ML20057D635
| ML20057D635 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/28/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20057D628 | List: |
| References | |
| NUDOCS 9310050097 | |
| Download: ML20057D635 (9) | |
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NUCLEAR REGULATORY COMMISSION
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WASHINGTON, O C. 20555-oooi ENCLOSURE
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1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
FOR INSERVICE PRESSURE TEST REllEF RE0 VESTS ISPT-2 AND ISPT-3 l
TENNESSEE VALLEY AUTHORITY SE000YAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NUMBERS 50-327 AND 328 1
1.0 INTRODUCTION
Technical Specification 4.0.5 for the Sequoyah Nuclear Plant (SQN), Units 1 and 2, states that inservice inspection and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be i
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(a)(3)(i) and 10 CFR 50.55a(g)(6)(i).
Paragraph 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 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) 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.
The regulations require that inservice examination of components and system pressure tests conducted during each 10-year interval comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by I
reference in 10 CFR 50.55a(b) on the date 12 months prior to the start of the 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 modification listed therein.
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with 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 9310050097 930923-PDR ADOCK 05000327 p
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2 lif e, 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 November 17, 1992 Tennessee Valley Authority (the licensee) submitted three requests for relief, designated ISPT-2, ISPT-3 and ISPT-4, pertaining to the hydrostatic test requirements of ASME Section XI.
The licensee provided supplemental information in a submittal dated April 2, 1993.
A telephone conference call was held on April 21, 1993 to discuss the licensee's technical bases for these requests.
The licensee responded in a letter dated May 28, 1993, with additional information on ISPT-2 and ISPT-3.
In additien, TVA withdrew relief request ISPT-4 because the licensee determined that the piping configuration is such that the appropriate Code hydrostatic tests may be performed.
The NRC staff has evaluated the remaining two requests in the following sections pertaining to both Sequoyah units.
2.0 STAFF EVALUATION 2.1.0 Relief Request ISPT-2 Safety Injection Systems 2.1.2 Components Subject to Examination The components subject to examination are pressure boundary piping between check valves or between a check valve and other types of valves.
The ASME Code Class 1 piping is located in the hot-leg and cold-leg injection lines.
The piping ranges in diameter from 3/4 inch to 10 inches and is identified by location and diameter in the licensee's letter dated November 17, 1992.
2.1.2 Code Requirements (Licensee's letter dated April 2, 1993)
ASME Section XI Subsection IWB-2500, Table IWB-2500-1, Category B-P Footnote I states that "The entire pressure retaining boundary of the reactor coolant system is subject to system pressure test conducted in accordance with IWA-5000 with the exceptions specified in IWA-5214 when system pressure tests are conducted for repaired, replaced or altered components."'
2.1.3 Impractical Code Requirement The licensee indicated that a hydrostatic pressure test on the segments of piping that contain at least one check valve cannot be performed to the pressures required by ASME Section XI without a significant hardship.
2.1.4 Licensee's Basis for Relief The subject injection line segments are located between the primary and secondary safety-injection check valves. The hot-leg injection line segments are not pressurized during normal operation or during cold shutdown. The cold-leg injection line segments are pressurized to the pressure of the safety-injection accumulators (650 pounds per square inch gauge [psig]) during normal operation.
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3 The pressurization of these line segments to a test pressure equivalent to nominal RCS pressure (2235 psig) during Modes 4, 5, or 6 is not possible because of insufficient RCS pressure to keep the primary check valve closed against the test pressure.
Pressurization of these line segments to full RCS pressure during Modes 1, 2, or 3 would risk injection of cold water into the RCS.
i Full compliance with the code would require either removal of the primary check valve disks or installation of temporary piping to provide a flow path around the primary check valve.
This option requires a modification to SQN's RCS, which would place an unusual hardship on the plant staff and would require several days of critical path outage time for installation and removal.
2.1.5 Licensee's Proposed Alternative Testing The cold-leg injection line segments will be visually examined (VT-2) during the RCS leakage test conducted during start-up following each refueling i
outage.
This leakage test is performed at safety-injection accumulator pressure (nominally 650 psig).
The hot-leg injection line segments will be visually examined (VT-2) once every 10 years with the unit in Mode 3.
