ML20195F508
| ML20195F508 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 11/17/1998 |
| From: | Swailes J NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NLS980189, NUDOCS 9811200016 | |
| Download: ML20195F508 (11) | |
Text
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1 Nebraska Public Power District Nebraska's Energy Leader j
NLS980189 November 17,1998 l
U.S. Nuclear Regulatory Commission Attention: Document Control Desk l
Washington, D.C. 20555-0001 j
Gentlemen:
Subject:
Main Steam Nozzle Weld Indication Revised Relief Request Cooper Nuclear Station, NRC Docket 50-298, DPR-45
Reference:
- 1. Letter (No. NLS980178) to USNRC Document Control Desk from J. H.
Swailes (NPPD), dated October 26,1998, " Main Steam Nozzle Weld i
Indication Relief Request"
- 2. Letter (No. NLS980182) to USNRC Document Control Desk from M. F.
Peckham for J. H. Swailes (NPPD), dated October 30,1998, " Main Steam i
Nozzle to Shell Weld Fracture Mechanics Evaluation" The purpose of this letter is to submit Relief Request RI-27, Revision I for Nuclear Regulatory j
Commission (NRC) review and approval. Relief Request RI-27, Revision 0 had been previously submitted per Reference 1, and supplemented per Reference 2. The attachments to this letter 1
(Relief Request RI-27, Revision 1, and Description ofIndication) supersede the information 1
provided in Reference 1. The attached information incorporates comments provided by the NRC in a telephone conference between NRC and the Nebraska Public Power District (District) on November 9,1998. The District requests approval of Relief Request RI-27 in accordance with 10CFR50.55a(a)(3)(ii).
The following is a summary of the changes reflected in the attached information:
i (Relief Request RI 27) has been reformatted to improve readability. Two subsections under section Basis for Relief have been created: Basis for Hardship, and Quality and Safety Basis for Relief. The technical information provided in this attachment, previously provided in Reference 1, has not been changed.
The Basis for Relief subsection of Attachment I contains additional discussion demonstrating l
hardship without a compensating increase in safety.
'^
9811200016 981117 PDR ADOCK 05000298 P
PDR r
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Cooper Nudear Station PO. Box 98/ Brownville, NE 68321-0098 Telephone: (402) 825-38H / Fax: (402) 825-5211 httpf/www nppd com
'NLS980189 November 17,1998 Page 2 of 3 l
The Quality and Safety Basis for Relief subsection of Attachment I contains expanded i
' discussion supporting the District's position that there is no quality or safety concern associated with the relief being requested. This section includes additional information i
supporting the position that the subject indication is from original construction, and is not l
service induced.
l l
The Proposed Alternate Examination section of Attachment I contains clarification as to which nozzles are to be inspected during the next period. The Proposed Alternate
. Examination section of Attachment I was also revised to reflect that reliefis based on l
10 CFR 50.55a(a)(3)(ii), instead of 10 CFR 50.55a(g)(6)(i).
- . (Description ofIndication) has been reformatted into three distinct subsections:
Dimensional Comparison, Sensitivity Comparison, and Acceptance Comparison to improve L
readability. The Conclusions section has been revised to provide explicit statements l
supporting the District's position that the subject indication is a welding discontinuity present l
since original construction. The sketches have been revised for clarification. The technical information for this attachment, previously provided in Reference 1, has not been changed.
l As required by Section XI of the ASME Code, the Main Steam Nozzle to Shell (Vessel) weld, N3A, will be reexamined during the next refueling outage. The nine (9) other nozzle to vessel L
welds scheduled for examination during the second period will also be examined during the next l
refueling outage. This includes the two additional Main Steam nozzle to vessel welds that were examined during the current refueling outage (Refueling Outage 18; RFO-18) in accordance with L
the proposed relief request. These two welds had no reportable indications.
' Based on the information provided in the attachments to this letter, in conjunction with
. Reference 2, the District requests approval of the relief request prior to startup from RFO-18, which is currently scheduled November 26,1998.
