ML17310B025

Unit 2 Steam Generator Tube Insp Plan Addendum.

ML17310B025
Person / Time
Site:	Palo Verde
Issue date:	01/27/1994
From:	ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:
Shared Package
ML17310B024	List: ML17310B023 ML17310B025
References
PROC-940127, NUDOCS 9402090138
Download: ML17310B025 (8)

Text

ENCLOSURE UNIT 2 STEAM GENERATOR TUBE INSPECTION PLAN ADDENDUM 9402090138 940127 PDR ADQCK 0500052'P Q . . PDR

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r UNIT 2 STEAM GENERATOR 'TUBE INSPECTION PLAN ADDENDUM CHEMICAL CLEANING The primary purpose of the chemical cleaning program in Unit 2 is to remove linear freespan deposits which led to the steam generator tube rupture event on March 14, 1993. Ridge deposits were identified as a contributor in the root cause of failure investigation. The chemical cleaning is also expected to remove tubesheet deposits and deposits from the flow distribution plate crevices. The chemical cleaning process began on January 24, 1994 in Steam Generator 21 and is scheduled to begin in Steam Generator 22 on January 29, 1994.

EDDY CURRENT TESTING EC POST CHEMICAL CLEANING The primary purpose of the post chemical cleaning ECT is to determine the effectiveness of the chemical cleaning process to remove ridge or bridging deposits on steam generator tubes and to a lesser extent to determine the potential for deposit masking of ECT flaw signals.

In addition to the steam generator tube inspection plan submitted by the referenced letter, the following ECT is being added post chemical cleaning. AII single/multiple axial indications identified by ECT in Steam Generator 21 during this outage, prior to chemical cleaning, will be re-examined with bobbin and Motorized Rotating Pancake Coil (MRPC).

In addition, sixty tubes (with possible deposits) in each steam generator will be examined with MRPC from the 08H support to the first. vertical support. The sixty-tube sample size .

was derived from a statistical evaluation based on the 1993 ECT results which identified a total population of less than 500 tubes with ridge deposits. APS will base the critical tube population on 1994 ECT results due to enhanced PDP'eporting.

The results of the statistical evaluation indicate that with a fifty-three tube sample of the critical tube population, there is a 95 percent confidence that 95 percent of the tubes have not been affected by chemical cleaning. The critical tube population is considered to be tubes with ridge or bridging deposits. The 95/95 evaluation confirmed the adequacy of a random sample of sixty tubes of the critical tube population. In addition, if the critical tube population increased to 1,800 tubes, the number of tubes in the sample size would increase from fifty-three to fifty-six tubes.

PDP - Possible Deposit; SAI - Single Axial Indication; MAI- Multiple Axial Indication; NDD - No Detectable Discontinuity; SCI - Single Circumferential Indication; MCI - Multiple. Circumferential Indication.

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'COPE OF ECT f,

SG21 ECT after chemical cleaning:

~ Bobbin coil and MRPC all SAI/MAI locations identified prior to cleaning MRPC 60 NDD tubes with PDP indications from the 08H support to the first vertical sUpport MRPC from 08H through the first Vertical Support (VS) and the remaining tubes in the arc of 1800 (approximately 30 percent) which were not MRPC prior to chemical cleaning SG22 ECT after chemical cleaning:

~ Bobbin coil and MRPC all SAI/MAI locations, identified prior to cleaning

~ MRPC 60 NDD tubes with PDP indications from the 08H support to the first vertical sUpport ECT EXPANSION CRITERIA If one or more of the sixty NDD tubes exhibits a significant change in ECT response, an additional 6 percent (1 08 tubes) will be inspected from the 08H support to the first vertical support by MRPC (See Figure 1). A significant change in ECT response is defined as a new pluggable (SAI/MAI) indication.

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Unit 2 Eddy Current Testing 1994 "NDD" SAMPLE EXPANSION CRITERIA

~ BASED ON TECH SPEC (EXCEPT "C" CATEGORIES ARE BASED ON 500) 60 NDD TUBES MRPC 08H-1st VS

) 1 SAI/MAI ADD 6% (108) ADD 95/95 8AMPLE OF 1800 FOR KIDNEYBEAN

) 1 8AI/MAI SLUDGE ARFW ) 1 NEW SCI/MCI ADD 12% (216)

OF 1800 AND 6% (108) IN ADD REMAINING OTHER SG ) 1 8AI/MAI TSH ADD REMAINING 1800 FIGURE 1

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