ML052150132
| ML052150132 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/22/2005 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML052150132 (7) | |
Text
SOUTHERN CALIFORNIA A. Edward Scherer E
ISO l
s Manager of
_ELDISON"Nuclear Regulatory Affairs An tl)ISO.\\' 1 TER.VATI0.'
Company July 22, 2005 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Docket Nos. 50-362 and 50-362 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c)
Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter (Relief Request ISI-3-15)
San Onofre Nuclear Generating Station (SONGS) Units 2 and 3
Dear Sir or Madam:
Pursuant to 10 CFR 50.55a(a)(3)(i), Southern California Edison Company (SCE) requests NRC approval of a proposed alternative to a 10 CFR 50.55a(c), Reactor Coolant Pressure Boundary, ASME Section III Code Case parameter. Specifically, SCE requests approval of an alternative to ASME Section 111, Sub-Section NB-3356, Code Case 1361-2, MSocket Welds,Section III," to allow a diametral clearance (cMAX) of 0.060 inch between replacement pressurizer heater sleeves and heater sheaths instead of 0.045 inch as specified in the Code Case. Details of the 10 CFR 50.55a request are enclosed. This reactor coolant pressure boundary relief request is being tracked by SCE as Inservice Inspection (ISI) Program Relief Request ISI-3-15.
The need for this relief request was identified, during the Unit 3 Cycle 13 emergent pressurizer repairs. The insertion of the new pressurizer heaters was accomplished with some degree of difficulty due to binding. Although the Unit 3 Alloy 600 sleeves were successfully replaced with Alloy 690 sleeves and the clearances met the 0.045-inch cMAX specified in ASME Code Case 1361-2, the increased diametral clearance is requested for Unit 2 for the Alloy 600 sleeve replacement currently scheduled for the Unit 2 Cycle 14 refueling outage and for Unit 3 for future emergent replacement activities. SCE requests approval of this relief request by January 3, 2006, to support the SONGS Unit 2 Cycle 14 refueling outage.
P.O. Box 128 San Clemente. CA 92672 949-368-7501 Fax 949-368-7575
Document Control Desk July-22, 2005 No commitments are being made in this letter. If you have any questions, please contact Mr. Jack Rainsberry at (949) 368-7420.
Sincerely,
Enclosure:
10 CFR 50.55a(a)(3)(i) Request for Altemative to a 10 CFR 50.55a(c)
Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter Attachments: 1.
Southern California Edison Calculation M-DSC-356, "Evaluation of Modified Pressurizer Heater Sleeves"
- 2.
Figure 'Typical Heater Arrangement" cc:
B. S. Mallett, Regional Administrator, NRC Region IV B. M. Pham, NRC Project Manager, San Onofre Units 2 and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3
Relief Request No. ISI-3-15, Revision 0 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter Background Information Each San Onofre Generating Station (SONGS) unit has a pressurizer containing 30 heater sleeves attached to the bottom head. In the last Unit 3 refueling outage 29 of the original Alloy 600 heater sleeves were replaced with Alloy 690 heater sleeves to address concerns with primary water stress corrosion cracking. One heater sleeve had previously been replaced with an Alloy 690 heater sleeve. The Alloy 600 sleeves in the Unit 2 pressurizer are scheduled to be replaced with Alloy 690 sleeves in the next Unit 2 refueling outage, which is currently scheduled to begin in January 2006.
It has been determined that increasing the maximum diametral clearance between the replacement Alloy 690 pressurizer heater sleeves and the heater sheaths to 0.060-inch maximum will facilitate the insertion of the heaters into the sleeves after sleeve replacement. SONGS UFSAR Section 5.2.1.2, 'Applicable Code Cases," identifies that ASME Section III Code Case 1361-2 was used for the original pressurizer assembly (heater sleeve to heater sheath fillet weld). In Figure 1 of Code Case 1361-2, the diametral clearance (cMAX) between connecting parts is specified as 0.045 inch.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(i) Southern California Edison (SCE) proposes an alternative of 0.060 inch in lieu of the 0.045-inch cMAX, diametral clearance specified in Code Case 1361-2. The other requirements specified in Code Case 1361-2 for joint configuration are met with the increased diametral clearance with no appreciable increase in stress. Although original Unit 3 Alloy 600 sleeves have been replaced with Alloy 690 sleeves and the clearances meet the 0.045-inch cMAX specified in ASME Code Case 1361-2, the increased diametral clearance is requested for Unit 2 for the Alloy 600 sleeve replacement currently scheduled for the Unit 2 cycle 14 RFO and for Unit 3 for future emergent replacement activities. As discussed in this relief request, this proposed alternative would provide an acceptable level of quality and safety and would therefore meet the requirements of 10 CFR 50.55a(a)(3)(i).
