ML20151Z069
| ML20151Z069 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/07/1987 |
| From: | Lewis J, Rose J, Shevlin E TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20151Z000 | List: |
| References | |
| WP-25-BFN, WP-25-BFN-R, WP-25-BFN-R00, NUDOCS 8808290154 | |
| Download: ML20151Z069 (8) | |
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WELDING PROJECT EMPLOYEE CONCERN EVALUATION REPORT WELD REPAIRS NOT MEETING ASME CODE REQUIREMENTS AT BROWNS FERRY NUCLEAR PLANT PREPARED BY
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Revision 0 EMPLOYEE CONCERN
SUMMARY
SHEET WELD REPAIRS NOT MEETING ASME CODE REQUIREMENTS AT BROWNS FERRY NUCLEAR PLANT I.
SCOPE OF EVALUATION This report addresses one employee concern dealing with piping repairs not meeting the ASME Code requirements in safety related applications at Browns Ferry Nuclear Plant (BFN).
The one issue derived from this concern is that TVA makes repairs which are not in accordance with the ASME Codes, such as overlays, patches.,
and furmanite. Each type of repair is discussed separately below.
Text of the concern is provided in the technical report (WP-25-BFN) under Attachment 1.
II. ANALYSIS OF ISSUE ADDRESSED BY CONCERN A.
The part of the concern relating to TVA making repales using furmanite (a viscous fluid sealing compound) is addressed by Operations Element Report 2850162005, and 's not considered further by this evaluation.
B.
TVA does use mechanical and welded patches to temporarily contain leakage. At Browns Ferry, this has occurred principally in the fire protection system.
These patches are not intended or used to cubstitute for proper repairs in accordance with the code and regulatory requirements. The affected piping is replaced as soon as practicable.
Further details of this issue may be found in the technical report WP-25-BFN, Paragraph III B.
C.
TVA does make temporary repairs to ASME piping using weld eterlays. Stainless steel piping in boiling water reactors is susceptible to intergranular stress corrosion cracking (IGSCC).
Overlay welding is the most commonly used method to correct for IGSCC, ana is an acceptable practice.
Complete details of this issue are discussed in Paragraph III C, WP-25-BFN.
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1 WP-25-BFN Revision 0 III. COLLECTIVE SIGNIFICANCE No significant effect on hardware or the TVA welding program at Browns Ferry was identified. The design of temporary repairs is not specified in ASME Sections III or XI.
The subject temporary repales are made in accordance with an approved TVA program.
IV.
ROOT CAUSE The type repairs discussed in this evaluation are not seen in new construction.
Ic is probable that the concern evolved from an unfamiliar activity being o'oserved.
One familiar only with construction may not be aware of the erosion problems encountered in operating piping systems, or of the intergranular stress corrosion cracking common to stainless steel piping in boiling water reactor plants.
V.
CORRECTIVE ACTION No corrective action is indicated.
VI.
REINSPECTION REQUIRED No.
VII.
ISSUE CLOSURE Closed.
VIII. ATTACHMENTS 1.
Evaluation Report WP-25-BFN, Revision O.
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WP-25-BFN Revision 0 WELDING PROJECT EMPLOYEE CONCERN EVALUATION REPORT WELD REPAIRS NOT MEETING ASME CODE REQUIREMENTS AT BROWNS FERRY NUCLEAR PLANT
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I.
SCOPE OF EVALUATION One employee concern. Text of the concern is provided under.
The subject concern was previously evaluated for Sequoyah Nuclear Plant, in Weld Project Report WP-25-SQN.
The expurgated text of the concern was compared with the requirements of Section II of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, USNRC publication NUREG-1061 and USNRC Ceneric Letter 84-11.
The findings presented herein are based upon a review of the previous evaluation, the above noted comparison, and interviews with cognizant TVA Engineering personnel.
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II.
ISSUES ADDRESSED BY CONCERNS TVA makes repairs which are not in accordance with the ASME Codes, such as overlays, patches, and furmanite.
III. ANALYSIS OF ISSUES ADDRESSED BY CONCERNS A.
The part of the concern relating to TVA making repairs using furmanite (a viscous fluid sealing compound) is addressed by Operations Element Report 2850162005, and is not considered further by this evaluation.
B.
TVA does use mechanical and welded patches to temporarily contain leakage. These patches are not intended or used to substitute for proper repairs in accordance with the code and regulatory requirements.
The temporary mechanical patches are typically metal formed to the curvature of the pipe and clamped in place over suitable gasket material.
The temporary welded patches are typically reinforcement plates formed and welded over the degraded area of the pipe. Division of Nuclear Engineering performs an unreviewed Safety Question Determination to determine the structural integrity and ef fect on the piping when temporary welded patches are used.
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WP-25-8FN Revision 0 The welding is performed using procedures and welders qualified in accordance with the rules of ASME Section IX.
The temporary repairs are documented and tracked. The pipe is then replaced as so6n as practicable.
The making of temporary piping repairs to contain leakage is not addressed by ASME Sections III or XI, or by USAS B31.1.0.
C.
TVA does make temporary repairs to ASME piping using weld overlays. This is an acceptable practice, widely used to correct for intergranular stress corrosion cracking (IGSCC). The American Society of Mechanical Engineers Boller and Pressure Vessel Code,Section XI at IVB 3640 provides standards for evaluation of flaws in piping to determine acceptability for continued service.
IVB 3640 states in part that the evaluation procedures and the acceptance criteria shall be the responsibility of the owner and shall be subject to the approval of the regulatory authority having jurisdiction at the plant site. The code does not discuss the design of the overlay repair welds,.
