ML20216F100

Safety Evaluation Accepting 980331 Licensee Proposal to Perform Alternative Testing for Containment Pressurization Test for Vynp

ML20216F100
Person / Time
Site:	Vermont Yankee
Issue date:	04/15/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20216F074	List: ML20216F069 ML20216F100
References
NUDOCS 9804160418
Download: ML20216F100 (3)

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I SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO ALTERNATIVE CONTAINMENT PRESSURIZATION TEST VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271 1

1.0 INTRODUCTION

The Technical Specifications (TS) for Vermont Yankee Nuclear Power Station (VY) states 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 (B&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). The 10 CFR 50.55a(a)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the Nuclear Regulatory  ;

Commission (NRC), if (i) the proposed attematives would provide an acceptable level of quality I and safety or (ii) compliance with the specified requirements would result in hardship or unusual i difficulties without a compensating increase in the level of quality and safety. I Pursuant to 10 CFR 50.55Mg)(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 inte vals 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 l modifications listed therein. Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that l conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose attemative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed. In a letter dated March 31,1998, Vermont Yankee Nuclear Power Corporation (the licensee), requested that the NRC staff approves an attemative to the requirements of the ASME Code,Section XI pertaining to testing of its VY containment.

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.; u l ' 2.0 EVALUATION j The licensee submitted the subject request to use an attemative to the requirements of ASME Code,Section X!. The Code of record for the third intervalis the ASME Code,Section XI,1986 Edition. The ir. formation provided by the licensee !n support of the request has been evaluated and the bases for disposition are documented below.

2.1 Code Reauirement: Section XI, paragraph IWE-5221 states: "Except as noted in IWE-5222, repairs or modifications to the pressure retaining boundary or replacement of Class MC

, or Class CC components shell be subjected to a pneumatic leakage test in accordance with the provisions of Title 10, Part 50 of the Code.of Federal Regulations, Appendix J

• l 2.2 Licensee's Code Relief Raamst: Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee  !

requested relief from the requirement to perform post repair testing of its VY containment as '

required by IWE-5221. '

2.3 Licensee's Basis for Rannastino Relief (as stated):

"The intent of 10 CFR [Part) 50, Appendix J is to ensure that the escape of containment air to the atmosphere fotowing c :ksign basis accident is maintained below established limits by the L performance of r. pneumatic leakage test. This testing requires extensive pressure stabilization er d ter@rature eaualization for the test. The actual performance of the test requires soproximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of stabilization, temperature equalization, leakage testing and 1 verification. In addition, the Type A test requires extensive system line-up and extensive l

l supplementalinstrumentation requirements. None of these issues apply to the concem of l structural integrit*/ or water leak tightness of the repair area. Since the repair being made to the l.

torus is entirely located below the normal and post accident water level of the torus, the repair  !

area is completely water-sealed against any potential air leakage. l The propesed attemative test is to pressurize the containment air volume to a minimum of 44 psig and hold for a minimum of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. This test exceeds the maximum suppression chamber

. pressure postulated during worst case accident conditions and will subject the repaired area of the torus shell to both the containment air volume pressure and the static pressure of the standing head of water.  !

This proposed altamative testing is also justified due to the extensive non-destructive testing i that will be conducted. The shell repair will a"empt to reuse the existing plate through the use

!- of thin cutting tools and techniques. New plate :nsterial, curved to match the contour of the torus, will be available if regi:! red. The shell repair will be accomplished under 1977 edition summer addenda of ASME Secton ill, class MC, subsections NE. In conformance to ASME NE requirements, full radiographic test (RT) will be performed on the final weld joint. In addition to the requirements of ASME, VY will be performing the following; liquid penetrant inspection of the weld props, visual inspection of the root pass of the weld, magnetic particle inspection and liquid penetrant inspection of the completed welds, and the use of charpy qualifed weld materials and weld procedures. This wili assure that the integrity of the repair meets or exceeds the quality requirements of the existing torus shell. Industry experience has proven that current state of the art non-destructive testing techniques provide an accurate assessment 3 of the acceptability of structural welds."

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2.4 Licensee's Pronomed Altamative Examination (as stated):

"The proposed alternative test is to pressurize the containment air volume to a minimum of 44

_ psig and hold for a minimum of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. This test exceeds the m=ximum suppression chamber pressure postulated during worm case accident conditions arm . vill ubject the repaired area of the torus shell to both the containment air volume pressure and the static pressure of the standing head of water."

Evaluation: The licensee has requested relief from the Code requirements to perform leakage test following repair as required by IWE-6221 of ASME Code,Section XI. The licensee is

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proposing to perform an altemative testing of the W torus. The need for the testing occurred

! because during the current refue!;ng outage, W will be replacing the core spray and residual heat removal system suction strainers which are located v#hin the torus. Because of the physical dimensions of tho new strainers, installation of the strainers cannot be accomplished by use of the existing hatches in the torus space. Consequently, W has opted to cut a

! temporary hatch into the torus rather than constructing the strainers inside the torus. The location for this new hatch was selected based can freedom from obstructions, ease of access, l and ability to facilitate traffic flow and rigging of the strainer sections. The temporary hatch will be made by cutting and removing a section of torus shell. The location of this entire hatch will be below the normal and post accident water line in tie torus.

Pursuant to 10 CFR 55a(a)(3)(i)W is proposing to perform attemative testing to that specified by IWE-5221. The proposed attemative testing to verify structuraland water leak tightness would be to perform a pressurization test of the entire containment (drywell and suppression chamber) including the affected torus area with the torus water volume at that specified by Technical l Specifications. This pressurizationtest will consist of pneumatically pressuri::ing the containment air volume to a minimum of 44 psig and holding the pressure for a minimum of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. During the performance of this test, a visualinspection of the torus shellin the area of the repair will be made

[. to verify that there is no visible leakage and/or structural deformation. In addition, the shell repair l '

will be accomplished underthe rules of 1977 edition summer addanda of ASME Section ill, class MC, subsections NE. In conformance to ASIVE NE requirements full RT will be performed on the final weld joint. In addition to the requiremeras of ASME, W will be performing the following; liqub p penetrantinspectionof the weld prepara r' 4.:rfaces,visualinspectionof the root pass of the weld, l

magnetic particle inspection and liquid penetrant inspection of the completed welds, and the use of charpy V-notch qualified weld materials and weld procedures. This will ensure that the integ-ity of the repair meets or exceeds the quality requirements of the existing torus shell.

3.0 CONCLUSION

The NRC staff concludes that the licensee has provided an acceptable attemative to the requirementsstatedin paragraphlWE-5221 of the ASME Code,Section XI. The staff, therefore, concludes that authorization of the licensee's alternative program would provide an ecceptable level of quality and safety, is authorized by law and will not endanger life or property o" cc inmon defense and security, and is otherwise in the public interest, giving due consideration to the butden upon the licensee and facility that could restift if the Code requirements were imposed on the facility.

Pursuant to 10 CFR 50.55a(a)(3)(i) the attemative is authorized.

Principal Contributor: G. Georgiev Date: