ML072000405

Ssg Tube Inspection Discussion Points Prepared by the Office of NRR for Diablo Canyon Nuclear Generating Station

ML072000405
Person / Time
Site:	Diablo Canyon
Issue date:	05/14/2007
From:	NRC/NRR/ADES/DCI
To:
Burke, J P, NRR/DCI/CSGB, 415-1529
Shared Package
ML072000353	List: ML072000367 ML072000405
References
TAC MD5549
Download: ML072000405 (10)

Text

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E STEAM GENERATOR TUBE INSPECTION DISCUSSION POINTS PREPARED BY THE OFFICE OF NUCLEAR REACTOR REGULATION DIABLO CANYON NUCLEAR GENERATING STATION, DOCKET NO. 05000275 The following discussion points have been prepared to facilitate the phone conference arranged with Pacific Gas and Electric to discuss the results of the SG tube inspections to be conducted during the upcoming Diablo Canyon Power Plant, Unit 1 refueling outage 13. This phone call is scheduled to occur towards the end of the planned SG tube inspection interval, but before the unit completes the inspections and repairs.

The staff plans to document a brief summary of the conference call as well as any material that is provided in support of the call.

1. Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed cycle.

PG&E Response: In Unit 1 Cycle 14, a small leak (0.02 gpd) was detected and measured in the steam jet air ejector. Subsequent weekly sampling showed no increase in leak rate.

2. Discuss whether any secondary side pressure tests were performed during the outage and the associated results.

PG&E Response: No secondary side pressure tests were performed.

3. Discuss any exceptions taken to the industry guidelines.

PG&E Response: There are no deviations to industry guidelines, with the exception of one minor deviation of shall requirements of Revision 6 of the Secondary Water Chemistry Guidelines. Tables 5-2 and 5-3 of the Guidelines establish limits for exceeding 5% power. Diablo Canyon Units 1 and 2 apply these limits to 8% power.

4. For each steam generator, provide a description of the inspections performed including the areas examined and the probes used (e.g., dents/dings, sleeves, expansion-transition, U-bends with a rotating probe), the scope of the inspection (e.g., 100% of dents/dings greater than 5 volts and a 20% sample between 2 and 5 volts), and the expansion criteria.

PG&E Response: Table 1 provides a summary of all inspections performed, and expansion criteria.

5. For each area examined (e.g., tube supports, dent/dings, sleeves, etc), provide a summary of the number of indications identified to-date of each degradation 1

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E mode (e.g., number of circumferential primary water stress corrosion cracking indications at the expansion transition). For the most significant indications in each area, provide an estimate of the severity of the indication (e.g., provide the voltage, depth, and length of the indication). In particular, address whether tube integrity (structural and accident induced leakage integrity) was maintained during the previous operating cycle. In addition, discuss whether any location exhibited a degradation mode that had not previously been observed at this location at this unit (e.g., observed circumferential primary water stress corrosion cracking at the expansion transition for the first time at this unit).

PG&E Response: Table 2 provides the 1R14 Repairable indications and Tube Status Report as of 5-14-07 at 1200, and provides the number of indications identified to date of each degradation mode and steam generator tube location. Table 3 provides a list of the most significant indications of each damage mechanism. For SCC, the largest voltage indications are listed. Axial ODSCC in the sludge pile region was detected for the first time in Unit 1 (never detected in Unit 2).

6. Describe repair/plugging plans.

PG&E Response: Table 2 provides the number of tubes to be plugged as of 5-14-07 at 1200. All repairs are performed by tube plugging at both hot and cold legs. Tubes being plugged with circumferential indications are evaluated for stabilization in accordance with vendor criteria.

7. Describe in-situ pressure test and tube pull plans and results (as applicable and if available).

PG&E Response: To date, there are no indications that require in-situ pressure testing or tube pull.

8. Provide the schedule for steam generator-related activities during the remainder of the current outage.

PG&E Response: SG inspections are completed in SG 1-2 and 1-4, and all inspections will be completed on May 15. SG tube plugging will begin on May 14 and continue through May 16.

9. Discuss the following regarding loose parts:

• what inspections are performed to detect loose parts

• a description of any loose parts detected and their location within the SG, and if the loose parts were removed from the SG

• indications of tube damage associated with the loose parts

• the source or nature of the loose parts if known PG&E Response:

2

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Inspections performed to detect loose parts.

