ML20042F905
| ML20042F905 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/01/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20042F904 | List: |
| References | |
| NUDOCS 9005100138 | |
| Download: ML20042F905 (4) | |
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,e ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF FROM CODE TEST REQUIREMENTS FOR RHR SPRAY PIPING TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS 50-327 AND 50-328 l
1.0 INTRODUCTION
By letters dated December 20, 1989 and March 5, 1990, the Tennessee Valley Authority (TVA) requested relief from the hydrostatic pressure test require-ments of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Csde (Code). The Section XI Code-Edition and addenda applica-ble to Sequoyah Nuclear Plant, Units 1 and 2 are the 1977 Edition with addenda through Summer 1978. The relief was for the containment spray piping oftheResidualHeatRemoval(RHR)Systemforbothunits. The relief is associated with the plant modifications on this piping during the 1990 Cycle 4 refueling outage for each unit to meet the commitments made for upgrading the units to satisfy the requirements in Regulatory Guide 1.97.
l The eight-inch diameter RHR spray piping for each train between the heat exchanger and the containment spray header is to be modified to receive an annubar flow element to indicate spray flow.
This modification requires a 1.06-inch dia-meter hole to be drilled into the piping and a 1.25-inch fitting welded onto the outside of the piping. The Code requires that a hydrostatic pressure test of the system be performed following a repair, replacement, or alteration of the system or component, during which welding of the pressure retaining bound-ary was performed.
Because the piping affected by the modification is an open-ended section between the spray header isolation valves and the spray header in containment, the Code provides that a flow test that demonstrates the t
flow is unimpaired in the piping is acceptable in lieu of a system pressure-test.
2.0 CODE REQUIREMENT Paragraph IWC-5222, Item c, of Section XI of the ASME Code states the following:
... For open ended portions of discharge lines in nonclosed systems (such as containment spray header), any test that demonstrates unimpaired flow shall be l
acceptable in lieu of a system pressure test."
i The test used by TVA to demonstrate unimpaired flow through the modified RHR spray piping consists of blowing hot air into the piping and through the containment spray nozzles and taking an infrared photograph of the spray header to ensure that all the piping and the nozzles are open.
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i 3.0 CODE RELIEF REQUEST In its letter dated December 20, 1989, TVA proposed performing a special hydro-static test in lieu of a system flow test through the open-ended portions of the RHR spray piping.
In evaluating this request, the staff discussed Code Case N-416 with TVA.
Code Case N-416. " Alternative Rules for Hydrostatic Testing of Repair or Replacement of Class 2 Piping", is an NRC accepted Code case which applies to this request for relief because the affected RHR spray piping is Class 2 piping that cannot be isolated by existing valves to perform a hydrostatic The Code Case allows the system hydrostatic test to be deferred pressure test.
until the next regularly scheduled test provided that certain conditions are met:
(1) Prior to or innediately upon return to service, visual inspection (VT-2) for leakage shall be conducted during a system functional test or during system inservice test in the repaired or replaced portion of the piping, and (2) The repair or replacement welds shall be examined in accordance with IWA-4000 and IWA-7000 of Section XI using volumetric examination methods (IWA-2330) for full penetrations welds or surface examination methods (IWA-2220) for partial penetration welds.
TVA explainef in its letter dated March 5,1990 that the required method of weld examinadon in the Code Case, for the full penetration welds for the installation t.f the annubar flow element in the RHR spray piping, is impracti-cal and might pr@ce indeterminate results, and, therefore, the Code case is not applicable to tH s situation.
4.0 DESCRIPTION
OF THE MODIFICATION TVA discussed in its letters that an open-ended section of piping between the heat exchanger and the RHR containment spray header is to be modified to receive a branch connection.
This section of piping is eight inches in dia-meter and is American Society of Mechanical Engineers (ASME) Class 2.
The modification requires a 1.06 inch diameter hole be drilled in the eight-inch piping and a 1.25-inch fitting be welded onto the outside wall of the pipe.
The normal installation method is to weld the sockolet in place and then drill out the inside diameter of the sockolet and the pipe wall to which it is connected to the desired dimension (1.06 inches). TVA stated that this drilling process removes both the parent metal and the root head of the weld leaving a-full penetration attachment weld.
5.0 PROPOSED ALTERNATIVE EXAMINATION Based on the letters dated December 20, 1989 and March 5, 1990 and discussions with the staff at Sequoyah TVA proposed performing the following:
(1)a special hydrostatic pressure test on the piping and (2) a VT-2 visual examina-tion of the welds for leakage at the welded connections.
The affected piping
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3-would be pressurized by filling it with water up to the maximum elevation l
possible without water discharging into containment through the spray header.
6.0 LICENSEE'S BASIS FOR REQUESTING RELIEF TVA stated that the hot air flow test which is used to demonstrate unimpaired flow in the RHR spray piping is a difficult test to perform since it requires a special air compressor to be brought onsite, which requires a five to seven week lead-time, to provide a source of heated compressed air and a special infrared camera to be used. This test is performed at 5-year intervals at Sequoyah as required by the plant Technical Specifications; however, this periodic test schedule does not coincide with the RHR spray modification in the e
Cycle 4 refueling outages for the units.
TVA stated in its letter dated March 5,1990 that the radiography of the 1.25-inch branch connection would offer no guarantee in the results because of large density changes over a cross section of the weld and the rapid curvature of a fitting of this size. TVA estimates a six-to eight-hour timeframe to perfonn a radiograph of this geometry and configuration with the possibility for indeterminate results. Ultrasonic examination would also be impractical because of the lack of a surface (parallel to the weld) of sufficient length to allow an ultrasonic scan.
TVA considers the alternative examination technique to be the best method available for testing the branch connection weld and an adequate demonstration of leak tightness of the modified RHR piping.
TVA stated that the unimpaired flow test required by the ASME Section XI code would have only subjected the weld to a flow of air past the weld. The alternative test proposed by TVA would subject the weld to a column of water with a static head pressure of approximately 45 pounds per square inch followed by a VT-2 visual leakage examination.
7.0 EVALUATION The staff has evaluated this request for relief to the requirements in Para-graph IWC-5222, Item c, of Section XI of the Code. The Code-required examina-tion methods would only test for flow blockage of the modified RHR spray piping whereas. the alternative examination method would be a measure of the leak tightness of the welds on the affected piping.
The Code Case N-416 allows for system hydrostatic tests to be deferred until the next regularly scheduled l
tests; however, the proposed alternative examination for this case does not meet the requirements of the Code Case N-416.
The proposed alternative examina-tion method is an adequate demonstration of leak tightness of the welds on the affected RHR piping which is at least at the same level of quality and safety as the five-year hot-air flow test and without the hardship described by TVA for this flow tett.
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The alternate method of the special pressure test of the piping and the surface examination of the piping and the surface examination of the weld will assure that the welded instrumentation connection to the piping is sound, and, therefore, provides an acceptable level of quality and safety.
This is because the affected piping is an open-ended section and discharges directly to the containment which has the low design pressure of 12 psig.
8.0 CONCLUSION
i The staff concludes pursuant to 10 CFR 50.55a(a)(3)(i) that the proposed alternative method to test the welds in the modified RHR spray piping provides an acceptable level of quality and safety at Sequoyah. Therefore, TVA should
've granted the requested relief from the test requirements in Paragraph IWC-5222, Item c, of Section XI of the Code.
Principal Contributor:
J. Donohew and G. Johnson Dated: May 1, 1990 4
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