
| ML20236S755 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 11/20/1987 |
| From: | Wilson R GENERAL PUBLIC UTILITIES CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20236S758 | List: |
| References | |
| 5000-87-1421, NUDOCS 8711300077 | |
| Download: ML20236S755 (119) | |
Text
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GPU Nuclear Corporation v Nuclear un;":::::, ora,.
201-316-7000 TELEX 136-482 Writer's Direct Dial Number:
November 20, 1987 5000-87-1421 Mr. John Stolz, Director Project Directorate No. I-4 Division of Reactor Projects I/II U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Stolz:
Oyster Creek Nuclear Generating Station Docket No. 50-219 License No. DPR-16 1
Oyster Creek Drywell Containment On November 13, 1987, the GPU Nuclear Staff met with NRR and Region 1 representatives to review the data and assessments related to UT measurements at elevations 50'-2" and 87'-5" of the Oyster Creek Drywell.
These measurements were initiated by GPUN during the current outage to confirm the condition of the drywell above the sand entrenchment region. As part of the meeting GPUN committed to forward a copy of the revised Safety Evaluation which incorporated this latest investigation.
This evaluation is attached.
As indicated in the safety evaluation and during our presentation on 11/13/87, GPUN assumed for analysis purposes that the upper regions of the drywell had experienced uniform thinning over the entire surface of the drywell vessel.
UT. measurements made on the drywell show that this is not the case, and the assumption of uniform thinning is conservative.
Using the above noted assumption GPUN concluded that the drywell is structurally adequate based on the analytical approach described in Attachment 5 to the safety evaluation.
This analysis is identical in method to earlier drywell evaluations we've reported to NRC except that allowable stress was derived from the lowest value of certified mill test report properties for the plate material actually used in constructing the O.C. drywell.
At the 11/13/87 meeting GPUN committed to also explore alternate analysis methods to demonstrate code compliance.
It is expected that the results of these alternate analysis will be available in approximately three or four g
weeks.
y GPU Nuclear Corporation is e subsidiary of General Pubhc Utilities Corporation 1
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If.yo'u should have any questions in.the interim, please. contact'Mr. M. W.
- Laggart at~(201) 263-6205.-
Very t ly yours, i
W i%
R. F. Wil on.
Vice' Presi dent..
1 Technical Functions-RFW/DJ/mg 5635g cc:
Mr.. William T. Russell, Administrator Region I
-'U.S. Nuclear Regulatory Commission 631. Park Avenue King of Prussia,.PA.
19406 NRC Resident Inspector.-
Oyster Creek Nuclear Generating Station' Forked River, N.J.
08731 Mr. Alex Dromerick, Jr.
U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Phillips Building, Mail' Stop 316 Bethesda, Maryland 20014 Mr. David M. Scott, Acting Chief Bureau of Nuclear Engineering Department of Environmental Protection CN 411 Trenton, NJ 08625 1
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GPU Nuclear Technical Functions Safety / Environmental Determination and 50,59 Review UNIT Oyster Creek Nucle _ar Generatinq Station '
PAGE 1 OF _ 16 SE No.00024't-007 DOCUMENT NO.
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.l Type of Activity Evaluation of Reduced Plate Thickness of the Drywell Steel Shell (Modification, procedure, test, expenment, or document) l 1.
18 this activityMocument listed in Section I or 11 of the matnces in Corporate Eyes CNo Procedure 100o ADM 1291.017 (f the answer to question 1 is "no" stop here. (Section IV activitiesMocuments
)
should be reviewed on a case oy case basis to determine if this procedure is applicaD6e.) This procedure is not applicacle and no documentation is required.
l if the answer is "yes" proceed to question 2.
l 2.
Is this e new activityMocument or a substantive revision to an activityMocu-Cyes CNo i
ment? (See Exhibit 1 paragraph 1 this procedure for examples of non-substantive changes)
If the answer to question 2 is "no" stop here..This procedure is not applicab6e f
and no documentation is required. If the answer is "yes" proceed to answer all remaining questions. These answers cocome the SafetyIEnvironmental Deter-mination and 50.59 Review.
1 Does this activityMocument have the potential.to adversely affect nuclear safety
[ Yes CNo
]
or safe plant operations?
4.
Does the activityMocument require revision of the system / component desenp-Cyes C No l
tion in the FSAR or otherwise require revision of the Technical Specifications or any other Licensmg Basis Document?
5.
Does the activityMocument require revision of any procedural or operstmg Cyes $No desenption in the FSAR or otherwise require revision of the Technical Specifications or any other Licensmg Basis Document?
6.
Are tests or experiments cWucted which are not desenbod in the FSAR, the Cyes ZNo Techn cal Specificahons or any other Licensmg Basis Document?
7.
Does this document involve any potential Non-Nuclear environmental impact?
Cyes ENo 8.
Does the activityMocument require a review of entena as outtined in SOO-C es ENo T1000. TMi t Dission i Plant Level Critena?
l If yes, identify TR/TPWR.
If any of the answers to questions 14,5. or 6 are yes, proceed to EXHIBIT 6 and prepare a wntten safety eve 6uabon. if the answers to a 4,5, or 6 are no, this proctudes the occurrence of an Unreviewed Safety Question or Technical Specifications enance. If the answer to question 7 is yes, either redesign or provide supporting documentation which will permit Environmental Licensmg to determme if an adverse environmental impact exists and if regulate, aa,,groval is required (Ref. LP410). If in doubt, consult the Radiological and Environmental Controis vivis' - or Environmental Licensmg for assistance m com-pletmg the evaluation.
i Date signatures - See attached Sidn-of f sheet Engineer /Ongmator l
Section Manager l
l Responsible Tecnnical Reviewer i
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MUCl48r TechnicalI neaons Safety baluation 9
16 Oyster Creek Nuclear Generating Station PAGE 2 OF UNIT SE No, nnnnhnn?
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Drywell Steel Shell Plate Thickness Reducl.
2 ACT?lTY/ DOCUMENT TITLE Document No. _._f
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. 8 Type of Activity / Document Evnluntinn of br nred 'ificl' ness of the DrWall Steel Shel l
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This Safety Evaluation provides the basis for detd' mining whether this activity / document involves an Unreviewed Safety Question or impacts on nu: lear safeq.
(
.t is Answer the following questions and provide reasa1(s) fonach answe'r per Exhibit 7. A simple statement of conclusion in itself is not sufficient. The scope and depth of each reason should be commensurate with the safety significance and tomplexity'cf the proposed change.
I 1.
Is the margin of safety as defined in Licensing Basis Documents other CNs,> MNo r, (
than the Technical Specifications reduced?
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- 2. Will implementation of the activity / document adversely affect nuclear d
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safety or safe plant operations?
Cyes ENo The following questions comprise the 50.59 considerations and I
evaluation to determine if an Unreviewed Safety Question exihn 3.
Is the probability of occurrence or the consequences of an accioent or i
malfunction of equipment important to safety previously evaluated in,
/
Cyes ENo the Safety Analysis Report increased?
4.
Is the possibility for an accident or malfunction! of a different type than i
any evaluated previously in the Safety Analysis heport created?
Cyes' Whn 5.
Is the margin of safety as defined in the baskfty any Technical Specification reduced?
D Cyes ENo if any answer above is "yes" an impact on nuclear sataty or an Unreviewed Sahty Question exists. If an adverse impact on nuclear safety exists revise or redesign. If an udreviewed salt-ty question v'ith no adverse impact on nuclear safety exists forward to Licensing with%ny ad-ditional documentation to support a request for NRC approval prior to implementing approval.T 6.
Specify whether or not any of the following are required, and if "yes" indicate how it was resolved o
Yes TR/TFWR/Other No,. ['
a.
Does the activity / document require X
TR AT3297 Y, h an update of the FSAR?
Yest an analysis to support the newfirwell siplli thickness Explain:
must be included in the Final Safe? y Analyhis Rhport Section 3.8.
I b.
Does the activity / document require a Technical Specification Amendment?
- h4 cW a =s f nun 4 'dnxing_.ca in spdc ion meet s t he
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DOCUMENT NO.
-(UClear SE No. 000243-002 l'
ME DRWELL STEEL SHELL PLATE THICKNESS REDUCTION REV
SUMMARY
OF CHANGE APPROVAL DATE 1
General revision to capture results of wall thickness evaluation for areas above the sand entrenchment region
- Revised title of document
- Repaginated document
- Revised P.2 Item 6D
- Added attachments 5 and 6
- Revised the following paragraphs (paragraphs have been renumbered) 1.0, 3.3.2D, 3.5.1, 3.5.7, 3.6, 3.7, 3.9, 3.11 3.15, 5.0 and 5.5, Att 2 page 2-1 Added 2-16.
- Added
- 2. 3. 5, 2. 3. 6, 2. 3. 7, 2. 3. 8 and 3.4 Leakage testing discussion on Att. 2-2 Preparers Signature Date Responsible Tec Tnical Reviewers S. Leshnof fdHt[f 1/!/1[87 G. Von Nieda T. Ruggiero j.rf/
F. S. Ciacobbe M. Sanford # L e
D. Covill
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Nuclear f
7o cert r, STEEt, sHELL PLATE THICA:iE55 RLDLL' wN W
APPROVAL DAit
$UMadARY OF CHANGE Rev
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Ceners' revision to capture results of wall l.
thi@ess evaluation fo r areas 'cbove the %nd vnt r ent.htte nt tegiwn tievised t uiu ul documer.t j
l-Repaginated docianent I
i Revised F.2 item bD i
Added attachments 5 and b Fevised rt'e following paragraphs (paragraphs I
have been renumbered /
I 3.5.1, 3.5.7, 3.6.
J.,', 3.9, 3.11 l
t.0, 3.3.2D.
1.15, 3,0 and 5.5, Att 2 page 2-1 Added 2-16.
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j 2.3.5 2.1.6. 2.1.7
- 2. 3. 3 and 3.4 i
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SE No. 000243-002
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Rev. 1 Page 5 of 16 TABLE OF CONTENTS Section Purpose 1.0 Systems Affected 2.0 i
Effects on Safety 3.0 l
Effects on Environment 4.0 Conclusion
5.0 Attachments
1.
Description of Drywell Design 2.
Extent of Damage in the Sand Cushion Region 3.
Causes of Corrosion and Corrosion Rate 4.
Structural Analysis of the Sand Cushion Region 5.
Minimum Drywell Plate Thickness at Upper Elevations 6.
Upper Level Inspections and Assessments 3781M/2099
1 SE No. 000243-002 l
Rev. 1 Page 6 of 16 1.0 PURPOSE The purpose of this safety evaluation is to assess the structural integrity of the drywell steel pressure vessel in light of an inspection finding in 1986 that sections of the drywell shell near the base sand entrenchment region are thinner than specified and in light of an inspection finding in 1987 that sections of the drywell shell above the sand entrenchment region are thinner than specified.
The shell thickness is below the thickness utilized in the original stress report prepared by Chicago Bridge & Iron Company (" Structural Design of the Pressure Suppression Containment Vessels," for JCPL/ Burns & Roe, Inc.,
Contract No. 9-0971, by CB&I Co., 1965).
This evaluation concludes that plant operation to the end of the eleventh operating cycle is justified based upon an evaluation of the drywell shell at the sand entrenchment region.
This evaluation also concludes that the drywell shell above the sand entrenchment region will 1
maintain adequate structural integrity provided its future exposure to l
water is limited to a total of 21 months.
2.0 SYSTEMS AFFECTED 2.1 System No. 243, Drywell and Suppression System, particularly the drywell shell structure, This structure is directly affected by l
the localized thinning.
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2.2 Drawings showing original thickness - Chicago Bridge and Iron Co.,
Contract Drawings 9-0971, Drawing Nos. 1,2,3,4,5,6,7,8,9, l
10, and 11.
2.3 Other References 2.3.1 Amendment #15 to OCNGS FDSAR, Primary Containment Design Report.
2.3.2 Updated FSAR, Paragraph 3.8.2.
2.3.3 OCNGS Technical Specification Section 5.2.
2.3.4 CB&I Stress Report, " Structural Design of the Pressure Suppression Containment Vessels" for JCPL/ Burns & Roe, Inc.,
CB&I Company Contract No. 9-0971, 1965.
2.3.5 GPUN Calculation C-1302-240-5320-002, Oyster Creek Drywell Thickness for UT July 20, 1987.
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.2.3.6 CB&I Drywell Modification Feasibility Study, Volume.'II, Table 8.14.
'2.3.7 Update on Magnesium Oxychloride Fireproofing, S.I. Kawaller;-
Fire' Technology, Vol.13, May 1977, pp 139-145.
2.3.8 GPUN. Sketch (Drawing No.) 3E-SK-S-89, " Ultrasonic Testing -
y Drywell Level 50'2" - 87'5" Plan".
3.0, EFFECTS ON SAFETY 3.1. Identification of Documents 3.1. 1 OCNGS Unit 1 Facility Description'and Safety Analysis Report
.. Licensing Application, Amendment 3,Section V
- Licensing. Application, Amendment 11, Question III-18
-- Licensing Application, Amendment 15
- Licensing Application, Amendment 68 3.1.2 Technical Specification Documents
- 3. l '. 2.1 Technical Specification and Bases - OCNGS Unit.
Appendix A~to Facility License DRP-16, JCP&L Docket-No. 50-219, Sections 3.5, 4.5, 5.2.
3.1.3 Regulatory Documents 3.1.3.1 10CFR50, Appendix A,- General Design Criteria for Nuclear Power Plants Criterion 2 - Design basis for Protection Against~ Natural Phenomena Criterion 4 - Environmental and Missile Design Bases.
- Criterion 16-Containment Design Criterion 50- Containment Design Basis 3.1.4 Industry Codes and Standards 3.1.4.1 ASME Boiler and Pressure Vessel Code,Section VIII, 1962 with Code Cases 1270N-5, 1271N and 1272N-5 Code Cases.Section III, Div. 1. Subsection NE.
3.1.4.2 See Attachment 1 for additional codes and standards.
3.2 Drywell Containment Structure
- 3. 2.1 ' Attachment 1 provides a description of the Oyster Creek drywell geometry, design bases, materials, shop and field fabrication and testing, and concrete interfaces.
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-3.3 Assessment of the Drywell' Wall in the Sand Entrenchment Region 3.3.1 Extent.bf'DrywellThinningin-theSandCushionRegion.
Background information on the source of the sand cushion wetting, UT techniques, drywell thickness measurements, and core: sample locations are included in Attachment 2.
Based on information contained in Attachment 2, the following conclusions can be stated:
A. The-ultrasonic thickness probing of the drywell L
containment has been confirmed to give accurate but conservative results.
The physical measurements of the thicknesses of'the plugs were approximately 0-4% greater than that determined by UT results.
B. Destructive metallurgical examination of one of the containment plugs verified that the highly localized UT indication was an inclusion and that pitting did not
- exist, i
C..The general areas characterized as broad exterior corrosion have been verified to be general wastage.
D. These broad areas of exterior corrosion are localized at an elevation corresponding to the exterior sand cushion.
Measurements of drywell thickness below the level of the
. interior concrete floor (which were made by removal of the interior concrete at two locations) show.that wastage c
below the floor level is not greater than that measured' just above the floor level. Measurements at the two locations show the drywell below floor level to be slightly thicker than the immediately adjacent area above the floor area.
