ML20217L851
| ML20217L851 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 03/27/1998 |
| From: | Muench R WOLF CREEK NUCLEAR OPERATING CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ET-98-0022, ET-98-22, GL-97-06, GL-97-6, NUDOCS 9804070399 | |
| Download: ML20217L851 (13) | |
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W$LF CREEK NUCLEAR OPERATING CORPORATION Richard A. Muench Vice President Engineering March 27, 1998.
ET 98-0022 U. S. Nuclear Regulatory Commission ATTN:
Document Control Desk Mail Station Pl-137 Washington, D. C.
20555
Reference:
NRC Generic Letter 97-06, " Degradation of Steam Generator Internals," dated December 30, 1997
Subject:
Docket No. 50-482: Response to NRC Generic
)
Letter 97-06 Gentlemen:
Attached is Wolf Creek Nuclear Operating Corporation's (WCNOC) response to NRC 4
Generic Letter 97-06, " Degradation of Steam Generator Internals."
WCNOC has evaluated the reference as it applies to Wolf Creek Generating Station (WCGS),
and has reviewed plant information to address the requests made in the Generic Letter. Based on the reviews completed to develop this response, WCNOC has reasonable assurance we are in compliance with our current licensing basis.
If you have any questions concerning this response, please contact me at (316) 364-8831, extension 4034, or Mr. Michael J. Angus, at extension 4077.
1 Very truly yours, j
Y WA l
Richard A. Muench Attachment RAM /jad cc:
W. D. Johnson (NRC), w/a E. W. Merschoff (NRC). w/a 1
J. F. Ringwald (NRC), w/a k
K, M. Thomas (NRC), w/a ma e\\
g 9804070399 900327 PDR ADOCK 05000482 P
PDR P.O. Box 411/ Burhngton, KS 66839 / Phone: (316) 364-8831 An Equal Opponunity Employer WF/HCNET j
i STATE OF KANSAS
)
)
SS COUNTY OF COFFEY
)
Richard A.
Muench, of lawful age, being first duly sworn upon oath says that he is Vice President Engineering of Wolf Creek Nuclear Operating Corporation; that he has read the foregoing document and knows the content thereof; that he has executed that same for and on behalf of said Corporation with full power and authority to do so; and that the facts therein stated are true and correct to the best of his knowledge, information and belief.
I By li/4h Richard A Muench i
Vice Pre ' dent
]
Engineering h 7 day of bQf"C b, 1998.
SUBSCRIBED and sworn to before me this vi),i 0
" '*f I'
JULIE A. DALE NotaryPubEc Stateof Kansas
<My Appt Expires lO/30 9P ;
Expiration Date
/O 3D if i
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.' Attachment to ET 98-0022 Page 1 of 11' Response to Generic Letter 97-06
" Degradation of Steam Generator Internals" Soope Generic. Letter (GL) 97-06,
" Degradation of Steam Generator Internals"- was issued ~to: (1) again alert addressees to the previously communicated findings of. damage to steam generator' internals, namely, tube m;. port' plates and tube bundle wrappers, at foreign Pressurized Water Reactot ' FWR)' f acilities; -(2)
' alert addressees to recent findings of damage to steam generator tube support plates at a United States PWR - facility; (3) emphasize to addressees the-importance of -performing comprehensive. examinations of steam generator internals to ensure steam generator tube structural integrity is maintained in accordance with. the requirements of Appendix B to 10 CFR Part 50; and (4) require.al1Jaddressees to submit information that will enable the NRC staff to
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verify ' whether addressees' steam' generator internals comply with and conform to the current licensing bases for their respective facilities.
Requested Information GL 97-06 requested the following information:
(1) Discursion of any program in place to detect degradation of steam generator internals and description of the inspection plans, including the inspection scope, frequency, methods, and equipment.
The discussions should include the following information:
(a)
Whether inspection records at the facility have been reviewed for indications of tube support plate ' signal anomalies from eddy current testing of the steam generator tubes that may be indicative of support plate damage or ligament. cracking.
If the addressee has performed such-a review, include a discussion of the findings.
(b)
Whether visual or video camera inspections on the secondary side of the steam generators 'have been petiormed at-the facility to. gain information on the condition of the steam 1
generator internals (e.g.,.
support
- plates, tube bundle wrappers, or other components).
If the addressee has performed' such inspections, include a discussion of the findings.
(c)
Whether degradation of steam generator internals has been detected at the facility, and how the degradation was assessed and dispositioned.'
