ML20134A434
| ML20134A434 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/24/1997 |
| From: | Sepp H WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Miraglia F NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20134A428 | List: |
| References | |
| AW-97-1072, NUDOCS 9701280301 | |
| Download: ML20134A434 (8) | |
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Westinghouse EnergySystems Nuclear Services Division
- Electric Corporation m ass i Pmsburgh Pennsylvanta 15230 0355 January 24,1997 AW-97-1072 Document Control Desk U.S. Nuclear Regulatory Commission
- Washington, DC 20555 1
Atten; ion: Mr. Frank J. Miraglia 3
APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE
Subject:
" Incomplete Rod Insertions During Cycle 8 - Interim Report on Inspection Plan, Inspection Results and Root Cause," Rev.1 (Proprietary)
Dear Mr. Miraglia:
The application for withholding is submitted by Westinghouse Electric Corporation (" Westinghouse")
pursuant to the provisions of paragraph (b)(1) of Section 2.790 of the Commission's regulations. It contains commercial strategic information proprietary to Westinghouse and customarily held in confidence.
The proprietary material for which withholding is being requested is identified in the proprietary version of the subject report. In conformance with 10 CFR Section 2.790, Affidavit AW-97-1072 accompanies this application for withholding, setting forth the basis on which the identified proprietary information may be withheld from public disclosure.
Accordingly, it is respectfully requested that the subject information which is proprietary to Westinghouse be withheld from public disclosure in accordance with 10CFR Section 2.790 of the Commission's regulations.
Correspondence with respect to this application for withholding or the accompanying affidavit should reference AW-97-1072 and should be addressed to the undersigned.
Very truly yours, H. A. Se , anager Regulatory and Licensing Engineering Enclosure cc: Kevin Bohrer/NRC (12H5) 9701280301 970124 PDR ADOCK 05000482 p PDR 2320-Dlot:012497
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i Proprietary Information Notice Transmitted herewith are proprietary and/or non-proprietary versions of documents furnished to the NRC in connection with requests for generic and/or plant-specific review and approval.
In order to conform to the requirements of 10 CFR 2.790 of the Commission's regulations concerning the protection of proprietary information so submitted to the NRC, the information which is proprietary in the proprietary versions is contamed within brackets, and where the proprietary information has been deleted in the non-proprietary versions, only the brackets remain (the infonnation that was contained within the brackets in the proprietary versions having been deleted). !
The justification for claimmg the information so designated as proprietary is indicated in both versions by means of lower case letters (a) through (f) contained within parentheses located as a superscript ,
, i immediately following the brackets enclosing each item of information being identified as proprietary I or in the margin opposite such information. 'Ihese lower case letters refer to the types of information Westinghouse customarily holds in confidence identified in Sections (4)(ii)(a) through (4)(ii)(f) of the affidavit accompanying this transmittal pursuant to 10 CFR 2.790(b)(1).
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1, Copyright Notice I
ne reports transmitted herewith each bear a Westinghouse copyright notice. The NRC is permitted to make the number of copies of the information contamed in these reports which are necessary for its
) internal use in connection with generic and plant-specific reviews and approvals as well as the i
issuance, denial, amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of 10 CFR 2,790 regarding l restrictions on public disclosure to the extent such information has been identified as proprietary by Westinghouse, copyright protection notwithstanding. With respect to the non-proprietary versions of these reports, the NRC is permitted to make the number of copies beyond those necessary for its
- internal use which are necessary in order to have one copy available for public viewing in the appropriate docket files in the public document room in Washington, DC and in local public -
document rooms as may be required by NRC regulations if the number of copies submitted is 3 insufficient for this purpose. Copies made by the NRC must include the copyright notice in all f instances and the proprietary notice if the original was identified as proprietary.