E. The drain line gasket was found to be leaking and was replaced.
Leak tests were performed on the bellows, and no leaks were detected. Observations of the areas where leakage had previously been found indicated that the leakage had been arrested.
F. Based on the conservative methodology utilized in, the effective drywell thickness at the sand entrenchment region has a mean value of 0.87.
This value exceeds the minimum required shell thickness calculated for structural stability and integrity (See Attachment 4).
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'3.3.2 Drywell Corrosion Mechanism and Rate In the Sand Entrenchment Region.
A review of.the potential causes of corrosion and a.
conservative prediction of a future corrosion rate is c
included in Attachment 3-.. Based on information contained in
! Attachment.3,.the following conclusions can be' stated:
.A.'In all. cases where general corrosion.was present, the.
sand cushion appeared to be wet.
B. No deep pitting was observed and no sulfide or substantial. concentration of manganese was detected'in.
the corrosion product.
This indicates that microbiological influenced corrosion is minimal.
l.
C, The corrosion observed can be explained by an aqueous
. corrosion mechanism assuming chloride contamination and j
oxygen depletion.
D. A conservative corrosion allowance rate of 48' mils'per year will account for any uncertainties in the assumptions of the corrosion mechanism, follow up
. Inspections of selected locations in this. region-(covering a period greater than nine. months) do not indicate a corrosion' rate which exceeds this value.
3.3.3 Structural-Assessment in the Sand Entrenchment Region provides an assessment of the drywell structural capability' assuming a reduced shell thickness of
.7 inches within'the sand entrenchment area for two critical load combinations.
Conclusions which can be made from this assessment are:
1 A. The original allowable stress criteria of ASME Boiler and Pressure Vessel Code,Section VIII, 1962 with appropriate code cases is met when credit is taken for the radially inward reaction due to the sand. Without the sand (a beyond design basis condition), code' allowable stresses are exceeded by 2.7% with a reduced shell thickness of 0.7 inches at the sand entrenchment region.
- However, ASME Section III, Olv. 1, Subsection NE allowable stress 3781M/2099
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criteria are: met without exception using stress intensities. While peak local membrane stresses are less
'than the allowable, the: meridional extent of these is more than allowed by Section III (but less than 2X).
The original code placed no' bounds on the extent'of a local stress.
It is reasonable to neglect this departure from present code guidance because the present situation is an in-service condition and not a design condition, and-because the departure from present code guidance is small'.
B. The load combinations. selected for this analysis represent the design basis' accident condition.
3.4 Assessment of the Drywell-Wall at Elevations above the Sand Entrenchment Region-3.4.1 Inspections of the Drywell Wall at Elevations above the Sand Entrenchment Region A. program was undertaken to accomplish a sampling of-drywell wall thickness above the sand entrench % nt region to ascertain actual ~ plate thickness.
A discussion of the UT inspection program for drywell wall thickness measurements and core samcle evaluations are included.in Attachment 6.
Also, a review of potential causes of corrosion and a conservative prediction of future corrosion rate is provided in Attachment 6.
Based on information contained in Attachment 6, the following
^
conclusions can be stated:
A. On the basis of the core samples reinoved, wall thinning where observed, has been caused by general corrosion.
The corrosion is fairly uniform with an occasional broad pit.
The corrosion products are characteristic of those formed in an oxygen deficient environment.
Microbiological influenced corrosion is not in evidence.
B. Based on the conservative methodology utilized in, the effective drywell thickness at elevation 50'-2" is 0.757" and at elevation 87'-5" is 0.619".
This value exceeds the minimum required shell g
l-thickness calculated for structural stability and l-integrity (See Attachment 5).
C. Use of an average drywell wall thickness is appropriate in evaluating the shell strength; individual localized pits will not alter the structural integrity of the drywell.
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- 0. Corrosion occurs when the region is wetted.
The calculated corrosion rate is based upon assumed periods.
of wetting'and 1s projected to be less than 16-h mils / wetted year.
E.'The margin available in the drywell wall above the sand entrenchment region is sufficient to ensure structural-strength and integrity provided its future exposure to water is limited to a total of 21 months.
3.4.2 Structural Assessment Above the Sand Entrenchment Region provides a discussion of the structural analysis' conducted to establish minimum required uniform i
-thickness.
Briefly, the design basis loading condition, 62 psig, is the controlling loading for the minimum wall thickness
-calculation above the sand entrenchment region.
Minimum wall thickness for the cylindrical region was calculated based on ASME Code equation (UG-27).
This differs from the spherical region which was calculated based on actual stresses from CB&I report-(Sec. 2.3.6) at the selected' elevations to account for the other loading in addition to design pressure and temperature. As a result, the minimum allowable wall thickness for the 50'2" elevation is 0.671".
The required minimum allowable wall thickness at elevation 87'5" is 0.591" (See Attachment 5. Table 2).
3.5 Effects of Thickness Reduction on the Safety Function of Drywell Containment Structure (DCS) 3.5.1 Structural. Performance The reduction in thickness of the drywell shell at both the
]
sant' entrenchment region and the upper elevations does not l
prevent the structure from performing its intended safety i
function.
3.5.2 Quality Standards Repair of the core samples taken were made in accordance with the quality standards of the plant.
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-l 3.5.3 Natural Phenomena Protection Since the DCS is protected from the outside elements by a e
safety class structure capable of withstanding a tornado or hurricane, and since the plant elevation prevents natural flooding, these loadings do not contribute to the concerns posed by this activity..However..in'the evaluation of structural performance, seismic loads were included and found that this event does not affect the integrity of the OCS when the event occurs singly or in combination with other design loads.
3.5.4 Fire Protection 4
The thinning of the drywell shell does not affect the. fire protectio _n program for the plant, since the drywell was not considered as one of the fire protection measures.
3.5.5 Environmental Qualifications The assumptions utilized in complying with 10CFR50.49,
" Environmental Qualification of Electrical Equipment Important to Safety for Nuclear Power Plants," have not been altered; therefore, there is no effect on environmental qualification.
L 3.5.6 Missile Protection The affected area is protected by a concrete shield wall as described in Section 3.2.1 and by the Reactor Building which provides protection from external missiles.
3.5.7 High Energy Line Break; Internal Flooding The maximum pressure inside the DCS after a high energy line break has been conservatively assumed to be 62 psig.
Subsequent evaluation of the affected areas considering this pressure increase together with SSE and deadioad as applicable shows that DCS structural integrity is still maintained, j
3.5.8 Electrical Separation The reduction in thickness of the affected area does not c
impact any electrical components.
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13.5;9 Ele'ctrical Isolation.
The reduction in' thickness of the affected area does not impact any ele'ctrical components.
-3.5.10 Electrical Loading Impact on Emergency Diesel Generators and-Safety Buses
.No effects per explanation 3.5.9.
3.5.11 Single Failure Criteria No. effects'on. single failure criteria since the structural' integrity and. stability of DCS is assured.
3.6 Licensing Basis Documents Margin of Safety Review of the FDSAR requirements.as to the structural integrity of the DCS during all modes of plant operation reveal that the thickness of.the affected regions still retain the margin of~ safety to satisfy Technical Specification 5.2 and-the intended design as stated'in'the FDSAR.
This was ascertained after re-analysis (see ) of the structural response to'the most severe load combinations considering'the minimum thickness of the sand entrenchment region and' analysis of upper elevations of the drywell' as' delineated in Attachment 5 3.7 Nuclear' Safety / Safe Plant Operation Since (a)1the structural integrity and stability of the DCS have not been affected by the thinning of the affected regions of the shell (b).the corrosion rate determined will not degrade the structural integrity and stability of the DCS-in the sand entrenchment region during Cycle 11 l
(c) the DCS above the sand entrenchment region will maintain adequate structural integrity provided its future exposure to water is limited to a total of 21 months nuclear. safety and safe plant operation will not be affected.
No evidence of damage to other safety related equipment was found.
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Rev. 1 Page 14 of 16 3.8. Probability of Occurrence or Consequences of an Accident Since the structural integrity and stability of.the DCS is still maintained, the minimum-thickness ~of the affected shell region of'
'the DCS will_not affect the probability of occurrence of any accident when the plant is in any mode of operation or plant condition.
Furthermore, since the containment isolation function of the DCS;is intact,' the consequences of any postulated accident I
at OCNGS will not be affected.
J' 3.9 Probability of Occurrence or Consequence of Malfunction of Safety Equipment 3
Given_the fact that the structural, integrity and stability of the DCS has not been affected by the condition, the probability of occurrence or-consequence of a malfunction of safety equipment in the plant will not be affected.
3.10 Probability for an Accident or Malfunction of a Different Type Than any Previously Identified in FDSAR Since the DCS still_ meets design requirements, no accident or malfunctions are different from what have been previously identified.
3.11 Margin of Safety on Basis of Technical Specification The thickness of the affected region of the shell in the sand entrenchment region has been ascertained to satisfy the original allowable stress criteria of ASME Boiler and Pressure Vessel Code, L
Section VIII, 1962 with appropriate code cases when credit is taken
-for the radially inward reaction due to the sand.
Without the sand (a beyond design basis condition), code allowable stresses are exceeded by 2.7%.
However, ASME Section III, Div. 1, Subsection NE allowable stress criteria are met without exception.
While peak local membrane stresses are less than the allowable, the meridional extent of these is more than allowed by Section III (but less than 2X).
The original code placed no bounds on the extent of a local stress.
It is reasonable to neglect this departure from present code guidance because the present situation is an in-service condition and not a design condition, and because the departure l_
from present code guidance is small.
The thickness of the affected regions of the shell above the sand entrenchment region have been found to be structurally adequate l
using ASME code methodology and allowable stress based on mill test l
reports for actual drywell plates.
l 1
l I
3781M/2099
.. =
7 SE.No. 000243-002-Rev. 1 Page:15 of.16 Conservatively projected corrosion rates provide assurance that the
'drywell wall. thickness will still be.acceptible.above the sand entrenchment' region will maintain adequate structural integrity provided its. future exposure'to water.is limited to a total of 21 months.
3.12 Violation of Plant Technical Specification The minimum thickness at-the affected regions does not violate any section of the OCNGS Technical Specification. 'As stated in
.Section 3.11, the allowable stress criteria is satisfied.
~
3.13 Violation of any Licensing Requirements or Regulations i
Review of OCNGS.'licepng requirements and commitments reveal that.
'l the thinning of the drywell shell does not. violate any licensing requiremen.ts or' regulations.
This is primarily due.to the fact that containment isolation function and the structural. integrity of the DCS have not been affected.
3.14 Radiological Safety' Concerns The reduction.in thickness of the drywel_l-shell will not affect any radiological safety concerns because the containment isolation safety function of the DCS is still intact.
Adequate shielding of
< occupied plant areas will.be maintained.
3.15 Change to'FSAR This condition will' require a change to the FSAR to reflect the change in the plate thickness, and the'results of the analysis which support this evaluation.
3.16 Change to Established Practice or Procedure This condition will not require any change to an established practice or procedure.
4.0 EFFECTS ON THE ENVIRONMENT 4.1 Changes to Plant Environmental Interface The reduction in thickness of the affected shell area will impose no changes to the OCNGS plant environmental interfaces, because the l
structural integrity and stability of the DCS is still intact.
l 3781M/2099 L
l L
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SE No.' 000243-002,
'Rev. 1 Page 1.6 of 16
'4. 2 ' Potential: Environmental Impact Since,the activity does not affect the environment, it does-not have any potential impact to the.following:
A.
Environmental Technical. Specification B.
Applicable Environmental Permit Requi'rements C. ' Final Environmental Statement 1
D.
Environmental: Impact Statement Consequently,,no additional: evaluation is required.
U
.5.0 CONCL'USION Inspections'during'1986 revealed that sections of the drywell wall near.
the base sand entrenchment region had-a mean thickness of 0.87 inch.
This is less.than the original thickness that was utilized'in the evaluation of structural ~ stability and integri y in support of licensing t
the 0CNGS'. Additionally UT measurements of other. portions of the drywell wall indicate some' general corrosion.
Extensive review of the original' calculations, load combinations ~and different plant' conditions,
'and new calculations generated to evaluate the structural stability and integrity.of DCS show that:
1
.The structural performance of the DCS during the most severe plant condition (DBA) will not be affected.
The remaining margins of
. safety found are enough to assure. structural stability and.
Integrity of the DCS.
2.
The containment isolation safety function of DCS is still intact.
Consequently, no environmental cr radiological. concerns exist due to the reduced thickness.
3.
FSAR and technical specification commitments have not been violated.
4.
Plant procedures and safe practices are not affected.
5.
The corrosion rate estimated for the shell in the sand entrenchment region will not degrade the structural integrity and stability of I
the drywell during Cycle 11.
The corrosion rate estimated for the
'shell above the sand entrenchment region will not degrade the structural strength of the drywell provided its future exposure to water is limited to a total of 21 months.
6.
Based on Sections 3.8, 3.9, 3.10 and 3.11, there does not exist an unreviewed safety question as defined in 10CFR50.59.
3781M/2099
(.
4 Jag l
SE No.-000243-002 l
Att. 1-1 DESCRIPTION OF DRYWELL DESIGN j.
Primary Containment Geometry The primary containment consists of a pressure suppression-system.with two
. large.. chambers-as shown in Figure 1.
The drywell houses the reactor vessel, the reactor coolant recirculating loops, and other components associated with the reactor system.
It'is a-70 ft. diameter spherical steel shell with a 33 ft diameter by'23 ft high cylindrical steel shell extending from the top.
i The pressure absorption chamber is a steel shell in the shape of a torus located below and around the base.of the drywell.
. The'two chambers are interconnected through 10 vent pipes 6 ft. 6 in. in diameter equally spaced around the circumference of the pressure absorption chamber.
The two chambers are structurally isolated by expansion bellows in the' interconnecting piping and analysis for each unit may be considered independently.
The drywell interior is filled with concrete to elevation 10 ft. 3 in. to provide a level floor. Concrete curbs follow the contour of the vessel up to I
elevation 12 ft. 3 in. with cutouts around the vent lines.
~
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~0n the exterior, the drywell is encapsulated in concrete of varying thickness from the base elevation up to the elevation of the top head, From there, the concrete continues vertically to the level of the top of the spent fuel pool.
i
n 1,
SE No. 000243-002 Att. 1-2
.The: proximity of'the' concrete surface to the steel shell varies with elevation. 'The concrete is in full contact with the shell over theLbottom of the sphere at.its invert elevation 2 ft 3 in. up to elevation 8 ft. 11 1/4 in. At that point, the concrete is stepped back 15 inches radially.to form a pocket-which continues up to elevation 12 ft. 3 in.
That pocket is filled with sand which forms a cushion to smooth the transition of the shell-plate o
from'a condition of fully clamped between-two concrete masses to a free standing condition.
The sand pocket is connected to drains provided to allow Ldrainage of any water which might enter the sand.
Above elevation 12 ft. 3 in. the concrete is stepped back 3" measured radially
~
from'the steel-shell.
