ML16141A910
| ML16141A910 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/21/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16141A909 | List: |
| References | |
| NUDOCS 9504280205 | |
| Download: ML16141A910 (6) | |
Text
REG, UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE SECOND TEN YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN REQUEST FOR RELIEF NO. ONS-004 REVISION 1 FOR DUKE POWER COMPANY OCONEE NUCLEAR PLANT, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
The Technical Specifications for Oconee Nuclear Station Units 1, 2, and 3, state that the inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Section 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the Oconee Nuclear Station, Units 1, 2, and 3, second 10-year inservice inspection (ISI) interval is the 1980 Edition, through Winter 1980 Addenda. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to Commission approval.
9504280205 950421 PDR ADOCK 05000269 G
-2 In a letter dated September 14, 1992, Duke Power Company submitted to the NRC its second 10-year interval inservice inspection program plan Request for Relief No. ONS-004 for the Oconee Nuclear Station, Units 1, 2, and 3.
2.0 EVALUATION AND CONCLUSIONS The staff, with technical assistance from its contractor, the Idaho National Engineering Laboratory (INEL), has evaluated the information provided by the licensee in support of its second 10-year interval ISI program plan Request for Relief No. ONS-004, Revision 1, for Oconee Nuclear Station, Units 1, 2, and 3.
Based on the information submitted, the staff adopts the contractor's conclusions and recommendations presented in the attached Technical Evaluation Letter Report. The licensee's proposal to use alternative calibration standards for the pressurizer and steam generator shell welds will provide an acceptable level of quality and safety. Accordingly, such alternative contained in Request for Relief No. ONS-004, Revision 1, is authorized pursuant to 10 CFR 50.55a(a)(3)(i).
Attachment:
Technical Evaluation Letter Report Principal Contributor:
T.K. McLellan Date:
April 21, 1995
TECHNICAL EVALUATION LETTER REPORT ON THE SECOND TEN-YEAR INTERVAL INSERVICE INSPECTION REQUEST FOR RELIEF ONS-004. REVISION 1 FOR DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 270, AND 287
1.0 INTRODUCTION
The licensee, Duke Power Company, submitted Revision 1 to Relief Request ONS-004 for the second 10-year inservice inspection (ISI) interval at Oconee Nuclear Station, Units 1, 2, and 3 (ONS-123), in a letter dated September 14, 1992. The second 10-year ISI interval at ONS-1 ended in July 1994, and the second 10-year ISI intervals at ONS-2 and ONS-3 ended in December 1994. Relief Request ONS-004 concerns the use of ultrasonic calibration blocks made of materials other than those required by ASME Section XI. The Idaho National Engineering Laboratory (INEL) has evaluated the subject request for relief in the following section.
2.0 EVALUATION The Code of record for the second 10-year interval at ONS-123 is the 1980 Edition, through Winter 1980 Addenda, of ASME Section XI. The information provided by the licensee in support of Relief Request ONS-004 has been evaluated and the basis for disposition is documented below.
Request for Relief ONS-004:
ASME Section XI. Article IWA-2000, Paragraph IWA-2232(a), Alternative Ultrasonic Calibration Blocks Code Requirement:
Paragraph IWA-2232(a) references ASME Code Section V, Article 4, Paragraph T-434.1 for the requirements for materials used to fabricate vessel ultrasonic (UT) calibration standards. Paragraph T-434.1 stipulates that UT standards be fabricated from materials that are: 1) a nozzle dropout from the component; 2) a component prolongation; or 3) of the same material specification, product form, and heat treatment as one of the materials being joined [welded].
Licensee's Code Relief Request:
Relief is requested from the material requirements of ASME Section XI, Paragraph IWA-2232 and, consequently, ASME Section V, Paragraph T-434.1, for UT calibration standards for examination of welds on the pressurizer and steam generators at ONS-1,2,3.
Attachment
-2 Licensee's Basis for Requesting Relief (as stated):
"(A)
The Class 1 Pressurizer shells, heads, and the Class 2 Steam Generator shells are fabricated from A-212 Grade B material.
This material is no longer available. The 1980 Edition of ASTM deleted reference A-212 Grade B material.
In place of A-212 Grade B material, the 1980 Edition of ASTM states that A-515 and A-516 material are compatible (with regard to the chemical and tensile properties) to A-212 Grade B material.
Calibration Blocks 40338 and 40394 are made from A-515 material and are therefore considered equivalent to calibration blocks made of A-212 Grade B material.
"(B)
The Class 1 Steam Generator heads are fabricated from 9-inch thick, SA-302 Grade B material. Attempts were made to locate 9-inch thick, SA-302, Grade B material, but were unsuccessful.
"Calibration Block 40305 was used during the first Inservice Inspection Interval for the examination of the steam generator head welds. Prior to using this calibration block, Relief Requests (OC-1-14, OC-2-14, and OC-3-13) were filed with the Commission stating that Calibration Block 40305 would be used for examination of the steam generator head welds, because the same material that was used to fabricate the steam generator head was not available. Calibration Block 40305 is A-515 material and does not match the SA-302 material used on the steam generator heads.
"Calibration Block 40393 (SA-5383, Grade B) is the closest to matching the Steam Generator head material as far as chemical, tensile properties and thickness are concerned. SA-533 Grade B is the same P-Number and Group Number as SA-302 Grade B.