(2) If the addressee currently has no program in place to detect degradation of steam generator internals, discussion and justification of the plans i'
/ and schedule for establishing such a program, or why no program is needed.
Background Information Wolf Creek Generating Station (WCGS) utilizes Westinghouse Model F steam generators.
Prior to issuance of GL 97-06, the Westinghouse Owners Group (WOG),. the Electric Power Research Institute (EPRI) and the Nuclear Energy Institute.(NEI) developed an action plan to assess the susceptibility of steam generators to secondary-side degradation.
Wolf Creek Nuclear Operating Corporation (WCNOC) intends to participate in, and follow this industry action plan.
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Included in the action plan is an initiative to understand the causal factors involved'in the degradation experienced in the French Units.
This information
'l has been captured in EPRI report GC-109558,
" Steam Generator Internals i
w
Attcchme?lt *O ET 98-0022 P:ga 2 of 11 Degradation:
Modes of Degradation Detected in EdF Units".
This report was submitted to the Nuclear Regulatory Commission via NEI letter dated December 19, 1997 The WOG has reviewed EPRI GC-109558 relative to the design of Series 51 steam generators and determined that they have limited susceptibility to secondary-side degradation.
This conclusion is documented in report WCAP-15002, Rev. 1,
" Evaluation of EdF Steam Generator Internals Degradation - Impact of Causal Factors on Westinghouse 51 Series Steam Generators," December 1997 The Series 51 steam generators include Westinghouse model designations 51, SIM, 51F, and 54F.
Because of a similarity in design, this report also covers any' implication of susceptibility for two replacement steam generator designs, the Delta 47 and Delta 75.
The Westinghouse 51 Series steam generator designs are most similar to the EdF units.
WCAP-15002, Rev.1, documents visual inspection of the plants.
It is concluded that the number of plants that have been inspected and the inspection results demonstrate that the causal factors identified by EdF do not jeopardize the continued operability of Westinghouse Series 51 steam generators.
Eddy current inspection of the tubes would detect any detrimental effects on the tubing due to wear caused oy tube support plate ligament degradation, loose parts, and secondary side flow distribution changes.
Foreign object search and retrieval efforts are conducted to discover loose parts.
A similar detailed evaluation is planned for the remaining types of steam generators (Model 44F, F,
D3, D4, D5 and El/E2) to be the subject of later reports.
Inspection recommendations for WCNOC may change as the Westinghouse detailed evaluation has not been completed for the Model F steam generators.
The more detailed evaluation should be completed by the end of May 1998.
WCNOC intends
. to perform all necessary steam generator inspections.
A response to item 1 for the Model F steam generator is provided below, including WCNOC's inspection plans.
Therefore, item 2 of the GL does not apply.
Response to Item 1 Item 1 1
(1) A discussion of any progran in place to detect degradation of steam generator internals and descriptive inspection plans, including the inspection scope, frequency, methods and equipment.
WCNOC Steam Generator Inspection Program The following program is being implemented at WCNOC to address the various types of steam generator secondary side internals degradation that may occur in Westinghouse designed steam generators.
The majority of this program has been in place at WCNOC since 1993.
Areas of interest identified in the industry generic inspection plan will continue to be added to our inspection scope as necessary.
Changes are continually made to WCNOC's inspection program as additional inspection tooling becomes available and as industry and site specific events or issues dictate.
WCNOC intends to perform all l
- necessary inspections on our steam generators.
I Current Program Visual inspections of the secondary side of the steam generator are performed on all steam generators on a rotating basis to track performance and document overall-condition.
The following inspections are performed:
tx
I Attachmrnt to ET 98-0022 Pega 3 of 11
-1.
Tubesheet cleanliness inspection is performed on each steam generator every time it is cleaned to determine the effectiveness of the sludge lance operation.
2.
Foreign Object Search and Retrieval (FOSAR) of the tubesheet annulus and blowdown lane is performed on each steam generator that is sludge lance cleaned or as eddy current inspection data indicates to check for foreign objects that could - cause tube degradation.
3.
A. support plate inspection is performed each outage on at least one steam generator to assess the overall condition of the steam generator.
Areas of concern that are monitored for sludge accumulation are the tubes, tube support plates and the quatrefoils of the support plates.
4.
An upper steam drum inspection is performed on at least one steam generator each outage.
The ~ inspection documents the overall condition of the steam drum and concentrates on the Chevron Separator and the feedwater ring.
