ML12325A612
| ML12325A612 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 12/12/2012 |
| From: | Jessie Quichocho Plant Licensing Branch II |
| To: | William Gideon Carolina Power & Light Co |
| Billoch,. Araceli | |
| References | |
| TAC ME9747 | |
| Download: ML12325A612 (23) | |
Text
December 12, 2012 Mr. William R. Gideon, Vice President Carolina Power & Light Company H. B. Robinson Steam Electric Plant, Unit No. 2 3581 West Entrance Road Hartsville, South Carolina 29550
SUBJECT:
H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 - RELIEF REQUEST-07 FROM IMMEDIATE ASME CODE REPAIR OF REFUELING WATER STORAGE TANK DRAIN VALVE (SAFETY INJECTION-837) FOR FIFTH10-YEAR INSERVICE INSPECTION PROGRAM PLAN (TAC NO. ME9747)
Dear Mr. Gideon:
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated October 5, 2012, as supplemented by letters dated October 25, 2012, and November 11, 2012, Carolina Power &
Light Company (the licensee), doing business as Progress Energy Carolinas, Inc., submitted Relief Request (RR)-07 for the Inservice Inspection Program Plan for the fifth 10-year interval for the H. B. Robinson Steam Electric Plant, Unit No. 2 (HBRSEP).
The licensee requested relief from the requirements of the 2007 Edition through the 2008 Addenda of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, IWC-3122.2. Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(a)(3)(ii), the licensee requested to use proposed alternatives on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The licensee proposed an alternative to temporarily repair a degraded drain valve that is connected to the Refueling Water Storage Tank. RR-07 proposes to install a mechanical clamp on the degraded valve to stop leakage until an ASME Code repair is performed either during refueling outage (RO)-28 in 2013 or during a forced outage of sufficient duration and scope to allow an ASME Code repair.
The details of the NRC staff review are included in the enclosed safety evaluation. The NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(ii) and, therefore, is in compliance with the ASME Code requirements.
W. Gideon Therefore, the licensee's proposed alternative is authorized in accordance with 10 CFR 50.55a(a)(3)(ii) at HBRSEP, to be completed during a forced outage of sufficient duration and scope to allow a code repair/replacement, but no later than RO-28 scheduled to begin in September 2013.
Sincerely,
/RA/
Jessie F. Quichocho, Acting Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-261
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv
- Via Memo OFFICE LPL2-2/PM LPL2-2/LA DE/EPNB/BC* LPL2-2/BC(A) LPL2-2/BC NAME ABillochColón BClayton TLupold JQuichocho ABillochColón DATE 11/20/12 11/27/12 12/4/12 12/12/12 12/12/12 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NUMBER RR-07 REPAIR OF SAFETY INJECTION VALVE SI-837 CAROLINA POWER & LIGHT COMPANY H.B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261
1.0 INTRODUCTION
By letter to the U.S. Nuclear Regulatory Commission (NRC) dated October 5, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12292A386), as supplemented by letters dated October 25, 2012 (ADAMS Accession No. ML12312A272), and November 11, 2012 (ADAMS Accession No. ML12340A441), Carolina Power & Light Company (the licensee), submitted Relief Request (RR)-07 for the Inservice Inspection (ISI) Program Plan for the fifth 10-year interval for the H. B. Robinson Steam Electric Plant, Unit No. 2 (HBRSEP).
The licensee requested relief from the requirements of the 2007 Edition through the 2008 Addenda of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, IWC-3122.2. Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(a)(3)(ii), the licensee requested to use proposed alternatives on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The licensee proposed an alternative to temporarily repair a degraded drain valve that is connected to the Refueling Water Storage Tank (RWST). RR-07 proposes to install a mechanical clamp on the degraded valve to stop leakage until an ASME Code repair is performed during a forced outage of sufficient duration and scope to allow an ASME Code repair but no later than refueling outage (RO)-28 scheduled for September 2013.