This' gap was created during the construction by applying a compressible, inelastic material to the outside of-the shell prior
-to concrete placement.
The material was later permanently compressed by controlled vessel expansion in order to create a gap between the vessel and the concrete.
Drywell' Design Bases 1
Design codes used for the original design are as'follows with the effective dates at the time of design:
6
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H SE.No. 000243-002 Att. 1-3
- ASME Boller and Pressure Vessel Code, Sections VIII and IX'with all
. applicable addenda in effect at the time of design, t
- Nuclear case interpretations 1270 N-5, 1271 N and 1272 N-5.
- ASME Boiler and Pressure Vessel Code,Section II with all applicable addenda for the following material SA-212 High Tensile Strength Carbon - Silicon Steel Plates for Boilers and Other Pressure Vessels SA-300-Steel Plates for-Pressure Vessels for Service at Low Temperatures SA-333 Seamless and Welded Steel Pipe for Low Temperature Service C
1
.SA-350 Forged or Rolled Carbon and Alloy Steel Flanges, Forged Fittings, and Valves and Parts for Low Temperature Service i
- ASTM A-36 Structural Steel i
- AISC Specification for the Design, Fabrication and Erection of Structural Steel'for Buildings i
Pressure and temperature parameters in the original drywell design include:
- Drywell and connecting vent system tubes are designed for 62 psig internal pressure at 175'F and/or 35 psig at 283*F, and an external pressure of 2 psig at 205*F.
- In addition, the drywell is designed to withstand a local hotspot temperature of 300*F with a surrounding shell temperature of 150*F concurrent with the design pressure of 62 psig.
- The lowest temperature to which the primary containment vessel pressure containing parts are subject to while the plant is in service is 50*F.
j To provide an additional factor of safety, 30*F was actually used for the design basis.
- During reactor operation, the vessel will be subjected to average
+
temperatures up to 150*F at approximately atmospheric pressure.
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0 - L' SE'No. 000243-002:
4 Att. 1-4
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Loadings' considered /in.the design of the drywell include
- Loads' caused by temperature'and internal.or. external pressure. conditions..
L.
- Gravity loads from the vessels, appurtenances and equipment supports.
- Horizontal and vertical seismic loads acting on the structures o
- Live loads.
- Vent thrusts.
1
- Jet forces on'the downcomers'
- Water loadings under normal and flooded conditions
' Weight of the contained gas in the vessels c
!* The effect of unrelieved deflection under temporary concrete loads during construction.
- Restraint due to compressible material
- Wind loads on the structures during erection i
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.SE 000243-002 j
~Att, 1-5.
Load combinations used the design of the.drywell and vent system for accident' conditions include:
- Gravity load'of. vessel and appurtenances-
- Gravity load from equipment supports
- Gravity load of. compressible material
- Gravity load on welding pads.
- : Seismic loads
'* Design pressure: maximum positive pressure of 62 psig at 175*F decaying to.35 psig at maximum temperature of 281*F, to maximum negative pressure-of 2 psig at 205'F,.
- Restraint due to compressible material 4,
Vent thrusts l
j
- Jet forces Allowable stress levels used in the design of the drywell are based on Code Case 1272 N-5
- General membrane (does not include thermal) = 19250 psi
- Local membrane (does not include thermal) = 28875 psi
- Surface stress - 52500 psi 1
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SE 000243-002 Att. 1-6 i
Drywell' Materials of Construction.
Steel plates are A-212-61T, Grade "B", made to ASTM A-300 requirements.
. Minimum charpy vee notch impact test values of 20 ft.-lbs.'at 0*F were used instead of 13 ft.-lbs. at O'F as permitted by Code Case-1317.. Test specimens were taken both parallel to and transverse to the direction of final rolling 4
of the plate.
i i
Forgings are A-350 Grade LF1. Minimum charpy vee notch impact test values were 13 ft.-lbs. at 0*F in addition to charpy keyhole impact test values
- required _by the Burns and Roe specifications.
Pipe is A-333, Grade "0" seamless. Minimum charpy vee notch impact test values were 13 ft.-lbs. at O'F on full size test specimens in addition to i
charpy keyhole.-impact test values required by the Burns and Roe specifications.
Miscellaneous plate and structural steel (not within the scope of ASTM A-36):
3 All permanent structural attachments and lugs, welded to the shells, were made of impact tested material for a distance of not less than 16 times the plate thickness.
The erection skirt supporting the drywell was also made of impact
. tested material.
L i
]d SE 000243-002 Att. 1 Drywell Shop Fabrication and Testing Components were shop welded, where jossible, into large size shipping pieces, utilizing either submerged or metallic coated arc. techniques.
In either case, low hydrogen electrodes were used, thus assuring the notch toughness requirements to meet the ASME Code Impact Tests.
All seam welds in the shell of the containment were of the double bevel butt type. All' butt welds in any accessories subject to the ASME Code were also of the double welded type'or equivalent, and all the joints were full penetration.
' welds' All welds subject to the Code were radiographer or otherwise examined in accordance with Code Case 1272 N-5.
All mandatory provisions of this code I
were followed and all recommended provisions were also followed where-practical.
Heavy'weldments and penetration weldments were furnace stress relieved as follows:
a.
Any plate segment wholly containing a penetration, nozzle, or column
. connection was furnace stress relieved at the shop after insertion of the penetration.
j I
b.
All large penetrations intersecting more than one shell plate were j
l Stress relieved as follows. Any portion of a penetration containing seams joining metal over 1 I/2 in, thick at the joint was furnace stress relieved as a unit before welding into a penetration assembly or into the shell.
q J
2.
SE No. 000243-002 Att. 1-8 In' keeping.with the above,'the vent line penetrations were shop assembled to
- the reinforc'*r collar and-the' completed' assemblies were stress' relieved.
The-weld between the collar and the shell plate'was made.in the field and'was not
' stress relieved.
-}
.A1.1 shop. welds were radiographer in the shop. All' welds in those parts of.the work subject to.the ASME Code were radiographer by methods complying with.
Paragraph UW-51 of.the code.
Prior to. shipment, all materials were cleaned and painted.
Surface preparation and painting was in accordance with the paint manufacturer's recommendations.
The interior of the drywell above the concrete floor, including jet deflectors and the exterior of the drywell above the water seal.
support bracket, received one-coat of Carboline Carbo-Zinc 11.
The interior of l
the drywell below elevation 8 ft. 11 1/4 in, and the exterior surface of the drywell adjacent to concrete surfaces at completion of construction were not coated. All other surfaces of the drywell' were given one coat of Carboline primer.
1 After erection and testing, all field welds and abraded places on the shop paint were cleaned by sandblasting and painted as noted above.
I i
1 Drywell Field Fabrication and Testing During field fabrication the drywell steel was supported on a steel skirt of approximately 39 ft diameter with its base plate at elevation-0 ft. I in. and invert of the sphere at elevation 2 ft. 3 in.
1
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1 l:
h SE No. 000243-002-l l
'Att. 1-9 l
The 70. foot diameter spherical drywell and upper cylinder were field assembled j
r and welded.
The transition knuckle and top head flanges were field stress I
. relieved in accordance with the ASME Code.
The heavy plate flanges for the 33 foot diameter cover and neck flanges of the drywell were subassembled in segments, welded, x-rayed and stress relieved as complete units.
All completed ~shell plate assemblies, with penetrations installed, were stress relieved after fabrication. All butt welds were 100% x-rayed. Other welds which could not be 100% x-rayed were magnafluxed before and after stress relieving.
Upon completion of fabrication of the drywell and pressure absorption chamber,
. acceptance testing was initiated.
This included soapsuds testing at 5 psig. a holding period at 40.25 psig and a second soapsuds test at the design pressure of 35'psig.
This was followed by the overload test at a pressure of 71.3 psig which corresponds to a 115 percent overload.
The procedures for the overload test fulfilled the requirements of Section VIII of the ASME Code and Code Case 1272 N-5.
At the time of the tests, the downtomers, designed to pass the released steam and gases from the drywell into the suppression chamber were capped in order that a separate test could be conducted on each vessel.
The drywell was tested with no pressure in the suppression chamber.
The suppression chamber, however, was tested with a balancing pressure in the drywell to avoid an excessive external pressure on the vent lines and header inside the suppression chamber.
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L SE No. 000243-002 Att. 1-10 Drywe'11/ Concrete Interfaces The'drywell shell is designed as a free standing structure and, with the exception of concentrated jet forces, will resist all required loads without interaction with the surrounding concrete.
The function of the concrete is to act-as a radiation shield, provide a "back-up" to-limit deformation due to concentrated jet forces and to form a support at the base of the schere.
At the base of.the sphere, subsequent to completion of pneumatic testing, the volume inside the skirt was filled with concrete while simultaneously pouring j
the concrete floor inside the bottom of the shell.
The concrete pour outside the vessel proceeded in full contact with the vessel up to elevation 8 ft.
~11 1/4 in. where=the concrete line was stepped back radially 15 inches.
This gap continues up'to elevation 12 ft. 3 in. At points on the perimeter of the vessel where the vent lines penetrate the concrete, the forms were set back around the vent lines to provide clearance which would prevent contact between the vent lines and the concrete surface during any design condition.
The 15 i
inch radial gap was filled with sand to provide a cushion for the shell plate during the transition from clamped between two concrete surfaces to free
- standing, i
At all elevations above the sand layer, the external concrete mass is set back from the surface of the steel vessel an amount calculated to allow unimpeded
)
expansion of the steel shell during any design condition.
The gap was created by applying a compressible, inelastic material to the exterior surface of the
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g SE No. 000243-002 Att. 1-11 vessel prior-to pouring concrete.
The material properties were chosen to
. provide resistance to crushing by the-pressure induced by the head of
-concrete, but of. low' compressive strength to allow collapsing by induced d
vessel expansion.
The criteria'for maximum gap was established to limit the deflection of the vessel wall due-to local impact of jet forces.
The criteria used was that the space.between the-steel drywell vessel and.the concrete shield outside must be sufficiently-small that, although local yielding of the steel vessel may occur under concentrated forces, yielding to the extent causing rupture would-be prevented. Using this criteria, the formed gap was 2 inches from elevation 12 ft. 3 in, to elevatioa 23 ft. 6'in.
Above 23 ft. 6 in. the formed gap was increased to 3 inches.
This dimension allowed for inelastic compression due l
to' concrete pressure during the pour and residual thickness of gap material after compression by controlled vessel expansion.
The' criteria used for selection of the gap material was as follows:
- It must adhere tightly to a curved, painted steel plate surface in flat, vertical and overhead positions.
- Could have relatively insignificant deformation under fluid pressure of j
wet concrete estimated at 3 psi.
- Would be reduced in thickness inelastically by about one inch from an i
initial thickness of 2 to 3 inches under a pressure of not more than 10 psi.
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- Wouldremaindimensionally;stableatthereducedth'f{knesswithout
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p significant flaking or powdering i.
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- Hould be unaffected by long term exposure to radiation,r,tdo heat
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- Shouldbesusceptibletominimumdamagewhichexposedghthesessel i
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before concrete placement.
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The 2 inch gap was formed using Owens-Corning Fiberglass SF Vapc/ Seal' Dect Insulation.
The material was supplied with a factory applied laminated in asphalt kraft paper waterproof exterior face, and was attached to'the vessel
<~r with mastic and insulation pins.
Jointsbetweenthe4 cards,andedk1and j
-r penetrations were sealed wi'th glass fabric reinforcN ustic! 3.
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oy4' The-gap material used above elevation 23 ft. 6 in, was Etrebat-G, a l
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- pray, proprietary asbestos fiber - magnesite. cement product poplied;d,a o
coat, The solid materials, asbestos fibers, magnesics and madnesiurt.pdt; hate re' /\\
-(roughlyL757. asbestos), were premixed and combined in a fno tar br:Iin ischine
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with water and, to control density, with foam to form a slurry..sW:able (c.
spray application. Af ter application and curing, the materisi stjrface was(
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faced with polyethylene sheets with all edges sealed by tEpe and held in pla:e j
by insulation pins.
The polyethylene sheets formed the trnd-breaker: fer ths,, y, 4
concrete pour.
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. Gap formation /und Results -
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A,t,the meist critical: location, 'dfywell expansion 'at 281*F and 35 q5,1g was l
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expej,edtobeapp'roximately0.7 inches. Considerin'g an alhiwan~ce for
-mattdial' rebound,itwascalculated;thattherequiredvesselexpansioncould
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be achtered by raising its temperature 140*F above ambient. Concurrent with
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4 ipduced theLmal loading, an internal pressure was created to t$alance> the shell i e ternal compressive forces ipduced by the crushing of the gap material. An internal pressure of 40.psig was calculated as appropr,iate for this ff.hction, u
and considering the expansion induced by internal pressure, the temperature 1
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d',fferential was reduced from 140'F to'130*F.
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.After placement of the gap material on the drywell shell,,cAncrete placement continued in;a staged schedule to complete encasement of the drywell.
The vessel was then expanded tW ;reate the required air gap required for thermal
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and pressure axpansion.
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,c Expansion of the vessel'waf monitored via use of pairs of extensometers at 7
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p'ints around the exterior of the vessel at locations of penetrat.ione.
The t
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"e ten;orieters were rWd and recorded hourl? end the readingso ccmpared with
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calcuiated theoretica) aalues.
While the notizontal,noverants were in good i
agreement with calculated val u s': Jne upward accumulation of expansion i
expected due to the embedment of tce lower ragton was at all points hss than Therefore, vessel discohtinSity stresses at the embed.r.e.\\ '
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predicted.
ic would h, ave beek 13ss than calculated and; the load on the concrete wall would have
<'beenmoreuniformlydistributedandwithalowermaximum.
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During the expansion, it was rbtad that the gap material had entrapped s
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1 moisture dde to incomplete curiL4 and introduction of water from external sources.
This was evidenced by appearanct of water at sleeves around several penetrations.
This was deemed to ?>e of r.c; practical significance since the moisture's effect on material compression characteristics would be a moderate improvement through a slight reduction in strength and a lesser rebound.
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SE No. 000243-002 Att. 2-1 Attach _ ment 2 Extent of Damace EXPECTED SOURCE OF SAND CUSHION WETTING During the.1980 Oyster Creek plant outage, water was found leaking from L
various locations.from the concrete-surrounding the drywell. Containment penetration X-46 (Elev. 86'-0") on the. south west, and penetration X-50 (Elev.
47'-0") on.the north east were reported to have water leaking from within the concrete biological shield.
These identified areas correspond to Bays 7 and Bays 17 &_19, respectively.
In addition it was reported that water was coming i
from the sand cushion drain lines in Bays 3, 11, and 15 into the torus room.
Efforts were made to identify the source of the water and its leak path.
The leakage was found to have the same range of radioactivity as that within the reactor.
The leak path for the water was believed to have been from the reactor cavity located immediately above the drywell.
This cavity is filled with water during refueling operations.
It was believed that a leak from this cavity through the bellows seal at the bottom drained to the space between the drywell and the surrounding concrete (i.e., the space filled with
]
insulation).
