ML092300551
| ML092300551 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/27/2009 |
| From: | Markley M Plant Licensing Branch IV |
| To: | Entergy Operations |
| Kalyanam N, NRR/DORL/LPL4, 415-1480 | |
| References | |
| EA-03-009, TAC ME0629 | |
| Download: ML092300551 (17) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 27, 2009 Vice President, Operations Entergy Operations, Inc.
Arkansas Nuclear One 1448 SR 333 Russellville, AR 72802
SUBJECT:
ARKANSAS NUCLEAR ONE, UNIT 2 - REQUEST FOR ALTERNATIVE AN02-ISI-002 FOR THE REMAINDER OF THE CURRENT (THIRD) 10-YEAR IS/INTERVAL AND THE FOURTH lSI INTERVAL UNTIL THE REACTOR VESSEL HEAD IS REPLACED (TAC NO. ME0629)
Dear Sir or Madam:
By letter dated February 9, 2009, Entergy Operations, Inc. (Entergy, the licensee), requested U.S. Nuclear Regulatory Commission (NRC) approval for request for alternative AN02-ISI-002 for Arkansas Nuclear One, Unit 2 (ANO-2).
Effective October 10, 2008, the Nuclear Regulatory Commission (NRC) amended Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a, "Codes and standards," to include the American Society of Mechanical Engineers (ASME) Code Case N-729-1, "Alternative Examination Requirements for Pressurized Water Reactor (PWR) Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1," with conditions. Once a licensee implemented the code case, the First Revised NRC Order EA-03-009 (the Order) was no longer applicable and should be deemed to be withdrawn.
However, ANO-2 was categorized as having a high susceptibility to primary water stress corrosion cracking (PWSCC) in accordance with the Order. As such, Sections IV.C.(5)(a) and (b) of the Order required certain inspections to be performed. Under the requirements of Code Case N-729-1, ANO-2 is still highly susceptible to PWSCC and is required to perform inspections that are similar to those required under the Order.
In its submittal, Entergy has, pursuant to 10 CFR 50.55a(a)(3)(i), requested an alternative to the requirements of Code Case N-729-1 for the remainder of the current (third) 1O-year inservice inspection (lSI) interval and the fourth lSI interval until the reactor vessel (RV) head is replaced for ANO-2. In accordance with 10 CFR 50.55a(a)(3)(i), proposed alternatives to the referenced requirements may be approved by the NRC prOVided an acceptable level of quality and safety are maintained.
The NRC staff has completed its review of the subject request for alternative. On the basis of the information submitted, the staff has determined that the proposed alternative provides reasonable assurance of structural integrity of the RV upper head and implementation of additional requirements would result in hardship without a compensating increase in the level of quality and safety. Therefore, while the licensee requested the authorization of this alternative pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff has authorized this alternative pursuant to
- 2 10 CFR 50.55a(a)(3)(ii), for the remainder of the current (third) 1O-year lSI interval and the fourth lSI interval until the RV head is replaced for ANO-2.
All other requirements for which relief has not been specifically requested remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
The NRC staffs safety evaluation is enclosed.
Sincerely, Michael 1. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor RegUlation Docket No. 50-368
Enclosure:
Safety Evaluation cc w/encl.: Distribution via ListServ
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ALTERNATIVE AN02-ISI-002 TO 10 CFR 50.55A(G)(6)(II)(D) EXAMINATION REQUIREMENTS ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE, UNIT 2 DOCKET NO. 50-368
1.0 INTRODUCTION
By letter dated February 9,2009 (Reference 1), Entergy Operations, Inc. (the licensee),
submitted relief request AN02-ISI-002 for U.S. Nuclear Regulatory Commission (NRC) review and approval. The licensee requested to implement an alternative to the requirements of paragraph 50.55a(g)(6)(ii)(D)(3) of Title 10 of the Code of Federal Regulations (10 CFR). The request pertains to inservice inspection (lSI) of reactor vessel (RV) upper head control element drive mechanism (CEDM) nozzles of a pressurized-water reactor (PWR) at Arkansas Nuclear One, Unit 2 (ANO-2). The duration of request is for the fall 2009 refueling outage, the last in the third 10-year lSI interval and the fourth lSI interval until the RV head is replaced.
