ML18058B894
| ML18058B894 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/01/1993 |
| From: | Slade G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML18058B895 | List: |
| References | |
| NUDOCS 9307060307 | |
| Download: ML18058B894 (11) | |
Text
- consumers Power POW ERIN&
MICHl&AN'S PRO&RESS Palisades Nuclear Plant: 27780 Blue Star Memorial Highway, Covert, Ml 49043 July 1, 1993 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 GB Slade General Manager DOCKET 50-255 - LICENSE DPR PALISADES PLANT - REQUEST FOR RELIEF FROM SPECIFIC ASME CODE REQUIREMENTS - SERVICE WATER SYSTEM LEAKAGE Pursuant_ to 10 CFR 50.55a(g), a relief request from certain prov1s1ons of Section XI of the ASME Boiler and Pressure Vessel (B&PV) Code is being submitted for NRC review and approval.
10 CFR 50.55a(g)(4) states that components which are classified as ASME Code Class 1, Class 2, and Class 3, shall meet the requirements of Section XI of the Code, to the extent practical within the limitations of design, geometry, and materials of construction of the components.
10 CFR 50.55a(g)(5 and 6) state that if the licensee determines that conformance with a certain code requirement is impractical, the Commission may grant relief. The Palisades service water return header to Lake Michigan has developed two leaks at the discharge of the component cooling water (CCW) heat exchanger.
Each leak has been characterized as a pin-hole type of leak.
One is located at a 4-inch pipe to valve weld and the other is located near a 16-inch pipe to flange weld at the discharge of the main and bypass CCW heat exchanger service water discharge valves.
Service water is required to remain in operation at all times to support operation of the CCW system.
During power operation, the CCW system provides control rod drive and primary coolant pump seal cooling, as well as spent fuel pool cooling. During plant shutdowns for refueling the CCW system provides
- shutdown cooling for the reactor core as well as spent fuel pool cooling.
The service water and CCW systems also service the e~ergency core cooling systems (safety injection, containment spray, and containment air coolers) and related pumps during design basis accident conditions.
9307060307 930701 PDR ADOCK 05000255 p
.PDR '
A Code r~pair cannot be completed during plant operation or during a normal refueling outage because the leak location (downstream of the last service water system isolation valve) cannot be isolated without removing the entire service water system from service.
Until the time when plans can be finalized to complete a Code repair, relief is requested from meeting the requirements of the Code.
The next available opportunity to complete a Code repair will be during an outage when the reactor is totally defueled.
Present plans are to complete a full core off-load to support reactor vessel lnservice Inspections (ISi) during the 1994 refueling outage.
. Attachment 1 provides the relief request for the 4-inch and 16-inch service water piping and proposed temporary non-Code repair as an alternative to the Codes IWA-4000 repair and IWA-7000 replacement requirements. provides the calculation and drawing for the temporary non-Code repairs for the 16-inch line.
The calculation and drawing for the temporary non-Code repair for the 4-inch line are not included with this transmittal but will be submitted under a separate cover letter as soon as the calculations and drawings are finalized.
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G;Kld B Slade O~
General Manager CC: Administrator Region Ill, USNRC NRC Resident Inspector, Palisades Attachments 2
ATTACHMENT 1 Consumers Power Company Palisades Plant Docket 50-255 REQUEST FOR RELIEF FROM SPECIFIC ASME CODE REQUIREMENTS SERVICE WATER SYSTEM LEAKAGE July 1, 1993 8 Pages
Consumers Power Company Relief Request From ASME Section XI Requirements Palisades Nuclear Plant
1.1 DESCRIPTION
OF FLAW Location 1: 16-inch: Pinhole leak at toe of weld (slip-on flange to pipe) in the 16" service water discharge line from the E-548 Component Cooling Water (CCW) heat exchanger.
Localized thinning of the pipe where the lowest reading recorded in the area of the leak is 0.141".
The nominal wall thickness is 0.375".
1 Piping Identification and Drawing Number:
H8 23-16", P&ID M-208 Location 2:
4-inch:
Pinhole leak in the toe of the butt-weld (pipe to valve) in the 4" service water discharge line from the E-548 CCW heat exchanger.
