ML20064B790
| ML20064B790 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 10/05/1978 |
| From: | Parker W DUKE POWER CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7810110084 | |
| Download: ML20064B790 (6) | |
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DUKE POWER COMPANY Powra Burtorwo 422 SocTa Gnuncu STureT, CRABLOTTz. N. C. 2e24a WILLIAM O. PAR M E R, J R.
VeCE Pats 6 DENT Tri(P, oseg Ant A 704 Sita e PacowcTioes 373-4083 October 5, 1978 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Attention:
Mr. Robert L. Baer, Chief Light Water Reactors, Project Branch No. 2
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Re: McGuire Nuclear Station Units 1 and 2 Docket Nos. 50-369 and 50-370 Er
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Dear Mr. Denton:
An October 2, 1978 Amendment 56 to the McGuire Application for Licenses was submitted which included a two-volume document entitled, "Augmerited Inservice Inspection for Iipe Rupture Protection, SRG-78-01, Revision 1."
This document was prepared to address specific NRC concerns discussed in an August 14/15, 1978 meeting. To assist the staff in reviewing this report, Attachment 1 identifies the concerns and provides a reference to where each concern is discussed in the report.
By letter of August 17, 1978 from Robert L. Baer, Duke was requested to consider the recommendations of the NRC consultant, Idaho National j
l Engineering Laboratory, contained in INEL Report RE-M-78-010, " Evaluation l
of Nondestructive Methods and Techniques for Pressurizer Surge Line Intermediate Pipe Rupture Protection, McGuire Nuclear Station, Units 1 l
and 2," J. F. Cook, March, 1978. Attachment 2 consists of detailed comments on this report.
With the submittal of this information it is felt that ample justification has,been provided to allow use of an augmented inservice inspection program in specific areas irr lieu of providing pipe break protection.
Very truly yours, William O. Parker, Jr.
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ATTACIOfENT 1 Revision 1 of SRG-78-01, " Augmented Inservice Inspection for Pipe Rupture Protection," was prepared to incorporate additional material requested by NRC.
Referring to NRC meeting summary dated August 17, 1978, the revised document now addresses the seven specific areas of concern as follows:
1.
Possible differences in the Unit 2 augmented ISI program from the Unit 1 program - Part II, Sections 1.2.7 and 2.5; Part III, Sections 1.5 and 2.5.
2.
Inservice and pre-service inspection program - Appendices I, II, and III.
Comments from EG&G have been incorp3 rated in the inspection procedures, but are not specifically addressed in the document. For a point-by-point discussion, refer to Attachment 2.
3.
Results of inservice inspection - Appendix II.
4.
Consequences of postulated ruptures - Appendix V.
1 5.
Leak detection enhancement program - Part I, Section 6.2; Part II, Sections 1.2.5 and 2.3; Part III, Sections 1.3 and 2.3.
A general description of a proposed leak detection system utilizing acoustic emission techniques is provided at this time. Final design information will be forwarded, upon request, at the earliest possible time.
6.
Equipment relocation evaluation - Part III, Section 1.5.
7.
ALARA analysis - Part I, Section 6.1; Part II, Sections 1.2.5 and 2.3; Part III, Sections 1.3 and 2.3.
A major effort was also made to reanalyze the unacceptable targets for each postulated break. A field verification of existing targets was made and electrical cables were identified by the equipment they supply power to.
Protection for some targets using physical restraints was investigated. As a result, some targets in the feedwater line breaks have been protected.
Some targets in the containment have been shown to be protected by existing steel structures which block the blowdown jet.
Revision 1 has deleted material contained in the original report concerning the pressurizer surge line, the pressurizer safety and relief lines, the pressurizer spray lines, and residual heat removal lines, as augmented inservice inspection is not proposed for these lines.
i ATTACHMENT 2' DUKE POWER COMPANY RESPONSES TO RE-M-78-010:
2
" EVALUATION OF NONDESTRUCTIVE METHODO AND TECHNIQUES FOR PRESSURIZER SURGE LINE INTERMEDIATE PIPE RUPTURE PROTECTION" MARCH, 1978 A short study was performed on 304 stainless steel material to demonstrate the capability of the ultrasonic examination method being used at the McGuire Station. Notches which represent the minimum through wall (or approximately) in accordance with the 1977 Section XI Table IWB-3514-3 were used as a guide.