There is no EPRI qualified eddy current technique for detection of loose parts. The techniques used at Diablo Canyon, described below, are consistent with industry practice and have proven effective in finding loose parts at Diablo Canyon and many other sites. Tubes with loose part signals are included on the site specific performance demonstration (SSPD) which all analysts are required to pass.

Detection of loose parts is accomplished using the bobbin probe for 100% of the tubes.

Both groups of analysts (primary and secondary) are required to review channel 8 (15 kHz) bobbin data in the strip chart and lissajous looking for potential loose part (PLP) indications. In addition, designated analysts perform a separate in-depth PLP analysis in the full length of tubes (including TSPs and top of tubesheet) in rows 1 to 3 and the three outer periphery tubes. If PLP indications are found, the indications require examination with a three coil rotating probe (0.115 pancake/+Point/0.080 pancake).

PLP detection with the three coil rotating probe is accomplished by screening the 15 kHz pancake coil. PLPs confirmed with the three coil rotating probe also require that the surrounding tubes be examined with the three coil rotating probe to bound the PLP.

Detection of potential loose parts is also accomplished by both analysis parties screening all three coil rotating probe data.

Description of any loose parts detected and their location within the SG, and if they were removed from the SG. There were no PLP signals detected in 1R14.

Indications of tube damage associated with the loose parts. No tube degradation or tube wear has been detected that could have resulted from loose parts. Detection of potential loose part wear was accomplished using the bobbin probe. EPRI ETSS 96004.1 for detection of wear at tube supports and AVB bars is extended for detection of loose part wear. A special bobbin turbo-mix evaluation at 100% of tubes at the cold leg top of tubesheet was also conducted as an augmented exam.

Detection of potential loose part wear is also accomplished by both analysis parties screening all three coil rotating probe data.

10. Discuss the results of any secondary side inspections.

PG&E Response: The SG hand hole covers were not removed in 1R14. No secondary side inspections (FOSAR) were performed, and no sludge lancing was performed.

11. Discuss any unexpected or unusual results.

PG&E Response: There were no unexpected or unusual results.

3

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Table 1 - 1R14 Eddy Current Inspection and Expansion Plan Item Area Probe Inspection Criteria Expansion Criteria Expansion Performed Full 100% (Except Rows 1 and 2 1 Bobbin N/A Length U-bend)

If a C-3 condition is identified in the hot leg TTS inspection, inspect 20%

of the cold leg TTS region in the affected SG in the current or Not required subsequent outage. The 20%

inspection should be biased to an area where degradation has the greatest potential to occur.

If cold leg TTS cracking is detected, then either:

Inspect 100% of the cold leg TTS region in the affected SG, plus 20%

cold leg sample in the other SGs. If cracking is detected in the 20%

sample, then inspect 100% of the 100% of hot leg TTS, +2 to - Not required cold leg TTS in the affected SGs.

8 OR Define a critical area (CA) and buffer Note: WEXTEX anomaly 2 +Point zone and inspect 100% of the tubes extent is same as above, in the CA and buffer zone in the except NTE anomaly extent is affected SG, plus 20% of the cold leg

+2 to tube end.

CA sample in the other SGs.

If cold leg TTS non-crack-line indications are detected, then either:

WEXTEX Define a critical area (CA) and buffer TTS zone and inspect 100% of the tubes Region in the CA and buffer zone in the affected SG, plus 20% cold leg CA sample in the other SGs.

OR Not required For Category C-2 cold leg results, inspect an additional 20% cold leg sample in the affected SG.

For Category C-3 cold leg results, inspect 100% of the cold leg TTS region in the affected SG, plus 20%

cold leg sample in the other SGs.

If crack-like indications are detected 100% of hot leg WEXTEX in hot leg WEXTEX anomalies, then 3 +Point Not required anomalies inspect 100% of the cold leg WEXTEX anomalies.

100% of previous W*

4 +Point indications within the W* N/A N/A length Distorted tubesheet signals (DTS):

100% of DTS in the hot leg W*

5 +Point N/A N/A length.

100% of DTS in the cold leg, independent of elevation.

Low Row 6 +Point 100% of Rows 1 and 2 N/A N/A U-bends 4

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Table 1 - 1R14 Eddy Current Inspection and Expansion Plan Item Area Probe Inspection Criteria Expansion Criteria Expansion Performed If circ PWSCC detected in Rows 3 to 8, expand to 100% of Rows 3 to 10 in Not required the affected SGs.