Localized thinning of the weld where* the lowest recorded reading in the area of the leak is 0.094".
The nominal wall thickness is 0.237".
Piping Identification and Drawing Number:
H8 23-4", P&ID M-208 1.2 IMPRACTICALITY OF REPAIR A Code repair cannot be completed during plant operation or a normal refueling outage.
The leaks are located downstream of the last service water system isolation valve one to two feet from where the pipe enters the main return header to Lake Michigan.
Therefore the leak locations cannot be isolated to complete a Code repair without removing the entire service water system from service.
Service water ts required to remain in operation at all times to support operation of the (CCW) system.
During power operation the CCW system provides control rod drive and primary coolant pump seal cooling as well as spent fuel pool cooling.
During plant shutdowns for refueling the CCW system supports shutdown cooling for the reactor core as well as spent fuel pool cooling.
The service water and CCW systems also service the emergency core cooling systems (safety injection, containment spray, and containment air coolers) and related pumps during design basis accident conditions.
Code repairs can only be completed when the service water return header can be isolated from the CCW heat exchangers.
In order to do this two significant activities are needed.
2 First, a total core off-load needs to be completed so that the shutdown cooling system is no longer required.
Presently Palisades does not have room in the spent fuel pool to complete a full core off-load. Current plans are to load a sufficient number of dry fuel storage casks after the completion of the 1993 refueling outage so that a full core off-load would be possible in the 1994 refueling.
Secondly, with the core totally off-loaded to the spent fuel pool, a temporary alternate spent fuel pool cooling system needs to be installed. The engineering and logistics to design and install alternate spent fuel pool cooling are extensive and complex.
We are developing a project to install alternate spent fuel pool cooling; however, the project is in the conceptual engineering stage and will not be ready for installation until the 1994 refueling outage.
1.3 DESCRIPTION
OF PROPOSED TEMPORARY REPAIR For the HB 23-16" line, a non-Code repair with load bearing capability consisting of a 360 degree sleeve welded to the pipe will be installed..
For the HB 23-4" line, due to the weld configuration and the inability to obtain all the data to characterize the flaw, a non-code repair with load bearing capability consisting of a 360 degree sleeve welded to the pipe and valve will be installed.
Installation of the temporary non-Code repairs will be completed after the plant leaves.cold shutdown but prior to power operation from the refueling outage that is in progress. This time has been selected to complete the repairs as it provides the most flexibility and greatest success path for configuring the CCW system and service water system for the repairs.
Once we leave cold shutdown we will no* longer have the shutdown cooling loads on the CCW system. This should provide some flexibility to arrange flows through the CCW system such that the two leak locations are made as dry as possible.
The calculation and drawing for the temporary non-Code repair for the HB 23-16 inch line are in Attachment 2.
The calculation and drawing for the temporary non-Code repair for the 4-inch line are not included with this transmittal but will be submitted under a separate cover letter as soon as the calculations and drawings are finalized.
3 Reference Calculations:
EA-SP-03316-03, REV.O, "Servi~e Water System - Evaluation of Pipe Wall Thinning Downstream of MV SW 136" EA-SP-03316-04, REV.O, "Service water System - Evaluation of Pipe Wall Thinning Downstream of CV-0826" EA-SP-03316-05, Temporary Non-Code Repair For Pipe Leak/Wall thinning Downstream of CV-0826, Service water System, Line HB-23-16" 1.4 SAFETY SIGNIFICANCE System Interaction Evaluation Flooding:
With the installation of the load bearing non-Code repair, flooding will not occur.
Jet spray~ With the installation of the load bearing non-Code repair, jet spray will not occur.
Loss of Flow:
The leaking sections of piping are downstream of the last isolation valves (CV-0826 and MV-SW 136) within one to two feet of the service water return header.
CV-0826, is the 16" CCW heat exchanger outlet valve and is used to balance accident condition service water flows through the CCW heat exchanger (E-548).
