ML103190311
| ML103190311 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/24/2010 |
| From: | Robert Pascarelli Plant Licensing Branch III |
| To: | O'Connor T Northern States Power Co |
| Tam P | |
| References | |
| TAC ME3527 | |
| Download: ML103190311 (12) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 24, 2010 Mr. Timothy J. O'Connor Site Vice President Monticello Nuclear Generating Plant Northern States Power Company - Minnesota (NSPM) 2807 West County Road 75 Monticello, MN 55362-9637
SUBJECT:
MONTICELLO NUCLEAR GENERATION PLANT - ALTERNATIVE TO NOZZLE-TO-VESSEL WELD AND INNER RADIUS EXAMINATIONS (TAC NO. ME3527)
Dear Mr. O'Connor:
By letter to the Nuclear Regulatory Commission (NRC) dated March 12, 2010 NSPM, the licensee for Monticello Nuclear Generating Plant (MNGP), submitted Relief Request No. 16, "Alternative to Nozzle-to-Vessel Weld and Inner Radius Examination," in accordance with Title 10 of the Code of Federal Regulations (10 CFR), Part 50.55a, paragraph (a)(3)(i). Specifically, NSPM proposed an alternative in accordance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case N-702, "Alternative Requirements for Boiling Water Reactor (BWR) Nozzle Inner Radius and Nozzle-to-Shell Welds."
The NRC staff has reviewed NSPM's Relief Request No. 16 and finds that the MNGP reactor pressure vessel meets four of the five plant-specific criteria specified in the December 19, 2007, safety evaluation on the BWRVIP-1 08 report, which provides the technical bases for use of ASME Code Case N-702. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the request for a proposed alternative set forth in Relief Request No. 16, is authorized through the end of the fourth 10-year inservice inspection interval from the requirements of Table IWB-2500-1 (Inspection Program B) of ASME Code,Section XI pertaining to inspection of the reactor pressure vessel nozzle-to-vessel shell welds and inner radii for the nozzles specified in of NSPM's submittal based on the use of ASME Code Case N-702 because an acceptable level of quality and safety will be maintained. Details of the NRC staffs review are set forth in the enclosed safety evaluation.
T.J. O'Connor
- 2 If you have any questions, please contact Mr. Peter Tam, the Monticello Project Manager, at 301-415-1451.
Sincerely, Robert J. Pascarelli, Chief Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-263
Enclosure:
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION NORTHERN STATES POWER COMPANY OF MINNESOTA (NSPM)
MONTICELLO NUCLEAR GENERATING PLANT (MNGP)
FOURTH 10-YEAR INSERVICE INSPECTION PROGRAM RELIEF REQUEST NO. 16, REACTOR PRESSURE VESSEL WELD INSPECTIONS DOCKET NO. 50-263
1.0 INTRODUCTION
By letter to the Nuclear Regulatory Commission (NRC) dated March 12, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100750660), NSPM, the licensee for MNGP, submitted Inservice Inspection Relief Request No. 16 (RR-16),
"Alternative to Nozzle-to-Vessel Weld and Inner Radius Examination," in accordance with Title 10 of the Code of Federal Regulations (10 CFR), Part 50.55a, paragraph (a)(3)(i). Specifically, NSPM proposed an alternative in accordance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case N-702, "Alternative Requirements for Boiling Water Reactor (BWR) Nozzle Inner Radius and Nozzle-to-Shell Welds."
The technical basis for ASME Code Case N-702 was documented in an Electric Power Research Institute (EPRI) report for the Boiling Water Reactor Vessel and Internals Project (BWRVIP), "BWR Vessel and Internals Project Technical Basis for the Reduction of Inspection Requirements for the Boiling Water Reactor Nozzle-to-Vessel Shell Welds and Nozzle Inner Radius (BWRVIP-1 08)," which was approved by the NRC in a safety evaluation (SE) dated December 19,2007 (ADAMS Accession No. ML073600374).
The December 19,2007, SE for the BWRVIP-108 report specified plant-specific requirements which must be met by licensees proposing to use this alternative. The licensee has provided information in its submittal to demonstrate that the relevant MNGP reactor pressure vessel (RPV) nozzle-to-vessel welds and their inner radii meet these plant-specific requirements so that the proposed alternative can be authorized.
2.0 REGULATORY EVALUATION
Inservice inspection (lSI) of ASME Code Class 1, 2, and 3 components is performed in accordance with Section XI of the ASME Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Section 50.55a(a)(3) of 10 CFR states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if: (i) the proposed alternative 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.