The pressure during this test will be the discharge pressure of the safety-injection pump, which is approximately 1500 psig.
2.1.6 Staff Evaluation The staff evaluated all the letters described in Section 1.0 " Introduction" and participated in a conference call on April 21, 1993.
The staff agrees with the licersee that a modification to the existing plant design would be required to achieve the test pressures specified by the ASME Codes. The staff evaluated only the ASME Code requirement defined in Section 2.1.2 pertaining to the segments of pipe identified by the licensee.
This clarification is necessary because the licensee's letter dated November 17, 1992 invoked ASME Code Case N-498.
ASME Code Case N-498 was referenced in Regulatory Guide 1.147, (Revision 9), because of an urgent need for this case.
The ASME Council decided in N-498 that a system leakage test, with conditions, is a suitable alternative to the scheduled 10-year hydrostatic pressure test for ASME Class 1 and 2 components. However, Code Case N-498 is not a regulatory requirement.
Regulatory Guide 1.147 states "The ASME considers the use of Code Cases to be optional for the user and not a mandatory requirement."
Therefore, 10 CFR 50.55a does not have provisions for relief to a portion of a code case because the licensee voluntarily invokes the code case.
Therefore, this safety evaluation is independent of the use of Code Case N-498.
In order to determine whether relief should be granted, the staff requested that the licensee provide the following:
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4 (A) A description of the nondestruction examination (NDE) that has been performed on the subject lines.
A list of the welds in the lines that have been examined, and type of examination.
(B) A determination of whether any degradation has occurred in the subject lines. A description of any repairs or replacements in the lines since the original hydrostatic test.
In the letter dated May 28, 1993, TVA responded with the following information:
There are four different pipe sizes within the ISPT-2 piping boundary:
10 inches, 6 inches, 2 inches, and 1-1/2 inches.
The following is a list, by size, of the construction code NDE requirements for this piping:
10-inch piping:
Fit-up (preweld inspection)
Final visual (postweld inspection)
Dye penetrant Radiograph 6-inch piping:
Fit-up (preweld inspection)
Final visual (postweld inspection)
Dye penetrant Radiograph 2-inch piping:
Fit-up (preweld inspection)
Final visual (postweld inspection)
Dye Penetrant 1-1/2-inch piping:
Fit-up (preweld inspection)
Final visual (postweld inspection)
Dye Penetrant The requirements performed for preservice and inservice examinations are found in SQN's Inservice Inspection Program.
The requirements are as follows:
1.
For pipe size equal to and greater than four-inch nominal pipe size, ultrasonic and dye penetrant examinations are required.
2.
For pipe size less than 4-inch nominal pipe size, dye penetrant examinations are required.
3.
In accordance with SQN's code of record for ISI, 25 percent of the total population of ASME Code Class 1 piping welds are required to receive an ISI during the first 10-year interval.
This means that the total population of Class I welds will receive one ISI during the 40-year life of the plant.
Construction code NDE and preservice examinations are performed after repairs or replacement by welding.
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TVA also listed the location size, rating, materials and internal work order requests for the check valves within the ISPT-2 piping boundary that were replaced during the first 10-year interval. The construction code NDE and the preservice examinations previously described were performed for these valves and pipe replacements.
No further repair or replacements on any pipe welds have been performed within the scope of ISPT-2.
The NRC staff has evaluated the NDE performed by the licensee and the licensee's alternative testing.
The large diameter piping welds were subject to volumetric examination during construction.
The small diameter pipe was liquid penetrant examined.
Inservice inspections were performed on a representative sample of ASME Class I welds.
The licensee has not detected any generic inservice degradation in segments of pipe subject to examination.
The licensee proposed to conduct a visual examination at a pressure less than ASME Code requirement as an alternative to the required hydrostatic test.
The NRC staff determined that the licensee's proposed alternative will be conducted at a sufficiently high pressure, when compared with the hydrostatic test requirement, to detect an unacceptable condition.
The staff concludes that the proposed alternative, as defined in Section 2 1.5, in combination with the NDE that has been performed and the service experience, will provide an acceptable level of quality and safety. Therefore, relief may be granted pursuant to 10 CFR 50.55a(a)(3)(i) for the pipe segments identified by the licensee.
