ML051290435
| ML051290435 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/09/2005 |
| From: | Grecheck E Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 05-100 | |
| Download: ML051290435 (12) | |
Text
Dominion Nuclear Connecticut, Inc.
,\\4iIl~toiie Power Star ion liopc. kcrry fled U.i I cr tord, C :T 0638 5 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 1 1555 Rockville Pike Rockville, MD 20852-2738 NIT 3
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May 9, 2005 Serial No.:
05-1 00 Docket No.:
50-423 License No.:
N PF-49 MPS Lic/RWM Rev 0 Dominion Nuclear Connecticut, Inc. (DNC) requests relief from the Section XI requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, pursuant to 10 CFR 50.55a(g)(5)(iii). This request is based upon the impracticality of performing ASME Code repairs to a brazed joint on a 3 inch drain line from the A train service water header (line 3-SWP-003-205-3) during plant operation. Attachment 1 to this letter describes the temporary compensatory actions taken by DNC and the basis for the proposed alternative non-Code repairs. Consistent with the Millstone Station Corrective Action Program, the permanent Code repair or replacement for this degraded and nonconforming condition will be completed during the next cold shutdown of sufficient duration, or the next refueling outage, whichever comes first.
If you should have any questions regarding this submittal, please contact Mr. Paul R. Willoughby at (804) 273-3572.
Very truly yours,
/
\\
M e n e S. Grecheck Vice President - Nuclear Support Services 1 OCFR 50.55a Request IR-2-37 Commitments contained within this letter: None cc: See next page
Serial No.: 05-1 00 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 Page 2 cc:
U. S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-1415 Mr. G. F. Wunder Project Manager, Millstone Unit 3 U. S. Nuclear Regulatory Commission One White Flint North 11 555 Rockville Pike Mail Stop 8 BIA Rockville, MD 20852-2738 Mr. S. M. Schneider NRC Senior Resident Inspector Millstone Power Station
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 ATTACHMENT 1 10 CFR 50.55a REQUEST IR-2-37 TEMPORARY NON-CODE REPAIR OF A BRAZED JOINT IN SERVICE WATER SYSTEM DRAIN LINE DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION, UNIT 3
1.o 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 1 of 9 10 CFR 50.55a REQUEST IR-2-37 IN SERVICE WATER SYSTEM DRAIN LINE TEMPORARY NON-CODE REPAIR OF A BRAZED JOINT CONTENTS ASME CODE COMPONENTS AFFECTED....................................................
2 APPLICABLE CODE EDITION AND ADDENDA............................................
2 APPLICABLE CODE REQUIREMENTS.........................................................
2 I M P RACTl CALI TY 0 F COM PLI AN C E............................................................ 3 BURDEN CAUSED BY COMPLIANCE..........................................................
3 PROPOSED ALTERNATIVE AND BASIS FOR USE.....................................
3 DURATION OF PROPOSED ALTERNATIVE................................................
7 PRECEDENTS...............................................................................................
7 FIGURE 1: PIPING ARRANGEMENT OF THE AFFECTED BRAZED................ 8 ELBOW JOINT FIGURE 2: TEMPORARY SUPPORT ARRANGEMENT FOR THE....................
9 AFFECTED BRAZED ELBOW JOINT
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 2 of 9 10 CFR 50.55a REQUEST IR-2-37 TEMPORARY NON-CODE REPAIR OF A BRAZED JOINT IN SERVICE WATER SYSTEM DRAIN LINE Relief Request In Accordance with 10 CFR 50.55a(g)(5)(iii)
- Inservice Inspection Impracticality -
1.O ASME CODE COMPONENTS AFFECTED:
The affected component is an ASME Code Class 3 service water brazed elbow joint, with Cu-Ni 466 piping, and associated bronze SB-61 socket fitting, for the 3-inch drain line from the 'A' train service water header in the intake structure (line 3-SWP-003-205-3). The affected joint has minor weepage of service water. The weepage is coming through the braze material from the field joint designated as FW-14, at the top of a vertically oriented 90 degree elbow. The drain line is located at elevation 1 foot 4 inches in the chlorination pit that is part of the Intake Structure. The affected joint (FW-14) is as shown in Figure 1.
System:
Design Code:
Safety Code Class:
Piping size:
Nominal Thickness:
Material (pipe / fitting):
Design Pressure:
Temperature :
Code Minimum Wall:
Service Water ASME I l l 1971 Class 3 3-inch 0.219 inches Cu-Ni SB 466 / Bronze SB 61 100 psi design / 63 psi max. operating 75 OF design max. / 33 OF min.
