ML033650400
| ML033650400 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 12/31/2003 |
| From: | Swamy S, David Tang Westinghouse |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| FOIA/PA-2005-0108 WCAP-16144-NP, Rev 0 | |
| Download: ML033650400 (99) | |
Text
Westinghouse Non-Proprietary Class 3 WCAP-16144-NP Revision 0 December 2003 Structural Integrity Evaluation of Reactor Vessel Upper Head Penetrations to Support Continued Operation:
Beaver Valley Unit 2 Westinghouse
WESTINGHOUSE NON-PROPRIETARY CLASS 3 WCAP-16144-NP Revision 0 Structural Integrity Evaluation of Reactor Vessel Upper Head Penetrations to Support Continued Operation: Beaver Valley Unit 2 S. Jirawongkraisorn December 2003 Verifier:
D. Tang Piping Analysis & Fracture Mechanics Approved:
S. A. Swamy Piping Analysis & Fracture Mechanics Westinghouse Electric Company LLC P.O. Box 355 Pittsburgh, PA 15230-0355 t 2003 Westinghouse Electric Company LLC All Rights Reserved
iii TABLE OF CONTENTS List of Tables.........................................
v List of Figures.........................................
vi 1
INTRODUCTION.1-1 2
HISTORY OF CRACKING IN HEAD PENETRATIONS.2-1 3
OVERALL TECHNICAL APPROACH.3-1 3.1 PENETRATION STRESS ANALYSIS.3-1 3.2 FLAW TOLERANCE APPROACH...............................
3-1 4
MATERIAL PROPERTIES, FABRICATION HISTORY AND CRACK GROWTH PREDICTION.4-1 4.1 MATERIALS AND FABRICATION.4-1 4.2 CRACK GROWTH PREDICTION.4-1 5
STRESS ANALYSIS 5-1 5.1 OBJECTIVES OF THE ANALYSIS.5-1 5.2 MODEL.5-1 5.3 STRESS ANALYSIS RESULTS - OUTERMOST CRDM PENETRATION (42.7°)5-1 5.4 STRESS ANALYSIS RESULTS - INTERMEDIATE CRDM PENETRATIONS 5-2 5.5 STRESS ANALYSIS RESULTS - CENTER CRDM PENETRATION.5-2 5.6 STRESS ANALYSIS RESULTS - HEAD VENT.5-2 6
FLAW TOLERANCE CHARTS.6-1
6.1 INTRODUCTION
.6-1 6.2 OVERALLAPPROACH.6-1 6.3 AXIAL FLAW PROPAGATION.6-2 6.4 CIRCUMFERENTIAL FLAW PROPAGATION.6-3 6.5 FLAW ACCEPTANCE CRITERIA.6-5 7
SUMMARY
AND EXAMPLE PROBLEMS
.7-1 December 2003 Revision 0
iv TABLE OF CONTENTS (Cont.)
7.1 SAFETY ASSESSMENT.........................
7-1 7.2 EXAMPLE PROBLEMS.........................
7-2 8
REFERENCES.........................
8-1 APPENDIX A CRDM HOOP STRESS Vs DISTANCE FROM BOTTOM OF WELD PLOTS.
A-1 December 2003 Revision 0
v LIST OF TABLES Table 1-1 Beaver Valley Unit 2 Head Penetration Nozzles with Intersection Angles Identified.......... 1-2 Table 4-1 Beaver Valley Unit 2 R/V Head Adapter Material Information.4-7 Table 6-1 Summary of R.V. Head Penetration Flaw Acceptance Criteria.6-8 Table 6-2 Beaver Valley Unit 2 Penetration Geometries [ 11].6-8 Table 7-1 Example Problem Inputs: Initial Flaw Sizes and Locations.7-5 December 2003 Revision 0
LIST OF FIGURES Figure 1-1 Reactor Vessel Control Rod Drive Mechanism (CRDM) Penetration................................ 1-3 Figure 1-2 Location of Head Penetrations for Beaver Valley Unit 2 [I1 C].......................................... 1-4 Figure 2-1 EDF Plant RN Closure Head CRDM Penetrations - Penetrations with Cracking............. 2-4 Figure 2-2 Inspection Results for U.S. CRDMICEDM Penetration Nozzle (Spring 2003).................. 2-5 Figure 3-1 Schematic of a Head Penetration Flaw Growth Chart for Part-Through Flaws.................. 3-3 Figure 3-2 Schematic of a Head Penetration Flaw Tolerance Chart for Through-Wall Flaws.............. 3-4 Figure 4-1 Yield Strength of the Various Heats of Alloy 600 Used in Fabricating the Beaver Valley Unit 2 and French Head Penetrations................................................................
4-8 Figure 4-2 Carbon Content of the Various Heats of Alloy 600 Used in Fabricating the Beaver Valley Unit 2 and French Head Penetration................................................................
4-9 Figure 4-3 Screened Laboratory Data for Alloy 600 with the MRP Recommended Curve (Note that the Modified Scott Model is also Shown)................................................................
4-10 Figure 4-4 Model for PWSCC Growth Rates in Alloy 600 in Primary Water Environments (3250C),
With Supporting Data from Standard Steel, Huntington, and Sandvik Materials............. 4-11 Figure 4-5 Summary of Temperature Effects on PWSCC Growth Rates for Alloy 600 in Primary Water................................................................
4-12 Figure 5-1 Finite Element Model of CRDM Penetration................................................................
5-3 Figure 5-2 Vent Pipe Finite Element Model................................................................
5-4 Figure 5-3 Stress Distribution at Steady State Conditions: Outermost CRDM Penetration Nozzle (42.7 Degrees) (Hoop Stress is the Top Figure, Axial Stress is the Bottom Figure)..................... 5-5 Figure 5-4 Stress Distribution at Steady State Conditions for the 40.0 Degrees CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure).................................... 5-6 Figure 5-5 Stress Distribution at Steady State Conditions for the 38.7 Degrees CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure).
5-7 Figure 5-6 Stress Distribution at Steady State Conditions for the 25.4 Degrees CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure).
5-8 Figure 5-7 Stress Distribution at Steady State Conditions for the Center CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure).
5-9 Figure 5-8 Stress Contours in the Head Vent Nozzle as a Result of Residual Stresses and Operating Pressure (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure).
5-10 Figure 5-9 Axial Stress Distribution at Steady State Conditions for the Outermost CRDM Penetration (42.7 Degrees), Along a Plane Oriented Parallel to, and Just Above, the Attachment Weld.
5-11 Figure 6-1 Stress Intensity Factor for a Through-Wall Circumferential Flaw in a Head Penetration...6-9 December 2003 Revision 0
vii Figure 6-2 Inside, Axial Surface Flaws,.5" Below the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2.................................................................... 6-10 Figure 6-3 Inside, Axial Surface Flaws,.5" Below the Attachment Weld, Nozzle Downhill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-11 Figure 6-4 Inside, Axial Surface Flaws, At the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2...........................................................................
6-12 Figure 6-5 Inside, Axial Surface Flaws, At the Attachment Weld, Nozzle Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2.................................................................... 6-13 Figure 6-6 Inside, Axial Surface Flaws,.5" Above the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2.................................................................... 6-14 Figure 6-7 Inside, Axial Surface Flaws,.5" Above the Attachment Weld, Nozzle Downhill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-15 Figure 6-8 Inside, Axial Surface Flaws, At the Attachment Weld, Head Vent-Crack Growth Predictions for Beaver Valley Unit 2...........................................................................
6-16 Figure 6-9 Outside, Axial Surface Flaws, Below the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2................................................................
6-17 Figure 6-10 Outside, Axial Surface Flaws, Below the Attachment Weld, Nozzle Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2................................................................
6-18 Figure 6-11 Outside, Circumferential Surface Flaws, Along the Top of the Attachment Weld - Crack Growth Predictions for Beaver Valley Unit 2 (MRP Factor of 2.0 Included)................... 6-19 Figure 6-12 Through-Wall Axial Flaws Located in the Center CRDM (0.0 Degrees) Penetration, Uphill and Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2........................ 6-20 Figure 6-13 Through-Wall Axial Flaws Located in the 25.4 Degrees Row of Penetrations, Uphill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-21 Figure 6-14 Through-Wall Axial Flaws Located in the 25.4 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2............................................... 6-22 Figure 6-15 Through-Wall Axial Flaws Located in the 38.7 Degrees Row of Penetrations, Uphill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-23 Figure 6-16 Through-Wall Axial Flaws Located in the 38.7 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2............................................... 6-24 Figure 6-17 Through-Wall Axial Flaws Located in the 40.0 Degrees Row of Penetrations, Uphill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-25 Figure 6-18 Through-Wall Axial Flaws Located in the 40.0 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2............................................... 6-26 Figure 6-19 Through-Wall Axial Flaws Located in the 42.7 Degrees Row of Penetrations, Uphill Side -
Crack Growth Predictions for Beaver Valley Unit 2......................................................... 6-27 December 2003 Revision 0
Figure 6-20 Figure 6-21 Figure 6-22 Figure 6-23 Figure 6-24 Figure 7-1 Through-Wall Axial Flaws Located in the 42.7 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2............................................... 6-28 Through-Wall Circumferential Flaws Near the Top of the Attachment Weld for CRDM Nozzle - Crack Growth Predictions for Beaver Valley Unit 2 (MRP Factor of 2.0 Included)................................................................
6-29 Section XI Flaw Proximity Rules for Surface Flaws (Figure IWA-3400-1)..................... 6-30 Definition of "Circumferential".................................................................
6-31 Schematic of Head Penetration Geometry................................................................
6-32 Example Problem 1................................................................
7-6 Figure 7-2 Example Problem 2................................................................
7-7 Figure 7-3 Example Problem 3................................................................
7-8 Figure 7-4a Example Problem 4 (See also Figure 7-4b)................................................................
7-9 Figure 7-4b Example Problem 4 (See also Figure 7-4a)................................................................
7-10 Figure 7-5 Example Problem 5................................................................
7-11 Figure A-I Hoop Stress Distribution Below the Weld Downhill and Uphill Side (0° CRDM Penetration Nozzle)..................................................................
A-2 Figure A-2 Hoop Stress Distribution Below the Weld Downhill Side (25.40 CRDM Penetration Nozzle)..................................................................
A-3 Figure A-3 Hoop Stress Distribution Below the Weld Uphill Side (25.40 CRDM Penetration Nozzle)..................................................................
A-4 Figure A-4 Hoop Stress Distribution Below the Weld Downhill Side (38.70 CRDM Penetration Nozzle)..................................................................
A-5 Figure A-5 Hoop Stress Distribution Below the Weld Uphill Side (38.7° CRDM Penetration Nozzle)..................................................................
A-6 Figure A-6 Hoop Stress Distribution Below the Weld Downhill Side (40.0° CRDM Penetration Nozzle)..................................................................
A-7 Figure A-7 Hoop Stress Distribution Below the Weld Uphill Side (40.00 CRDM Penetration Nozzle)..................................................................
A-8 Figure A-8 Hoop Stress Distribution Below the Weld Downhill Side (42.70 CRDM Penetration Nozzle)..................................................................
A-9 Figure A-9 Hoop Stress Distribution Below the Weld Uphill Side (42.70 CRDM Penetration Nozzle)..................................................................
