ML14079A533
| ML14079A533 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 03/20/2014 |
| From: | Ameren Missouri, STARS Alliance |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ULNRC-06092 | |
| Download: ML14079A533 (22) | |
Text
Enclosure to ULNRC-06092 Page 1 10 CFR 50.55a Request Number I3R-16 Proposed Alternative in Accordance with 10 CFR 50.55a(a)(3)(ii)
--Hardship or Unusual Difficulty without Compensating Increase in Level of Quality or Safety--
- 1. ASME Code Component(s) Affected Train A Component Cooling Water Heat Exchanger (EEG01A) tube side manway access, an ASME Class 3 Component.
2. Applicable Code Edition and Addenda
ASME Boiler and Pressure Vessel Code,Section XI 1998 Edition through 2000 Addenda
3. Applicable Code Requirement
ASME Section XI requires that repair/replacement activities on ASME Class components be performed in accordance with the rules found in Article IWA-4000, "Repair/Replacement Activities." IWA-4133, "Mechanical Clamping Devices used as Piping Pressure Boundary," allows mechanical clamping devices to be used as piping pressure boundary provided the requirements of Mandatory Appendix IX, Mechanical Clamping Devices for Class 2 and 3 Piping Pressure Boundary, are met. Relief is requested to use IWA-4133 and to apply the provisions of ASME Section XI, Mandatory Appendix IX for a temporary repair to an ASME Class 3 vessel, i.e., heat exchanger EEG01A.
4. Reason for Request
Train "A" Component Cooling Water (CCW) heat exchanger EEG01A has developed a pinhole, through-wall flaw that has resulted in leakage of essential service water (ESW). ASME Code Case N-705, Evaluation Criteria for Temporary Acceptance of Degradation in Moderate Energy Class 2 or 3 Vessels and Tanks, which has been accepted by the NRC and incorporated into Revision 16 of Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, has been used to evaluate this flaw and has determined that this flaw is acceptable and that structural integrity of EEG01A will be maintained through the evaluation period that ends with Refuel 20 which is scheduled to begin October 2014. A copy of the evaluation is provided for information as Attachment A.
The flaw is due to localized pitting and has been analyzed with ultrasonic examination. The bounding size of the flaw has been conservatively determined to be a pit with a 1/2 inch diameter. Should the flaw and the through-wall portion grow to this size, the maximum calculated leak rate is 59.4 gallons per minute (gpm).
The postulated 59.4 gpm ESW leak would reduce the inventory of the ultimate heat sink (UHS) over the 30-day ESW mission time. Compensatory actions have been taken to assure the minimum UHS level is maintained above 75.5% full in order to provide sufficient inventory to compensate for existing ESW leakage plus the postulated 59.4 gpm loss and keep the UHS and ESW system Operable. In an effort to increase the margin of Operability, a temporary mechanical clamping device is proposed which would reduce leakage and would be able to be credited as a pressure boundary in the area of the flaw.
Enclosure to ULNRC-06092 Page 2 Section C.12 of Chapter 0326 of the NRC Inspection Manual states in part that the NRC has no generically approved alternative (non-Code repair) for temporary repair of flaws in a Class 3 vessel (such as EEG01A) and therefore the component must be repaired in accordance with the Code, or Code relief must be requested and approved from the NRC in order to apply a non-code repair.
An ASME Code Repair/Replacement of the heat exchanger would require draining of ESW from the CCW heat exchanger, thereby making one train of CCW and one train of ESW inoperable. The inoperable ESW train would also make one emergency diesel generator inoperable. This activity would therefore place the plant in Action statements for Technical Specifications 3.7.7, "Component Cooling Water System;" 3.7.8, "Essential Service Water System;" and 3.8.1, "AC Sources - Operating;" each of which requires restoration of the inoperable train to Operability within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> in Modes 1, 2, 3 and 4. The Code Repair/Replacement activity on the CCW heat exchanger is expected to challenge the 72-hour completion times for the Technical Specification Action statements listed above and would therefore necessitate a unit shutdown. Cycling the plant to perform an ASME Code repair of EEG01A would create a hardship based on the potential risks associated with unit cycling and any emergent equipment issues incurred during shutdown and startup evolutions, without a compensating increase in level of quality or safety.
5. Proposed Alternative and Basis for Use
A mechanical clamp will be installed over the leakage location and will act as a credited pressure boundary in the vicinity of the pinhole leak. The mechanical clamp will consist of square stock welded between existing hub nut mounts of the manway. The square stock will be drilled and tapped to accept a threaded rod that will secure a gasketed steel block over the pinhole leak. All materials will be procured safety-related and the resulting repair credited for maintaining pressure boundary at the pinhole leak location. The gasket will measure 1 x 1 such that it is engaging portions of the closure hub beyond the pinhole leak. The leak repair device has been analyzed to perform the credited pressure boundary function for the full range of design conditions to which EEG01A is credited in the licensing basis. The nominal operating pressure and temperatures of the ESW side of EEG01A is 40 psig and 95 °F inlet / 106.4 °F outlet, and the design operating pressure and temperature is 200 psig and 200 °F. A detailed description of the mechanical clamping device and the supporting calculations are supplied in Attachment B.
