L-90-005, Relief Request 3-43 for Temporary Repair to Service Water Pipe
| ML072910355 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 09/27/2007 |
| From: | Robert Walpole Entergy Nuclear Northeast |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-90-005, NL-07-118 | |
| Download: ML072910355 (7) | |
Text
Entergy Nuclear Northeast Indian Point Energy Center 450 Broadway, GSB
"=== En e Buchanan, NY 10511-0249 Robert Walpole Licensing Manager Tel (914) 734-6710 September 27, 2007 Re: Indian Point Unit 3 Docket 50-286 NL-07-118 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
SUBJECT:
Relief Request 3-43 for Temporary Repair to Service Water Pipe
Reference:
- 1. Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping", dated June 15, 1990.
Dear Sir or Madam:
Entergy Nuclear Operations, Inc (Entergy) is requesting relief in accordance with 10 CFR 50.55a(a)(3)(i) for a temporary non-code repair to an ASME Code Class 3 piping elbow in the Indian Point 3 (IP3) Service Water System. The circumstances regarding this request were discussed with NRC staff in a conference call on September 26, 2007.
On September 18, 2007, with IP3 in operation at 100% power, a nuclear plant operator identified two through-wall leaks in a piping elbow in the service water system with leakage of approximately 5 drops per minute. Entergy has performed ultrasonic testing non-destructive examinations to characterize the affected areas and has prepared evaluations in accordance with Generic Letter 90-05 (Reference 1) and ASME Code Case N-513-1. These examinations and evaluations conclude that the leakage is a result of wall-thinning due to localized corrosion on the inside of the pipe. The remaining wall thickness currently provides sufficient structural integrity to maintain operability of the service water system. The evaluation also concludes that, with ongoing corrosion, operability cannot be assured for the remainder of the operating cycle (Spring 2009) and a near-term repair is needed.
Implementing an ASME code repair will require removing this section of service water piping from service, which is not practical because that will remove three containment fan cooler units from service. IP3 Technical Specification 3.6.6 does not have a Condition Statement for this configuration. Therefore, Entergy has designed a temporary engineered repair which meets the applicable stress criteria for normal and seismic loading conditions. ASME Code Section IWA-4422.1 requires that a defect be removed as part of repair installation. Since defect removal is not possible with the system in service, Entergy is requesting relief from this code requirement.
NL-07-118 Docket 50-286 Page 2 of 2 Implementation of the repair will include periodic monitoring and the duration will be limited in accordance with GL 90-05. The details of the Relief Request are provided in Attachment 1:
Entergy requests an expedited review of this relief request to support our efforts for a prompt installation of the repair because an increase in leakrate could preclude the proposed repair approach. Although no increase in leakrate has been detected since initial discovery, Entergy would like to initiate repair activities on October 3, 2007. There are no new commitments being made in this submittal. Ifyou have any questions or require additional information, please contact Mr. Robert Walpole, Manager, Licensing at (914) 734-6710.
Sincer~ely, Licensing Manager Indian Point Energy Center cc: Mr. John P. Boska, Senior Project Manager, NRC NRR DORL Mr. Samuel J. Collins, Regional Administrator, NRC Region 1 NRC Resident Inspector, IP3 Mr. Paul D. Tonko, President NYSERDA Mr. Paul Eddy, New York State Dept. of Public Service
ATTACHMENT 1 TO NL-07-118 INDIAN POINT 3 RELIEF REQUEST 3-43 REGARDING TEMPORARY NON-CODE REPAIR TO SERVICE WATER PIPING ENTERGY NUCLEAR OPERATIONS, INC INDIAN POINT NUCLEAR GENERATING UNIT NO. 3 DOCKET NO. 50-286
NL-07-118 Attachment 1 INDIAN POINT UNIT 3 RELIEF REQUEST 3-43, REVISION 0 PAGE 1 OF 4 Proposed Alternative in accordance with 10 CFR 50.55a (a)(3)(i)
Alternative Provides Acceptable Level of Quality and Safety A. ASME Code Component Affected 18" Service Water supply line number 408 to the Containment Fan Cooler Units (FCU). This line is one of two lines which supplies Hudson River water to the FCUs which are used to remove containment heat during normal plant operation and following a design bases accident.
B. Applicable Code Edition and Addenda The applicable Code of Record for the current 10 year inservice inspection interval is the ASME Section XI Code, 1989 Edition with no Addenda. However, for Repair and Replacement activities, Entergy has requested and the NRC has approved (Reference 1) the use of subsection IWA-4000 of the ASME Section Xl, 2001 Edition through the 2003 Addenda.
The affected portion of the service water piping was designed and constructed in accordance with the requirements of the USAS B31.1.0, 1967 Edition of the Power Piping Code.
C. Applicable Code Requirement IWA-4422.1 requires that defects be removed or reduced to an acceptable size prior to implementing a repair or replacement in accordance with the requirements of IWA-4000. Since the current through wall defects are beyond the acceptance criteria of IWD-3000 and removal is not practical without system depressurization, the proposed repair method would not be consistent with IWA-4422.1.
D. Reason for Request On September 18, 2007 a Nuclear Plant Operator conducting a routine plant walkdown noted minor leakage of approximately 5 drops per minute in one of the two cement-lined 18" diameter, 0.375" nominal thickness service water supply lines for the containment fan cooler units. As a result of this leak a volumetric examination of the surrounding area was performed and the results were evaluated against the requirements of ASME Code Case N-513-1. Although this evaluation confirmed that the affected piping remains within the requirements of Code Case N-513-1, the calculated corrosion rate does not support continued structural integrity through the remainder of the current operating cycle.
A weld repair/replacement fully compliant with the requirements of IWA-4000 is not practical.