USNRC Generic Letter 84-11. Inspections of BWR Stainless Steel Piping, Attachment 2 at 2 (b) (i) recognizes repair by weld overlay, stating that the thickness of the overlay must be sufficient to provide the full margin required by ASME Section XI.
IVB-3640 during the proposed operating period.
In NUREG 1061, Volume 1. Investigation and Evaluation of Stress Corrosion Cracking in Piping of Boiling Water Reactor Plants, the USNRC Pipe Crack Task Group recognizes weld overlay as the most commonly used short term solution to IGSCC problems. This report states that the radial shrinkage caused by the weld overlay induces strongly compressive residual stresses, which should prevent initiation of new IGSCC and inhibit the growth of existing flaws.
In NUREG-1061. Volume 5. Piping Review Committee Conclusions and Reconsnendations, weld overlay 'is considered an acceptable repair technique.
TVA Engineers have reviewed a draft Revision 2 to NUREG 0313.
When issued, this revision will provide for use of the overlay repair for extended periods.
An overlay design drawing was reviewed (TVA Drawing 67M47B2408-1).
This overlay repair was designed by TVA Engineers, and an independent r eview was performed by Structural Integrity Associates (SIA). It was concluded in SIA Report number PCR-85-032 that the design was adequate.
Presently, there are 42 overlays on Browns Ferry Unit 1 primary piping, two overlays on Unit 2 primary pipint. and two overlays on Unit 3 jet pump instrument nozzle safe ends.
The overity welds on the BFN units are designed to provide safety margins required by the ASME Code using Section XI. Subarticle IWB-3640 as a guide.
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WP-25-BFN Rovision 0 The results of the overlay repair procedures for BFN Unit 1 were reported to the USNRC in late 1983. The NRC then Casued a Confirmatory Order and Safety Evaluation (Docket No. 50-259), which granted approval, for Unit 1 to be returned to power and operated in its repaired configuration.
The results of the overlay repair procedures for Units 2 and 3 were also reported to the NRC.
Approval has not yet been granted for Unit 2 to be returned to power. The NRC did, however issue a Safety Evaluation Report (Docket No. 50-296) which granted approval for Unit 3 to be returned to power and operated in its repaired configuration.
Currently, the use of the overlay at Browns Ferry remains on a short term basis.
Regulatory approval is on a cycle by cycle basis, dependent on the data obtained through regular volumetric examination.
Most of the items repaired by overlay will eventually bt replaced.
Based on the forthcoming revision to NUREC 0313, some of the repairs may be made permanent.
In making weld overlay repairs to piping affected by intergranular stress corrosion cracking, TVA at Browns Ferry Nuclear Plant is in compliance with the regulatory requirements.
This is not a violation of ASME Section XI.
Rather, it is a means of complying with the flaw limitations outlined in Section II at IWB-3600.
IV.
COLLECTIVE SIGNIFICANCE The design of temporary repairs is not specified in ASME Sections III or II.
The subject temporary repales are made in accordance with an approved TVA program.
This evaluation revealed no adverse hardware or programmatic effect on the TVA welding program at Browns Ferry.
V.
ROOT CAUSE(S)
The type repairs discussed in this uvaluation are not seen in new construction.
It is probabi'e that the concern evolved from an unfamiliar activity being observed. One familiar only with construction may not be aware of the erosion problems encountered in operating piping systems or of the intergranular stress corrosion cracking common to stainless steel piping in boiling we.ter reactor plants.
VI.
CORRECTIVE ACTION No corrective action is indicated.
VII.
ATTACKMENTS 1.
Text of concern.
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WP-25-8FN Revision 0 WELDING PROJECT EMPLOYEE CONCERN EVALUATION REPORT ATTACHMENT 1 TEXT OF EMPLOYEE CONCERNS
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Evaluatioc Report WP-25-BFN addresses one' employee concern. The text of the concern is shown on the following page.
2850162005 I
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REFERENCE
- ECPSI32J-ECPS132C TENNESSEE VALLEY AUTHORITY IPEQUENCY
- REQUEST OUP - 1555 - RWM OFFICE OF NUCLEAR P0HER PAGE
.-I' EMPLOYEE CONCERN PROGRAM SYSTEM (ECFS)
RUN TIME - 11:56 4' EMPLOYEE CONCERN INFORMATION BY CATEGORY / SUBCATEGORY RUN DATE - 83/16/87 ATEGORYs HE NON QA/QC WELDING HP - 25 EFFECTS OF NELDING R0D NOT MEETING ASME CODE S
H I REPORT APPL SUB R PLT 2 SAF RELATED HISTORICAL CONCERN REF. SECTI0t.
CONCERN NUMBER CAT CAT D LOC BF BL SQ WB REPORT ORIGIN CONCERN DESCRIPTION SUBCAT - 25 CAT
- NE 2850162005 01 OP 30803 S NPS IY N Y Y NSRS TVA MAKES REPAIRS TO THEIR NUCLEAR P 2 SS NA $$ SS LANTS HHICM ARE NOT IN ACCORDANCE NI 02 NE 50825 5 NPS IY Y Y Y TH ASME CODES, SUCH AS OVERLAYS, PAT 2 SS SS SS SS CHES, AND EVEN FURMATITE (SOPHISTICA TED GLUE). CSSN ISSUES ADDRESSED IN RPT HP-25-SQh 20) 1 CONCERNS FOR CATEGORY HE HP - 25 O
CONCERNS ARE GROUPED BY LAST 2 DIGITS OF SUBCATEGORY NUMBER.
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