"We have performed a calibration comparison on Calibration Block 40305 (which has been used in the past to examine the Steam Generator heads) and Calibration Block 40393 to assure that the previous examination results obtained with Calibration Block 40305 can be considered acceptable without re-examination.
"The calibration comparison bet4een Basic Calibration Blocks 40305 and 40393 shows that an increase in gain of 8 dB for 45 degree shear waves, and 11 dB for 60 degree shear waves is required to establish an equivalent sensitivity from Block 40393. This difference is believed to be caused by weld deposited cladding of Block 40305. The cladding was later removed from one side, but a dilution zone exists at the surface making the block more attenuative.
-3 "Any flaws detected and sized using Block 40305 were reported larger than they actually were. The use of Calibration Block 40393 will more closely reflect the actual material conditions."
Licensee's Proposed Alternative (as stated):
"(A)
Calibration Blocks 40338 and 40394 are considered equivalent to A-212-Grade B material and will be used for the examination of the Pressurizer head to shell welds; nozzle to head welds; Steam Generator secondary shell; shell to tube sheet and secondary nozzle to shell welds which were originally fabricated from A-212 Grade B material.
"(B)
Calibration Block 40393 will be used in the examination of the Class 1 Steam Generator head to tube sheet and Steam Generator primary nozzle to head welds for the second ten-year interval at Oconee."
Evaluation: The Class 1 pressurizer shells and heads, and Class 2 steam generator shells at ONS-123, were fabricated from American Society for Testing and Materials (ASTM) A-212 Grade B material.
The ASTM material specification for A-212 Grade B was replaced in 1980 with those for A-515 and A-516 Grade B.
Chemical and tensile properties of A-515 and A-516 Grade B materials are comparable to those required by the earlier A-212 Grade B specification. It would not be possible for the licensee to acquire calibration block materials that match the "retired" ASTM A-212 Grade B specification. Therefore, the licensee's proposal to use the A-515 and A-516 Grade B materials in lieu of the retired ASTM A-212 Grade B materials for Class 1 pressurizer and Class 2 steam generator ultrasonic calibration blocks is appropriate.
For the first 10-year ISI inspection interval, Relief Requests OC-1-14, OC-2-14, and OC-3-13, concerning the use of alternative calibration block materials for Class 1 steam generator head welds, were granted (reference SER dated April 8, 1982). At that time, the licensee was unsuccessful in locating ASME SA-302 Grade B materials to match those of the actual steam generator heads, and the staff concluded that the ASTM A-515 materials proposed by the licensee would be acceptable. Prior to use during the first 10-year ISI interval, this calibration block was inadvertently clad with stainless steel on both surfaces. The cladding was subsequently removed from the simulated "outside" surface, however a carbon-to-stainless dilution zone near this surface still exists in the material, which the licensee believes contributes to a higher level of acoustic attenuation than is present on the actual vessel.
The licensee proposed using a different calibration block, made of SA-533 Grade B material, for the second 10-year ISI interval Class 1 steam generator head weld examinations. SA-533 Grade B is of the same ASME P-Number and Group Number as SA-302 Grade B, the material from which the steam
-4 generator head welds are fabricated, and the new block would only be clad on one side to represent the vessel condition. Therefore, the licensee concludes that the new calibration block will more closely match the vessel material.
The reason for the stated Code requirements for UT calibration standard materials is to ensure that an appropriate level of ultrasonic sensitivity is maintained during component examinations. The acoustic properties of steels are affected by chemical composition, heat treatment, degree of cold-working, and inherent grain structure of the materials. Because these conditions vary for different materials, the acoustic properties of the vessel materials at ONS-123 will probably not match those of the licensee-proposed calibration blocks. However, the deviation in acoustic properties between the calibration blocks and actual vessel materials may be compensated for by procedures used during calibration and examination to ensure adequate scan sensitivity.
Supplemental information relative to ONS-123 examination procedures was provided by the licensee in a letter dated November 14, 1994. This submittal states that while the reference level established during ultrasonic calibration on the alternative blocks is only the minimum required by the Code, the detection scan levels are increased to +14dB above the primary reference. This scanning level is greater than two times that required by the Code. In addition, the licensee stated that all flaw sizing evaluations are conducted to 20% of the distance amplitude correction (DAC) curve at primary reference level, whereas the Code only requires that flaws be sized to 50% of DAC. The ultrasonic detection and flaw evaluation practices described above should result in a conservative examination methodology.
The INEL concludes that it is unlikely for the acoustic property deviations between the proposed calibration blocks and the actual vessel materials to adversely affect the sensitivity of the examinations, provided the increased scanning level (+14dB) and 20% DAC flaw evaluation criteria are implemented consistently. The use of the alternative calibration standards in combination with the conservative examination approach used by the licensee provides an acceptable level of quality and safety. Therefore, it is recommended that the licensee's proposed alternative be authorized.
3.0 CONCLUSION
The licensee's proposal concerning the use of alternative calibration standards for the pressurizer and steam generator shell welds is a conservative approach to ultrasonic examinations and provides an acceptable level of quality and safety. Therefore, in accordance with 10 CFR 50.55a(a)(3)(i), it is recommended that the licensee's proposed alternative be authorized.