A-10 December 2003 Revision 0
1-1 1
INTRODUCTION In September of 1991, a leak was discovered in the Reactor Vessel Control Rod Drive Mechanism (CRDM) head penetration region of an operating plant. This has led to the question of whether such a leak could occur at the Beaver Valley Unit 2 CRDM or head vent nozzle penetrations. The geometry of interest is shown in Figure 1-1. Throughout this report, the penetration rows have been identified by their angle of intersection with the head.
The locations of the head penetrations for Beaver Valley Unit 2 are shown in Figure 1-2 and the angles for each penetration are identified in Table 1-1.
The CRDM leak resulted from cracking in Alloy 600 base metal, which occurred in the outermost penetrations of a number of operating plants as discussed in Section 2. This outermost CRDM location, as well as a number of intermediate CRDM locations and the head vent were chosen for fracture mechanics analyses to support continued safe operation of Beaver Valley Unit 2 if such cracking were to be found. The dimensions of all the CRDM penetrations are identical, with a 4.00 inch Outside Diameter (OD) and a wall thickness of 0.625 inches [1lA]. For the head vent, the OD is 1.315 inches and the wall thickness is 0.250 inches [liB]. All of these dimensions are summarized in Table 6-2.
The basis of the analysis was a detailed three-dimensional elastic-plastic finite element stress analysis of several penetration locations, as described in detail in Section 5 and a fracture analysis as described in Section 6.
The fracture analysis was carried out using crack growth rates recommended by the EPRI Materials Reliability Program (MRP). These rates are consistent with service experience. The results are presented in the form of flaw tolerance charts for both surface and through wall flaws. If indications are found, the charts will determine the allowable service life of safe operation. The service life calculated in the flaw tolerance charts are all in Effective Full Power Years (EFPY).
Note that there are several locations in this report where proprietary information has been identified and bracketed.
For each of the bracketed locations, reasons for proprietary classifications are given using a standardized system. The proprietary brackets are labeled with three different letters to provide this information. The explanation for each letter is given below:
- a.
The information reveals the distinguishing aspects of a process or component, structure, tool, method, etc., and the prevention of its use by Westinghouse's competitors, without license from Westinghouse, gives Westinghouse a competitive economic advantage.
- c.
The information, if used by a competitor, would reduce the competitor's expenditure of resources or improve the competitor's advantage in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product.
- e.
The information reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.
Introduction December 2003 Revision 0
1-2 Table 1-1 Beaver Valley Unit 2 Head Penetration Nozzles with Intersection Angles Identified Nozzle No.
Type Angle (Degrees)
Nozzle No.
Type Angle (Degrees) 1 CRDM 0.0 2
CRDM 8.7 3
CRDM 8.7 4
CRDM 8.7 5
CRDM 8.7 6
CRDM 12.4 7
CRDM 12.4 8
CRDM 12.4 9
CRDM 12.4 10 CRDM 17.6 11 CRDM 17.6 12 CRDM 17.6 13 CRDM 17.6 14 CRDM 19.8 15 CRDM 19.8 16 CRDM 19.8 17 CRDM 19.8 18 CRDM 25.4 19 CRDM 25.4 20 CRDM 25.4 21 CRDM 25.4 22 CRDM 27.0 23 CRDM 27.0 24 CRDM 27.0 25 CRDM 27.0 26 CRDM 28.6 27 CRDM 28.6 28 CRDM 28.6 29 CRDM 28.6 30 CRDM 28.6 31 CRDM 28.6 32 CRDM 28.6 34 CRDM 33.1 35 CRDM 33.1 36 CRDM 33.1 37 CRDM 33.1 38 CRDM 33.1 39 CRDM 33.1 40 CRDM 33.1 41 CRDM 33.1 42 CRDM 37.3 43 CRDM 37.3 44 CRDM 37.3 45 CRDM 37.3 46 CRDM 38.7 47 CRDM 38.7 48 CRDM 38.7 49 CRDM 38.7 50 CRDM 38.7 51 CRDM 38.7 52 CRDM 38.7 53 CRDM 38.7 54 CRDM 40.0 55 CRDM 40.0 56 CRDM 40.0 57 CRDM 40.0 58 CRDM 42.7 59 CRDM 42.7 60 CRDM 42.7 61 CRDM 42.7 62 CRDM 42.7 63 CRDM 42.7 64 CRDM 42.7 65 CRDM 42.7 33 CRDM 28.6 Introduction December 2003 Revision 0
1-3 Uphill Side (1800)
\\-~~Downhill
\\
Cladding Side L
eld (00)
Weld Head Penetration Nozzle Figure 1-1 Reactor Vessel Control Rod Drive Mechanism (CRDM) Penetration Introduction December 2003 Revision 0
1-4
- . LUG (~HD 4-LUC.
~
Figure 1-2 Location of Head Penetrations for Beaver Valley Unit 2 [1iC]
Introduction December 2003 Revision 0
2-1 2
HISTORY OF CRACKING IN HEAD PENETRATIONS In September of 1991, leakage was reported from the reactor vessel CRDM head penetration region of a French plant, Bugey Unit 3. Bugey 3 is a 920 megawatt three-loop Pressurized Water Reactor (PWR) plant which had just completed its tenth fuel cycle. The leak occurred during a post ten year hydrotest conducted at a pressure of approximately 3000 psi (204 bar) and a temperature of 1940F (90'C). The leak was detected by metal microphones, which are located on the top and bottom heads. The leak rate was estimated to be approximately 0.7 liter/hour. The location of the leak was subsequently established on a peripheral penetration with an active control rod (H-14), as seen in Figure 2-1.
The control rod drive mechanism and thermal sleeve were removed from this location to allow further examination. A study of the head penetration revealed the presence of longitudinal cracks near the head penetration attachment weld. Penetrant and ultrasonic testing confirmed the cracks.
The cracked penetration was fabricated from Alloy 600 bar stock (SB-166), and has an outside diameter of 4 inches (10.16 cm) and an inside diameter of 2.75 inches (7.0 cm).
As a result of this finding, all of the control rod drive mechanisms and thermal sleeves at Bugey 3 were removed for inspection of the head penetrations. Only two penetrations were found to have cracks, as shown in Figure 2-1.
An inspection of a sample of penetrations at three additional plants were planned and conducted during the winter of 1991-92. These plants were Bugey 4, Fessenheim 1, and Paluel 3. The three outermost rows of penetrations at each of these plants were examined, and further cracking was found in two of the three plants.
At Bugey 4, eight of the 64 penetrations examined were found to contain axial cracks, while only one of the 26 penetrations examined at Fessenheim 1 was cracked. The locations of all the cracked penetrations are shown in Figure 2-1. At the time, none of the 17 CRDM penetrations inspected at Paluel 3 showed indications of cracking, however subsequent inspections of the French plants have confirmed at least one crack in each operating plant.
Thus far, the cracking in reactor vessel heads not designed by Babcock and Wilcox (B&W) has been consistent in both its location and extent.
All cracks discovered by nondestructive examination have been oriented axially, and have been located in the bottom portion of the penetration in the vicinity of the partial penetration attachment weld to the vessel head as shown schematically in Figure 1-1.
] a.c,e History of Cracking in Head Penetrations December 2003 History of Cracking in Head Penetrations December 2003 Revision 0
2-2 a.c,e Non-destructive examinations of the leaking CRDM nozzles showed that most of the cracks were axially oriented, originating on the outside surface of the nozzles below the J-groove weld and propagating primarily in the nozzle base material to an elevation above the top of the J-groove weld. Leakage could then pass through the annulus to the top of the head where it was detected by visual inspection. In some cases the cracks initiated in the weld metal or propagated into the weld metal, and in a few cases the cracks propagated through the nozzle wall thickness to the inside surface.
]ace History of Cracking in Head Penetrations December 2003 Revision 0
2-3 Ia,c,e The cracking has now been confirmed to be primary water stress corrosion cracking. Relatively high residual stresses are produced in the outermost CRDM penetrations due to the welding process. Other important factors which affect this process are temperature and time, with higher temperatures and longer times being more detrimental. The inspection findings for U.S. plants are shown in Figure 2-2. From this figure, it is interesting to note that low percentage of CE-fabricated vessels have been found cracked (only 9 of 1332 penetrations UT and/or ET inspected in CE-fabricated vessels have shown cracking whereas 117 of 628 penetrations in non-CE-fabricated vessels experienced cracking or leakage). In addition, no cracks in head vent have been found.
History of Cracking in Head Penetrations December 2003 Revision 0
2-4 270-270-0' 0'
I
- Leoking Penetrotion 90
- Crocked Penetration BUGEY 3 90
- Crocked Penetration BUGEY 4 2?0 -
0O 90'
- Cracked Penetration FESSENHEIM I Figure 2-1 EDF Plant RNV Closure Head CRDM Penetrations - Penetrations with Cracking History of Cracking in Head Penetrations December 2003 Revision 0
2-5 CRDMWCEDM Penetrations Inspected CRDM/CEDM Inspection Results 3500 3000-2500-I 2000-
- 1500-I 1000-500-I0 I
C.
E 2
1400 1200 1000 0o0 600 400 200 CE Vessels Non-CE Vessels I
L UT and/or ET 13 BMV Only lG Not Yet Inspected CE Vessels Non-CE Vessels I EDUT/ET wtih No Cracks Cl Cracked (not leaker)
- Leaker Figure 2-2 Inspection Results for U.S. CRDM/CEDM Penetration Nozzle (Spring 2003)
History of Cracking in Head Penetrations December 2003 Revision 0
3-1 3
OVERALL TECHNICAL APPROACH The primary goal of this work is to provide technical justification for the continued safe operation of Beaver Valley Unit 2 in the event that cracking is discovered during in-service inspections of the Alloy 600 reactor vessel upper head penetrations.
3.1 PENETRATION STRESS ANALYSIS Three-dimensional elastic-plastic finite element stress analyses was performed to determine the stresses in the head penetration region [6]. These analyses have considered the pressure loads associated with steady state operation, as well as the residual stresses that are produced by the fabrication process.
]ace 3.2 FLAW TOLERANCE APPROACH A flaw tolerance approach has been developed to allow continued safe operation until an appropriate time for repair, or the end of plant life. The approach is based on the prediction of future growth of detected flaws, to ensure that such flaws would remain stable.
If an indication is discovered during in-service inspection, its size can be compared with the flaw size considered as allowable for continued service. This "allowable" flaw size is determined from the actual loading (including mechanical and residual loads) on the head penetration for Beaver Valley Unit 2. Acceptance criteria are discussed in Section 6.5.
The time for the observed crack to reach the allowable crack size determines the length of time the plant can remain online before repair, if required. For the crack growth calculation, a best estimate is needed and no additional margins are necessary.
The results of the evaluation are presented in terms of simple flaw tolerance charts. The charts graphically show the time required to reach the allowable length or depth, which represents additional service life before repair. This result is a function of the loading on the particular head penetration as well as the circumferential location of the crack in the penetration nozzle.