Should you have any questions concerning this matter, please contact me, j
Sincerely, i
L Jo H. S aile ice ent o uclear Energy l'
Itpm/dnm L
.- Attachments u
a
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o NLS980189 November 17,1998 Page 3 of 3
- cc: Regional Administrator
. USNRC - Region IV Senior Project Manager -
USNRC - NRR Project Directorate IV-1 Senior Resident Inspector USNRC NPG Distribution 1
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! to Cooper Nuclear Station l
NLS980189 Inservice Inspection Program Page1of3 l
l RELIEF REQUEST NUMBER: RI-27, REVISION 01 i
COMPONENT IDENTIFICATION l
Code Class:
1
References:
IWB-2430(a), ASME XI,1989 Edition l
Examination Category:
B-D Item Numbers:
B3.10
==
Description:==
Additional Examinations Component Numbers:
Main Steam Nozzle to Vessel Weld NVE-BD-N3A CODE REOUIREMENT IWB-2430(a) states that when examinations performed in accordance with Table IWB-2500-1 reveal indications exceeding the acceptance standards of Table IWB-3410-1, additional l
eraur. stions shall be performed during the same outage. The additional examinations shall include the remaining welds, areas, or parts included in the inspection item listing and scheduled c. ihis and the subsequent period.
BASIS FOR RELIEF During the Fall 1998 Refueling outage, the last outage of the first period, an indication was identified in Main Steam Nozzle toVessel weld N3A that exceeds the acceptance criteria of IWB-3512. This condition did not appear on the radiographs but it does have a sufficient interface to reflect ultrasonic signals. The indication was previously identified in 1976 and 1986.
However, it was incorrectly dispositioned as being located in the nozzle forging. The indication was identified again in 1998 (RFO-18) and dispositioned to be located in the weld. The indication has been evaluated as original construction and is acceptable for continued operation in accordance with IWB-3600. The evaluation results (fracture mechanics evaluation) were previously submitted to the NRC in Reference 2. This indication is similar to weld indications previously identified in three (3) of the Feedwater nozzle to vessel welds (Reference Relief Request RI-19). Specific reliefis requested on the basis that the required exanunations present a hardship and that the proposed alternative would provide an acceptable level of quality and safety.
Basis for Hardship The nine (9) nozzle to vessel weld examinations, scheduled for the first period of the Third Ten-year Interval, have been performed during the Fall 1998 Refueling oute;;e with the discovery of one reportable indication. The Code requires the current sample size to be expanded to include examinations required for the subsequent period, which is nine (9) additional nozzles. In l
order to plan, schedule, and perform the ultrasonic examinations of these additional welds, the nozzles are first hydrolyzed to reduce the dose, and then scaffolding is erected (as needed),
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Attachment I to Cooper Nuclear Station NLS980189 Inservice Inspection Program Page 2 of 3 insulation and shield blocks are removed, and the surface is cleaned. These activities, plus the time for the examinations, followed by the reinstallation of shield blocks and insulation, and scaffold removal will add several days to the outage. The dose for performing these additional weld examinations during RFO-18 is estimated to be 12 person-rem after hydrolyzing the nozzles. The district plans to reduce future outage radiation dose by implementing a j
modification to inject zine before RFO-19. Based on zine injection, less than 12 person-rem is estimated to be received when the examinations are performed again during the second period.
Furthennore, the performance of these additional examinations during RFO-18 would generate additional radioactive waste for disposal due to the housekeeping required after the completion of examinations. The increased exposure coupled with the increased industrial safety risk with erecting and working off scaffolding outweighs the benefits of examining the nira (9) additional nozzles. The above activities represent an unnecessary hardship without a compensating increase j
in safety as discussed below.
Quality and Safety Basis for Relief In regards to Quality and Safety, the following four (4) points provide the basis for relief from performing the second period inspections during RFO-18:
1)
The indication is a welding discontinuity that has been present since original construction based on the following:
a.
The indication is subsurface near the mid-depth of the nozzle and is considered to be an original fabrication discontinuity and not service induced. The only potential service degradation mechanisms that could affect the steam nozzles are fatigue, stress corrosion cracking and erosion corrosion. For all these mechanisms, cracking indications would be expected to occur at the inside surface.
b.
The indication is the same indication as was identified in 1976 and 1986. The two (2) previous examinations identified the indication as being in the nozzle forging instead of the weld as determined in 1998. (See Dimensional Comparison discussion in Attachment 2.) Since the location of the indication was incorrectly identified by previous examinations, the discrepancy or " condition" was entered into the District's corrective action program. A review of past examination records of the other nozzle to vessel welds was conducted to determine the " extent of conditions" with no similar conditions being identified.
c.