In a letter dated September 9,2005, the licensee submitted the ANO-2 relaxation request #5 (Reference 2), requesting to use an alternative to the requirement of the First Revised NRC Order EA-03-009 dated February 20,2004 (Order) (Reference 4). The NRC authorized relaxation request #5 by letter dated May 17, 2006 (Reference 3). The Order was later revoked by rulemaking dated September 10, 2008 (73 FR 52742). Then, the requirements for the lSI of RV upper head penetration nozzles have been changed from the Order (Reference 4) to 10 CFR 50.55a(g)(6)(ii)(D) by NRC. In its February 9, 2009, submittal, the licensee is requesting to use an alternative examination technique previously authorized by the NRC for lSI of ANO-2 CEDM nozzles (NRC letter dated May 17, 2006 (Reference 3)), used under the similar requirements of the Order (Reference 4).
2.0 REGULATORY EVALUATION
The lSI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Class 1,2, and 3 components shall be performed in accordance with the requirements of Section XI, "Rules for In-service Inspection of Nuclear Power Plant Enclosure
- 2 Components," of the ASME Code and applicable editions and 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)(4), throughout the service life of a PWR, components which are classified as ASME Code Class 1, 2, and 3 must meet the requirements, except design and access provisions and pre-service 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. Further regulations under 10 CFR 50.55a(g)(4)(i) require that the lSI of components and system pressure tests conducted during the first 10-year lSI interval and subsequent intervals shall comply with the requirements in the latest edition and addenda of the ASME Code,Section XI, incorporated by reference in paragraph (b) of 10 CFR 50.55a on the date 12 months prior to the start of the 120-month lSI interval, (or the optional ASME Code cases listed in NRC Regulatory Guide 1.147, Revision 15, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," that are incorporated by reference in 10 CFR 50.55a(b)), subject to the limitations and modifications listed herein.
The regulations in 10 CFR 50.55a(g)(6)(ii) state that the Commission may require the licensee to follow an augmented lSI program for systems and components for which the Commission deems that added assurance of structural reliability is necessary. Further regulations under 10 CFR 50.55a(g)(6)(ii)(D) define the requirements for RV head inspections.
Pursuant to 10 CFR 50.55a(a)(3), proposed alternatives to the requirements of 10 CFR 50.55a(g) may be used when authorized by the Commission 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.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Components Affected
Eighty-one ASME Code Class 1 RV upper head penetration nozzles and the associated welds identified by item number 84.20 in Table 1 of ASME Code Case N-729-1, "Alternative Examination Requirements for Pressurized Water Reactor (PWR) Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial Penetration Welds,Section XI, Division 1."
3.2
Applicable Code Edition and Addenda
The 2001 Edition through 2003 Addenda to the ASME Code,Section XI, is the current Code of record for the lSI program at ANO-2.
3.3
Applicable Code Requirement
The regulations in 10 CFR 50.55a(g)(6)(ii)(D)(1) state, in part, that licensees of existing operating PWRs shall augment their lSI program with ASME Code Case N-729-1 subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (6) of this section by December 31, 2008. Once a licensee implements this requirement, the First Revised NRC Order EA-03-009 no longer applies to that licensee and shall be deemed to be withdrawn.
- 3 The regulations in 10 CFR 50.55a(g)(6)(ii)(D)(3) require, in part, the licensee to perform a volumetric and/or surface examination of essentially 100 percent of the required volume or equivalent surfaces of the nozzle tube, as identified by Figure 2 of ASME Code Case N-729-1.
Figure 2 identifies the required volume of tube to be inspected, a distance "a" above the highest point of the root of the J-groove weld to a distance "a" below the lowest point of the toe of the J-groove weld. Distance "a" is equal to 1.5 inches for incidence angle less than or equal to 30 degrees (0) to the horizontal plane, or 1.0 inch for incidence angle greater than 30° to the horizontal plane. A demonstrated volumetric or surface leak path assessment through all J-groove welds shall be performed. If a surface examination is being substituted for a volumetric examination on a portion of a penetrating nozzle that is below the toe of the J-groove weld, the surface examination shall be of the inside and outside wetted surface of the penetration nozzle not examined volumetrically.