- 2 The regulation at 10 CFR 50.55a(g)(4) further states that ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except design and access provisions and preservice examination requirements, set forth in the ASME Code,Section XI 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 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. The applicable lSI Code of Record for the fourth 10-year lSI interval for MNGP is the 1995 Edition through the 1996 Addenda of ASME Code,Section XI. In addition, for ultrasonic examinations,Section XI, Appendix VIII, "Performance Demonstration for Ultrasonic Examination Systems," of the 1995 Edition, with the 1996 Addenda, is implemented as required and modified by 10 CFR 50.55a(b)(2)(xv).
For all RPV nozzle-to-vessel shell welds and nozzle inner radii, ASME Code,Section XI requires 100 percent inspection during each 10-year lSI interval. However, ASME Code Case N-702 proposes an alternative which reduces the inspection of RPV nozzle-to-vessel shell welds and nozzle inner radius areas from 100 percent to 25 percent of the nozzles for each nozzle type during each 10-year interval. As mentioned earlier, the NRC has approved the BWRVIP-108 report, the underlying technical basis document for ASME Code Case N-702. However, each licensee should demonstrate the plant-specific applicability of the BWRVIP-108 report to its unit when requesting to use the proposed alternative of ASME Code Case N-702, by showing that all the following general and nozzle-specific criteria are satisfied.
The following plant-specific information is required by the NRC staff to ensure that the probabilistic fracture mechanics (PFM) analysis documented in the BWRVIP-108 report applies to the RPV of the licensee's plant.
(Criterion 1) The maximum RPV heatup/cooldown rate is limited to less than 115 of/hour.
For the recirculation inlet nozzles (Criterion 2)
(pr/t) / CRPV < 1.15 P = RPV normal operating pressure, r =RPV inner radius, t =RPV wall thickness, and CRPV =19332 [i.e., 1000 psi x 110 inch/5.69 inch, based on the BWRVIP-108 recirculation inlet nozzle/RPV finite element method (FEM) model]
(Criterion 3)
[p(ro2+ rj2) / (ro2 -
r?)]/CNOZZLE < 1.15, where:
p =RPV normal operating pressure, ro =nozzle outer radius, rj = nozzle inner radius, and CNOZZLE =1637 [i.e., 1000 psi x (13.9882+ 6.8752) / (13.9882-6.8752)]
based on the BWRVIP-108 recirculation inlet nozzle/RPV FEM model]
- 3 For the recirculation outlet nozzles (Criteria 4)
(pr/t) 1CRPV < 1.15 P = RPV normal operating pressure, r = RPV inner radius, t = RPV wall thickness, and CRPV =16171 [i.e., 1000 psi x 113.2 inch 17.0 inch, based on the BWRVIP-108 recirculation outlet nozzle/RPV FEM model]
(Criteria 5)
[p(ro2+ rj2) 1(ro2-rj2)] 1CNOZZlE < 1.15, where p = RPV normal operating pressure, ro = nozzle outer radius, r, = nozzle inner radius, and CNOZZlE = 1977 [i.e., 1000 psi x (22.31 2 + 12.782) 1(22.312-12.782), based on the BWRVIP-108 recirculation outlet nozzle 1RPV FEM model]
3.0 TECHNICAL EVALUATION
3.1 The Licensee's Evaluation ASME Code,Section XI, Table IWB-2500-1, Examination Category B-D, Item Numbers B3.90, "Nozzle-to-Vessel Welds," and B3.100, "Nozzle Inside Radius Section," delineate the examination requirements for ASME Code, Class 1 nozzle-to-vessel welds and nozzle inner radii. The required method of examination is volumetric. All nozzles with full penetration welds to the vessel shell (or head) and integrally cast nozzles require examination each interval.
Relief Request No. 16 is concerned with components described verbatim as follows:
Code Class:
1 Component Numbers:
N2, N3, N5, N6 and NB Nozzles (See below table for complete list of nozzle identifications.)