If circ PWSCC detected in Rows 9 to 10, expand to 100% of rows 11 to 20 Not required in the affected SGs.

20% of Rows 3 to 8 in each If circ PWSCC detected in Rows 11 High Row SG. through 14, redefine critical area (CA)

U-bends 7 +Point and buffer zone based on review of for Circ 40% of Rows 5 and 6 in SG 1- Figure 10 of WOG U-Bend report and PWSCC Not required

4. application of a factor of two reduction in longitudinal strain, and inspect 100% of the new CA and buffer zone in the affected SGs.

If circ PWSCC detected in Rows 15 or higher, expand to 100% of all Not required remaining rows in the affected SGs.

If axial PWSCC detected in Rows 3 to 4, expand to 100% of Rows 3 to 4 Not required and 20% of Rows 5 to 7 in the affected SGs.

High Row If axial PWSCC detected in Rows 5 U-bends 20% of Rows 3 to 4 in each or greater, then review Figure 5 and 8 +Point for Axial SG Figure 8 of the WOG U-Bend report PWSCC to define a critical area and buffer Not required zone based on tube ovality data and tube total strain data, and inspect 100% of the CA and buffer zone in the affected SGs.

SG 1-1: Axial PWSCC at 7C (1.26 volt dent) detected by bobbin and confirmed by Plus Point, expansion required:

100% of >2 volt dents 5H to 7C, 20% at 6C. Actual expanded scope was more conservative and

• SG 1-1: 100% 1H to 4H; includes 100% of >2 volt 20% 5H to 7H If PWSCC (at any size dent),

dents in cold leg.

circumferential indications (at any

• SG 1-2: 100% 1H to 7C; size dent), or AONDB (at >5 volt 20% 6C SG 1-3: Preliminary eval dent) are detected at a TSP elevation

• SG 1-3: 20% 1H to 7H where 100% inspections were not of signal at 7C was

• SG 1-4: 100% 1H to 6H; potential axial PWSCC, required, expand the Plus Point 5 Volt 20% 7H which initiated an inspections (in a step-wise manner, 9 Dented +Point For any 20% sample, a expansion program, but 100% to affected TSP and 20% at TSP minimum of 50 5 volt dents signal was subsequently next TSP) up through the hot leg side shall be inspected. If the dispositioned as NDD of the SG and down the cold leg side population of 5 volt dents at based on tracing bobbin until a 20% sample is obtained that is that TSP elevation is less than signal to baseline free from PWSCC, circumferential 50, then 100% of the 5 volt inspection. 100% of >2 cracking, or AONDB at >5 volt dent.

dents at that TSP shall be volt cold leg dents (103 inspected. cold leg dents) and 33%

of >2 volt hot leg dents that were not originally planned for inspection (140 hot leg dents) were inspected as part of expanded scope prior to termination of the expansion program.

5

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Table 1 - 1R14 Eddy Current Inspection and Expansion Plan Item Area Probe Inspection Criteria Expansion Criteria Expansion Performed

• SG 1-1: 100% 1H to 4H; 20% 5H If PWSCC (at any size dent),

circumferential indications (at any

• SG 1-2: 100% 1H to 7C; size dent), or > 2 inferred volt 20% 6C AONDB (at >2 and <5 volt dent) are

• SG 1-3: 20% 1H detected at a TSP elevation where

> 2 Volt

• SG 1-4: 100% 1H to 6H; 100% inspections were not required, and <5 20% 7H expand the Plus Point inspections (in See above expansion 10 Volt +Point For any 20% sample, a a step-wise manner, 100% to scope.

Dented minimum of 50 > 2 volt and < affected TSP and 20% at next TSP)

TSP 5 volt dents shall be up through the hot leg side of the SG inspected. If the population of and down the cold leg side until a

> 2 volt and < 5 volt dents at 20% sample is obtained that is free that TSP elevation is less than from PWSCC, circumferential 50, then 100% of the > 2 volt cracking, or > 2 inferred volt AONDB.

and < 5 volt dents at that TSP shall be inspected.

