ML20153B472
| ML20153B472 | |
| Person / Time | |
|---|---|
| Issue date: | 06/16/1995 |
| From: | Sheron B NRC (Affiliation Not Assigned) |
| To: | Beckham J SOUTHERN NUCLEAR OPERATING CO. |
| Shared Package | |
| ML20153B354 | List: |
| References | |
| NUDOCS 9809230143 | |
| Download: ML20153B472 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION o
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June 16, 1990 l
Mr. J. T. Beckham Chairman, BWRVIP i
Southern Nuclear Operating Company 42 Inverness Center Parkway Birmingham, Alabama 35242
SUBJECT:
EVALUATION OF "BWR CORE SHROUD INSPECTION AND EVALUATION i
GUIDELINES," GENE-523-ll3-0894, REVISION 1. DATED MARCH 1995, 1
AND "BWRVIP CORE SHROUD NDE UNCERTAINTY & PROCEDURE STANDARD," DATED NOVEMBER 22, 1994
Dear Mr. Beckham:
On September 2, 1994, the Boiling Water Reactor Vessels and Internals Project (BWRVIP) issued its "BWR Core Shroud Inspection and Evaluation Guidelines."
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These guidelines provided the BWRVIP's recommended inspection strategy for performing examinations of BWR core shrouds and recommended flaw evaluation methodology. The staff issued its safety evaluation report (SER) regarding the original version of the guidelines on December 28, 1994. The staff issued a follow-up letter on March 6,1995, in order to clarify some of the content in their SER of December 28, 1994. By letter dated April 21, 1995, the BWRVIP submitted the report, "BWR Core Shroud Inspection and Evaluation Guidelines, Revision-1." This report was intended to provide the latest updates and changes to the original version of the "BWR Core Shroud Inspection and Evaluation Guidelines," which were issued on September 2, 1994.
By letter dated November 22, 1994, the BWRVIP submitted its "BWRVIP Core Shroud NDE Uncertainty and Procedure Standard." The standard provides the i
BWRVIP's recommended methods for performing non-destructive examinations (NDE) of BWR core shrouds. This letter provides the staff's SER regarding the BWRVIP submittals of November 22, 1994 (NDE standard) and April 22, 1995 (inspection and evaluation guidelines). The staff has identified the following items to be addressed by the BWRVIP.
1.
In regard to the BWRVIP's " Guidance for Reinspection of Core Shrouds,"
the staff urges the BWRVIP to determine if this document can be submitted at an earlier date, in order to support upcoming reinspections.
2.
Qualification of the inspection methods utilizing mock-ups of H-7 welds with and without backing rings should be expedited by the BWRV!P.
3.
The BWRVIP should develop inspection guidelines which address the inspection of core shroud welds that are considered to be critical in terms of assuring the structural integrity of core shroud repair assemblies. These guidelines should be submitted for NRC review pricr to the first reinspection of a repaired BWR core shroud.
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w Mr. J. T. Beckham 4.
In regard to performing limit load or linear elastic fracture mechanics evaluations of BWR core shrouds, the staff has not yet given credit for fillet welds in the shroud designs. Further justification and guidelines must be provided should licensees seek credit for core shroud fillet welds. The. content of the justification and guidelines should include supporting finite' element modeling and should address the capabilities and limitations ~ (e.g. threshold of detection) of the inspection method used for these fillet weld inspections. The justification and guidelines should also address flaw evaluation methods and criteria should cracking be detect 2d in the fillet welds. Where appropriate qualified field or test data on shroud fillet w growth rates is lacking, a bounding growth rate of 5 x 10', eld crack inches /hr should be assumed.
5.
The Staff finds the NDE uncertainty values for inspection delivery l
systems that haven't been evaluated by the BWRVIP to be reasonable based upon the inspection experience to date and experience with IGSCC.
It is unclear, however, from the submittal what procedures are available to evaluate or certify a given delivery system /NDE technique for use.
Additional guidelines should be established to clarify what sort of actions and steps are necessary in order to qualify NDE inspection technologies for use.
6.
The staff agrees that full size mock-ups for assessing the performance of NDE techniques will enhance core shroud evaluations. The staff requests that a schedule for completion and evaluation of these mock-ups be provided.
7.
The staff agrees that the UT sizing and detection methods employed by the 83WRVIP appear to be conservative. The staff is in agreement that UT creeping wave detection and sizing capabilities are reasonably accurate down to 0.02 inch crack depths. However, the lack of confidence in the far side UT measurements needs to be evaluated in a timely manner.
8.
The staff has reviewed the ET standard of the "BWR-VIP Core Shroud NDE i
Uncertainty and Procedure Standard," and does not have any unresolved issues in regard to its content at this time. However at this time ET has not been qualified as an acceptable method for performing examinations of core shrouds.
It appears that the schedule for j
qualification of ET techniques for internals is covered by the scopes of BWRVIP Inspection Milestones Numbers 2-8 [ Reference 7].
If not, the staff requests that a schedule be provided for ET qua'ification milestones. Should ET inspections be performed on core shrouds or other i
BWR internals in the field prior to qualification of the technique by i
the BWRVIP, the staff requests that the details of the technique, and appropriate field data and experience be included in future submittals i
to the staff, i
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t Mr. J. T. Beckham 9.
The current CWRVIP position in regard to performing examinations of BWR core shrouds is that UT testing is the preferred method of inspection.
Should VT be chosen as the primary examination method, the staff requests that the BWRVIP establish further criteria to account for VT sizing (measurement) uncertainties. These criteria should include establishment of a minimum acceptable VT adjustment value that shall be added VT determined flaw indications (flaw lengths).
These items are more comprehensively discussed in the staff's Safety Evaluation Report enclosed with this letter. Please address any questions regarding the staff evaluation to Mr. Robert A. Hermann of my staff at (301) 415-2768.
e s$'N[d#$GNED BY o
ga M W.SHERON Brian W. Sheron, Director Division of Engineering Office of Huclear Reactor Regulation cc:
E. G. Carpenter Di tribution:
t Central Files KKavanagh EMCB RF RCJones Concurrence:
DOCUMENT NAME: G:\\ SHROUD \\BWRVIP.EVL
- See Previous Concurrences To rsceive e copy of tNe document. indicate in the bes: *C' = Copy without enclosuree *E' = Copy with enclosures /$ = No copy 0FFICE
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