Schematic drawings of the head penetration flaw tolerance charts are presented as Figures 3-1 and 3-2. These two types of charts can be used to provide estimates of the remaining service life Overall Technical Approach December 2003 Revision 0
3-2 before a leak would develop from an observed crack. For example, if a part-through flaw was discovered, the user would first refer to Figure 3-1, to determine the time (tp) which would be remaining before the crack would penetrate the wall or reach the allowable depth (ta) (e.g. a/t =
0.75). Once the crack penetrates the wall, the time (tB) required to reach an allowable crack length would be determined from Figure 3-2. The total time remaining would then be the simple sum:
Time remaining = tp + tB Another way to determine the allowable time of operation with a part-through flaw would be to use Figure 3-2 directly, in effect assuming the part-through flaw is a through-wall flaw. This approach would be more conservative than that above, and the time remaining would then be:
Time remaining =tB Overall Technical Approach December 2003 Revision 0
3-3 1.0 Flaw Becomes Through - Wall
~/t =.75 Allowable Time (IC",) Befrl Reaching Allowab epth Detected !ndicaiicn A lowable Time Before Depth
~~
Wall Penetration, p
Time ( Months )
Figure 3-1 Schematic of a Head Penetration Flaw Growth Chart for Part-Through Flaws Overall Technical Approach December 2003 Revision 0
3-4 Critical Length ( Excessive Leakage )
UL.
D etected Indication e
~~Length 01 Allowable Operating IMargin Time Before Repair, tB rime ( Months )
Figure 3-2 Schematic of a Head Penetration Flaw Tolerance Chart for Through-Wall Flaws Overall Technical Approach December 2003 Revision 0
4-1 4
MATERIAL PROPERTIES, FABRICATION HISTORY AND CRACK GROWTH PREDICTION 4.1 MATERIALS AND FABRICATION The head adapters for Beaver Valley Unit 2 were manufactured from material produced by Huntington Alloys in the USA. The carbon content and mechanical properties of the Alloy 600 material used to fabricate the Beaver Valley Unit 2 vessels are provided in Table 4-1. The Certified Material Test Reports (CMTRs) were used to obtain the chemistry and mechanical properties for the vessel head penetrations. The materials were annealed for 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> at 17250F and air cooled. Figures 4-1 and 4-2 illustrate the yield strengths and carbon content based on percent of heats of the head adapter penetrations in Beaver Valley Unit 2 vessels relative to a sample of the French head adapters that have experienced cracking. The general trend for the head adapter penetrations in Beaver Valley Unit 2 is of a higher carbon content, higher mill annealing temperature, and lower yield strength relative to those on the French vessels. These factors should all have a beneficial effect on the material resistance to PWSCC in the head penetrations.
4.2 CRACK GROWTH PREDICTION The cracks in the penetration region have been determined to result from primary water stress corrosion cracking in the Alloy 600 base metal and, in some cases, the Alloy 182 weld metal.
There are a number of available measurements of static load crack growth rates in primary water environment, and in this section the available results will be compared and a representative growth rate established.
Direct measurements of Stress Corrosion Cracking (SCC) growth rates in Alloy 600 are relatively rare. Also, care should be used when interpreting the results because the materials may be excessively cold worked, or the loading applied may be near or exceeding the limit load of the penetration nozzle, meaning there will be an interaction between tearing and crack growth. In these cases the crack growth rates may not be representative of service conditions.
The effort to develop a reliable crack growth rate model for Alloy 600 began in the spring of 1992, when the Westinghouse Owners Group began to develop a safety case to support continued operation of plants.
At the time, there was no available crack growth rate data for head penetration materials, and only a few publications existed on growth rates of Alloy 600 in any product form.
The best available publication at that time was that of Peter Scott of Framatome, who had developed a growth rate model for PWR steam generator materials [1]. His model was based on a study of results obtained by McIlree, Rebak and Smialowska [2] who had tested short steam generator tubes which had been flattened into thin compact specimens.
Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-2 An equation was fitted to the data of reference [2] for the results obtained in water chemistries that fell within the standard specification for PWR primary water. Results for chemistries outside the specification were not used. The following equation was fitted to the data at 3301C (6260F):
da 2 8 0
(K _9)1.16 Mr/sec dt (4-1) where:
K is in MPa H The next step was to correct these results for the effects of cold work.
Based on work by Cassagne and Gelpi [3], Scott concluded that dividing the above equation by a factor of 10 would be appropriate to account for the effects of cold work. The crack growth law for 330'C (6260F) then becomes:
da 2.8x1 0 -1 2 (K _ 9)1.16 rn/sec dt (4-2)
Scott further corrected this law for the effects of temperature. This forms the basis for the PWR Materials Reliability Program (MRP) recommended crack growth rate (CGR) curve for the evaluation of SCC where a power-law dependence on stress intensity factor was assumed [411].
The MRP recommended CGR curve was used in this report for determining the primary water stress corrosion crack growth rate and a brief discussion on this recommended curve is as follows:
] a,c,e Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-3 I
There is a general agreement that crack growth in Alloy 600 materials in the primary water environment can be modeled using a power-law dependence on stress intensity factor with differences in temperature accounted for by an activation energy (Arrhenius) model for thermally controlled processes. Figure 4-3 shows the recommended CGR curve along with the laboratory data from Huntington materials used to develop the curve.
[
] a,c,e Material Properties, Fabrication History and Crack Growth Prediction December 2003 Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
44 ac,e The applicability of the MRP recommended model to head penetrations was recently confirmed by two independent approaches. The first was a collection of all available data from Standard Steel and Huntington Alloys materials tested over the past ten years [4H]. The results are shown in Figure 4-3, along with the Scott model for the test temperature.
The MRP crack growth curve was structured to bound 75 percent of the 26 heats for which test results were available. Fits were done on the results for each heat, and the constant term was determined for each heat. This was done to eliminate the concern that the curve might be biased from a large number of results from a single heat. The 75th percentile was then determined from these results. The MRP expert panel on crack growth endorsed the resulting curve unanimously in a meeting on March 6 tb and 7tb 2002. This approach is consistent with the Section XI flaw evaluation philosophy, which is to make a best estimate prediction of future growth of a flaw.
Margins are incorporated in the allowable flaw sizes. The entire data set is shown in Figure 4-3, where the data have been adjusted to a single temperature of 3250C.
A second independent set of data were used to validate the model, and these data were obtained from the two inspections carried out on penetration no. 75 of D. C. Cook Unit 2, which was first found to be cracked in 1994 [4G]. The plant operated for one fuel cycle before the penetration was repaired in 1996 and the flaw was measured again before being repaired. These results were used to estimate the PWSCC growth rate for both the length of the flaw and its depth. These two points are also shown in Figure 4-4, and are consistent with the laboratory data for Huntington materials. In fact, Figure 4-4 demonstrates that the MRP model is nearly an upper bound for these materials. The D. C. Cook Unit 2 penetrations were made from Huntington materials.
Since Beaver Valley Unit 2 operates at a temperature of 313'C (5950F) in the head region [9], and the crack growth rate is strongly affected by temperature, a temperature adjustment is necessary.
This temperature correction was obtained from study of both laboratory and field data for stress corrosion crack growth rates for Alloy 600 in primary water environments. The available data showing the effect of temperature are summarized in Figure 4-5. Most of the results shown here are from steam generator tube materials, with several sets of data from operating plants, and results from two heats of materials tested in a laboratory [4A].
Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-5 Study of the data shown in Figure 4-5 results in an activation energy of 31-33 Kcal/mole, which can then be used to adjust for the lower operating temperature. This value is slightly lower than the generally accepted activation energy of 44-50 Kcallmole used to characterize the effect of temperature on crack initiation, but the trend of the actual data for many different sources is unmistakable.
] ace Therefore the following crack growth rate model was used for the Beaver Valley Unit 2 head penetrations for crack growth in all the cases analyzed.
da 1.55 x 102 (K _ 9)1.16 m/sec dt Material Properties, Fabrication History and Crack Growth Prediction December 2003 Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-6 where:
K = applied stress intensity factor, in MPaV/I This equation implies a threshold for cracking susceptibility, KScc = 9 MPaV/;. The crack growth rate is applicable to propagation in both axial and circumferential directions.
Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-7 a,c,e Table 4-1 Beaver Vallev Unit 2 R/V Head Adapter Material Information Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-8 100 90 I
I, M EdF (11 Heats) 90 r
O~~~
Beaver Valley Unit 2
_ 80 r 2
4 (4Heats) 70 CW 60 a)I IIIII.I 50 0
I C 40 a) 2M30 20 0
Yield Strength (ksi)
Figure 4-1 Yield Strength of the Various Heats of Alloy 600 Used in Fabricating the Beaver Valley Unit 2 and French HeadPenetrations Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-9 80 70 E EdF (11 Heats) 70 II II t OBeaver Valley Unit 2 st 60 (4 Heats)
° 50 ----
l-T-----~--- ~
~
~
I 40 ----.-
i.
0 20
-I - -
-I m1° l1 1
- ~~~~~~~~~
bI:
1 0
- - - - - - - - -I Carbon Content (Weight %)
Figure 4-2 Carbon Content of the Various Heats of Alloy 600 Used in Fabricating the Beaver Valley Unit 2 and French Head Penetration Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-10 ac,e Figure 4-3 Screened Laboratory Data for Alloy 600 with the MRP Recommended Curve (Note that the Modified Scott Model is also Shown)
Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-11 a~c,e Figure 4-4 Model for PWSCC Growth Rates in Alloy 600 in Primary Water Environments (3250C), With Supporting Data from Standard Steel, Huntington, and Sandvik Materials Note that the data have been normalized to a temperature of 3250C. The actual test temperatures are listed in parenthesis after the caption. For example, the Huntington data were obtained at temperature ranging from 315'C to 331'C.
Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
4-12 TEMPERATURE, DEG. C 333 315 372 352 298 1 E-08 1 E-09 U) co l
LU cc X 1E-10 3:
0 X
0 0
1 E-1 1 282 1,000
_ -100 I
z 0
=
w I-.E
-~10 c
~
I 0
cc C) m 1
cc
~I.DRW O
0.0.1 0.0018 1E-12
+
0.00155 0.0016 0.00165 0.0017 0.00175 RECIPROCAL TEMPERATURE, 1 /DEG. K Note:
All symbols are for steam generator materials, except the solid circles, which are head penetration laboratory data.
Figure 4-5 Summary of Temperature Effects on PWSCC Growth Rates for Alloy 600 in Primary Water Material Properties, Fabrication History and Crack Growth Prediction December 2003 Revision 0
5-1 5
STRESS ANALYSIS 5.1 OBJECTIVES OF THE ANALYSIS The objective of this analysis was to obtain accurate stresses in each CRDM or head vent and its immediate vicinity.
To do so requires a three dimensional analysis which considers all the pertinent loadings on the penetration [6]. An investigation of deformations at the lower end of the housing was also performed using the same model. Five CRDM locations were considered:
the outermost row (at 42.7 degrees angular position from the RV centerline), rows at 40.0 degrees, 38.7 degrees, 25.4 degrees and the center location.
In addition, the head vent was analyzed.
The analyses were used to provide information for the flaw tolerance evaluation, which follows in Section 6. Also, the results of the stress analysis were compared to the findings from service experience, to help assess the causes of the cracking which has been observed.
5.2 MODEL A three-dimensional finite element model comprised of isoparametric brick and wedge elements was used to obtain the stresses and deflections.
Views of CRDM and head vent models are shown in Figures 5-1 and 5-2 respectively. Taking advantage of the symmetry of the vessel head, only half of the CRDM penetrations were modeled. Similarly, only half of the center penetration was modeled.
In the models, the lower portion of the Control Rod Drive Mechanism (CRDM) penetration nozzle, the head vent, the adjacent section of the vessel closure head, and the joining weld were modeled.
The vessel to penetration nozzle weld was simulated with two weld passes. The penetration nozzle, weld metal, cladding and the vessel head shell were modeled in accordance with the relevant materials.