Examination Category:
B-D (Inspection Program B)
Item Number:
B3.90 and B3. 100
==
Description:==
Alternative to ASME Code,Section XI, Table IWB-2500-1 (for the components described above)
- 4 Table 1: ASME Components Affected (Reproduced From Licensee's Enclosure 2)
Nozzle ID Nozzle-to-Vessel (NV)
Inner Radius (lR)
Category Number
/tem Number System Nominal Pipe Size (Inches)
Exam Year (POI)
N-2A (NV) 8-0 83.90 Recirculation (Inlet) 12 2009 N-2A (lR) 8-0 83.100 Recirculation (Inlet) 12 2009 N-28 (NV) 8-0 83.90 Recirculation (Inlet) 12 2007 N-28 (IR) 8-0 83.100 Recirculation (Inlet) 12 2007 N-2C (NV) 8-0 83.90 Recirculation (Inlet) 12 N-2C (IR) 8-0 83.100 Recirculation (Inlet) 12 N-2o (NV) 8-0 83.90 Recirculation (Inlet) 12 2005 N-2o (lR) 8-0 83.100 Recirculation (Inlet) 12 2005 N-2E (NV) 8-0 83.90 Recirculation (Inlet) 12 2005 N-2E (lR) 8-0 83.100 Recirculation (Inlet) 12 2005 N-2F (NV) 8-0 83.90 Recirculation (Inlet) 12 N-2F (IR) 8-0 83.100 Recirculation (Inlet) 12 N-2G (NV) 8-0 83.90 Recirculation (Inlet) 12 2007 N-2G (lR) 8-0 83.100 Recirculation (Inlet) 12 2007 N-2H (NV) 8-0 83.90 Recirculation (Inlet) 12 N-2H (IR) 8-0 83.100 Recirculation (Inlet) 12 N-2J (NV) 8-0 83.90 Recirculation (Inlet) 12 2005 N-2J (lR) 8-0 83.100 Recirculation (Inlet) 12 2005 N-2K (NV) 8-0 83.90 Recirculation (Inlet) 12
N-2K (IR)
B-D B3.100 Recirculation (Inlet) 12 N-3A (NV)
B-D B3.90 Main Steam 18 2005 N-3A (IR)
B-D B3.100 Main Steam 18 2005 N-3B (NV)
B-D B3.90 Main Steam 18 N-3B (IR)
B-D B3.100 Main Steam 18 N-3C (NV)
B-D B3.90 Main Steam 18 2009 N-3C (IR)
B-D B3.100 Main Steam 18 2009 N-3D (NV)
B-D B3.90 Main Steam 18 N-3D (IR)
B-D B3.100 Main Steam 18 N-5A (NV)
B-D B3.90 Core Spray 8
N-5A (IR)
B-D B3.100 Core Spray 8
N-5B (NV)
B-D B3.90 Core Spray 8
2005 N-5B (IR)
B-D B3.100 Core Spray 6
2005 N-6A (NV)
B-D B3.90 Closure Head Spare 6
2007 N-6A (IR)
B-D B3.100 Closure Head Spare 6
2007 N-6B (NV)
B-D B3.90 Closure Head Spare 6
2009 N-6B (IR)
B-D B3.100 Closure Head Spare 6
2009 N-8A (NV)
B-D B3.90 Jet Pump Instrumentation 4
2005 N-8A (IR)
B-D B3.100 Jet Pump Instrumentation 4
2005 N-8B (NV)
B-D B3.90 Jet Pump Instrumentation 4
2009 N-8B (fR)
B-D B3.100 Jet Pump Instrumentation 4
2009 The licensee proposed the following alternative:
In accordance with 10 CFR 50.55a(a)(3)(i), relief is requested from performing the required examinations on 100 percent of the nozzle assemblies identified in Table 5-1 [reproduced as Table 2 below] below. As an alternative for all welds and inner radii identified in Table 5-1 the NSPM proposes to examine a minimum of 25 percent of the MNGP nozzle-to-vessel welds and inner radius sections, including at least one nozzle from each system and nominal pipe size, in accordance with ASME Code Case N-702. For the nozzle assemblies identified in Enclosure 2 [reproduced as Table 1 above], this would mean that examinations would be required for three of the Recirculation Inlet (N2) nozzles and one from each of the other nozzle groups, as identified below.
- 6 Table 5-1: MNGP [Inspection] Summary Nozzle Group Nozzles per Group Minimum Number to be Examined Number Examine d to Date Year(s)
Examined Recirculation Inlet (N2) 10 3
6 Three in 2005 Two in 2007 One in 2009 Main Steam (N3) 4 1
2 One in 2005 One in 2009 Core Spray (N5) 2 1
1 One in 2005 Closure Head Spare (N6) 2 1
1 One in 2007 One in 2009 Jet Pump Instrumentation (N8) 2 1
2 One in 2005 One in 2009 Therefore, upon authorization, no further nozzles in the applicable groups would remain to be inspected for the remainder of the interval.