Until a permanent repair is performed in accordance with IWA-4000 to restore EEG01A to its design condition, the following actions are also being performed to satisfy the ASME Code Case N-705 requirements for monitoring and examination of the flaw.
Daily leakage monitoring is performed during Operator rounds to assure the leakage remains within acceptable limits established in the Code Case N-705 evaluation. At present, there is no active leakage of ESW through the flaw. Following installation of the mechanical clamping device, this daily monitoring will also provide assurance that integrity of the credited pressure boundary is maintained.
Ultrasonic examinations are performed quarterly to verify whether the degradation, including growth, continues to meet the acceptable limits established in the Code Case N-705 evaluation. The mechanical clamp pressure block has been designed to allow removal during these periodic examinations to facilitate measurement of the flaw.
Enclosure to ULNRC-06092 Page 3 Results of daily leakage monitoring and periodic examinations, and other existing leakage from the ESW system are evaluated to assess continued acceptability of the degraded condition of EEG01A.
Compensatory actions to maintain UHS level sufficient to compensate for existing leakage plus postulated leakage from the flaw will continue until the mechanical clamping device can be credited to provide a pressure boundary in the area of the leak. Prior to removal of the mechanical clamp pressure block to perform periodic examinations of the flaw, compensatory actions will be taken to assure UHS level is sufficient to compensate for existing leakage plus postulated leakage from the flaw.
As use of a mechanical clamping device for temporary repair of a leaking Class 3 vessel is not in accordance with IWA-4000 or an approved alternative, relief is requested in accordance with the provisions of 10 CFR 50.55a(a)(3)(ii) in order to apply IWA-4133 and Mandatory Appendix IX to the temporary repair of EEG01A, and thereby allow the mechanical clamping device to be credited as providing a pressure boundary in the area of the flaw.
6. Duration of Proposed Alternative
The requested Code relief shall be applied within the current (third) 10-year ISI interval until a permanent internal weld repair is performed on EEG01A during the next refueling outage for Callaway, i.e., Refuel 20, which is scheduled to begin in October 2014. The permanent repair will be performed in accordance with the requirements of IWA-4000, will restore EEG01A to its design condition within the evaluation period as specified in Code Case N-705, and will satisfy the provisions of and Mandatory Appendix IX and NRC Inspection Manual Chapter 326 Appendix C.12 that respectively limit the time the mechanical clamping device can be credited as a pressure boundary, and require restoration of the component to its design condition prior to completion of the next refueling outage.
- 7. References
- 1. ASME Code Case N-705, "Evaluation Criteria for Temporary Acceptance of Degradation in Moderate Energy Class 2 or 3 Vessels and Tanks,Section XI, Division 1"
- 2. Regulatory Guide 1.147 Rev. 16, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1"
Attachment A of Enclosure to ULNRC-06092 Page 4 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation This evaluation utilizes Code Case N-705 to evaluate the structural integrity of the 'A' CCW Heat Exchanger (EEGO 1 A) following the discovery of a pinhole leak as documented in CAR 201307879. The intent of this evaluation is to support a repair to be implemented by end of RF20 in accordance with the time frame permitted by Code Case N-705.
The initial evaluation that supported the Prompt Operability under CAR 201307879 evaluated the pinhole leak and the CCW heat exchanger's structural integrity as found at initial discovery.
This revision is to evaluate the CCW heat exchanger's structural integrity with the existing pinhole and the new leak repair device installed that is approved and implemented per MP 14-0002 and Job 13006144. This evaluation will continue to analyze the heat exchanger with and without the leak repair device installed.
ASME Code Case N-705 states the stresses at the degradation location shall include the appropriate combination of applied loadings from the Design Specifications for the vessel being evaluated. Therefore, the new stresses that are created due to the new leak repair device need to be added to the existing stresses evaluated in the original Stress Intensity Factor equations below.
The results will then be compared to the acceptance criteria in Code Case N-705 Section 5 to ensure the CCW heat exchanger is still structurally sound with the existing pinhole and the temporary repair device installed.
Structural Integrity using ASME Code Case N-705 ASME Code Case N-705 provides evaluation criteria for temporary acceptance of degradation in moderate energy class 2 or 3 vessels and tanks including heat exchangers as an alternative to lWA-3000, IWC-3120, and IWD-3120, for a limited time not exceeding the evaluation period defined in the Code Case.
The following provisions of Code Case N-705 must be satisfied.
- 1. This Code Case applies to vessels and tanks, including heat exchangers, classified by the Owner as Class 2 or 3, and whose maximum operating temperature does not exceed 200'F and whose maximum operating pressure does not exceed 275 psig.
- 2. This Code Case defines the requirements to demonstrate the structural integrity of the vessel or tank but not the consequences of leakage. The Owner shall determine what constitutes acceptable leakage, evaluate the consequences of leakage, and determine system operability.