The only loads used in the analysis are the steady state operating loads. External loads, such as seismic loads, have been studied and have no impact since the penetration nozzles are captured by the full thickness of the reactor vessel head (about 6 and 3/16 inches [liD]) into which the penetrations are shrunk fit during construction. The area of interest is in the penetration near the attachment weld, which is unaffected by these external loads.
5.3 STRESS ANALYSIS RESULTS - OUTERMOST CRDM PENETRATION (42.70)
Figure 5-3 presents the hoop and axial stresses for the steady state condition for the outermost CRDM penetration.
Stress Analysis December 2003 Revision 0
5-2
]ache I'
I ace 5.4 STRESS ANALYSIS RESULTS - INTERMEDIATE CRDM PENETRATIONS
] a,ce 5.5 STRESS ANALYSIS RESULTS - CENTER CRDM PENETRATION
]ace 5.6 STRESS ANALYSIS RESULTS - HEAD VENT
] a,ce Stress Analysis December 2003 Revision 0
5-3 1-,I_
F7--
Kf Figure 5-1 Finite Element Model of CRDM Penetration Stress Analysis December 2003 Revision 0
5-4 Fie-2 n P Fi---nt E
t Md-e Figure 5-2 Vent Pipe Finite Element Model Stress Analysis December 2003 Revision 0
5-5 ANSYS 5.7 JUL 10 2003 06 :01 :06 PLOT NO.
3 ELEMENTS PowerGraphics EFAcET=1 MAT NUN N'
~~~~~~~~~~~~~~NODAL SOLUTION TINE =40 04 SY (AVG)
RSYS= 11 Powercraphics EFACET=1 AVRES =Mat UNIX =.401049
-10000 0
10000 30000 5 tt~40000 5V2 CRDN)42.65d,CYC SS,4/2.75,2.5E 03,A)
Operating ANSYS 5.7 JUL 10 2003 06: 01 :07 PLOT NO.
4 ELEMENTS MAT NUN NODAL SOLUTION TIME=4004 SE (AVG)
RSYS=11 Poweroraphics EFACET=1 AVRES=Mat DMX =. 401049 SMN =-38843 SMIX =75904 36843
-10000 0
10000 30000 40000 4 0000 100000 BV 2 CRDM(42.65dC GYC SS,4/2.75,2.5E 03,A)
Operating Figure 5-3 Stress Distnibution at Steady State Conditions: Outermost CRDM Penetration Nozzle (42.7 Degrees) (Hoop Stress is the Top Figure, Axial Stress is the Bottom Figure)
Stress Analysis December 2003 Revision 0
5-6 ANSYS5.
JUL 10 2003 03:47 :28 PLOT NO.
3 ELEMENTS
~~~~~~~~~~~Power~raphics EFACST= 1 MAT NUNM NODAL SOLUTION TIME=4 004 SY (AVG)
RSYS=11-Power~raphics EPACET=1 AVRES=Mat 310000 40000 3V2 CRDN(40d,CYC SS,4/2.75,2.5E-03,A)
-Operating ANSYS 5.7 JUL 10 2003 03:47:29 PLOT NO.
4
~~~~~~~~~~ELEMENTS MAT NUN-I NODAL SOLUTION TIME=40 04 SE (AVG)
RSYS=1i Poweroraphics EFACST= 1 AVRSS=Mat DM.00001 21000 0
.~30000 ili40000 50000 100000 5V2 CRNOM(40d,CYC SS,4/2.75,2.5E--03,A)
-Opera:ing Figure 5-4 Stress Distribution at Steady State Conditions for the 40.0 Degrees CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure)
Stress Analysis December 2003 Revision 0
5-7 ANSYS 5.7 JUL 10 2003 01:13:57 PLOT NO.
3 ELEXENTS PowerGraphics EFACET=1 MAT NUN NODAL SOLUTION TIME=4004 SY (AVG)
RSYS=11 PowerGraphics EFACET=1 AVRES=Mat DXX =.400601 SXN =-26639 SXX =84171
_-2 663 9
-10000 0
3g 10000 40000 100000 N.
BV2 CRDM(38.65d,CYC SS,4/2.75,2.5E-03,A)
Operating ANSYS 5.7 JUL 10 2003 01: 13: 58 PLOT NO.
4 ELEXENTS NAT NUN NODAL SOLUTION TIME=4004 SZ (AVG)
RSYS=1l PowerGraphics EFACET=1 AVRES=Mat DXX =.400601 SMN =-39806 SX =75822 m
-39806
-10000 0
10000 20000 30000 40000 a50000 100000 BV2 CRDLM(38.65d,CYC SS,4/2.75,2.5E-03,A)
Operating Figure 5-5 Stress Distribution at Steady State Conditions for the 38.7 Degrees CRDM Penetration (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure)
Stress Analysis December 2003 Revision 0
5-8 ANSYS 5.7 JUL.
9 2003 2 2:3 1:4 0 PLOT NO.
3 ELEMENTS PowerGraphics EFACET=1 MAAVO) f i ~~~~~~~~~~~NODAL SOLUTION TIME=~~~~~~~~~~40000 fl(4r AN~~~~~SYS 5.7 PowLr9ra2003 V~~~~~~~~~~~EAE~
CTE 0040
-10000 0100 000 8V2 CRDM(25.37d,CYC SS,4/2.75,2.5E-03,A)-
Operazing Figure -6 Stres Distrbution t Steay StateConditins for Ahe-25.
Deres RD Penetatio (Hop Stess s th TopFigue; Aialtres is th2 BtomFgue Stress Analysis December 2003 Revision 0
5-9 20:05:34 PLOT NO.
3 ELEMENTS PowerGraphics EFACET=1 NAT NUM r
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5NODAL SOLUTION
,~~~w
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C Ss, 4/2. 7 5, 0.
A) - Operating JU 20030 24~~~~~~~~~~~~~~00 TIME40040 100000 BV2 CRDM(Od,CYCSS,4/2.75,0,A)
Operating Figure 5-7 Stress Distribution at Steady State Conditions for the Center CRDM Penetration (Hoop Stress is the Top Figure, Axial Stress is the Bottom Figure)
Stress Analysis December 2003 Revision 0
5-10
-~~~~~~~~~~~~~ ::
0 0
PowcANSYSS.7 JUL 15 2003 15: 51:27 PLOT NO.
3 ELEM-ENTS
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~~~~~~~~~Power~raphics 4, i t EFACET=
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~~~~~~~~JUL 15 2003 01
~~~~~~~~~~15:51:20 PLOT NO.
4 ELEMENTS Ji
~~~~~~~MAT NUY NODAL SOLUTION I~~~~~~~~~~~
TME=8004 SE (AVG)
ROYSM-Il PowerGraphics EPACET=1 AVRES=Ma 310000 40000 50000 100000 aV2 iiV(6.1-5d,CYC SS,1-.315/0.815,0,A)
Operating Figure 5-8 Stress Contours in the Head Vent Nozzle as a Result of Residual Stresses and Operating Pressure (Hoop Stress is the Top Figure; Axial Stress is the Bottom Figure)
Stress Analysis December 2003 Revision 0
5-11 ANSYS 5.7 JUL 10 2003 06:01:23 PLOT NO.
9 DISPLACEMENT TIME=4004 RSYS=SOLU DMX =.401049
- DSCA=10 XV
=-1 ZV =2 DIST=7.344 XF
=-.217541 YF
=52.872 ZF =64.485 VUP =Z PRECISE HIDDEN NODAL SOLUTION TIME=4004 SZ (AVG)
RSYS=SOLU DMX =.392526 SMN =-45306 SMX =72580
-45306 10000 0
30000 40000 50000 100000 i 1 1,;
4/1 BV2 CRDM(42.65d,CYC SS,4/2.75,2.5E-03,A)
Operating Figure 5-9 Axial Stress Distribution at Steady State Conditions for the Outermost CRDM Penetration (42.7 Degrees), Along a Plane Oriented Parallel to, and Just Above, the Attachment Weld Stress Analysis December 2003 Stress Analysis December 2003 Revision 0
6-1 6
FLAW TOLERANCE CHARTS
6.1 INTRODUCTION
The flaw tolerance charts were developed using the stress analysis of each of the penetration locations as discussed in Section 5. The crack growth law developed for Beaver Valley Unit 2 in Section 4.2 was used for each case, and several flaw tolerance charts were developed for each penetration location. The first series of charts characterizes the growth of a part through flaw, and the second series of charts characterizes the growth of a through-wall flaw in the length direction.
The allowable safe operating life of the penetration nozzle may then be directly determined, using the combined results of the two charts. All times resulting from these calculations are effective full power years, since crack growth will only occur at operating temperatures.
6.2 OVERALL APPROACH The results of the three-dimensional stress analysis of the penetration locations were used directly in the flaw tolerance evaluation.
The crack growth evaluation for the part-through flaws was based on the worst stress distribution through the penetration wall at the location of interest of the penetration. The highest stressed location was found to be in the immediate vicinity of the weld for both the center and outermost penetrations.
The stress profile was represented by a cubic polynomial:
a(x)=AO +Aix+A 2 x2 +A 3 x3 (6-1) where:
x
= the coordinate distance into the nozzle wall aY
= stress perpendicular to the plane of the crack A,
= coefficients of the cubic polynomial fit For the surface flaw with length six times its depth, the stress intensity factor expression of Raju and Newman [5A] was used. The stress intensity factor K1 (c1) can be calculated anywhere along the crack front. The point of maximum crack depth is represented by (D = 0, and this location was also found to be the point of maximum K, for the cases considered here.
The following expression is used for calculating K1 ((D), where (D is the angular location around the crack. The units of K I (4) are ksiin.
0.5 3 KI (4) =
- ]
,Gj (a/c, a/t, t/R, <D) Aj ai (6-2)
The boundary correction factors Go (c1), GI (0), G2 (0) and G3 ((i)) are obtained by the procedure outlined in reference [5A]. The dimension "a" is the crack depth, and "c" is the semi crack Flaw Tolerance Charts December 2003 Flaw Tolerance Charts December 2003 Revision 0
6-2 length, while "t" is the wall thickness. "R" is the inside radius of the tube, and "Q" is the shape factor.
] a,c,e 6.3 AXIAL FLAW PROPAGATION CRDM Surface Flaws The results of the calculated growth for inside surface flaws growing through the wall thickness of the CRDM penetration nozzles are shown in Figures 6-2 through 6-7 for inside surface flaws.
For outside surface flaws, the results are shown in Figures 6-9 and 6-10. Based on the discussion in MRP-55 report [4H], the use of stress intensity factors less than 15 MPaVrn involves assumption not currently substantiated by actual CGR data for CRDM nozzle materials.
Therefore, these crack growth curves begin at a flaw depth that results in a stress intensity factor of 15 MPaV/m, which exceeds the threshold value of 9 MPairm. This may result in curves with different initial flaw sizes, as seen for example in Figure 6-3. Note that results are only provided for the uphill and downhill sides of each penetration nozzle; the stresses for the regions 90 Flaw Tolerance Charts December 2003 Revision 0
6-3 degrees from these locations are compressive. If flaws are found in such a location, the results for either the uphill or downhill location, whichever is closer, can be used.