I.
ASME Code Component(s) Affected SONGS Units:
2 and 3 Item Number:
B15.20
==
Description:==
Pressurizer Heater Sleeves, 30 per Unit.
Code Class:
1 1 of 5
Relief Request No. ISI-3-15, Revision 0 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter II.
Applicable Code Edition and Addenda
The third 10-year inservice inspection interval code for San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 is the American Society of Mechanical Engineers (ASME) Code, Section Xl, 1995 Edition, through 1996 Addenda. ASME IlIl NB-5000 shall be used for ASME Xl Repair/Replacement non-destructive examination (NDE) of welds.
The construction code for the SONGS Units 2, and 3 pressurizer vessels is ASME Section 1I1, 1971 Edition through Summer 1971 Addenda.
111.
ApDlicable Code Requirements Sub-article NB-3356 ASME Section III 1971 Edition through Summer 1971 Addenda states in part: uFillet welds shall not be used in vessels for joints of Categories A, B, C or D (NB-3351)."
Code Case 1361-2 states in part:
"Appurtenances with outside diameter equal to that of 2-inch standard pipe size and less may be constructed using weld joints in accordance with Figure. 1, provided the following requirements are met:
- 1) The design of the joint shall be such that stresses will not exceed the limits described in NB-3220 and tabulated in tables 1-1.1 and 1-1.2.
- 2) A fatigue strength reduction factor of not less than 4 shall be used in the fatigue analyses of the joints.
- 3) The finished welds shall be examined by a magnetic particle or by a liquid penetrant method in accordance with Section V and the Acceptance Standards of NB-5000.
- 4) End closure connections may be made with fillet welds or partial penetration welds provided the conditions stated above are met.
Figure 1 note cMAX = diametral clearance between connecting parts cMAX = 0.045 in."
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Relief Request No. ISI-3-15, Revision 0 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter IV. Reason For Request The SONGS Unit 3 heater sleeve replacement project conducted during the Unit 3 Cycle 13 refueling outage identified challenges in sleeve alignment and subsequent installation of heaters. As a result, a significantly longer duration than originally expected was required for sleeve welding. During the U3C13 emergent pressurizer repairs, the insertion of the new pressurizer heaters was accomplished with some degree of difficulty. It was observed that the relatively tight clearance, averaging 0.039" (0.045" max.), between the new heater and the new half sleeve combined with any potential mismatch between the new half sleeve and the original sleeve remnant was causing the new heater to bind in the sleeve at many of the locations.
Based on information received from Palo Verde Nuclear Generating Station (PVNGS), SONGS learned that PVNGS had experienced similar difficulties inserting the new heaters during their first (Unit 2) pressurizer repair outage. For the second PVNGS (Unit 3) pressurizer repair outage, the clearances were opened up to 0.062-inch maximum. The ease and efficiency with which the new heaters were installed was greatly increased. This lesson learned from PVNGS 2 and 3 is the basis for the request from SCE to increase the heater to sleeve clearance to 0.060 inch. The inside diameter of the replacement sleeve that will be used for the Unit 2 Cycle 14 sleeve replacement has been increased to 1.298 inch maximum.
The installation of new heaters in SONGS Unit 3 required approximately three twelve hour shifts and 1.7 REM to complete. It is SCE's expectation that by having the additional internal clearance combined with improved alignment methods, the new heater installations should be completed in approximately half the time.
Reducing the time to install the new heaters by one-half should also reduce the dose by approximately one-half.
V.
Proposed Alternative and Basis for Use Pursuant to 10 CFR 50.55a(a)(3)(i), SCE propose an alternative to Code Case 1361-2 by using a maximum 0.060-inch (0.053-inch nominal) diametral clearance between the pressurizer heater and heater sleeve in lieu of the Code Case requirement of 0.045-inch (cMax). This proposed alternative would provide an acceptable level of quality and safety and thus would meet the requirements of 10 CFR 50.55a(a)(3).