In addition to visual inspections, applicable steam generator components are included in the In-Service Inspection (ISI) Program at WCNOC and are inspected in accordance with Section XI 1989
- edition, in-service inspection requirements.
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Attechment to ET 98-0022-Pega 4 of-11 Discussion of WCNOC Inspection Results
'A steam generator inspection summary for WCNOC is included in the WOG format of Table 1.0, WCNOC has performed a sample of these inspections on our steam generators..
-Additional methodology and inspections are detailed in the paragraphs that follow.
Table 1.0 WOG internal Degradation Program SG Inspection Summary for WCNOC Component Location Condition Type of Inspection Tube Support Plates TSP Cracked Missing E/C 7
N N
N Visual (SID) 6 N
N N
Visual (SID).
5 N
N N
Visual (SID, UBIB) 4 N
N N
Visual (SID, UBIB) 3 N
N N
Visual (SID, UBIB) 2 N
N N
Visual (SID, UBIB) 1 N
N N
Visual (SID)
Wrapper Lower Upper Seam Cracked Deform Drop sample N
N N
Visual (SWATS, Sludge Lance Installation)
Chemical Cleaning Shell TSPs Other Pitting Wastage Crack 7
N N
N Visual (SID) --
6 N
N N-Visual (SID) 5 N
N N
Visual (SID) l 4
N N
N Visual (SID) 3 N
N N
Visual (SID) 2 N
N N
Visual (SID) 1' N
N N
Visual (SID)
Other Secondary Side Pitting Wastage Crack Girth Welds N
N/A N
UT/MT Feed Ring N
N N
Visual J-Tute N
N N
Visual Water Box N/A N/A i
Riser Barrels N
N N
Visual Tangential Nozzle NI NI NI Symbols:
E/C = Erosion / Corrosion X- = Found in some Steam Generators N = Inspected: no indications NA = Not applicable to Model F Steam Generator NI = Not inspected
.e : Attechment'to ET 98-0022
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- WCNOC'Steae Generator History-
'Since 1990, R.
Brooks ' Associates.(Brooks), Inc. has - been providing ' steam
, generator L visual.' inspection ' services to WCNOC.
- WCNOC - decided to play a proactive role. in determining the health of the i steau generators. 'Since 1990, Brooks has developed and used several new technologies.at'WCNOC, allowing =a l majority 1 'of the steam generator to be inspectedo and providing WCNOC - the information needed to-operate'these components safely and efficiently.
1990 Refuel IV
'In.1990i WCNOC contracted Brooks to-perform annular tubesheet inspections and remove foreign ~ debris from all four steam generators.
All foreign debris (i.e., pieces of scale, gaskets,.etc.) was removed successfully.
After.the 1990 outage.was complete, WCNOC entered into a contract for Brooks to provide inspection services for two (2)' outages.
As' part of.the contract, Brooks worked with WCNOC to develop a plan that allowed for the entire steam generator secondary. side. to be inspected.
Brooks, through c long term in-house tool' development program, was to design, engineer, and implement tooling.
to remotely inspect top,. mid-section and tubesheet areas of,the steam' generator.
- Necessary tooling would - be developed to inspect and clean the
- upper bundle /in-bundle..(UBIB) areas as well.
1991 Refuel V During the 1991 outage, FOSAR was performed at the tubesheet in all four steam
~ generators, and the feedring and "J" nozzles were inspected.
Inspections at the tubesheet showed foreign objects in the annulus, which were removed.
The li objects -were pieces of flexitallic gasket material.
- The, "J"
nozzle inspections showed no wear, erosion or anomalous conditions.
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1993 Refuel VI
. Prior - to REVI, tooling was developed to inspect support elevations in the flowslot area.
As part of a continuing commitment to operate the steam generators safely and efficiently, WCNOC decided to use the new tooling (Support Plate Inspection Device, SID) in two steam generators.
'During the 1993 outage, FOSAR was performed at the tubesheet in all four steam
- generators.. Minor foreign objects. (i.e., pieces of scale, gaskets, etc.) were located. and retrieved.
The upper steam drums 'of two steam generators were opened to allow inspection of the feedring and "J" nozzles.
Normal mechanical inspections (welds, primary and secondary separators, etc.) were performed at the same time.
The SID' inspection showed sludge accumulation at all support elevations.
No wear, erosion or anomalous conditions were identified during these inspections.
1994 Refuel VII WCNOC held meetings with Brooks between RFVI and RFVII.
These meetings
- addressed additional. inspections desired by WCNOC.
