ML20057A364
| ML20057A364 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/01/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20057A362 | List: |
| References | |
| NUDOCS 9309140086 | |
| Download: ML20057A364 (7) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE RE00EST FOR RELIEF UNDER 10 CFR 50.55a(c)(6)(i)
METROPOLITAN EDISON COMPANY JERSEY CENTRAL POWER AND LIGHT COMPANY PENNSYLVANIA ELECTRIC COMPANY GPU NUCLEAR CORPORATION THREE MILE ISLAND NUCLEAR STATION UNIT NO. 1 DOCKET NO. 50-289
1.0 INTRODUCTION
i Technical Specification 4.2 for Three Mile Island Nuclear Station, Unit No. 1, states that inservice inspection (ISI) and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 ccmponents shall be t
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). The Code of Federal Regulations at 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 difficulty without a compensating increase 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) must meet the requirements, except the design and access prov' ions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Componants," to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The regulations i
require that inservice examination of components and system pressure tests conducted during the second 10-year interval comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the j
120-month inspection interval, subject to the limitations and modifications listed therein. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein.
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with certain examination requirements of Sectica XI of the ASME Code are not practical for its facility, information shall be submitted to the Commission 93091400P6 930901 PDR ADOCK 05000289 P
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. 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.
The licensee, GPU Nuclear Corporation (GPUN), submitted the Three Mile Island Nuclear Station, Unit 1 (TMI-1) second 10-Year Interval Inservice Inspection (ISI) program plan to the NRC by letter dated April 19, 1991. The second ISI interval for THI-l commenced on April 20, 1991. The plan commits to the requirements of the 1986 Edition of Section XI of the ASME Boiler and Pressure Vessel Code and was approved by the NRC on October 8, 1992.
By letters dated February 16, 1993, and April 16 1993, the licensee requested relief from 3
various Code requirements.
Relief requests 1, 2, and 3 were made in the February 16 letter.
Relief request 4 was made in the April 16 letter.
Specifically, the licensee requested (1) schedular relief for hydrostatically testing a portion of main steam line piping, (2) relief from the requirement to remove thermal insulation from pressurizer heater connections for the purpose of visual inspection, (3) approval to conduct visual inspection of emergency feedwater piping at lower than nominal operating pressure, and (4) temporary relief from the requirement to remove a bolt for visual inspection in certain cases when leakage is discovered on a bolted flange.
2.0 EVALUATION Relief Reouest 1 Components: Class 3 Main Steam System piping segments extending from MS-V2A/B to the turbine driver for the turbine-driven Emergency Feedwater (EFW) Pump, EF-Pl.
Code Reouirement: The 1986 Edition of ASME Section XI, Table IWD-2500-1 Examination Category D-B, Item No. D2.10 requires a hydrostatic test of Class 3 piping each 10-year interval.
Relief Reouested: GPU Nuclear requests schedular relief until the THI-l Cycle 11 Refueling Outage (September 1995) pending action by the ASME Section XI Code Committee to eliminate the requirement for a hydrostatic test.
This would result in a postponement of the test approximately 5 months beyond the 1-year extension allowed by the Code. The licensee noted that this would be only a 1-month extension under the previous definition of how the 10-year ISI interval was divided into three segments (i.e., 36 months compared to 40 months). Relief is requested for Cycle 10 operation to use the operational leakage test for this section of the Class 3 piping.
Basis for Reouest: The licensee considers it to be impractical to blank the relief valves in this segment of piping, blank the inlet nozzle of the turbine, and pin the affected piping supports only for the purpose of hydrostatically testing these relatively short lengths of piping (one is 40 feet, the other is 50 feet). The licensee proposes operational VT-2 leak
. testing in conjunction with the quarterly operational test of the EFW pump as an alternative to the hydrostatic test. ASME Code Case N-498 allows j
substitution of operational leakage tests for hydrostatic testing of Class 1 and 2 piping. The licensee states that a revision to Code Case N-498 has been drafted that, if approved, would allow substitution of operational leak tests for hydrostatic tests for Class 3 piping as has already been approved by the NRC for Class 1 and 2 piping. The staff has confirmed that the Code Case is being revised to allow alternative testing for Class 3 piping.
This revision must be reviewed and approved by the ASME Section XI Code Committee and the ASME Main Committee and endorsed by the NRC before it can be used for permanent relief to the Class 3 piping hydrostatic test requirement.
Assessment: The staff has no advanced knowledge that the revision to Code Case N-498 will eventually be approved by ASME and endorsed by the NRC.
It is possible that volumetric testing (ultrasonic or radiographic) could be required in addition to the proposed operational leak testing. The licensee has provided adequate justification to defer the hydrostatic test required by the Code until the end of Cycle 10 (Refueling Outage llR). At that time, the test will have to be performed as required by the Code or alternative testing performed if Code Case N-498 has been approved by ASME and endorsed by the NRC.
In the interim, the staff hereby grants the schedular relief as requested pursuant to 10 CFR 50.55a(a)(3)(ii).