Tlie indication has not changed in size based on the recording data and evaluation of that data. (See Sensitivity Comparison discussion in Attachment 2.)
l 2)
Reportable indications have not been observed during previous examinations of the l
additional nine (9) nozzle to vessel welds.
3)
The District expanded the sample by completing examinations of two (2) additional Main Steam nozzle to vessel welds pursuant to later editions of the Code. No reportable
i Attachment I to Cooper Nuclear Station NLS980189 Insen' ice Inspection Program Page 3 of 3 indications were identified. The basis for limiting the expansion to two (2) additional Main Steam to vessel welds is discussed below-In the 1991 Addenda, IWB-2430(a) was revised to clarify that the additional examinations shall be selected from welds, areas, or parts of similar material and service.
This clarification was provided to ensure that the additional examinations focused on welds, areas, or parts that would be subject to a possible common service degradation mechanism. A common senice degradation mechanism does not exist for original welding related discontinuities. The Main Steam nozzles are unique when considering all aspects of service conditions applicable to reactor vessel nozzles. The most notable factor is that the main steam nozzles are in a steam anvironment during normal plant operation. The thermal cycles that the vessel can experience are not grealy different when comparing the upper vessel where the steam nozzles are located and the mid-vessel where most other nozzles are located. Ilowever, the steam environment has significantly different heat transfer properties which make the thermal response of the nozzles in the steam region different from those below the water line.
In addition to the main steam nozzles, the top head nozzles are also in the steam region.
However, the top head nozzles are small diameter nozzles welded to the hemispherical top head, where it isjust over three inches thick. The steam nozzles are 24 inch diameter nozzles welded to the six inch thick cylindrical shell. Therefore, the stress conditions associated with the nozzle-specific geometries are signific mtly difTerent. Therefore, it is appropriate to limit the expansion sample to two (2) Ma* i Steam to vessel welds.
4)
During RFO-19, at the beginning of the second period, al; nine (9) nozzles will be examined in accordance with the requirements for ASME Section XI. In addition, the nozzle N3A will be reexamined.
PROPOSED ALTERNATE EXAMINATION Based on the above discussion, the District requests that the additional examinations of nozzle to vessel welds during RFO-18 be limited to the two (2) completed Main Steam nozzle to vessel welds. In addition, as noted above, the nine (9) nozzle to vessel weld examinations scheduled for the second period will be completed in RFO-19 along with the reexamination of Main Steam Nozzle to Vessel weld N3A. This includes the reexamination of the two (2) additional Main Steam nozzle to vessel welds examined during RFO-18. Since the hardship is significant with no compensating increase in safety, reliefis requested in accordance with 10CFR50.55a(a)(3)(ii).
APPLICABLE TIME PERIOD Reliefis requested for the first period of the Third Ten-year Interval of the Inservice Inspection l
Program for CNS.
i r
- to NLS980189 Page1of4 Description ofIndication Examination IIistory Preservice ultrasonic examinations were performed in accordance with ASME Section XI,1971 Edition. No actual data reports were available for review; however the summary report for the preservice examinations shows Main Steam nozzle N3A as having no recordable indications.
)
During the first refueling outage in 1976, manual ultrasonic examinations were performed on nozzle N3A in accordance with the 1974 Edition of ASME Section XI. During the examination i
with the 60 shear wave transducer one (1) indication with the following parameters was i
recorded: Distance to weld centerline = 3.25"; Metal path to reflector = 5.4"; Length from Wo to maximum amplitude = 14.5"; and Maximum amplitude = 100% distance amplitude correction (DAC). The evaluation of this indication determined that it was located in the nozzle forging and not in the weld. See attached Sketch A.
Main Steam nozzle (N3A) was examined again in 1986 with similar results. During the examination with the 60 shear wave transducer one (1) recordable indication with the following parameters was recorded: "W" distance = 1.75"; Metal path to reflector = 5.3"; and Maximum amplitude = 90% DAC. The evaluation of this indication also determined that it was located in the nozzle forging and not in the weld. See attached Sketch B.
In 1998 (RFO-18) the examination with the 60 shear wave transducer identified one (1) recordable indication with the following parameters: "W" distance = 1.20"; Metal path to reflector = 5.5"; Length to maximum amplitude = 13"; and Maximum amplitude = 80% DAC.