2.0 REGULATORY EVALUATION
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 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 the first 10-year ISI interval and subsequent intervals 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) 12-months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
Pursuant to 10 CFR 50.55a(a)(3), alternatives to the ASME Code requirements may be authorized by the NRC if the licensee demonstrates that: (i) the proposed alternative provides 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.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component Affected The affected ASME Code component is identified as safety injection (SI) system valve SI-837, which is a Class 2, 150 pound, manually-operated, 6-inch, wedge, gate valve manufactured by Crane Company model number L61174AM. The valve body is made of SA351, CF8M cast stainless steel material. The SI-837 valve is an isolation valve within the RWST drain line, line number 6-SI-151R-141. The valve is horizontally orientated approximately 2 feet from the connection of the drain line to the RWST and is subject to a pressure of approximately 15 pounds per square inch (psi), which is the static head of the RWST. The drain line connects to the RWST approximately 1 foot above the base of the tank on the upstream side of the valve and is capped approximately 3 feet downstream of the valve.
The maximum operating temperature of the valve and line number 6-SI-151R-141 is bounded by the operating temperature of the RWST that is 100 degrees Fahrenheit. The line is normally maintained in a static condition due to the single connection to the RWST and insulated with a sheet metal exterior containing silicon/aluminum oxide/carbonate insulation. The insulation has been removed at the valve extending beyond the valve weld ends. Valve SI-837 is located in an outdoor environment next to the RWST, and is exposed to seasonal temperatures and precipitation.
To determine the extent of condition, the licensee visually examined in a walk down of the RWST, and piping and valves located outdoors within the vicinity of the RWST. The walk down was focused on identifying any other leaks as indicated by the buildup of boric acid crystals on the exterior to the insulation. The licensee did not note additional evidence of boric acid residue in the extent-of-condition inspection.
Valve SI-837 provides system boundary isolation for the RWST and is normally closed and locked. The welded cap on the end of line number 6-SI-151R-141 provides a permanent secondary system boundary. Containment boundary is maintained through various isolation valves of various systems that penetrate the containment structure. The SI system is one such system that has various components inside and outside the containment structure.
The RWST is located outside the containment structure and is the source of borated water for the Emergency Core Cooling systems and Containment Spray systems during and post design basis events. The RWST is vented to the atmosphere. Containment boundary is provided with redundant isolation provisions to assure that no unrestricted release of radioactivity to the environment will occur. This action is provided by normally open valves SI-864A and SI-864B.
The containment boundary is established by the closure of valves SI-864A and SI-864B. Valve
SI-837 is not a containment isolation valve, and does not provide a containment boundary function.
3.2 Applicable Code Edition and Addenda HBRSEP entered the fifth, 10-year ISI Inspection Interval effective July 21, 2012. The ASME Section XI Code applicable to the fifth 10-year interval is the 2007 Edition through the 2008 Addenda.
3.3 Applicable Code Requirement ASME Section XI Code, subsection IWC, Requirements for Class 2 Components of Light-Water Cooled Power Plants, subparagraph IWC-3122.2, Acceptance by Repair/Replacement Activity, requires either a repair or replacement of the degraded component.
3.4 Reason for Request On September 7, 2012, the licensee identified an active leakage from a small circumferential flaw on the upstream side of the SI-837 valve body at the transition between the valve pipe run and the valve neck following investigation of boric acid deposits on the exterior of the insulation of line number 6-SI-151R-141. The flaw visually appears to be approximately one-half inch in length. The licensee quantified the leakage at about one drop every 5 minutes and estimated it to be about 0.25 gallons per week. The licensee stated that it has not observed any change in the leak rate since initial discovery and quantification of the leak rate. The licensee further stated that the current leak rate does not challenge the RWST inventory make-up capabilities.
The licensee noted that an ASME Code Repair and/or Replacement of the valve will require entry of the unit into either Mode 5 (cold shutdown) or Mode 6 (refueling) where the RWST is not required to be operable. The unit is currently operating in Mode 1. Installation of a clamp on the body of valve SI-837 would constitute a non-Code repair.
3.5 Proposed Alternative and Basis for Use Referencing ASME Section XI Code subparagraph IWC-3122.3, Acceptance by Analytical Evaluation, the licensee proposed to temporarily accept the through-wall flaw at valve SI-837, which would allow continued service instead of performing immediate flaw correction by an ASME Code Repair/Replacement activity described in ASME Section XI Code subparagraph IWC-3122.2, Acceptance by Repair/Replacement Activity.