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AW-97-1072 AFFIDAVIT COMMONWEALTH OF PENNSYLVANIA:
ss I COUNTY OF ALLEGHENY: )
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Before me, the undersigned authority, personally appeared Henry A. Sepp, who, being by me duly sworn according to law, deposes and says that he is authorized to execute this Affidavit on l behalf of Westinghouse Electric Corporation (" Westinghouse") and that the averments of fact set forth in this Affidavit are true and correct to the best of his knowledge, information, and belief: I I
h //N Henry A. Sepp, Manager Regulatory and Licensing Engineering Sworn to and subscribed befo e this JYM day o _ e.A>./ -
, 1997 Notarial Seal Janet A. Schwab, Notary Public Monroeville Boro, Allegheny County My Commission Expires May 22,2000
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/y- Notary Public Member, Penrcylvania Ascaelation et flotaries 0
2321C-DW1:012497
AW-97-1072 l
l (1) I am Manager, Regulatory and Licensing Engineering, in the Nuclear Services Division, of the Westinghouse Electric Corporation and as such, I have been specifically delegated the function of reviewing the proprietarv information sought to be withheld from public disclosure in connection with nuclear power plant licensing and rulemaking proceedings, and am authorized to apply for its withholding on behalf of the Westinghouse Energy Systems Business Unit.
(2) I am making this Affidavit in conformance with the provisions of 10CFR Section 2.790 of the Commission's regulations and in conjunction with the Westinghouse application for withholding accompanying this Affidavit.
(3) I have personal knowledge of the criteria and procedures utilized by the Westinghouse Energy Systems Business Unit in designating information as a trade secret, privileged or as confidential commercial or financial information. l i
(4) Pursuant to the provisions of paragraph (b)(4) of Section 2.790 of the Commission's regulations, the following is furnished for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld.
(i) The information sought to be withheld from public disclosure is owned and has been held in confidence by Westinghouse.
(ii) The information is of a type customarily held in confidence by Westinghouse and not customarily disclosed to the public. Westinghouse has a rational basis for determining the types of information customarily held in confidence by it and, in that connection, utilizes a system to determine when and whether to hold certain types of information in confidence. The application of that system and the substance of that system constitutes Westinghouse policy and provides the rational basis required.
Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential competitive advantage, as follows:
2321C-Dir-2:012407
l AW-97-1072 l
i l (a) De information reveals the distinguishing aspects of a process (or component, l structure, tool, method, etc.) where prevention of its use by any of Westinghouse's competitors without license from Westinghouse constitutes a competitive economic advantage over other companies.
(b) It consists of supporting data, including test data, relative to a process (or component, structure, tool, mahod, etc.), the application of which data l secures a competitive economic advantage, e.g., by optimization or improved marketability.
i (c) Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, l assurance of quality, or licensing a similar product.
l (d) It reveals cost or price information, production capacities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers.
(e) It reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.
l (f) It contains patentable ideas, for which patent protection may be desirable.
There are sound policy reasons behind the Westinghouse system which include the following:
(a) he use of such information by Westinghouse gives Westinghouse a competitive advantage over its competitors. It is, therefore, withheld from disclosure to protect the Westinghouse competitive position, i
(b) It is information which is marketable in many ways. The extent to which such information is available to competitors diminishes the Westinghouse abPity to sell products and services involving the use of the information.
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, AW-97-1072 l
(c) Use by our competitor would put Westinghouse at a competitive disadvantage by reducing his expenditure of resources at our expense.
(d) Each component of proprietary information pertinent to a particular competitive advantage is potentially as valuable as the total competitive advantage. If competitors acquire components of proprietary information, any one component may be the key to the entire puzzle, thereby depriving Westinghouse of a competitive advantage.
(e) Unrestricted disclosure would jeopardize the position of prominence of Westinghouse in the world market, and thereby give a market advantage to the competition of those countries.
(f) De Westinghouse capacity to invest corporate assets in research and l l
development depends upon the success in obtaining and maintaining a competitive advantage.
(iii) De information is being transmitted to the Commission in confMence and, under the provisions of 10CFR Section 2.790, it is to be received in .:onfidence by the Commission.