3.4 Proposed Alternative The licensee's proposed alternative is:
Ultrasonic examination - The volume of base material of each CEDM nozzle tube and the associated weld is scanned by ultrasonic testing (UT) from the tube inside diameter (ID) surface from the applicable point above the root of the J-groove weld (per Code Case N-729-1, 1.5 inches for nozzles with an incidence angle less than or equal to 30°,
and 1.0 inch for nozzles with an incidence angle greater than 30° on a horizontal plane perpendicular to the nozzle axis) to 1.544 inches above the bottom of the nozzle. In addition, a leak path assessment is performed to determine if leakage has occurred into the interference fit zone.
Analysis - For the region of nozzle not examined by UT (Le., threaded, chamfer, and acoustic uncoupling), analysis has been performed to:
L Determine whether sufFicient free-span (Le., bottom of weld minus unexamined region) exists between the unexamined region and the weld to facilitate one operating cycle of crack growth without the crack reaching the weld, iL For nozzles or portions of nozzles not meeting item i above, determine how much propagation length (Le., bottom of weld minus top of crack tip) is required to facilitate one cycle of crack growth without the crack reaching the weld. This length is composed of the distance between the weld and the unexamined region plus some additional distance into the unexamined region. The additional distance into the unexamined region is subject to augmented inspections.
The licensee's analysis methodology includes a finite element stress analysis and fracture mechanics evaluation of the nozzles, which is documented in Engineering Report M-EP-2003-002, Rev. 1 (Reference 2). Based on the results of this evaluation, the augmented inspections zone boundaries (Le., minimum axial lengths into the unexamined region and circumferential extents to be examined) for each nozzle group location are established and summarized in Table 1.
- 4 Table 1: Augmented Inspections Criteria (Table 1, Reference 2)
Boundary for Augmented Inspections(1)
Nozzle (Head Angle)
Nozzle Azimuth Top Elevation (inch)
Bottom Elevation (inch)
Axial Length (inch)
Circumferential Extent(2) 0° Downhill 1.544 1.090 0.454 DH +/- 180° 8.8° Downhill 1.544 1.090 0.454 DH +/- 67.5° 28.8° Downhill 1.544 1.224 0.320 DH +/- 22.5° 49.6° Downhill 1.544 0.883 0.661 DH +/- 45°
- 1) Measured from the bottom end of the nozzle.
(2) DH stands for downhill.
The results of the fracture mechanics evaluations for predicted crack growth per one cycle of operation for each nozzle group location are summarized in Table 2. The crack growth analysis was performed in accordance with Electric Power Research Institute (EPRI) Report, "Materials Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Material (MRP-55)" (Reference 7). Postulated cracks for the analysis include axial ID and outside diameter (OD) part through-wall and through-wall cracks. Axial cracks are selected for evaluation in this analysis because of their potential to propagate to the weld region. Axial ID and OD part through-wall crack sizes that equal the smallest crack sizes are successfully detected by UT under the EPRI MRP Inspection Demonstration Program. Through-wall cracks are sized based on the stress distribution in the area of interest. Table 2 indicates that the downhill location of nozzles is the critical location at which a crack could potentially grow to the bottom of the weld in less than one cycle of operation. In two cases, fracture mechanics evaluations could not be performed for OD part through-wall and through-wall cracks at the downhill location due to the extension of the weld into the blind zone or unexamined region (Le., threaded, chamfer, uncoupling).