Referencing ASME Section Xl Code subparagraph IWA-4133, Mechanical Clamping Devices Used as Piping Pressure Boundary, the licensee requested relief from Mandatory Appendix IX of ASME Code Section Xl, Article IX-1000(b) specification of allowable clamp locations.
Specifically, relief is requested from the limitation of the installation of clamping devices only on the weld ends of valves to allow installation of a clamp on the valve body. Besides this exception, the relief request would otherwise comply with all requirements of ASME Section XI Mandatory Appendix IX. Following installation of a clamp that would encompass the entire valve body, volumetric monitoring would not be feasible. However, as the flaw is circumferential
in nature volumetric monitoring is not required under Mandatory Appendix IX of ASME Xl, Article IX-6000 (a) and (b).
The licensee stated in the October 5, 2012, submittal that the proposed alternative is based on the licensee performing the following actions and regulatory commitments.
- 1. Completion of a walk down on September 25, 2012 of all piping and valves located outdoors within the vicinity of the RWST with no additional evidence of boric acid crystals on the exterior of piping and valve insulation indicative of a potential leak.
- 2. The valve will be shielded from environmental elements with access for inspection until a Code Repair/Replacement.
- 3. Until installation of a clamp or until a Code Repair/Replacement is performed:
- a. Operations personnel will visually monitor the leak each shift with results entered into AUTOLOG. A crack length greater than 1 inch or a leakage increase greater than 16 drops/minute will require station management attention and entered into the Corrective Action Program for appropriate evaluation and further actions.
- b. Nondestructive examination personnel will perform ultrasonic volumetric examination of the flaw location every 90 days. A crack length greater than 7 inches will require station management attention and entered into the Corrective Action Program for appropriate evaluation and further actions.
- 4. Installation of a mechanical clamp complying with the requirements of ASME Section Xl, Appendix IX. All materials will be in accordance with the licensee's Quality Assurance Program for Safety Related material. The sealant and its interface with the Class 2 stainless steel piping has been evaluated and is acceptable for use in this application per plant procedures.
- 5. Following installation of a clamp:
- a. A system leakage test at normal operating pressure and normal operating temperature and a visual testing (VT)-2 examination in accordance with the ASME Code,Section XI, IWA-5000 will be performed on the portion of line number 6-SI-151R-141 containing the clamp.
- b. The area around the clamped valve will be monitored for leakage on a weekly basis in accordance with the ASME Code,Section XI, Article IX-6000 (c) with a record entered into AUTOLOG and with an entry made into the Corrective Action Program for appropriate evaluation and disposition in the event leakage is observed.
- 6. An ASME Section Xl Code Repair/Replacement shall be performed during the next scheduled RO-28, which is currently scheduled to begin September 2013. If
a condition leads to a forced outage of sufficient duration and scope to allow a code Repair/Replacement, the repair will be performed during this forced outage.
3.6 Duration of Proposed Alternative The requested relief will be used until an ASME Section XI Code Repair/Replacement activity is performed during a forced outage of sufficient duration and scope to allow an ASME Code Repair/Replacement activity but no later than RO-28 scheduled for September 2013.
3.7 Staff Evaluation Mechanical Clamp Design The November 11, 2012, submittal contains the design drawings and the results of the stress analysis of the clamping device, which is a Furmanite (trademark) injection box installed to enclose the entire valve SI-837. Sealant is injected at the interface between the outside diameter of the drain line and the inside diameter of the box to form an o-ring type seal. Sealant is applied both upstream and downstream of the valve. Sealant is also injected at the interface between the clamping surfaces of the Furmanite box to seal the box. The licensee will monitor and control the amount of Furmanite material injected to prevent introduction of sealant material into the piping and/or valve. The Furmanite box is designed to provide a pressure boundary that prevents discharge from the leak through the valve body to the environment under expected pressures and temperatures.
The Furmanite box is designed such that all calculated stresses are less than allowable stresses for each material and that the materials are suitable for the intended use. Sealant will not be used to seal the leak through the body of the RWST drain valve. The licensee stated that the leak limiting mechanical clamping device is not designed to exert forces on the flaw in the valve body sufficient to mitigate its growth and/or reduce leakage through the valve body.