When an accident occurs, CV-0826 goes to the open position but is limited in reaching the full open position by a hard stop.
By prohibiting*the valve from going full open the service water flow is throttled at the outlet of the heat exchanger. A pipe break down stream of this valve, therefore, would not result in a significant increase in service water flow as system pressure in this area of the discharge header is usually low and therefore, the pressure drop across the throttle valve will not be significantly changed by the line break.
MV-SW 136 is a 4" isolation valve just 'downstream of the E-548 CCW heat exchanger service water temperature control valve (CV-0822).
On a post accident recirculation actuation signal, CV-0822 receives a closed signal, and also fails closed on loss of control air. Thus, CV-0822 would limit flow during a down stream pipe break since it would go to a closed position.
Pipe failure at either of these locations would not significantly alter the service water system flows such that the service water pump performance was altered. Also the CCW system would remain in-service as the leak locations are downstream of the CCW heat exchanger.
Other interactions: None.
Failure Consequences:
None.
Impact to Safe Shutdown:
None.
1.5 ROOT CAUSE INVESTIGATION Root Cause
Description:
Suspect localized degradation due to erosion in both locations.
Other Systems affected:
None 1.6 AUGMENTED INSPECTION The corresponding locations on the service water discharge line from the second CCW heat exchanger (E-54A) were inspected as the piping, valves, and operation of the second heat exchanger are similar to the one where the leaks were identified.
No significant wall thinning was identified from these inspections.
4 We are scheduled to examine up to five additional areas of service water piping previously identified and scheduled for the 1993 refueling outage as part of our response to Generic Letter 89-13.
These areas have been identified as possible high erosion areas.
Some of these suspect areas were also inspected during the 1990 refueling outage and no significant wall thinning was identified at that time.
2.0 STRESS ANALYSIS 2.1 Design Details System:
Service Water Component:
16" and 4" piping Piping Size and schedule:
16" (schedule 30) and 4" (schedule 40)
Nominal Wall Thickness:
0.375" (16") and 0.237" (4")
Safety Code Class: 3 Material:
Carbon Steel, ASTM A-53 Grade B Design Conditions:
100 psi at 300°F
Operating Pressure:
65 psig Operating Temperature:
75"F Code Minimum Wall Thickness:
0.053" for H8 23-16" pipe 0.015" for H8 23-4" pipe 2.2 FLAW CHARACTERIZATION Location 1:
H8 23-16" 5
Flaw Description and Size:
Leakage through a single pinhole leak in an area of localized wall thinning.
The lowest thickness measurement in the area of the leak is 0:141" where the nominal wall thickness expected is 0.375".
The majority of the pipe wall thinning covers an area from the weld, downstream for a distance of approximately one to three inches and runs approximately five inches circumferentially at the six o'clock position.
Some wall thinning at the very bottom of the pipe continues out eight to ten inches from the leak location.
Flaw Location:
The leak is located at the toe of the weld of the slip-on~flange to pipe connection, downstream of CV-0826 at the discharge of the E-548 CCW heat exchanger about 24 inches from the main service water discharge header.
Evaluation Method:
Visual and Ultrasonic wall thickness measurements.
Flaw Type:
Single through wall pinhole in a localized area of general erosion.
Reference UT*Measurement Report:
RDW-01, RDW-02; Figure 1 Location 2:
H8 23-4" Flaw Description and Size:
Leakage through a single pinhole leak in an area of local thinning.
The lowest thickness measurement in the area of the leak is 0.094" where the nominal wall thickness expected is 0.237".
Coupled with the leak is a localized area of thinning of the weld, with only minor thinning of the adjacent pipe.
The localized area of thinning in the weld appears in the 8:30 to 11:00 o'clock position.
Flaw Location:
The leak is located in the toe of the butt-weld of the 4" manual isolation valve (MV-SW 136), downstream of the temperature control valve (CV-0822) at the discharge of the E-548 CCW heat exchanger.
Evaluation Method:
Visual and Ultrasonic wall thickness measurements.
Flaw Type:
Single through wall pinhole in a localized area of general erosion.