The volume below the bellows was pressurized with service air and the bellows checked for bubbles. Another leak test was performed by
)
injecting helium behind the bellows and the bellows sniffed.
The results of these tests were negative.
The 2 inch reactor cavity drain line that includes a flexible pipe section was also tested with no significant leakage detected.
l Plans were made during the following operating cycle to locate and seal any potential leak path from the reactor refueling cavity.
(See Fig. 1)
[
SE No. 000243-002 Att. 2-2 During.the 1983' outage the welds of the refueling cavity were leak tested.
f-Some minor' leaks were detected and repaired.
The bellows' area between the containment.and the' refueling cavity was cleaned to remove contaminants.
The area was then inspected and attempts were made to apply various pressure tests t'o the bellows, however, no leaks were detected. Also, during the 1983 outage.the water level was dropped.to the lowest reactor cavity shield plug j
. step. At this' time it was observed that leakage from penetrations X-46 and
'X-50 stopped.
Furthermore, leakage into the torus room had diminished.
i Three.of the four shield plug steps were. inspected.via liquid penetrant for the full circumference:
no indications were detected.. The single drain line~
1 L
'used to detect leakage from the refueling cavity was suspected of being l
restricted. A restriction.in this line would cause any leakage to be
-directed into.the area between the containment and. biological shield.
This drain line was purged with air and did not appear to have any flow
~
restrictions..'When the refueling cavity was filled, similar leakage was l
found as previously described, however., it had been reduced appreciably.
During the Cycle 11 outage'the drain line.from the refueling cavity was inspected.. Drain line gasket (30" x 7") was found to have leaks, and it was replaced.
Leak tests were performed on the bellows, and no leaks were detected. Observations of.the areas where leakage had previously been found indicated that the. leakage had been arrested.
~
It has additionally been postulated that leaks in the refueling cavity liner can permit water to bypass the refueling bellow and allow water into the trough below the bellows.
In October-November, 1987 the refueling cavity liner was inspected visually and by dye penetrant testing to approximately seven feet above the cavity bottom. A number of indications were found in welds. Several of these were confirmed to be through wall by using vacuum box testing.
Remedial steps and testing of the remainder of the cavity liner is planned.
t 3935M/2121 i
.......,J
f-SE No. 000243-002 Att. 2-3
'DRYNELL' THICKNESS MEASUREMENTS l-rBecause of these' wetting conditions, there was' concern that' repeated exposure of the.drywell steel to water could result in degradation of the drywell.
Measurements of the drywell portion of the containment shell were made to
' verify <its. thickness during the llR outage.
These measurements were-made-
,using UT, a Non Destructive. Examination'(NDE) method, that is able to I
accurately determine the thickness of material or presence of abnormalities,
-i.e., nonmetallic inclusions.
UT plate thickness' measurements were made on the Oyster Creek drywell.
Approximately 1,000 UT readings were eventually taken utilizing an ultrasonic thickness gauge device.(0-meter). Measurements were obtained by transmitting ultrasound through the plate and measuring the time it takes for the-longitudinal wave mode to travel to a reflector (front wall interface or mid-wall reflector or backwall) and back.
Since the electronic measurement of
.I time results in the digital thickness measurement of the first significant sound reflector, the probability of a mid-wall reflector being measured verses the backwall is dependent on the size of the reflector related to the surface area of the ultrasound transducer.
The larger the mid-wall reflector, the more likely the digital thickness reading will be the mid-wall number, and not the backwall value.
)
I
- ! T.
?
i.
SE No. 000243-002 Att. 2-4 L
.To'further characterize the drywell and "A-Scan" UT technique.was also amployed. ' A-Scan" is important for the' expanded analysis of the character, location and amplitude of various ultrasound reflectors.
The "A" scan is the
. ultra' sonic-indication displayed on a cathode ray tube (CRT).
The front-r surface pip'or. amplitude appears first, and the back surface pip or' amplitude appears'sometime later.in the CRT Sweep display.
The space between the pips i
is a' measure of the distance between the surfaces.
Pips in between the front and back surfaces may be,mid-wall reflectors such as laminations, inclusions Lor isolated holes and/or pits.
Other characteristics of the reflector can be observed by a qualified technician.when.using an "A" scan that are not available with a 0-Meter.
t -
. Profile of the amplitude,' break pattern at the baseline, number of doublets following the amplitude pip, multiples of original reflectors, and amplitude height on the screen and other characteristics all give information that may be useful in. analyzing origins of ultrasound reflectors.
MEASUREMENT 1.0 CATION Initial UT measurements were made from the inside of the drywell containment a
at elevations 51 feet and 10 feet.
A digital UT system was used.
The j
measurements opposite the sand cushion at the 10 ft. elevation in the Bays corresponding to where water leaks were observed, indicated that the containment wall was thinner than expected. Measurements above these areas in I
the same plate indicated thicknesses within the original plate thickness variability. Additional UT readings in the same Bay quadrants at elevation 51 l
l
SE No. 000243-002 Att. 2-5 indicated no abnotaal thickness variations.
Although there are no specific requirements for surveillance of the containment wall thickness, it was considered prudent to make these measurements due to the wetted conditions that had occurred.
The. initial measurements were made through the protective coatings on the inside of the containment.
Since the effect of the protective' coating on the UT measurements was questioned, special test blocks were made that included the coating material to_ quantify the effects of the coating on the UT readings The accuracy of the UT system was established for the coating
- thickness of the upper portions of the drywell.
The effects of' Carboline Carbo-Zinc 11 coating on the accuracy of UT measurements was verified through an-experiment conducted by GPUN.
Two carbon steel plates.approximately 1.15-inch thick and six by six-inch square were coated with carbon zinc. One plate had five mils coating and the other plate had 10 mils coating.
Both plates had a' half inch wide strip on one edge left uncoated. Both plates were laid out in a half inch grid pattern across the entire partially coated side including the uncoated strip.
Similar equipment (0-meter of same make and model) transducers, and couplant as used in the field was utilized and measurements taken. Approximately 149 readings of thickness were taken for each plate. Additionally each grid (excluding the uncoatea strip:) was measured by Dry Film Technique (DFT) gauge to determine the coating thickness.
The uncoated strip for each was measured by micrometer.
The three readings:
- 1) ultrasonic (coated and uncoated); 2) dry film technique; and 3) micrometer (uncoated strip) were compiled, averaged and final factors
.,a o < -
j' SE'No. 000243-002l 1
~Att. 2-6 developed.
The. uncoated micrometer-reading <plus.the DFT reading was, treated
- as the.'.true readin'g of' combined' thickness.
The UT.Lreading was found.to
. overcall 0.3% for:5 mil coatings and!1.5% for 10 mil coatings after subtr. acting.the DFT reading from.the combined UT reading of. steel and coating.
thickness.
It should be noted that.the coating application on the test plates and the upper portion of the'drywell were consistently uniform..The coating-along the-basement aall', however,~was found.to be' considerably thicker at.
' places' effecting the UT readings.
For this reason the coating'was removed and-
- a new set of UT measurements were made.
The new readings indicated that the
- containment wall was thinner than expected in several areas along the basementc floor.
The areas of indicated thinning was adjacent to the sand cushion.
l
. EXTENDED UT. MEASUREMENTS As a result of.the initial UT readings adjacent to the sand cushion.being
. considerably thinner than expected, a' program was initiated to obtain detailed-o
- measurements to determine the extent and characterization of the thinning.
UT measurements were made in each Bay at the lowest accessible locations. Where thinning was detected, additional measurements'were made in a cross pattern at p
the thinnest section to determine the extent and direction. Measurements over
- a six by:six inch grid were.then made, moving over the thinnest area to further' quantify the wastage area.
l
- To' determine the vertical profile of the thinning, a trench was excavated into the floor in Bay.17 and Bay 5.
The concrete floor and rebar was removed to expose a portion of the drywell wall about 18 inches wide and sufficiently deep'to allow measurement to the bottom of the sand cushion area.
Bay 17 was selected since the extent of thinning at the floor level was greatest in that 3
+
l t
area.
It was measured that the thinning below the initial measurements were L
h 1* D fw' SE No. 000243-002'
.Att. 2-7 no more. severe and became less severe at the lower portions of the sand cushion.
Bay 5 was excavated to determine if the thinning line was lower than the floor, level in areas where no thinning was detected although several.
inclusions were found, there were no significant indications of thinning.
The Safety Evaluation (SE No. 328227-001) for the excavation and its treatment for
)
continued plant operation is. separate from this evaluation.
'I Heat Affected Zones & Reinforcement Structure Other areas of concern requiring additional-UT investigation were the plate to
. plate welds under the torus' vents and the vent opening reinforcement plates.
These areas.were given extra consideration on the basis that material sensitized by welding may have been attacked by a corrosion mechanism with greater damage or cracking occurring at those locations.
The extra UT investigation was conducted at three spots equal distance along side each toe of the vertical plate to plate weld and on either side of the bottom center gusset of the vent opening reinforcement plate.
D-meter thickness measurements were taken at all eight spots for Bay 5, 7.and
- 19. At these three Bay sites the six spot locations on each side of the plate to plate weld under the torus vent openings were also 45' shear tested to interrogate the weld Heat Affected Zone (HAZ). The 45* shear wave test was especially done to detect HAZ cracking.
The top two spots were also the sites from which the plate to torus vent reinforcement plate weld was examined for
1 i
- l i
SE No. 000243-002 1
1 Att. 2-8 i
HAZ cracking. No' crack indications were found and no wastage of the torus i
vent' reinforcement plate'was found. =The plate to plate weld.HAZ as well as
.the weld when tested as part of a B or C location grid (6"x6") indicated wastage.-similar to the surrounding plate wastage.
Alternate UT Techniques and Verifications EPRI NDE Center UT personnel were invited.to independently analyze the containment vessel plate'.
Their objective was to independently analyze the.
condition of the drywell liner.
They scanned two areas using a "Zero Degree Longitudinal' Wave Method". One area compared was just above.the curb that we indicated had general wastage. Another area was where we had indications of mid-wall deflections'or laminar inclusions.
Their observation and i
measurements independently verified GPUN's results.
Mapping of the wall profile indicated a corrosion transition at seven to eight inches up from the concrete curb in Bay 19.
This detailed map was corroborated by the GE Ultra Image III "C" Scan topographical mapping system that will be used to obtain a baseline profile to track continued wastage.
GPUN experimentally utilized the I.D. Creeper or "30-70-70" technique (a UT j
integration method) to detect minor changes in back wall surface conditions.
This technique compared "A" scan presentations from one inch thick corroded
-samples the results from Bay 13 locations "A" and "E".
Reference standards l
i were utilized representing light, moderate and heavy corrosion conditions.
l This 30-70-70 technique defined surface roughness conditions by matching "A" Scan presentations from materials that have light, medium and heavy corrosion f
on their back surfaces.
It was able to verify the roughness condition of I.
f wastage and the light corrosion areas of the containment wall.
1 L
SE No. 000243-002 1
Att. 2-9 The "A" scan displays from the vessel plate were categorized by comparing them to the reference "A" scan displays.
Location A of Bay 13 (0"-6" up from concrete' curb) showed typical "A" scan display of moderate corrosion on average.and local sites of heavy corrosion.
Bay 13 locations "A" and "E" indicated heavy corrosion between 0 to 6 inches above the curb, moderate' corrosion 6 to 14 1/2 inches above the curb', and very low or no corrosion 14 1/2 to 17 inches above the curb.
I LOGIC OF CORE SAMPLE LOCATION The selection of areas to obtain the core samples was made to evaluate if the UT measurements represented indicated material wastage or if there was localized " pitting".
Those measurement areas that indicated thickness readings of less than half of the thickness expected, i.e.,
.4 to.7 inches, and had adjacent measurements of the expected thicknesses (nominally 1.154"),
were designated as " pitted" areas. Areas that had indicated thinning at adjacent measurements were designed as wastage areas.
A third area, above the wastage area, and within the sand cushion that appeared to have no thinning or
" pits", was also selected as a sample site.
The core sampling sequence and logic were to first obtain a sample of a suspected " pitted" area and two samples of a wastage areas but in different bays. Should the " pitted" sample turn out to be an inclusion as suspected from the UT evaluation and the adjacent areas were actually the thickness as measured by UT, additional samples of areas that were suspected as being " pitted" would not be required.
i
__-_ _ ___________ A
4 I f j'
q k
SE No. 000243-002 Att.-2-10
.a Core Samples-4 Core' samples of the.Drywell wall were taken at seven locations.
The samples.
-were 2 inches in-diameter.
This was. considered the minimum diameter.to produce an adequate sample of the wastage area and provide an opening large enough to_ remove sand samples.
The opening size also permitted insertion'of a I
miniature video camera. Larger openings.would have required a more complex.
plug. design-to restore the structure to its original condition.
~
The " pitted" sample #2 from bay 15 location "A" (GPUN 3E-SK-S-85) was'found to be;an inclusion in the plate with little to no indication of corrosion on the
.ou st ide of the' sample.
Samples #1 and #3 were from bays 19 location "C" and bay 17 "D", respectively.
Both showed significant wastage with good correlation of actual micrometer measurement'with the UT measurement (See Table 1).
The wastage samples (plug 1 & 3) were measured for thickness by ultrasonic (D-meter) and dimensional (micrometer) in a four-point cross pattern and a center location.
The micrometer readings were taken with a ball micrometer to minimize the error observed when a flat bottom micrometer measures a locally lrregular surface. The micrometer measurements through the oxidized surface indicated the UT measurements to be between 0% and 4% less than the micrometer measurements.
H,,'Y-R 4
+
~
gpvg 1
SE-No. 0002431002
^'
j,..
Att. 2-11 Two. additional. wastage' locations were. Selected below the severely' thinned i:,
c b
. locations'(Samples 4&5) and two locations above the wastage. areas (Samples
~
6&7) were selected.to bound the conditions.
The wastage. samples 4&5 were-isimilar to sampies 1&3 confirming the UT measurement accuracy Samples 6&7 g
ididfnot have wastage ~and the. sand behind.them was found to be dry,.also
~
. confirming UT' measurement' accuracy.
4 4
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- .9 SE No.'000243-002
.w.
Att. 2-12 TABLE.'l
~
CORE SAMPLE.T!!ICKNESS EVALUATION-
,, +
A ;,-.
'f s
,q -:
-Sample No.
! Location.
Type of Sample Pre-removal Thick.
Post-Removal
. Thick.-(Ave.)
,I
.19C' l'I'3 5/8" Wastage
.815" (avg.)
.825"-
2 15A - 11' 5 1/4" Pitting
.490" (min.)
1.170" center 1.17 (avg.)
only p
/
.3 170 - 11' 3 3/4" Wastage
.840" (avg.)
.860" J P 4
19A - 11' 3 3/8" Wastage
.830" (avg.)
.847" 5'
ilA - 11' 3 Wastage
.860" (avg.)
.885"
_6 IlA - 12' 2.3/4" Above Wastage 1.170" (avg.)
1.19" center only
- 7 19A - 12' 1" Above Wastage 1.140" (avg.)
1.181" center only i
i, t
a no SE No. 000243-002 Att. 2-13 The openings in;the Drywell wall were repaired and sealed with a special
~
designed-and fabricated steel plug.