Each of these figures allows the future allowable service time to be estimated graphically, as discussed in Section 3. Results are shown for each of the penetration nozzles analyzed in each of these figures. The stresses are much higher near the attachment weld than at 0.5 inch below or above it, so separate figures have been provided for these three regions. For more than 0.5 inch below the weld, the crack growth will eventually come to rest since the stresses are compressive as shown for the CRDM nozzles in Appendix A. Also, the stresses are different on the downhill side of the penetration as opposed to the uphill side, so these two cross sections have also been treated separately.
Example problems are provided in section 7 for a range of possible flaw types.
CRDM Through-Wall Flaws The projected crack growth of a through-wall flaw in the CRDM penetration nozzles are the primary concern in evaluating the structural integrity of head penetrations. In some cases, the through-wall flaw may be located sufficiently below the attachment weld that additional time may be required for the flaw to grow to the attachment weld. To provide a means to evaluate the duration of this additional time, a series of flaw tolerance charts for through-wall flaws were prepared.
Charts were prepared for each of the penetrations evaluated, for both the uphill and downhill locations, as shown in Figures 6-12 through 6-20. In each figure, the location of the upper extremity of the postulated through-wall crack is identified by the distance measured from the bottom of weld. Note that in all the cases, the crack slows down significantly as it grows above the weld, due to the decreasing magnitude of the stress field. This provides further assurance that axial flaws will not extend to a critical length which exceeds 15 inches, regardless of the duration of crack growth.
Head Vent The only flaw tolerance chart that is necessary for the head vent region is for flaws at and above the weld, since there is no portion of the head vent which projects below the weld. Figure 6-8 provides the projected growth of a part through flaw in the head vent just above the attachment weld. The growth through the wall is relatively rapid, because the thickness of the head vent is small.
6.4 CIRCUMFERENTIAL FLAW PROPAGATION Since circumferentially oriented flaws have been found at five plants (Bugey 3, Oconee 2, Crystal River 3, Davis Besse, and Oconee 3), it is important to consider the possibility of crack extension in the circumferential direction.
The first case was discovered as part of the destructive examination of the tube with the most extensive circumferential cracking at Bugey 3. The crack was found to have extended to a depth of 2.25 mm in a wall thickness of 16 mm. The flaw was Flaw Tolerance Charts December 2003 Revision 0
6-4 found at the outside surface of the penetration (number 54) at the downhill side location, just above the weld.
The circumferential flaws in Oconee Unit 3 were discovered during the process of repairing a number of axial flaws, whereas the circumferential flaw in Oconee Unit 2 and Crystal River Unit 3 were discovered by UT. Experience gained from these findings has enabled the development of UT procedures capable of detecting circumferential flaws reliably.
To investigate this issue completely, a series of crack growth calculations were carried out for a postulated surface circumferential flaw located just above the head penetration weld, in a plane parallel to the weld itself. This is the only flaw plane that could result in a complete separation of the penetration nozzle, since all others would result in propagation below the weld, and therefore there is no chance of complete separation because the remaining weld would hold the penetration nozzle in place.
]ace The results of this calculation are shown in Figure 6-21. From this figure, Flaw Tolerance Charts December 2003 Revision 0
6-5 it can be seen that the time required for propagation of a circumferential flaw to a point where the integrity of the CRDM penetration nozzle would be affected (330 degrees [10]) would be about 24 years. Due to the conservatism in the calculations (the time period for a surface flaw to become a through-wall flaw was conservatively ignored) the service life is likely to be even longer. In addition, due to uncertainties in the exact composition of the chemical environment in contact with the nozzle OD, a multiplicative factor of 2.0 is used in the Crack Growth Rate (CGR) for all circumferential surface flaws on the OD of the head penetration nozzles located above the elevation of the J-groove weld.
6.5 FLAW ACCEPTANCE CRITERIA Now that the projected crack growth curves have been developed, the question remains as to what flaw size would be acceptable for further service.
Acceptance criteria have been developed for indications found during inspection of reactor vessel upper head penetration as part of an industry program coordinated by NEI (formerly NUMARC).
Such criteria are normally found in Section XI of the ASME Code, but Section XI does not require in-service inspection of these regions and therefore acceptance criteria are not available.
In developing the enclosed acceptance criteria, the approach used was very similar to that used by Section XI, in that an industry consensus was reached using input from both operating utility technical staff and each of the three PWR vendors. The criteria developed are applicable to all PWR plant designs.
Since the discovery of the leaks at Oconee and ANO-1, the acceptance criteria have been revised slightly to cover flaws on the outside diameter of the penetration below the attachment weld, and flaws in the attachment weld. These revised criteria are now formally endorsed by the NRC [12],
and will be used in these evaluations. Portions of the acceptance criteria will be noted below.
The criteria presented herein are limits on flaw sizes, which are acceptable. The criteria are to be applied to inspection results. It should be noted that determination of the future service during which the criteria are satisfied is plant-specific and dependent on flaw geometry and loading conditions.
It has been previously demonstrated by each of the owners groups that the penetration nozzles are very tolerant of flaws and there is only a small likelihood of flaw extensions to larger sizes.
Therefore, it was concluded that complete fracture of the penetration nozzle is highly unlikely.
The approach used here is more conservative than that used in Section XI applications where the acceptable flaw size is calculated by placing a margin on the critical flaw size. For the current application, the critical flaw size would be far too large to allow a practical application of the approach used in Section XI applications, so protection against leakage is the priority.
The acceptance criteria presented herein apply to all the flaw types regardless of orientation and shape. Similar to the approach used in Section XI, flaws are first characterized according to established rules and then compared with acceptance criteria.
Flaw Tolerance Charts December 2003 Revision 0
6-6 Flaw Characterization Flaws detected must be characterized by the flaw length and preferably flaw depth.
The proximity rules of Section XI for considering flaws as separate, may be used directly (Section XI, Figure IWA 3400-1). This figure is reproduced here as Figure 6-22.
When a flaw is detected, its projections in both the axial and circumferential directions must be determined.
Note that the axial direction is always the same for each penetration, but the circumferential direction will be different depending on the angle of intersection of the penetration nozzle with the vessel head. The "circumferential" direction of interest here is along the top of the attachment weld, as illustrated in Figure 6-23. It is this angle which will change for each penetration nozzle and the top of the attachment weld is also the plane which could cause separation of the penetration nozzle from the vessel head. The location of the flaw relative to both the top and bottom of the partial penetration attachment weld must also be determined since a potential leak path exists when a flaw propagates through the penetration nozzle wall and up the penetration nozzle past the attachment weld. Schematic of a typical weld geometry is shown in Figure 6-24.
Flaw Acceptance Criteria The maximum allowable depth (af) for axial flaws on the inside surface of the penetration nozzle, at or above the weld is 75 percent of the penetration wall thickness. The term af is defined as the maximum size to which the detected flaw is calculated to grow in a specified time period. This 75 percent limitation was selected to be consistent with the maximum acceptable flaw depth in Section XI and to provide an additional margin against through wall penetration. There is no concern about separation of the penetration nozzle from the vessel head, unless the flaw is above the attachment weld and oriented circumferentially. Calculations have been completed to show that the geometry of all penetrations can support a continuous circumferential flaw with a depth of 75 percent of the wall thickness.
Axial inside surface flaws found below the weld are acceptable regardless of depth as long as their upper extremity does not reach the bottom of the weld during the period of service until the next inspection. Axial flaws that extend above the weld are limited to 75 percent of the wall thickness.
Axial flaws on the outside surface of the penetration nozzle below the attachment weld are acceptable regardless of depth, as long as they do not extend into the attachment weld during the period of service until next inspection. Outside surface flaws above the attachment weld must be evaluated on a case by case basis, and must be discussed with the regulatory authority.
Circumferential flaws located below the weld are acceptable regardless of their depth, provided the length is less than 75 percent of the penetration nozzle circumference for the period of service until the next inspection.
Circumferential flaws detected in this area have no structural significance except that loose parts must be avoided.
To this end, intersecting axial and circumferential flaws shall be removed or repaired. Circumferential flaws at and above the weld must be discussed with the regulatory authority on a case by case basis.
Flaw Tolerance Charts December 2003 Revision 0
6-7 Surface flaws located in the attachment welds themselves are not acceptable regardless of their depth. This is because the crack growth rate is several times faster than that of the Alloy 600 material, and also because depth sizing capability does not yet exist for indications in the attachment weld.
The flaw acceptance criteria are summarized in Table 6-1. Flaws that exceed these criteria must be repaired unless analytically justified for further service. These criteria have been reviewed and endorsed by the NRC, as documented in references [7, 8, 12].
It is expected that the use of these criteria and crack growth curves will provide conservative predictions of the allowable service time.
Flaw Tolerance Charts December 2003 Revision 0
6-8 Table 6-1 Summary of R.V. Head Penetration Flaw Acceptance Criteria Axial Circumferential Location at af C
Below Weld (ID) t no limit t
.75 circ.
At and Above Weld (ID) 0.75 t no limit repair repair Below Weld (OD) t no limit t
.75 circ.
Above Weld (OD) repair repair repair repair Note: Surface flaws of any size in the attachment weld are not acceptable.
af = Flaw Depth C = Flaw Length t
= Wall Thickness Table 6-2 Beaver Valley Unit 2 Penetration Geometries [llA, liB]
Penetration Type Wall Thickness (in.)
Penetration OD (in.)
CRDM 0.625 4.000 Head Vent 0.250 1.315 Flaw Tolerance Charts December 2003 Revision 0
6-9 70 60 c~
I C,)
50 40 30 20 10 0
0 50 100 150 200 Crack Half Angle Figure 6-1 Stress Intensity Factor for a Through-Wall Circumferential Flaw in a Head Penetration Flaw Tolerance Charts December 2003 Flaw Tolerance Charts December 2003 Revision 0
6-10 1ir Nozzle Angle:
0.9 38.7 deg 0.8 Nozzle Angle:
40.0 deg 0.7 Nozzle Angle:
CD A,
s 25.4 deg 0.6 Nozzle Angle:
42.7 deg 0.5 a-0.4 Nozzle Angle:
0.3 deg.
d 0.2 0.1 0~
0 0 ;
0 S S Beaver Valley Unit 2 0
1 2
3 4
5 6
7 8
9 time (year)
Figure 6-2 Inside, Axial Surface Flaws,.5" Below the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 December 2003 Flaw Tolerance Charts December 2003 Revision 0
6-11 1
'--.....--------,,-,,,,,-.v,...~~~~~~~-.----.........-.--.-..
-~~~
0.9 0.8NozeAge 0.7~ ~~~~~~~~~~~~~~~~~~3.1e
~~~~~~~~~Nozzle Angle:
~~~ 0.6
~~~~~40.0 deg
~Nozzle Angle:-
0.5
% 04~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.4-~~~~~~~~~~~~~~~2.
e:
0.3-0.2-0.1 Beaver Valley Un it 2 0
1 2
3 4
5 6
7 8
9 10 time (year)
Figure 6-3 Inside, Axial Surface Flaws,.5" Below the Attachment Weld, Nozzle Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-12 1
0.9 0.8 0.7 Fn U) 0 X 0.6 a
3- 0.5 3 0.4 M
0.3 0.2 0.1 0
Nozzle Angle:
38.7 deg \\
Nozzle Angle:
40.0 dog Nozzle Angle:
42.7 deg
\\.
0 deg Nozzle Angle:
25.4 deg Beaver Valley Unit 2 1
2 3
4 5
6 0
7 time (year)
Figure 6-4 Inside, Axial Surface Flaws, At the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-13 0.9 Nozzle Angle:
38.7 deg 0.8 0.7-Nozzle-Anglea:.
w) 40.0 degs a)
- ~0.6-co Nozzle Angle:
~0.5 -4.
e Nozzle Angle:
- 0.