- 3. This Code Case provides procedures and criteria for evaluating failure conditions for fracture and overpressure (blowout). The Owner shall verify that other potential failure modes are not relevant for the observed degradation (e.g., buckling).
- 4. The evaluation period is the operational time for which the temporary acceptance criteria are satisfied, but not greater than 26 months from the initial discovery of the condition.
Page 1 of 13
Attachment A of Enclosure to ULNRC-06092 Page 5 CAR 201307879 - CCW HX 'A' Pin Hole Leak Evaluation The degradation being evaluated is a pinhole leak in the Component Cooling Water (CCW) heat exchanger, EEGOlA, which is an ASME Section III Class 3 component with a design temperature of200"F and a design pressure of200 psig per Specification M-072 Appendix A.
The maximum operating temperature and pressure are below the design parameters.
CAR 201307879 Action 5 addresses and evaluates acceptable leakage, consequences ofthe leakage and determined the system was operable with this degraded condition.
After discussions with the System Engineer it was determined that there is no other potential failure mode relevant for the observed degradation on the CCW Heat Exchanger other than fracture or overpressure.
Lastly, the leakage was initially discovered on October 141h, 2013. A full repair of the pinhole leak will be implemented during Refuel20 which starts approximately mid-October, 2014; therefore, this evaluation period will be less than half of the allowed 26 months. Based on the above, all of the provisions of this Code Case N-705 have been satisfied.
Methodology As with the evaluation of the leakage rate completed in CAR 201307879 Action 5, the analysis of structural integrity is based upon a bounding characterization of the flaw in accordance with Code Case N-705 Section 2.2. Section 2.2(a) states the vessel or tank shall be examined to characterize degradation in the affected section in accordance with IW A-3300, unless the alternative methods of Section 2.2( e) or 2.4( a) are implemented. Section 2.2( e) provides guidance for estimating the geometry of degradation in inaccessible or uninspectable regions.
This degradation is accessible; therefore section 2.2(e) does not apply.
Section 2.4(a) provides the guidance for bounding flaw length for structural evaluation purposes, based on one or more limiting factors (i.e., geometric, stress, or environmental). The bounding characterization will be the assumption of zero remaining wall thickness in the 1/2" diameter encompassing the flaw. The 1/2" diameter is based upon the physical (geometric) limitation of the Y.. dian1eter ultrasonic probe and represents the area in which accurate wall thickness measurement cam10t be attained. The bounding flaw will be assumed to be a planar through-wall flaw over its entire length per Section 2.4(b). Section 2.4(c) directs users of the code case to Section 3.1 for an acceptable method for the required stmctural integrity evaluation to determine acceptance ofthe bounding flaw. The acceptance criteria are provided in Section 5 ofthe code case.
However, the through-wall leak identified in the CCW Heat Exchanger is considered a nonplanar flaw and according to Section 2.2(d) shall be projected into the axial and circumferential planes to allow for detcm1ining the worst crack orientation in accordance with Figure 4. As stated above, the through-wall flaw is a Y/' diameter hole. A picture of the pinhole flaw is shown he low along" ith Figure 4 from N-705.
Page 2 of 1 '2,
Attachment A of Enclosure to ULNRC-06092 Page 6 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation FIG. 4 ILLUSTRATION OF NONPLANAR THROUGH-WALL DEGRADATION DUE TO WALL THINNING I
~=t....U.II dlrwctlon
-<~-L-Page 3 of13
Attachment A of Enclosure to ULNRC-06092 Page 7 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation As stated above the evaluation methodology for planar degradation shall be evaluated in accordance with the requirements of Section 2.4 or 2.5. Additionally, Section 2.3 states to prevent bursting, nonplanar part-through-wall degradation shall also be evaluated in accordance with the requirements of 2.6. Therefore, the requirements of section 2.4 and 2.6 will be applied to this evaluation. For bounding flaws that do not meet the acceptance criteria, the provisions of 2.5 shall be met.
In addition to the requirements of Section 2.4 above, nonplanar part-through-wall degradation shall be evaluated in accordance with the requirement in 3.3 per Section 2.6. Therefore, structural integrity will be demonstrated using the methodology in Section 3.1 and 3.3. The acceptance criteria in Section 5 must be met in order to demonstrate structural integrity. Section 3.1 will be reevaluated in this revision to include the stresses added to the CCW heat exchanger due to the installation of the leak repair device in addition to the existing stresses. The installation of the leak repair device will have no impact on the evaluation completed in Section 3.3.
Section 3.1 requires the stresses at the degradation location to be identified including appropriate combinations of applied loadings for Levels A, B, C, and D and test conditions from the Design Specification for the vessel being evaluated. These shall include, as appropriate, deadweight, pressure, hydrostatic, thermal, and Safe Shutdown Earthquake (SSE) including seismic sloshing.
Stresses from extemalloadings shall also be included. Additionally, any residual stresses resulting from original welding and any rework, bolt-up stresses, and cladding-induced stresses shall be evaluated.