Reference UT Measurement Report:
RDW-01, MFS-03; Figure 1 2.3 PRELIMINARY FLAW EVALUATION
SUMMARY
6 Preliminary operability assessment details: Location l; HB 23-16" Method Used:
Code standard formula for minimum wall thickness based on internal pressure.
Minimum Wall Thickness:
0.053" based on Code allowable stress.
Period of Time to Reach Limiting Flaw Size:
The time period will be addressed in the final operability assessment and verified by period'c monitoring.
Evaluation
Reference:
EA-IO-SP-03316-02 Preliminary operability assessment details:
Location 2; HB 23-4" Method Used:
Verification of minimum wall for load case combinations of pressure, dead weight and seismic compared to Interim Operating Criteria (IOC) stress allowables.
Minimum Wall Thickness:
0.016" based on IOC allowables.
Period of Time to Reach Limiting Flaw Size:
The time period will be addressed in the final operability assessment.
Evaluation
Reference:
EA-IO-SP-03316-01, REV.O 2.4 END OF CYCLE FLAW EVALUATION
SUMMARY
Final Operability Assessment Details:
Method Used for the HB 23-4" and HB 23-16" Pipe Flaw:
The fracture mechanics (proposed code case N-513), branch reinforcement (proposed Code Case N-513) and wall thinning (Code Case N-480) methods were used.
Estimated Wall Erosion Rate:
The estimated wall erosion rate is 0.14 inches per year. Without the temporary non-code repair, for both leak locations it would take in excess of 18 months to reach the minimum wall limit at the leak locations.
With the addition
7 of the temporary repairs the wall erosion rate is not a concern.
Projected Flaw Size: The pipe wall reduction limit for each line using the Code Case N-480 limit of 0.3 times the pipe wall nominal thickness.
HB 23-4" :
HB 23-16":
Period of Time to locations will be where the core is completing a full 0.071" 0.113" Permanent Repair or Replacement:
Both leak Code repaired during the next refueling outage totally off-loaded.
Present plans are for core off-load during the 1994 refueling outage.
Provide a Discussion of Evaluation of Design Loading Conditions:
The method and design loading condition per the Code of record are ANSI B31.l-1973 with additional requirements per FSAR (i.e.,
faulted allowables of 2.4Sh)
Evaluation
Reference:
For HB 23-04:
EA-SP-03316-04, REV.O For HB 23-16:
EA-SP-03316-03, REV.O 2.5 FLAW MONITORING Walkdown Frequency:
System Engineering will be performing monthly walkdowns to inspect the leak locations.
Frequency of Follow-up NOE:
No other follow-up NOE is planned due to the substantial temporary repair that is being made.
Ultrasonic and radiographic examinations are not practical and indication of leakage can easily be observed via the operations walkdown inspections.
2.6 ADDITIONAL COMMENTS One leak is located in the HB 23-16" p1p1ng downstream of CV-0826 and the other in the butt-weld joining the HB 23-4" piping to the downstream end of valve MV-SW 136.
Based on NRC guidance, both flaws were evaluated using the wall thinning approach of ASME Code Case N-480 (per Generic Letter 90-05) and the branch reinforcement method of proposed ASME Code Case N-513.
In addition, the fracture mechanics method of Code Case N-513 was included in the calculations. Furthermore, due to the weld configuration on the HB 23-4" line and the inability to obtain all the data necessary to fully characterize the flaw, an interim operability analysis was performed in order to determine the minimum uniform wall thickness required to meet all interim operability loading combinations.
8 The calculations concluded the following:
For the HB 23-16" line, the piping satisfies the requirements of both the wall thinning and fracture mechanics methods of evaluation, but fails the branch reinforcement method described in the proposed Code Case N-513.
The calculated wear rate indicates the predicted wall thickness at the end of eighteen months will satisfy the wall thinning method requirements.
For the HB 23-4" line, the calculations indicate the interim operability criteria as well as those of the three flaw evaluation methods are satisfied.
Based on the above, both leak locations have sufficient structural integrity for continued service and qualify for temporary non-Code repairs.