ML20204G818
| ML20204G818 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 03/17/1999 |
| From: | Alexander J BOSTON EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2.99.021, GL-90-05, GL-90-5, NUDOCS 9903260292 | |
| Download: ML20204G818 (4) | |
Text
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Boston Edison A BEC ENERGY COMPANY 10 CFR 50.55a Generic Letter 90-05 J. F. Alexander Nuclear Assesment Group Manager March 17,1999 BECo Ltr. 2.99.021 U. S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555 Docket No. 50-293 License No. DPR-35 4
Reauest for NRC Review of a Proposed Non-ASME Code Pipe Repair This letter reports degradation of a spool piece associated with Pilgrim Nuclear Power Station's (PNPS) salt service water (SSW) system. The SSW system is a moderate energy system and provides the ultimate heat sink for process building heat removal. The subject repair is to an area previously repaired by a non-ASME repair described in a Pilgrim letter to the NRC dated April 7,1998 (BECo letter 2.98.046). Verbal NRC permission to perform this repair was received February 18,1999.
A detailed discussion of the original temporary repair performed in accordance with Generic Letter (GL) 90-05 and, in part, ASME Code Care N-562 was provided in Pilgrim's April 7,1998, request for NRC review of a proposed Nun-/sSME Code pipe repair. The original repair was made. This request is considered an extension of the April 7,1998, request, the formal closure of which is pending with the NRC. Therefore, Pilgrim requests that this request be treated as an extension to the April 7,1998, request for purposes of NRC review and closure.
The most recently proposed repair adds structural build-up welding on the existing fillet Neld and the slip-on flange hub (See attached Figure 1). The thickness of the structural weld build-up is 1/8 to 1/4 inch from sector 22 to 29.
Description A pin hole leak has developed in the flange hub adjacent to the stainless steel patch installed on SSW spool JF29-9-5 downstream of butterfly valve MO-3805. The through-wall leak is q
attributed to localized loss of the rubber lining and subsequent erosion / corrosion of the carbon g
steel pipe flange. The potential concerns are with pipe / flange structural integrity and the effect from SSW leakage into the auxiliary equipment bay when pressure in this location is positive 9903260292 990317 O
PDR ADOCK 05000293 Page 1 of 4 P
PDR Pilgrim Nuclear Power Station, Rocky Hill Road, Plymouth, Massachusetts 0?360
cnd/or air in-l aktgs into tha flow stream whan tha pressura is n:gativa at this location. Tha SSW systsm is rIquirsd to d:livsr a minimum of 4500 GPM to ths RBCCW hsat exchanger (Hx) xvhen operating in the emergency mode. The discharge from TBCCW Hx. E-1228 ties into a common 22" discharge header with the discharge from RBCCW Hx E-2030 Evaluation Pilgrim considers this temporary repair an extension of the temporary repair described in Pilgrim's April 7,1998, letter to the NRC.
The pipe repaired under this request is 12 inches in diameter. Structural integrity for a comparable 18 inch pipe was evaluated by Calculation M-747 and bounds the 12 inch pipe.
Calculation M-747 shows a flaw up to 3.45 inches long is acceptable, but a limit of 3 inches is j
imposed by GL90-05. The structural evaluation was performed for a design pressure of 100 psi, which is much greater than the maximum operating pressures of about 1 psi to a slight vacuum that this pipe experiences. There is no structural concern with the pin hole leak and local area thinning of the flange.
As discussed in Pilgrim's April 7,1998, letter, Pilgrim performed an analysis using a hydraulic model of the SSW system to evaluate the actual pressure at the subject location in the SSW l
piping. This analysis showed the pressure at this location is slightly negative except at high tides. At high tides this location has a slight positive pressure, which resulted in service water leakage at the flaw site. No safety-related components are within the proximity of the leak location that would be directly affected. Leakage is accommodated by the design of the auxiliary bay. The small vacuum in the pipe at this location related to the changing tides results in air in-leakage but has a negligible effect on the flow rate through the heat l
exchangers or system performance.