(iv) De information sought to be protected is not available in public sources or available information has not been previously employed in the same original manner or method to the best of our knowledge and belief. l (v) De proprietary information sought to be withheld in this submittal is that which is 1 appropriately marked in " Incomplete Rod Insertions During Cycle 8 - Interim Report on Inspection Plan, Inspection Results and Root Cause," Rev.1 (Proprietary), for the Wolf Creek Nuclear Station, being transmitted by the Westinghouse Electric Corporation O!(.) letter and Application for Withholding Proprietary Information from Public Disclosure, Mr. H. A. Sepp to the Document Control Desk, Attention Mr. Frank J. Miraglia. De proprietary information as submitted for use by the Westinghouse Electric Corporation is expected to be applicable in other licensee 2321C-DLC-4S12W7
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AW-97-1072 !
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submittals in response to certain NRC requirements for justification of RCCA insertions, inspections and evaluation criteria.
- This information is part of that which will enable Westinghouse to:
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(a) Establish applicable RCCA inspection and evaluation criteria.
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(b) Perform and provide RCCA inspections and evaluations. l 1
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- Further this information has substantial commercial value as follows:
(a) Westinghouse can sell support and defense of RCCA inspection and evaluation criteria.
Public disclosure of this proprietary information is likely to cause substantial harm to the competitive position of Westinghouse because it would enhance the ability of competitors to provide similar RCCA inspection and evaluation criteria and licensing defense services for commercial power reactors without commensurate expenses. l J
Also, public disclosure of the information would enable others to use the information j to meet NRC requirements for licensing documentation without purchasing the right to I use the information. l l
l The development of the technology described in part by the information is the 1 ault of applying the results of many years of experience in an intensive Westinghouse effort and the expenditure of a considerable sum of money.
In order for competitors of Westinghouse to duplicate this information, similar technical programs would have to be performed and a significant manpower effort, having the requisite talent and experience, would have to be expended for developing RCCA inspection and evaluation criteria.
Further the deponent sayeth not.
2321C-DLf-5:012&7
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Westinghouse Non Proprietary Class 3 i
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1 ENCLOSURE 2 Wolf Creek Nuclear Operating Corporation Wolf Creek Nuclear Station Incomplete Rod Insertions During Cycle 8 Interim Report on Inspection Plan, Inspection Results and Root Cause Westinghouse Non-Proprietary Class 3 - REV l
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! Wolf Creek incomplete Rod insertions During Cycle a i
interim Report on Inspection Plan, inspection Results and Root Cause l March,1996 i
5 l J. F. Duran j J. Halligan
- N. R. Singleton l
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Preface -
Several activities were undertaken by Wolf Creek and Westinghouse to address the t
^ incomplete RCCA insertions that occurred at Wolf Creek near the end of cycle 8.
These activities included the preparation, review and implementation of a test plan and !
j the formation of a root cause team. !
i This report includes the test plan, a summary of the test results and a summary of the 1 I
work and conclusions of the root cause team. i l This report was prepared to provide information to support cycle 9 core loading at Wolf A Creek.
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Contents- '
1.0 Test Plan 2.0 Results of Inspections 3.0. Root Cause Evaluation 4 1
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! 1.0 Test Pfan j 1.1 Cold Drop Tests
)i PURPOSE To determine the behavior of the RCCA's in a simulated trip. It is noted conditions will be different due to temperature. This will be a ' worst case' i
since the compression on the assemblies as well as the water density will be j
higher than operating conditions. Traces on a strip cr art are taken to determine j
the velocity of the RCCA's as a function of axial position. Recoils are to be j
observed to estimate the amount of drag on assemblies that are f. illy seated.
1 The behavior of the once burned assemblies are used as a base line for i comparison.
! TEST ASSEMBLIES - All RCCA locations.
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- 1.2 Drag Test with Upper Intemals in Place i
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- PURPOSE - To detem1ine the drag on RCCA's in the fuel assemblies with the 1 i
j drive shaft latched. Traces are taken to show drag as a function of axial position. j This data will be compared to drag data taken later in the spent fuel pool to '
i determine the impact of the upper intamals on the RCCA drag. Specification F-l 5.1 is used as a starting point to define 'high' and ' low' drag.