This indication is located at mid-wall along the nozzle side fusion line between 10.5" and 22.75".
No flaw indication could be found in the nozzle forging as was found in 1976 and 1986. The following comparisons clarify the size and locational differences.
Comparison Dimensional Comnarison The construction drawings show the weld prep to be a 1.5" gap between the nozzle and the vessel wall with a backing ring attached to the outside. After welding, the backing ring was removed and a cosmetic weld cap was installed. This cap was machined to a 5.5" radius to provide a smooth transition between the nozzle outside diameter ar.d the vessel wall. This resulted in a weld cap which is approximately 3.5" wide on top of a weld which is 1.5" wide. Due to this 2.0" difference between the weld cap and weld width. the plotted location ofindications could also vary by 2.0" dependent on where the initial reference point "Wo" is located.
l l
The metal path to the reflector is very consistent in all three examinations which would indicate the same reflector. The 14.5" length from location in 1976 is consistent with the length of the I
1998 location. The differences in "W" locations (distance from the initial reference point "Wo")
.. to NLS980189 Page 2 0f 4 mdy be explained by differences in the reference point. If the 1976 data used the center of the weld crown cap as "Wo", then the 3.25" recorded is essertially the same measurement as the 1.2" location recorded in 1998 which used the nozzle blend radius weld toe as "Wo" reference.
Sensitivity Comnarison The 1976 and the 1986 examinations were performed to editions of the ASME code which required only a 50% DAC recording level with 0.9" increment measurements. Using this criterion, this indication was recorded as a series of spot indications which were observed all around the weld at this metal path. The 1998 data was recorded at 20% DAC levels which resulted in the 12.25" length. Other indications were observed below the 20% recording levels at the same metal path around the weld.
Acceptance Comnarison The flaw signal characteristics are typical of those of a slag type flaw with multiple reflectors and the ability to maintain signals over a wide range of skew angles. The flaw signal characteristics are not similar to those expected from lack of fusion or fatigue cracking. These indications have been recorded since 1976 considering the observed signal characteristics.
Because of the change in recording criteria, no direct comparisons can be made to the length of these indications. If the indications have been characterized as planar flaws in the weld metal in 1976 and 1986, additional information would have been recorded as required by procedure, and the flaw indications would have been evaluated for acceptance. Due to the evaluation of the indications as being non-relevant reflectors in the nozzle forging in 1976 or as being laminar reflectors in 1986, sufficient planar sizing data is not available to determine the acceptability of the indications to the standards of the Code Editions in effect at those times.
Conclusium 1)
The subject indication is a weld discontinuity indicative of slag inclusion that has been present since original construction.
2)
The subject indication is the same indication found in the 1976 and 1986 examinations.
3)
The change in dimensional characteristics of the subject indication is related to the change in sensitivity of the new technology and inspection techniques.
N 3A SK E-~C A
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NLS980189 s i PAGE 3 OF 4 lj 1998 INDICATION d
1976 EXAM SUPERIMPOSED 1976 INDICATION f
OVER THE 1998 EXAM SHADED AREA REPRESENTS 1998 Wo f
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SHADER AREA REPRESENTS 1998 INDICATION o
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- ATTACHMENT 3 LIST OF NRC COMMITMENTS l
l Corresporidence' No:
NLL980189 The'followinn table identifies those actions committed to oy the District in this document. Any other actions. discussed in the submittal represent intended or planned-actions by the District.
They are described to the NRC for the NRC's information and are
(
<nct' regulatory commitments.
Please notify the NL&S Manager at Cooper Nuclear Station of 9
any questions regarding this document or any associated regulatory commitments.
COMMITTED DATE col'MITMENT -
OR OUTAGE Reexamine Main Steam Nozzle to Vessel weld N3A,_as Refueling Outage
~
No.19 required by ASME XI.
Perform nine (9)' nozzle to vessel weld exan.inations, scheduled for the second period, during RFO-19.
This Refueling Outage
" *19 includes the reexamination of the two (2) additional Main Steam nozzle to vessel welds' examined during RPO-18.
1 L
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PROCEDURE NUMBER 0.42 l
REVISION NUMBER 6 l
PAG:] ' ' C;F 13 l
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