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Therefore, the piping is structurally sound and capable of performing its design function and l
remains so after the weld repair of the pin hole leak.
I Conclusion of Evaluation The above discussion and that contained in Pilgrim's April 7,1998, letter demonstrate that the pipe structural integrity is acceptable. The effect from SSW leakage into the auxiliary j
equipment bay and/or air in-leakage into the flow stream (i.e., when the pressure is negative l
at this location) are acceptable Therefore, the system associated with the degraded spool piece is capable of performing its safety function; hence, it is operable.
The root cause determination indicates the pitting can be attributed to delamination of the rubber lining exacerbated by localized high flow velocities from throttling the upstream j
butterfly valve.
Monitorina Measures immediate compensatory measures are not required to assure system operability or safe operation because the piping is currently structurally sound and leakage does not adversely impact system operability, i
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.GL90-05 r:quir s that a minimum of L Y,ations be subjset to augm:ntzd inspections to cviluits other syst:m locations for similar digradition. All augm:nt:d inspection results at the 5 selected locations found values greater than the manufacturer's tolerance.
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' fteason for Non-Code Temporary Repair The impact a code repair would have on plant operation has been assessed. The code repair methods require removing one loop of the SSW system from service and cross tying the RBCCW systems during power operation. The removal of one loop of tbt SSW system would place Pilgrim in a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limiting condition for operation (LCO) unden hehnical Specification section 3.5.B.3. The code repair (spool replacement) requires removing a loop from service for greater than the LCO's 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (preliminary installation schedule estimates are 4 to 5 days), which would. result in an unnecessary p' ant shutdown.
Not cycling the plant is i
preferable from a safety perspective. Therefore, rehef is requested in accordance with the guidance of GL 90-05 for a non-code repair that can be executed without cycling the plant.
_Dgicription of Proposed Temporary Repair Repair requires welding the pin hole in accordance with an approved ASME IX procedure for P1 to P8 material for the fillet welds. The structural weld build-up is to be 1/8 to 1/4 inch thick.
The surface shall be examined by the visual test method prior to welding and shall satisfy the j
surface examination acc6ptance criteria of ND-4000.
The completed welds shall be examined by the visual test method and shall satisfy the surface examination acceptance criteria of ND-4000. Because this weld has been done on water-backed piping, this visual examination will not be performed sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after weld completion, and an in-service leak check is required.
Repair's Safety impaCl Pilgrim has performed a safety impact evaluation of this proposed repair which determined the following:
The safety-related functions of the SSW system remain qualified for plant design bases loads after comotetien of this temporary repair.
The proposed temporary repair does not increats the probability of occurrence or consequences of an accident or malfunction of equipment important to safety. The possibility of creating an accident or malfunction other than those evaluated in the UFSAR is not increased tecause the temporary modification does not introduce any interaction with other safety-related systems.
This temporary repair dees not create the possibility of a now type of accident or malfunction because no new failure mechanisms are introduced.
. Commidnents This letter continues the commitments found in Pilgrim's April 7,1998, letter for the original repair until the permanent ASME code repair / replacement is performed at the next scheduled outage exceeding 30 days and no later than startup from our next scheduled refueling outage (RFO#12).
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Should you requira furthtr information on this issus, plus3 contrct P.M.Kthl:r at (508) 830-7939.
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PMK/c's 299021 Attachments: Pictorial Depiction of the Repair a
cc: Mr. Alan B. Wang, Project Manager U.S. Nuclear Regulatory Commission
'roject Directorate 1-3 Region I Office of Nuclear Reactor Regulatbn 475 Allendale Road Mail Stop: OWFN 14B2 King of Prussia, PA 19406 l
U. S. Nuclear Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockville, MD 20852 l
Senior Resident inspector Mr. Peter LaPorte, Director l
Pilgrim Nuclear Power Station Massachusetts Energy Management Agency 400 Worcester Road P.O. Box 1496 Framingham, MA 01701-0313 Attn: Mr. James Muckerheide l
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