The affected piping section would need to be removed from service which would result in 3 FCUs inoperable. Indian Point 3 Technical Specification 3.6.6 does not have a Condition Statement for that configuration.
NL-07-118 Attachment 1 INDIAN POINT UNIT 3 RELIEF REQUEST 3-43, REVISION 0 PAGE 2 OF 4 Entergy has evaluated two alternative options to repair this degraded location; (1) weld overlay consistent with ASME Code Case N-661 and (2) a welded plate to reinforce the degraded region. The weld overlay based on Code Case N-661 does not have a high probability of success due to the risk of "burn-through" in small areas where the remaining pipe thickness is insufficient to deposit weld metal. To protect against "burn-through" as demonstrated in EPRI testing, a modified version of Option 1 would involve use of a small intermediate plate over the localized area subject to 'burn-through' and then a weld overlay could be applied over that plate.
Both the reinforcing plate option and the overlay-with-intermediate-plate option are designed to adequately restore the required structural margin for the remainder of the current operating cycle. Entergy's preferred alternative is the Option 2 welded plate because the amount of welding is not as extensive and the structural integrity provided is the same as the intermediate plate / weld overlay.
The current leak is located in an area adjacent to a leak which was identified and repaired during refueling outage 3R14, in the Spring of 2007. The repair performed during 3R14 was fully compliant with the requirements of the ASME,Section XI Code, IWA-4000 and included excavation of the defect area followed by a weld repair. However, the inside of the piping was not coated to protect against future corrosion since the corrosion rate obtained from the inspection results indicated that the remaining wall thickness was sufficient to operate through the current operating cycle. This general corrosion rate was obtained based on the average thickness readings for the degraded area but it did not provide individual corrosion rates for each of the measured locations. The current readings indicate that some localized corrosion rates are greater than those calculated during 3R14 while others are lower. These higher localized corrosion rates are the cause of the current areas which can not be demonstrated to retain sufficient structural margin through the remainder of the current operating cycle.
E. Proposed Alternative and Basis for Use As discussed above, IWA-4422.1 requires that a defect be removed prior to implementing an IWA-4000 repair. However, this is not practical for the reason described in Section D regarding Technical Specification 3.6.6 for the FCUs. The preferred alternative proposed under this relief request would install a plate over the degraded area to allow the attachment welding to be located in an area with minimal degradation therefore ensuring a structurally sound load path while minimizing the risk of "burn-through" and increased leakage.
The design will also ensure that the configuration of the repair will allow continued monitoring of the region by volumetric examination to ensure that future degradation will not adversely impact the structural capability of the repaired section.
- 1. Materials The material of the component to be repaired is concrete lined Carbon Steel, A 234, Grade WCB. The proposed repair plate material is ASTM A-36/A-106 Grade B or equivalent carbon steel material, while the welding process to be used in this repair is SMAW with a Carbon Steel, 7018 weld wire.
NL-07-118 Attachment 1 INDIAN POINT UNIT 3 RELIEF REQUEST 3-43, REVISION 0 PAGE 3 OF 4
- 2. Design Parameters The welded plate/weld repair option will be designed and installed consistent with the original USAS B31.1.0, 1967 Edition of the Power Piping Code requirements for a reinforcing plate (paragraph 104.3). A structural evaluation has been performed to ensure that the resulting stresses in the piping, the plate and the attaching welds do not exceed the allowable stresses of the USAS B31.1.0 Code, 1967 Edition.
- 3. Non Destructive Examination The area to be repaired has been characterized by performing straight beam UT mapping of the region to (1) bound the degraded area and (2) to ensure that the welds are located in areas of sound base metal.
Additional inspections are planned to determine the extent of condition of the degradation mechanism. As a result of a review of the system operating conditions, five additional locations most likely to be subjected to the same degradation mechanism will be selected for inspection as required by Code Case N-513-1.
All repairs will be examined, consistent with the examination requirements provided in Code Case N-661. This includes performing a surface examination of the area to be welded, a surface examination after the first weld pass and a final surface examination of the completed weld.
- 4. Post repair monitoring plan After completion of the repair, the area will be UT inspected with a straight beam UT technique to obtain a base line measurement of the thicknesses of the repaired region.
These areas will then be re-inspected on a quarterly basis until the next refueling outage which is currently scheduled for the Spring of 2009. These thickness measurements will be used to ensure that the structural requirements of the original construction code are maintained through the remainder of the current operating cycle.
- 5. Degradation mechanism The exact cause of the degradation which resulted in this pin hole will be established during the next refueling outage when the affected component is replaced. However, based on the location of the defect and based on the UT inspections of the degraded area, it has been concluded that this was likely caused by degradation of the protective concrete lining directly under the degraded area which allowed brackish water from the Hudson River to contact the unprotected carbon steel piping resulting in localized corrosion. The degradation of the concrete lining was likely caused by the high flow velocities from the valve located just upstream of the degraded area.
- 6. Applicable Loads The repair will be designed to accommodate all appropriate deadweight, pressure, thermal and seismic loads. Since the system is a moderate energy system which operates at a low temperature, differential thermal expansion between the repair plate and the repaired component is not a concern.
NL-07-118 Attachment 1 INDIAN POINT UNIT 3 RELIEF REQUEST 3-43, REVISION 0 PAGE 4 OF 4 F. Duration of Proposed Alternative The duration of the temporary repair is limited in accordance with GL 90-05 until the next scheduled outage exceeding 30 days, but no later than the next refueling outage currently scheduled for the Spring of 2009.
G. References
- 1. NRC Safety Evaluation dated April 24, 2007 for Relief Request 3-42 (ML070880358).