Leakage through the valve body may occur after installation of the clamping device (Furmanite box) into the free volume between the valve body and inside surface of the Furmanite box.
The weight of such leakage is included in the weight of the clamping device used in assessing the capability to meet applicable structural requirements.
The NRC staff finds that the licensee has designed the clamp device to provide a pressure boundary that will contain leakage and will support structural integrity of the valve. The NRC staff finds that the mechanical clamp satisfied the design requirements of the ASME Code,Section XI, Appendix IX and, therefore, is acceptable.
Defect Characterization Using a phased array technique, the licensee ultrasonically examined the cast austenitic stainless steel valve body of valve SI-837 to characterize the leak and adjacent areas on the upstream side of the valve. The licensees ultrasonic testing examinations have estimated the actual flaw length in the inside surface of the valve to be approximately 2.5 to 3.5 inches. The flaw visually appears to be approximately one-half inch in length on the valve outside surface.
The licensee stated that a visual examination of the flaw and area surrounding the flaw did not indicate the evidence of any previous repairs to the valve casting. Valve SI-837 is part of
original plant construction and manufacturing records are not readily available. The licensee used a digital microscope to obtain magnified images of the flaw indication. The licensee observed that the indication appears to be a relatively tight crack with some rust colored areas suggesting corrosion was involved. The licensee explained that a water droplet is seen forming at one end of the surface crack indication indicating that the through wall flaw does not extend the entire length of surface indication.
The licensee analyzed specimen samples of deposits from the heat tracing, piping, and valve.
The licensee found that the samples taken from the valve consisted of boric acid (or a related compound) and an insulation-like material composed of silicon/aluminum oxide/carbonate with a trace amount of chlorine.
Based on the digital microscopic examination of the valve, the licensee understood that the most likely cause of failure is an outside diameter initiated environmentally assisted cracking mechanism such as stress corrosion cracking. Based on the reported thickness of 0.4 inches at the indication location, the licensee also understood that there is a relatively high probability of a casting defect (e.g., shrinkage porosity) present at this location.
Article IX-2000 of the ASME Code, Appendix IX requires that ... [t]he size, location, and apparent cause of the defect shall be determined.... The NRC staff finds that the licensee has determined the size, location, and possible causes of the defect. Therefore, the licensee has satisfied Article IX-2000 of the ASME Code,Section IX.
Flaw Evaluation The licensee performed fracture mechanics analyses using the procedures of IWC-3600 of the ASME Code,Section XI, to evaluate the flaw tolerance of the SI-837 valve body containing postulated through-wall flaws. The allowable through-wall circumferential flaw length was determined to be 12.9 inches (without the mechanical clamp) and 10 inches (with mechanical clamp installed). The corresponding allowable through-wall flaw length for the axial flaw type is 23.2 inches (with and without the mechanical clamp installed).
The calculated allowable planar through-wall flaws are larger than the dimensions of the reported flaw. Therefore, the licensee concluded that the SI-837 drain valve should be considered operable but degraded until the end of the evaluation period (approximately 15 months).
The NRC staff noted that the licensee did not calculate flaw growth even though the licensee has demonstrated by analysis that the degraded valve can tolerate a much larger flaw than the detected flaw size. It is not known how fast the flaw would grow between the discovery and the ASME Code repair of the valve (approximately 15 months). However, the licensee designed the clamp device as a pressure boundary. Therefore, the device will provide the structural integrity for the degraded valve. The NRC staff finds that (1) the licensee's flaw tolerance analysis is acceptable because it follows IWC-3600 of the ASME Code,Section XI, (2) the licensee provided reasonable assurance that the degraded valve can tolerate a much larger flaw size than the detected flaw size, and (3) the clamp device provides the new pressure boundary to support the structural integrity of the drain line. In addition, the licensee will perform weekly walkdowns per Article IX-6000(c) of the ASME Code,Section XI to monitor any potential
leakage from the clamp. If leakage does occur the licensee will take corrective actions as discussed below.