The original SONGS pressurizer stress reports prepared by Combustion Engineering (CE) evaluated the integrity of the heater sleeve-to-heater sheath fillet weld applying internal pressure and the effects of steady state temperature.
The original construction for the heater sleeve was Alloy 600. The original 3 of 5
Relief Request No. 1SI-3-15, Revision 0 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter construction for the heater sheath was Type 316 Stainless Steel. The materials of construction for the replacement sleeve are SB 166 Alloy N06690. The material of the heater sheath utilized in the SONGS pressurizers for the new design has not changed (Type 316 stainless steel). The original fillet weld connected a sleeve with an inside diameter (ID) of 1.273 inch and an outside diameter (OD) of 1.660 inch, and a heater sheath with an OD of 1.245 inch. The resulting fillet weld had a leg of 0.1875 inch with a nominal diametral clearance between the parts of 0.028 inch.
For Unit 2, the new design replacement heater sleeve has an ID of 1.298 inch maximum and an OD of 1.660 inch, with the same heater sheath OD of 1.245 inch. The fillet weld size connecting these parts is the same as the original construction, namely a 0.1875-inch leg. However, the maximum diametral clearance is 0.060 inch (0.053-inch nominal). The reason for the increased diametral clearance is explained in section IV of this relief request.
The original stress reports from CE modeled the fillet weld with a nominal design clearance between the parts of 0.028 inches using finite element analysis (FEA) techniques. Subsequent analyses by SCE, provided as Attachment 1, evaluate the same fillet weld with a maximum diametral clearance between the parts of 0.060 inches (0.053-inch nominal). The results of the evaluation demonstrate compliance with the ASME Code NB-3220 allowables for Primary Membrane, Primary Membrane plus Bending, Primary plus Secondary and Fatigue stresses.
See the attached calculation for further details (Attachment 1).
Code Case 1361-2 was approved in March of 1972. At that time, the ASME Code did not prepare a basis document for their Code Case assumptions as is being done presently. Thus, the basis for the diametral clearance requirement of 0.045 inch in Code Case 1361-2 is not specified. However, it is surmised that by maintaining the clearance between the parts relatively small, the amount of bending stresses that can be imparted on the fillet weld due to deflection of the parts is negligible. The manner in which the SONGS pressurizer heaters are held in place, fixed at one end by the fillet weld and supported at the other end by two consecutive heater support plates satisfies this criteria (i.e., minimizes bending stresses at the fillet weld (see Attachment 2). The clearance between the heater and heater support plates is nominally 0.037 inch (1.282 inch minus 1.245 inch).
Based on the above discussion, the reconfigured weld joint is acceptable from a stress/fatigue perspective for the remaining plant life.
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Relief Request No. ISI-3-15, Revision 0 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter VI.
Duration of Proposed Alternative SCE requests that the 10 CFR 50.55a(a)(3)(i) relief for the alternative to the cMAX value in Code Case 1361-2 for the pressurizer sleeves be granted for each SONGS unit and that the relief remain in effect for the remainder of plant life.
VII. Precedent Palo Verde Nuclear Generating Station (PVNGS) Units 1, 2, and 3, Docket Nos.
STN 50-528, 50-529, and 50-530, 10 CFR 50.55a(a)(3)(i) Request for Alternative to a 10 CFR 50.55a(c) Reactor Coolant Pressure Boundary ASME Section III Code Case 1361-2 Parameter (ISI Relief Request 30), Submitted to the NRC: November 11, 2004; Approved by the NRC: November 19, 2004 Vil. Conclusion 10 CFR 50.55a(a)(3) states:
'Proposed alternatives to the requirements of paragraphs (c), (d), (e), (f), (g), and (h) of this section or portions thereof may be used when authorized by the Director of the Office of Nuclear Reactor Regulation. The applicant shall demonstrate that:
(i) The proposed alternatives would provide an acceptable level of quality and safety, or (ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety."
The proposed alternative discussed in this relief request would provide an acceptable level of quality and safety, as the reconfigured weld joint is acceptable from a stress/fatigue perspective. In addition, a liquid penetrant examination in accordance with ASME Section III, Class I requirements will be performed on the subject welds for acceptability. Therefore, SCE requests that the proposed alternative be authorized pursuant to 10 CFR 50.55a(a)(3)(i).
SCE requests NRC approval of the proposed relief request by January 3, 2006, to support the Unit 2 cycle 14 refueling outage.
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