ML072770613
| ML072770613 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/29/1993 |
| From: | AmerGen Energy Co |
| To: | NRC/SECY |
| SECY RAS | |
| References | |
| 50-219-LR, Amergen-Applicant-27, FOIA/PA-2009-0070, OCLR00029151, RAS 14234 | |
| Download: ML072770613 (45) | |
Text
12,d DOCKETED USNRC October 1, 2007 (10:45am)
OFFICE OF SECRETARY RULEMAKINGS AND ADJUDICATIONS STAFF Technical Data Report APPLICANT'S EXH. 27 0;/01/04 12.31:03 TOR No.
1108 Revision Nao.
0 Budget
- Activity No.
402950 I ra~e I of 45 C
Project:
Depanment/Sceion 550065550 Oyster Creek Drywel1 Vessel corrosion Mitigation Revision Date Document
Title:
Summary Report of Corrective Action Taken from Operating Cycle 12 through 14R" Originator Sýgnaltue Date Approval(s) Signature Date Approval for External Disidbution Date Does this TDR include recommendation(s)7 0] Yes ka No If yes. TFWR/TR#
Dstrilbution Abstract:
J. D. Abramovici This report summarizes the activities performed by GPUN to
" R. Aitken mitigate the corrosion mechanism attacking the Oyster Creek A.. Baig Drywell vessel.
The report provides a "road map" of the
" F. Barbieri documents created to implement corrective actions taken
" J. Barton during the 14R refueling outage-
- W. Behrle J. J. Colitz.
A bay-by-bay discussion of the condition of the vessel, D. Covill results of UT inspections and structural evaluation, with B. D. Elam respect to code requirements, is included.
J. Frew C. Gaydos It is concluded that, by completing 14R.activities, future R. W. Keaten corrosion has been stopped in the sand bed region, but that M. Laggart the pending pressure reduction submittal to NRC must be S. D.Leshnoff approved to provide a corrosion allowance for upper.
S. Levin elevations.
W. P. Manning J. Martin A. H. Rone U.S. NUC REUGULATORY COMMSSION S Saha o.
D,. G. S16ear M.9l(ro E-IZ -
(.,
t J. Sullivan C. R. Tracy DodetMNo.0'idal Exhibit N°....
S. Tumminelli O
m.../
icensee Intervefor
-M. Yekta OIR ces.
tveo R. Zak NR Staff Other e
- o.
Witness/Pael AtionTake: 4M~Ir REJECTED WTHDRAWN This is a report of work conducted by an individual(s) for use by GPU Nuclear Corporation. Neither GPU Nuclear Corporation nor the authors of the report warrant that the report is complete or accurate. Nothing contained in the report establishes company policy or constitutes a commitment by GPU Nuclear Corporation.
- Abstract Only N 0030 (02-88)
OCLRQ0029151
=f y_,
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Page /of 45 TABLE OF CON4TENTS ARTICLE PAGE
1.0 INTRODUCTION
4 1.1 Background..............................
4 1.2 Sand Bed Repair 4....................4
2.0 REFERENCES
5
- 3.0 CYCLE 13 WORK.
6 3.1 Sheet Metal Removal................
6 3.2 Sand Removal............
6 3.3' Access oles..
6 4.0 14R WORK........
7 4.1 General 7
4.2 SAnd Removal...........
7 4.3 Surface Preparation 10 4.4 As Found Conditions 10 4.5 Coating of the Drywell! Shell 14 4.6 Access Hole Closure 14 4.7 Repair Contingency 14 5.0 lT READINGS 14 5.1 General.........................
14 5.2 Initial Approach for UT Inspections from the Sand Bed 15 5.3 Modified Approach i.....15 5.4 Selection of Locatlons for UT Surveys..........
16 5.'5
-Structural Acceptance Criteria 16 6.0 RESULTS 19 6.1 General.................
19 6.2 Bay #1 Data.....
19 6.3 Bay #3 Data.....
24 6.4 Bay #5 Data 26 6.5 Bay #7 Data 28 6.6 Bay #9 Data 30 6.7 Bay #11 Data......
32 6.8 Bay #13 Data.................................
34 6.9 Bay #15 Data 39 6.10 Bay #17.Data...............
41 6.11 Bay #19 Data......................................
43
7.0 CONCLUSION
44 APPENDIX A WASTE DISPOSAL 45
.012/107 OCLROO029152
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'.3 EXECUTIVE
SUMMARY
The potential for corrosion of the drywell vessel was first recognized whenwater was noticedcoming from the sand bed drains in 1980.
It was confirmed by ultrasonic thickness (UT) measurements taken in 1986 during 11R. Since that time a great deal of evaluation, inspection, analysis, planning and corrective action has been directed toward mitigating the problem.
The first extensive corrective a6tion, i.e. installation of a cathodic protection system, proved to.be ineffective.
In 1990 an intenqified effort was initiated.
As a result of laboratory experiments the corrosion mechanism in the sand bed was determined to be galvanic.
The upper regions of the vessel, above the sand bed, were handled separate from the sand bed region because of the significant difference in corrosion rate and physical difference in design.
Corrective action for' the upper vessel involved providing a corrosion allowance by demonstrating, through analysis, that the design pressure was conservative.
A Technical Specification change request was submitted-to the NRC in July of 1991 to reduce the design pressure from 62 psig to 44 psig.
The pew design pressure, when approved, coupled with effective measures to prevent water intrusion into the gap between the vessel and the concrete will allow the upper portion of the vessel to meet ASME code for the projected life of the plant.
The high rate of corrosion, in the sand bed region required prompt cor-rective action of a physical nature.
Corrective action was defined as; (1) removal of sand to break up the galvanic cell, (2) removal of the corrosion product from the vessel and (3) application of a protective coating.
Keeping the vessel dry was also identified as a requirement even though it would be less of a concern in this region once the coating was applied.. The work was initiated during 12R by removing sheet metal from around the vent headers to provide access to the sand bed from the Torus Room.
During operating cycle. 13 some sand was removed and access holes were cut into the sand bed region through the shield wall.
The work.was finished during 14R.
After sand removal, the concrete floor was found to be unfinished with improper provisions for water drainage.
Corrective actions taken in this region during the 14R outage included; (1) cleaning of loose rust from the drywell shell, followed by application of epoxy coating and (2) removing the loose debris from the concrete floor followed by rebuilding and reshaping the floor with epoxy to allow drainage of any water that may leak into the region.
During the 14R outage UT measurements of the drywell vessel were taken from the sand bed region..
In general these measurements verified pro-jections that had been made based on measurements taken from inside the drywell.
There were however, several areas thinner than projected.
In all cases these areas were found to meet ASME code requirements after structural analysis.
The details of this analytical work are presented in Section 6 of this report.
The cleaning, reshaping and coating effort that was completed in 14R should mitigate corrosion in the sand bed area.
Since this was accom-plished while the vessel thickness was sufficient to satisfy ASME code requirements, the drywell vessel in the sand bed region is no longer a limiting factor in plant operation.
Inspections will be conducted in future refueling outages to ensure that the coating remains effective.
In addition, UT measurements will also be taken.
The frequency and extent of these measurements will be evaluated after 15R.
012/107 0CLROO29153
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1.0 INTRODUCTION
1.1 Background
Leakage was observed from the drains in the sand bed, which surround the lower exterior surface of the carbon steel drywell vessel, during the 1980, 1983 and 1986 refueling outages.
Inspections performed during the 1986 refueling outage 11R confirmed that corrosion was occurring in the sand bed region (elevation 8 feet, 11 inches. to 12 feet, 3 inches).
Later investigations confirmed that corrosion was also taking place at elevations above the sand bed.
A program of repetitive ultrasonic thickness (UT) measurements was established to monitor the corrosioa in the vessel.
During 12R (1988) a cathodic. protection system was installed in the sand bed region to minimize corrosion in this area where the rate of corrosion was greatest.
The monitoring program was also-expanded during 12R.
By the Spring of 1990 it was evident from the UT monitoring program that the cathodic protection system installed during 12R was not sufficient to abate the high corrosion rate in the sand bed.
A multi discipline project team was formed and charged with identi-fying the corrosion mechanism and developing a corrective action plan.
The team had'determined by the fall of 1991 that the cor-rosion was galvanic in nature.
circumstances that helped to promote this phenomenon were the fact that water had leaked into the sand bed region and that the drain system failed.
