ML20117G965
| ML20117G965 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/30/1996 |
| From: | Katz P BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9609090043 | |
| Download: ML20117G965 (9) | |
Text
. _ _ _ _ _ _
PETER E. KATz Baltimore Gas and Electric Company Plant General Manager Calven Cliffs Nuclear Power Plant Calvert Cliffs Nuclear Pcser Plant 1650 Calvert Cliffs Parkway Lusby. Maryland 20657 410 495-4101 August 30,1996 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No.1; Docket No. 50-317 Steam Generator Tube Inspection Results in the spring of 1996, Baltimore Gas and Electric Company conducted a scheduled refueling outage at Calvert Cliffs Nuclear Power Plant (CCNPP) Unit 1. An inspection of the Unit I steam generator tubes was performed during the outage. The results of the Steam Generator Tube Inspection fell into the C-3 category, as described in CCNPP Technical Specification 4.4.5.2. A presentation was made to the Nucler; Regulatory Commission staff in Rockville, Maryland on June 13,1996, in which the results of the inspection were provided. in accordance with Technical Specification 4.4.5.5.c, a written follow-up of this report, providing a description of the investigations conducted to determine the cause of the tube degradation and corrective measures taken to prevent recurrence is provided below.
INSPECTION SCOPE The examination of Calvert Cliffs Unit 1 Steam Generators (Nos. I1 and 12) consisted of bobbin coil and motorized rotating plus point (MRPP) inspection technologies.
A.
Bobbin CoilInspections The bobbin coil examinations for Steam Generator Nos. I1 and 12 included 100 percent bobbin coil full length examination of all inservice tubes.
B.
Motorized Rotating Plus Point Inspections The MRPP examinations for Steam Generator Nos. I1 and 12 included:
1.
One hundred percent of the hot leg inservice tubes at the top of the tube sheet (TTS),
(TFS+5" above to 'ITS-1" below).
2.
Twenty percent of rows 1 and 2 (U-Bend Region). The vertical extent of the exam was from tube support 0611 to tube support 06C.
9609090043 960830
- 0. L PDR ADOCK 05000317 T
p PDR
(
t\\ \\
\\
Docum:nt Control Desk i
August 30,1996 Page 2 3.
Twenty percent random sample of all the dented intersections 2 5 volts. Axial and circumferential indications were identified at the 9th tube support plate (TSP), the lowest solid TSP. Subsequently,100 percent of the 9th TSP intersections were inspected. No degradation was identified at the other dented intersections.
4.
One hundred percent of rows 6 through 12 in the Steam Blanket Region.
5.
.All unexpanded tubes, the full length of the tube sheet.
6.
Rows 35 to 140 (Stay Dome / Arc Region). These upper bundle freespan inspections j
were conducted from the 4th TSP to vertical middle support in the areas identified by the i
Athos model, to be susceptible to dryout.
C.
Spelal Motorized Rotating Plus Point inspections All MRPP inspections were performed using the "Plus Point" probe technology. All distorted bobbin coil indications and all percent through-wall indications identified by bobbin were dispositioned with the plus point probe.
EDDY CURRENT INSPECTION RESULTS Attachment (1) contains the results of the MRPP and bobbin for Steam Generator Nos. I1 and 12. All steam generator tubes with crack-like indications, both circumferential and axial, all the anomalous indications (Volumetric and Plus Point Indication), and all indications greater than 40 percent through-wall were removed from service.
j IN-SITU PRESSURE TEST RESULTS Attahment (2) contains the scope and criteria for the in-situ pressure testing. In-situ pressure tests were 1
conducted on two tubes in Steam Generator No.11 and seven tubes in Steam Generator No.12. The tubes selected for in-situ pressure testing contained the largest axial voltage, the largest axial length, the i
largest circumferential voltage, and the largest circumferential length indications at 'ITS.
These indications also contained the deepest estimated percent through-wall. The test methods used included both localized and full tube length.
The most limiting case for CCNPP is pressurization without burst to three times noimal differential operation pressure (3 x 1400 psi = 4200 psi). The minimum test pressure for tubes with axial indications was set at 4750 psig to account for temperature correction. The minimum test pressure for tubes with circumferential indications was set at 5300 psig to account for temperature correction and possible axial loading due to tube lock effects. Three of the tubes exhibited leakage. All tubes were pressurized greater than 4750 psig, no tubes burst.
Six of the nine tubes were tested to pressures in excess of the above values to further verify the substantial remaining structural integrity of the defective tubes. The test pressure achieved was limited by the test device. The test pressures reached a maximum pressure of 5750 psig.
The test results of the in-situ pressure test are summarized in Attachment (3).
n
)
Document Control Desk August 30,1996 Page 3 j
All steam generator tubes in-situ pressure tested were found to have exceeded the Regulatory' Guide 1.121 requirements for structural integrity.