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TEST ASSEMBLIES - Assemblies are selected based on the following: i a) Failure to fully insert in trip or cold drop b) Number of recoils
, c) Various bumups are included i
1.3 Drag Tests in Spent Fuel Pool -
! PURPOSE - To determine the location of the interference causing the high drag. ,
! Possible Locaties Upper intomale l
} -RCCA )
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- Fuel assembly
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Combination of the above i
j TEST SEQUENCE:
- a) Drag test RCCA's in current fuel assemblies ,
j b) Drag test RCCA's in reference fuel assemblies l j c) Drag test dummy RCCA in selected fusi assemblies I TEST ASSEMBLIES - Fuel assemblies (with RCCA's) are selected based )
- on the following
i a) Failure to fully insert in trip or cold drop i
i b) Results of drag tests in core 4
- c) Assemblies at various burnups are included i
d) Assembly H81 (removed last cycfc due to i
high drag) is included.
The results of the above drag tests may determine the interference is in the upper intemals. In this case the internals will be examined. If it is determined the interference is caused by a prcblem in the RCCA, the following inspections j will be conducted.
a) visual inspection of spider and rodlets, if the cause of the high drag I can be determined by this visual, additional inspections will not be j
necessary to determine the root cause. At this point a new plan would be needed to determine a corrective action. i l
b) If the cause of the high drag is not determined an ed6/ carrent l l inspection will be conducted. At this point a new plan will be needed to j determine a corrective action or continue the investigation cf the root i cause.
l If it is determined from the above drag tests that the interference is caused by a j problem in the fuel assemblies, the following actions will be taken. .
1 i a) All of the fuel assemblies drag tested in the spent fuel pool are to receive :
- a visual inspection of the top nozzle and tcp nozzle inserts.
- F/A length measurements Fuel assembly bow measurements i b) Boroscope inspection of thimble tubes (on selected assemblies)
- If the cause of the high drag can be determined from these inspections a new plan would be needed to determine a corrective action. If the root cause has not been determined selected fuel assemblies will be drag tested with the short RCCA standard. The bases for selection is the results of the spent fuel pool drag ,
tests and the value of other assemblies for comparison. l if the short RCCA standard indicates the top of the fuel assembly is the location ;
of the interference, a fuel assembly will be selected (based on short standard drag results) and rotested with 22 lock tubes removed. The two remaining lock tubes will be in opposite corners. The data will be put aside for future comparison.
The remaining two lock tubes and the top nozzle will then be removed and the top nozzle inserts inspected. If the cause of the high drag can be determined at this point, a new plan will be needed to determine a corrective action.
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A RRTN will then be installed and the drag with the short standard repeated.
! Using the data from the three drag tests with the short RCCA standard the
! incremental change from removing the lock tubes and use of the RRTN can be j determined. Judgement will be used to determine if this is significant. At this j point a new plan may be needed to determine a corrective action or continue the investigation.
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j If it was determined by the short standard that there is no problem at the top of the fuel assembly, the focus will be on the dashpot. The thimble tubes of j~ selected fusi assemblies will be probed with a series of single tube probes at various diameters and lengths designed to determine the condition of the dashpot i.e. bowed , kinked or restricted. The assemblies are selected based on previous drag tests with the full length RCCA's. A control assembly (once burned) will also be tested and the data used for comparison.
If the root cause of the high drag can be determined at this point a how plan will be needed to determine a corrective action. If it is determined the dashpot shows I no anomaly, or is only a partial cause, the upper part of the guide thimbies will !
be investigated. A series of probes similar to the dashpot probes are designed to l determine the condition of the guide thimbles (major diameter).
If the root cause can be determined at this point, a new plan will be required to determine a corrective action. If the root cause is not determined, a new plan will be needed to continue the investigation.
The inspection plan logic tree is shown in Figure 1-1.
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I Figure 1 Wolf Creek Decision Tree for RCCA Insertion Anomaly I
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) 0'89 feelLocesses aw o we'arce'eg
]
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- eve Seers eMer wrweicecy 1
! '.$w l Orne few teen Asaemosy .n spo b asses inseraes
,,, l_ ,, , l:
i 8emove eCCAe & Crag wan i,o, I C m eCCA '
'aseos eCCAs
"'?' 'or Corneo.