Table 2: Results of Crack Growth Analysis (Table 3, Reference 2)
Nozzle Head Angle Nozzle Azimuth Axial Crack Evaluated Crack Evaluation Results 0° All 10 part through-wall Greater than 1 cycle to reach weld 00 part through-wall Greater than 1 cycle to reach weld Through-wall Less than 1 cycle to reach weld 8.8° Downhill 10 part through-wall Greater than 1 cycle to reach weld 00 part through-wall Greater than 1 cycle to reach weld Through-wall Less than 1 cycle to reach weld Uphill 10 part through-wall Greater than 1 cycle to reach weld 00 part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld lVIid-plane 10 part through-wall Greater than 1 cycle to reach weld 00 part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld 28.8° Downhill 10 part through-wall Greater than 1 cycle to reach weld
- 5 Table 2: Results of Crack Growth Analysis (Table 3, Reference 2)
Nozzle Head Angle Nozzle Azimuth Axial Crack Evaluated Crack Evaluation Results OD part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld Uphill ID part through-wall Greater than 1 cycle to reach weld OD part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld Mid-plane ID part through-wall Greater than 1 cycle to reach weld OD part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld 49.6° Downhill ID part through-wall Greater than 1 cycle to reach weld 00 part through-wall Not analyzed; Weld extends into blind zone Through-wall Not analyzed; Weld extends into blind zone Uphill ID part through-wall Greater than 1 cycle to reach weld OD part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld Mid-plane ID part through-wall Greater than 1 cycle to reach weld OD part through-wall Greater than 1 cycle to reach weld Through-wall Greater than 1 cycle to reach weld Furthermore, to assess the crack-growth potential for an individual nozzle the analytically predicted crack-growth length for individual nozzle is compared against the available crack-growth length obtained from the 2003 UT data. The results of this assessment are documented in Table 3. It is shown in Table 3 that 24 nozzles have adequate available propagation lengths and, thus, meet the requirements. However, 57 of the 81 nozzles have inadequate propagation lengths and, thus, will be subjected to augmented inspections.
Table 3: Nozzle Augmented Inspection (Table 4, Reference 2)
Nozzle Analytical Crack Growth Length per Cycle(1) (inch)
Available Crack Growth Length(4)
(inch)
Crack Growth into Weld within 1-Cycle No.
Head Angle (Degree) 1 0
0.576 0.520 Yes 2
8.8 0.560 0.320 Yes 3
8.8 0.560 0.440 Yes 4
8.8 0.560 0.480 Yes 5
8.8 0.560 0.600 No 6
12.4 0.560(£)
0.760 No 7
12.4 0.560(£)
0.800 No 8
12.4 0.560(£)
0.560 No 9
12.4 0.560(£)
0.800 No
10 20 30 40 50
- 6 Table 3: Nozzle Augmented Inspection (Table 4, Reference 2)
Nozzle Analytical Crack Growth Length per Cycle(1) (inch)
Available Crack Growth Length(4)
(inch)
Crack Growth into Weld within 1-Cycle No.
Head Angle (Degree) 17.7 0.5601l) 0.680 No 11 17.7 0.5601l) 0.520 Yes 12 17.7 0.5601l) 0.640 No 13 17.7 0.5601l) 0.800 No 14 19.9 0.560(2) 0.720 No 15 19.9 0.560(2) 0.640 No 16 19.9 0.560(2) 0.440 Yes 17 19.9 0.560(2) 0.520 Yes 18 19.9 0.560(2) 0.600 No 19 19.9 0.560(2) 0.720 No 19.9 0.560(2) 0.800 No 21 19.9 0.560(2) 0.840 No 22 25.5 0.560(2) 0.560 No 23 25.5 0.5601l) 0.280 Yes 24 25.5 0.560(2) 0.480 Yes 25 25.5 0.560(l) 0.720 No 26 27.2 0.560(l) 0.440 Yes 27 27.2 0.560(~)
0.320 Yes 28 27.2 0.560(2) 0.520 Yes 29 27.2 0.560(2) 0.480 Yes 28.8 0.086(2) 0.520 No 31 28.8 0.086(2) 0.440 No 32 28.8 0.0861~)
0.320 No 33 28.8 0.0861~)
0.280 No 34 28.8 0.0861l) 0.520 No 35 28.8 0.0861l) 0.600 No 36 28.8 0.0861l) 0.480 No 37 28.8 0.086(2) 0.720 No 38 33.3
(;j) 0.320 Yes 39 33.3
(")
0.000 Yes 33.3 (3) 0.000 Yes 41 33.3
(;j) 0.000 Yes 42 33.3
(;j) 0.280 Yes 43 33.3
(;j) 0.000 Yes 44 33.3
(;$)
0.360 Yes 45 33.3
(;$)
0.000 Yes 46 37.6
(;j) 0.000 Yes 47 37.6
(;$)
0.000 Yes 48 37.6
(;j) 0.000 Yes 49 37.6
(;j) 0.160 Yes 38.9 l;j) 0.360 Yes
- 7 Table 3: Nozzle Augmented Inspection (Table 4, Reference 2)
Nozzle Analytical Crack Growth Length per Cycle(1) (inch)
Available Crack Growth Length(4)
(inch)
Crack Growth into Weld within i-Cycle No.