TUBE PULL TEST RESULTS i
Three tubes were removed from Steam Generator No.12 for laboratory analysis. The tubes pulled included two with multiple defects in the upper bundle Freespan Region (R46L76, R111L67) and one with a combined axial /circumferential defect at the TTS (R67L71) as identined by field eddy current testing. Laboratory testing performed has included visual, eddy current, and ultrasonic examinations, burst testing, metallurgical analysis, scanning electron microscope examinations, and chemical analysis of tubes and tube deposit samples. A chemical cleaning test has been performed on a tube section with heavy deposits.
Major results of the exam are:
+
Burst tests of eight tube sections with freespan defects have yielded burst pressures in excess of 10,000 psi. No tube section leaked prior to bursting, indicating none of them had inservice leaks.
These burst pressures are essentially equivalent to burst pressures of tubes with no defects. The burst tests prove the tubes retained ample structural integrity to withstand any postulated accident as well as normal operating conditions.
In tubes RI1IL67 and R46L76, a total of 66 individual eddy current indications were identified by re-analysis of the Geld eddy current data. These defects are all in the Upper Bundle Region between the 5th and 9th support, a region where indications have not been previously observed in Calvert Cliffs' steam generators. An attempt is being made to locate and determine the size of each of these defects through the destructive exam. A small number of additional defects have been located by the destructive examination which were not identified by the field eddy current testing. The data will be used to generate a probability of detection curve for these type of defects.
The tubes had heavy deposits in the region between the 5th and 9th support. Chemical analysis of these deposits indicate they are mostly iron oxide in the form of magnetite (Fe30 ). The 4
deposits also include a larger amount of silica than is typically seen in steam generator tube deposits, and isolated copper deposits.
All defects are intergranular stress corrosion cracking (IGSCC).
The destructive exam confirmed the defects are all axially oriented in tubes RlllL67 and R46L76. The defect at the TTS in tube R67L71 was found to consist of axial cracks only.
CAUSE OF TUBE DEGRADATION AND CORRECTIVE MEASURES Three tubes were pulled from Steam Generator No.12 for laboratory analysis, to fully assess the cause of the tube degradation and to develop effective corrective measures to mitigate further degradation. All defects are IGSCC. The IGSCC was all outside diameter initiated. This type of tube degradation is due to material stresses, environment, and age. The size distribution of the indications is very small and are normal age related type indications. A correlation between steam generator upper bundle freespan tube cracking and the steam generator dryout region was established. The ATHOS model developed for the CCNPP Unit 1 steam generators predicted the dryout areas which supported the indications detected in
Document Control Desk August 30,1996 Page 4 i
the upper bundle region of the steam generators. All steam generator tubes with crack-like indications, both circumferential and axial, all the anomalous indications (Volumetric and Plus Point Indication), and all indications greater than 40 percent through-wall were removed from service. We plan to re-inspect the appropriate steam generator tubes during the next scheduled Unit I refueling outage (spring 1998).
Should you have questions regarding this matter, we will be pleasei to discuss them with you.
Very tr.ay yours,
[-
f for P. E. Katz Plant General Managw i
PEK/RCG/bjd 1
Attachments: As stated cc:
D. A. Brune, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident inspector, NRC Director, Project Directorate I-1, NRC R. I. McLean, DNR A. W. Dromerick, NRC J. H. Walter, PSC
- _~
- =-
ATTACIIMENT (1)
RESULTS OF THE MOTORIZED ROTATING PLUS POINT AND BOBBIN FOR STEAM GENERATOR NOS.11 AND 12 The following outline summarizes the final results of this examination.
-!INDICATIONSI
- 1. STEAM.. GENERATOR),
j STEAM GFRERATORi
!!;NO/11f.
iNO.123 sal, MAI @ TTS 116 166 SCI, MCI @ TFS 56 33 VOL @ TTS 0
1
]
SVI @ TFS 7
7 5
sal, MAI @ 09H 15 5
SCI, MCI @ 09H 2
5 sal, MAI, MSI - FREESPAN 164 391 PPI-FREESPAN 55 73 VOL 3
4 0-19 %
129 150 20-39 %
54 90 40-100 %
8 18 TUBES REPAIRED 340 500 NOTE:
Numbers denote indications. Some tubes contain multiple indications.
LEGEND:
MAI Multiple AxialIndication MCI Multiple Circumferential Indication MSI Multiple Single Indication PPI Plus Point Indication i
sal Single AxialIndication SCI Single Circumferential Indication SVI Volumetric Pit Indication TTS Top of the Tube Sheet VOL Volumetric Indication 1
ATTACIIMENT (2)
SCOPE AND CRITERIA FOR TIIE IN-SITU PRESSURE TESTING These tubes were selected for testing:
STEAM GENERA TOR NO.11 l
iRsWLinej iFlaw Type; /FIAwlAsation[ 4 Fla#Lisgtlf i;Flawyoitage)
[R$gion;j 100,88 PPI 0911 + 11.55 4.5 inches 1.57 Freespan 95,129 PPI DH + 4.00 2.5 inches 1.49 Freespan STEAM GENERA TOR NO,12 iRohlinel 4Fisw;Typ.el lFlawIlication3 LFlaw Length? l Flaw Voliage:i FRegions 9,129 SAI VM 1.0 inches 3.70 Steam Blanket 9,137 SAI VM 1.0 inches 3.78 Steam Blanket 90,84*
MCI TSil + 0.10 0.9 inches 3.10 TTS 50,80 MCI TSli + 0.15 2.3 inches 0.85 TTS 74,100 SCI TSII + 0.01 2.0 inches 6.51 TTS 76,78 SAI TSII+1.35 1.6 inches 3.50 TTS 82,90 mal TSH +0.61 1.1 inches 38.11 TTS 72,98 sal TSli + 0.32 0.6 inches 21.39 TTS This tube was not tested due to the test fixture not being capable of entering the tube due to a physical obstruction.
