ML20036C216
| ML20036C216 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 06/09/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20036C205 | List: |
| References | |
| NUDOCS 9306150277 | |
| Download: ML20036C216 (4) | |
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WASHINGTON, D.C. 205 % 4001 SAFETY EVALUATION BY THE 0FFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION RE0 VEST FOR RELIEF FOR DUKE POWER COMPANY MCGUIRE NUCLEAR STATION. UNIT 2 DOCKET NO. 50-370
1.0 INTRODUCTION
Technical Specification 4.0.5 for McGuire Nuclear Station Unit 2 states that inservice inspection and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed!in accordance with'Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required _ by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(1).
Section 10 CFR 50.55a(a)(3) states that alternatives' to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements 'would result.in hardship or unusual difficulties without a compensating inc~rease in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear. Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components.
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission
'in support of that determination-and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
By letter dated June 4,1993, Duke Power Company (the licensee) submitted to the NRC a request for relief (Relief Request 93-03) from a pressure test requirement of Section XI of the ASME Code. The licensee determined that to 9306150277 930609 PDR ADOCK 05000369 P.
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. perform the specific requirement would be impractical. The staff has evaluated the licensee's request for relief from the Code requirement, and its evaluation and conclusions are discussed in the following sections.
2.0 REQUIREMENTS AND SUPPORTING INFORMATION Code Reauirements:
The component for which the licensee is requesting relief is the 90* elbow socket weld, Weld Number NV2FW216-27, pipe Schedule 40, pipe size 2" SA-312/TP 304.
The weld in question is within the Letdown Header of the Chemical and e
Volume Control System (NV), between letdown orifice 2NVFE6200 and valve 2NV-458.
The ASME Code Section XI requirement that the licensee has determined to be impractical is that contained in ASME Code Section XI, 1980 Edition through Winter 1980 Addenda, Subsection IWC, Subarticle IWC-5222(a) System Hydrostatic Test.
Licensee's Basis for Reouestino Relief:
On May 31, 1993, Weld Number NV2FW216-27 developed a crack which resulted in.
about I gpm leak.
The leak was located downstream of the 2NVFE6200 letdown orifice in one of the socket welds associated with a 90' elbow within the piping system.
In response, the normal letdown flowpath was isolated and the alternate letdown flowpath (excess letdown) was established.
Following isolation of the leak, the weld was repaired. A liquid penetrant examination of the final pass of the weld repair was performed.
IWA-5214 specifies that a system hydrostatic test be performed of the component that was repaired prior to resumption of service.
Subsequent to the repair of the weld, a hydrostatic test was attempted.
Since this is a class 2 weld, IWC-5222 specifies the pressure and temperature at which the test is to be performed.
IWC-5222 requires that the test pressure be at least 1.25 times the design pressure for the system. The design pressure specified for this portion of the system is 2485 psig. Accordingly, the pressure range for the hydrostatic test would be 3100 psig, i
When.the system hydrostatic test was performed, a pressure of 2150 psig could only be achieved. The suspected reasons for not being able to reach the required test pressure was attributed to packing leakoff and/or to leakage past one or more of the valves used to form the boundary for conducting the test. At this pressure of 2150 psig, a VT-2 exam was performed and no evidence of leakage from the repaired weld area was observed.
This test pressure is well above the normal operating pressure that the weld would experience. The location of the repaired weld is downstream of' the letdown orifice. When the reactor coolant system fluids pass through this letdown orifice, a large pressure reduction occurs, resulting in an operating pressure t
of approximately 335 psig.
The test pressure that was achieved (2150 psig) is significantly greater than 1.25 times the expected normal operating pressure
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. of 335 psig.
Since there was no evidence of any leakage, reasonable assurance of the integrity of the weld repair to withstand the expected normal operating pressure of approximately 335 psig is provided.
In addition to the reduced pressure system hydrostatic test, a liquid penetrate test of the final pass of the weld repair was also performed.
When the system is returned to service, another VT-2 exam will be performed. The expected test pressure for this exam is approximately 335 psig. These two alternate tests, in combination with the reduced pressure system hydrostatic test, provides an equivalent means of verifying the adequacy of the weld repair.
If the requirement specified by the Code was imposed, a significant burden could occur.
To achieve the test pressure as specified by the code would require a significant effort to identify what is causing the inability to achieve this pressure, and possibly an extensive amount of time and effort to correct the problem.
There exists an immediate need to return to service this portion of the NV system.
Operating for an ertended period of time (24 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) with normal letdown isolated and only excess letdown flowpath inservice will result in primary side chemistry problems that may result in the need to shut down the unit pursuant to Technical Specifications 3.4.7 or 3.4.8.
Licensee's Proposed Alternative Examination:
In lieu of the system hydrostatic test to be performed, the following alternate testing is proposed:
1)
A VT-2 exam at a reduced test pressure of 2150 psig.
2)
A liquid penetrate test of the final pass of the weld repair.
3)
A VT-2 exam at normal operating temperature and pressure (650*F and 335 psig).
4)
Observe for possible leakage by monitoring inputs to the containment sump once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The proposed alternate tests 1 and 2 have already been performed.
The proposed alternate test 3 will be performed when the system is returned to service.
The proposed alternate test 4 will be implemented when the system is returned to service and will be continued until the unit is shut down for the start of the refueling outage, currently scheduled to begin July 1,1993.
3.0 STAFF EVALUATION AND CONCLUSION Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee determined that conformance with certain Code requirements are impractical for its facility and submitted supporting information. The staff has reviewed the licensee's submittal and agrees with the licensee that it is impractical to perform the Code-required VT-2 visual examination at the pressure specified by the Code.
The staff has reviewed the licensee's submittal and has concluded that compliance with the Code requirements would be impractical to perform because operating for an
o t extended period of time with normal letdown isolation and only excess letdown path flowpath inservice would result in primary side chemistry problems that may result in the need to shut down the unit pursuant to Technical Specifications 3.4.7 or 3.4.8.
The licensee has achieved a test pressure of 2150 psig verses the Code required hydrostatic test pressure of 3100 psig. As alternative examinations, the licensee performed liquid penetrant test on the final pass of the weld repair, a VT-2 examination of the weld repair at the reduced test pressure of 2150 psig and did not identify any leakage at the weld repair.
The licensee will also monitor containment sump conditions on a once per shift (each 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />) schedule.
Pursuant to 10 CFR 50.55a(g)(6)(i),
the staff has concluded that the licensee's request for relief may be granted as requested.
The alternative examinations should provide an acceptable level of quality and safety, and reasonable assurance that the structural integrity of the plant's systems, components, ar.d supports will be maintained.
Such relief is authorized by law and will not endanger life, property, or the common defense or security, and is otherwise in the public interest.
Relief has been granted giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Principal Contributors:
Victor Nerses Thomas McLellan Dated:
June 9, 1993 i
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