0 deg.
0.4 0.3 0.2-0.1 Beaver Valley Unit 2 0
0 1
2 3
4 5
6 7
time (year)
Figure 6-5 Inside, Axial Surface Flaws, At the Attachment Weld, Nozzle Downhili Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-14 it 0.9 0.8 0.7 7
= 0.6
> 0.5
'a
~: 0.4 0.3 0.2 0.1 0
42.7 deg Nozzle Angle:
25.4 deg -
Nozzle Angle:
40.0 deg Nozzle Angle:
38.7 deg:
Nozzle Angle:
0 deg Beaver Valley Unit 2 l
0 1
2 3
4 5
6 7
time (year) 8 9
10 Figure 6-6 Inside, Axial Surface Flaws,.5" Above the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-15 0.9
~~~~~~~~~~~~~~~~~~~~~~~Nozzle Angle:
-38.7 deg 0.8 0.7 Nozzle Angle:_
.40.0 deg 06-
~0.6 Nozzle Angle.
0.4 0.3 -
~~~~~~~~~~~~~~~~~~~~~~Nozzle Angle:
0.2 -....
0.1 -
Beaver Valley Unit 2 0
0 12 3
4 5
6 7
8 time (year)
Figure 6-7 Inside, Axial Surface Flaws,.5" Above the Attachment Weld, Nozzle Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-16 1
0.9 0.8 0.7 en a)
C
= 0.6
.5 M
a 0.5 c
B 0.4 Cu 0.3 0.2 0.1 0
Head Vent Nozzle Beaver Valley Unit 2 0
1 2
time (year) 3 Figure 6-8 Inside, Axial Surface Flaws, At the Attachment Weld, Head Vent-Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Flaw Tolerance Charts December 2003 Revision 0
6-17 0.9 Nozzle Angle:
.40.G deg 0.8 -
0.7 -
Nozzle Angle:
38.7 deg 0.6 y
Nozzle Angle:
.25.4 degNoeAg:
Q 0 0 0 0 0 0 0.5-0 0 0 00 0 0 \\4 0 0 0 0 0 ; jlrV. 0 0 42.7 deg 0.4 0.3 Nozzle Angle:
0.2 -
0.1 -
Beaver Valley Unit 2 0
1 2
3 4
time (year)
Figure 6-9 Outside, Axial Surface Flaws, Below the Attachment Weld, Nozzle Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-18 0.9 0.8 0.7 00
- S Ci
, 0.6 05
¢ 0.4 a
0.3 0.2 0.1 0
Figure 6-10
(
0 1
2 3
4 time (year)
)utside, Axial Surface Flaws, Below the Attachment Weld, Nozzle Downhill Side - Crack Growth Predictions for Beaver laley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-19 0.9 0.8 0.7 W
cC
= 0.6 0.5 a.
co
¢ 0.4 0.3 0.2 0.1 0
0 1
2 3
4 5
time (year)
Figure 6-11 Outside, Circumferential Surface Flaws, Along the Top of the Attachment Weld - Crack Growth Predictions for Beaver Valley Unit 2 (MRP Factor of 2.0 Included)
Flaw Tolerance Charts December 2003 Revision 0
6-20 2.5 C) 0 0
E0 0) 0 0.
C) 0.
0.2 0
U-2.0 1.5 1.0 0.5 0.0
-0.5
-1.0 0
1 2
3 4
5 6
7 8
9 10 Period (Year)
Figure 6-12 Through-Wall Axial Flaws Located in the Center CRDM (0.0 Degrees) Penetration, Uphill and Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-21 2.0 1.5 S
Gs 2
0 E 1.0 0
m E0 4-0 I
0.5 to a
.2-E 0.0 0.
0.
3-IL -0.5
-1.0 0
1 2
3 4
5 6
7 8
Period (Year)
Figure 6-13 Through-Wall Axial Flaws Located in the 25.4 Degrees Row of Penetrations, Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-22 2.0 1.5 E0 0E/
E 1.0 CRDM NozzleWeld Region 2a a
0.5 0.
-0.5
-1.0 0
1 2
3 4
5 6
7 8
9 10 11 12 13 Period (Year)
Figure 6-14 Through-Wall Axial Flaws Located in the 25.4 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolrance Carecmer20 Flaw 'tolerance Charts December 2003 Revision 0
6-23 2.0
'1.5 E )
0 E0 CRDM No'zzle Weld Region 0.5 0.0 C)
- u. -0.5-
-1.0 0
12 3
4 5
6 7
8 Period (Year)
Figure 6-15 Through-Wall Axial Flaws Located in the 38.7 Degrees Row of Penetrations, Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-24 3.0 2.5
.2
- 4) 2.0 0
E 0
o 1.5 m
E0 c
1.0 a
- ~0.5 0
N c) 0.
D.
0.0 (U
U-
-0.5
-1.0 0
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 Period (Year)
Figure 6-16 Through-Wall Axial Flaws Located in the 38.7 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Flaw Tolerance Charts December 2003 Revision 0
6-25 2.0
-~1.5 E 1.0 0
Eo RD Nozzle Weld Region 0.5 1!0.
L 0.5 01.
0.0234 C.)~ ~ ~
~
~ ~
~ ~~~~~~~~Peid(er Fiue61 hog-alAilFasLctdi h
00Dges)o fPntainUhl ie-CakGot rdcin o
BevrVllyUi.
Flaw Tolerance Charts December 2003 Revision 0
6-26 3.0 2.5 1-:
) 2.0 0
E0 o
1.5 m
E 0
aD C
1.0 c) 0.
- Q 0.5 0.5
-)
a.
- 0.
0.0 a)
U-
-0.5
-1.0 0
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 Period (Year)
Figure 6-18 Through-Wall Axial Flaws Located in the 40.0 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-27 2.0 C
.4-0 E
0 0
E0 C
co 0.
0 0)
C)
CU 1.5 1.0 0.5 0.0
-0.5
-1.0 0
1 2
3 4
5 6
7 8
Period (Year)
Figure 6-19 Through-Wall Axial Flaws Located in the 42.7 Degrees Row of Penetrations, Uphill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Revision 0
6-28 3.0 2.5 E
0 a) 0.
0 a.L d) 2.0 1.5 1.0 0.5 0.0
-0.5
-1.0 0
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 Period (Year)
Note that flaw upper crack tip of the longitudinal through-wall flaw for 42.7 degree penetration nozzle is postulated at 0.4" below the J-weld on the downhill side instead of 0.5". This is because the stress intensity factor at 0.5" region is small (less than 9.0 Mpa*sqrt(M)).
Figure 6-20 Through-Wall Axial Flaws Located in the 42.7 Degrees Row of Penetrations, Downhill Side - Crack Growth Predictions for Beaver Valley Unit 2 Flaw Tolerance Charts December 2003 Flawl'olerance Charts December 2003 Revision 0
6-29 180.000 150.000
'a 120.000 X
90.000 C.)
0 C
c60.000 U
30.000 i
[mop /2 i i.'
I ude"j 0.000 0
5 10 15 20 25 Period (Year)
Figure 6-21 Through-Wall Circumferential Flaws Near the Top of the Attachment Weld for CRDM Nozzle - Crack Growth Predictions for Beaver Valley Unit 2 (MRP Factor of 2.0 Included)
Flaw Tolerance Charts December 2003 Revision 0
<w ft xt a
0 02
-m IV N) t 0
I I
ii Nj
- 3 ft 0m M
SItI ff O
0.
I A
0
.g f-I I
m I
I
-I n
_I i
I CD w~~~~~~~~~~~
- i.
C~I
./,,
Z~~~~~~~~~~~:3 It II~
0)~ ~ ~ ~~~N
'a~~~~~~~~~~~:
\\V A t E,,
-- I 0
1 I
Cz C,,
3 3
r-T
'A S
2a 0
-2.
0)
'a 3
T col A
I i'
5'
- ~3 C,, -
I N)
- 3
6-31 Figure 6-23 Definition of "Circumferential" Flaw Tolerance Charts December 2003 Revision 0
6-32 N,OZZLE t
BOTTOM OF WELD I V Figure 6-24 Schematic of Head Penetration Geometry Flaw Tolerance Charts December 2003 Revision 0
7-1 7
SUMMARY
AND EXAMPLE PROBLEMS An extensive evaluation has been carried out to characterize the loadings and stresses, which exist in the head penetrations at Beaver Valley Unit 2 reactor vessel head. Three-dimensional finite element models were constructed [6], and all pertinent loadings on the penetrations were analyzed. These loadings included internal pressure and thermal expansion effects typical of steady state operation. In addition, residual stresses due to the welding of the penetrations to the vessel head were considered.
Results of the analyses reported here are consistent with the axial orientation and location of flaws which have been found in service in a number of plants and that the largest stress component is the hoop stress, and the maximum stresses were found to exist at the attachment weld.
The most important loading conditions were found to be those which exist on the penetration for the majority of the time, which are the steady state loading and the residual stresses.
These stresses are important because the cracking observed to date in operating plants has been determined to result from primary water stress corrosion cracking (PWSCC). These stresses were used in the fracture calculations to predict the future growth of flaws postulated to exist in the head penetrations. A crack growth law was developed specifically for the operating temperature of the head at Beaver Valley Unit 2 reactor pressure vessel, based on the EPRI recommendation, which is consistent with laboratory data as well as crack growth results for operating plants.
The crack growth predictions contained in Section 6 show that the future growth of cracks which might be found in the penetrations will be typically moderate, however, a number of effective full power years would be required for any significant extensions.
7.1 SAFETY ASSESSMENT It is appropriate to examine the safety consequences of an indication which might be found. The indication, even if it were to propagate through the penetration nozzle wall, would have only minor consequences, since the pressure boundary would not be broken, unless it were to propagate above the weld.
Further propagation of the indication would not change its orientation, since the hoop stresses in the penetration nozzle are much larger than the axial stresses. Therefore, it is extremely unlikely that the head penetration would be severed.
If the indication were to propagate to a position above the weld, a leak could result, but the magnitude of such a leak would be very small, because the crack could not open significantly due to the tight fit between the penetration nozzle and the vessel head. Such a leak would have no immediate impact on the structural integrity of the system, but could lead to wastage in the ferritic steel of the vessel head, as the borated primary water concentrates due to evaporation.
Davis Besse has demonstrated the consequence of ignoring such leaks.
Summary and Example Problems December 2003 Revision 0
7-2 Any indication is unlikely to propagate very far up the penetration nozzle above the weld, because the hoop stresses decrease in this direction, and this will cause it to slow down, and to stop before it reaches the outside surface of the head.
The high likelihood that the indication will not propagate up the penetration nozzle beyond the vessel head ensures that no catastrophic failure of the head penetration will occur, since the indication will be enveloped in the vessel head itself, which precludes the opening of the crack and limits leakage.
7.2 EXAMPLE PROBLEMS The flaw tolerance charts in Figures 6-2 through 6-21 can be used with the acceptance criteria of Section 6.5 to determine the available service life.
In this section, a few examples will be presented to illustrate the use of these figures. The example cases are listed in Table 7-1.
Example 1. Determine the service life of an axially oriented inside surface flaw whose upper extremity is located 1.25" below the weld on the uphill side of penetration no. 50. First, the penetration locality angle is obtained from Table 1-1 and, in this case, the locality angle is 38.7 degrees. The initial flaw depth, aiiual, is 0.078" and the initial flaw length, 2clitai, is 0.195".