-Camage seen-s swa e.sermessen of No Carnage Seen (aw Nesse &insens 1t ir
,, Oreg e Owevisy rr/A C*'*'une sees of esmoge I 7 A Langei weeswomenes l
1r N s/A ges useawomene 4 EserC m ras I **=ese I 1
,, A Crag.e sn : smos rm !
Eveemse ses
- Crag wei snest STO -te, ,,
l l Crag een Long Sage twee s eraeve ed out 2 We fuese
& Creg man Shen 370 b ew i% ,
L uneepenese Ceanese e samme er asses e arneee too neene n W eteest eemq. 0
,, Coenseie eenos insten ARTM & nos est sourse W Cesennae Casse tuees #**""""
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7 teessetNesse8erCameps ----e Canee W
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.an targer meHus stones IP L88 ,b ;
senses fee fhenees Twees Camage Oteerwee
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2.0 Results of Inspections l
l 2.1 i Trip near EOC 8 - 5 RCCA's failed to fully insert. The following fuel assemblies were involved, 1 i Core Position Fuel Assembly
' H02 H16 '
F06 H50 K06 H53 1
, K10 H59 H08 H38 1
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NOTES: - all involved fuel assemblies are three times burned.
j burn up ranges from approximately 49100 to 51500.
I 2.2 Cold drop tests - Cold drop tests were performed on all RCCA's
- In addition to the five assemblies above the following three assemblies failed to
- fully insert.
Core Position Fuei / ssembly H14 H11 PO8 H03 l
B08 H32 .
j OBSERVATIONS - Drag seems to correlate with high burnup
- Assembly H16 (using a hafnium RCCA) stuck at 96 steps.
] - The magnitude of the initial recoil bounce and the quantity 1 of subsequent bounces appears to decrease with burnup i but the data is more difficult to reliably interpret and j appears less consistent than the drag force measurement.
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] DATA : Summary sheet from Wolf Creek I
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2.3 Drag Tests With Upper Intemals in Place - A total of 27 RCCA's were tested with the upper intomale in place, including all of the assemblies that failed to fully insert (except H18, H03, H59 and H53) during the cold drop tests, and various bumups, Core Position Fuel Assembly Tested Tested HOS J35 j KOS J29 B10 J58 i POS J63 i F14 J50 j P10 J64 1
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a 808 H32 i H14 H11 FOS H50 F10 H45 012 J32
- D04 J08 H08 H38 002 K06 812 K46
)l 014 K22 l M02 K15 i C09 J28 NC7 J30 C07 J03 J03 J25 i L13 J37
[ NOS J52 .
j N11 J39 l LO3 J45 l HM HM
- H12 H54 f
j Observadons The high bumup assemblies continue to show the highest drag.
The observed drags do not exceed the weight of the ACCA and drive rod.
f In general, drag decreases with distance from the dashpot j - Chatter appeared on a number of the traces for the ' problem'
- assemblies.
l DATA: Summary sheet from Wolf Creek
- 2.4 Drag Test in Spent Fuel Pool - RCCA's in Fuel Assembly A total of 18 j assemblies were selected for this test, induding all eight that failed to fully
{ insert during cold drops.
l - Two additional region 'H' assemblies that showed high drag.
l - Four 'J' assemblies with various bumups
! - Two 'K' assemblies (control) i l FUEL ASSEMBLIES TESTED l Fuel Assem:Ay RCCA I H16 R27 i H53 RS31
- H32 RS42 i H50 RS19 i H11 RS21
- H59 RS13 H03 RS11 li H38 RS29 j
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J37 RS28 j
J03 RS23 i K48 RS40 l J52 RS30 j J50 RSO9 i
K06 RS01 H45 RS22 H54 RS18
, OBSERVATIONS; i i
- The data continues to show a correlation between high bumup and !
high drag. '
- Chatter was observed on most of the high drag assemblies.
j It starts above the dashpot on withdraw and stops at about halfway up I i the F/A 4 l
- Observed at the same location on insertion i
- The hafnium RCCA showed chatter at a much different frequency and I amplitude .
l - On assembly H38 and H50, the RCCA did not fully insert by its' own 3 weight. '
i In general drag decreases with distance from the dashpot.