0.01 8 inches (thickness) 2.0 APPLICABLE CODE EDITION AND ADDENDA:
Millstone Unit 3 is currently in the second 10-year Inservice Inspection (ISI) interval, which started on April 23, 1999. The 1989 Edition of Section XI with No Addenda applies to the IS1 program and the 1998 Edition of Section XI with No Addenda is used as the primary ASME Code Edition for the Section XI Repair/Replacement program activities.
3.0 APPLICABLE CODE REQUIREMENTS:
Applicable ASME Code requirements are those contained in ASME Section XI, 1989 Edition, IWA-4000, Repair and Replacement.
NRC approved analysis methods are those contained in Generic Letter (GL) 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2 and 3 Piping,"
dated June 15, 1990 and 10 CFR 50.55a. GL 90-05 also provides guidance for performing temporary non-Code repairs of ASME Code Class 1, 2 and 3 piping.
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 3 of 9 4.0 IMPRACTICALITY OF COMPLIANCE:
There is no acceptable method for analyzing leaking brazed socket joints in Generic Letter 90-05 or that are permitted by ASME Section XI, 1989 Edition, IWA-4000. Additionally, NRC approved Code Cases, such as N-513, "Evaluation Criteria for Temporary Acceptance of Flaws in Class Three Piping,Section XI, Division 1,I1 are not applicable to brazed socket joints.
The repair planned in this instance is to replace the brazed joint with a butt-welded fitting. However, an on line repair or replacement is not practical because the leak cannot be isolated from the 30 inch 'A' train service water header, which would require draining.
Technical Specification 3.7.4 requires that at least two independent service water loops are OPERABLE in MODES 1, 2, 3 and 4. With only one service water loop OPERABLE, restoration of at least two loops to an OPERABLE status is required within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the plant must be in HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
5.0 BURDEN CAUSED BY COMPLIANCE:
The permanent repair for this condition could potentially require an unnecessary shutdown of the unit without a commensurate safety benefit. The structural analysis of the current piping configuration using this temporary non-Code repair indicates that all required functions would be maintained for postulated design basis accidents and transients.
6.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:
For the purpose of analyzing structural capacity, the total loss of the braze material within the leaking pipe joint has been assumed. Therefore, additional supports were added to prevent pipe separation from the affected brazed socket fitting. If braze material failure occurs, the added supports maintain structural continuity of the degraded configuration and will restrict the potential for leakage to annular clearances between the affected socket fitting and piping. This use of temporary supports is shown in Figure 2 and will ensure the affected service water piping is structurally adequate for all design loading conditions.
An operability determination (OD) has been completed.
The OD will remain applicable until the permanent butt-welded replacement for the joint can be installed, and the piping fully qualified. Based on the evaluations, examinations and monitoring procedures associated with this temporary repair, the proposed actions provide reasonable assurance that the joint will maintain the structural integrity and functional performance of the line. Specific considerations associated with the basis of this request are discussed in the balance of this section.
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 4 of 9 6.1 Flaw Characterizations and Mechanism of Degradation:
Non-destructive examination included ultrasonic testing (UT) on the affected piping and elbow, which determined that the degradation is limited to the brazed joint. Visual examination (VT-1) on the flaw, adjacent components and augmented inspections were performed.
The extent of the braze disruption is very small and not distinguishable by visual examination. The resulting leakage is slow and can be characterized as weepage (less than 1 drop per 10 minutes). Adjacent pipe material and fittings have no cracking or wastage.
UT examination showed no deterioration in the piping or the fittings and, consequently, erosion rate estimates are not applicable to this condition.
The degradation mechanism appears limited to braze material fill in the affected joint that has resulted in through-braze leakage and assumed braze material failure.
Fitting and piping are intact.
Therefore, any potential leakage area is limited to the annular area of 0.055 square inches (derived from nominally 0.005 inches of gap within the joint) between pipe and sockets.
6.2 Augmented Inspections:
This condition was first observed on February 1, 2005.
Additional examination of similar pipes and adjacent piping was performed to provide assurance that other brazed joints were not leaking and that no damage had occurred due to leaking service water.
On February 1, 2005, other similar three 3 inch brazed joints were inspected on the same line and no leakage was identified. On February 9, 2005, four other 3 inch brazed joints were inspected on the corresponding line in the B train of service water and no leakage was identified. On March 1, 2005, seven 3 inch brazed joints were inspected in both the downstream portion of the affected line, and a separate 3 inch line off of the 30 inch service water header, and no leakage was identified.
On March 1, 2005, a UT examination and visual inspection were also performed on the piping at the affected joint, FW-14. The UT inspection found no change in the wall thickness of the piping adjacent to the weeping brazed joint and visual inspection found no change in amount of weepage coming from the joint.