WCNOC was informed the tooling = development program was on target and remote inspection tooling was expected to be used during REVII.
Brooks also had started development of.an UBIB Inspection System.
This system would be capable of inspecting all support plates, both hot and cold leg, from the flowslots to the wrapper.
WCNOC engineering agreed to use this new tooling as soon as it became available.
During the 1994 outage, Pre-Pressure Pulse Cleaning (PPC) visual inspections
.were' performed in two-steam generators with SID.
A Post-PPC visual inspection wasi performed in all four steam generators.
Attachment to ET 98-0022 Paga 6 of 11 indicated that the units could benefit from a chemical cleaning.
Remote FOSAR l
at the tubesheet was performed in all four steam generators, minor foreign
,obj ects. (i. e., pieces of scale, gaskets, etc.) were located and removed.
The upper steam drums of two steam generators were opened to allow inspection of feedring and "J"
nozzles.
Normal mechanical inspections (welds, primary and secondary separators, etc.) were performed at this time.
No wear, erosion, or anomalous conditions were identified during these inspections.
1996 Refuel VIII During the 1996 outage, Pre-Chemical Cleaning visual inspections were performed in two steam generators with SID.
Post-Chemical Cleaning visual inspections were performed in all four steam generators.
The Vertical Support Bars in one steam generator were also inspected following chemical cleaning.
FOSAR was performed at the tubesheet of all four steam generators.
The upper steam drums of two steam generators were opened to allow inspection of feedring and "J"
nozzles.
Normal mechanical inspections (welds, primary and secondary separators, etc.) were performed at this time.
No wear, erosion or anomalous conditions were identified during these inspections.
Brooks completed the design and qualification of the UBIB inspection system and a remote Shell, Wrapper, Annulus Transport System (SWATS).
Both systems were contracted for use at WCNOC during Refuel IX.
The UBIB system is capable of visually inspecting the tube support plates at all elevations of the steam generator.
The SWATS system as capable of being mounted on the handhole and driven into and around the inside of a steam generator.
1997 Refuel IX As part of the outage work scope, WCNOC chose to use the new UBIB technology.
This technology allowed further inspection of support plates and ligaments in-bundle.
It was also used to verify sludge loading after one cycle of operation since the chemical cleaning.
The Upper Bundle /In-Bundle inspection was performed in two steam generators.
This information provides a basis for future work and decisions.
POSAR was performed at the tubesheet of all four steam generators.
No foreign objects were found.
The SWATS tool was used to i
visually inspect the annulus, flow distribution baffle (underside),
and wrapper.
The lower supports and standoffs were viewed from below the wrapper level.
SWATS. was also driven past the handholes to view the canopy and l
shroud.
The upper steam dram of two steam generators were opened to allow inspection of the feedring and "J"
nozzles.
Normal mechanical inspections i
(welds, primary and secondary separators, etc.) were performed at this time.
No wear, erosion or anomalous conditions were identified during these inspections.
Inspection Summary l
Additional inspections are performed on the feedwater nozzles in accordance with the steam generator shell,Section XI 1989 edition in-service inspection requirements.
In addition to Section XI requirements, WCNOC has performed ultrasonic examinations to look for cracking induced by thermal stratification of the feedwater nozzles on all four steam generators.
No cracking or other anomalies have been identified as a result of these inspections, A five year plan was established in 1991 to baseline the steam generators through visual inspection of the secondary sides.
Data from previous inspections is compared with current steam generator conditions.
Visual inspections are rotated each outage to obtain a representative sample from all steam generators.
Visual inspection results have been used as the basis for decisions to perform specialized processes such as Pressure Pulse Cleaning and Chemical Cleaning.
Tubesheet cleanliness inspections, FOSAR, support plate inspections, and upper steam drum inspections are performed each outage to assess the overall condition of the secondary side of the steam generators.
Attachment to ET 98-0022 l
Paga 7 of 11 To date, no structural degradation has been identified.
As industry and site specific concerns dictate and inspection tooling becomes available, WCNOC
. intends to perform secondary side visual inspections to ensure continued safe operation and longevity of the steam generators.
Industry Background As discussed in WCAP-15002, Rev.
1, surv
- were sent to all WOG utilities requesting the results of all steam generat secondary side inspections and relevant tube inspections for tube support plate (TSP) conditions.
Completed surveys were received for 37 of 49 plants.
For the Model D,
E, 44F and F steam generators, responses were received for 12 plants.
Of these, 11 plants responded as having inspected or reviewed inspection data for TSP ligament indications and 8 having performed steam generator secondary side entries that give confidence of not having wrapper drop.
TSP ligament indications were not found in either steam generators with carbon steel or with stainless steel, support plates.
Of all the WOG surveys received, the modes of degradation detected include many cases of flow-assisted corrosion, or erosion-corrosion, and of premature cracking that results from either surface fatigue or from corrosion cracking that is associated with surface conditions such as pitting or geometric concentrations.
For the most part, however, the surveys do not report detection of several modes of degradation experienced in the EdF units.
There is no evidence of post chemical cleaning inspections discovering any significant material losses.
There is no evidence of any wrapper having dropped.
There is no evidence of TSP ligament cracking or thinning that is 4
progressive and continuing.
TSP.igament cracking or missing pieces of ligaments have been observed, but only in units with carbon steel support 1
plates with drilled round tube holes and flow holes.
These conditions are generally traceable to initial inspections and are not progressing based on sequential inspection data.
Many of the conditions appear to be related to I
original TSP drilling alignment.
There are cases of indications in TSPs that have been linked to patch plate welds.
Plants with significant hour glassing of the tube support plates as a result of the denting process have exhibited ligament cracking throughout the thickness tf the support plate between the flow holes in the plate or the flow holes in the tube lane.
If denting remained uncontrolled, as subsequent support plate corrosion occurs, the potential exists for fragments of the support plate material to become completely free of the main TSP structure.
i However, these plate segments generally remain locked in place because of the in-plane forces that give rise to denting, as well as the deformation that contains the individual piece.
Operating plants with active denting are under periodic monitoring by the utility and have long-standing criteria and review by the NRC.
In addition, the EdF experiences reported are not related to support plate degradation that has progressed to the tube denting stage.
These plants are therefore not included in this response to GL 97-06.
The secondary side internal degradation types found in Westinghouse steam generators are identified in Table 2.0.
WCNOC applicability is noted.
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Attcchment to ET 98-0022 Prga 8 of 11 Table 2.0 Secondary Side Internal Degradation Types In Westinghouse Design Steam l
Generators Feed Ring Preheat. Carbon Feed Ring Preheat STEAM Carbon Steel TSPs Stainless Stainless Steel GENERATOR Steel TSPs Steel TSPs TSPs Category:
(WOLF CREEK)
Degradation Type:
Erosion-Corrosion Moisture.
X S
X S
(
Separator Water 4x NA X"'
NA S
TSP F1 S
S NA NA Hole /
Ligaments Feed Ring /
X NA X
NA J-Tubes Cracking TSP X
S L
L.
Li aments m (2>
Wrapper L
L L
L z
Near i
Support s <2:
Transition X
L X "'
L i
Cone Girth Weld' Other:
Wrapp2ier-L L
L L
Drop X =. Observed in some steam generators, but not at Wolf Creek Susceptible
~S
=
Low Susceptibility L
=
NA = Not Applicable i
- 1. Various indications of possible tube degradation may be artifacts of manufacturing anomalies related to patch plate welds and drilling alignment.
- 2. Various Westinghouse design features are beneficial relative to some steam
... generator design features of foreign manufacturers.
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- 3. In steam generator replacements with the original shell.
i 4 This mechanism does not apply to the Model D3 because of the Alloy 600 inlet manifold designed used.
t
Attachment'to RT; 98-0022 Peg.t 9 of 11' h
!=
. Industry Inspection Plan l
. Tube Support Plate Ligament Erosion / Corrosion and' Cracking:
This is=ennsidered a' low susceptibility event since the' tube" support plates in the Model F steam. generators at WCNOC are stainless steel.
-A number of
~studiesi have' reported that the. chromium : content in carbon-steel has -a
~
i
.significant effect! on resistance to a erosion / corrosion mechanism, The chromium content of-stainless steel. support plates is expected-to preclude the occurrence. of. this degradatien mechanism.
Eddy ' current'- inspection + is. not
' applicable for tha support plates with-'a. quatrefoil broached hole design.
As WCNOC has earl'y Model F-design. steam generators, a sample inspection of the patch plate,1 plug _ weld regions, will be performed..For all Model F designs,-a sample inspection'of the top support plate, tube lane'rsgion (where flow holes are provided -instead of elongated slots) will be performed,'
Flow holes are
= used to provide strengthening of the ' top tube support plate for u-bend support.