Generic criteria: On a SG-specific basis, if a circ indication or >2 inferred volt AONDB is detected in a dent of x volts, where x is less than or equal to 2.3 volts, then expand Plus Point inspections to include 100% of dents greater than x SG 1-1: 100% at 1H, 20% at - 0.3 volts up to the affected TSP, 2H. plus 20% of dents greater than x -

0.3 volts at the next higher TSP.

+Point inspection of < 2 volt dents is not required in SGs 1- Note: For any 20% sample, a

< 2 Volt 2, 1-3, and 1-4, unless minimum of 50 x - 0.3 volt dents 11 Dented +Point dictated by expansion shall be inspected. If the population Not required TSP requirements. of x - 0.3 volt dents at that TSP elevation is less than 50, then 100%

Note: Bobbin is used for of the x - 0.3 volt dents at that TSP detection of axial PWSCC in shall be inspected.

<2 volt dents, and +Point is used to confirm bobbin calls. Specific criteria for 1R14: If a circumferential indication or >2 inferred volt AONDB is detected in a dent less than 2.3 volts in SG 1-1 (at 2H or higher), or any TSP elevation in SGs 1-2, 1-3, or 1-4, then expansion to less than 2 volt dents would be required.

Repeat PWSCC 12 ARC +Point 100% N/A N/A Indications at Dents 100% of distorted ID support 13 DIS +Point plate bobbin signals (DIS) at N/A N/A dented TSP 6

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Table 1 - 1R14 Eddy Current Inspection and Expansion Plan Item Area Probe Inspection Criteria Expansion Criteria Expansion Performed 100% of bobbin distorted OD support signals (DOS) at 14 +Point N/A N/A dented intersections (no lower voltage cutoff) 15 +Point 100% of DOS > 1.7 volt N/A N/A DOS with suspected TSP 16 +Point N/A N/A ligament cracking (SLC)

Any bobbin indication in the 17 +Point N/A N/A wedge region exclusion zone th DOS at 7 TSP exclusion 18 +Point N/A N/A zone TSP DOS that extend outside the 19 +Point N/A N/A Inspection TSP crevice for 100% of hot leg intersections ODSCC with >2.3 volt SPR (mixed 20 ARC +Point residual signal), and minimum N/A N/A of 5 largest hot leg SPR per SG.

21 +Point TSP with copper signals N/A N/A 100% of prior cycle AONDB (bounds commitment to 22 +Point inspect 100% of AONDB that N/A N/A continue to be NDD by bobbin in current inspection) 100% of prior cycle TSP SAI-23 +Point OD that are NDD by bobbin in N/A N/A current inspection 100% of existing baseline Plus Point confirmed TSP 24 TSP +Point N/A N/A ligament cracking (LIC or LIG)

Ligament indications.

Cracking 100% of new bobbin SLC 25 +Point N/A N/A indications.

20% of >5 volt dings in U-bend 20% of >5 volt dings in If ding ODSCC is detected, then straight legs, biased to cold 26 +Point inspect 100% of > 5 volt dings in Not required leg straight sections.

affected SGs Note: Bobbin is credited for detection of axial SCC in 5 volt dings 100% of paired dings that If circumferential ODSCC is detected Free Span were not inspected in 1R12 or in a paired ding that is greater than or Dings 1R13, to ensure that 100% equal to 2 volts (voltage cutoff for 27 +Point Not required are inspected in 60 EFPM, ding calling criteria), then inspect and to ensure that at least 100% of paired dings in the affected 20% are inspected in 1R14. SGs.

If ODSCC is detected at dings in the 20% of > 2 volt dings in the U- U-bend coincident with AVB 28 +Point bend that are coincident with locations, then inspect 100% of > 2 Not required AVB location volt ding indications coincident with AVB structures.

Free span bobbin 100% of free span bobbin 29 indications +Point indications that are new or N/A N/A (MBI, FSI, exhibit growth or change.

DNI) 100% of new CLT indications and indications >= 40%TW.

Cold leg If ODSCC detected at CLT TSP, 30 thinning at +Point inspect 100% of CLT indications in Not required 100% of >1.5 volt repeat CLT TSP each SG.

indications from 1R9 to 1R12, plus CLT never inspected.

7

Diablo Canyon 1R14 Steam Generator Inspections - Phone Call with NRC and PG&E Table 1 - 1R14 Eddy Current Inspection and Expansion Plan Item Area Probe Inspection Criteria Expansion Criteria Expansion Performed Bobbin turbo mix is used to augment normal bobbin analysis techniques at cold Possible leg TTS for detection of loose loose Bobbin part wear.

