ML20205S254

Safety Evaluation Accepting Rev 2 to Nuclear Const Issues Group Spec 1, Visual Weld Acceptance Criteria for Structural Welding at Nuclear Power Plants, for non-ASME Code Welds

ML20205S254
Person / Time
Site:	Brunswick
Issue date:	06/04/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20205S249	List: ML20205S247 ML20205S254
References
NUDOCS 8606120126
Download: ML20205S254 (3)

Text

1 M, UNITED STATES

~

[(ps %q p, NUCLEAR REGULATORY COMMISSION g

l WASHINGTON, D. C. 20555

....+

/

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION P. ELATING T0_ APPLICATION OF VISUAL WELD ACCEPTANCE CRITERIA FOR STRUCTURAL WELDING AT CAROLINA POWER AND LIGHT COMPANY BRUNSWICK STEAM ELECTRIC PLANT, UNITS _ 1 AND 2 DOCKET N05. 50-325/324

1.0 INTRODUCTION

By letter dated December 10, 1985, Carolina Power & Light Company (CP&L) proposed to use Nuclear Construction Issues Group Specification-01, Revision 2 " Visual Weld Acceptance Criteria for Structural Welding at Nuclear Power Plants" (VWAC) for non-ASME Code welds at the Brunswick Steam Electric Plant (BSEP). Use of the VWAC has been approved on a generic bases through James Knight's June 26, 1985 letter to Mr. D. E. Dutton of the Nuclear Construction Issues Group. Approval for the use of VWAC on a plant-specific basis is based on the licensees not taking significant

/ exception to VWAC, Revision 2. Approval of VWAC for an operating plant results in a subsequent annual amendment to the Final Safety Analysis Report to incorporate the necessary changes related to the use of VWAC.

The licensee stated that " Brunswick will implement VWAC through appropriate BSEP specifications which take no significant exceptions to VWAC, Revision 2. Changes to VWAC were made for clarification and specific applicability to the Brunswick facility." In their subsequent submittal, dated March 25, 1986, the licensee demonstrated that the exceptions to VWAC are more conservative than the approved criteria. The following is our evaluation of the VWAC.

2.0 EVALUATION The staff concludes that the use of " Visual Weld Acceptance Criteria for Structural Welding at Nuclear Power Plants" (VWAC), Revision 2, May 7, 1985, will provide adequate quality of non-ASME Code structural steel welds. These criteriu are limited to non-ASME class welded steel structures where fatigue is not the governing design censideration.

Typical examples of structures to which these criteria may be applied are main building framing members and connecting members, supports for equipment and piping (non-ASME Code), cable tray and cor.duit, HVAC ducts and duct supports, and miscellaneous steel including bracing and stiffeners, embedments, stairways and handrails, doors and door frames, windows and window frames, gratings, covers, etc.

• B606120126 860604 .

PDR ADOCK 05000324 p PDR

There are eleven criteria addressed in VWAC. For cracks, the same criteria as exists in American Welding Society Standard AWS DI.1 is specified; the welds shall have no cracks. For underfilled craters, if proper weld size is achieved and cracks are absent, there is no reason for rejecting them, and therefore, they are acceptable.

For arc strikes, surface slag and weld spatter, the VWAC criteria are based more on the effects of structural strength rather than workmanship. Arc strikes are acceptable provided cracks are not visually detectable. Weld spatter remaining after cleaning is acceptable. For surface slag, the criteria are designed to prevent the acceptance to a weld which shows a gross lack of control by the welder.

Isolated surface slag which remains after weld cleaning has no structural significance.

Criteria for the following types of defects / faults are also provided in VWAC:

(a) fillet weld size (b) incomplete fusion (c) weld overlap (d) weld profiles (e) undercut (f) surface porosity (g) weld length and location The basis for the acceptance criteria in VWAC is the amount of reduction in cross sectional area caused by the defect or fault. In such calculations, the conservative approach used is to consider the length of weld in which a defect occurs as being non-existent, i.e., does not support any of the load. Such cross section reductions are usually less than 12.5 percent.

There are some exceptions to this, particularly in thinner section members. This occurs because measurements of defects / faults are rounded off up to the smallest measurement unit specified. For instance, a 1/32 inch maximum undercut of the entire length cn side for 3/16 inch thickness material results in a 16.7 percent reduction in area. Because the 1/32 inch undercut will not be uniform along the entire length, most of the undercut will be less than 1/32 inch in depth. Although the 16.7 percent maximum reduction is a theoretical possibility, it is not likely to occur.

The 12.5 percent " benchmark" was chosen based upon the presently allowed percent reduction in area affected by the undercut criteria in AWS D1.1-85 for the most limiting case in the thinnest member. The reasoning behind this is that if undercut is allowed to reduce the load carrying capability by a given number, other defects / faults that would result in a reduction of similar or less magnitude should also be acceptable.

The acceptance by engineering evaluation of thousands of field weldments with similar defects / faults not meeting the criteria of AWS D1.1 has resulted in the decision to use the weldments "as is" without repair.

This is possible because common engineering design practices results in significant margins above design requirements, such that a small reduction of 10 to 12 percent can be easily accomnodated. The present undercut criteria in AWS D.1.1-85 is a practical demonstration of this.

The deviations from AWS D1.1 as proposed in VWAC are relatively insignificant in that the redundancy of these structures and their l individual welds, and the conservative design practices used, allow non-ASME Code structural steel weldments (which are not designed for fatigue) to use alternative criteria as provided in Criterion II of 10 CFR Part 50, Appendix B.

3.0 CONCLUSION

We find the criteria denoted in VWAC are appropriate and provide adequate integrity of the affected structures at Brunswick Steam Electric Plant, Units 1 and 2 and accordingly, General Design Criterion I of Appendix A to 10 CFR Part 50 has been met.

Principal Contributor: S. Kim Dated: June 4, 1986 i

1

_ _