The final repair was accepted by the
. Authorized Nuclear Inspection (ANI) after successfully completing a magnetic partical examination of the welds on each plug. A final acceptance test for each plug was performed using a vacuum box bubble test.
In addition a local
-leak rate test'was conducted on each plug and met the integrated leak rate requirements of the Code of Federal Regulations.10CFR50 Appendix J.
Actual leak ' ate measurement at each' plug was 0.000 standard liters per minute at 35
~
r psi. 1The repair left the interior surface flush with the inside of the drywell wall. A separate Safety Evaluation (SE No. 328227-001) for the
. removal of the samples.and for the repair of the Drywell openings has been conducted.
i DATA
SUMMARY
The thickness measurements obtained adjacent to the sand cushion are tabulated
.on GPUN drawing number 3E-SK-S-85.
Initial measurements were taken at four locations near the. lower curb at each torus vent.
These locations, A-B-C-D, were selected to provide two thickness measurements of the left and right drywell plates that make up each Bay section.
Each tabulation heading defines the location of the tabulated matrix of measurements with respect to the top I
l '^
1
'~
m
(-
SE No. 000243-002 Att. 2-14 of the curb and to the weld between the two plates at the center of the vent line. The matrix of measurements are at one inch increments both vertical and-horizontal.
Those measurements around heat.affected zones and on the vent line reinforcement were taken one inch on each side of the' weld.
No degradation or wastage was indicated on the reinforcement plate or around the reinforcement plate to the containment plate weld.
Wall thinning indications on the containment plate on each side of the containment plate weld was the same magnitude as surrounding areas indicating that the weld heat effected zone did not cause or accelera.te wastage.
Data Reduction UT drywell thickness data was collected in each of the ten bays.
The UT data is presented on GPUN Drawing No. 3E-SK-5-85 Rev. 1 The primary concentration of data was within a 6 inch wide circumferential band above the drywell floor curb since data above this band indicated minimal wastage of the drywell wall l material.
A new nominal wall thickness was sought for the affected lower portion, 6" wide band, of the drywell shell.
Two approaches were taken.
The first, was
.to establish the mean and standard deviation values of all the UT data in the affected region of the drywell.
The second approach was to establish the mean and standard deviation values of the UT data in the affected region which is contained within a 60 inch circumferential extent of the drywell.
The second approach using six measurement locations in each bay yielded nine (9) 60 inch combinations of mean and standard deviation values for each of the ten (10) i drywell bays.
The significance of the 60 inch spans is that it represents a physical property of the shell.
- __ _ _ _ =
R f,'
l
[
SE No. 000243-002 Att. 2-15
'This property is the deflection half wave length which defines the shell boundary relative to the location of applied primary and secondary loads
.beyond which the applied load does not cause shell deflection.
This. property was calculated by Professor A. Kalnis of Lehigh University, y
Although.some of the low value UT indications were identified as inclusions in some of the. areas measured, they were used as thickness measurements for the statistical reduction of data.
The first approach yielded a mean and standard deviation value of 0.96 inches l
for all of the UT data in the affected region.
The.second approach yleided a value of 0.87 in. for the minirrim mean wall thickness within the 60 inch arc length criteria.
This segment included 50 data points within a 26 x 6 inch segment of the drywell shell in Bay #19.
A wall combinat'lon in the same bay within the 60 inch criteria included 148 data points with the data points extending over an area 57 x 6 inch and including.
the data within the former 26 inch segment.
This latter segment also yielded a value of 0.87 in. for the mean wall thickness.
For purposes of the engineering calculations regarding the structural integrity of the shell, based on the above minimum mean values, a nominal wall thickness of 0.87 in. should be utilized.
_----__-___-_._Q
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ATT 2-16 T9 PWTS E
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SE No. 000243-002 L
Att.'3-1 t
' Attachment 3' BACKGR00NO.
~
Water Intrusion Detection The first documented evidence of the. intrusion of water into the
- annular space between the drywell shell and concrete shield wall came to light during the 1980 refueling outage when water was visible around-penetrations X-46 at elevation 86' 0" and running down the wall to floor elevation 75' 3".
Water was also observed at penetration X-50 at elevation n
47' 0and running down the wall to floor elevation 23' 6".
Water collection was^also observed on the torus room floor coming from the leak
' drains in bays 3, 11, and 15.
Informal, undocumented communications, however, also indicate water was observed on the torus room floor following r
construction.
Construction The primary containment pressure vessel is contained within a concrete shield with a 3" annular space between the two structures.
The tnnulus is filled with sand specified as ASTM: C33 from elevation 8' 11 1/4" to l
elevation 12' 3" and from the bottom of this sand bed are 5 drain lines.
The sand appears to be a natural sand composed of silica with some alumina. An Owens-Corning Fiberglass SF vapor seal duct insulation
p,..
y l-
, 4l SE No..000243-002-Att. 3-2' p
was applied,to.the vessel shell from elevation 12' 3"'to 23' 6".
The
.insul' tion'was supplied 'as individual. boards 2" thick with a factory -
a applied laminated asphalt kraft paper waterproof exterior face.
These boards were. attached to.the vessel shell with masticiand insulation pins.
The joints between.the boards and edges.and penetrations were then sealed with' fabric: reinforced mastic.
The remaining annular region above' elevation 23' 6" is filled with a Firebar-D material. lit was applied as a spray coat (approximateij 2.75": thick). over the vessel shell.
The material l
15 composed of asbestos' fiber (approximately 757.),= magnesite, magnesium
' sulphate and a foaming agent.(Aerosol PK) to control density. Over the top of-the Firebar-D was placed a 4 mil thick polyethylene sheet.
The primary. vessel-is fabricated from ASTM-A 212 Grade B which is equivalent to SA-516 Grade 70.
The vessel was coated on the I.D. with Carbo-zinc 11 and on the 0.0. with " Red Lead" primer identified as TT-P-86C Type I.
Coating on the exterior of the vessel extends from elevation 8'-11 1/4".
)
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b, 's SE, No. 000243-002 n
h,
.Att. 3
' POTENTIAL SOURCES OF WATER INTRUSION Probable Sources' 0bservat ons'o. eakage from the sand bed drains during the 1980 and i
fl 1983 refueling. outages' indicated that water had intruded into the annular-
' region between.the'drywell' shell andLthe concrete shield wall.
In addition, water samples withdrawn from the drains in 1980 were.
W' radiologically analyzed and showed' activity similar to primary water.
From,
this.informationLit was concluded-that the probable sources of water were
-(1);the equipment' storage: pool, (2) the reactor cavity, or (3) the fuel
, pool.
It.was further concluded that the le'akage only occurred during
~
refueling when the. reactor cavity, the equipment storage pool, and the fuel pool are flooded.
During the 1986 refueling outage, water samples were.
~
-again taken from.a drain line and analyzed.
In addition to tritium, these
. samples were also analyzed for contaminants.
The results of these analyses
.are.shown in Table 1-M.
i 1
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Att. 3 4' g.
m
- 9..
c.F TABLE 1-M Drywell Drain Line Water Analysis
- p..
t.
Sample I Sample II-Parameter-(ppm)
(ppm)
~Na
-:145
'96 K'
142-85 J-Ca 7.5 6.4 Mg 30 11 Al
.33
.02 Ni
<.01-
<.02 Fe
<.01
.74 Cr
<.01-
< '.02 Mn-
<.01
.02
- 44 Pb~
.06
<.02
..,c NH3(N) 3.6
. ~ -
- +.
C1 32.5 25 NO3 8.7 6
4.
50.
153 60 P0.
5 N.D.
F.
<1
' TOC 51 23.3 Organic Acid
.1 Total Sulfur-153 Conductivity 1100 us/cm 814 us/cm
- pH 8.9 8.7 Alkalinity (HCO3) 130 Samples taken-12/86 u
.a--_,
..._ _,.w.__,____
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SE No. 000243-002 I
Att. 3-5 i
UT Data. Interpretation Prior to core sample removal possible causes of the low UT. thickness L
readings were attributed to external corrosion, laminations or a field of inclusions within.the plate.
Because the very low readings were localized it was expected that they would be a result of laminations.
The general wastage, however, extended-from plate to plate and the affected areas of c
the shell were within the sand bed only.
Thus it was concluded that the plate thinning was most likely due to corrosion.
In addition, a qualitative assessment of the plate condition was made using an "A" scan presentation with a-5 mghz transducer.
This data was also indicative of corrosion on the outside.
Numerous ultrasonic thickness readings were taken in the drywell particularly at the elevation of 11' 3".
Review of this ultrasonic test data showed that potential corrosion damage appeared to be confined to regions in Bays 11, 13, 17 and 19.
Furthermore, the thinned parts of the drywell were limited to those areas which were in contact with the sand bed from elevation 10to 11' 9".
Numerical analysis of this data determined the minimum mean remaining wall thickness was.87".
UT thickness readings below the concrete floor elevation showed the thickness to be greater than.87" and at the bottom of the sand bed to be nearly nominal design thickness.
1
______________________J
i;.
t
?
SE No. 000243-002 Att. 3-6 Sampling-After the completion of'the ultrasonic testing (UT) of each of the drywel1 bays above the. concrete floor, the data was assembled and reviewed. This data indicated that there were at least three regions which..
- showed different-characteristics. One set of data showed regions of
.overall. general. wall reduction which we characterized as wastage. Another set showed regions with little.or no general wall reduction but localized-areas with large. wall reduction which we characterized as pitting /
inclusions.
The last set of. data showed regions of little or no wall reduction and no random large reductions, which we characterized as minor
' wastage.
The characterization of each bay is summarized in Table 2-M.
L; m m
' f SE No. 000243-002 Att.- 3-7' TABLE 2-M Bay No.
UT Characterization 1
Minor wastage
- 3 Minor wastage I
5 Pitting / inclusion 7-Minor wastage 9
. Pitting / inclusions 11 Wastage 13 Wastage 15 Pitting / inclusions
-17 Wastage l'
19 Wastage 1
In addition to the above general characterizations, it was also observed
.from the UT readings that above an elevation of approximately 11'9" the wall-thickness would return to the nominal value.
This occurred even though the readings were still within the sand bed and there was wastage below this.
elevation.
Likewise, there were regions of the sand bed below the concrete
-which heretofore had not been ultrasonic tested and hence no characterization
{
could be made.
I l
______-_a
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SE No. 000243-00/
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1 Att. 3-8
(/ l.
( y $.o
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It was decided, therefore, that core samples should be removed from the x) y drywell in each of these different reg)cns in order to achieve the following 4
[
- i goals:
t
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p
'\\)
.,' /)
\\
a)
Verify UT thickness reading l
{r
/
b)
Characterize the form of corrosion
>[ > t.
'I c)
Obtain sand samples and samples cf other angius, materials e
d)
If corrosion existed, characterize corrosto buducts and s
/
environment a
l it e)
Provide access for visual examination of the outstde surface of.the
')
/
drywell
\\
(-
Allow for sampling of sand and/or corrosion proQuds Vdk/Mcteria f)
- )/ : I 's s
p 4s b
fy With these goals in mind, a first cet watlr; e a}t, selbetlpq regions for sampling of the drywell steel.
Twelve regions wfre selected:
four from wastage regions, four from " pitted" re; ions, 'two from above tN,hastage region v
These tri;tial selectk s w9re, and two from below the concrete level.
however, modified slightly as the program progripsed and additional 4
s information became available from ultrasonic testing up Mial core sample j
s I
L examinations.
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- No.
Location Type-Elevation,
. Samples)Obfained
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. - [,,p. 19C Wastage:
.11'-3 5/8"-
Core, sand, bacteriological-
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11'-5 1/4" Core, sand, bacteriological
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4
., 19A Wastage.
11.'-3 3/8" Core, sand, bacteriological
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5 11 A ~.a. Wastage.
1 1 ',3
Core, sand, bacteriological-
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IIA Minor wastage 12',2 3/4" Core, sand i-i.
' - 19A Minor wastage' 12' t" Core, sand 7
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a-9 SE'No. 000243-002-4
Att,. 3-10; 1
g 2 S lt v
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. Evaluation of Pitting /Inci dion Sample-r>
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[:l' r
Core sample #2 which was removed from bayL15 was taken to. assess whether.
pltting'or inclusions: were responsible for the' low ultrasonic" thickness j
f readings observed in random location:,
In region C where the' sample was lW
- removedn the general' area had thickness readings on the average of about 1.17" f
- with random low readings-of.t8".
This particular plug had a region B
approximately 1/2"M n diameter where the low readings resided.
.); p
- r yr %. %,
'1b I6...
,Upon removil'of.~this plug it.was immediately evident-visually that no, serious corrosion or pitting had occurred.
The outside surface of the plug-
+
b mis.coveredwithareddishbrowqoxideandtheactualmeasuredthicknessof
.the plug;wa gill?" (avg K Figure IM.
Elemental. analysis of:this. oxide by p
E0AX.indidatedfronasthemajorconstituentalthoughinrandomIccationvery f
This lead isp rom reminants of the red f
high levels of lead were observed.
i lead' primer originally applied to the shell. Other elements observed at trace i
- levels were Al, Si, Mn Ca, K. Cl, S.
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I 7-1 SE No. 000243-002 l
a H
1.
Att. 3-11 Metallographic specimens were prepared from the core plug both parallel n
to the rolling direction and' perpendicular to it.
Examining the micro specimen at the outside surface'of the core revealed some minor' pitting.
$.0 These pits were filled with: oxide which. appeared normal for carbon steel
- o..
-corrosion..At the mid-plane of the. specimen, however, a band of aluminide stringers was found in'the. region where the low UT readings existed,-Figures
'2M.- 3M.
These stringers were sufficiently dense as to form'a lamination which could easily reflect' ultrasound.
This observation validates'the conclusion drawn by the GPUN NDE people via their "A" scan UT analysis of.this region that the low'"D" meter readings'were a result of.laminations.
In
. addition',.the examination of this plug also validated the accuracy of the
. thickness measurements.
It was concluded that UT could adequately define this type of condition and additional samples from pitting / inclusion regions were not required.
m E
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SE No. 000243-002 Att. 3-12 1
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6 Figure 1-M Plug #2 outside surface of drywell.
Uniform red brown corrosion product.
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SE No. 000243-002 Att. 3-13 q
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-n 50X e
g' 1
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h 500X Figure 2-M Plug #2 Aluminide stringer at mid-wall.
Plane parallel to rolling direction.
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Att. 3 >
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1, l-Figure 3-M Plug #2 Aluminide Stringer at mid-wall.
Plane perpendicular to rolling direction.
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.y SE No. 000243-002 J O' +
Att. 3-15 p b).
w h ;4 J'
Examination of Wastage Samples As discussed previously,.four samples.were1 removed from wastage regions..
(1 D-Three of these samples were sent to General Electric (Sample Nos. 3,'4 & 6) m for_analysisLand one was analyzed by GPUli (Sample No. 1).
. When' core samples (numbers 1, 3, 4 and 5)'were cut, it was noted that a.
hard black-crust remained in the hole on top of the sand.
This crust was 1
approximately.1/2" thick.