Head Angle (Degree) 51 38.9 (3) 0.360 Yes 52 38.9 (3) 0.000 Yes 53 38.9 (3) 0.000 Yes 54 38.9 (3) 0.000 Yes 55 38.9 (3) 0.160 Yes 56 38.9 (3) 0.280 Yes 57 38.9 (3) 0.000 Yes 58 40.3
(;j) 0.520 Yes 59 40.3 (J) 0.360 Yes 60 40.3 (J) 0.240 Yes 61 40.3
(;j) 0.320 Yes 62 43.0 (3) 0.440 Yes 63 43.0 (3) 0.320 Yes 64 43.0
(;j) 0.320 Yes 65 43.0
(;j) 0.240 Yes 66 43.0
(;j) 0.160 Yes 67 43.0
(;j) 0.360 Yes 68 43.0
(;j) 0.280 Yes 69 43.0 (3) 0.320 Yes 70 49.6 (3) 0.400 Yes 71 49.6 (3) 0.400 Yes 72 49.6 (31 0.160 Yes 73 49.6 (3) 0.000 Yes 74 49.6 (3) 0.400 Yes 75 49.6 (3) 0.320 Yes 76 49.6
(;j) 0.000 Yes 77 49.6
(;j) 0.000 Yes 78 49.6 (3) 0.360 Yes 79 49.6 (3) 0.000 Yes 80 49.6 (3) 0.200 Yes 81 49.6 (J) 0.000 Yes (1) Crack growth distance per cycle is taken from Table 19 of Reference 5.
(2) Nozzles at the 12.4°,17.7°,19.9°,25.5°, and 27.2° locations are evaluated for the predicted crack growth on nozzles at the 8.8° nozzle location since it is larger than the predicted crack growth on nozzles at the 28.8° nozzle location.
(3) Nozzles at the 33.3°, 37.6°, 38.9°,40.3°, and 43.0° locations must be bounded by fracture mechanics analysis results on nozzles at the 49.6° nozzle locations. Because certain nozzles in these groups have welds that extend into the unexamined region at the downhill azimuthal location, a bounding fracture mechanics analysis could not be performed for the OD part-through-wall and through-wall cracks. Therefore, the nozzles in these groups will be inspected.
(4) Based on UT data obtained during the fall 2003 refueling outage at ANO-2.
- 8 Augmented inspections - The nozzles that have been demonstrated by analysis to have inadequate free-span to ensure a crack will not grow to the J-groove weld within one operating cycle are to be subjected to the augmented inspections. These nozzles have been identified in Table 3. The boundaries of the augmented inspections have been specified in Table 1. The top of the augmented inspections zone is defined by the upper limit of the unexamined region (Le., 1.544 inches above the bottom end of each nozzle) while the bottom limits and the circumferential extents are specified in Table 1 as the axial lengths and the circumferential extents, respectively. The augmented inspections of 00 are to be performed using either eddy current testing (ECT) or penetrant testing (PT), or a combination of both.
3.5 Licensee's Basis for Relief Similar to the previously approved relaxation request for ANO-2 (NRC letter dated May 17, 2006 (Reference 3)), from the volumetric inspections requirement of the Order (Reference 4), the licensee has identified that the geometric limitations of the RV upper head penetration nozzles include a threaded guide cone connection section and a chamfer region approximately 1.344-inch long at the bottom end of the nozzles. In addition, the UT probe has acoustic uncoupling region of 0.200 inch. The dimensional configurations of the nozzles and the acoustic uncoupling are such that the inspectable distance from the lowest point of the toe of the weld to the bottom of scanned region is less than the 1.0-inch or 1.5-inch lower boundary limit as defined by Figure 2 of ASME Code Case N-729-1.