ASME Code Case N-702 stipulates that a VT-1 examination may be used in lieu ofthe volumetric examination for the inner radii (i.e., Item No. B3.100, "Nozzle Inside Radius Section). NSPM is only requesting to perform volumetric examinations of the applicable nozzle inner radius sections. NSPM is not requesting use of the VT-1 examination provisions included in the Code Case in lieu of performing volumetric examinations. The NSPM is not currently using ASME Code Case N-648-1 ["Alternative Requirements for Inner Radius Examinations of Class 1 Reactor Vessel Nozzles,Section XI, Division 1'1 at the MNGP for the identified components for enhanced magnification visual examination and has no plans of using ASME Code Case N-648-1 on those components in the future.
Electric Power Research Institute (EPRI) Technical Report 1003557, "BWRVIP 108: Boiling Water Reactor Vessel and Internals Project Technical Basis for the Reduction of Inspection Requirements for the Boiling Water Reactor Nozzle-to Vessel Shell Welds and Nozzle Blend Radii, " (Reference 1) provides the basis for ASME Code Case N-702. The evaluation found that failure probabilities at the nozzle blend radius region and nozzle-to-vessel shell weld due to a Low Temperature Overpressure event are very low (i.e., <1 x 10-6 for 40 years) with or without inservice inspection. The report concludes that inspection of 25 percent of each nozzle type is technically justified.
Section 5.0, "Plant Specific Applicability," of the December 19, 2007, NRC SE approving BWRVIP-108 indicates that each licensee who plans to request relief from ASME Code,
- 7 Section XI requirements for RPV nozzle-to-vessel shell welds and nozzle inner radius sections may reference the BWRVIP-1 08 report as the technical basis for the use of ASME Code Case N-702 as an alternative. The NRC SE further states that each licensee should demonstrate the plant-specific applicability criteria from the BWRVIP-1 08 report to its unit in the relief request by showing that all the general and nozzle-specific criteria addressed below are satisfied. The licensee addressed each of the criteria as follows:
(1) The maximum RPV heatup/cooldown rate is limited to less than 115°F per hour.
MNGP Technical Specification (TS) 3.4.9, "RCS Pressure and Temperature (PIT)
Limits," provides a limiting condition for operation (LCO). The heatuplcooldown rate is referenced in the MNGP operating procedures where applicable such as scrams and start-ups. The maximum heatup/cooldown rate of 100°F per hour is specified within the MNGP Updated Safety Analysis Report in Table 4.1-1, "Reactor Coolant System Data." (reproduced below) of the licensee's request provides verification of Monticello specific applicability to Code Case N-702 in accordance with BWRVIP-108:
(Criteria 1) Maximum RPV heatuplcooldown rate limited to less than 115°F per hour.
- The Monticello Updated Safety Analysis Report indicates a maximum heatup/cooldown rate of 100°F per hour. This heatuplcooldown rate is referenced in the MNGP operating procedures, where applicable, such as scrams and start-ups.
- MNGP Technical Specification 3.4.9, "RCS Pressure and Temperature (PIT) Limits," provides a limiting condition for operation (LCO).
Values for Monticello Recirculation Inlet and Outlet Nozzles:
Monticello specific values:
p = RPV normal operating pressure = 1025 psig r = RPV inner radius = 102.5 inches t = RPV wall thickness = 5.0625 inches ro = Recirculation inlet nozzle outer radius = 14.1875 inches r, = Recirculation inlet nozzle inner radius = 7.0625 inches ro =Recirculation outlet nozzle outer radius =24.375 inches r, = Recirculation outlet nozzle inner radius = 13.0625 inches BWRVIP-108 Constants:
C C
CRPV (Recirculation Inlet Nozzles) = 19332 NOZZLE (Recirculation Inlet Nozzles) = 1637 CRPV (Recirculation Outlet Nozzles) =16171 NOZZL E (Recirculation Outlet Nozzles) = 1977
- 8 For the Recirculation Inlet Nozzles:
(Criteria 2)
(pr/t) / CRPV < 1.15
[(1025 x 102.5) /5.0625] /19332 = 1.07351 < 1.15 (Criteria 3)
[p(ro 2 + r, 2) / (ro 2-r, 2)] / CNOZZLE < 1.15
[1025 (14.18752 + 7.06252) / (14.18752 -7.0625 2) ] /1637 = 1.0387 < 1.15 For The Recirculation Outlet Nozzles:
(Criteria 4)
(pr/t) / CRPV < 1.15
[(1025 x 102.5)/5.0625]/16171 =1.28335> 1.15 (does not pass)
(Criteria 5)
[p(ro 2 + r,2) / (ro 2-rj 2)] / CNOZZLE< 1.15
[1025 (24.3752 + 13.06252) / (24.3752 - 13.06252)] /1977 = 0.93623
< 1.15 3.2 NRC Staff's Evaluation The NRC staff's December 19,2007, SE on the BWRVIP-108 report specified five plant-specific criteria that a licensee must meet to demonstrate that the BWRVIP-1 08 report results apply to its plant. The five criteria are related to the driving force of the PFM analyses for the recirculation inlet and outlet nozzles. The December 19, 2007, SE stated that the nozzle material fracture toughness-related RTNDT values used in the PFM analyses were based on data from the entire fleet of BWR RPVs. Therefore, the BWRVIP-1 08 report PFM analyses are bounding with respect to fracture resistance, and only the driving force of the underlying PFM analyses needs to be evaluated. The SE also stated that, except for the RPV heatup/cooldown rate, the plant-specific criteria are for the recirculation inlet and outlet nozzles only because the probabilities of failure, for other nozzles are an order of magnitude lower.