It was.quickly realized that this crust was'the
- corrosion product from the iron and as such was collected along with the sand..
m..
'beneath it:for.later analysis.
u.
hy' In general,-all the wastage. samples looked similar showing a relatively
. uniformly corroded surface with some' hills and valleys (Figure 4-M).
0verall.,
the surfaces were~ covered with a thin' black'adherant type deposit with some regions having a thicker more dense buildup of deposit (approx..030" thick).
Elemental analysis of this deposit showed iron to be the major constituent witn varying levels of chloride contamination. Minor traces of manganese, aluminum and silica were also noted and on occasion a trace of sulfur (Figure
.5-M).
On sample #1 a cross section was prepared through one of the valleys on the corroded surface (Figure 6-M).
This valley had a layer of corrosion l
product on it approximately 30 mils thick.
EDAX analysis of this deposit I
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1
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N SE No. 000243-002 c
v 1
Att, 3-16' 4
x
~
s
. revealed.a:high chloride concentration in a 2 mil thick layer of deposit'
' adjacent toIthe: steel, while'further'into the oxide.but adjacent to this region the; chloride levels were very. low (Figure 7-M).
Although other samples did not show-this' dramatic variation in chloride,'all did show that chlorine was a major contaminant.
-In addition-to EDAX analysis, x-ray diffraction was performed by GE on the black. deposit.
The results showed the material to be primarily Fe30.
. (magnetite)..This confirmed an initial observation that the' deposit was
- magnetic;.no'other compounds were identified.
fMetallography on the core samples showed that there was no deep pitting so
- and no signs.cf any. type of cracking or intergranular attack. Manganese sulfides were observed within the microstructure which were typical for this type' material (Figure.8-M).
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SE No. 000243-002 Att. 3-17 s
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Plug #1
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Figure 4-M Plug #2 outer wall surf ace microplane is located _
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SE No. 000243-002 Att. LIB C L U G 4 1 T L E ' 1 J - G ElJC R /41.. D C r 'JI i r 4
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l Figure 5-M Typical elemental analysis of sample #1 corrosion product.
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.1 56X Figure 6-M Thin layer of corrosion product remaining on sample #1 showing dif ferent layers and the presence of volds.
j
SE No. 000243-002 Att. 3-20 FLUG 1 GCALE 1.
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I Figure 7-M l'
EDAX scan through deposit shown in Figure 6M.
Deposit runs from 0% - 49% full screen.
Chloride peak is at steel / oxide interf ace, I
L L
SE No. 000243-002
-21 l
J J
l 100X 0.D. surface; Plug #1 4
200X MnS inclusions below surf ace.
Figure 8-M
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SE No.'000243-002 Att. 3 '
-Analysis'of Sand and Firebar-D As was shown in Table 3-M sand samples were removed from behind each core plug.
In addition, sand was removed from'the Bay 11 drain.line. 'EDAX analysis as_well as leachate analysis was performed on representative samples of;the sand.
The'results-are shown in. Figures 9-M and Table 4-M.
The sand; appears-to.be-a natural sand composed of silica with some alumina present. As y
noted on the EDAX spectrum, some chloride is present and this was confirmed by the leachate analysis which showed chloride in the' range.of 6.5.- 93 ug/gm.
- Also noted in'the.leachage analysis was magnesium and sulfate which most probably came from the Firebar-D.
Some organic carbon was also detected.
-These analysis indicate that a source of the. chloride found in the corrosion product existed in the sand which was probably leached from the Firebar-D and that organic material as.well as a source of sulfur exist which could provide nutrients'for bacterial growth.
A sample of the Firebar-D was obtained through one of the drywell penetrations and subjected to a leachate analysis. As might be expected, this i
material was high in Na, K, Ca, Mg and 50. as well as chlorine.
The results of these analyses are also shown in Table 4-M.
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ym NKCMANFCMPNCNSPFT nl B up l a a a d
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SE No. 000243-002 Att. 3-24 i
S AfJD / OROUP OF B r1 AL i.
l '. ?i f.
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a.
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Figure 9-M Photo shows distribution ard type of sand particles.
Spectra shows basic elemental composition.
L.
l SE No. 000243-002 Atti 3-25'
't
- Microbiological Assessment In order to assure a complete assessment of the corrosion damage'it was decided early on that a microbiological analysis needed to be 3
performed.
Because of limited.in-house expertise in this area, an outside consultant, Dr. Carolyn Mathur from York College, was contracted to perform this analysis.
It was decided that four samples of material from the sand bed would be analyzed from the regions indicated in Table 3.M.
Two samples would be sand and two would be corrosion product.
These samples were
. secured immediately upon removal of the core plugs to assure minimal environmental effect on the bacteria.
Samples were treated for microscopic evaluation as well as for future culturing.
During core removal close
. attention was also paid.to metal temperatures to assure temperatures did not exceed 150* which would kill the bacteria.
Results of the cultures are not yet available; however, preliminary indications are that there is no strong presence of sulfate reducing bacteria (SRB).
The microscopic evaluation results are shown in Table 5-M.
Cell counts appear typical for levels of bacteria found in natural environments.
In addition, it was reported that the bacteria appear filamentous and in some cases bacteria was observed to be attached to the corrosion product.
I
?
h SE'No. 000243-002 Att. 3-26
' Currently cultures are 'being grown aerobically and anaerob1cally to establish.the type of bacteria present including the presence of sulfate reducing bacteria.
~ Ground Potential Measurements l
' The possibility of stray currents influencing the corrosion rate was also considered.
In' order to provide an assessment of this, external potential measurements were conducted to check for the presence of stray
' currents.
Potential measurements were taken between the ground and each of the.five sand bed drain lines using a copper-copper sulfate reference cell.
The measurements revealed no evidence of. stray currents while the 1
reactor is. shut down, however, these measurements will need to be repeated during power operation.
t l
t
9,j p;;.<.
w c
.)-
SE No, 000243-002-Att. 3-27 H
f TABLE 5-M Bacteriological Studies Preliminary Results 1
Sample'No.
.lype Cell Count
- SRB 2-15A Sand (dry).
lx10' cells /gm' negative Adjacent to Drywell 71% viable 1-19C Corrosion Product 5x10 cells /gm' weak' pos, Adjacent'to Drywell~
-50% viable g6-11A Sand (moist) 4x10' ce'lls/gm weak-pos.
Away from Drywell 74% viable
'4-19A Corrosion Product 6x10' cells /gm negative Adjacent to Sand 40% viable Stained with fluorescein isothiocyanate l
s j
I l
7 i'
SE No. 000243-002
=
Att.'3-28 Corrosion Assessment As' discussed in-the background section, wetting of the' sand bed may have' occurred as early.as initial construction.
The only.other documented evidence of leakage was during the 1980, 1983 and 1986 outages. Although the exact source of leakage during construction is unknown, it was reported l
that during the application of the Firebar-D material that copious quantities of water were observed coming from the Firebar and runn ng down i
the drywell.' presumably into the sand bed.
During outages water was most
'likely coming from a leaking gasket in the seal plate region.
This: gasket l
was. replaced during the 1986 refueling outage and the leakage appears to be stopped. On'the.above basis and in view'of the fact that there would'not'be..
other sources of water to enter the annular region-behind the drywell;during'
<l operation, it'has been concluded that the introduction of water was an j
intermittent' occurrence (i.e. during outages) which may have occurred during construction but definitely occurred in 1980, 1983 and 1986. Also, it can be concluded that the sand as a result of this water introduction is contaminated with chloride and sulfate along with numerous metal ions.
)
l
L j:
.5E No. 000243-002
(
Att. 3-29 Sand is generally ascribed with good drainage properties which would allow'for the bulk of the water which entered the sand bed to flow out of the drain lines; however, because this region is fairly enclosed with little-air circulation, high humidity is believed.to exist in the annular space which could result in the sand remaining moist for indefinite periods of time.
This is_ partially substantiated by the fact that high humidity and sweating is generally observed in the torus room where1the sand bed drains e x i t '. Above the sand bed, however, fiberglass boards and above that Firebar are applied to the exterior drywell steel which would help prevent moisture from coming directly in contact with it.
In addition, during operation the average drywell air temperature is approximately 140' F which again would prevent condensation from forming on any exposed steel surfaces.
The overall environment within the annular region can therefore best be described in the following manner:
Water was introduced into the sand bed possibly as early:as in the late sixties and probably contained magnesite L
and magnesium sulfate from the Firebar.
The bulk of this water would have drained off leaving moist sand behind. We know that the exterior of the drywell was coated with red lead primer over which Firebar and fiberglass I
boards were applied which would afford general protection to these steel surfaces from corrosion. Coating damaged areas and with time all areas within the sand bed would be expected to experience general corrosion as long as the sand remained moist or until a protective oxide film built up on the steel surface as a result of the corrosion process.
It appears,
(
i I(.
j '
SE No. 000243-002' I
I Att. 3 F
.however, that a. completely protective film did not result most prob'bly a
because of.the presence of chloride..The actual. metal loss which may have occurred during the time frame from initial'startup until-the next time water was reintroduced as a result of leakage into the cavity.is unknown'.
B.
4 The first documented incident of water intrusion following startup which.
would-definitely initiate corrosion was in 1980.
Water' samples collected E
and analyzed at this time for radioactivity measurement, indicated that it was. refueling water and hence adds credence to the assessment that the source of the water was the leaking bellows gasket. Corrosion rates would therefore be properly based on the assumption that the corrodent was refueling. quality water contaminated with chlor :e from the Firebar and that y
the corrosion process was aqueous general corrosion.
Some shallow pitting is also occurring but it is considered only in view of its contribution to overall thinning,
'The po'ssibility of stress corrosion cracking and hydrogen embrittlement
~
were also considered.
However, these forms of corrosion are generally associated with high strength steels or high temperatures and not considered a damage mechanism for the environment or material associated with the drywell. Ultrasonic examination of the welds and heat-affected zone in the wastage regions also showed no indication of cracking.
f c
SE No. 000243-002 i.
Att. 3-31 o
An upper bound general corrosion rate for carbon. steel would be L
L l
expected to be'in the' range of 10-20' mpy depending on the drywell plate temperature. 'These corrosion rates, however, if applied generally to the drywell region in contact with the sand bed are consistent with the average wall loss of.288" only if the corrosion is assumed to have occurred since 1969 which was the first possible time water could enter the sand bed drains.
In fact, however, close scrutiny of the UT thickness data indicates i
that corrosion was extremely non-uniform as defined above in the section on i
UT measurements.
First, the region above the 11' 9" elevation shows little or no wall loss.
Then the region from.10' 3" to 11' 9" shows the greatest
{
t wall loss followed by the region.below.10' 3" which shows substantially.le'ss" wall loss.
Lastly,'only two regions of the drywell encompassing four bays q
show any significant wall loss. A.possible explanation for this is that due 1
to channeling only these regions became wetted. This assumption is l
potentially confirmed by the observation that the sand in the minor wastage i
regions was dry. Also. the intimacy of the contact between the sand and the plate is a factor.
If the sand had been pushed away from the drywell in certain regions due to the reoperation pressure test causing the drywell to i
expand; this also can result in variations in corrosion rate.
The protectiveness of the red lead primer will be a function of its integrity in l
the various regions and again may be leading to variable corrosion rates.
Lastly, differential aeration may be playing a role in where corrosion is occurring. Clearly the presence of magnetite, an oxygen defficient oxide, in some regions and hematite in other regions suggests this is occurring.
i
.________________________-__O
4.p..
i-Ni p
g h,
SE No. 000243-002 Att. 3-32 l-
. Conclusion i
l l
Aqueous corrosion of the carbon steel drywell.is estimated to have-initiated-in 1969 resulting from the.first intrusion of water into the sand bed region.
This inventory of water may have been added to during subsequent outages but was definitely added during the 1980, 1983 and 1986 o
refueling outages.
This latter water is expected to flow down over the
-insulation material in the annular space and pass through the sand and out through the drains.
Depending on flow rates, an inventory of water may tse accumulated in the sand bed or channeling of the water may also occur' t
leading to wetting in specific-locations.
Irrespective of the water flow-rate some sand will become wetted with oxygen saturated water and corrosion will' result.
This corrosion was most likely influenced by the presence of chloride, leached from the Firebar-0, as it was found to be incorporated within the 1
Fe30. corrosion product.
Bacteria are not believed to have been a major influence on the corrosion.
This latter conclusion is based on the facts that no deep pitting was observed and no sulfide or substantial I
concentration of manganese was detected in the corrosion product, all of 1
l which are typical evidence of microbiological influenced corrosion.
In addition, the corrosion observed can be explained solely on the basis of chemical attack.
However, because there is viable bacteria present, any plans for inhibiting future corrosion may also require destroying or rendering this bacteria harmless.
l J
s
- i. ' '
SE No. 000243-002 Att. 3-33' Review of the literature suggests t.orrosion rates can vary widely for carbon' steel'in aqueous environments.
Rates can be as low as 1-2. mpy in high pH aqueous environments.or greater than 50 mpy in acid solutions. Dr Uhlig in'his " Corrosion Handbook" lists corrosion rates for ambient temperature, seawater at approximately 1-7. mpy which at 140'F would conservatively equate to-approximately 17 mpy. Uhlig further states that with the formation of corrosion products the rate of corrosion will be less
~than it would be if'the steel were in direct' contact with seawater and that
.the rate will stabilize and not change with time.
In addition, he observed-that, " specimens of steel have been exposed to seawater where sulfate reducing bacteria were known to be present, and in fact were found in the corrosion products which contained appreciable percentages of iron sulfide.
The observed rates of corrosion and pitting of such steel fell within the normal range previously defined."
If we then take the 17 mpy corrosion rate and project this over the 17 year life of the plant it correlates closely with the average corrosion loss of 288 mils. However, in order to insure conservatism in the structural analysis a factor of safety should be applied to this rate.
To arrive at a defendable factor it has been assumed that all corrosion occurred over the past stx years as a result of the water intrusion in 1980.
This would equate to a corrosion rate of 48 mpy and give a factor of safety of 2.8.
I l
l
+
- w. -
3.0 O:
.: s
[g '
1
'SE No. 000243-002 Att. 3 :p ConclusionSummari-1, Wastage of the.drywell plate;is the result'of an aqueous general
. corrosion' process influenced by localized oxygen depletion. the degree to which' moisture is present, temperature'and chloride contamination.
2.
Although' viable bacteria were identified.in the sand and corrosion product, no substantive evidence exists as to its involvement in the corrosion process, at least in. terms of currently publicized mechanisms. However, because of the variableinature of microbial
' induced corrosion any attempts at mitigating corrosion should consider this mechanism.
3.
'0-Meter thickness readings, which initially were thought to be either
~
pitting and later characterized by "A" scan UT as inclusions, were confirmed by metallography to be aluminide inclusions in the carbon steel.
4.
The combination of using a D-Meter for ultrasonic thickness measurements and an "A" scan for qualitative assessment of the plate condition are adequate for engineering evaluations.
5.
Corrosion is limited to the steel in contact with the sand bed and is present to a significant amount (i.e.,.25"
.35") only in bays 11, 13, 17 and 19 and only within elevations 10' 3" to 11' 9".
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J 6.
