ML18033B092
| ML18033B092 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 12/21/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18033B091 | List: |
| References | |
| GL-88-01, GL-88-1, NUDOCS 8912280069 | |
| Download: ML18033B092 (7) | |
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I UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE SAFETY EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPLEMENTAL RESPONSES TO GENERIC LETTER 88-01 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR POWER PLANT UNIT 2 BFN
1.0 INTRODUCTION
This evaluation addresses supplemental responses by the licensee, the Tennessee Valley Authority (TVA), dated January 12, 1989, and June 30, 1989, to GL 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping".
TVA's original response to GL 88-01, a letter dated August 1, 1988, was evaluated by NRC in a letter dated December 8; 1988.
The review of TVA's letter and previous responses to GL 84-11 revealed that TVA had not conducted sample expansion inspections as required by the ASME Code or by NRC as a condition for the acceptance of performing post-induction heat stress improvement (IHSI) inspections of only 25 percent of the IHSI treated welds.
Because indications had been found, TVA was required to re-inspect all those welds which had been IHSI treated prior to restart.
The NRC letter of December 11, 1988 requested TVA responses to three items:
1.
Provide a commitment concerning sample expansion inspections in accordance wi,th GL 88-01; 2.
Provide a
a restart inspection schedule for the 71 welds which have not been post-IHSI inspected; and 3.
Propose technical specification changes reflecting leak detection require-ments specified in GL 88-01.
TVA's letter of January 12, 1989 addressed Items 1 and 2.
Item 1 was addressed by a TVA commitment to conform to the NRC "Staff Position on Sample Expansion" as specified in GL 88-01 for future IGSCC examination efforts.
For Item 2, TVA committed to examine before restart the remaining Unit 2 welds that had not received post-IHSI inspection and to provide NRC with the results of this inspection before restart.
The inspection results were provided in TVA's letter of June 30, 1989.
This letter also requested changes in the scope and category of IGSCC susceptible welds and to the commitments made in TVA's August 1, 1988 original response to GL 88-01.
Item 3 was provided by TVA's letter dated December 9, 1988.
The proposed technical specification changes were reviewed by the staff and approved by letter dated May 19, 1989.
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2.0 EVALUATION TVA's responses to Items 1 and 3 above are acceptable and, therefore, are considered closed by the staff.
TVA's followup response to Item 2, dated June 30, 1989, is evaluated below.
TVA in this letter also initiated changes to their original response to GL 88-01 dated August 1, 1988 which are also addressed below.
2.1 TVA'S Unit 2 Post-IHSI Ins ections of 71 Welds TVA's letter of June 30, 1989, reported on the completion of the post-IHSI inspections of 66 Unit 2 welds.
TVA's August 1, 1988, response stated that 71 welds were to be post-IHSI inspected.
The difference in numbers is due to eight welds in the August 1988 letter listed as not having had post-IHSI inspections but which in fact had these inspections, and three welds which had been listed as having had the post-IHSI inspections but which in fact did not have these inspections.
These changes resulted in 66 welds requiring post-IHSI inspection (71 - 8 + 3
= 66).
Because of the confusion concerning how many welds were to be post-IHSI inspected prior to restart, it would appear that TVA had temporarily lost track of which of Class 1 (equivalent) welds at the Browns Ferry Nuclear Plant had been inspected to which standard.
The NRC Project Manager was informed by TVA of these changes by telephone on December 6, 1988.
The discrepancy in'umbers was also noted in Inspection Report 50-259/89-05, 50-260/89-05 and 50-296/89-05 of March 1, 1989, as a part of Unresolved Item 50-259, 50-260, 50-296/89-05-01.
The other part of this Unresolvea Item, Inclusion of Reactor Cleanup Piping Outside of the Drywell, is addressed later in this Safety Evaluation.
TVA provided a response to both parts of the Unresolved Item in their letter of May 22, 1989.
Full staff resolution of Unresolved Item 50-259, 50-260, 50-296/89-05-01 involv-ing this discrepancy in numbers will be addressed in a separate correspondence.
2.1.1 Ins ection Results The post-IHSI inspection of 66 welds revealed eight welds with IGSCC indica-tions.
Structural analysis was conducted on all eight welds.
The analysis demonstrated that the indications in welds GR-2-53, DRHR-2-9 and DRHR-2-22, were acceptable as is without weld repair, since each weld had only one indication with a maximum depth of 16 to 18 percent of the wall thickness.