Flood Analysis The licensee stated that a catastrophic failure of valve SI-837 would drain the contents of the RWST onto the ground on the north side of the auxiliary building with an initial leakage rate of about 60 gallons per second. The grade in the area of the RWST would flow the water toward a catch basin. There are limited restrictions to the flow to the catch basin such that there is sufficient open area around the RWST to allow flow away from the auxiliary building. The auxiliary building door closest to valve SI-837 is not water tight. However, if a catastrophic failure were to occur there is a weir just inside the door that would prevent any significant water intrusion into the building. Equipment in the area is elevated such that a localized flood would not have any impact.
In the October 25, 2012, letter, the licensee explained that make-up to the inventory in the RWST tank of borated water is provided via the Chemical and Volume Control System (CVCS).
Water from the Boric Acid Storage Tank at a rate of 9.5 gpm and from the Primary Water Storage Tank at a rate of 75 gpm is supplied to the CVCS Blender to provide a nominal make-up capability of 84 gpm to the RWST. This make-up capability, if only available for 10 minutes once a week, would provide on average, more than 100 gallons per day of make-up to the RWST. This make-up rate would more than offset RWST inventory losses through the flaw that occur if the actual leak rate was slightly less than the established leak rate limit of 16 drops per minute or about 1 gallon per day.
In the November 11, 2012, letter, the licensee stated that approximate maximum leakage flaw sizes that do not challenge the nominal RWST inventory make-up capability of 84 gpm to be either no less than 2.5 inches long with a width 0.377 inches or no less than 12.9 inches long with a width of 0.073 inches.
The NRC staff finds that the licensee has demonstrated that no safety equipment will be affected by the catastrophic failure of the valve. Should the valve fail, the clamp device will contain the leakage with minimal leak rate as the clamp is designed to limit potential leakage.
There is sufficient makeup to the RWST to address the potential leakage from the clamp device.
The operator can perform corrective actions in time to maintain the function of RWST.
Therefore, The NRC staff finds that the licensee's flood analysis is acceptable because the licensee has evaluated the impact of a potential flood from the catastrophic failure of the subject valve.
Monitoring After installation of the mechanical clamp the licensee will perform a system leakage test at normal operating pressure and temperature and a VT-2 examination in accordance with IWA-5000 on the portion of line number 6-SI-151R-141 containing the clamp. The licensee will monitor the area around the clamped valve for leakage on a weekly basis in accordance with ASME Code,Section XI, Article IX-6000 (c) with a record entered into AUTOLOG and with an entry made into the Corrective Action Program for appropriate evaluation and disposition in the event leakage is observed. The NRC staff finds that the licensee proposed monitoring of the
leaking valve satisfies the monitoring requirements of the ASME Code,Section XI, Article IX-6000 (c), and, therefore, is acceptable.
Hardship The licensee explained that an ASME Code repair and/or replacement of the subject valve will require entry of the unit into either Mode 5 (cold shutdown) or Mode 6 (refueling) where the RWST is not required to be operable. The unit is currently operating in Mode 1. The licensee stated that performing a Code repair and/or replacement activity at this time to correct a flaw that has such a minor leak rate (approximately 1 drop every 5 minutes) would create a hardship based on the potential risks associated with unit cycling and emergent equipment issues incurred during shutdown and startup evolutions. The licensee further stated that no compensating increase in the level of quality and safety would be gained by immediate repair of the flaw. The NRC staff finds that performing an ASME Code repair or replacement of the subject valve under these circumstances and operating conditions does constitute a hardship without a compensating increase in the level of quality and safety.
4.0 CONCLUSION
As set forth above, the NRC staff determines that the proposed alternative provides reasonable assurance of structural integrity and leak tightness of Valve SI-837. The NRC staff finds that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(ii) and is in compliance with the requirements of the ASME Code,Section XI, for which relief was not requested. Therefore, the NRC authorizes the use of RR-07 at HBRSEP up to RO-28, which is currently scheduled to begin in September 2013, or a forced outage of sufficient duration and scope to allow a code repair/replacement, whichever event occurs earlier.
All other ASME Code,Section XI requirements for which relief has not been specifically requested and approved in this relief request remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: John Tsao Date: December 12, 2012