The water contained impurities that were leached out of the insulation material in the upper elevations.
Corrective action for the sand bed region required that water leaking into the cavity be stopped and that the galvanic cell be broken.
It was determined that the original design pressure. for the vessel was unrealistically high.
A Technical Specification change request was developed and submitted to the NRC on July 7, 1991.
The change involved a reduction in the design pressure for the vessel from 62 psig to 44 psig.
When approved this will provide a corrosion margin, for the upper elevation, sufficient to insure ASME code compliance through the life of the plant.
1.2 Sand Bed Repair To disrupt the galvanic cell, the water leak must be stopped and-the sand. in the sand bed region would have to be moved away from the vessel.
Since the sand performed a structural function in the.
original design concept, removal of the sand had to be supported by analysis.
GE Nuclear Energy Division of San Jose, California performed the above analysis.
The results confirmed that if the sand was removed, the'structure would still meet ASME code re-quirements.
(See references 2.1 -2.3).
Based. on the results of this analysis a plan was developed to: (a) remove the sand, (b) clean the vessel of the corrosion product, (c) measure wall thickness from the exterior of the drywell, (d) weld repair of localized thin areas if necessary and (e) apply a protective coating.
012/107 OCLROO0291.54
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'Rev. 0 Page 5 of 45
2.0 REFERENCES
2.1 GE Nuclear Energy, DRF # 00664, Index No.
9-3, Revision 0 "An ASME Section VlII Evaluation of Oyster Creek Drywell for Without Sand Case Part i stress Analysis",
2.2 GE. Nuclear Energy, DRF # 00664, Index No.9-4, Re 2 "An ASME Section VIII Evaluation of Oyster, Creek Drywell
- hout Sand Case - Part 2.Stability Analysis" 2.3 Teledyne Engineering Services, "Justification for U ion III, Subsectibn NE, Guidance in Evaluating the Oyste:
'ywell-,
'Technical Report TR-7377-1 2.4 OC-MM-402950-004, "Removal of Sand from Sand Bed" 2.5 OC-MM-402950-006, "Reactor'Building Torus Wire Lif,
?porta" 2.6 ASB Impell Report No.
370194-01, "Structural Evalua-.
of the Reactor Building with Manways in. the Drywell Shield Wall it Oyster Creek'Nuclear Station" 2.7 OC-MM-402950-009, "Setup for Boring Holes in Drywall Shield Wall" 2.8 OC-MM-402950-007, "Boring of Holes in Drywell Shield Wall" 2.9 MPR Associates, MPR-TR-83156-O0l, "Test Plan for Concrete Cutting Tests for Manway Holes in Shield Wall" 2.10 MNCR-93-0062, Reactor Building Shield Wall Concrete Formation, 1/25/93 2.11 FCN.088664, Cut Rebar Location 2.12 OC-MM-402950-O01, "Cleaning and Coating the Drywell Exterior in the Sand Bed Area" 2.13 GPUN Memo, 5383-93-008, S.M. French to S.C. Tumminelli, "Oyster Creek Drywell scale", dated 1/20/93 2.14 GPUN Laboratory Report 5383-92-1204, Rev.0, "Oyster Creek Drywell Scale Evaluation", dated 12/15/92 2.15 GPUN Calculation,
- C-1302-243-5340-067, Rev.0, "Calculation for Drywell Wall Loss" 2.16 GPUN.Memo, 5320-92-029, T.
H.
Chang to J.
C.
Flynn, "Assessment for F Frame Rebar Location at the Sand Bed Region", dated 2/5/93 2.17 MNCR-92-0188, Sand Bed Concrete Floor Condition, 12/28/92 2.18 GPUN Memo 5511-92-073, Saig to Dietribution, dated 9/8/92.
2.19 GPUN TDR -
948,. "Statistical Analysis of Drywell Thickness Data" 2.20 OC-IS-402950-008, "Drywell Vessel Thickness Examinations from Sand Bed" 2.21 GE Letter Report, "Sandbed Local Thinning and Raising the Fixity Height Analysis (Line Items 1 and 2 In Contract # PC-0391407)", dated December 11, 19ý92
.012/107 OCLR00029155
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- TDR 1108 Rev. 0 Page 6 of 45 2.22 GPUN Memo 5320-93-020, K.. Whitmore to J..C.Flynn, "Inspection of Drywell Sand Bed Region and Access Holes", dated January 28, 1993.
2.23 OPUN Calculation # C-1302-187-5320-024, Rev. 0, Oyster creek Drywell External UT Evaluation in Sandbed,': dated 4/16/93.
2.24 isotope Survey of Sand Removed fropoyster Creek Sand Bed.
2.25 GPUN System Chemistry Laboratory Analysis Report, dated 1/15/93, See DRF 133903.
3.0 CYCLE 13 WORK 3.1 Sheet Metal Removal During the 13R outage (1991) sheet metal was removed from around the ten vent headers in the Torus room to provide access into the top of the sand bed region.
Due to schedule constraints some of this work was deferred to the operating cycle.
3.2 Sand Removal The high rate of drywell corrosion in the sand bed required that the sand be removed as soon as possible.
To accomplish this, a scheme was devised to remove the sand through the vent header gaps and the holes put in the shield wall for cathodic protection installation by using a high volume vacuum machine (Vacuum Engineering Corporation VecLoader HEPA VAC ).
(See reference 2.4).
The work was started in November of 1991 and stopped in April of 1992.
Some sand was removed from all bays. Approximately sixty percent of the sand calculated to be in the sand bed (77 55 gallon drums of sand) was removed.
Before work could be done from the top of the torus, the Safety department required that the existing safety line be replaced.
(See reference 2.5).
3.3 Access Holes Completion of the sand bed repair required access to the sand bed region.
Access paths from both inside the drywell and from the Torus room were considered.
With the. aid of the Kepner Tregoe (KT) deci-sion analysis technique, the Torus room option was finally chosen.
A structural analysis of the Reactor building and the concrete shield wall was conducted by ABB Impell Corporation to determine if cutting access holes in the shield wall. was acceptable structurally.
The analysis was done for ten twenty inch diameter holes, one in the vicinity of each vent header.
The results verified that this approach was acceptable.
(See reference 2.6).
To expedite the work, since the results of the structural analygis were not available, the job was split into two work packages.
One covered equipment setup ( reference 2.7 ) and the other the actual cutting of the holes (reference 2.8).
A full scale mockup of one half a bay was constructed at the Forked River site adjacent to Building 2 to debug the core boring setup that would be. used to cut the access holes in the drywell shield wall.
MPR Associates developed a test plan for this purpose (reference 2.9).
ý The mockup proved to be very useful.
Several changes were made to the work packages as a. result of the mockup tests.
In addition, the mockup proved to be a valuable, asset for training and orientating workers for the unique work environment 012/107 OCLROO029156
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A specialty contractor, Urban H.A.R.T, Inc.,
was retained to train Emergenoy Medical Technicians in rescue techniques, provide space training and acclimate workers to the sand bed environment.
Work platforms were. built in four bays.
The other six bays had platforms which were installed during the cathodic protection project.
Temporary shielding was also installed next to the vent header to reduce worker radiation exposure.
The cutting process was initiated on 9/8/92 and. completed on 11/19/92.
The process included cutting ten holes completely through to the sand bed region and removing the concrete core for a distance of six feet (see Figure 1).
The total length of the holes was approximately eight feet.
Video cameras installed in the sand bed region through the vent header gap provided a clear picture of the drill bit as it broke through into the. region.
A concrete core approximately two feet thick was left in the hole to serve as a radiation shield during plant operation.
The larger pieces of core material (rubble) were. bagged and carried up to the 23 foot elevation.
Small pieces were vacuumed up using an electric vacuum machine staged in the northeast corner room at the minus 19 foot elevation.
In general, this phase of the work went very-well.
Much more steel was encountered in the shield wall than anticipated and this affected the overall productivity.
In bays 15 and 9 voids were encountered that affected the drill rig water cooling system.
Water leaked out of the core hole and seeped through the shield wall.
Catch basins and "wet Vace" were used to capture the water.
Reference 2.10 documents the condition of the shield wall concrete as witnessed from access holes.
Reference 2.11 documents the shield wall reinforcement that was cut in the process of cutting the access holes.
4.0
.14R WORK 4.1 General Reference 2.12 documents this phase of work which is referred to as the cleaning/coating phase.
