ML18016A718
| ML18016A718 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 11/06/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18016A716 | List: |
| References | |
| NUDOCS 9811170109 | |
| Download: ML18016A718 (5) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMIVIISSION WASHINGTON, D.C. 20555-0001 gO SA ETY EVAL ATI B
E OF ICE OF.NU LEAR REACTOR REGULATION CAROLI W
8 LIG T OMPANY SHE ON HARRIS NUCLEAR POWE PLANT IT 1 DO E
COO MBOOUC I
The Technical Specifications (TS) for the Harris Nuclear Plant (HNP) state that the inservice inspection (ISI) 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 (B8 PV) Code and applicable addenda as required by 10 CFR 50.55a(g),
except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
10 CFR 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
'cceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficultlywithout 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 pre-service 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) 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 Shearon Harris Nuclear Power Plant second 10-year ISI interval is the 1989 edition.
By "HNP-98-161, Requests Relief from 1989 Edition of ASME Code Section XI,IWA-4120 Requirements for Repair of Control Rod Drive Mechanism Housing [[Topic" contains a listed "[" character as part of the property label and has therefore been classified as invalid..Supporting Calculation,Encl|letter dated November 4, 1998]], the Carolina Power 8 Light (CP8L or the licensee) proposed an alternative to the Code requirements for repair of a Control Rod Drive Mechanism (CRDM) canopy seal weld (penetration ¹18) at HNP. Specifically, CP8L proposes to use an 8 power magnification (Sx) camera to perform visual examination of the in-process automatic welding and a post-weld visual examination using the same camera.
In addition, a visual examination VT-2 of the canopy seal weld would be performed during a hydrostatic test of the reactor.
This alternative is proposed in lieu of the required liquid penetrant (PT) examination required by the ASME Code.
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~EALU Request for Relief RR-2R1-012 Section IWA-4210(a) of Section XI of the ASME Code, 1989 edition, requires that repairs be performed in accordance with the Owner's Design Specification and the original Construction Code of the component or system, or later editions and addenda of the Construction Code.
The HNP CRDM housing canopy seal welds were designed and fabricated in accordance with the 1974 Edition of ASME,Section III, including Winter 1976 Addenda of ASME Section III.
These editions and the 1989 edition of ASME Section III require a PT surface examination for repairs.
In accordance with 10 CFR 50.55a(a)(3)(ii), the licensee proposed an alternative on the basis that a repair consistent with the requiremerits of the original Construction Code (ASME Section III)would result in hardship or unusual difficultywithout a compensating increase in the level of quality and safety. The license stated that:
Access to the canopy seal being repaired does not provide adequate clearance to gain complete access to the inner rod travel housing to perform the liquid penetrant examination of the weld repair. Additionally, the canopy seal being repaired is located in a high radiation area.
As a result of the limitations discussed supra, the licensee proposed an alternative to Section IWA<120(a) of Section XI of the ASME Code. The licensee's alternative proposes to perform the weld repair consistent with the requirements of the 1989 edition of ASME Section III,with the exception of performing the PT surface examination.
In lieu of the PT surface examination, the alternative would: (1) examine the surface to be repaired by using an 8x camera during the surface preparation; (2) use a fullyautomatic Gas Tungsten Arc Welding process to deposit the weld buildup; (3) complete a final visual examination of the weld surface using the same 8x camera; (4) perform a VT-2 examination of the lower canopy seal weld area during the post outage system leakage test; and (5) use an authorized Nuclear Inservice Inspector to approve alternative testing and NIS-2 acceptance.
To demonstrate that an adequate visual inspection of the weld surface can be performed using the camera, the licensee submitted a test report giving the results of resolution test of the
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camera equipment that willbe used by the welding contractor.
The test was performed in support of a similar repair on CRDM canopy seal welds at Prairie Island. The camera and system used at Prairie Island is equivalent to the camera and system that will be used at HNP.
In the test, a wire 0.0005-inch diameter by 0.4 inch-long was taped to the surface of a mockup of the production welds. The wire was filmed using weld head lighting for illumination. Review of the tape demonstrated the visibilityof the test wire with the camera system.
Although the test results indicate that the camera can detect indications as small as the test wire (0.4 inch-long), the minimum sized Code-allowable linear indication is 1/16 inch. Therefore, a bounding analysis for the maximum allowable flaw size was also performed to demonstrate that the camera can detect indications much smaller than the maximum allowable flaw size.
Limitload (net section collapse) and linear elastic fracture mechanics (LEFM) analyses were performed to determine the niaximum allowable (critical) flaw sizes for longitudinal and circumferential flaws under design conditions (modeling the CRDM housing as a pipe with through-wall flaws).
The materials employed at the weld location are type 304 stainless steel for the CRDM and an austenitic nickel based Alloy625 for the fillermaterial. A conservative fracture toughness value of 135 ksi-in" was used for both the base material and the weld material. The limitload analyses provided the most realistic calculation of the maximum tolerable flaw before structural failure would occur for the materials of construction.
Although known to be less accurate for the high toughness material used, the LEFM results provide an independent verification of the limit load analyses.
Using the limit load method for longitudinal and circumferential flaws, the maximum crack lengths would be at least 4.8 inches and 7.43 inches, respectively.
The LEFM analyses for axial and circumferential through-wall flaws gave results of 5.05 inches and 7.31 inches respectively.
Both sets of analyses gave critical flaw sizes greater than 10 times larger than either the Code acceptance criteria for PT examinations or the length of wire demonstrated to be visible with the 8x camera.
Creating a large undetected flaw in or adjacent to a weld in high toughness material is not plausible.
Due to weld shrinkage, any crack would exhibit significant crack opening displacement, thereby enhancing detectability, regardless of length As a further process control during welding, the 8x camera will be employed to monitor the weld puddle during performance of the production welds. This enables the welding operator to further verify the welding process, take corrective actions during the course of welding, and identify potential problem locations pri'or to weld completion and performance of weld acceptance examinations.
With the additional process monitoring this method provides, the probability of undetected weld defects is substantially diminished. Therefore, completing the PT examination as required by the ASME Code would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety in that the PT examination would be unusually difficultto complete given the clearance between the outer rod travel housing of 8 inches and the high radiation fields of approximately 500-800 mrem/hr (1-11/2 rem/hr on contact).
For Request for Relief 2R1-012, the staff concluded that the licensee's proposed alternative provides reasonable assurance that CRDM willbe repaired adequately.
Moreover, the staff concluded that imposing the Code requirements on the licensee results in a burden without a "compensating increase in quality and safety. Therefore, the licensee's proposed alternative is authorized, for the stated repair, pursuant to 10 CFR 50.55a(a)(3)(ii)
Principal Contributor:
S. Flanders Date:
Novanber 6, 1998
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