1" The ultrasonic procedure used was ISI-120 Rev. 5 which uses side drilled holes in accordance with the 1971 Edition of Section XI thru Winter 1972 Addenda which is the Code applicable to the McGuire Station, Unit 1.
Measure-ments were taken of the notches using the ultrasonic procedure and by the i
Standards Laboratory. No attempt was made to fabricate actual cracks because of the complexity of doing this in piping.
Comments on the report are detailed below under the headings in Mr. Cook's report.
1.
Test Results In the opening r2 marks it is stated that data published for aluminum indicates the electrodischarge machine flaws give significantly larger ultrasonic responses than similar sized fatigue cracks. This may be true for aluminum but making it applicable to stainless steels without 4
any experimental evidence is not conclusive. There are several properties of aluminum that make it much different from that of the stainless steels or steel materials concerning crack detection. Aluminum is a very soft material and deforms readily upon contact. When the surfaces of a crack j
are in good contact in aluminum, the reflective properties of the crack l
may change. Several experimenters have looked at fatigue cracked aluminum l
specimens having tensile or compressive stresses which have shown a variable ultrasonic response because the crack transmits more or less ultrasonic energy with contact across the crack faces. Stainless steels being much harder are not the same,~ but by inference to this study, are being included in the same type of nondetectability.
The report goes further to state that their experience with ultrasonic examination of actual defects in stainless steels (fabrication cracks in
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welds and stress corrosion cracks) shows that the Code procedure required sensitivity is not adequate for a reliable detection of real flaws. There was nothing stated about these flaws as to their particular size in relation to the tolerable flaws in the materials or their location in the cross section.
The report goes on to state that we should demonstrate the effectiveness of the ultrasonic procedure on fatigue cracks in stainless steel. This could be a very involved program with the various material sizes to determine the range of detectability in the measurements obtained and p.u
, any special examination conditions that are needed to produce these.
The report goes on to state that the electrodischarge machined flaws are all oriented in the transverse direction.
It was assumed in the original study that the direction the fatigue flaws will most likely occur is in the transvetse direction. However, it is a simple matter to electro-discharge machine flaws in the axial direction and also do these exami-nations. The 1977 Code requires both direction notches.
The report states that the review of the calibration data and indication recordings show that side drilled holes were used for calibration, not notches as are specified by the 1977 Edition of Section XI reference.
The work at the McGuire Station is being performed to the 1972 Winter Addenda of Section XI while the acceptable flaws were referenced from the 1977 Code. This Addenda refers to additions of Section III in which side drilled holes are used for calibration. The notches in the calibration blocks were not required until the Winter 1975 Edition of Section XI, which is not a legally recognized document by NRC for this plant. However, it is possible to comment that the procedure that is used does, in Duke's opinion, provide for greater detectability and sensitivity in piping materials than the newer versions of Section XI using the notch cali-bration standards. This is confirmed from the actual data in this investigation. The side-drilled holes which were used for the cali-brations provided lower amplitude signals than the notches. The notches required by the 1977 Section XI procedure for calibration blocks are larger than the minimum notches fabricated to represent the minimum defect sizes.
2.
Ultrasonic Examination Data and Procedures The report goes on to make comments on the completed data sheet (Form 106 indicates recording to half maximum amplitude while the procedure specifies recording to 100% DAC.). These recording sheets are used for a multiple number of procedures, and the procedures contain the exact recording requirements for each procedure.
As stated before, the calibrations were done on side-drilled holes since that is the Code applicable to the McGuire Plant at the present time.
The report goes on to state that the procedure ISI-120 is a general procedure and this is true. It is used for all the Code required piping examinations at McGuire. In addition, a separate procedure has been written for the detection of stress corrosion cracking, (ISI-125), and will be added to the requirements for examination of welds that have been specified for the augmented inspection program. Throughout the Evaluation Report the writer has. flipped back and forth between fatigue cracks and stress corrosion cracks. Fatigue cracks, depending upon the stress distribution, would have a definite orientation within the pipe and pipe area. Scans should be made across the direction of the fatigue cracks. A swivelling motion may cause one to miss a fatigue crack whereas it is more likely to pick up a stress corrosion crack. The angle beam scanning provided in the Procedure ISI-120 does provide for full V-path examination in four directions with the angle beam.