Assuming that the initial aspect ratio of 2.5:1 is maintained throughout the time that the inside surface flaw becomes a through-wall flaw, the final length of the flaw (2cfial) will bel.563". The upper extremity of the flaw is now located 0.566" below the weld and validates the use of a single crack growth curve. The crack growth curve for the 38.7 degrees nozzle angle of Figure 6-2 is applicable and Figure 6-2 has been reproduced as Figure 7-1. The flaw is initially 12.5 percent of the wall thickness, and a straight line is drawn horizontally at a/t = 0.125 that intersects the crack growth curve. Using the acceptance criteria in Table 6-1, the service life can then be determined as the remaining time for this flaw to grow to the limit of 100 percent of the wall thickness or approximately 3.8 years (labeled as "Service Life" in Figure 7-1)
Example 2. In this case, the flaw is identical in size to that used in Example 1, but located on the outside surface and on the downhill side of penetration no. 50. This flaw, just as the flaw in Example 1, will not cross into the weld region. The applicable curve to use is Figure 6-10. The ratio a/t and initial reference time are likewise found using the same approach as used in Example
- 1. Using the acceptance criteria in Table 6-1, the determination of service life is illustrated in Figure 7-2, where we can see that the result is approximately 1.9 years.
Example 3.
An axial inside surface flaw is located at the weld and on the downhill side of penetration no. 20. The initial length of the flaw is 0.250" and the initial depth is 0.05". From Table 1-1, the angle of this penetration nozzle is 25.4 degrees. The applicable curve is Figure 6-5 and is reproduced here as Figure 7-3. In this case, the initial flaw depth is 8.0 percent of the wall thickness. The initial reference time can be found by drawing a horizontal line at a/t = 0.08.
Using the acceptance criteria in Table 6-1, the allowable service life can then be determined as the time for the flaw to reach a depth of 75 percent of the wall thickness. The final reference time is found through a horizontal line drawn at a/t = 0.75. The service life can be determined through the intersection points of these lines and the crack growth curve. The resulting service life is approximately 5.5 years, as shown in Figure 7-3.
Summary and Example Problems December 2003 Revision 0
7-3 Example 4. In this case, we have postulated an axial inside surface flaw with an upper extremity located 1.0 inch below the attachment weld on the uphill side of penetration no. 60 (42.7 degrees). The flaw has an initial depth of 0.079" and an initial length of 0.395". Assuming that the initial aspect ratio of 0.395" / 0.079" or 5:1 is maintained as the flaw propagates into the nozzle wall, the final length of a through-wall flaw would be 0.625" x 5 = 3.125" long. The location of the upper extremity of this flaw would have reached within 0.5 inch below the weld as it propagates into the nozzle wall (1.0 - ((3.125" / 2) - (0.395" / 2))). Therefore the evaluation will require the use of two flaw charts. The first step is to estimate the time required for the initial flaw to grow to within 0.5 inch from the weld. This can be accomplished with the use of Figure 6-2 and is reproduced here as Figure 7-4a. The upper extremity is 1 inch below the weld and is assumed to grow until the extremity is 0.5 inches below the weld. The final half-length of the flaw when it reaches 0.5 inches below the weld will be the sum of the initial half-length and the 0.5 inches it has grown or 0.395" / 2 + 0.5" = 0.6975". Multiplying this by two and then dividing by the aspect ratio gives the flaw depth when the upper extremity is 0.5 inches below the weld: 2 x 0.6975" / 5.0 = 0.279". Figure 7-4a can be used to find the time it takes to grow from 12.6% through-wall (alt = 0.079" / 0.625" = 0.126) to 44.6% through-wall (a/t = 0.279" /0.625" =
0.446). The time is estimated as 2.2 years. Using the flaw depth calculated previously (a/t =
0.446) as the initial flaw depth, the curves in Figure 6-4 reproduced here as Figure 7-4b, for inside surface flaws near the weld can be used to determine the remaining service time before the flaw depth reaches the allowable flaw size (alt = 0.75). Using the acceptance criteria in Table 6-1, Figure 7-4b shows an additional 0.7 years of service life for a total of 2.9 years.
As shown above, flaws whose upper extremities grow within 0.5 inch below weld require the use of both the 0.5 inch below weld and "near the weld" flaw tolerance charts. To avoid the use of these two charts, the "near the weld" chart may solely be used in determining the service life.
This shall provide a conservative estimate of the crack growth due to larger stress field.
Example 5. This case is an axial through-wall flaw with its upper extremity located 0.40 inches below the weld region on the uphill side of penetration no. 1. The angle of the penetration nozzle is 0 degrees as shown in Table 1-1. The crack growth curve of Figure 6-12 is applicable and has been reproduced as Figure 7-5. The initial reference time is found by drawing a horizontal line 0.40 inches below the line representing the bottom of the weld, then dropping a vertical line to the x axis. The final reference time is found by drawing a vertical line where the crack growth curve intersects the bottom of the weld horizontal line.
The service life is estimated to be approximately 2.2 years for the postulated flaw to grow to the bottom of the attachment weld.
Several guidelines are important to understand when using these flaw evaluation charts.
- 1. If a flaw is found in a penetration nozzle for which no specific analysis was performed and there is a uniform trend as a function of penetration nozzle angle, interpolation between penetration nozzle is the best approach.
- 2. If a flaw is found in a penetration nozzle for which no specific analysis was performed and there is no apparent trend as a function of penetration nozzle angle, the result for the penetration nozzle with the closest angle should be used.
Summary and Example Problems December 2003 Revision 0
7-4
- 3. If a flaw is found which has a depth smaller than any depth shown for the penetration nozzle angle of interest, the initial flaw depth should be assumed to be the same as the smallest depth analyzed for that particular penetration nozzle.
- 4.
The flaw evaluation charts are applicable for aspect ratio of 6 or less.
Consult with Westinghouse if the as-found flaw has an aspect ratio larger than 6.0.
- 5. All references to service life are in Effective Full Power Years.
- 6. Results are only provided for the uphill and downhill sides of the selected penetration nozzles.
If flaws are found in locations between the uphill and downhill side, use the results for either the uphill or downhill location, whichever is closer.
Summary and Example Problems December 2003 Revision 0
7-5 Table 7-1 Example Problem Inputs: Initial Flaw Sizes and Locations Example Vertical Circumferential Penetration Penetration Source No.
Orientation Location Location Row Length Depth No.
Figure 1
Axial - Inside 1.25" Uphill 38.70 0.195" 0.078" 50 6-2 Surface Below Weld 2
Axial - Outside 1.25" Downhill 38.70 0.195" 0.078" 50 6-10 Surface Below Weld 3
Axial - Inside At Weld Downhill 25.40 0.250" 0.05" 20 6-5 Surface 4
Axial - Inside 1.0" Uphill 42.70 0.395" 0.079" 60 6-2, 6-4 Surface Below Weld 5
Axial 0.4" Uphill 00 1
6-12 Through-Wall Below Weld Summary and Example Problems December 2003 Revision 0
7-6 Locality Angle from Table I -1:
Nozzle No.
Type Angle 50 CRDM 38.7 u,
- C 0.6 0
-5 3 0.5 0.
3: 0.4 V-9 time (year)
Figure 7-1 Example Problem 1 Summary and Example Problems December 2003 Revision 0
7-7 Example O
- etato Crack Tip Circumferential Penetration Length Depth Wall aft Penetration Source No.
Onenton Location Location Row (2c)
(a)
Thickness No.
Figure Axial -
1.25" 2
Outside Below Downhill 38.70
- 0. 195" 0.078" 0.625" 0.125 50 6-10 Surface Weld Locality Angle from Table 1-1 :
Nozzle No.
ype Angle 50 CRDM 38.7 (A
C 0.
IM S
0 1
2 3
4 time (year)
Figure 7-2 Example Problem 2 Summary and Example Problems December 2003 Revision 0
7-8 Example Orientation Crack Tip Circumferential Penetration Length Depth Wall a/t Penetration Source No.
Location Location Row (2c)
(a)
Thickness No.
Figure Axial -
3 Inside At Weld Downhill 25.4° 0.250" 0.05" 0.625" 0.08 20 6-5 Surface I
I I
I 1
Locality Angle from Table I -1:
Nozzle No.
pe Angle 20 CRDM 25.4 0.9 0.8 0.7
'i4)C
- ' 0.6 i
0.2 a 0.4 0.2 0.1 0
0 1
2 3
4 5
6 time (year) 7 Figure 7-3 Example Problem 3 Summary and Example Problems December 2003 Revision 0
7-9 Example Oretio Crack Tip Circumferential Penetration Length Depth Wall Penetration Source No.
rientation Location Location Row (2c)
(a)
Thickness No.
Figure Axial -
1.00" 6-2, 4
Inside Below Uphill 42.70 0.395" 0.079" 0.625" 0.126 60 6-4 Surface Weld I.I I
I I
I Locality Angle from Table 1-1:
Nozzle No.
Type Angle 60 CRDM 42.7 Nozzle Angle:
40.0 deg 0.7 C
-W 0.6 0.5 i 0.4
'U Nozzle: Angle:
42.7 deg
- t.
~. s
.I.
0.3 0.2 I
I I.
. I I 11
..Z I I - 11
:...I
- i I I
]S;rvice Life I Ii
._6l ",.,
11 :
i Nozzle Angle:
0 degi eaver Valley Unit 2 0.1 0
0 1
2 3
4 5
6 7
8 9
time (year)
Figure 7-4a Example Problem 4 (See also Figure 7-4b)
Summary and Example Problems December 2003 Revision 0
7-10 Example Orientation Crack Tip Circumferential Penetration Length Depth Wall Penetration Source No.
Location Location Row (2c)
(a)
Thickness al No.
Figure Axial-1.00"-
4 Inside Below Uphill 42.70 0.395" 0.079" 0.625" 0.126 60 6-24, Surface Weld 6_4 t
Locality Angle from Table I-1 :
0.9 Nozzle No.
pe Angle 60 CRDM 42.7 38.7 deg 0.8 t
0.7 X 0.6 c 0.5 B0.4 C)
- 0 3: 04 cC 0.3 0.2 0.1 0
40.0 deg 42.7 deg Nozzle Angle:
Nozzle Angle:
0 deg I Beaver Valley Unit 2 6
7 T
2c I
- 1:
0 1
2 3
4 5
time (year)
Figure 7-4b Example Problem 4 (See also Figure 7-4a)
Summary and Example Problems December 2003 Revision 0
7-11 Example
.e Crack Tip Circumferential Penetration Length Depth Wall a/t Penetration Source No.
Orientation Location Location Row (2c)
(a)
Thickness No.
Figure ToAxial W0.4Beldow Uphill OO N/A N/A 0.625" N/A 1
6-12 W a ll I
_I__
I__
I__
I__
I__
I_
2.5 Locality Angle from Table 1-1:
Nozzle No.
Type Angle 1
CRDM 0
0 0.
0 E
E 2
a.
a.
0.
3t LU 2.0 1.5 1.0 0.5 0.0
-0.5
-1.0 0
1 2
3 4
5 6
7 8
Period (Year) 9 10 Figure 7-5 Example Problem 5 Summary and Example Problems December 2003 Revision 0
8-1 8
REFERENCES
- 1.