Training and qualification of the workers was completed prior to plant shutdown thus allowing work to start on 11/28/92, the first day of the 14R outage.
The schedule called for two ten hour shifts.
working seven days. a week.
After mobilization of equipment and supplies, the first activity was to remove the two foot concrete plug in each of the. holes.
Once the plug was out, a team of safety and radcon inspectors surveyed the bays before workers were allowed to enter the holes.
4.2 Sand Removal There were thick crusts of corrosion product laying on top of the.
sand.
(See Fig. 2).
It was necessary to remove this material before the task of removing sand could begin.
In most bays, very little corrosion product was left on the vessel.
(See Fig. 3).
The oxide crusts may have spalled off the vessel as the plant went to cold shutdown in preparation for the 14R outage.
The last video views taken during the operating cycle 13 sand removal effort showed that some material had fallen off the vessel, but not to the extent found.
The corrosion product pieces were removed and bagged.
The sand was then removed using an electric VecLoader vacuum.
Appendix A contains 012/107 OCLROO029157
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,~
. '~- t I V 1 Figure 1 Access hole drilling set up view from the top of the Torus.
012/107 OCLROO29158
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~
I Figure 2 Sand Bed Region - Typical condition found on initial entry.
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Figure 3 Corrosion product on drywell vessel.
(
012/107 OCLROO029159
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0 Page 10 of 45 a list of the waste materials created during this work.
The thick-ness of some of the corrosion product raised a concern regarding how much base metal was left on the vessel.
One 12 x 12 inch (approximate) piece of oxide crust with a thickness varying in the range of 1.25 to 1.50 inches was sent to the GPUN Materials Laboratory for analysis (see reference 2.13, 2.14 and 2.15).
The result of the analysis essentially validated projections based on UT readings from inside the drywell and later readings taken from the sand bed region.
In general, two bays were worked at one time.
Init'ially, the bays judged to be in the worst shape, i.e. the most corroded, were worked first.
However, due to reactor cavity water leaking into bays 11, 13 and 15 during the third week of the outage, work in these bays was postponed until after the completion of refueling and the refueling cavity was drained.
4.3 Surface Preparation As part of the qualification process for surface preparation and coating that preceded the outage, workers were trained in the use of tools.
The tools had been evaluated to ensure that the surface preparation effort removed corrosion product and loose rust without removing metal from the vessel.
Pneumatic wire brush and needle gun tools were the primary means of preparing the vessel surface for the coating system.
Devoe Devprep 88 cleaner, was used to clean grease; oil, salts and loose rust off the surface prior to applying the coating.
The Devprep was washed off by high pressure hydrolasing.
4.4 As Found Conditions Inspection of the sand bed region after the sand was removed brought to light some conditions that deviated from the construction drawings.
The shield wall reinforcement that the construction drawings showed as passing through the sand bed is one example.
Only one row of bars was visible, and only about half that row in most bays.
The condition of the sleeves that cover the bars was good, i.e. no evidence of deep corrosion.
This resulted in an additional space of about nine inches and this extra space between the, vessel and the reinforcement made working in this area easier than had been anticipated.
Engineering Mechanics personnel inspected this con-dition and found evidence that the second row of reinforcement was buried in the shield wall.
(See reference 2.16).
A more serious finding was the condition of the floor in the sand bed.
The concrete was not finished, there were holes and-craters along side the vessel, there was no evidence of a drainage ditch as shown on the drawings and in most cases the drain pipes were higher than the floor.
(See Figs. 4 and 5).
This was a general condition in all bays,. however some were 'worse than others.
Apparently the finish pour of concrete was not installed.
This condition had a significant effect on the project's schedule and cost.
To make the drain system effective the holes and craters needed to be filled, and the floor leveled using a suitable material compatible with both concrete and the steel shell.
(See Figs. 6 and 7).
The Devoe epoxy product 184 was used to refurbish the floor.
This was done after evaluation of the suitability of the material in the sand bed.
environment.
This condition was documented using a MNCR (see reference 2.17).
As a part of the floor refurbishment, a wedge of Devoe 140S caulking material was placed at the intersection of the vessel shell and the floor.
The caulking material will keep water away from the vessel in the event a volume of water greater than the drains capacity is introduced into the area.
(See Figs. 8 and 9).
012/107 OCLROO029160
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Fy....
40:?
- ÷*7
" ':'J Figure 4 As found condition of floor bed.
I: ;j4. ~
2
-'4' Figure 5 Deep depression in.floor adjacent to drywell vessel.
1 012/107 0CLR00029161
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Figure 6 Finished floor & vessel.
.-,.:-.A-:.;.:..>
C*,.,
Figure 7 Drain after floor has been refurbished; 012/107 OCLROO029162
06/01/04 11;31:03 TDR 1108, Rcv. (0 Page 13 of 45
-C-1'~
7 I..
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Figure 8 Close up of caulking.
Figure 9 Finished floor, vessel with two top coats - caulking material applied.
t 012/107 OCLROO029163
.06/02/04 12:31,t03 TDR 1108 Rev. 0 Page 14 of 45 4.5 coating of the Drywell Shell The coating system consists of a prime coat of Devoe Pre-prime 167 rust penetrating sealer and two top coats of Devoe 184 epoxy coating.
The first top coat was tinted light gray and the second one a darker gray.
This helped to insure complete coverage of the surface and avoid the potential for a localized galvanic celi to develop.
All coating work was done using brushes and 3/4 inch nap rollers.
4.6 Access Hole Closure The access holes provide direct access to an area that is a high radiation area during operation.. Therefore a barrier is required to restrict access.
This was accomplished by placing sand bags in the entire length of the-hole.
The bags weigh about twenty five pounds each and can be removed during future outages to conduct inspections and repairs of the coating if necessary.
One row of small plastic bags (3 x ' inches) was filled with granular boron carbide to help shield any neutron radiation that might stream from the 20 inch access holes.
4.7 Repair Contingency.
As :a precautionary measure, a repair approach designed to address local, as opposed to global, drywell repair requirements was identi-fied and partially funded.
Representatives from CBI, MPR and GPUN met in August 1992 to discuss repair strategies (see reference 2.18).
The outcome of the meeting was that the most appropriate, repair scheme for relatively small areas would be weld overlay.
Competitive bids were solicited from three sources to provide weld proceduresand to test the feasibility of doing the repair in the sand bed by using the mockup.
CBI was the successful bidder.
The mockup demonstration was very successful.
It demonstrated that the weld overlay repair process was not only feasible, but relatively straight forward in spite of limited working space.
However, the mockup demonstration.
raised a technical concern regarding the effect of residual stresses introduced Into the vessel during the welding process.
CB1 submitted a quote for analysis to resolve this concern.
However, no further action was taken when It became obvious that weld repair of the vessel was not necessary, 5.0 UT READINGS 5.1 General The UT readings taken from the inside of the drywell do not cover the entire surface of the sand bed area because most of the area. is below the internal drywell floor and therefore not accessible from inside the: drywell.
The access provided during 14R from the Torus room provided an opportunity to investigate the entire area.
A number of UT readings in each bay were taken to evaluate the condition of the vessel.
See reference 2.19 for a description of UT readings from inside the drywell.
012/107 OCLR00029164
06J0[/04 11:31-03 TDR 1108 Rev. 0 Page 15 of 45 5.2 Initial Approach for UT Inspections from the Sand Bed It was recognized in the pre-14R planning process that UT readings from the sand bed should be taken once access was achieved.
To this end a specification was prepared, and issued (reference 2.20).
- However, it was not clear, during the planning stage, how the detail requirements of the specification wou.d be carried out.
It was known that the surface was irregular, bu4 the degree of irregularity was pure speculation.
During a meeting held on 8121/92 it was decided to assign a OPUN materials engizieer (S. "Saha) the responsibility for deciding the extent of UT coverage and selection of the locations to be UT.'d.
This was done to enpure consistency.
NDE would have the final word as to whether or not the areas were prepared properly for UT readings.
At this point in time it was planned to identify, the two thinnest ýocations in three bays and prepare a six inch by six inch grid similar to the grids used to monitor from the inside of the
- drywell, The bays selected would be the three in the worst condition as determined from UT readings taken previously from inside the drywell and visual observations during the sand removal effort.
These bays were 19, 17 and 11.
If during the process of getting a bay ready for coating, additional suspect areas were identified, readings would also be. taken in those areas.