The areas of observed corrosion appear to be those areas in which the sand has remained significantly wetted.
This wetting most likely occurred during initial construction and then periodically during refueling outages as a result of leakage from the drywell bellows.
Documented evidence of such leakage exists since 1980.
7.
Corrosion rates have been conservatively set at 48 mpy although more 1
typically, through review of industry experience and corrosion literature, would be expected to be approximately 17 mpy.
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References-n!
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i N.E. Hammer,NACECorrosionDataSurvey,5thEdition,N74.
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7 s
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2.
H. H. Uhlig, The Corrosion Handbook, John Wiley & Soni:Inc.,' 1948 IIf y
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3.
M. G. Fontana, N. D. Greene, Corrosion Engineering, 2nd Ed., McGraw r.
L Hill, 1978.
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L b
a' 4.
Corrosion of Metals in Marine Environments, MCIC-86 50, Battel'le Columbus Laboratories, 1986.
j p.
f.
5.
M. Pourbaix, Chemical Aspects of Denting in Steam Generators, EPRI' NP-2177, Final Report 1981.
4 6.
Corrosion of Carbon Steel, Republic Steel Research Center l Chemical s
/
g Engineering, March 12, 1979.
)
,1
'l'
- /
}
r 7.
D. H. Pope, Review of Microbiological 1y Influenced Wrrosion i'r, Nucl63r
.V Power Plants and Practical Guide for Countermeasures, EPRI RF-11(6 6,
[
.\\
1
- 1986, f
t,
8.
C. R. Allen etal, Control Program for MIC in the Construction Phase of a
the South Texas Project Electric Generating Station, 1985. 'l i
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.SE No. 000243-002' i
"i 4m7
- i Att. 4-1 a-1 ir jg
} Shuc* gal! Analysts Bases y
jf A reevaluation of the drywell containment,' structure has been performed 'to y - i.
-insure structural integrity for the combined effects of local;shell thinning, operating basis earthquake, pressure.and temperature due to a postulated Design Basis Accident (06A) and the mechanical loads.
In performing this N
analysis the follo nng design bases were'used.
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A$licable CodesrEstablishing Allowable Stress Criteria
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1 0) ASME Boiler and Pressure' Vessel Code,Section VIII,,1962 Edition.
(2) Nuclear Code Case 1270N-5,'1271N and'1272N-5 3
1.
,(
l (3) ASME Boiler and Pressure 1essel Code,Section III, Division 1, applicable t
sortions of Subsection Nf.2 ')00, namely, NE-3213.10,-NE-3221-2, NE-3221.4-
. { \\.[,f 3.
D 1
- ,3 and Table NE 3217-1.
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1 V
q Materials of Construction C
/
3 According'to the Chicago. Bridge and Iron drawing No. 9-0971 sheet No. 1, Rev.
2, the material used in the fabrication of the drywell shell is ASTM SA-212 grade B Firebox. The examination of the original mill certificates reveals
,'that all 1.154" plates used in fabrication of the drywell shell have a yield str:ngth of about 5 to 337. greater than the minimum specified in the ASTM.
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.1 Att. 4-2 N
Design Condition The crywells shell is analyzed for the maximum positive pressere 35 psig at 281*F and 62 911g a,t 175'F.
The former condition represer.ts the double end breaks of' a rec,iped$ tion loop.
This is the design basis accident.
/!,
Other Loads All other loads' considered concomitant with accident conditions were taken from the Chicago Bridge and Iron original anal.rsis.
Load Combination q
M(
The load combination representing a DBA curing normal operation, as specified in the original Chicago Bridge and Ircn original "eport, was chosen for analysis.
This load co.cbintion includes the, gravity load of vessel and appurtenances, gravity load from equipment supports, seismic loads (OSE), as weli/as accident conditions for temperature and pressure.
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Attachment'4 SE No. 000243-002 f
- f Methods Att. 4-3 1
Structural Model i
The mathematical model used to evaluate effects of the reduced shell~ thickness withl'n the-sand entrenchment _ area consists.of a lower region of the spherical shell between elevations 23'-6 7/8" and.the point of complete fixity against transnational movement and rotation at the foundation level at elevation 8'-11 i
1/4".
This'model is developed to calculate the membrane and bending stresses at the point of fixity due to the accident. internal pressure and thermal loads as well as loads associated with normal operation.
The results of the structural analysis will allow the determination of the minimum allowable pressure boundary thickness using ASME Code allowable stress criteria.
Except for the sand pocket zone, all other shell thicknesses used in the analyses'were those shown in the Chicago Bridge and Iron Drawing No. 9-0971 Sheet No. 4 Rev. 1.
The function of the sand pocket is to provide a proportional reaction so that the discontinutby stresses due to the embedment will be gradual and. lower j
rather than abrupt and high.
In order to evaluate the sensitivity of the sand pocket, two separate structural models were considered.
In the first model, the sand is assumed to provide an inward reaction. linear in proportion to shell displacement.
The second model assumes the sand to offer no resistance against the drywell shell movement.
I l
l J
SE No. 000243-002 Att. 4 4 The thermal gradient in the sand entrenchment zone is assumed to be linear.
The attenuation of the thermal gradient in the meridional direction is assumed to be complete within the sand pocket, that is, the temperature distribution is 175'F/281*F at elevation 12'-3" and 60*F (ambient temperature) at elevation 8'-11 1/4".
The drywell shell membrane loads from the original Chicago Bridge and Iron analysis are introduced at the top boundary of the structural models to simulate shell continuity.
~~
The structural model and the loading are assumed to be symmetrical; the penetration and their effects are not considered.
This is reasonable since the reinforcement at the penetrations restores the shell to its original condition.
The fiberglass insulation material within the annulus between the drywell and the concrete shield wall is assumed to have no structural stiffness.
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SE No. 000243-002 3
Att. 4-5 i
Stress Analysis i
1 The drywell containment structure model described above is analyzed by the Chicago Bridge & Iron Corporation utilizing the Kalnins KSHEL Program for axisymmetric shells of revolution to evaluate the adequacy of the lower shell region within the sand entrenchment area, i
Each of the two models, with and without sand entrenchment, is subjected to the mechanical loads, operating basis earthquake and the accident pressure and temperature conditions of 35 psig at 281*F and 62 psig at 175'F.
This analysis identifies meridional and circumferential membrane and f
meridional and circumferential bending stresses for the dead weight, earthquake, pressure, and thermal loads.
________ _ _ _ _ _ L
L
. Attachment 4-SE No. 000243-002 t
.7 Att. 4-6 I
The acceptance cr'iteria used to establish structural adequacy of the drywell
-are:taken.from'Section VIII, ASME Boller and Pressure Vessel Code, 1962
- Edition, Nuclear Code Case 1272N-5, and Section III, ASME Boiler and Pressure Vessel Code 1986 Edition, Division I,-Subsection NE, paragraphs NE-3213-10, NE-3221-2, NE-3221-4 and Table NE 3217-1.
4 i
For purposes of analysis,'the shell thickness in the sand entrenchment zone is taken to be equal to 0.700".
Mean of thickness readinos as representing structural response Structural loads will follow paths through the affected region having the largest stiffness (thickness).
Less stiff.(thinner) sections will follow the strain of the stiffer sections such' that there will be a compatibility of strain through-out, as governed by the stiffer sections
~The condition of strain compatibility means that the stress in the thinner sections will be equal to the stress in the adjacent thicker sections.
It is reasonable to use the mean thickness, as opposed to the minimum thickness, because the mean represents the actual' load reacting action of the shell.
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_' Attachment' 4 SE No. 000243-002 q,.,
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Att. 4-7
+
e ce Potential for' Buckling.
l In L
In addition, another analysis has been performed by Professor A. Kalnins of K
Lehigh University using the-Kalnins shell of revolution computer program to evaluate the potential of buckling of the drywell shell in the sand entrenchment zone.
The mathematical model used to perform buckling analysis is basically similar
.to'the model used for the stress analysis, except that credit was taken for
.the structural effect of the concrete that extends upward from the: foundation-
.around'the inside of the drywell and for the sand which provides an inward reaction'in direct proportion to shell expansion.
For purposes of analysis the shell thickness in the sand entrenchment zone is taken to be equal to 0,700".
l i
7_
SE'No. 000243-002 Att. 4-8 STRESS AhALYSIS RESULTS FOR SHELL THICKNESS TAKEN TO BE EQUAL'TO 0.700"
)
1 x
The allowable stress criteria are:
l 1)
' Local primary membrane stress (not including thermal) - Pc -
1 1.5.Smc - 28,875 psi (No change since 1962).
'2)
Surface stresses (local membrane and secondary stresses, both i
thermal and mechanical axial and bending) - Q - 3 Sm = 52,500.
l (0-3 S..-57,900 from Sect. III, Div. 1. Subsect NE)
Table 1 shows the results of the stress analysis at the point of embedment j
taking credit for the radially inward reaction because of the resistance of the sand and.also for analytically removing it. Using stress intensity, the stresses satisfy the former Code allowable stress criteria except for the condition of full sand removal when allowable stresses are exceeded by 2.77..
1 This. load combination considered the accident condition of 62 psig and 175'F, i
which is not the same as the design basis accident (DBA) representing a double l
ended break of a recirculation line.
Present Code Allowable stress criteria are satisfied in all cases.
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-SE No. 000243-002 l
Att. 4 <
Except.as mentioned above the stresses shown satisfy.the. allowable. stress
. criteria of ASME: Sect. VIII,1962, with Nuclear Code' Cases 1270 N-5,1271 N
- and.1272 N-5, as1well as those ofL.ASME Sect. III, Div. 1, Subsection.NE, 1986, using stress ~1ntensities:as directed in the latter code. Meridional extent,
.but'not the. peak value. of local primary membrane stress slightly exceeds (but-Hj
.)
< 2X) the guidance given in Sect. III.
It is reasonable to neglect this small departure:from present code: guidance because the present situation:is an
'in-service condition'and not a design condition, ana because the departure is smal l:.
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SE No. 000243-002 Att. 4-10 Results of the analysis for buckling potential Stability margin is identified in Table 2.
Margin is defined as the ratio of the calculated buckling load to the actual applied load.
The reference is the
-point of the embedment.
Normal and accident load combinations are considered with and without the radially inward resistance of the sand. The stiffness of the concrete on the inside of the shell is included in both cases.
The shell is considered to be imperfect. The minimum margin to safety is 3.80, i
Conclusion Structural integrity of the primary pressure boundary is maintained with a local shell thickness reduction limited to the sand entrenchment region. Code allowable stress criteria are met using a thickness equal to 0.700".
l A large margin to buckling exists such that buckling of a locally thinned shell is not a technical issue.
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o SE No. 000243-002-
'l Page 1 of 3 1
ATTACHMENT 5 Minimum Drywell Plate Thickness at Upper Elevations j
l The design basis loading condition, 62 psig, is the controlling loading for
~
the minimum wall thickness calculation for-the upper elevation above the sand' region.
' Stability is not a concern per CB&I report (see 2.3.6).
There is considerable-j margin against buckling for all load combinations using the nominal i
thicknesses at the upper elevations.. Small deviations are not expected to change this conclusion (Drywell Modification Feasibility Study, Volume II, Table-8.14 Section 2.3.7).
Minimum required plate thicknesses _were derived based on allowable stress-determined from' certified mill test report properties for the actual drywell plate.
GPUN Calculation No. C-1302-240-5320-002 (see 2.3.5), "0C Orywell Thickness for UT" identifies minimum required drywell plate thickness at several upper elevations. Minimum wall thickness for the cylindrical region was calculated' based on ASME Code equation (UG-27). Minimum wall thicknesses for the spherical region were derived based on actual stresses from CB&I report (See 2.3.6) _at the selected elevations to account for the other loading in addition to design internal pressure and temperature.
Therefore, the basis of calculation remains the same as used in Attachment 4.
ASME,Section VIII, App. P " Basis for Establishing Allowable Stress Values for Ferrous Material," 1962, was used to establish allowable stress.
Lowest actual material test data from the original CB&I material test reports was used to calculate the allowable stress values shown on Table 1.
Table 2
. summarizes minimum wall thicknesses at several upper elevations.
In addition for the spherical region surrounding the penetration X-1 (Personnel Lock and Equipment Hatch), the nominal plate thickness is 1-1/16".
Based on survey of lowest actual material properties for these plates versus ASME Code allowable, there is.8.57. available margin.
Therefore, the nominal thickness for these plates can be reduced from 1-1/6" to.972".
The minimum wall thicknesses shown on Table 2 are based on general primary membrane stress criteria.
Table 8.14 of CB&I "Drywell Modification Feasibility Study, Volume II" report, shows the calculated capacity margins based on general primary membrane stress criteria.
The lowest capacity margin for the entire drywell has been calculated to be 1.00 for the cylindrical region.
Therefore, the cylindrical region is found to be the most critical l
region of the drywell.
The minimum wall thickness calculated for the cylindrical region, based on CMTR values, is found to be.591" as shown on Table 2.
l The minimum wall thicknesses identified on Table 2 are used as the acceptability criteria for the average or uniform plate thicknesses.
f 3935M/2121 3
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.SE-No. 000243-002'
-Attachment.5 Page 2 of 3 L-
~-TABLE 1 ASME Section VIII 1962 Lowest Actual Mill Certificate,from-
' Survey of CB&I Material Test Report Su Sy Allowable.
. Su.,
Sy Allowable = 1.1 Sm Location 1.'l x Sm Sm <1/4 Su or 5/8 Sy
' CYLINDER-t1, From
.el, 72'0" 70,000 38,000
- 1.1 '. x 17,500 75,480 51,170 1.1x18,870 - 20,757 To
- 19,250 el'. 92-0" SPHERE
.From-e1. 23'6-7/18" To-el. 50'11-1/8" 70,000 38,000 19,250 75,620 42,930 1.1x18,905 - 20.796
.i I
From el. 50'11-1/8"
.To el. 65'2-7/16" 70,000 38,000 19,250 74,640 48,780 1.tx18,660 - 20,526 i
3935M/2121-
SE No. 000243-002
-Attachment 5 g
Page 3 of 3 i
TABLE 2 Minimum Allowable Thickness i
Nominal' Mat'l Thick Based on ASME Sect.
Based on Actual Mat'l Location Per CB&I Dwg.9-0971 VIII Allowable Stress Te:;t Data from CBI i
CYLINDER-i From el. 72'0"
.64"
.639"
.591" To el. 92'0" l
SPHERE From i
el. 23'6-7/8"
.770"
.725"
.671" To el. 50'11-1/8" From el. 50'11-1/8"
.722
.685"
.643" To el. 65'2-7/16" 3935M/2121 l
1 I
SE No. 00243-002 Page 1 of 15 UPPER LEVEL INSPECTIONS AND ASSESSMENTS Inspections at the Upper Elevations of the Drywell 1.0 Purpose A program was undertaken to accomplish a sampling of drywell wall thickness above the sand entrenchment region to ascertain actual plate thickness.
2.0 Methods l
2.1 Methodology for Measurements of Wall Thickness Wall thickness measurements using "D" meter-equipment, as described in Attachment 2, were taken at elevation 50'2" approximately eleven inches below the seam weld on the joint to the next highest plate.