The licensee has evaluated the impact of resolving the geometric limitations to achieve the Code-required complete volumetric coverage by redesigning the penetration nozzles and the associated J-groove welds. Taking such an approach would impose hardship and unusual difficulties without a compensating increase in the level of quality and safety. The hardship due to redesigning includes unnecessary component removal and redesign, personnel exposure to high radiation dose during removal and reinstallation of components, and impact on the outage schedule. The licensee has estimated that removing and reinstalling 81 guide cones would result in radiation exposure of approximately 1.25 roentgen equivalent man (rem) per nozzle for a total exposure of 101.25 rem (Reference 2).
Furthermore, the licensee has evaluated the impact of inspecting the inside wetted surface of penetration nozzles using either PT or ECT methods. For 10 surface examinations, all guide cones should be removed prior to performing PT or ECT. Taking such an approach would expose the personnel to significant radiation exposure. The licensee has estimated the radiation exposure from removal and reinstallation of guide cones and performing PT or ECT inspections of the 10 wetted surface under the RV head to be approximately 2.50 rem per nozzle for a total exposure of 202.50 rem (Reference 2). The licensee has further indicated that performing ECT inspections, as with UT inspections, would not yield results in the 1.344 inches threaded connections and chamfer region of the nozzles.
The proposed alternative would be for the licensee to perform the VOlumetric examinations of nozzles to the maximum extent possible to at least 1.544 inches above the bottom of the nozzle.
The nozzles that have been demonstrated by analysis to have inadequate free-span will be SUbjected to the augmented inspections in accordance with the boundary criteria established in Table 1. Table 1 provides the minimum inspection coverage required to ensure that a
- 9 postulated axial through-wall flaw in the unexamined region of the penetration nozzle would not propagate into the pressure boundary formed by the J-groove weld prior to lSI at the subsequent refueling outage.
The licensee has performed a finite element (FE)-based stress analysis to determine the stress distributions from the bottom of the nozzle to just above the top of the weld at the downhill, uphill, and mid-plane azimuthal locations. To ensure FE produces conservative stresses, the licensee has used an as-built configuration of the subject nozzles and welds rather than an as-designed configuration. The stresses are used to perform the fracture mechanics evaluations. The downhill and mid-plane locations have been selected because they represent the shortest distances that a crack would have to propagate to reach the nozzle weld region.
The licensee previously (Reference 2) performed lSI examinations of the subject nozzles, under the Order (Reference 4) during the fall 2003 and the spring 2005 refueling outages. These lSI examinations showed no indications of PWSCC and penetration leakage. These examinations included:
The volumetric examinations using UT and the ID surface examinations using ECT of the subject CEDM nozzle tubes and the associated J-groove welds, from 2 inches above the J-groove weld to the lowest achievable extent below the weld, at a minimum, were performed. The UT included a 0° leakage path assessment and time-of-flight diffraction (TOFD) examinations 0.060 inch into the J-groove weld-to-tube interface including the triple-point area of the weld. No indications of PWSCC were identified.
The licensee performed manual ECT of the OD of nozzle tubes and J-groove welds where UT examinations could be achieved below the J-groove weld due to nozzle geometrical limitations. The licensee was able to attain greater coverage than the minimum criteria specified in Table 1. Specifically, the licensee attained axial coverage of approximately 0.8 inch below the top of the unexamined region.
No indications of PWSCC were identified.
The licensee performed supplemental visual inspections from above the RV cooling shroud. In addition, the licensee performed bare-metal visual examinations on the RV head flange and the portion of the RV head extending out of the cooling shroud as well as 360 0 around the in-core instrumentation nozzles. Specifically, during the spring 2005 refueling outage, the licensee removed the cooling shroud and insulation, and performed bare-metal visual examinations of the carbon steel surface of the reactor closure head, including 360 0 around each penetration in accordance with Section IV.C.(5)(a) of the Order (Reference 4). No indications of penetration leakage, boric acid residue, or material wastage were identified.
The licensee believes that its proposed alternative (Le., limited UT inspections and analysis supplemented with augmented surface inspections) provides adequate means for the inspections and evaluations of the conditions of the subject CEDM nozzles and welds.
- 10 3.6 Duration of Relief The relief request is submitted for the remainder of the current (third) 10-year lSI interval and the fourth lSI interval until the RV head is replaced for ANO-2.