How to identify the thinnest areas to locate the inspection grids presented a dilemma that was also discussed at the 8/21/92 meeting.
Several schemes were discussed.
The most promising being one using a UT probe to survey the bays for relative thickness through rust and pits.
The NDE representative accepted an action item to pursue this approach.
Two major challenges were involved with this assignment.
One, to replicate the physical condition of the drywell surface so that inspection techniques could be evaluated and two, to anticipate the physical space limitations associated with conducting inspections in the sand bed.
The second one was not a problem as it turned out.
There is adequate space in the sand bed region to conduct inspections.
- However, all attempts to replicate the, physical condition, of the drywall *surface failed.
This drove us to experimenting with a UT probe suspended in a film of water to compensate for surface irregularities.
Since we were only looking for relative thickness this appeared to be a solution.
Once the thinnest location was selected we planned to prepare the surface so that reliable UT readings could be obtained.
.5.3 Modified Approach AS is documented below, once access.to the sand bed region of bays 17 and 19 was obtained it was soon apparent that meaningful UT in-formation could not. be obtained without preparing the surface by grinding on the drywell shell where heavy corrosion had taken place.
several probes were tried..
None provided useful information including the experimental immersion probe.
The corroded vessel shell resembled a cratered golf ball-surface.
The areas where the heaviest corrosion had taken place appeared obvious from a visual inspection since the inside shell wall was relatively uniform.
The GPUN metallurgist (S. Saha) identified on a sketch, areas to be prepared for UT readings.
At a later time he reviewed the surface preparation and thickness data and identified additional locations to ensure that the thinnest areas were surveyed.
He has documented his observations in Section 6 of this TDR.
Because of a high level of confidence in the visual inspection and the fact that the surface preparation for adequate UT inspection required removal of some metal not corroded, the idea of preparing six inch by six inch grids was abandoned.
That approach no longer seemed necessary or prudent.
012/107 OCLROO029165
06/01/04 11:31:03 TDR 1108 Rev. 0 Page 16 of 45 Sam Saha visually surveyed each bay and identified locations for UT readings that provided an adequate profile'of the areas judged to he the thinnest in the bay.
The acceptance criteria was that a bay would be deenqed to be acceptable if the general area thickness is determined by UT readings to be equal to or greater than 0.736 inches.
The 0.736 inch limit is based on an analysis which shows that the drywell meets ASHE code requirements (references 2.1 and 2.2).
Thickness readings less than 0.736 inches were referred to the GPUN Engineering Mechanics group for evaluation.
Each evaluation is documented in Section 6 of this report.
5.4 Selection of Locations for UT Surveys As detailed in paragraph 5.3, the selection of locations for ultra-sonic thickness measurements rested on the visual examination of the vessel shell'in each bay.
The vessel shell, from the sand bed side, looked like a typical golf ball, i.e. a rough surface full of dimples except that the dimples varied in size.
It was reasoned that since the inside surface of the vessel shell is smooth and not corroded, any thin area on the outer surface should represent the minimum thickness in that region.
It was further reasoned that if six to twelve scattered spots, located in the area of worst corrosion, are ground smooth and the thickness of each spot is measured by UT method we will have a high level, of confidence that we have identified the thinnest shell thickness for a bay.
This approach is conservative
- since, (a) we are forcing a statistical bias in choosing only the thinnest areas and (b) grinding of the selected spots to obtain a flat surface for reliable UT readings will remove additional good metal.
This conservative approach for selection of UT spots was finally adopted after assuring that the interior vessel wall is indeed smooth.
This was proven in bays 17 and 19 by obtaining a uniform backwall reflection of the. sound waves with UT equipment.
GPUN metallurgist (S. Saha) located, mapped and identified the worst corroded areas in each bay for thickness measurements.. The selected spots and the measured thickness are discussed in Section 6 of this TDR.
5.5 Structural Acceptance Criteria Acceptance Criteria - General Wall The acceptance criteria used to evaluate the measured drywell thickness is based upon GE reports 9-3 and 9-4 (Ref. 2.1 & 2.2) as well as other GE studies (Ref. 2.21) plus visual observations of the drywell surface (Ref. 2.22).
The GE reports used an assumed uniform thickness of 0.736 inches in the sand bed area.
This area is defined to be from the bottom to top of the sand bed, i.e., El. 8 feet, 111/2 inches to El. 12 feet, 3 inches and extending circumferentially one full bay.
Therefore, if all the UT. measurements for thickness in.
one bay are greater than 0.736 inches the bay is evaluated to be acceptable.
In bays where a reading. or measurements are below 0.736 inches, more detailed evaluation is required.
This detailed evaluation is based, in part, on visual observations of the shell surface plus a knowledge of the inspection process.
The first part of this evaluation is to arrive at a meaningful value for shell thickness for use in the structural assessment.
This meaning-ful value is referred to as the thickness for evaluation.
It is computed by accounting for the depth of the spot where the thickness measurement were made and the roughness of the shell surface.
The 012/107 0CLR00029166
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,TDR 1108 Rev. 0 Page 17 of 45 surface of -the shell has been characterised-as being "dimpled" as in the surface of a golf ball where the dimples are about one half inch in diameter.
- Also, the surface contains some depressions 12 to 18 inches in diameter not closer than 12 inches apart, edge to edge (Ref. 2.22).
The depth of surface roughness using the drywell. shell impressions taken in the roughest bhy was calculated.
Two locat-ions in bay #13 were selected since bay 13 is the roughest bay.
Approxi-mately 40 locations within the tt.d impressions were measured for depth and thb average plus one standard deviation was calculated to be at 0.186 inches, A value of 0.2D0 inches was used in this calculation as a conservative depth of uniform dimples for the entire outside'surface of the drywelI in the sand bed region.
The inspection focused on the thinnest portion of the drywell, even if it was very local, i.e., the inspection did not attempt to define a shell thickness suitable for structural evaluation.
Observations indicate *that some inspected spots are very deep.
They are much deeper than the normal dimples found, and very local, not more than I to 2 inches in diameter.
(Typically these observations were made.
after the spot was surface prepped for UT measurement,- This results in a 'ide dimple to accommodate the meter and slightly deeper than originally found by 0.030 to 0.100 inches).
The depth of these areas was measured.and averaged with respect to the top of local areas.
These depths are refertced to herein as the AVG micrometer measurements.
The thickness for evaluation is then computed from the above information as:
T (evaluation)
U OT (measurement)
+ AVG (micrometer) 0.200 inches where:*
T (evaluation)
=
thickness for evaluation UT (measurement) thickness measurement at the area (location)
AVG.(micrometer) average depth of the area relative to its imrmed-iate surroundings 0.200 inch
=
a conservative value of depth of typical dimple on the shell surface.
After this calculation,, if the thickness for analysis is greater than 0.736 inches; the area is evaluated to be acceptable.
Aceeptance Criteria - Local Wall:
If the thickness for evaluation is less than 0.736 inches, then the use of specific GE studies is employed (Ref. 2.21).
These studies contain analyses. of the drywell using the pie. slice finite element model, reducing the thickness by 0.200 inches. in an area 12 x 12 inches in the sand bed region, tapering to original thickness over an additional 12 inches, located to result in the largest reduction possible.
This location is selected at the point of maximum deflection of the eigen-vector shape associated with the lowest buckling load.. The theoretical buckling load was reduced by 9.S% from. 6.41 to 5.56.
Also, the surrounding areas of thickness greater than 0.736 inches is used to adjust the actual buckling values appropriately.
Details are provided
.in the body of the calculation.
012/107 OCLROO029167
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'Rev.
0 Page 18 of 4S Acceptance 9riteria Very Local Wall (24 rnch Diameter):
All UT measurements below 0.736 inches have been determined to be in isolated locations less than 2h inches in diameter.
The acceptance criteria for these measurements confined to an area lebs than 2h inches in diameter is based on the ASME Section III Subsection NE Class MC Components paragraph NE 3332.1 and NE 333S.1 titled "OPENING NOT REQUIRING REINFORCEMENT AND REINFORCEMENT OF MULTIPLE OPENINGS."
These Code provisions allow holes up to '21/2 inches in diameter in Class MC vessels without requiring reinforcement.. Therefore, thinned areas less than 21/2 inches in diameter need not be provided with reinforcement and are considered local.
Per NE 3213.10 the stresses in these regions are classified as local primary menibrane stresses which are limited to an allowable value of 1.5 Sm.