Relief Recuest 2 Components: Class 1 Pressure Retaining Bolted Connections (pressurizer heaters)
Code Recuirement: The 1986 Edition of ASME Section XI, Table IWB-2500-1, Examination Category B-P, Item B15.20 and B15.21 requires a system leakage test each refueling outage and a hydrostatic test once each 10-year interval.
NRC Safety Evaluation dated October 8,1992 granted relief from VT-2 visual test for the Class 1 bolted connections with two conditions:
(1) a minimum of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> at nominal operating pressure before VT-2 visual examination of the insulated connections; and (2) the insulation be removed from the affected Class 1 bolted connections during each refueling outage for a VT-3 visual examination.
Relief Recuested: The licensee has requested relief from the requirement to remove insulation from the pressurizer heaters for the purpose of visual inspection. The proposed alternative inspection would be to conduct a VT-2 leakage test (visual examination) of the areas around the pressurizer heater electrical connections each refueling interval with the plant at Hot Shutdown conditions but with the insulation around the heater connections installed.
Basis for Recuest: The licensee is concerned with the potential damage to the he;ters associated with removal of the insulation around the heater connections and with the personnel radiation exposure associated with that operation. Wear and tear of the heater cable jackets has been noted to result in the past from activities such as removal and replacement of the insulation.
There are a total of 117 heater elements in three banks. To date, 38 of these heaters have become inoperable for various reasons. A minimum of 63 elements are needed for operational purposes. The licensee has performed this inspection in the past and has never found evidence of leakage. The licensee also noted that this closure is different than the typical bolted connection
. partly because some of the joints are seal welded and that if the seal welds leaked, the leakage would be apparent without removal of the insulation. The licensee has concluded that the benefit to be derived from removal of the insulation in the area of the pressurizer heater connections does not justify actions that could potentially cause significant damage to pressurizer heater connections.
Assessment: The staff agrees that compliance with the Code requirement to remove insulation from the pressurizer heater electrical connections at THI-l for leakage testing results in hardship or unusual difficulty without a compensating increase in the level of safety or quality. The stipulation in the previous Safety Evaluation, that the pressurizer be at nominal operating pressure a minimum of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> before conducting the VT-2 visual examination of the insulated ccnnections, is still required. The staff finds that the proposed alternative provides an acceptable level of quality and safety. On the basis of the discussion above, the staff hereby grants the requested relief pursuant to 10 CFR 50.55a(a)(3).
Relief Recuest 3 Components: Six-inch Class 2 EFW piping from the EF-V30 control valves to the EF-V12 check valves Code Reauirement: ASME Section XI Table IWC-2500-1 Category C-H requires a VT-2 leakage Test each inspection period.
IWC-5221 states that the nominal operating pressure shall be acceptable as the system test pressure.
Relief Reouested:
GPU Nuclear requests relief from testing the EFW piping at nominal pressure for EFW operation (~1050 psig). As an alternative, GPUN proposes to perform the VT-2 leakage test at nominal operating pressure for the Once Through Steam Generators (OTSG), which is about 900 psig.
Basis for Recuest:
The EFW system is a standby system used only for emergency addition of feedwater to the OTSGs.
The only other time the EFW pumps are operated is for testing in accordance with the Technical Specifications and the Inservice Testing (IST) program. Testing this section of piping at nominal EFW pressure requires operating one or more EFW pumps and injecting room temperature condensate onto the hot tubes in the upper region of the OTSGs. This thermal shock increases the likelihood of initiating or propagating OTSG tube cracks. The water from the condensate storage tank is also highly oxygenated, causing increased corrosion in the OTSGs. The staff has already agreed with minimizing injection of cold oxygenated water into the OTSGs in relief granted in the Safety Evaluation (dated October 3,1986) for the second 10-year IST program.
The leakage test for welds in this piping would be performed using the corresponding OTSG as the pressure source if there is sufficient backleakage past check valves EF-V12A/B.
If there is not sufficient backleakage, a hvdrostatic test pump would be the source of pressure and the piping will be pressurized to slightly less than OTSG pressure (to avoid unseating the check valves and potentially creating backleakage).
4
. The licensee evaluated alternatives that would allow this section of piping to be tested at nominal EFW pressure without injecting cold oxygenated water into the OTSGs. One option would involve throttling the EFW Pump discharge control valves EF-V30A/B/C/D to minimize the amount of condensate injected into the OTSGs.
However, the pressure drop across the throttled valve would still result in a pressure less than nominal EFW pressure in the piping covered by this request. Another option considered was to replace the tilting disc check valves with stop check valve so that the valves could be used to isolate that section of piping for hydrostatic testing. The licensee concluded that the cost of this modification would be too high considering that the only benefit gained would be a slight increase in pressure during the leakage test.
The section of piping included in this relief request falls within the inservice inspection (ISI) program requiring volumetric and surface testing an a periodic (sampling) basis.
Three of the eleven welds in this part of the t
EFW system are between the V30 and V12 valves. All welds are similar in types and welding techniques and experience similar service conditions.