Relief Request No. 16 provided the MNGP plant-specific data and its evaluation of the five driving force factors, or ratios, against the criteria established in the December 19, 2007, SE.
The licensee's evaluation indicated that 4 criteria of the 5 criteria were satisfied (Criterion 4 for the recirculation outlet nozzles was not satisfied), and the NRC staff independently confirmed the licensee's results. In an e-mail datedJuly28,2010(ADAMSAccession No. ML102090751 )
the licensee stated that the recirculation outlet nozzles are not included in RR-16 and as a result the NRC staff will not discuss the recirculation outlet nozzles further in this evaluation.
The licensee states that for each of the identified nozzle assemblies, both the inner radius and the nozzle-to-shell weld will be examined. As described for all welds and inner radii identified in of Relief Request No. 16, the licensee proposes to examine a minimum of 25 percent of the MNGP nozzle-to-vessel welds and inner radius sections, including at least one nozzle from each system and nominal pipe size, in accordance with ASME Code Case N-702.
For the nozzle assemblies identified in the licensee's Table 5-1 (reproduced on page 6 of this
- 9 SE), this would mean that examinations would be required for three of the Recirculation Inlet (N2) nozzles and one from each of the other nozzle groups.
For the examination of the inner radii, ASME Code Case 1\\1-702 proposes that visual examination may be used in lieu of volumetric examination. However, the licensee states in its submittal that MNGP is not currently using ASME Code Case N-648-1 on enhanced magnification visual examination and has no plans of using ASME Code Case N-648-1 in the future. The licensee further states that MNGP will continue to perform volumetric examinations of all required nozzle inner radii. The NRC staff finds the licensee's continued use of volumetric examination of required nozzle inner radii to be consistent with current regulatory guidance.
4.0 CONCLUSION
The NRC staff has reviewed the licensee's Relief Request No. 16 and finds that the MNGP RPV meets four of the five plant-specific criteria specified in the December 19, 2007, SE on the BWRVIP-108 report, which provides the technical bases for use of ASME Code Case N-702.
Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the request for a proposed alternative set forth in Relief Request No. 16, is authorized through the end of the fourth 10-year lSI interval from the requirements of Table IWB-2500-1 (Inspection Program B) of ASME Code,Section XI pertaining to inspection of the RPV nozzle-to-vessel shell welds and inner radii for the nozzles specified in Enclosure 2 of the licensee's submittal based on the use of ASME Code Case N-702 because an acceptable level of quality and safety will be maintained.
All other requirements of the ASME Code,Section XI, not specifically included in the licensee's March 12,2010, Request No. RR-16 will remain in effect.
Principal Contributor: Thomas McLellan, NRR Date: November 24, 2010
T. J. O'Connor
- 2 If you have any questions, please contact Mr. Peter Tam, the Monticello Project Manager, at 301-415-1451.
Sincerely, IRAJ Robert J. Pascarelli, Chief Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-263
Enclosure:
Safety Evaluation cc w/enci: Distribution via ListServ DISTRIBUTION:
PUBLIC RidsOgcRp Resource LPL3-1 Reading RidsAcrsAcnw_MailCtr Resource RidsNrrDorlLpl3-1 Resource RidsRgn3MailCenter Resource RidsNrrPMKewaunee Resource RidsNrrDciCptb Resource RidsNrrLABTully Resource T. McLellan, NRR D. Merzke, EDO R-1I1 Accession No. ML103190311 OFFICE LPL3-1/PM LPL3-1/LA CVIB/BC*
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RPascarelli DATE 11/19/10 11/18/10 10/29/10*
11/24/10
- Safety evaluation transmitted bye-mail of 10/29/10 (Accession No ML103040024).
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