ML113070387

Fall 2011 RFO - Steam Generator Inspection Call - Part II, Summary of the ANO1 1R23 Steam Generator Inspection

ML113070387
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/02/2011
From:	Clark R Entergy Operations
To:	Kalyanam N Plant Licensing Branch IV
Kalyanam N, NRR/DLPM, 415-1480
Shared Package
ML113070371	List: ML113070376 ML113070387
References
TAC ME7368
Download: ML113070387 (4)

Text

Summary of the ANO1 1R23 Steam Generator Inspection Arkansas Nuclear One - Unit One (ANO1) shutdown on 10/16/2011 for the 23rd refueling outage.

During that outage, both steam generators were inspected. The generators were installed in 2005 and are AREVA Enhanced Once Through Steam Generators (EOTSG). This is the fourth inspection since replacement.

The scope included:

100 % full length bobbin in both generators X-probe of all bobbin indications X-probe of all tubes with tube-to-tube indications (proximity) due to tie rod bowing Visual inspection of previously installed plugs (SGA = 10 and SGB = 6)

There were no secondary side visual inspections performed.

Results:

There are two damage mechanism currently associated with the ANO1 steam generators. These include mechanical wear at the tube support plates and tie rod bowing which results in tube to tube contact during cold conditions. These will be addressed separately below:

Tube Support Plate Wear (Indications)

SG ID  % TW 1-19% %TW 20-39% %TW 40-100%

SGA 1456 36 0 SGB 1344 68 2 Maximum Depth was 46% TW (previous indication) 95/50 Growth = (~ 3 % TW per EFPY)

Plugging was performed at > 35% to justify an interval equal to three cycles. All condition monitoring parameters were met and no in-situ was required.

Tie Rod Bowing Historically, tie rod bowing was isolated to SGA only. The bowing is a result of the edges of the tube support plates being frictionally locked to the inner shroud during cool downs. During operation, the support plates go back to their free movement status and the rods straighten out. This is evident by no in-service tube to tube wear.

During the 1R23 inspection, bowing was identified in both steam generators. The extent of the bowing will be discussed by generator below:

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SGA This is the fourth inspection where bowing has been identified. An operability was developed that addresses the projected curve of bowing based on the number of thermal cycles the unit experiences.

Currently the unit has experienced six total thermal cycles. The operability was developed based on both laboratory testing of the tie rods and the support plates and various other analytical models. The maximum extent of the bowing is projected to be ~ 2.0 inches of lateral bow in the first span tie rods.

The first span is defined by the area between the top of the lower tube sheet to the first support plate.

This span has the longest vertical distance and the smallest diameter tie rods. Therefore the maximum extent of bowing is exhibited in the first span. Based on the projected curve, at 6 thermal cycles, the bowing could be as much as 1.6 inches of vertical bow. The actual results were consistent with the last inspection results of slightly below 1.3 inches. SGA has been consistent with the previous results and within the projected estimates in the operability.

Two tubes in SG A (SG 11), with tie rod bowing in the first span, display what appears to be geometric deformations just above the lower tube sheet, at the mid-span (point of maximum bow) and just below the first TSP. The two tubes are Row 43 Tube 8 and Row 88 Tube 9. These deformations are seen by the various eddy current (ET) techniques (bobbin, array and +Point) as fill factor or lift-off variations with no evidence of tube wall loss.

The geometric indications in these two tubes are basically the same. There is one indication just above the lower tube sheet (LTS) which responds like a bulge; multiple indications at the mid-span which respond like a wrinkled area and one indication at the lower edge of the first TSP (01S) which responds like a dent.

Both tubes were removed from service.

SGB This is the first time that bowing has been identified in SGB. The extent of the bowing was ~ 0.5 inches which is well below that of SGA. There is a delta in that the direction of the bowing in the first span in SGA is typically toward the center of the generator. The bowing in SGB is multi-directional. It is on the X side of the generator as compared to SGA which is on the Z side of the generator. This is being addressed through the condition report system under CR-ANO-1-2011-1925.

Tube sheet maps for the proximity indications (based on the bowed tie rods) for both steam generators are attached.

Repair:

The following tubes were repaired during the outage. There were seven in SGA and nine in SGB:

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SG Count Row Tube Indication HL Plug CL Plug Location Stabilizer A 1 42 8 PTR Stabilizer Standard Roll Upper Span Hybrid Full Roll Length A 2 43 8 PTB Roll Standard Roll Lower Span Hybrid Full Length A 3 88 9 PTU Stabilizer Standard Roll Lower Span Hybrid Full Roll Length A 4 43 7 NDD Stabilizer Standard Roll Preventative Hybrid Full Roll Length A 5 44 8 NDD Stabilizer Standard Roll Preventative Hybrid Full Roll Length A 6 44 9 PTU Stabilizer Standard Roll Lower Span Hybrid Full Roll Length A 7 43 9 PTU Stabilizer Standard Roll Lower Span Hybrid Full Roll Length B 1 1 3 WAR Stabilizer Standard Roll 11S-0.67 Hybrid Full Roll Length B 2 1 5 WAR Stabilizer Standard Roll 11S-0.70 Hybrid Full Roll Length B 3 2 22 WAR Stabilizer Standard Roll 11S-0.82 Hybrid Full Roll Length B 4 11 15 WAR Stabilizer Standard Roll 10S-0.76 Hybrid Full Roll Length B 5 12 15 WAR Stabilizer Standard Roll 10S-0.80 Hybrid Full Roll Length B 6 26 1 WAR Stabilizer Standard Roll 11S-0.70 Hybrid Full Roll Length B 7 150 4 WAR Stabilizer Standard Roll 12S-0.67 Hybrid Full Roll Length B 8 109 109 PTR Stabilizer Standard Roll Upper Span Hybrid Full Roll Length B 9 110 106 PTR Stabilizer Standard Roll Upper Span Hybrid Full Roll Length 3

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