The pinhole leak is located on a 24" manway on the end of the CCW heat exchanger. The entire manway is 8" in length. The stub piece of the manway where the pinhole is located is approximately 3" in length. The CCW heat exchanger was seismically analyzed under M-072-00016; however, the analysis did not specifically address the 24" manway. The manway was likely excluded from the analysis due to the minimal stresses at this location since it is short in length and is not an integral part of the operation of the heat exchanger; which allows the stresses to be neglected. The manway would see an internal pressure stress (calculated below); however, the thermal and dead weight stresses would be negligible at this location. There are no hydrostatic stresses at this location either. Since the manway is so short in length, any developed moment arm would be negligible, as well as any resulting seismic (SSE) stresses. There are no external stresses applied to this manway and are, therefore, not a factor for this evaluation.
Lastly, there was no original welding or rework in this area, nor are there any bolt-up stresses or cladding-induced stresses at the location of the degradation. Therefore, the only stress that will be calculated is an internal pressure stress to satisfy the requirements of Section 3.1(a). Section 3.1(c) and (d) to not apply to this evaluation and will be ignored. Now using the stresses identified above the stress intensity factors can be calculated (see below) per Section 3.l(e).
In addition to the above originally defined pressure stress, the stresses added due to the installation of the new leak repair device per MP 14-0002 need to also be evaluated. The leak repair device will consist of a square stock welded between existing hub nut mounts on the T-bolt closure (manway). The square stock will be drilled and tapped to accept a threaded rod or bolt that will push a gasketed steel block over the pinhole leak. All materials will be procured Page4of13
Attachment A of Enclosure to ULNRC-06092 Page 8 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation safety-related and the resulting repair credited for maintaining pressure boundary at the pinhole leak location. The gasket will measure 1" x 1" such that it is engaging portions of the closure hub beyond the pinhole leak. The leak repair device was analyzed under EG-57, Rev. 0. Refer to MP 14-0002 and EG-57 for further details.
The leak repair device will be located at the bottom of the T-bolt closure (manway). The weight, location and size of this leak repair device does not create any deadweight or seismic stresses acting on the CCW heat exchanger of any concemable magnitude. The leak repair device also does not create any new external pressure, thermal, or hydrostatic stresses either. All the welding that will be completed in order to implement this repair will not occur at the degradation location; therefore there is no new welding, bolt-up or cladding-induced stresses at the location of the degradation.
The stresses of concern for the new leak repair device that will be considered for this evaluation are bending and shear stresses at the location of the degradation. For the shear stress at the pinhole leak, the concern is shearing the sides of the gasketed steel block right through the CCW heat exchanger. It was stated in MP 14-0002 that a force of 1200 lbs was required to compress a rubber gasket. At the degradation location, the shear stress would see the full 1200 lb force. For purposes of this evaluation, 1300 lb force was used for conservatism. The stress created at this location due to this force was determined to be 2,167 psi.
Where:
F = 1300 lbs A= 0.6 in2 F
1300 a= ::i=D.6= 2,167 ps1 Required force to compress gasket 3 inches (3-1 inch sizes of the gasketed steel block) x 0.2 inches (minimal thickness of the CCW Heat exchanger surrounding the pinhole leak)
The CCW Heat exchanger is made of SA-516 Grade 70 material, which has an ASME allowable stress of 17.5 ksi. Per ASME Section III-1974 Edition Subsection NC with Summer 1975 Addenda Section NC-3216.2, the average primary shear stress across a section loaded under design conditions in pure shear shall be limited to 0.6Sm. Sm is defined as the design stress intensity value (allowable stress), which is 17.5 ksi for the CCW heat exchanger. So, 0.6 x 17.5 is 10.5 ksi. Comparing the calculated 2.2 ksi to the lO.Sksi allowable ( z.z ksks\\ this 1300 lb force 10.5 I
would only stress the CCW heat exchanger to 21% of its allowable; therefore, the gasketed steel block will not shear through the CCW heat exchanger. Based on this information, shear stress will not be included in the below code case evaluation.
The bending stress; however, will be included in the below evaluation. See below for details.
Page Sof13
Attachment A of Enclosure to ULNRC-06092 Page 9 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation ASME Code Case N-705 Section 3.1 Evaluation (Fracture Mechanics) prior to MP 14-0002 Stress Intensity Factor (SIF) Formula (Flat plate solution is conservative compared to the more detailed formulations in Section XI, 1998 Edition through 2000 Addenda, Appendix A-3320 Equation 5 and Appendix C-7300).
Where:
K1 = Calculating cr = see below D=Y."
a= Y."
Stress Intensity Factor for a flat plate model (conservative model)
Internal Pressure Stress Through-wall Flaw diameter Half Crack Length Since pressure stress is the only viable stress for this degradation location the following formula can be used to calculate the internal pressure stress.
Where:
P= 135 psig R= 12" t = 0.127" PR (1:::;-
t Operating System Pressure Outside Radius ofManway, Wall Thickness at Location of Flaw (minimum wall calculated below conservatively), actual wall thickness at the flaw is 0.2" Using ASME Section III 1974 Edition with Summer 1975 Addenda Subsection ND-3324.3, we can establish the minimum wall thickness of the cylindrical shell where the pinhole leak resides.