Local areas not exceeding 2N inches in diameter have no impact on the buckling margins.
Using the 1.5 Sm criteria given above, the required minimum thickness in these areas Is:
T ( required ).
( 2/3 ) * (.0.736 0
O.490 inches Where 2/3 is SM/1.SSm and is the ratio of the allowable stresses.
012/107 OCLR00029168
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'TDR 1108 Rev. 0 Page 19 of 45 6.0 RESULTS 6.1 General The locations and thickness measurements for each bay are sketched and tabulated in paragraphs 6i2 through 6.11.
The EngineeringMechanics section reviewed all of the UT.readings and documented their conclusions in. a calculation..
(See reference 2.23).
Following is a summary for each bay.
All "location" measurements in the graphics contained in Sections 6.2 through Section 6.11 are measured from the intersection of the drywall shell and vent pipe/reinforcement plate welds for vertical measurements and from the drywell shell butt weld for horizontal measurements.
Average micrometer measurements.listed in the tables are the average.of four readings taken at 0/45°./90°/.135' azimuth within a 1 inch band surrounding spots that were ground for UT measurements.
These were only taken in areas 4here remaining wall thickness was below'0.736 inches.
6.2 Bay #1 Data BAY #1 DATA 2010 DW 513 3
SHELL 9
21
- ..7 e s
a IB Figure 10 012/107 0CLR00029169
06/01/04 11:31.03 TDR 1108 Rev. 0 Page 20 of 45 Bay 1 Data - Table 1 Location T!r M esurements I (inches)
Avg Micrometer (inches) 1 0.720 0.218 2
0.716 0.143 3
0.705 0.347 4
0,760 5
0.710 0.313 6
0.760 7
0.700 0.266 8
0.805
- 9.
0.805 10 0.339 11 0.714 0.212 12 0.724 0.301 13 0.792 14 1.147 15 1.156 16 0.796 1?
0.860 18 0.917 19 0.890 20 0.965 21 0.726 0.211 22 0.52 23 0.850 Condition R.. Overview of Bay's Physical The shell in bay 1 is characterized by a rough surface full of dimples of varying sizes up to h inch in diameter.
The most remarkable feature is the presence of a band 8 incheg to 18 inches wide which is 4 to 6 inches 1below the vent pipe reinforcement plate weld and.about 30 inches in length.
This bathtub ring contains the worst corrosion.
Spots #1, 2, 3, 4,
5,.1, and 12 are located in this bathtub ring.
Below the band the corrosion is much less.
Above the band no corrosion was seen (spot #14 and #15) and the original red lead coating was still visible.
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- 8.
Summary of Structurai Evaluation The inspection focused on the thinnest areas of the drywell, even if it was very local, i.e., the inspection, did not attempt to define a shell thickness suitable for structural evaluation.
The shell appears to be relatively uniform in thickness except for a band of corrosion which looks like a "bathtub" ring (s9Q Fig. 10).
Beyond the bathtuib'ring on both sides, the shell appears 'to be uniform in thickness at a conseryative value of 0.800 inches.
measurements 14 and 15 confirm that the thickness above the bathtub ring is at 1.154 inches starting at elevation 11 feet, 09 inches.
Below the bathtub ring the shell is uniform in thickness where no abrupt changes in thicknesses are present.
Thickness measurements below the bathtub ring are all above 0.800 inches except location 7 which is %very 'local area.
Therefore, a conservative mean thickness of 0.800 inches is estimated to represent the evaluation thickness for this bay.
Given a.uniform thickness of 0.800 inches, the buckling margin for the refueling load condition is recalculated based on the GE report 9-4 (Ref. 2.2).
The theoretical buckling strength from report 9-4 (ANSYS Load Factor) is a square function of plate thicknesses.
Therefore, a new buckling capacity for the controlling refueling load combination is calculated.to be at
.13% above the ASME factor of safety of 2.
Locations 1, 2, 3,
4, 5,
10, 11, 12, 13, 20, and 21 are confined to the bathtub ring as shown in Figure 10. An average value of these measurements is an evaluation thickness for this band as follows; Location Evaluation Thickness 1
0.738" 2
0.659" 3
0.852" 4
0.760" 5
0.823" 10 0.839" 11 0.726, 12 0.825" 13 0.792" 20 0.9651 21 0.737" Average 0.792" An average evaluation thickness of 0.792 inches for the bathtub ring may raise concern given that the bathtub ring is notice-able and that the difference between its average evaluation thickness (0.792 inches) and the average thickness taken for the entire region (0.800 inches) is only 0.008 inches.
This results from the fact that average micrometer readings were generally not taken for the remainder of the shell since each reading. was greater than 0.736 inches.
In reality, the remainder of the shell is much thicker than 0.800 inches.
The appropriate evaluation thickness can not be quantified since no micrometer readings were taken.
012/107 0CLR00029171
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- ,TDR 1108 Rev. 0 Page 22 of 45 The individual measured thicknesses must also be evaluated for structural compliance.
Table I identifies 23 locations of UT measurements that were selected to represent the thinnest areas, expept locations 14 and 15, based on visual examination.
These locations are a deliberate attempt to produce a minimum measurement.
Locations 14 and 15 were selected to confirm that no corrosion had taken place in the area above the bathtub ring.
Eight locations shown in Table 1 (1, 2, 3,
5, '7, 11, 12, and
- 21) have measurements below 0.736 inches.
Observations indi-cage that these locations were very deep and not more than 1 to 2 inches in diameter'.
The depth of each of these areas relative to its immediate surroundings was measured at 8 locations around the spot and the average is shown in Table 1.
Using thb general wall thickness acceptance criteria described earlier, the evaluation thickness for all measurements below 0.736 inches were found to be above 0.736 inches except for too locations, 2 and 11, as shown in Table 2.
Locations 2 and 11 are in the bathtub ring and are about 4 inches apart.
This area is characterized as a local area 4 x 4 inches located'at about 15 to 20 inches below the vent pipe reinforcement plate with an average thickness of 0.692 inches.
This thickness of 0.692 inches is a full 0.108 inch reduction from the conser-vative estimate of a 0.800 inch evaluation thickness for the entire bay.
In order to quantify the effect of this local region and to address structural compliance, the GE study on local effects is used (Ref. 2.21).
This study contains an analysis of the drywell shell using the pie slice finite element model, reducing the thickness by 0.200 inches (from 0.736 to 0.536 inches) in an area 12 x 12
. inches in the sand bed region located to result in the largest reduction possible.
This location is selected at the point of maximum deflection of the eigenveotor shape assoclated with the lowest, buckling load.
The theoretical buckling load was reduced by 9.5%.
The 4 x 4 inch local region is not at the point of maximum deflection.
The area of 4 x 4 inches is only 11% of the 12 x 12 inch area used in the analysis.
Therefore, this small 4 x 4 inch area has a negligible effect on the buckling capacity of the structure.
In summary, using a conservative estimate of 0.800 inches for evaluation thickness for the entire bay and the presence of a bathtub ring with a evaluation thickness of 0.792 inches plus
-the acceptance of a local area of 4 x 4 inches based on the GE study, it is concluded that the bay is acceptable.
012/107 OCLRO0029172
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'Rev. 0 Page 23 of 45 SUMMAY OF Measurements BELOW 0.736 Inches Table 2 Location UT Measurement Avg Micrmeter
- Mena Depth/Valley T (Evaluation)
Rcmarks
()
(2)
(3)
(4)-(1) + (2)-(3) 1 0.720" 0.218" 0.200'.
0.739" Acceptable 2
0.716" 0.143" 01200" 0.659" Acceptable 3
0.705" 0.347' 1
0.200' 0852' Acceptable 5
0.710" 0313" 0.200' 0.823" Acceptable 7
0.700w 0.266" 0.200" 0.766" Acceptable 11
.0.714".
0.212" 0.200' 0.726*
Acceptable 12 0.724' 0.301*
0.200, 0.825 Acceptable 21 0.726"
- 0.211" 0.200" 0.7371 Acceptable 1*...
012/107 OCLROO029173
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- TDR 1108 Rev.
0 Page 24 of 45 6.3.
Bay #3 Data BAY #3 DATA 3
2 0
9 S
4 0
e.
