ML20217F313

Safety Evaluation Accepting Proposed Alternative to ASME Code for Surface Exam of Nonstructural Seal Welds,For Plant, Unit 1

ML20217F313
Person / Time
Site:	Point Beach
Issue date:	04/17/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217F308	List: ML20217F304 ML20217F313
References
NUDOCS 9804280124
Download: ML20217F313 (4)

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9 . . . . . ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REVIEW OF PROPOSED ALTERNATIVE TO THE ASME CODE FOR SURFACE EXAMIN'ATION OF NONSTRUCTURAL SEAL WELDS WISCONSIN ELECTRIC POWER COMPANY POINT BEACH NUCLEAR PLANT. UNIT 1 DOCKET NO. 50-266

1.0 INTRODUCTION

Title 10, Code of Federal Regulations (CFR), 50.55a(c)(4) states that for a nuclear power plant whose construction permit was issued prior to May 14,1984, the applicable Code edition and Addenda for a component of the reactor coolant pressure boundary continue to be that Code

! Edition and Addenda that were required by Commission regulations for such components at the time of issuance of the construction permit.

10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (c) 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 difficulty without a compensating increase in the level of quality and safety.

By letter dated April 3,1998, Wisconsin Electric (WE or the licensee) Power Company stated its intent to remove the part-length control rod drive mechanisms (CRDMs), cut the reactor vessel penetrations for the part-length CRDMs at locations E7, G5, G9, and 17, install threaded caps, and seal weld the caps. In accordance with 10 CFR 50.55a(c)(4), the modification would be to the requirements of the original 1965 Edition of the Code for the reactor coolant pressure boundary. WE has proposed an attemative to the surface examination requirements of paragraph N-518.4 of the 1965 American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The proposed attemative would be used in conjunction with the four nonstructural seal welds on the threaded caps for the Unit i reactor vessel head penetrations.

The welds will be used to ensure leak tightness of the thread joints holding the new caps Because the threads constitute the pressure boundary, the seal weld is nonstructural.

The staff has reviewed and evaluated the licensee's request and supporting information on the proposed attemative to the Code requirements for Point Beach Unit 2, pursuant to the provisions of 10 CFR 50.55a(a)(3)(i).

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2.0 DISCUSSION

Component Identification:

Reactor vessel penetrations E7, G5, G9, and 17, for the part-length CRDM housings.

l Code Requirement.

l ASME Section 111,1965 Edition, paragraph N-518.4, specifies a surface examination of welded l attachments. Paragraph N-518.4 of the 1965 ASME Code, Section lil, requires that attachments (welds) to the pressure boundary be inspected by means of a liquid penetrant examination (PT). For PT examinations, the acceptance criteria of paragraph N-627 must be met. The most stringent among the acceptance criteria is the requirement for "no linear indications." Later editions of the Code define 1/16 inch as the smallest length of a relevant l linear indication.

l Alternate Reauirement: (As stated) l In accordance with the provisions of 10 CFR Part 50, Section 50.55a(a)(3), Wisconsin Electric l (WE) Power Company proposes the following:

1. Use of a controlled automatic welding process.

2. Observation of the weld puddle / deposit via a 8X camera during the welding process.

3. A final visual examination of the weld surface using the same 8X camera.

4. Performance of a VT-2 inspection of the seal weld and CRDM penetration cap for leakage during the reactor coolant system (RCS) leak test. The RCS leak test is performed at 2085 psig,100 psig above the normal operating pressure of 1985 psig.

5. Authorized Nuclear Inservice inspector approval of alternative testing a.1d NIS-2 acceptance.

l Reason for Proposed Alternate Reauirement:

WE stated that the PT examination of the welds would be difficult. The seal welds will be in a high radiation area of approximately 1000 millirem / hour. Additionally, access to the weld locations is difficult due to the limited clearance between adjacent CRDMs. The separation between the housings is approximately 7 inches. This is not adequate clearance to gain complete access to perform the PT examination. Surface preparation (grinding) of the welds, PT examination, and subsequent cleanup would be difficult to execute properly, would be time consuming, and would incur substantial personnel radiation exposure.

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. s 3.0 - EVALUATION Section lli of the ASME Code,1965 Edition, specifies a surface examination of weld-repaired areas (paragraph N-514.2) or welded attachments (paragraph N-518.4). For PT examinations, the acceptance criteria of paragraph N-627 must be met. The most stringent among the acceptance criteria is the requirement for "no linear indications." Later editions of the Code define 1/16 inch as the smallest length of a relevant linear indication.

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! The proposed alternative would include an 8-power visual examination (by means of a remote l video camera) of the in-process automatic welding and a post-weld visual examination with the same camera. Although the seal weld is nonstructural, the licensee had an analysis performed that treated the weld as a pressure boundary in order to calculate a critical flaw size (critical l through-wall axial flaw length of 4.17 inches and critical through-wall circumferential flaw length l of 6.95 inches). The results were used as a reference for the evaluation of the effectiveness of the visual examination with the camera. The results of the analysis demonstrated that the ,

predicted critical flaw size ir, all cases is of significant length and therefore the proposed -l 8-power visual examination will be able to reliably detect much smaller flaws than the calculated .

critical flaw size. A VT-2 visual examination of the welds would also be performed during a l hydrostatic test of the reactor This inspection assures that the function of the seal weld is i being satisfied.  !

I The licensee subminea a test report giving the results of a resolution test of the camera equipment used by the welding contractor during the weld repairs. In the test, a wire .

0.0005-inch in diameter and another 0.001-inch in diameter, both 0.4-inch long, were taped to I the surface adjacent to a mockup of the production welds. The wire was filmed using the weld ,

head lighting for illumination. Review of the tape demonstrated the visibility of the test wires  :

with the camera system.

As a further process control during welding, the same video camera will be employed to monitor the weld puddle during performance of the production welds; This technique is now commonly .

employed in the industry with positive results. It enables the welding operator to further verify the welding process, take corrective actions during the course of welding, and to identify potential problem locations prior 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.

The use of a controlled automatic welding process, observation of the weld puddle / deposit during the welding process, a final visual examination of the weld surface using the camera, l and a VT-2 examination of the weld and the cap for leakage during the post-outage hydrostatic test will provide assurance of the integrity of the seal welds. Therefore, the proposed alternative will provide an acceptable level of quality and safety.

4.0 CONCLUSION

Under the provisions of 10 CFR 50.55a(a)(3)(i), the staff has determined that the licensee's proposed attemative to the ASME Code for surface examination (PT) of the seal welds on threaded caps for the Unit i reactor vessel head penetrations for the part-length CRDMs will l

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4 l provide an acceptable level of quality and safety. The proposed attemative inspection is l authorized for the four stated repairs at Point Beach Nuclear Plant Unit 1. Authorization of the l proposed attemative does not extend to future use without prior staff review. If similar repairs l are necessary for the Unit 2 penetrations in the future, a separate relief request must be submitted.

i Principal Contributor: A. Kugler Date: April 17, 1998 l

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