The minimum thickness of the cylindrical shell must be the greater of the thickness as determined in equations (a) Circumferential Stress, or (b) Longitudinal Stress. The material has been identified per CAR 201307879 attached file "CAR 201307879 Code Data Report. pdf.
Also attached to that CAR is file "CAR 201307879 Code Info.pdf which has code excerpts that show the applicable minimum wall equations.
P=200psig R=ll" S = 17,500 psi E=l Design System Pressure Inside Radius ofManway (UT Report 5019-13-149 shows a thickness of 0.562", which yields an inside radius of 11.438"; however, conservatively this calculation uses 0.5" nominal thickness per the Code Data Report 801192-09068852)
Allowable Stress for SA-516 Gr. 70 (ASME Section III 1974 Edition with Summer 1975 Addenda Subsection NA Table I-7.1)
Seamless Joint Circumferential Stress:
t = ~
=
(Z00)(11)
= 0.127" SE-0.6P 17500(1)-0.6(ZOO)
Page6 ofl3
Attachment A of Enclosure to ULNRC-06092 Page 10 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation Longitudinal Stress:
t = ___!!__ =
(200)(11)
= 0 063 II 2SE+0.4P (2)(17500)(1)+0.4(200)
The greatest required minimum thickness is therefore 0.127". All areas outside the flaw exhibited wall thickness greater than 0.127" per the attached "CAR 201307879 UT Report 5019-13-149.pdf'.
Using the above calculated minimum wall thickness the internal pressure stress can be calculated at operating and design system pressure:
u = ~ = (135)(12) = 12 756 psi= 12 8 ksi t
0.127 Now the associated SIFs can be calculated:
K1 =a..fT(i. = 12.8../n 0.25 = 11.3 ksiv'iii Using the acceptance criteria in Code Case N-705 Section 5(a), for bounding flaws, the applied stress intensity factor, K~o shall satisfy the following limits:
K <Krc I
3.0 Where
K1 = 11.3 ksi../iil K1c = 35 ksi..Jiii (Levels A and Band Test Conditions, at 135 psig)
(Levels C and D, at 135 psig))
Calculated Stress Intensity Factor at 135 psig Material fracture toughness (Defmed in Code Case N-705 Section 5(b) for ferritic steels, SA-516 Grade 70)
Levels A, Band Test Conditions at 135 psig:
Kr < Krc = 3.0 K1 < K1c = 3.0 < Kic = 3.0 < ~
= 3.0 < 3.09 3.0 K1 11.3 And for Levels C and D Kr < ~~= = 1.4 K1 < K1c = 1.4 < ~: = 1.4 < 1 3
- 3 = 1.4 < 3.09 Therefore:
The acceptance criteria in Section S(a) for Levels A, B, C, D and test conditions have been met.
Page 7 ofl3
Attachment A of Enclosure to ULNRC-06092 Page 11 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation ASME Code Case N-705 Section 3.1 Evaluation including repair approved in MP 14-0002 The same SIF formula as above will be used for determining the SIF with the new leak repair device installed per MP 14-0002. However, the stress value will be recalculated to include the new bending stress created by the installation of the leak repair device in addition to the internal pressure stress.
Where:
K1 = Calculating a = see below D=Y:I" a=\\4" Stress Intensity Factor for a flat plate model (conservative model)
Total Stress (Internal Pressure Stress plus Bending Stress)
Through-wall Flaw diameter Half Crack Length The bending stress created by the installation of the new leak repair device was calculated using simple beam equations for a point load of 1300 pounds as was discussed above in the Methodology section. The bending stress was calculated in Mathcad, which is in Attachment 1 to this document; however, a summary of the Mathcad file is below. Refer to Attachment 1 for further details.
Below is the formula for calculating the bending stress per the Mechanical Engineering Reference Manual, 9th Edition.
Where:
M. = 366 in-lbs C=0.227in I= 0.025391 in4 Moment at the point load Distance from the composite neutral axis to farthest (exterior) membrane of the smallest area Composite area moment of inertia The moment at the point load (M.) was determined per Manual of Steel Construction AISC 9th Edition (page 2-301), using the below formula for a beam fixed at both ends with a concentrated load at any point. The existing hub nut mounts on either side of the pinhole leak are assumed to be fairly stiff; therefore, the hub nuts are considered fixed ends for the purposes of this evaluation.
Where:
P = 1300 lbs a= 3 in b=lin 1=4 in Point load Distance from farthest support (Refer to page 4 in Attachment 1)
Distance from nearest support (Refer to page 4 in Attachment 1)
Beam Length (Distance between hub nuts)
Page 8of13
Attachment A of Enclosure to ULNRC-06092 Page 12 CAR 201307879 - CCW HX 'A' Pin Hole Leak Evaluation A composite neutral axis (I) was evaluated in Attachment 1 to determine the moment of inertia.