There were no Freespan Region axial indications in-situ pressure tested due to the pulled tube laboratory burst test demonstrating the worst case characteristics for all freespan axial indications recorded this outage The tubes selected exhibited the worst case characteristics for the listed indication types in their particular region of the steam generators. For example:
=>
There are no TTS axial indications in either Steam Generator Nos.11 or 12 with a higher voltage i
than tubes 82,90 and 72,98 in Steam Generator No.12.
There are no TTS axial indications in either Steam Generator Nos. I1 or 12 with greater lengths
=>
than 76,78 and 82,90 in Steam Generator No.12.
=>
There are no TTS circumferential indications in either Steam Generator Nos.11 or 12 with a i
higher voltage than tube 74,100 in Steam Generator No.12.
I
~
ATTACHMENT (2)
SCOPE AND CRITERIA FOR THE IN-SITU PRESSURE TESTING There are no TTS circumferential indications in either Steam Generator No.11 or 12 with greater
=>
lengths than 50,80 and 74,100 in Steam Generator No.12.
=>
There are no Steam Blanket Region axial indications in either Steam Generator Nos. I1 or 12 with greater lengths or voltages than 9,129 and 9,137 in Steam Generator No.12.
There are no Freespan Ppis in either Steam Generator Nos.11 or 12 with greater lengths or
=>
voltages than 100,88 and 95,129 in Steam Generator No.11.
LEGEND:
DH Diagonal Support Hot Leg MAI Multiple AxialIndication MCI Multiple Circumferential Indication PPI Plus Point Indication SAI Single AxialIndication SCI Single CircumferentialIndication TSH Tube Sheet Hot Leg TFS Top of the Tube Sheet VM Vertical Middle Tube Support 1
I l
i 4
5 2
ATTACHMENT (3)
SUMMARY
OF TIIE IN-SITU PRESSURE TEST RESULTS STEAM GENERATOR NO.11
- Row lLine'
- J s FlawType j; Flaw Locationy s Flaw Le gth} jMAw,Voltags): iTat Plressurel jTubelisk%A?j 100,88 PPI 09II + 11.55 4.5 inches 1.57 5,750 psig None 95,129 PPI Dll + 4.00 2.5 inches 1.49 5,750 psig None STEAM GENERATOR NO.12 lRowiLinef nFlawType)
Flaw Lobstios i Flaw Lengtifi jFlapVoltage) LTsst Pressure;l ETalk LAnksk 9,129 SAI VM 1.0 inch 3.70 5,750 psig None 9,137 SAI VM 1.0 inch 3.78 5,750 psig None 50,80 MCI TSil + 0.15 2.13 inches 0.85 5,750 psig None 74,100 SCI TSil + 0.01 2.0 inches 6.51 5,300 psig Yes 76,78 SAI TSII + 135 1.6 inches 3.50 5,300 psig Yes 82,90 MAI TSil + 0.61 1.1 inches 38.11 5,750 psig None 72,98 SAI TSil + 032 0.6 inches 2139 4,750 psig Yes LEAK RATE DATA 1 Row, Linej ilaitial Lesk (Initial Leak?
5Lesk?
4Lsak'Rste$
s12aki SIlsliRats iLeald iIial(R$te:i JPressure?
iR$ tis Pnssere]
[Pressres Pressures 76,78 4,750 psig Not Measured 5,300 psig 81.2 gpd NA NA NA NA 74,100 4,200 psig 41.9 gpd 5,300 psig 37.5 gpd NA NA NA NA 72,98 2.800 psig Not Measured 3,000 psig 17.8 gpd 4,200 psig 87.5 gpd 4,750 psig 111.6 gpd All tubes were reinspected with plus point upon completion of testing.
I
ATTACHMENT (3)
SUMMARY
OF THE IN-SITU PRESSURE TEST RESULTS LEGEND:
+
Dil Diagonal Support Hot Leg I
MAI Multiple AxialIndication t
MCI Multiple Circumferential Indication PPI Plus Point Indication sal Single AxialIndication SCI Single CircumferentialIndication TSil Tube Sheet Hot Leg VM Vertical Middle Tube Support j
I i
1 2
L i
_,. ~..
_., - _.. _ _. ~,
.