Readings were taken in a one inch wide circumferential band extending around the drywell.
Readings were taken in all accessible areas (areas that could be accessed from existing floors or gratings without scaffolds or equipment removal).
UT readings were obtained on six inch centers.
If four consecutive readings (on six inch centers) yielded readings more than 25 mils lower'than nominal thickness, the interval between readings was shortened to one inch centers.
In addition to this band, "D" meter readings, on six inch centers, were taken in a two foot long one inch wide circumferential band above accessible drywell i
penetrations between elevations 46'6" and 49',
At elevation 87'5" a one inch wide circumferential band was scanned with an "A" scan in all accessible areas to characterize the outside surface of the drywell wall. Readings were also taken with a "0" meter on six inch centers.
As done on elevation 50'2", the reading interval was shortened to one inch on center if four consecutive readings were more than 25 mils less than nominal wall.
If a drywell penetration intersected the inspected band at elevation 87'5"thenanadditionaltwofootband(centeredonefoo on each side of the penetration) located six inches below the i
penetration was inspected.
3964M/2122 L----
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[z+a SE No 00243-002 k*
Page 2 of 15 y
h'.
M In three areas on the 50'2" elevation and four areas'of the 87'5" elevation, assix inch grid of'49 UT measurements was taken to p
provide additional data on the extent of. wall' thinning.
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2.2 Methodology'for Assessment of Corrosion.
h Assessment of corrosion was performed by removing two core samples from elevation 50'2".
A metallurgical assessment of the plugs.was performed to. characterize the form of corrosion, obtain Firebar samples, characterize corrosion products and environment and provide access for visual examination of the outside surface of.the drywell if.a gap.. exists between the Firebar and the drywell.
i I
'2.3 Methodology for Estimating Corrosion Rate and Material Margin Remaining Corrosion rate is estimated'by establishing a period in which the i
drywell.is exposed to water and comparing this period to material
.j loss.
Material margin is determined by subtracting the minimum-allowable thickness (Attachment 5,-Table 2) from the lowest average 3
thickness for any 49 reading grid.
H 3.0 Results 3.1 UT Measurements UT data obtained at the upper elevations of the drywell is presented on GPUN Sketch Drawing No. 3E-SK-S-89.
b l
A.
Measurements at Elevation 50'-2" The one inch wide circumferential band at elevation 50'2" covered over half of the drywell's circumference.
Approximately 230 readings, on six inch centers, were taken in l
plate specified as.770 inch. 907. of the readings were within 25 mils of specified wall thickness. Approximately 30 readings i were taken on plate specified as 1.063 inch.
Three readings-were less than nominal of these two isolated readings were more than 25 mils below nominal.
The wall thickness for the.770 inch specified wall plates ranged from.705 to.800 inch.
The wall thickness for the 1.063 inch plates ranged from 1.04 to 1.11 inches..
There were two areas where the reading interval was shortened to one inch due to consecutive low readings (as outlined in Section 2).
The two areas were at approximate f
l azimuth 188 to 194* (area 1) and between approximate azimuth 63 to 66* (area 2) (see GPUN Dwg. 3E-SK-5-89).
3964M/2122
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SE No. 00243-002 y
Page 3 of 15.
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-Area 1 included several of th'e lowest readings-(,705 inch) and
'is directly above Bay 11 and below the refueling bellows drain cover plate.
To surround the' lowest. reading, five additional measurements one. inch above and five measurements one inch below the site were:taken on one inch centers.
The thickness I
readings in this area ranged from.705 to.770 indicating that the--thickness of the wall was not uniform.
The' area 2 readings indicated an approximately uniform wall thickness ranging from.730 inch.to.755 inch.
All of the 49 points in a grid were averaged. Of the three.49.
point grids taken at elevation 50'2" the lowest average thickness is.757 inch.
i Incremental averaging of the data in a circumferential band has yielded a minimum average within 12 mils lower of the minimum grid average.
B.
Measurements at Elevation 87'5" All of the plates at this elevation are specified as.640 inch thick.
The one inch band at elevation 87'5" covered approximately 75% of the_drywell circumference.
"A" scan presentation was relatively smooth with occasional depressions.
Approximately 150 "D" meter readings, on six inch centers were taken.
About 90% of the readings were within 25 mils of nominal wall. All of the low readings were isolated with the single lowest reading.540 inch.
There were no instances where consecutive low readings required the interval between readings to be shortened.
Of the grids at this elevation the lowest average thickness was
.619 inch.
Incremental averaging of the data in a circumferential band has yielded a minimum average within three mils (lower) of the minimum grid average.
3.2 Assessment of Wall Thickness Measurements at Elevation 50'2" The "0" meter measurements indicated some thinning of the arywell shell.
3.3 Assessment of Hall Thickness Measurements at Elevation 67'5" A-scan of the evaluated band indicated a smooth outside surface with occasional depressions.
"0" meter readings indicated some wall thinning.
I 3964M/2122 i
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l' SE No. 00243-002 Y
. Attachment 6 Page 4 of 15
' 3 '. 4 Core Plug' Selection and Visual Assessment
.The basis for selection of the core plug locations is as follows.:
LP'ug 8 (plugsjl thru 7 were in the sand entrenchment region and are l
described in' Attachment 3) was removed from an area of apparent
.gtneral thinning.
Plug 9 was removed from an area where the UT indicated'that nominal thickness or.above' existed with isolated low readings.
This plug was centered between~a reading of 0.798" and-1
,0.710".
See Table 6-1 for details.
Both plugs removed from the elevation had surface corrosion.
The Firebar in the" region of'the drywell surface for both plugs was
" chunky" and denser than the Firebar toward the concrete which fell apart rather easil.y. This observation is consistent with the application of the.Firebar described in Attachment 3.
There was no visible gap between the Firebar and drywell.
There was no visible evidence of water or moisture on either plug or Firebar sample, 3.5 Laboratory Assessment of the Core Plugs-
.A.
Core Plug 8 Visually, the outside surface of Core Plug 8 in contact with the Firebar-D displayed a dark brown oxide which was tenacious and fairly dense.
The Firebar was in contact with the drywell as evidenced by the staining of the Firebar_with corrosion products.
No loose scale or flakes on the plug were observed.
The surface texture was rough with random shallow penetrations.
No visible ~ evidence of red lead primer was observed; however, EDAX analysis showed the' presence of.the low levels of lead.
In addition to lead, EDAX also showed the presence of low levels of chlorine and sulfur in the oxide (Figures 1 - 3).
A metallographic specimen was prepared in order to view the cross section (in the thickness direction) in the vicinity of the lowest UT thickness reading.
It was evident from the micro specimen that a broad (.12
.22" diameter) shallow pit existed in this region. Section thickness below the pit was.714" which compares favorably to the.693 thickness measured by UT.
In the regions away from this pit, thickness ranged from.722"
.752" using a point micrometer.
The base material also showed the presence of manganese sulfide i
inclusions which appeared typical for air melt material and i
would not be expected to reflect ultrasound.
l 3964M/2122 y
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'8 SE No.'00243-002-.
Page 5 of 15 '
,j B.
LCore Plug 9 Plug 9 had approximately 20% of its" surface covered ~with red lead primer.- ~There~was no corrosion <in the area where'the rede
. lead primer. remained.
The'Firebar was' stained with' corrosion products lexcept in:the area of the plug-covered with: red lead
.where'the'Firebar was white..
0-meterithickness in this region' was 0 783";' micrometer-measured thickness was-0.797"..~ The-rest
'of the surface was corroded, and'a. piece of scale covered.'about 10%'f the surface.
The minimum'D-meter' thickness'in the1 o
region of theiscale was 0.705"., A metallographic cut through the. region with the scale revealed corrosion'underneath.
The minimum. micrometer-measured thickness.in this region was 0.'699".
EDAX analysis of the painted area revealed,mostly.leadLwith some iron.
The scale analysis show a large iron peak with:a moderate amount of lead.
The' general corrosion deposit was mostly iron with small amounts of lead (Figures 4-6).
Conclusio's of Plug' Analysis C.
n The results of these analysis indicate that the corroslo'n is due to aqueous general corrosion of carbon steel.
Minimal sulfur detected in the corrosion product indicates that i
i microbiological influenced corrosion is unlikely, 3.6' Cause of Corrosion Observations by others (Reference 2.3.7) of steel' exposed to magnesium oxychloride (constituent'of firebar) showed a dark black crust typical of corrosion in a low-oxygen environment.
This is similar to'what was observed on the Oyster Creek plug.
It is, therefore, likely that most of the corrosion occurred during the pre-operational phase of construction because the'Firebar was applied as a slurry (see Attachment 3 for details).
Thus, the drywell surface was exposed to oxygenated, chloride-containing water which would result in corrosion of unprotected steel.
It is expected that entrapped, stagnant, moisture-laden air. limits the oxygen content at the interface of the steel to inhibit further corrosion. Where the red lead primer is not intact on the drywell wall, it is expected that some corrosion with minor pitting will occur.
It is also expected that the corrosion layer inhibits further corrosion, by blocking the migration of oxygen to the steel.
l
.i 3964M/2122 U - _ _
SE No. 00243-002 Page 6 of 15 The analyses of the nine core plugs removed from the drywell shell indicate that aqueous corrosion is responsible for the thinning observed. Gradients, however, existed in the aggressiveness of the environments in the various core sample locations which accounted for the difference in the amount of corrosion observed.
In the mid portion of the sand bed region, high levels of chloride coupled with sand which remained water laden, produced an aggressive corrosion environment which promoted greater corrosion damage.
In the upper portion of the sand bed, which dried out with time, corrosion was significantly less as was the case above the sand bed region where the Firebar exists.
Firebar does not have good water retention capability and therefore, in the absence of a water source, dried out as was observed at the core sample locations removed at the 50'2" alevation.
As with most occurrences of corrosion, rates are generally highest in the initial stages of corrosion and gradually level off at some lower rate or stop as protective oxides build up on the surface.
Additionally, the presence of the red lead coating on the external surface would afford some degree of protection.
In fact, examination of Core Plug 9 substantiates this assumption.
The portion of this plug with remaining red lead had no evidence of corrosion.
The plug samples removed (6 and 7) from the top of the sand bed had significant amounts of lead on the external surfaces and neither plug exhibited significant corrosion (both had thicknesses above the minimum specified thickness (see Attachment 3).
3.7 Estimated Corrosion Rate and Material Margin Remaining A.
Material Loss The material loss on elevation 50'2" is determined by averaging l
UT readings in a grid around Core Plug 8 where general thinning l
occurred and was verified by examination of the plug.
This gives a thickness of.757 inches.
Examination of all the readings in this area show that the predominant maximum thickness for this plate is 5 to 10 mils below nominal.
Examination of the remaining plates shows predominant readings l
up to 20 mils above nominal.
The material loss is, therefore, based upon the minimum average thickness of.757 inches and the nominal of.770 inches plus 20 mils.
This gives a material loss of 33 mils or less up to November, 1987.
3964H/2122 l
SE No. 00243-002 l
3
-V__
Page 7 of 15 Calculation of material loss on elevation 87' is based on an average measured plate thickness of.619 inches in an area of general thinning.
This is acceptable given the comparable indications of thinning seen on elevation 50'2" which was verified by Core Plug 8.
Examination of all the readings in this area show that the predominant maximum thickness for this plate is 5 to 10 mils above nominal.
Examination of the remaining plates also shows readings up to 25 mils above nominal.
The material loss is, therefore, based upon the minimum average thickness of.619 inches and the nominal of
.640 inches plus 25 mils.
This gives a material loss of 46 mils or less up to November, 1987.
B.
Corrosion Rate I
The rate is established when the drywell is exposed to water.
i Periods _of exposure are assumed as follows.
Eighteen total months between the time the Firebar was a.
applied as a slurry and the time the refueling bellows l
were installed.
b.
Eighteen total months between 1980 and November, 1987 when the reactor cavity was flooded.
1980 was the first
,1 documented evidence of leakage in the sand entrenchment region (see Attachment 3).
Therefore, total time exposed to water is three years.
The rate is as follows:
]
Material Loss (Mils) to 11/87 Rate (mils / wetted yr.)
El. 50'-2 33
<ll El. 87'5" 46 (16 For consistency, the larger calculated rate will be used when
)
determining the remaining life.
l Since corrosion is postulated to occur when the Firebar is wetted, it is considered that the corrosion rate based on wetted periods is a more realistic and technically sound approach.
Therefore, 16 mils / wetted year is the rate used for assessing remaining life.
An alternative to the above approach is to calculate the rate 4
of material loss over the period from when the Firebar was initially applied to the present.
This alternative approach assumes that general aqueous corrosion is active and occurs continuously.
Using this method gives a maximum corrosion rate 3
of 2-3 mils per year.
3964H/2122 i
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f tj SE No: 00243-002
.. F'
-Attachment 6'
.f Page 8 of 15 t
.Using.the alternative annual corrosion rate gives a remaining i
life.offreater.than12 years.
This method does not yleid the.
most' limiting projection.of remaining life and.'is, therefore, not' considered further.
C. ' Remaining Life The corrosion mechanism is expected to be'the same at all elevations above.the sand entrenchment region. -Of the 0.640,-
/.'
O.722, and 0.770 plates, the 0.640". plate'has the lowest margin remaining between the average thickness-(0.619") and the.
minimum thickness (0.591") which is'28 mils. Using 16 mils / wetted year yields 1.75 wetted years (21 wetted months) dur.ing which the. structural integrity is maintained.. Should' the-corrosion rate' prove to be lower, the additional wetted years will be' acceptable.
L 4.0l Conclusions-4.1 On the basis of the core samples removed, wall' thinning has been caused.by general corrosion.
The corrosion is fairly uniform with.
.l an occasional broad pit.
The corrosion products are characteristic of.those formed in an oxygen deficient environment.
l Microbiological influenced corrosion is not a factor.
l 4.2 At elevations 50-2" and 87'5" the wall loss is 33 mils and 46 mils
respectively; This is estimated from the " average" drywell wall thickness in areas of general wall thinning compared to.the maximum.l encountered wall thickness. Use of an " average" wall thickness is j appropriate in evaluating the shell strength; individualized j
localized pits will not alter the structural integrity of the j
drywell.
The calculated corrosion rate is based upon assumed l
periods of wetting (3 years) and is projected to be less than 16 i
mils / wetted year.
The drywell wall above the sand entrenchment region will maintain adequate structural integrity provided its future exposure to water is limited to a total of 21 months.
3964M/2122 i
C
_l
SE No. 00243-002 E'
- l Page 9 of 15 TABLE 6-1 50'2" ELEVATION THICKNESS EVALUATION Sample Type of In-situ measured Post-Removal Measured No.
Location-Sample Thickness by UT Thickness 8'
Bay 5 Uniform 0.695 inch 0.693" min. (UT) (Pit)
Thinning 0.714" (micro-meter).
9 Bay 7 Uniformly Midpoint Paint intact at or above between.798 0.783" (UT) nominal with and.710 0.797" (micrometer) low spots reading Corrosion area (Pit) 0.705" min. (UT) 0.699" min (micro-meter) s i
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