A composite neutral axis was determined using the parallel axis theorem shown in Equation 12.80 of the Mechanical Engineering Reference Manual because the thickness of the CCW heat exchanger is not uniform. Therefore, Attachment I looked at the degraded cross sectional area of the manway as two distinct areas with differing thickness to accmmt for the fact that there is more wall loss on the interior side of the manway in the vicinity of the pinhole leak. This area of concern is 3 inches in length. Using the data in UT Report 5019-13-149, it was assumed the wall thickness is below the nominal 0.5 inches in about 1 inch of that interior side and at the 0.5 inches or better in the other 2 inches of that area The wall thickness used for the inch of area that is below nominal was 0.3 inches, which is an average of all the thickness data taken in the UT Report 5019-13-149. Refer to Attachment 1 for details.
The distance from the composite neutral axis to the farthest membrane in both the large (A) and small (B) areas (see drawing on page 4 of Attachment 1) is defined as C in the bending stress equation above. The large area is the part of manway where the wall thickness is nominal or better and the small area is the part of the manway that is below nominal wall thickness. Both C values are calculated in Attachment 1.
Using this information the above, the bending stress was calculated at the point ofload at the inner membrane of area A (large area) using the appropriate C value and at the point of load at the outer membrane of area B (small area) using its appropriate C value. Both bending stresses are calculated in Attachment 1. It was determined to use the bending stress calculated in the small area ( O"Ma_B = 3268 psi) since this is the area that best represents the area of degradation.
To calculate the SIFs, the internal pressure stress calculated in the first revision will now be added to the bending stress calculated due to the installation of the leak repair device.
O"p = 12.8 ksi crs = 3.3 ksi Stress operating pressure at 135 psig Bending Stress So the combined stresses are 12.8 + 3.3 = 16.1 ksi at operating pressure.
Now the associated SIFs can be calculated:
Using the acceptance criteria in Code Case N-705 Section 5(a), for bounding flaws, the applied stress intensity factor, K1. shall satisfy the following limits:
K <Klc I
3.0 (Levels A and Band Test Conditions, at 135 psig)
(Levels C and D, at 135 psig))
Where:
K1 = 14.27 ksiv'fii Calculated Stress Intensity Factor at 135 psig Page9 of13
Attachment A of Enclosure to ULNRC-06092 Page 13 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation K1c = 52.42 ksi~
Material fracture toughness (KSME International Journal, Volume 14, No.
1, pp. 11-18, 2000, "Effect of Temperature on the Fracture Toughness of A516 Gr. 70 Steel")
Levels A, Band Test Conditions at 135 psig:
K1 < Klc = 3.0 K1 < K1c = 3.0 < KJc = 3.0 < ~
= 3.0 < 3.67 3.0 K1 14.27 And for Levels C and D K1 < ~~: = 1.4 K1 < K1c = 1.4 < ~: = 1.4 < ~:::~ = 1.4 < 3.67 Therefore:
The acceptance criteria in Section 5(a) for Levels A, B, C, D and test conditions continue to still be met with the installation of the new leak repair device.
ASME Code case N*705 Section 3.3(a) Evaluation (Nonplanar Flaw)
For nonplanar part-through-wall degradation (Figure 2) in cylindrical portions of vessels or tanks, including degradation growth through the evaluation period, the vessel or tank is acceptable when the remaining wall thickness (tp) is greater than or equal to the minimum wall thickness (tmin). Figure 2 is shown below:
Page 10ofl3
Attachment A of Enclosure to ULNRC-06092 Page 14 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation FIG. 2 ILLUSTRATION OF NONPLANAR PART-THROUGH-WALL DEGRADATION DUE TO WALL THINNINC Where:
p = 135 psig Do = 24" s = 17,500 psi Therefore:
t
=~
mm 2(S+0.5p)
- -~---I
~::,"':,.nuon direction Maximum Operating Pressure at the Degradation Location Vessel Outside Diameter ofManway Allowable Stress at Operating Temperature for SA-516 Gr. 70 (ASME Section III Subsection NA Table 1-7.1) t
= ~
=
(135)(24) 0.092" min 2(S+0.5p) 2(17500+0.5(135))
Per Code Case N-705 Section 5( c), for nonplanar part-through-wall degradation in cylindrical portions of vessels or tanks, including degradation growth through the evaluation period, the vessel or tank is acceptable when the remaining wall thickness (tp) is greater than or equal to the minimum wall thickness required for pressure loading, where lmin is determined above in accordance with 3.3(a).
The greatest required minimum thickness is therefore 0.092" as shown above. According to CAR 201307879 attachment "CAR 201307879 UT Report 5019-13-149.pdf' the minimum remaining wall thickness (tp) outside the flaw is 0.200 inches. Therefore, tp is greater than tmln Page 11 of13
Attachment A of Enclosure to ULNRC-06092 Page 15 CAR 201307879 - CCW HX 'A' Pin Hole Leak Evaluation and the acceptance criterion in Section 5(c) is also met. This continues to remain valid with the installation of the new leak repair device.
