ML20196A524

Safety Evaluation Accepting Proposed Alternative to Use UT Techniques Qualified to Objectives of App Viil as Implemented by PDI Program in Performing RPV Shell Weld & Shell to Flange Weld Examinations

ML20196A524
Person / Time
Site:	Cooper
Issue date:	11/23/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20196A519	List: ML20196A516 ML20196A524
References
NUDOCS 9811300021
Download: ML20196A524 (4)

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NUCLEAR, REGULATORY COMMISSION

WASHINGTON, D.C. 30ses 40tH

. < [A E SAFETY EVALUATION BY THE OFFICE OF NUCLFAR ' REACTOR REGULATION OF THE THIRD TEN-YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN REQUEST FOR RELIEF NO. Rl-04  :

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NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION n DOCKET NUMBER: 50-298 i

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1.0 INTRODUCTION

~ Section .50.55a(g) of Title 10 of the Code of Federal Regulations provides that inservice inspection of American Society of Engineers (ASME) Code Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME Boilers and Pressure Vessel (B&PV)

LCode and applicable addenda. Section 50.55a(a)(3) states that proposed altematives to the requirements of paragraph (g) may be used when authorized by the NRC, if (i) the proposed altematives would provide an acceptable' level of quality and safety or (ii) compliance with the -- l specified requirements would result in. hardship or unusual difficulty without a compensating ,

. increase'in the level of quality 'and safety.

. By letter dated August 31,1998, the Nebraska Public Power District (NPPD) submitted a -  ;

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. request for relief from the method of performing certain augmented examinations of the reactor pressure vessel (RPV) shall welds at the Cooper Nuclear Station (CNS). NPPD proposes to - ,

use an alternate ultrasonic examination technique, known as the GERIS 2000 system, whbh  !

does not meet the explicit requirements of ASME Section V or Regulatory Guide 1.150,  ;

' Revision 1.  :

l 2.0 EVALUATION The information provided by Nebraska Public Power District in support of the proposed attemative to the Code requirements has been evaluated and the basis for disposition is documented below. The Code of record for the Cooper Nuclear Station, third 10-year ISI interval, which began March 1,1996, and ends February 28,2006, is the 1989 Edition of

~ Section XI of the ASME Boiler and Pressure Vessel Code.

h o" M g ^ ENCLOSURE PDR

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F 2.1 Code Reauirement/ Licensee's Proposed Altemative-E d i ASME Section XI,1989 Edition, Table IWB-2500-1 requires a volumetric examination of the belt line region shell circumferential and longitudinal welds and the shell to flange weld. The automated RPV shell weld and shell to flange weld UT examinations sMll be performed

' using personnel and procedures qualified to the objectives of the 1992 Edition,1993

Addenda to Appendix Vill of Section XI of the ASME Code in lieu of or in Wdition to the L 1989 Edition of Section XI of the ASME Code UT examination requirereents. Reliefis 4'  : requested for the balance of the Third Ten-year interval.

p , 2.2' Licensee's Basis for the Prooosed Alternative:

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' The Cooper Nuclear Station reactor pressure vessel has limited access from the outside

diameter for ultrasonic inspection. This has resulted in the need to perform an automated weld inspection from the inside diameter. Based on equipment limitations and proven U results, Cooper has selected the GERIS 2000 System to perform the examination. The

!- ultrasonic testing (UT) technique (procedures, personnel and equipment used with this L system does not meet the explicit requirements of ASME Section V or Regulatory Guide 1.150 Revision 1 for examination technique.

For the remote examinations, the licensee will use the GERIS 2000 system operated with i

. y Performance Demonstration Init!ative (PDI) qualified personnel using PDI qualified

. procedures. The procedures were qualified at the PDI qualification Session No. 61-02.  !

P Personnel qualifications are recorded and maintained at PDI. The examination and sizing procedures use echo-dynamic motion and tip diffraction characteristics of the flaw instead of .

- the amplitude characteristics required by the ASME Code. The same straight and angle

beam search units willinterrogate the examination volume as an ASME Section V, Article 4

[ procedure. An examination using 70 degree refracted longitudinal search units will be -

performed.

The GERIS 2000 system inspection procedures qualified at PDI do not comply with ASME Section XI paragraph IWA-2232, ASME Section V Article 4, or USNRC Regulatory Guide 1.150. The examination and sizing techniques are considered an attemative that provides a higher quality result than ASME Section XI. Included in the August 31,1998 letter, the

. licensee provided supporting information in an attachment titled "GERIS 2000 invessel .

' System Alternate Method for Compliance to Regulatory Guide 1.150," dated March 1997.