If initial drilling produced a separated ligament, an evaluation of-the effect on the u-bend will be made.
Wrapper' Drop:
WCNOC verifies that sludge lance equipment can be inserted in Model' F steam generators without ' interference.
If. interference with the. sludge lance.
i equipment is detected, the lower' wrapper support. blocks will be visually
' inspected.
Sludge -lancing is performed at WCNOC each refuel outage unless trending indicates thats there 'will be very little sludge removed.
At this-point, sludge lancing is' performed every other outage.
Wrapper Cracking:
No inspection' is' recommended unless - evidence of wrapper misposition or tube damage in the periphery of the first tube support plate is. detected.
If-degradation is. detected, a visual inspection ' of the lower wrapper support-blocks will be conducted.
L Upper Package:
. Primary and Secondary moisture separators and the feed ring are inspected as part of WCNOC's normal upper steam drum inspection.
- The ~ significance..to tube integrity as a resultl of degradation of these ecomponents is primarily a loose part.
v Transition Cone Girth Weld:
- Inspected in accordance with the steam generator shell,Section XI 1989 edition,.in-service inspection requirements.
Feed Water Nozzle:
' Degradation of the thermal sleeve may affect the feed water nozzle.
Loose parts monitoring and in service inspection requirements for the feed water
[.
nozzle are completed as required.
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Attechment to ET 98-0022 P ga 10 of 11 Bafety Assessment 7he following safety concerns have been identified relative to ~ the French steam generator, internals degradation experience.
- Loss of tube support leading to steam generator tube wear and possible primary-to-secondary leakage or inadequate burst margins.
- More significant tube support plate deformation during a postulated LOCA
+SSE event resulting in unacceptable steam generator tube collapse or secondary-to primary in-leakage.
The generation of a loose object in the secondary side of a steam generator which may result in tube wear or impacting and possibly primary-to-secondary leakage.
Based on a review of Table 2.0, the only degradation types that may occur domestically that may result in the loss of tube support plate integrity are:
TSP flow hole / ligaments erosion-corrosion, TSP ligament cracking near the patch plates, and TSP ligament cracking in random areas.
There are no observations of post chemical cleaning inspections discovering any significant material losses.
There are no observations of any wrapper having dropped.
There are no observations of TSP ligament cracking or thinning that is progressive and continuing.
TSP ligament cracking or missing pieces of l
ligaments have been observed, but only in units with carbon steel TSPs with drilled round holes and flow holes.
WCNOC's Model F steam generators have stainless steel support plates with a quatrefoil design.
If used, future application of the voltage-based plugging criteria will also consider the presence of any missing ligaments.
The alternate plugging criteria would not be applied at these locations.
It is expected that there is no increased susceptibility to ligament cracking
)
near the wedge supports in the Model F steam generator design.
Existing calculations evaluating the effects of LOCA + SSE loadings on the tube bundle continue to apply in determining whether certain tubes should be removed from service in plants which do not currently apply voltage based plugging criteria; but, which may have steam generator tubes experiencing cracking at the tube support plate intersections.
Cracking has not been identified at WCNOC.
Another occurrence resulting from steam genurator internals degradation that may affect a steam generator from performing its intended safety function is the potentia? for tube wear and primary-to-secondary leakage due to the I
generation of a loose object on the secondary side of the steam generator.
This may occur due to erosion-corrosion of the moisture separators, tube l
support plate flow holes, or the occurrence of tube support plate ligament l
cracking.
If primary-to-secondary leakage should occur due to tube wear from a loose object, the expected consequences would be bounded by a single tube i
rupture event and, therefore, would remain within the current licensing bases of the plant.
It is WCNOC's position that loose objects should be removed from the steam generator.
Tubes observed to have visible damage will be eddy current inspected and plugged if found to be defective.
For the types of steam generator internals degradation anticipated at WCNOC, our program contains these elements such that steam generator internals degradation would be limited, and the tubes will remain capable of sustaining the conditions of normal operation, including operational transients, design basis accidents, external events, and natural phenomena permitting the affected steam generator to perform its intended safety function.
Eddy current inspection, FOSAR activities (during each refueling outage) and loose
Attcchment to ET 98-0022 P ga 11 of 11 parts monitors should help to ensure the maintenance of tube integrity during subsequent plant operation.
I Reference
{
1.
WCAP-15002, Rev.
1,
" Evaluation of EdF Steam Generator Internals Degradation - Impact of Causal Factors on Westinghouse Series 51 Steam Generators" 1
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