Welds GR-2-45, DSRWC-2-3 and DSRWC-2-4 had multiple axial indications.
A "design" weld overlay in accordance with GL 88-01 was applied to each weld.
Welds GR-2-59 and GR-2-61 had multiple circumferential indications with maximum depths of 40 percent of the wall thickness.
These welds were repaired by the application of a "full structural" weld overlay in accordance with GL 88-01.
2.2 Reactor Water Cleanu RWCU Pi in Outside the Dr well A portion of Unresolved Item 50-259, 260, 296/89-05-01 concerned the scope of weldments included in TVA's August 1, 1988, response.
The response had not included the non-code classed RWCU piping after the first isolation valve outside of the drywell penetration.
TVA's response to Inspection Report 89-05 dated May 22, 1989, explained the discrepancy as a matter of interpretation of the wording in GL 88-01.
In discussions with the staff, the GL 88-01 term,
"...regardless of Code classification,"
was clarified so that TVA now under-stands it to include both Code class and non-Code class piping.
As a result of this clarification, TVA presented a plan to the NRC at a meeting on April 20, 1989, to address the status of the RWCU piping (NRC Meeting Summary dated April 24, 1989).
In its letter of May 22, 1989, TVA committed to replace the four inch and larger, stainless
TVA will also replace the four inch and larger stainless steel RWCU piping outside of the drywell before restart of Units 1 and 3.
Since this piping is to be replaced during the next refueling outage, the staff concludes that this is an adequate alternative to the staff's position on inspections.
Requiring inspections to be performed during this current outage on piping which will be replaced at the next refueling outage is above the requirements of GL 88-01.
The staff also concludes that adequate protection to public health and safety is assured during the one cycle of operation before replacement at Unit 2 because this particular portion of RWCU piping is non-safety-related, has automatic isolation capability and leak detection is available.
The commitment of replacing this particular piping at the next refueling outage closes the related portion of Unresolved Item, 50-259/50-260 and 50-296/
89-05-01.
2.3 TVA's Revised GL-88-01 Res onse 2.3.1 Bimetallic Welds In TVA's original response to GL 88-01 dated August 1, 1988, TVA had not included three bimetallic welds from the Residual Heat Removal (RHR) piping system and had classified six bimetallic welds in the Core Spray (CS) piping system as "D" welds.
TVA states in its June 30, 1989, letter that these welds should be classified as "A" welds in accordance with GL 88-01.
Although these welds join low carbon steel to cast austenitic steel, both of which are IGSCC resistant, the weld material itself is not IGSCC resistant.
As NUREG-0313, Revision 2 notes:
"Welds joining resistant material that meet the ASME Boiler and Pressure Vessel Code requirement of five percent (or FN) ferrite, but are below 7.5X may be sufficiently resistant.
These will be evaluated on an individual case basis".
Experience and laboratory efforts have shown that the weld metals, such, as used at BFN, are susceptible to cracking unless the preventative factors are present.
Those welds not inspected should be con-sidered Category "G" welds unti 1 they meet the requirements of other cate-gories.
It is assumed that the six bimetallic welds in the CS system have been inspected and the correct category is "D".
Welds not UT inspectable shou ld be
- replaced, "sleeved", or local leak detection applied, etc.,
as outlined in GL 88-01, unless other information indicating an acceptable level of IGSCC resis-tance exists in these welds.
2.3.2 Installation of Leak Detection on Penetration Pi in Welds In the August 1, 1988, response, TVA stated that inaccessible piping welds in the RHR and RWCU systems will either be removed, have corrosion resistant clad
applied, or have local leak detection applied.
For Unit 2, this was to be applied during the cycle 6 outage and for Units 1 and 3 this was to be applied prior to restart.
The supplemental response of June 30, 1989, requested a
modification of this commitment.
These inaccessible welds are located inside containment piping penetrations.
The previous commitments to remove, apply corrosion resistant clad, or apply local leak detection for inaccessible RWCU welds still remain.
However, for the inaccessible RHR welds, TVA performed an engineering evaluation which concluded that these RHR welds experience tempera-tures higher than 200'F for only a brief period (one to two hours) during unit shutdown cooling.
The Unit 2 accessible welds directly adjacent to these penetration welds have been and will continue to be a part of the GL 88-01 inspection plan.
TVA proposes that the Unit 2 summary list will continue to list the RHR penetration welds as category "G"; however, TVA proposes that no additional leak detection be required beyond those in the Technical Specifica-tions.