] DATA: Traces from Wolf Creek & summary data sheets from CNFD.
i j CONCLUSION: Results are generally consistent with drag tests performed with j the intomals in place. Drag increases with increasing bumup.
2.4.1 Drag Test with Short RCCA -
A drag test was performed using a mock RCCA with 13 inch long rodlets.
The tested fuel assemblies are J03, H53, H50, H38, H16. H81, and K06. ;
OBSERVATIONS . ]
- The drag was measured at [ ] pounds with the exception of assembly H16 which was [ ]
- pounds. The once burned control assembly (K06) had less drag than the twice and thrice burned assemblies.
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2.5 Orag Test of RCCA's in Reference Fuel Assembly The 16 RCCA's tested above, were drag tested in a new fuel assembly.
i CBSERVLTIONS - All 16 RCCA's (including the Hafnium) showed a drag of less than [ ] pounds. It was concluded the high drag is resulting from the fuel assembly. No further testing of the RCCA's is required.
i b DATA: Traces from Wolf Creek and summary from CNFD.
i l CONCLUSION: Since all RCCA's tested showed low drag, the source of friction 3 must be the fuel assembly.
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- 2.6 Fuoi Assembly Length Measurements - Length measurements were conducted on the above fuel assemblies (drag tested) and assembly H81(removed from core last cycle due to high drag). Additional measurements were taken on the j following fuel assemblies: G46, G35, G18 H43. H62, H07, J61 J29 and J46.
i i OBSERVATIONS: - The region 'H' assemblies showed higher than expected j growth .
i - Growth of the fuel rods was less than anticipated .
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- The fuel rods were observed to be resting on the top plate of the bottom nozzle (as expected)
{ - The gap between the fuel rod top end plugs and the j bottom surface of the top nozzle adapter appears to be j significantly larger than anticipated .
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- DATA
- Video tapes from Wolf Craok. and measurement summary sheets from CNFD.
I j CONCLUSION: Region 'H' assembeles showed a higher growth than previous i experience. Although tPc fuel assemblies were longer than anticipated, as built l i
reactor core dimensiorn iedicate there was no ' solid
- Interference with intomals. i i
i 2.7 Fuel Assembly Bow Measurements Bow measurements were taken on the
- same 17 fuel assemblies on which length measurements were taken.
t l OBSERVATIONS: Fuel assembly bow was judged to be within the ' normal' l j range based on the Westinghouse experience base. Bow tended to be larger on ,
j the higher bumup asw )blies.
! DATA: Video tapes from Wolf Creek, and measurement summary sheets from
! CNFD.
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i CONCLUSION:
j Since these measurements indicate ' banana
- bow cf simil shape and magnitude as previously observed in other plants and fuel types, it 1 should not in itself be a major contnbutor to the high drag observations .
' 2.8.
Boroscope inspection - The following assemblies were selected for borescope inspection; H38, H16, H81, J03, K06. {
OBSERVATIONS: Rub marks possibly indicating high drag were observed on H38, H18 and H81.The extent and pattom of rub marks varies with burnup. The marks on higher burnup assemblies tend to form a spiral pattern in the axial direction. The marks on lower bumup assemblies tend to be less pronounced and relatively straight.
DATA: Tapes from Wolf Creek, and summary sheets from CNFD.
CONCLUSION: These observations indicate deformation in the thimble tubes which increase with burnup. This deformation at high burnup has' a spiral shape or characteristic.
2.9 Single Tube Probes . The following fuel assemblies were selected for probing the single guide thimbles with the single tube probee: K06,H16,H38,H53,H81, H50,J03.
GO/NO GO tests have been completed on the above assemblies. Also drag measurements have been made on selected assemblies using probe 5 (small probe for upper guide thimble) and the .381 diameter full length probe (simulation of RCCA rodlet).
OBSERVATIONS: .
The drag is not predominately due to grid distortion or growth
- Single tube probing shows drag in all region 'H' assemblies.
- Thimbles on the periphery do not show higher drag than thimbles close to the axial centerline.