Scott, P. M., "An Analysis of Primary Water Stress Corrosion Cracking in PWR Steam Generators," in Proceedings, Specialists Meeting on Operating Experience With Steam Generators, Brussels Belgium, Sept. 1991, pages 5, 6.
- 2.
McIlree, A. R., Rebak, R. B., Smialowska, S., "Relationship of Stress Intensity to Crack Growth Rate of Alloy 600 in Primary Water," Proceedings International Symposium Fontevraud II, Vol, 1, p. 258-267, September 10-14, 1990.
- 3.
Cassagne, T., Gelpi, A., "Measurements of Crack Propagation Rates on Alloy 600 Tubes in PWR Primary Water, in Proceedings of the 5h International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors," August 25-29, 1991, Monterey, California.
4A.
Crack Growth and Microstructural Characterization of Alloy 600 PWR Vessel Head Penetration Materials, EPRI, Palo Alto, CA. 1997. TR-109136.
4B.
Vaillant, F. and C. Amzallag. "Crack Growth Rates of Alloy 600 in Primary Water," Presentation to the EPRI-MRP Crack Growth Rate (CGR) Review Team, Lake Tahoe, NV, presented August 10, 2001, and revised October 11, 2001 4C.
Vaillant, F. and S. Le Hong. Crack Growth Rate Measurements in Primary Water of Pressure Vessel Penetrations in Alloy 600 and Weld Metal 182, EDF, April 1997. HT-44/96/024/A.
4D.
Framatome laboratory data provided by C. Amzallag (EDF) to MRP Crack Growth Rate Review Team, October 4, 2001 (Proprietary to EDF).
4E.
Cassagne, T., D. Caron, J. Daret, and Y Lefevre. "Stress Corrosion Crack Growth Rate Measurements in Alloys 600 and 182 in Primary Water Loops Under Constant Load," Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors (Newport Beach, CA, August 1-5, 1999), Edited by F. P. Ford, S. M. Bruemmer, and G S. Was, The Minerals, Metals & Materials Society (TMS), Warrendale, PA, 1999.
4F.
Studsvik laboratory data provided by Anders Jenssen (Studsvik) to MRP Crack Growth Rate Review Team, October 3, 2001 (Proprietary to Studsvik).
4G
[
Iace 4H.
"Materials Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick Wall Alloy 600 Material (MRP-55) Revision 1," EPRI, Palo Alto, CA:, November 2002. 1006695.
- 41.
"Crack Growth Rate Tests of Alloy 600 in Primary PWR Conditions," Communication from M.
L. Castafo (CIEMAT) to J. Hickling (EPRI), March 25, 2002.
4J.
G6mez-Bricefio, D., J. Lapefia, and F. Blizquez. "Crack Growth Rates in Vessel Head Penetration Materials," Proceedings of the International Symposium Fontevraud III: Contribution of Materials Investigation to the Resolution of Problems Encountered in Pressurized Water Reactors (Chinton, France, September 12-16, 1994), French Nuclear Energy Society, Paris, 1994, pp.
209-214.
References December 2003 Revision 0
8-2 4K.
G6mez-Bricefio, D. and J. Lapefia. "Crack Growth Rates in Vessel Head Penetration Materials,"
Proceedings: 1994 EPRI Workshop on PWSCC of Alloy 600 in PWRs (Tampa, FL, November 15-17, 1994), EPRI, Palo Alto, CA, TR-105406, August 1995, pp. E4-1 through E4-15.
4L.
G6mez-Bricefio, D., et al. "Crack Propagation in Inconel 600 Vessel Head Penetrations,"
Eurocorr 96, Nice, France, September 24-26, 1996.
4M.
Castafio, M. L., D. G6mez-Bricefio, M. Alvarez-de-Lara, F. Bldzquez, M. S. Garcia, F.
Herndndez, and A. Largares.
"Effect of Cationic Resin Intrusions on IGA/SCC of Alloy 600 Under Primary Water Conditions," Proceedings of the International Symposium Fontevraud IV:
Contribution of Materials Investigation to the Resolution of Problems Encountered in Pressurized Water Reactors (France, September 14-18, 1998), French Nuclear Energy Society, Paris, 1998, Volume 2, pp. 925-937.
5A.
Newman, J. C. and Raju, I. S., "Stress Intensity Factor Influence Coefficients for Internal and External Surface Cracks in Cylindrical Vessels," in Aspects of Fracture Mechanics in Pressure Vessels and Piping, PVP Vol. 58, ASME, 1982, pp. 37-48.
5B.
Hiser, Allen, "Deterministic and Probabilistic Assessments," presentation at NRC/Industry/ACRS meeting, November 8, 2001.
- 6.
[
a,c,e
- 7.
USNRC Letter, W. T. Russell to W. Raisin, NUMARC, "Safety Evaluation for Potential Reactor Vessel Head Adapter Tube Cracking," November 19, 1993.
- 8.
USNRC Letter, A. Ci Hansen to R. E. Link, "Acceptance Criteria for Control Rod Drive Mechanism Penetrations at Point Beach Nuclear Plant, Unit 1," March 9, 1994.
- 9.
Materials Reliability Program Response to NRC Bulletin 2001-01 EPRI MRP Report 48 (TP 1006284), August 2001.
- 10.
"PWR Reactor Pressure Vessel (RPV) Upper Head Penetrations Inspection Plan (MRP-75)
Revision 1." EPRI, Palo Alto, CA: 2002. 1007337.
11A.
Combustion Engineering Drawing No. E-9071-112-002, "Control Rod Mechanism Housing Details," Revision 4.
1 lB.
Combustion Engineering Drawing No. C-9071-107-001, "Vent Pipe," Revision 3.
1 lC.
Combustion Engineering Drawing No. E-9071-101-005, "Closure Head Assembly," Revision 3.
liD.
Combustion Engineering Drawing No. E-9071-171-004, "General Arrangement - Elevation-,"
Revision 4.
- 12.
USNRC Letter, R. Barrett to A. Marion, "Flaw Evaluation Guidelines," April 11, 2003 References December 2003 Revision 0
A-1 APPENDIX A CRDM HOOP STRESS VS DISTANCE FROM BOTTOM OF WELD PLOTS In this section, CRDM hoop stresses are plotted against corresponding distance from the bottom of weld for 42.7 degrees, 40.0 degrees, 38.7 degrees, 25.4 degrees and the center location penetration rows on the downhill and uphill sides. The inspection zones are assumed to be at least 1.0" below the root of the J-groove welds on the downhill side for all the CRDM penetrations with the exception of the outermost one (42.70), where the inspection zones are assumed to be at least 0.8" below the weld. The inspection zones for the uphill side for all the CRDM penetrations below the welds are assumed to cover an additional distance that is equal to the difference in the bottom of the weld elevation between the uphill and downhill sides weld.
Appendix A December 2003 Revision 0
A-2 Figure A-1 Hoop Stress Distribution Below the Weld Downhill and Uphill Side (00 CRDM Penetration Nozzle) 70,000 60,000 50,000 il 40,000 a-IA4' 30,000 a) 0 o
20,000 10,000 iz i
Izi ii iz i
i i
iiz i
j I
-10,000 W-0.0 0.5 1.0 1.5 2.0 2.5 3.0 Distance from Bottom of Weld (in) 3.5
+
Inside a Outside Appendix A December 2003 Revision 0
A-3 Figure A-2 Hoop Stress Distribution Below the Weld Downhill Side (25.40 CRDM Penetration Nozzle) 70,000 60,000 50,000
,, 40,000 R
0.
E 30,000 00I 20,000 10,000 0
-10,000 III-1IIIII II L
I I
1 I
I I
I I
1 l
-z zz z
zii
-i zit
-tI z
3 3.0 0.0 0.5 1.0 1.5 2.0 2.5 Distance from Bottom of Weld (in)
I -
Inside -*-Outside Appendix A December 2003 Revision 0
A-4 Figure A-3 Hoop Stress Distribution Below the Weld Uphill Side (25.40 CRDM Penetration Nozzle) 70,000 60,000 50,000 40,000 X 30,000
- 0. 20,000 00 10,000 0
-10,000
-20,000 I-0.0 1.0 2.0 3.0 4.0 5.0 Distance from Bottom of Weld (in) 6.0
-.- Inside -
Series2 Appendix A December 2003 Revision 0
A-5 80,000 I 70,000 1 60,000 -
50,000 -
- o. 40,000-C I' 30,000,-4 00 20,000 -
O-,
-10,000
-20,000 0.1 Figure A-4 Hoop Stress Distribution Below the Weld Downhill Side (38.70 CRDM Penetration Nozzle)
Inspection Zone X ~
~~~
~~~
-f - - - -
I I
i E
La=:;-.-'
D 0.5 1.0 1.5 Distance from Bottom of Weld (in) r 4Inside --
Outside 2.0 2.5 3.0 Appendix A December 2003 Revision 0
A-6 Figure A-5 Hoop Stress Distribution Below the Weld Uphill Side (38.7° CRDM Penetration Nozzle) 60,000 -
5 50,000 40,000 -
0 Z-0 rW 00 a.
00 30,000 20,000 -
10,000 -
0 -
Inspctiononj~
I I
I l
l r
-I I
I l
l
. I i
I I
I 1,
I -
I I
I
_ I
_ _I I
l I
_ I
_ _I I
l I
I I.
I I
l
=
I I
I
-10,000
-20,000 -
-30,000 -
0.0 1.0 2.0 3.0 4.0 Distance from Bottom of Weld (in) 5.0 6.0 7.0 I --_-Inside -
Outside Appendix A December 2003 Revision 0
A-7 Figure A-6 Hoop Stress Distribution Below the Weld Downhill Side (40.0° CRDM Penetration Nozzle) 80,000 70,000 60,000 50,000 40,000 E 30,000 C.
° 20,000 10,000-0
-10,000
-20,000 0.0 I
I.
Ii I
I 0.5 1.0 1.5 2.0 2.5 Distance from Bottom of Weld (in)
I --
Inside --- Outside I 3.0 Appendix A December 2003 Revision 0
A-8 Figure A-7 Hoop Stress Distribution Below the Weld Uphill Side (40.00 CRDM Penetration Nozzle)
W 0.
0.0 0
0u X
60,000 -_
50,000 -X 40,000 -
30,000 20,000 10,000 0
-10,000
-20,000
-30,000 -
0.0 I
. I I
I 1.0 2.0 3.0 4.0 5.0 6.0 Distance from Bottom of Weld (In)
I---Inside --
Outside 7.0 Appendix A December 2003 Revision 0
A-9 Figure A-8 Hoop Stress Distribution Below the Weld Downhill Side (42.70 CRDM Penetration Nozzle) a-
- a 0
o I
80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 0*
-10,000
-20,000
-30,000 4- - - - - -
- -I
- -T
- - -r I -- - n ie usd 0.0 0.5 2.0 2.5 Appendix A December 2003 Revision 0
A-10 Figure A-9 Hoop Stress Distribution Below the Weld Uphill Side (42.70 CRDM Penetration Nozzle) 60,000 50,000 40,000 30,000
- a. 20,000 00
,. 10,000 o
0
-10,000
-20,000
-30,000 z
-iI i
I-i
- i i
i ii It t
---4 7.0
-40,000 -
0.0 1.0 2.0 3.0 4.0 5.0 6.0 Distance from Bottom of Weld (in)
-*-Inside
- OutsideI Appendix A December 2003 Revision 0