07 DW SHELL Figure 11 Bay 3 Data - Table 3 Locmfon
.fT Readings Avg Micivnrta (is.c,>)
Cinches) i 0.795 2
1.000-3 OS 4
0U898 1
0.8f 6
0.968 7
0.826 8
0.780
- t.
012/107 OCLR00029174
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0 Page 25 of 45 A.
Overview of Bay's Physical Condition Except for a "band" approximately 6 inches below the vent header weld and 8 -
20 inches wide, the corrosion observed was uniform and characterized by a uniformly dimpled surface.
The upper portion of the shell beyond the "bathtub ring" and the vent pipe was not corroded.
The original "red lead" primer coating is still visible.
The reinforcement bar sleeves, on the-concrete side, were corroded uniformly.
No perforation was seen in any of these sleeves.
The concrete floor was in poor shape.
It had a huge crater about half the length of the bay ruhning along the drywell shell.
It was about 18 inches.deep at the worst location.
'No drainage channel was found on the floor.
From the visual appearance, it was evident that the concrete floor was never constructed to the original design.
"B.
Summary of Structuxral Evaluation The outside surface of this bay is rough, similar to bay one, full of dimples comparable to. the outside surface of a golf ball. This observation is made by the inspector who located the thinnest areas for -the UT examination.
Eight locations were selected to represent the. thinnest areas based on the visual observations vof the shell surface (see Fig. 11).
These locations are, a deliberate 'attempt to produce a minimum measurement.
Table 3 shows measurements taken to measure the thicknessee of the dryweal shell using a D-meter.
The results indicate that all of the areas have thickness greater than the 0.736 inches.
Given the UT measurements, a conservative mean evaluation thickness of 0.850 inches is estimated for this bay and therefore, it is concluded that the bay is acceptable.
012/107 OCLROO029175
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0 Page 26 of 45 6.4 Bay #5 Data NOTE:
In this bay the drywell shell (butt) weld is about 8 inches to the right of center line of the vent pipe.
Therefore, all'measurements were taken from a line drawn on shell which approx. coincide with the vent pipe center line.
SAY #5 DATA DW SHELL 4
2
-5.° i""
Figure 12 Bay 5 Data - Table 4 LomtIon Ur Readivpg Avg hicrometer inche)
(inchcs) 2
.1.040-3____
1.020 4
0.910-5 0.890 6
-1.060-7 WM0 a
1.010-l
)
012/107 OCLROO029176
06/01/04 11:31,03 TUR 1108 Rev. 0 Page 27 of 45 A.
Over'iew of Bay's Physical Condition.
This bay was very similar to bay 3 in physical condition except that, (1) the. floor crater was 12 inches deep at the worst location and (2) the localized low spots from corrosion were clustered at the junction of bays 3 and 5, 30 -
32 inches above the floor.
S. Summary of Structural Evaluation Eight locations were selected to represent the thinnest areas based. on the visual observations of.the shell surface (see Fig. 12).
These locations are a deliberate attempt toproduce a minimum measurement.
Table 4 shows readings taken to measure the thicknesses of the drywell shell using a D-meter.'
The resultý indicate that all of the areas have thickness greater than the 0.736 inches.
Given the UT measurements, a conservative mean evaluation thickness of 0..950 inches is estimated. for this bay and therefore, it is concluded that the bay is acceptable.
012/107 OCLR00029177
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0 Page 28 of 45 6.5 Bay #7 Data BAY47 DATA,
.D 6
S 3
DW 2 1 SHELL Figure 13 Bay 7 Data -
Table 5 location UT. Readings Avg Micromeier (inches)
(Inch=s) 1 0.920 2
1.016 3
0.9*4 4
1.040 5
.1.030 6
1.045 7
1.000 D12/107 OCLR00029178
06/01/04 11:31:03 TDR 1108 Rev. 0 Page 29 of 45 A.
Overview of Bay's Physical ConditioO The 'drywell surface showed uniform dimples in the corroded area, but it was shallow in depth, The bathtub ring, seen below the vent header in other bays, was not very prominent in this bay.
The sleeves for the reinforcement bars showed no perforations and were uniformly corroded.
The concrete floor had no drainage channel, was unfinished and had a few small crateri.
B.
Spmmary of Structural Evaluation Seven locations were selected to represent the thinnest areas based on the visual observations of the shell surface (see Fig. P).
These locations are a deliberate attempt to produce a minimum measurement.
Table S shows readings taken to measure the thicknesses of the drywell shell using a D-meter.
The results indicate that all of the.areas have thickness greater than the 0.136 inches.
Given the OT measurements, a conservative mean evaluation thickness of 1 inch is estimated for this bay and therefore, it is concluded that the bay is acceptable.
022/107 0CLR00029179
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0 Page 30 of 45 6.6 Bay #9 Data BAY #9 DATA Figure 14 Bay 9 Data - Table 6 Location UTr Readings Avg Micrometer (inches)
(inches) 2 0.940-3 0.994-4 L.020 5
0.915 6
0.820 7
0.825 9
0.791 9
.82-10 0.980-(
012/107 OCLROO029180
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- TDR 1108 Rev. 0 Page 31 of 45 A.
Overview of Bay's Physical Condition, This bay was similar to bay 7 in physical condition except that the bathtub ring that is 6 to 9 inches wide and 6 to 8 inches below the vent pipe reinforcement plate contained some localized corrosion.
Above this band no corrosion had occurred.
I B.
Summary'of Structural Evaluation Ten locations were selected to represent the thinnest areas based on the visual observations of the shell surface (see Fig. 14). These locations are a deliberate attempt to produce a minimum measurement.
Table 6 shows.readings taken to measure the thicknesses of the drywell shel. using a D-meter.
The results' indicate that all of the areas have thickness greater than the 0.736 inches.
Given the UT measurements, a conservative mean evaluation thickness of 0.900 inches is estimated for this bay and therefore, it is concluded that the bay is acceptable.
(
0 o12/107 OCLROO029181
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0 Page 32 of.45 6.7 Bay #11 Data BAY #11 DATA I
I 3
4 1
DW SHELL 02
,7
,8 Figure 15 Bay 1i Data - Table 7.
Location U. 1ea:dings Avg Micromccer Cimches)
Cinches)
S D.70.5 0.246 2
0.77M 3
0.832 4
0.755 5
0.831 6
0.800 7
0.31 8
. 0.81
(
I...
012/107 OCLROO029182
06/01/04 11:31:03 TDR 1108 Rev. 0 Page 33 of 45 A.
Overview of Bayas.Physical Condition This bay was wet, during the initial inspection, from the water leaking put of the reactor cavity.
The water was seen trickling/dripping down the concrete wall on the inside of the sand bed.
No water stream/trickle was seen on the drywell shell.
Most of the localized corroded spots were on the upper right hand side (i.e.. toward bay 9) 10 to 12 inches below the vent pipe reinforcement plate.
The shell on the left hand side (i.e. toward bay 13) showed an uniformly corroded (dimpled) surface.
The concrete reinforcement bar sleeves were corroded bue not perforated.
The concrete floor was unfinished and no drainage channel was seeh.
B.
Summary of Structural Evaluation Eight locations were selected to represent the thinnest areas based on the visual observations of the shell surface (see Fig. 15).
These locations are a deliberate attempt to produce a minimum measurement.
Table 7 shows readings taken to. measure the thicknesses of the drywell shell using a D-meter.
the results indicate that all of the areas have thickness greater than thQ 0.736 inches, except one location.
Location I as shown in Table 8,-
has a
reading below 0.736 inches.
Observations indicate that this location was very deep and not more than 1 to 2 inches in diameter.
The depth of area relative to its immediate surrounding was measured at 8 locations around the spot and the average is shown in Table 8.
Using the general wall thickness acceptance criteria described earlier, the evaluation thickness for location 1 was found to be above 0.736 inches as shown in Table 8.
Given the UT measurements, a
conservative mean evaluation thickness of 0.790 inches is estimated for this bay and therefore, it is concluded that the bay is acceptable.
Summary of Readings Below 0.736 Inches Table 8 Lowtaton Ur Measurement Avg Mieromter Mea Dth/V. ly T (Evlutin)
Remarks
,(,)
)
O(3)
(4)=
S)+2-3) 0.*709' 0.2A6' 0 -20D 0.7SI" Acmeptable 012/107 OCLR00029183
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- TDR 1108 Rev.
0 Page 34 of 45 6.8 Bay #13. Data NOTE:
Spots with suffix (e.g. IA or 2A) were located close to the.
spots. in question and were ground carefully to remove minimum amount of metal but adequate enough for UT.