DATA : Data sheets from Wolf Creek, and analysis summary from CNFD.
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CONCLUSIONS:
Since the probes were designed in a combination of diameters and i
lengths to determine the extent, nature, and shape of any distortion, the following conclusions can be drawn:
- Thimbles are distorted at both dashpot and major diameter elevations.
The probes were designed at diameters to test this.
- Thimble tube cross section distortion (such as ovaling) is not a major .
- contributor to the drag on the RCCA rodlets. The probes are designed i
in a combination of lengths and diameters to detect this.
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! 3.0 i
Root Cause Evaluation i
j 3.1 Background 1
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! On February 19,1996 a root cause team was organized to determine the root J cause of the incomplete RCCA insertion issue. The team included j representatives from Wolf Creek, South Texas and several Westinghouse divisions.
jl The team evaluated three established root cause analysis tools, shown below, to select a method which would be the most effective in evaluating the data which j was available at the time.
- Root Cause Analysis (Causal Factor)
- Change Analysis -
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- Kepner-Tregoe Problem Analysis '
1 The Kepner Tregoe Problem Analysis technique was selected by the team since I
! the specific cause of the incomplete RCCA insertion was not known at the time j the team was convened.
! The Kepner-Tregoe Problem Analysis approach consists of the four main l phases shown below.
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- Describe Problem I
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- Identify Probable Causes l
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- Evaluate Probable Causee
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- Confirm True Cause l 3.2 Summary of Evaluadon i
i The apparent cause of the incomplete RCCA insertion at the Wolf Creek plant j has been determined to be fuel assembly thimble tube distortion. The possible l contributing and root causes which are considered to be associated with the .
l thimble tube distortion are shown in Figure 3-1. The possible causes that were
! determined not to be root causes and the bases for these determinations are j shown in Figure 3-2.
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! A plan for confirmation of the root cause(s) and development of predictive i analytical techniques is being developed.
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}' At appropriate times in the future the root cause team will meet with the l l
designers to complete the root cause confirmation phase of the Kepner Tregoe l process. l 14
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j Figure 31: Olrect Cause ofincomplete Rod insertion at Wo:f Creek i
j Direct CJuee: Thimble tube distortion i
Possible contributina causes Primary Focus :
i Fuel rod (less than expected) to thimble tube (greater than expected) differential growth
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'a Thimble tube to thimble tube differential growth l Secondary Focus :
{ Fuel assembly bow i
! Fuel assembly axial growth l
Thimble tube wall thickness variation f j Thermal creep
{ Irradiation creep l Thimble tube fixity i
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Possible rxt causes 4 1
Higher burnup causes atypical growth
! Region 'H' assemblies have unique manufacturing or materials issue
! Standard Zirc-4 vs. Improved Zre 4 h
j Thimble tube increased axial compression loading i
t
- Residency tirne 1
Grid spring ' orientation Y
j 15 t
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- Figure 3-2
i Possible Causes incomplete That RCCA Insertion Have Been Discounted For The Wolf Cre j Possible Cause
- Reason Cause Discounted
) Control Rod Drive Mechanisms Large clearances between driveshaft and rod (CROMs) travel housing. Drag testing indicated high j
2 RCCA/ fuel assembly drag following removal of the CRDMs with the reactor vessel closure head.
RCCAs Successful drag testing of the RCCAs in a j
1 fresh fuel assembly i Reactor Vessel Intemals Drag testing of the RCCAs and fuel assemblies i Package and CRDM drive shaft in the spent fuel pool were similar to the drag
! test performed in the vessel l
Grid Distortion / Radial Growth Drag exists with single cylinder probes. Outer i thimble drag equal to or less than drag on inner j thimbles.
l Thimble Tube Ovality An .008 inch clearance probe passed through j
some upper thimbles, when a longer, smaller i j diameter probe would not. 1 I Localized Thimble Tube Wear marks inside thimbles having higher drag l Diameter Reductions were over most of the length of the thimble l Nk.
l Fuoi Assembly Top Nozzle Not apparent in visual observations, no RCCA l Cocking insertion degradation apparent earty in the
! drop test traces.