A similar approach would be applied to the RHR penetration welds for Units 1 and 3.
Operating experience at other nuclear power plants has shown instances of continuous valve leakage resulting in reactor coolant at operating temperatures entering inactive valved-off systems during reactor operation.
Accordingly, the staff maintains, based upon past experiences and performance, that the these RHR welds should continue to be considered under GL 88-01.
Accordingly, the staff does not believe it prudent to concur in this commitment change unless other pertinent information is provided.
Therefore, TVA is requested to withdraw this change in its commitment.
3.0 CONCLUSION
3.1 Unit 2 Post-IHSI Ins ection That portion of Unresolved Item (URI 50-260, 261, 296/89-05-01) concerning only 66 welds being subjected to post-IHSI inspection prior to startup will be addres'sed by the NRC staff in a separate correspondence.
The results of eight welds out of 66 becoming category "E" welds, a slightly higher proportion than six out of 58 (54 in the August 1988 submittal less one weld found not to exist in the RWCU system less three "C" welds reclassified to "G" plus eight "G" welds reclassified to "C" (54 -
1 - 3 + 8
= 58)) demonstrates the prudence of performing the post-IHSI inspections prior to startup of Unit 2.
3.2 RWCU Pi in Inside the Dr well The portion of the Unresolved Item (URI 50-260,261, 296/85-05-01) which ad-dresses the RWCU piping beyond the first isolation valve outside of the dry-well has been resolved and is considered closed.
This piping will not be inspected at the next refueling outage as stipulated in GL 88-01 because this piping will be removed and replaced with IGSCC resistant material.
Requiring this non-safety related piping to be inspected during this outage, although extensively of long duration, was determined not'to be required by GL 88-01 because the system is to be replaced.
- Also, GL 88-01 specifies inspections as an Inservice Inspection Program to be implemented at the next refueling outage.
That this system is non-safety related,
- isolable, and has a Teak detection system installed outside the drywell provides adequate assurance of system integrity and protection to the public health and safety until it is replaced at the next refueling cycle.
8.3 Bimetal lic Welds TVA has not provided the sufficient information as stipulated by GL 88-01, or additional data which would justify the re-classifying of the weld metal in bimetallic joints as being resistant to IGSCC.
Accordingly, these welds are considered Category "G" or "D", as appropriate, until information specific to
'each weld is provided.
3.4 Installation of Leak Detection on Penetration Pi in Melds TVA requested that the commitment to the NRC of removing, applying corrosion resistant clad to the inside surface of the piping, or providing local leak detection of inaccessible RHR welds located in containment penetrations be rescinded for the three Browns Ferry Units.
In essence, TVA wants to consider these welds to be outside the requirements of GL 88-01 because these welds would-see reactor coolant water above 200'F for only short times.
The staff believes it would not be prudent to consider these welds outside of GL 88-01.
Although these welds, on a design basis, should see reactor coolant over 200'F for only a short time, the practical aspects of valve leakage, backed up with experience, has demonstrated that these welds may see reactor coolant at temperatures over 200'F for considerable periods of time. Accord-ingly, TVA is requesting to withdraw its request for a change in commitments.
4.0 REFERENCES
TVA Letters 1.
Tennessee Valley Authority, August 1, 1988, letter from R.
Gr idley to NRC, response to GL 88-01.
2 ~
3.
-, January 12, 1989, letter from R. Gridley to NRC, GL 88-01 sample expansion and 71 restart welds.
-, May 22, 1989, letter from M. Ray to NRC, responding to Inspection Report 50-259/89-05.
4.
---, June 30, 1989, letter from M. Ray to NRC, supplemental GL 88-01 Responses.
NRC Letters 1.
U. S.
Nuclear. Regulatory Commission, December 8, 1988, letter from S. Black to 0.
D. Kingsley (TVA), forwards safety evaluation on GL 84-11 and GL 88-01.
2.
~ ---, March 1, 1989, letter from F.
McCoy to 0.
D. Kingsley (TVA) trans-mitting Inspection Report 50-259/89-05, 50-260/89-05 and 50-296/89-05.
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-, April 24, 1989, Meeting Sumoary from T. Daniels, NRC, "Discussion of Generic Letter 88-01 During April 20, 1989 meeting.
4.
-, May 19, 1989, letter from S. Black to 0.
D. Kingsley (TVA), approving Technical Specification changes per GL 88-01.
Principal Contributor:
D. Smith Dated:
December 21, 1989
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