By letter dated October 2,1998, the licensee also provided a comparison between Cooper's altemative using GERIS 2000 System and the ASME Section XI,1989 Edition.

A comparison between the ASME Section V based ultrasonic methods and procedures

- developed to satisfy the PDI can be described as a comparison between a compliance-based procedure (ASME.Section V) and a results-based procedure (PDl). ASME Section V procedures use an amplitude-based technique and a known reflector. The ultrasonic j technique was established independently from the acceptance standards for flaw size found in ASME Section XI. The PDI sizing UT technique is considered more accurate than the UT

. technique used in ASME Section V.

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The PDI process specifies the required results of the examination. The PDI qualification is based on a group of samples, which validate the acceptable flaw sizes in ASME Section XI. i The sensitivity to detect these flaws is considered to be equal or greater than the sensitivity l obtained through ASME Section V because the PDI process requires the detection of diffracted signals whereas the Section V procedures rely on the larger specular reflectors.

Qualified Level lli data analysts using the applicable PDI qualified procedure will perform analysis and sizing ofindications.

Regulatory Guide 1.150 " Ultrasonic Testing of Reactor Vessel Welds During Preservice and Inservice Examinations" is also a prescriptive examination. The regulatory guide does not provide a structure for procedure demonstration and therefore allows for various interpretations of the examination results. Also, the regulatory guide does not provide for a number of samples, a blind test _ or an acceptable level of performance, all of which are addressed in the PDI program. The PDI program, based on ASME Section XI, Appendix Vill, requires the ultrasonic equipment, procedures and examiners be tested on l flawed and notched materials and configurations similar to those found in actual plant conditions.

The use of PDI qualified procedure results in a more sensitive examination for the detection of potential flaws than the code described techniques. The error band for sizing has been established within the limits of Appendix Vill. The inspection method's capability to reliably l detect flaws in the areas of restricted access was satisfactorily demonstrated at the PDI session.

2.3 Staff Evaluation-NPPD plans to use the GERIS 2000 system to perform the remote controlled, automated ultrasonic (UT) examination of the CNS reactor pressure vessel. The GERIS 2000 System uses an alternative procedure to the ASME Code and RG 1.150. The examination procedure is dependent on the echo-dynamic motion and tip diffraction characteristics of the flaw instead of the amplitude characteristics required by the applicable edition of the Code.

The areas where the procedure deviates from the RG 1.150 positions are explained in NPPD's letters dated August 31 and October 2,1998. An examination performed with the proposed procedure will result in the examination volume being interrogated by the same straight and angle beam search units as an ASME Section V, Article 4 procedure. Any areas of limited access would be the same as for tne use of the Article 4 procedure. The proposed procedure would also include an examination by the 70* longitudinal search units.

In November 1994, General Electric successfully demonstrated the proposed procedures at the Performance Demonstration Initiative (PDI) qualification session No. 61-02, in accordance with the 1992 Edition,1993 Addenda of ASME Section XI, Appendix Vill requirements. Appendix Vill was developed to ensure the effectiveness of UT examinations within the nuclear industry by means of a rigorous, item specific performance demonstration. The performance demonstration was conducted on a RPV mockup containing flaws of various sizes and locations. The demonstration established the capability of equipment, procedures and personnel to find flaws that could be detrimental to the integrity of the RPV. Although Appendix Vill is not a current requirement, the

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4 qualification of equipment, procedures and personnel to Appendix Vill criteria demonstrates examination and evaluation techniques that equal or surpass the requirements of paragraph IWA-2232, " Ultrasonic Examination," of Section XI of the ASME Code, and the guidance in RG 1.150. The NRC staff has previously approved similar relief requests employing this

' attemate examination technique (see March 26,1996, letter from S. Shankman, NRC to E.

Boulette, Boston Edison Company).

3.0 CONCLUSION

The staff has reviewed and evaluated the licensee's proposed attemative to use UT techniques (personnel, equipment, and procedures) qualified to the objectives of Appendix Vill as implemented by the PDI program in performing RPV shell weld and shell to flange weld examinations. Based on the information submitted, the staff concludes that the proposed alternative examination of the RPV shell weld and shell to flange weld would provide an equivalent or better examination than current Code requirements and Regulatory Guide 1.150 recommendations and thus would provide assurance that flaws that could be determental to the integrity of the RPV would be detected. Therefore, the staff has determined that the proposed

. attemative would provide an acceptable level of quality and safety.

Pursuant to 10 CFR 50.55a(a)(3)(i), the proposed alternative is authorized for the RPV shell weld and flange to shell weld examinations during the Third Ten-year interval.

Principal Contributors: J. R. Hall D. L. Wigginton Date: November 23, 1998