! Crud and Debrie Drags - repeatable for several (all tries) excursions. Heavy crud / debris not evident in
{
- the thimble tube boroscope examinations.
j Relatively similar scram / drag results for several
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assemblies, e
l Hard Contact of the Fuel Overall height of the highest fuel assembly was l Assembly with the Reactor determined to be within the as-built core cavity j Intemals Upper Core Plate height.
4 l Reactor Coolant System No basis as causal factor is known j Chemistry I l j
16 l
j - .-
i 3.3 Description of Problem The statement of the problem for the root cause evaluation was:
- *RCCAs Do Not Fully insert into Fuel Assemblies During Red Drop' Following the Kepner Tregoe methods, the information on what, where, extent and wnen the problem occurs in Wolf Creek data are listed in Figure 3 3 (Fuel Assembly core j tocations may be taken from Figure 3 4). These results show that i
all RCCAs entered the dashpot prior to stopping duitng the scram f
- the RCCAs, stopped after entry into the dashpot (32 steps) on a!I assemblies j during cold drop except H16 which had Hafnium in the RCCA rodlets j
- all of the assemblies that had incomplete insertion after trip had incomplete j insertion during cold rod drop testing and three additional assemblies that inserted fully during the trip did not fully insert during the cold rod drop testing, j
Factors that differ between hot and cold reactor conditions include:
l -
thermal differential growth between the fuel assemblies and core cavity, resulting in a somewhat higher assembly hold down spring force at cold conditions Primary coolant viscosity, resulting in higher hydraulic friction forces acting on the RCCA and Driveline surfaces at cold conditions a
the assembiles with incomplete insertion had bumups between 49,100 MWD /MTU and 51,500 MWD /MTU.
The Kepner Tregoe technique next calls for Identification of what, where, extent and when the problem did not occur. This is shown in Figure 3-5 which lists the remainder of the fuel assemblies in rodded poestions during cycle 8 at Wolf Creek (5 additional 'H', 32 'J, and 8
'K' assemblies) and their bumup at the time of the rod drop tests. It is noted that
- the burnup of the assemblies was less than or equal to 44,700 MWO/MTV with the exception of assembly H46
- RCCA inseition velocity traces indicated that some resistance also occurred in assembly H46 during the drop test (as evidenced by no recoil of the RCCA at the end of insertion).
In preparation for listing possible root causes, the distinctions felt to be notable between assemblies for which incomplete insertica occurred and other assemblies were listed (Figure 3-6).
17
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I l Figure 3-3 PROBLDE . GENERAL: RCCA'S DO NOT FULLY INSERT INTO FUEL AS i
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4 Figure 34 Locations of Rodded Core Locations at Wolf Creek 4
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- PROBLEM - GENERAL: RCCA'S DO NOT FULLY WSEAT WTO FUEL 1
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Figure 34. DISTINCTIONS (IS vs IS NOT)
- 1. Burnup (greater than 49K vs. less than 45)
- 2. Bank (D + C vs. all others (SE))
- 3. Region 'H' assy's only affected (but not all)
- 4. Region 'H' ase/s affected/ region 'G"s not affected (?) similar BU L
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3.4 Possible Root Causes and Evaluation of Causes i
! Possible root causes developed by the root cause team are listed in the first column of Figure 3-7. This table was initiated before the implementation of the j
inspection plan in Section 2 was begun. To eliminate or support these causes, i results from Wolf Creek inspections and tests, and the successful rod drops at the beginning of cycle 8 were used as well as judgement and experience. Key
! Wolf Creek inspection and test results used by the root cause team in j eliminating possible root causes are described in Section 2.0, From these results, some of which are reflected in Figure 3 7, the root causet listed in Figure 3-2 were eliminated and the remaining root cause - thimble distortion -
remained.
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- 3.5 Confirmation of Root Cause 1
Based on the present knowledge of the problem, a program of additional inspections, tests and analyses is being developed.
i 1
1 The primary intents of this program are:
1 To improve the understanding and enable quantification of the sources of
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the forces that are significant to cause thimble tube distortion
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To refine tools for prediction of thimble distortion and their e ' set on i
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