ML19312E547
| ML19312E547 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee, Yankee Rowe, Maine Yankee |
| Issue date: | 05/29/1980 |
| From: | Heider L YANKEE ATOMIC ELECTRIC CO. |
| To: | Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| IEB-79-03, IEB-79-03A, IEIN-80-15, WYR-80-59, NUDOCS 8006050283 | |
| Download: ML19312E547 (2) | |
Text
N Telephone tl7 366-90ll TwX 740 393 0739 YANKEE ATOMIC ELECTRIC COMPANY Mib*-se om, hVY 80-84 M..
hMY 80-85
=L 20 Turnpike Road Westborough, Massachusetts 01581 Ya}uxe~/s May 29, 1980 United States Nuclear Regulatory Commission Washington, D.C.
20555 Attention:
Mr. Victor Stello, Director Office of Inspection and Enforcement
Reference:
(a) License No. DPR-3 (Docket No. 50-29)
(b) License No. DPR-28 (Docket No. 50-271)
(c) License No. DPR-36 (Docket No. 50-309)
(d) USNRC - IE Bulletin 79-03, dated March 12, 1979 (e) USNBC - IE Bulletin 79-03A, dated April 4. 1980 (f) USNRC - IE Information Notice 80-15, dated April 21, 1980
Subject:
IE Bulletins 79-03 and 79-03A
Dear Sir:
We are in the process of addressing your Bulletin, reference (e), which, although not significantly affecting our plants, has required a diversion of engineering resources from identified safety issues. This letter does not constitute our response to Reference (e), which is forthcoming, but rather is intended to direct your attention to some points we feel are of significance regarding piping defects. References (d) and (e) went to great lengths to describe the detection of centerline lack of weld penetration (CLP) which occurred during the fabrication of longitudinally welded pipe; howevoc, we believe your concerns fail to adequately balance these findings against the l
conservatism built into the applicable design code or past operating l
experience.
It is known that CLP or other defects in the seam weld of rolled and welded pipe can effect the capability of that pipe to withstand pressure (or
" hoop") stresses. However, this has always been recognized by the piping design codes, which require a weld efficiency factor to be used when calculating the minimum required wall thickness in pressure calculations.
Other design loads would induce bending stresses which are not affected by CLP or other defects in longitudinal seam welds.
Any judgement of piping defects should take into consideration the implicit conservatisms in the codes used to design and fabricate the pipe in It should be recognized that while both ASME Section III and ANSI question.
B31.1 require volumetric examination of longitudinal welded pipe prior to use [00 /
5 ffD 8006050 2(3 k
%g U.S. Nucicer R:gulatery Commission May 29, 1980 Att2nticn Mr. Victor Stollo, Dir:ctor Pcgo 2 in systems designed to 100% of allowable stress, ANSI B31.1 permits systems designed to 85% of allowable stress without volumetric examination of longitudinal welds. Each of the plants identified in References (a), (b), and (c) have been designed under the latter provisions of ANSI B31.1.
The discovery of CLP in longitudinal welds has not been related to any known piping failures, and we would greatly appreciate any information you might have regarding events of longitudinal weld failures under operating conditions.
If CLP were a "significant deficiency" one would expect to see a significant number of piping systems fail during the hydrotest, which requires pressures of 125 or 150 percent of design pressure; however, your staff has not provided documentation of such failures.
In the unlikely event a failure should occur there is considerable expa ience from both fossil and nuclear power plants, in addition to studies by the NRC and various NSSS, which has reasonably established that a defective pipe weld would slowly develop into a through-wall crack, which would in turn propagate at a slow enough rate to permit detection by leakage prior to a complete pipe rupture or break.
In conclusion, we believe the issues identified in your letter, Reference (d), are not generic problems of "... a significant deficiency which requires extensive evaluation...", but are rather minor design deficiencies.
We do not believe this issue warrants the level of licensee attention or degree of concern so dramatically expressed above. In the absence of any evidence of longitudinal pipe weld failures, we suggest that a more effective approach would have been to issue an IE Information Notice informing all licensees of the detection of weld defects, as your staff had done in Reference (f). This action would enable each licensee to assess your findings and document a position which could easily be examined by your I&E resident or site inspectors, without prematurely diverting engineering resources currently involved in resolving safety issues.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY Y
L. H. Heider Vice President Engineering and Operation RHG/kar cc: Boyce H. Grier William J. Dirks Havete*R**DefmMP