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 5 of 9 6.3 Structural Assessment:
The flaw is located in a brazed joint and therefore previously approved methodologies to show structural integrity are not applicable. The operability determination conservatively assumes a potential for a total loss of the braze material in the joint FW-14 of this service water elbow. Figure 1 shows the piping arrangement of the affected joint. The structural integrity of the service water system is adequate based on the joint design and the location of new temporary supports as shown in Figure 2, (i.e., the affected piping will remain within the fitting socket even if braze material were to totally fail). This service water piping is subject to deadweight, thermal, seismic inertial, and fluid pressure thrust loading. The new supports from this temporary non-Code repair ensure affected piping is structurally intact for all design loading conditions for this application.
6.4 System Interactions:
Specific considerations from system interactions such as consequences of flooding and spraying water on equipment, and potential for loss of flow from leakage, are discussed in the balance of this section.
Flooding:
Currently, only weepage has been observed at the affected brazed joint.
Catastrophic failure of the joint is not expected from this condition.
However, a conservative assumption of the total loss of braze material in the affected joint has been considered. Any potential leakage area is limited to the annular area (derived from nominally 0.055 square inches of gap within the affected joint) between pipe and socket. The greatest leakage postulated to result from such an assumption is estimated at 11 gpm with two service water pumps operating and 9 gpm with one service water pump operation on the A train.
The only safety related equipment in the access enclosure that could be affected by flooding are valves 3SWP*MOVll5A and B, the circulating water pumps lubricating water valves. These motor operated valves are normally open supplying service water to the shafts of the circulating water pumps. The function of these valves is to close on a containment depressurization actuation (CDA) or loss of power (LOP) signal to preserve cooling water flow for the safety related heat exchangers in the system. However, if a complete loss of brazed material at the degraded joint did cause water to collect on the floor, there is a non-safety level switch in the Access Enclosure that annunciates in a local panel, noting Chlorine Pit Level Hi. A control room annunciator on the main board will also alarm noting Chlorination System Trouble and the alarm response procedure directs that an operator be sent to the local panel to determine
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 6 of 9 the cause of the alarm. The setpoint level of this alarm is at 6 inches above the floor. These valves are located sufficiently above (approximately 15 feet) the Access Enclosure floor that a 9 to 11 gpm brazed joint leak would reasonably not affect the isolation valves if leakage were to collect on the floor.
Considering that the assumptions of this leakage estimate are conservative and actual leakage is limited to weepage (less than 1 drop in 10 minutes), and there exists control room annunciation for level in the chlorine pit, the potential for a flooding condition is remote and would reasonably be identified and mitigated before any safety related components could become affected.
Jet sprav:
If further degradation of the affected joint was to take place, spray or jet impingement upon adjacent components is not a concern.
No safety related targets vulnerable to spray or dripping are within close proximity to the affected joint.
Loss of flow:
The analysis shows that in the unlikely event of a maximum leakage from the affected joint (9 to 11 gpm), that service water flow will remain adequate to support required safety functions. The flow margin in the service water flow model bounds the maximum leakage potential from this joint, and is negligible with respect to the service water system header flow margins.
6.5 Compensatory Monitoring Plan:
Leakage monitoring shall be performed. The degraded joint will be observed every four weeks. Periodic follow-up nondestructive examinations (NDE) will be performed within 90 days from the last examination. These periodic NDE examinations will include UT examinations of the piping at the affected brazed joint location and a visual inspection. These follow-up examinations shall continue until a permanent Code compliant butt-welded replacement field weld is performed. Any significant changes that are observed in the condition of the joint or its temporary supports that could affect system(s) operability or structural integrity will be evaluated. Based upon the observations from this monitoring plan, any needed evaluations will determine if further remedial measures or corrective actions are needed. This monitoring plan is being administrated under the control of the Millstone Station Corrective Action Program and with the station procedure for Operability Determinations.
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 7 of 9 7.0 DURATION OF PROPOSED ALTERNATIVE:
A permanent Code repair for this flaw will be completed during the next cold shutdown of sufficient duration, or the next refueling outage (Fall 2005), whichever comes first.
8.0 PRECEDENTS
The NRC Staff's review and approval of a similar temporary non-Code repair of a brazed joint leak at Millstone Unit 3 is in a letter dated May 21, 2004, "Request for Relief From ASME Code Class 3 Piping, (TAC No. MB9996)." The request is at ADAMS Accession No. ML032040024.
Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 8 of 9 FIGURE 1 : PIPING ARRANGEMENT OF THE AFFECTED BRAZED ELBOW JOINT
OQ Serial No.: 05-100 Docket No.: 50-423 10 CFR 50.55a Request IR-2-37 / Page 9 of 9 3
1 FIGURE 2: TEMPORARY SUPPORT ARRANGEMENT FOR THE AFFECTED BRAZED ELBOW JOINT