2.2.0 Relie# Request ISPT-3 Reactor Coolant Pressure Boundary 2.2.1 Components Subject to Examination The components subject to examination are ASME Code Class 1 vents, drains, test and fill piping that range in diameter from 3/4 inch to 2 inches. The licensee identified the location of the segments of pipe in his letter dated November 17, 1992.
2.2.2 Code Requirement (Licensee's letter dated April 2,1993)
ASME Section XI Subsection IWB-2500, Table IWB-2500-1, Category B-P, Footnote I states that "The entire pressure retaining boundary of the reactor coolant system is subject to system pressure test conducted in accordance with IWA-5000 with the exceptions specified in IWA-5214 when system pressure tests are conducted for repaired, replaced or altered components."
2.2.3 Impractical Code Requirement A hydrostatic pressure test on the segments of piping identified is impractical and cannot be performed to the pressures required by ASME Section XI without a significant hardship due to the potential for high radiation exposures to personnel.
2.2.4 Licensee's Basis for Relief Various piping segments are located in open-end tailpipes that serve as vent, drain, test, or fill lines.
Manual valves and flanges bound these piping
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segments to provide the design-required double isolation at the reactor coolant pressure boundary.
These piping segments are not normally pressurized.
Pressure testing of these piping segments at nominal operating pressure in Mode 3 would require that the inboard isolation valve be opened when the reactor coolant system (RCS) is at full temperature and pressure (547*F and 2245 psig).
The action would violate the design requirement for
-double isolation valve protection.
The potential for spills when opening the system presents a significant risk of personnel contamination.
Pressure testing in Mode 6 would require that a hydrostatic pump be connected at each segment location.
However, for some segments there is no connection available and would require a modification for installation of a pump connection.
These piping segments are located in high-radiation areas and testing would result in high-personnel radiation exposure. A breakdown of the dose estimates for each radiation area in the plant is provided below:
1.
RCS Loop Drains 6 items at 10 person-hours per item 300 millirem (mrem)/ hour 18,000 person-roentgen equivalent man (person-rem) 2.
Reactor Vessel Head Vents 2 items at 10 person-hours per item 150 mrem / hour 2 items at 8 person-hours per item 20 mrem / hour 3.320 person-rem 3.
Pressurizer Spray Vents 2 items at 10 person-hours per item 200 mrem / hour 4.000 person-rem 4.
Excess Letdown Drain 1 item at 8 person-hour per item 50 mrem / hour 0.400 person-rem 5.
RCS Seal Drains and Vents 4 items at 8 person-hours per item 20 mrem / hour 4 items at 8 person-hour per item 50 mrem / hour 2.240 person-rem Based on estimated durations and actual survey data from SQN's cycle 5 outages, a total dose estimate of 27.960 person-rem is predicted for the subject pressure test.
These radiation exposure estimates are based on a pressure test in Mode 6 when each of the blind flanges would have to be removed, a test flange installed, and a hydrostatic pump connected.
Personnel would remain in the area to perform the test, disconnect the test equipment, and reinstall the blind flange.
These piping segments are visually inspected each refueling outage as the unit returns to operation.
These segments are not specifically pressurized past the first isolation valve for this inspection.
It is possible that the piping is pressurized because of leakage at the first isolation valve. With these
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inspections being performed approximately six times in each inspection interval, the increase in safety achieved from the required nominal operating pressure test is not commensurate with the hardship of performing such testing.
2.2.5 Licensee's Proposed Alternative Testing:
These piping segments will continue to be visually inspected following each refueling outage for leakage and evidence of past leakage during the RCS leakage test.
This test is conducted with the RCS at full operating temperature and pressure.
2.2.6 Staff Evaluation The staff evaluated only the ASME Code requirement defined in Section 2.2.2 pertaining to the segments of pipe identified by the licensee.
The staff agrees with the licensee that a modification to the existing plant design would be required to achieve the test pressure required by the ASME Code and compliance could result in significant radiation exposure to personnel. The Safety Evaluation is independent of the use Code Case N-498.
(See 2.1.6 regarding the status of code cases).
In order to determine if relief should.
be granted, the staff requested that the licensee provide the following:
(A) A description of the NDE that has been performed on the subject lines.