This gives added assurance that, if degradation of the welds should occur, it should be detected by nondestructive examination before leaks develop.
The licensae concluded i the benefit to be gained by conducting the test at only a slightly higher te.m pressure does not justify the cost and risk of the actions that would be required to meet the Code requirement.
Assessment: The staff has reviewed this request and finds that the pressure test at slightly lower than normal operating pressure, in conjunction with the periodic volumetric and surface testing, provides an acceptable level of quality and safety. On the basis of the discussion above, the staff hereby grants the requested relief pursuant to 10 CFP. 50.55a(a)(3)(i).
Relief Reauest 4 4
Components:
Bolted connections (Class 1)
Code Reouirement: The 1986 Edition of ASME Section XI, Section IWA-5250(a)(2) introduced a requirement to remove Class 1 bolting and perform a VT-3 visual inspection at bolted connections identified as leaking during an ASME Section XI system pressure test.
i Relief Reauested: The licensee has requested temporary relief (for one operating cycle) from the absolute Code requirement that requires removal of j
at least one bolt in all cases when a bolted connection is found to have j
leakage.
The licensee has proposed that in certain such cases, a decision to 4
remove a bolt should be preceded by an engineering evaluation when the connection cannot be isolated without delaying plant startup or shutting the plant down.
In their April 16, 1993, the licensee stated its belief that removal of bolting for examination should not be required (1) if the bolts / studs have been replaced or inspected during the current plant or system j
outage and have little or no exposure to service conditions, or (2) the bolts are part of a non-face bolted connection and there is sufficient access and l
visibility of the bolt / stud shank for inspection without bolt removal.
. When bolt removal would require a delay in plant startup or require a plant shutdown because the connection cannot be isolated, the licensee has requested deferral of bolt reme' ai until the next time the system containing the connection is out of service (no later than the next refueling outage) if an engineering evaluation concludes that the connection will not degrade appreciably from leakage of the process fluid before the next scheduled plant or system outage.
Periodic evaluation / observation of the leaking connection would be made at least monthly until the leak is repaired.
Basis for Reouest: The purpose of bolt removal in the event of leaking bolted flanges is to inspect the bolt material for degradation due to corrosion.
The licensee believes that an absolute requirement to remove at least one bolt in a leaking bolted connection without an engineering evaluation of the necessity to do so could present a hardship or unusual difficulty and potentially unnecessary personnel exposure without a compensating increase in the level of quality and safety. This would be the case if bolt removal would delay a plant startup or require a plant to shut down and cool down, imposing what may be an unnecessary thermal cycle on the plant. The licensee cited certain types of non-face adjacent bolted connections, such as reactor coolant pump main flanges, where the bolt shanks are not hidden by the flanges and can therefore be adequately examined visually without removal. The licensee also cites cases where the bolt had recently (during a current outage period, for example) been inspected for this purpose or replaced.
In these cases the condition of the bolting material is known and an engineering evaluation would be appropriate to assess expectations of satisfactory bolt performance until the next scheduled opportunity to remove, inspect and/or replace one or more bolts.
The licensee's submittal stated that the ASME Section XI Code Committee has recognized the hardship imposed by the required removal of bolting, especially during plant startup, and is drafting a Code Case that would alleviate the undue burden imposed by requirements for bolt removal introduced in the 1986 Section XI Code Edition.
The schedular exemption (until the end of Cycle 10) is based on the licensee's expectation that a Code Case providing the relief requested will be approved by ASME and endorsed by the NRC.
Assessment:
The staff has reviewed this request and agrees that strict compliance with the Code requirements for bolt removal in all cases could result in hardship or unusual difficulty without a compensating increase in the level of safety or quality. However, lacking a specific situation at THI-1 that requires such relief, the staff denies relief at this time on the basis that such blanket relief, even for only one fuel cycle, would preempt the normal process of the ASME Code Committee developing relief via the Code case process and requesting NRC approval of that Code case.
Should a specific hardship situation arise at THI-1, the staff prefers to handle the relief requested on a case basis as has been done for other licensees. Therefore, this relief is denied.
3.0 CONCLUSION
The staff has reviewed GPUN's request for relief and the supporting i
justification.
The cited regulation (10 CFR 50.55a(g)(5)) requires a determination by the licensee that a Code requirement is impractical for that facility and 10 CFR 50.55a(g)(6) requires the Commission to evaluate such determinations. The justification provided by GPUN demonstrates the burden that would re; ult from adherence to the Code requirements discussed above at THI-l could p.esent a hardship or unusual difficulty (including unnecessary personnel exposure) without a compensating increase in the level of quality and safety. With the exception of Relief Request 4, the staff has concluded that GPUN's request for relief is justified in recognition of the proposed alternative testing and/or engineering evaluations and therefore grants the relief pursuant to 10 CFR 50.55a(a)(3).
The NRC staff has determined that granting this relief pursuant to 10 CFR 50.55a(a)(3) is authorized by law and will not endanger life, property, or the common defense and security and is otherwise in the public interest.
Principal Contributor:
R. W. Hernan Date: September 1, 1993 i
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