ML19309F572
| ML19309F572 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/04/1980 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TAC-11793, NUDOCS 8004300078 | |
| Download: ML19309F572 (4) | |
Text
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'o UNITED STATES e[h c, h NUCLEAR REGULATORY COMMISSION 80043og C 3 8
- C WASHINGTON, D. C. 20555 April 4,1980 Docket tio. 50-336 Mr. W. G. Counsil, Vice President Nuclear Engineering & Operations flortheast fluclear Energy Company P. O. Box 270 Hartford, Connecticut 06101
Dear Mr. Counsil:
SUBJECT:
W. G. C0Vf1SIL LETTER TO H. R. DENTON DATED NOVEMBER 13, 1979 Enclosed are comments provided by the staff regarding the technical considerations leading to the recommendations given to Northeast Utilities at the meeting held on fiovember 6,1979, in regards to steam generator feedwater line repair at Millstone, Unit No. 2.
'1e staff does not share your view that the repair of the feedwater piping was a foregone conclusion prior to re-examination of the feedwater piping on November 3, 1979. The presentation by your staff and consultants did not, to the view of the staff, provide conclusive evidence that crack growth had not occurred.
Further-more, fracture mechanics analyses are not appropriate for predict-ing the behavior of flawed components when flaw sizes cannot be determined with scme degree of reliability, (i.e., the pipe side flaw sizes).
Sincerely, AfS Harold R. Denton, Director Office of Nuclear Reactor Regulation
Enclosure:
Technical Considerations of the Staff Leading to the Position that it was " Prudent" to Repair the Millstone 2 Piping cc w/ enclosure:
See next page 4
Northeast Nuclear Energy Company cc w/ enclosure (s):
William H. Cuddy, Esquire Day, Berry & Howard Mr. John T. Shediosk Counselors at Law U S 1
One Constitutien Plaza p," 0$
rawer X Hartford, Conne:ticut 06103 Niantic, CT 06357 Anthony Z. Rois man Natural Resourc !s Defense Council 917 15th Stree:, N.W.
Washington, D.C.
20005 Connecticut Energy Agency Mr. Lawrence Bt ttencourt. First Selectman. ATTN: Assistant Director, Research and Policy Development Town of Waterf. rd Hall of Record; - 200 Boston Post Road Department of Planning and Energy Waterford, Cornecticut 06385 Policy 20 Grand Street Northeast Nuclear Energy Company Hartford, Connecticut 06106 ATTN:
Superintendent Millstone Plant Post Of fice Box 128 Waterford, Connecticut 06385 Director, Technical Assessment Division Office of Radiation Programs (AW-459)
U. S. Environmental Protection Agency Crystal Mall #2 Arlington, Virginia 20460 U. S. Environmental Protection Agency Region I Office ATTN:
EIS COORDINATOR John F. Kennedy Federal Building Soston, Itassachusetts 02203 Waterford Paolic Li' rary o
Rope Ferry Road, Route 156 Waterford, Connecticut 06385 Northeast Utilities Service Company ATTN: Mr. James R. Himmelwright Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut, 06101 1
TECHNICAL CONSIDERATIONS OF THE STAFF LEADING TO THE POSITION THAT IT WAS " PRUDENT"TO REPAIR THE MILLSTONE 2 PIPING 1.
The results of the ultrasonic inspection performed 11-4-79 did not preclude the possibility that crack growth had occurred. This is based on the following:
a.
an increase to 3 to 4 db in amplitude was noted between 44" and 46" location en SG-A pipe to safe end examination.
b.
a new reflector was located when examining SG-B pipe to safe-end weld area.
This reflector shadowed the original reflector resulting in a decrease of the amplitude of the original reflector. This " shadowing" effect makes the ability to size the original reflector questionable.
The licensee previously had made a co m.itment to repair the affected piping if crack growth occurs.
2.
After reviewing the radiographs at the site, the NRC Staff believes the cracking on the pipe side of the pipe to safe-end weld to be similar in magnitude to the safe-end side cracking. The licensee was unable to size pipe side cracking and was postulating the depth of the flaws by estimation of the crack depths from the radiography. The staf', from the oral and written presentations of the licensee, was not aware that the unsized pipe side cracks were of similar severity to those on the safe-end side.
3.
With the inability to clearly demonstrate that crack growth had not occurred and the inability to size flaws which appear from radiography to be of the same order as those which were sized by UT originally, fracture mechanics analyses are not apprcpriate since flaw depths cannot be determined.
In addition to the items stated above, the following factors also have bearing on the staff position that removal of the flaws was " prudent."
1.
The ASME Code Section XI analysis using LEFM is not appropriate for feedwater piping.
2. The ASME Code has not adopted a position on elastic-plastic fracture mechanics and/or plasticity analyses for evaluating flaws.
3.
The NRC Staff has not adopted a formal position on elastic / plastic fracture mechanics methodology, including definition of the appropriate criteria for acceptance.
The data base for establishing toughness of piping materials is extremely 4
This is a rather significant factor since specifications for piping limited.
materials are generally based on chemical composition and tensile properties and therfore, significant variability may exist regarding material toughness.
An additional after the fac.t consideration which bears mentioning is the actual depths which were determined as the flaws were removed prior to repair of the The depth of material requiring removal to eliminate the flaws Millstone piping.
a
2 were measured as 0.249 inches by the NRC Staff and 0.330 inches by the licensee QC Staff. These results are two to three times the maximum crack depths (.110 inches) estimated by ultrasonic inspection.
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b