Section 5(d) discusses acceptance criteria for nonplanar part-through-wall degradation in non-cylindrical portions of vessels or tanks, which does not apply to the degradation on the CCW heat exchanger; therefore, does not need to be satisfied. Section 5(e) states for through-wall penetrations, the potential leakage flow area of the degradation, or the total of the potential leakage flow areas of multiple degradation locations that are combined into a single degradation location for the purpose of evaluation, shall not exceed 20 in2* The CCW heat exchanger only has one pinhole leak and the total flow area is 0.196 in2 therefore, there is a substantial amount of margin remaining. When the leak repair device is installed on the CCW heat exchanger this portion of the code case no longer is required. The leak repair device will eliminate the loss of ESW water out ofthe pinhole.
Section 4 of Code Case N-705 discusses the degradation growth portion of this evaluation stating "if degradation growth is evaluated, the analysis shall include the relevant growth mechanisms determined in the cause evaluation". The active crack growth mechanisms including stress corrosion and fatigue are not applicable to the present flaw. The System Engineer has determined that the pinhole leak was caused by localized pitting. The pinhole leak is located in an area of localized internal coating degradation and in a crevice environment created by the sealing surface between the 24" manway and the manway cover. This coating degradation creates an anode/cathode environment between the carbon steel still protected by a coating and the carbon seal directly exposed to the fluid. An Ultrasonic Testing (UT) pit mapping inspection has been performed twice on the identified pinhole leak and is documented in UT reports 5019-13-149 and 5019-13-152. The UT inspections were performed on 10/14/2013 and 12/05/2013, respectively (52 days apart), and both UT inspections identified the lowest UT thickness surrounding the pinhole leak as 0.093" and as having a pit diameter of Yz. With no measured change of the pit size or geometry, from UT inspections measurements, there is no a significant degradation rate present. In addition, other pitting degradation mechanism factors (temperature, water chemistry, flow rates) are not anticipated to change of significant magnitude to adversely impact the current degradation rate. As a result, the pinhole leak is not expected to increase in size beyond the currently assumed Yz pinhole, before Refuel20 (October 11, 2014).
Additionally, a non-compensatory measure tracked by Action 3 of CAR 201307879 and Job 13006144 will monitor the condition of the flaw by perfonning ultrasonic characterization of the flaw on a quarterly basis to ensure the bounding flaw characterization remains valid. The current leakage rate indicates that there is significant margin between the current pit size and the postulated Y2' diameter through-wall pit. Quarterly trending is adequate to ensure the pit will not grow beyond the scope covered in this evaluation before detection.
After installation of the new leak repair device per MP 14-0002, the quarterly trending will continue. During the inspections, the leak repair device will be removed from the heat exchanger in order to complete the UT. During that time, the original ASME Code Case evaluation completed for CAR 20 t 307879 Prompt OD will be the applicable evaluation at that time. This revision of the code case evaluation contains the <tnalysis fot* both situations to 'how we arc acceptable "*hcther the leak repair dc,*icc ts install eel or not installed.
Attachment A of Enclosure to ULNRC-06092 Page 16 CAR 201307879-CCW HX 'A' Pin Hole Leak Evaluation Although not credited in this evaluation, the location of this leak is such that the normal rounds by Operation Technicians allows regular inspection of this component and area. After installation of the new leak repair device per MP 14-0002, Operation Technicians will continue to inspect the component area to ensure no leakage is occurring and leaking under the new repair device.
Lastly, the following actions shall be implemented for degradation determined to be structurally acceptable at the end of the evaluation period (a) Daily leakage monitoring (e.g., vessel or tank level indications, sump measurements, etc.)
shall be performed to ensure that leakage, if any, does not exceed acceptable limits.
(b) Degradation, including growth, that meets the acceptance criteria of the Case shall be determined by examination at one-half of the allowable operating time (i.e., 0.5 tallow), to verify the growth predictions, unless tanow exceeds twice the time to the end of the evaluation period, as allowed by 2.5( d).
The above evaluation determined the CCW Heat Exchanger 'A' was structurally acceptable and would remain so till the end of the evaluation period, which is 26 months from initial discovery, December 14, 2015 with or without the leak repair device installed per MP 14-0002. Also, stated above the location of the leak is such that the normal rounds by the Operations Technicians allows regular inspection of this component and area; therefore, the leak will be monitored daily. As stated in Section 2.4(d) of the code case, ifleakage limits are exceeded within the evaluation period, structural integrity shall be reconfirmed and leakage limiting measures applied, or repair/replacement activities shall be performed. Item (b) listed above discusses the use ofta11ow (calculated in Section 2.5), which was not calculated in the above evaluations, because Sections 2.4 and 2.6 were satisfied. Therefore, it was not required to evaluate Section 2.5. However, the degradation will be monitored daily by Operator rounds and quarterly ultrasonic characterization of the flaw will also occur on a quarterly basis to ensure the bounding flaw characterizations remain valid.
ASME Code Case N-705 has been successfully applied to evaluate the structural integrity of the Component Cooling Water Heat Exchanger with the current pinhole leak and with a leak repair device installed per MP 14-0002. Daily monitoring shall continue to occur and full repairs to return the CCW heat exchanger to its original design must be implemented in Refuel20.