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. One of the confusing things in the document is the switching back and forth between fatigue cracks and stress corrosion cracks. It is necessary to know the mode of failure in order to properly select the examination technique.
In PWR systems to date, stress corrosion cracking in the piping under consideration for the augmented ISI has not been a problem. The report goes on to talk about using transfer and transfer is fine for a single pulse echo search unit. If one uses the accepted two transducer element search unit that is detailed in most procedures for stress corrosion crack detection, one has no way of applying transfer of these units. Transfer has been found to be an unacceptable consideration by the various Code bodies, since it can take away the repeatability of the examination by providing a variable which is of ten hard to determine.
The attenuation may vary within the material or through the weld and by periodically making adjustments in the attenuation differences, one looscs all reference to the original sensitivity which the calibration provided.
The report goes on to comment about the beam angle determined in the paragraph 4.2.2.2 of the procedure using a standard steel IIW block. A stainless steel IIW block is used on stainless steel welds and a steel IIW block is used on carbon steel welds to make sure the angle beams are within tolerance.
The report further comments on paragraph 7.4 of the procedure that 10 percent overlap may not be adequate to obtain complete scan coverage with adequate sensitivity.
In fact, it is probably more than adequate since the procedure requires scanning at 6dB hotter than the DAC sensitivity.
Very small amplitude indications must be investigated and measured. Again, however, this point is difficult to prove without doing a study on a range of fatigue crack sizes. All ASME and ASTM ultrasonic requirements specify 10 percent overlap. His final comment in Section 2 of the report is that we are recording information not required in the procedure.
It is always permissible to record more than the requirements and since this was a study being conducted instead of an actual examination, more data was included in the study.
3.
Certifications In the third section, Certifications, the report states that "The certifi-cations for the ultrasonic test block are satisfactory in that all relevant dimensions are defined.
It is assumed that the identity of heat number on the certification form provides traceability to identify the material as type 304 stainless steel, as is stated in Section I of Appendix A, Reference 2."
These blocks were meant to show that certain size indi-cations were detectable and they were not meant to be calibration blocks for these particular applications.
The report comments that the certificates of personnel qualifications for nondestructive examination do not contain all the record information as required by SNT-TC-1A.
It also states that the certifications fail to show, for example, grades of current examinations and descriptions of practical test objects are not included. SNT-TC-1A 1968 does not require that these items be included in the certification forma. Later editions i
of SNT-TC-1A 1975 do include some of these requirements. However..the I
NRC does not recognize this edition of SNT-TC-1A and does not permit its use in a nuclear power plant by its reference documentation.
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Supplemental Techniques 3
Under Supplemental Techniques,'the report discusses other techniques which may be applicable. No comment will be made on the acoustic emission section; however, where the report talks about fatigue damage that may initiate at the OD surface, a supplemental surface examination is recom-mended. I agree that a surface examination should be conducted but do not agree that it is necessary to use the fluorescent penetrants.
I agree that they have better sensitivity, but use of fluorescent penetrants here would provide a large overkill. There is no need to require a very high detection sensitivity where the dye penetrant applications being used can see the desired range of crack sizes that would find both acceptable and nonacceptable conditions.
Conclusion In conclusion, we will incorperate a procedure which meets the intent of Mr.
Cook's comments. This procedure will require that the calibration blocks be fabricated from actual pipe materials of a similar material specification to the materials being examined. These calibration blocks will have notches that are approximately the depth as required in calibration standards fabricated to the 1977 Section XI for piping materials.
(These are in line with EPRI requirements.) A two-transducer pitch catch arrangement of the search unit transducers will be used for scanning the 14 stainless steel welds involved. A penetrant examination has.also been included on each of these stainless steel welds and a magnetic particle examination on the eight (8) ferritic welds.
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