31 parts and and N/A N/A loose part +Point If possible loose part (PLP) damage indication is detected by eddy current, perform eddy current inspection to bound the loose part.

8

TABLE 2 DIABLO CANYON UNIT 1 R14 Preliminary Repairable Indication and Tube Status Report Tube Steam Generator Location Total Degradation 1-1 1-2 1-3 1-4 Number of DIS @ <2v DNT 32 67 18 16 133 (Excludes known flaws)

DIS Overcall Rate 100% 91% 100% 100% 95.5%

1. of Confirmed SAI in Above DIS 6 6 Axial PWSCC (New) 13 2 15 Axial PWSCC (Repeat) 26 174 19 219 DENTED TSP Wedge Region / 7th TSP Bending Axial ID/Axial OD 3 3 SAI ID with TSP LIC/LIG Circ ODSCC 11 1 12 Circ PWSCC 1 1 Mixed Mode (SAI ID+SCI ID)

PWSCC Preventive Low Burst Fail PWSCC ARC OA Burst Fail PWSCC ARC DOP >=40% TW 1 1 Repairable Indications 1 15 0 1 17 DOS > 2.0 V (Inds) 5 2 3 0 10 DOS =< 2.0 V (Inds) 839 588 285 210 1922 TSP ODSCC AONDB/OD SAI @ >5 V Dent 4 2 6 GL 95-05 ARC Wedge Region / 7th TSP Bending 1 1 SAI OD with TSP LIC/LIG 2 2 Preventative Plugging (High +Pt Voltage)

Repairable Indications 6 8 3 2 19 Axial PWSCC (New) in W* Length 1 1 2 Axial PWSCC (Repeat) in W* Length 5 3 5 5 18 Axial PWSCC Failed W* Criteria Tubesheet Circ PWSCC @ TTS Axial ODSCC @ TTS 2 2 Axial ODSCC in Sludge Pile 1 1 Circ ODSCC @ TTS 8 9 17 Repairable Indications 9 0 9 2 20 Axial PWSCC (Inds)

Axial ODSCC (Inds)

U-bends Circ PWSCC (Inds)

Innermost/Outermost Rows with Degradation High Row U-bends AVB Wear >=40% 2 1 3 Cold Leg Thinning Thinning >=40% 1 1 TSP Volumetric OD Indication 2 1 1 4 Misc. Non-ARC Preventive Total Pluggable Indications 17 27 14 6 64 Total Pluggable Tubes 17 23 14 6 60 This table shows the number of indications with each type of degradation (not the number of tubes).

• AREVA Tube Integrity Engineering 9 Daily Results: 5/14/2007 1:08 PM

Table 3 List of Most Significant Indications DCPP 1R14 (Preliminary Results)

Plus Point Estimated Estimated Degradation SG Row Col Location Bobbin Volts Volts Max Depth Length 1 Cold Leg Thinning 11 31 81 2C - 0.18 3.69 0.98 45 %TW -

2 AVB Wear 12 39 57 7H + 68.69 3.19 - 44 %TW -

3 Axial PWSCC @ Dented TSP 12 34 53 2H - 0.11 NA 3.15 83 %TW 0.51 4559 psi Calculated BP 4 Circ PWSCC @ Dented TSP 11 33 37 2H - 0.03 NA 0.91 41 %TW 24 deg 5 Axial ODSCC @ TSP 11 12 2 1H - 0.00 4.2 TBD - -

6 Circ ODSCC @ Dented TSP 12 5 75 1H + 0.34 NA 0.37 TBD 61 deg 7 Circ ODSCC @ TTS 11 7 32 TSH - 0.07 NDD 0.52 TBD 36 deg 8 Axial ODSCC @ TTS 14 30 49 TSH - 0.07 NDD 0.1 23 %TW 0.15 6%TW Axial ODSCC in Sludge Pile 11 21 45 TSH + 1.34 0.13 0.11 0.32 9 Bobbin 10 Axial PWSCC in W* Region 12 1 87 TSH - 9.31 NA 2.66 TBD 0.4 Note: Significance for SCC Indications determined by Plus-point Voltage, except for bobbin coil ARC.

AREVA Tube Integrity Engineering 5/14/2007 10