Prepared by: ~. ~ 2ol.3£1.
Nicole Green
"""""""hr. C)d.:: ~
lt..:SS I Ed Vaughn Page 13of13 Date: 2/24/14 Date: 2/24/14
Attachment A of Enclosure to ULNRC-06092 Page 17 Mathcad Files Code Case N-705 Evaluation for MP 14-0002 Point Load Bending Stress Determination See pages 4 and 5 for variable definitions and formula derivations.
1.0 Input Beam Loading Parameters P := 1300 lb Point Load a:=3 in b :=I in L:=a+b L=4oin Distance from farthest support Distance from nearest support Beam length 1.1 Summing Momenta atR1, Solve for Reaction and Shear Forces R2 :=P*a L
R2 =975*1b Rl :=P-R2 Rl =325*1b Reaction force at nearest support Reaction force at farthest support 1.2 Solve for Moments at Point of Load 2*P*a2*b2 Ma:=---
L3 Ma = 366 oin *lb Moment at the point force
Attachment A of Enclosure to ULNRC-06092 Page 18 Mathcad Ales 2.0 Detarmlne a Compoalta Neutral Axis and Reaultl ng Moment of Inertia This section looks at the degraded eros sectional area of the closure hub (manway) as two distinct areas with differing thickness to account for the fact that there Is more wall loss on the Interior side of the hub In the vicinity of the pinhole leak.
The parallel axis theorem Is used In generating an equation for the composite area moment of Inertia as a function of the location of the new com poslte neutral axis. The composite neutral axis location that yields the minimum composite area moment of Inertia (i.e. the axis about which the composite area Is weakest) is the axis about which the composite area will bend.
LA :=2.0 in T A :=O.SO in AA:=LA-TA AA = l"in2
- - LA*T AJ IA*-- I A = 0.020833 -in 4 La:= 1.0 in T 8 :=0.30 in As :=La*Ta As =0.3-in2
- -La*TaJ Ia*--~ r 8 = o.00225 -in 4 TA Ta D:=---
2 2
D=O.J-in Aa*D d:=---
AA+Aa d = 0.02308 -in length of largest crossectional area "A *.
Thickness of largest crossectlonal area "A".
Crossection area of largest area "A".
Area moment of Inertia about Its centroidal axis for the largest area "A".
length of sm sliest crossectlonal area *e*
Thickness of smallest crossectlonal area *e*.
Crossection area of smallest area "B".
Area moment of inertia about its centroldal axis for the smallest area *e*.
Distance between Individual neutral axes for the two areas Composite neutral axis displacement from the neutral axis of the largest area
- A *.
2
Attachment A of Enclosure to ULNRC-06092 Page 19 Icomp =0.025391 "in4 Mathcad Files Composite area moment of inertia 2.1 Determine Bending Stresses c A= 0.2730769 'in TB c 8 :=T+D-d c B = 0.2269231 'in Ma*cA aMa A:"--
1comp 1b a Ma A =3932.__
in2 Ma*cs aMa B:=--
1comp lb a Ma_B =3268":2 m
Distance from composite neutral axis to farthest (Interior) membrane of the largest area "A".
Distance from composite neutral axis to farthest (exterior) membrane of the smallest area "B".
Bending stress at the point of load at the Inner membrane of area "A".
Bending stress at the point of load at the outer membrane of area "B".
3
Attachment A of Enclosure to ULNRC-06092 Page 20
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Attachment A of Enclosure to ULNRC-06092 Page 21 I
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Attachment A of Enclosure to ULNRC-06092 Page 22 STARS INFORMATION REQUEST SHEET
Title:
N-705 Evaluation for CCW Hx A, EEG01A Document No./Rev:
'(V\\"\\>\\4 -0002..RQ\\L ooo I CP.,(t 20\\30'1S11\\
Route To NEDX Ed Vaughn Department Print Name Requestor NEDX Nikki Green Department Print Name 0
a me to any o
~ add r fth bl eta es, place th e cursorm e ast ce
. th I 0
CSII' taean 11 fd ' ed bl d<rA B>.
Requested Action:
Perfonn QR ofN-705 Evaluation for CCW HX A, EEGOIA.
Response
I.
Calc uses Radius of II inches for the stub end based on wall thickness of 0.5 butUT report says nominal wall is 0.562". Need to address discrepancy between the evaluation and the UT report. Note-using ID of22" is conservative.
- 2.
Page II of evaluation uses max operating pressure of200 psig instead of 135 psig.
- 3. shows force of 3000 lbs instead of 1300 lbs I
Evaluator/
I Ed Vaughn I E,/rJ..: f'J._
Reviewer I
Print Name I
SignWbe Disposition I. Added a note to resolve discrepancy
- 2. Changed the pressure from 200 to 135 per the Code Case
- 3. Fixed the 3000 to show 1300.
Disposltioned By Nicole Green PriniName I of!
I I
02/24/14 I NEDX I Date I Dept I Ext STARS-ENG-5001-8.7 10/06/09