Include a list of the welds in the lines that have been examined and type of examination.
(B)
A determination of whether any degradation has occurred in the subject lines. Describe any repairs or replacements in the lines 1
since the original hydrostatic test.
(C)
Details of the work sequence to explain the reason for such high man-rem exposure.
(D)
Details to explain the reason it is impractical to connect a pump to pressurize vents and drains.
In the letter dated May 28, 1993, TVA responded with the following information:
" Performance of the pressure test during Mode 3 requires that the-isolation valves be opened with the reactor coolant system (RCS) at full pressure and temperature (2235 pounds per square inch gauge, 547'F).
Personnel safety concerns have been raised for this mode of testing.
The concerns are as follows:
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If the test is performed while in Mode 3 during plant shutdown, there is a concern about a possible gasket failure when the isolation valve is open and full RCS pressure is applied to the blind flange and gasket.
Since the test personnel would be directly facing the valve and blind flange when opening the valve, the potential exists for exposing the personnel to high-temperature, high-pressure RCS fluid.
"2.
If the test is performed in Mode 3 during plant start-up, the same concerns will exist for those blind flanges that may not be opened during a plant shutdown. The piping between the isolation valve and the blind flange will contain pressurized fluid for the remainder of the operating cycle even after the isolation valve is closed. When the unit is brought down again for the next refueling outage, the same potential for personnel injury would exist for maintenance personnel when removing blind flanges for venting, draining, or any other maintenance activities on the RCS."
Performance of the pressure test in Mode 6 presents an as-low-as-reasonably-achievable concern.
Each of the blind flanges would have to be removed, a test flange installed. and hydrostatic pump connected.
Personnel would remain in the area to perform the test, disconnect the test equipment, and reinstall the blind flange.
The dose estimates provided for ISPT-3 in TVA's November 17, 1992, letter were based on this method of testing.
There have been no repairs or replacements on any pipe weld within the scope of ISPT-3.
Piping within the scope of ISPT-3 is either 3/4-inch or 2-inch diameter.
The 3/4-inch-diameter piping (piping with blind flange connecticns) is exempt from scheduled ISI because of size.
The 2-inch-diameter pipe (pipe without blind flanges) is included in the ISI program.
There are 25 welds within the 2-inch-diameter piping that have been examined under the ISI program using the liquid penetrant method.
All welds were accepted.
One weld had a 3/4-inch linear indication that was removed. The weld was reexamined and found acceptable.
The NRC staff has determined that the ASME code requirement is impractical for the existing configuration at Sequoyah, in addition, the staff has evaluated the NDE performed by the licensee and the licensee's alternative testing.
A representative sample of the 2-inch diameter piping was liquid penetrant tested as part of the ISI program. Although the 3/4-inch-diameter pipe is exempt by size from volumetric and surface examinations, periodic visual examinations for leakage are required by the ASME Code.
The licensee has not detected any generic inservice degradation in the subject segments of pipe.
As an alternative, the licensee proposed to visually inspect following each refueling outage for leakage and evidence of past leakage during the RCS leakage test.
This test is conducted with the RCS at full operating temperature and pressure. The staff determined that the licensee's proposed alternative will be conducted at a sufficiently high pressure, when compared with the hydrostatic test requirement, to detect an unacceptable condition.
The staff concludes that the proposed alternative, as defined in Section 2.2.5, in combination with the NDE that has been performed and the service experience, will provide an acceptable level of quality and safety for the pipe segments identified by the licensee.
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9 Therefore, relief may be granted pursuant to 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(g)6)(i).
3.0 CONCLUSION
Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee determined that conformance with certain Code requirements is impractical for its facility and submitted supporting information.
The staff has reviewed the licensee's submittal and has concluded that relief can be granted as requested for both ISPT-2 and ISPT-3 pursuant to 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(g)(6)(i).
Such relief is authorized by law and will not endanger life, property, or the common defense and security, and is otherwise in the public interert.
Relief has been granted giving due consideration due to the burden upon the licensee that could result if the requirements were imposed on the facility.
Furthermore, there is reasonable assurance that the proposed alternative examinations will provide an acceptable level of quality and safety.
Principal Contributor:
M. Hum Date:
September 28, 1993 t
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