ML20059B828

SER Granting Relief & Concluding That Code Required Exam Impractical to Perform to Extent Required by Code & That Limited Section XI Surface Exam Provide Results Which Demonstrated to Be Superior or Equivalent to Surface Exam

ML20059B828
Person / Time
Site:	South Texas
Issue date:	10/21/1993
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20059B794	List: ML20059B792 ML20059B828
References
NUDOCS 9310290109
Download: ML20059B828 (3)

Text

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/ E UNITED STATES

.  ! NUCLEAR REGULATORY COMMISSION

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... 4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE INSPECTION PROGRAM RELIEF REQUESTS HOUSTON LIGHTING & POWER COMPANY SOUTH TEXAS PROJECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 1.0 MIE90VCTION  ;

Technical Specification 4.0.5 for South Texas Project, Units 1 and 2, states l that the inservice inspection and testing 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.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 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(c.)(4), ASME Code Class 1, 2, and 3 components (including sLpports) 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, l geometry, and materials of construction of the components. The regulations I require that inservice examination of components and system pressure tests I conducted during the first ten-year interval 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 twelve months prior to issuance of the operating license, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the South Texas Project, Units I and 2, first 10-year inservice inspection (ISI) interval is the 1983 Edition, through Summer 1983 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. ,

1 Pursuant to 19 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facilities, 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 9310290109 931021

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alternative 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.

The licensee, Houston Lighting & Power (HL&P), submitted Relief Request No. RR-ENG-12, by letter dated December 9, 1992, for the first 10-year ISI interval, which began August 25, 1988 (Unit 1) and June 19, 1989 (Unit 2).

The staff, with technical assistance from its contractor, the Idaho National Engineering Laboratory (INEL), has evaluated the subject request for relief in the following section.

2.0 DISCUSSION The information provided by the licensee in support of the request for relief from impractical requirements has been evaluated and the bases for granting relief from those requirements are documented below.

Reauest for Relief No. RR-ENG-12 (Units 1 & 2). Examination CateaorY 1 B-G-1. Item B6.10. Reactor Vessel Closure Head Nuts Code Reauirement: Table IWB-2500-1, Exa.mination Category B-G-1, Item Number B6.10 requires a 100 percent surface examination of all reactor vessel (RV) closure head nuts during the 10-year interval.

Licensee's Code Relief Reauest: Relief is requested from the surface examination requirements for the inside surface (threaded area) of the reactor vessel closure head nuts. The licensee states that although there is no description or figure referenced in Section XI depicting the area of the examination, it has been interpreted to include all surfaces of the nut (i.e.,

top, bottom, outside, inside threads).

Licensee's Basis for Reauestina Relief: The licensee states that typically a fluorescent magnetic particle (MT) examination is performed on threaded areas because of its suitability for revealing relevant indications in the root of the thread. Due to the poor viewing angle and limited access to the threaded surface with the MT equipment and black light, a meaningful MT examination can not be performed.

1 Licensee's Proposed Alternative Examination: The licensee will conduct an NT 1 examination on the outside surfaces of the RV nuts. In lieu of the Code- l required surface examination of the threaded surfaces of the RV nut, the licensee will perform an ultrasonic (UT) examination of the threaded region from the outside and end surfaces of the nut. The UT examination provides coverage of the thread root area in two directions. A 0-degree UT (UTC) examination is performed 360 degrees around the nut end surface to examine the threaded area for circumferential flaws. A 43-degree UT (UT43) I examination from the outside surface is used to examine the threaded area in l clockwise and counterclockwise directions to detect axial flaws.

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g 4 A spare RV nut will be used for the calibration block. Circumferential notches cut 0.115 inch deep and an axial notch cut through the threads to the -

thread root will be used to establish the sensitivity for the UT examinations.

No limitations are encountered with the UTO examinations. Scanning for the UT43 examinations is limited by the six wrench slots located on the upper end of the nut. These slots reduce the UT43 coverage of the threaded region by approximately 7.5 percent.

3.0 EVALUAIJ03 The Code requires a surface examination of all surfaces associated with the reactor vessel head closure nuts. As a result of the nut design, it is impractical to perform a meaningful surface examination of the threaded region. The UT43 examination is sensitive to critical, axially orientated fl aws. The combined UT43 and UTO examinations provide a qualitative examination of the nut inside thread region. Imposition of the Code requirement on the licensee would cause a burden because redesign or replacement of the nut would be required in order to yield meaningful results.

In addition, in NRC Inspection Report 50-498/92-28; 50-499/92-28 dated October 28, 1992, the inspector discusses his c'. syations and findings regarding the licensee's proposed alternative m nation. The inspector found that based on the observed sensitivi* , , was achieved in calibration of the ultrasonic equipment, he considerN ' na ultrasonic examination method to be an acceptable alternative to surfac6 examination of the inner diameter surface of the reactor vessel closure head nuts.

The licensee's proposed UT technique, in addition to the surface examination of the accessible surfaces of the reactor pressure vessel head closure nuts, provides an acceptable level of quality and assurance of the nut (s) structural .

integrity. The proposed UT technique may be substituted for the surface i examination of the nut thread region provided the results are demonstrated to be equivalent or superior to those of the surface examination. Based on the above and pursuant to 10 CFR 50.55a(g)(6)(1), relief may be granted as l requested. ,

4.0 CONCLUSION

Based on the above evaluation, it is concluded that the Code-required examination is impractical to perform to the extent required by the Code and that the limited Section XI surface examination, in conjunction with the proposed volumetric examination, provide results which are demonstrated to be equivalent or superior to those of a surface examination. The staff has determined that granting relief, pursuant to 10 CFR 50.55a(g)(6)(1) is authorized by law and will not endanger life or property, or the common defense and security and is otherwise in the public interest.

Principal Contributor: T. K. McLellan Date: October 21, 1993