I D BAY
- I3 DATA 620 16'6 12',
8 oll 14 1
014
-"1.3 SHELL
.18 "3
- 10 o19
(
Figure 16 i
0121107 OCLR00029184
06101104 11:31:03 TDR 1198 Rev. 0.
Page 35 of 45 Bay 13 Data - Table 9 Lonati~o UT Reading Avg M nometer (hiches)
(inCeO)
- /-A 0.67_/0.&90 0.351.
2/2A 0.722/0.943 0.360
- 3.
0.941 l--
4 0.915 s/SA 0.718/0.81:
0.21' 6/6A 0.655/0.976 0.301 717A 0.618/0.752 0.257 8/&A 0.718/0.900 0.278
- 9.
0.924 10/10A 0.728/0.810 0.211 11/11A 0.685/0.854 0.256 12
-0.885 13 0.932 14
.0.868 15/15A 0.683/0.859 0.273 16 0.829.
17 0.807 18 0.825 19 0.912 20 1,170 A.
Overview of Bay's Physical Condition The drywall shell in this bay appeared uniformly. dimpled except around a plug in 'the upper right hand corner (towards bay.11)..
The plug was'located in the worst corroded area of the shell, but it was not corroded.
The bathtub ring below the vent pipe reinforcement plate was less. prominent than was seen in other bays.
The concrete floor in this bay was in better shape as compared to other bays, but it was. still uneven and craters were presentý There was no drainage channel.
The reinforce-ment bar sleeves were uniformly corroded, but. no perforations of the sleeves were seen.
0121107 OCLROO029185
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'TDR.1108 Rev. 0 Page 36 of 45 B.
Summary of Structural Evaluation The variation in shell thickness is greater in this bay than in the other bays.
The bathtub ring below. the vent pipe
-reinforcement plate was less prominent than was seen in other bays.
The corroded areas are about 12 to 18 inches in diameter and are at.12 inches apart, located in the middle of the sand bed.
Beyond the corroded.areas on both sides, the shell appears to be uniform in. thickness at a conservative value of 0.800 inches.
Near-the Vent pipe and reinforcement plate the shell exhibits no corrosion since the original lead primer on the vent pipeIreinforcejent plate is intact.
Measurement 20 confirms that the thickfiess above the bathtub ring is at 1.154 inches.
Below the bathtub ring the shell, appears to be fairly uniform in thickness where no abrupt changes in thick-nesses -are present.
Thickness measurements below the bathtub ring are all 0.800.inches or better.
Therefore, a conservative mean thickness of 0.800 inches is estimateO to represent the evaluation thickness for this bay.
Given a uniform thickness of 0.800 inches, the buckling margin for the refueling.load condition is recalculated based on the GE report 9-4 (Ref.. 2.2).
The theoretical bucklipg strength from. report 9-4 (ANSYS Load Factor) is a square function of plate. thicknesses.
Therefore, a new buckling capacity for the controlling. refueling load combination is calculated to be at 13% above the ASME factor of safety of 2.
Locations 5, 6,
7,
.8, 10, 11, 14, and 15 are confined to the bathtub ring as shown. in Figure 16.
An average value of these measurements is an evaluation thickness for this band as follows:
Location Evaluation Thickness 5
'0.735" 6
0.756",
7 0.675" 8
0.796" l0" 0.739" 11 0.741" 12 0.885" 14 0.868" 15 0.756" 16 0.829" Average = 0.778" The inspector suspected that soine of the above locations in the bathtub ring were over ground..
Subsequent locations with
'suffix A, e.g.
5A, 6A, were located close to the spots in question and were ground carefully to remove the minimum amount.
of metal but adequate enough for UT examination as shown in Figure 16.. The results indicate that all subsequent measure-ments were above 0.736 inches.
The average micrometer readings taken for these locations confirm the depth of measurements at these locations.
In spite of the fact that the original readings were taken at heavily ground locations, they are the one used in the evaluation.
012/107 OCLROO029186
06/01/04 11:31:03 TDR 1108 Rev. 0 Page 37 of 45 The individual measurements must also be evaluated for structural compliance.
Table 9 identifies 20. locations of UT measurements that were selected to represent the thinnest areas, except location 20, based on visual examination.
These locations are a deliberate attempt to produce
- a. minimum measurement.
Location 20 was selected to confirm that. no corrosion had taken place in the area above the bathtub ring.
Nine locations shown in Table 9 (1, 2, 5, 6, 7, 8, 10, 11, and
- 15) have measurements below 0.736 inches.
Observations indicate that these locations were very deep, overly ground, and not more than 1 to 2 inches in diameter.. The depth of each of these areas relative to its immediate surroundings was measured at 8 locations around the spot and the average is shown in Table 9.
Using the general wall thickness acceptance criteria, described earlier, the evaluation thickness for all measurements below 0.736 inches were found to be above 0.736 inches except for* two locations, 5 and 7, as shown in Table 10.
in addition, subsequent measurements close to-the locations identified above, were taken and they were all above 0.736 inches.
Locations 5 and 7 are in the bathtub ring and are about 30 inches apart.
These locations are characterized as local areas located at about 15 to 20 inches below, the vent pipe reinforcement plate with an evaluation thicknesses of 0.735 inches and 0.677 inches.
The location 5 is near to location 14 for an average value of 0.801 inches and therefore acceptable.
Location 7 could conservatively exist over an area of 6 x 6 inches for a thickness of 0.677 inches. -This thick-ness of 0.677 inches is a full 0.123. inches reduction from the conservative estimate of a 0.800 inch evaluation thickness for the entire bay.
In order to quantify the effect of this local region and to address structural compliance, the GE Study on local effects is used (Ref. 2.21)..
This study contains an analysis of the drywell shell using the pie slice finite element model, reducing the thickness by 0.200 inches (from 0.736 to 0.536 inches) in an area 12 x 12 inches in the sand bed region located to result in the largest reduction possible.
This location is selected at the point-of maximum deflection of the eigenvector shape associated with the lowest buckling load.
The theoretical buckling load was reduced by 9.5%.
The 6 x 6 Inch local region is not at the point of maximum deflection.
The area of 6 x 6 inches is only 25% of the 12 x 12 inch area used in the analysis.
Therefore, this small 6 x 6 inch area has a negligible effect on the buckling capacity of the structure.
in summary, using a conservative estimate of 0.800 inches for evaluation thickness for the entire bay and the presence'of a bathtub ring with.a evaluation thickness of 0.778 inches plus the acceptance of a local area of 6 x 6 inches based on the GE study, it is concluded that the bay is acceptable.
012/107 OCLROO029187
06/01/04 12.31:03
,TDR 1108 Rev. 0 Page 38 of 45 Summarv of Measurements Below 0.73S Inches Table 10 Location UT Measurement Avg Micromecter Mean Depthl/Valley T (Eualuation)
Remarks (1)
(2)
'.)
(4)-(1)+ (2-(3) 1 0.672" 0.351" 0.200" 082Y Acceptable 2
0.722" 0.3'"
0.20D" 0.882" Acceptable 5
0.718" 0.217 0200" 0.735" Acceptable 6
0.655" 0.301" 0.200" 0.756" Acceptable 7
0.618.
0.257-0.300" 0.675s Acceptable 8
0.718" 0.278" 0.200' 0.796" Acceptable 10 0.728" 0.211" 0.200" 0.139" Acceptable I1 0.680 0..256" 0.20(r 0.741" Acceptable is 0.683" 0.273" 0.200" 0.756" Acceptable 012/107 OCLROO029188
06/01/04 11:32=03 TDR 1108 Rev.
0 Page 39 of 45 6.9 Bay #15 Data BAY #15 DATA 6'
11 10 8
7 9
DW 2
SHELL.
.3 4
(
i Figure 17 Bay 15 Data -
Table 11 Location UT RPadings Avg Micromcccr (inches)
(inches) 1 0.786 2
0.829-
.3
.0.932 4
0.95 5
0.850 6
0.794 7
.0098 8
0.770 9
0.722 0.337 10 0.860 11 0.225 012/107 OCLR00029189
06/01/04 1103103 "TOR 1108 Rev. 0 Page 40 of 45 A.
Overview of Bay's Physical Condition The drywell shell in this bay was uniformly dimpled and the upper part of the shell (i.e. near the vent pipe/reinforcement blade and up) was not corroded.
The original "red lead" primer was still visible in this region.
The bathtub ring was less prominent than other bays.
The reinforcement bar sleeves were
- corroded, but not perforated.'
The concrete floor had no drainage channel and there were craters in the floor.
B. Summary of Structural Evaluation Eleven locations were selected to represent the thinnest areas based on the visual observations of the Shell surface (see Fig. 17).
These locations are a deliberate attempt to produce a minimtum measurement.
Table 11 shows readings taken to measure the thicknesses of the drywell shell using a D-meter.
The results indicate that all of the areas have thickness greater than the 0.736 inches, except one location.
Location 9 as shown in Table 11, has a reading below 0.736 inches.
Observaiions indicate that this location was very deep and hot more than 1 to 2 inches in diameter.
The depth of area relative to its immediate surrounding was measured at 8 locations around the -spot and the avekage is shown in Table 11.
Using the general wall thickness acceptance criteria described earlier, the evaluation thickness for location 9 was found to be above 0.736 inches as shown in. Table 12.
Given the UT measurements, a conservative mean evaluation thickness of 0.800 inches is estimated for this bay and therefore, it is concluded that the bay is acceptable..
Summary of Measurements Below 0.736 Inches Table 12 Location T Measulement
- Avg Meromcler Mean Depth/Vally T (Evaluation)
Rernmarks 9
0.72' 03(2)
(3).
- 0)
Acepiab.
9' 0.7/22, 0.337" 020 0.859" Acce'ptable 012/107 OCLROO29190
/0O1/0O4 11:312:3
)
,TDR 1108 Rev.
0 Page 41 of 4S 6.10 Bay #17 Data BAY #17 DATA
.2 DW 10 9
- SHELL 0
3 4
0 7
0 8
0*
Figure 18 Bay 17 Data -Table 13 Locitioa Ur Readings Avg Micrometer (inche)
Cnches) 1 0.916 2
1.150 3
.0.898 4
0.951 5
0.913.
6 0.992 7
0.970 8
0.990 9
0.720 0.351 10 0.830 116 0.770M 012/107 OCLROO029191
06/01/04 11:31:03
.TDR 1108 Rev. 0 Page 42 of 45 A.
Overview of Bay's Physical condition This bay (along with bay 19) provided the first glimpse of the conditiorns of the drywell shell.
The most remAr-kable feature of this bay was the presence of the bathtub ring 8 to 10 inches wide that was located 8 to 10 inches below the vent tube reinforcement plate.
UT spots # 1,3,5 and 7 are located in this band which is the most corroded area in this bay.
Spots
- 1 through 8 were ground carefully to minimize loss of good metal.
spots # 9,10 and 11 were ground flat ind most likely removed good metal.
The reinforcement bar sleeves were
- coiroded, but not perforated.
The concrete floor was unfinished with no sign of a drainage channel.
B. Summary of Structural Evaluation Eleven locations were selected to represent the thinnest areas based on the visual observations of the shell surface (see Fig. 18).
These locations are a deliberate attempt to produce a minimum measurement.
Table 13 shows readings taken to ineasure the thicknesses of the drywell shell using a D-meter.
The results indicate that all of the areas have thickness greater than theO0.736 inches, except one location.
Location 9 as shown in Tablet 13, has a reading below 0.736 inches.
Observations indicate that this location was very deep and not more than 1 to 2 inches in diameter.
The depth of area relative to its immediate surrounding was measured at 8 locations around the spot and the average is shown in Table 13.
Using the general wall thickness acceptance criteria described
- earlier, the evaluation thickness for location 9 was found to be above 0.736 inches as shown in Table 14.
Given the UT measurements, a conservative mean, evaluation thickness of 0.900 inches is estimated for this bay and therefore, it is concluded that the bay is acceptable.
Summary of Measurements Below 0.736 Inches Table 14 Location LIT Mesurement" Avg Micrometer Mean Deptl/VaUl y T (Evalation)
Remarks 9
(172r 0351" 0.200, 0.871 Acceptable 012/107 OCLROO029192
06/01/04 11:31:03
'V i
TDR 1208 Rev.
0 Page 43 of 45 6.11 Bay #19 Data BAY #19 DATA W
D 1D
- 9 DW "SHELL-
.I 7-1 4
.3 Figure 19 Bay 19 Data - Table 15 Location UT Readinp Avg Micromeaer (inches).
(inches) 0.932 2
0.924
.3
.0.955 4
0.940.
s 0950 6
0.860 7'
0.969 8
.0.753 9
0.776 t0 0.790
{
0121107 OCLRQ0029193
06/01/04 11:31:03 TDR 1108 41 Rev. 0 Page 44 of 45 A. Overview of bay's Physical Condition The physical condition of this bay was similar to bay 17 except that UT spots I through 7 were ground carefully -to 'Minimize loss of good metal, whereas spots 8, 9 and 10 were ground flst.
B.
Summary of Structural Evaluation Ten locations were selected to represent the thinnest areas based on the. visual observati6ns of the shell surface (see Fig. 19).
These locations are a deliberate attempt to produce-a minimum measurement.
Table 15 shows readings taken to measure the thicknesses of the drywell shell using a D-meter.
The results indicate that all of the areas have thickness greater than the 0.736 inches.
Given the UT measurements, a conservative mean evaluation thickness of 0.850 inches is estimated for. this bay and therefore, it is concluded that the bay is. acceptable.
7.0 CONCLUSION
The cleaning and coating effort that was completed in. 14R will stop corrosion in the sand bed area.
Since this was accomplished while the vessel thickness was sufficient to satisfy ASME code requirements the
.drywell vessel in the sand bed region is no longer-a limiting factor in plant operation.
Inspections will be conducted in future refueling outages to insure that the coating remains effective.
In addition, UT investigations from inside the drywell will also be taken.
The frequency and extent of these Investigations will be evaluated after 15R.
012/107
- OCLR00029194
06101/04 I1.31:03
, TDR 1108 Rev. 0 Page 45 of 45 APPENDIX A WASTE DISPOSAL This Appendix describes the disposition of waste generated during the implementation of the project.
The various wastes generated are given, below:
- 1. Sand 172 barrels (55 gall6n/barrel)
- 2.
Concrete 59 barrels
- 3.
Corrosion scale 7 barrels
- 4.
Concrete slurry' 16 barrels
- 5.
Coating products, (Approximately 1600 cans, application tools etc.
buckets, brushes, rollers,etc.)
The sand removed from the Sand bed was slightly contaminated.
Reference 2.24 provides the 'activity levels found in various barrels of sand.
The threshold of activity below which a bulk waste is considered clean is as follows:
cesium 137 :S 1.1 X 10"4 micro curies/gm.
All other isotopes no detectable activity with a f scan machine with a range of 1 x 104 uc/gm - mirco.curies/gm.'
About 15 barrels of sand were bagged and used as shielding in the ten twenty inch diameter access manways.
The remaining sand will be stored in building #9 at the Forked River site until the sand activity reduces below the threshold activity.
Approximately 59 barrels of concrete were removed while cutting the access manways.
Thirty two barrels of concrete came in. large pieces and was disposed of as clean waste after frisking.
Twenty seven barrels of bulk concrete are being surveyed by the plant chemistry department using gamma scan, and depending on the outcome,. will be disposed of as clean waste, if the criteria for the threshold limits can be met.
If very low activity levels are found 'as. in the case of sand, it-will be stored in building #9.
If activity levels are higher, the concrete will be disposed of as regular low level radwaste.
Approximately seven barrels of' corrosion scale were removed.
the material was frisked and released as non radioactive waste.
Chemical analysis was performed by GPUN Materials Lab in Reading for the presence of hazardous metals.
Reference 2.25 provides the lab test results.
The corrosion scale was released as clean non radioactive waste as no hazardous metals were. found.
Approximately 16 barrels of concrete slurry were removed during the access manway core boring operation.
The slurry was allowed to settle, the water was checked for ph and then processed through radwaste (ph was below the limit).
Concrete was disposed of as regular low level radwaste.
Paint cans, paint-barrels, brushes, rollers and similar items that were used during the Devoe coating application processes, were kept on-site until the coating got hardened and then were frisked and released as clean waste.
Paint cans generally had to be coated on the exterior with the epoxy coating to eliminate the sticky condition prior to frisking for radioactivity.
012/107 OCLROO029195