3.7
NRC Staff Evaluation
The susceptibility of RV upper head penetration nozzles in PWRs to PWSCC is a potential safety concern. The nozzles are welded with partial penetration J-groove welds to RV upper head and nickel-based alloys are used in the nozzles and the associated welds. Primary coolant water and the operating conditions of PWRs can cause cracking of the nickel-based alloys due to PWSCC in the areas of the highest tensile stress. The subject CEDM nozzles at ANO-2 meet the conditions for PWSCC and, therefore, may be susceptible to cracking in the nozzles and associated welds which could cause nozzle ejection or leakage of boric acid causing corrosion of the low-alloy steel head.
The requirements for the lSI of RV upper head penetration nozzles have been changed from the Order (Reference 4) to 10 CFR 50.55a(g)(6)(ii)(D) by the NRC. Pursuant to 10 CFR 50.55a(g)(6)(ii)(D)(1), the NRC requires, in part, all licensees of existing operating PWRs to augment their lSI program with ASME Code Case N-729-1 subject to the conditions by December 31, 2008. Once a licensee implements this requirement, the First Revised NRC Order EA-03-009 (Reference 4) no longer applies to that licensee and shall be deemed to be withdrawn. The regulations in 10 CFR 50.55a(g)(6)(ii)(D)(3) require, in part, the licensee to perform a volumetric and/or surface examination of essentially 100 percent of the required volume or equivalent surfaces of the nozzle tube, as identified by Figure 2 of ASME Code Case N-729-1.
Previously, the licensee submitted the ANO-2 relaxation request #5 dated September 9,2005 (Reference 2), requesting to use an alternative to the requirement of the Order (Reference 4).
By letter dated May 17, 2006 (Reference 3), the NRC authorized the relaxation request #5 which pertained to lSI of the ANO-2 CEDM nozzles for the fall 2006 refueling outage. However, the Order (Reference 4) was later revoked by NRC rulemaking dated September 10, 2008 (73 FR 52742). By this change, all previous NRC authorized relaxation requests from the requirements of the Order were withdrawn due to the change in the regulatory requirements.
Therefore, the licensee submitted the current relief request AN02-ISI-002, dated February 9, 2009 (Reference 1), requesting to use the same proposed alternative to the requirements of 10 CFR 50.55a(g)(6)(ii)(D)(3). It is noted that the specific requirement for the inspections of RV penetration nozzles below the J-groove weld has not been changed significantly between the two regulatory requirements.
The regulations in 10 CFR 50.55a(g)(6)(ii)(D)(3) require, in part, the licensee to perform a volumetric and/or surface examination of essentially 100 percent of the required volume or equivalent surfaces of the CEDM nozzle tubes, as identified by Figure 2 of Code Case N-729-1.
The required volume is a distance "a" above the highest point of the root of the J-groove weld to a distance "a" below the lowest point of the toe of the J-groove weld. Distance "a" is equal to 1.5 inches for incidence angle less than or equal to 300 to the horizontal plane, or 1.0 inch for incidence angle greater than 300 to the horizontal plane. If a surface examination is being substituted for a volumetric examination on a portion of a penetrating nozzle that is below the
- 11 toe of the J-groove weld, the surface examination shall be of the inside and outside wetted surfaces of the penetration nozzle not examined volumetrically. A demonstrated volumetric or surface leak path assessment through all J-groove welds shall be performed.
Consistent with the evaluation of the licensee's previous ANO-2 relaxation request #5 dated September 9, 2005 (Reference 2), the NRC staff has reviewed the request AN02-ISI-002 pursuant to 10 CFR 50.55a(a)(3)(ii), such that proposed alternatives to the requirements of paragraph 10 CFR 50.55a(a)(g) may be used when authorized by NRC if compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The NRC staff evaluation focuses first on whether the compliance with the specified requirements of 10 CFR 50.55a(a)(g) or portions thereof would result in hardship or unusual difficulty.
Within the context of relief request AN02-ISI-002, the licensee has specified the limitations preventing full volumetric inspections of the nozzle below the J-groove weld. These limitations include nozzle bottom-end geometry (such as guide cone-threaded connection and 45° chamfer) and the design of the UT probe. To overcome these limitations, the RV upper head and nozzles would have to be removed, redesigned, and reinstalled. Taking such an approach would have consequences of increasing occupational radiation exposure to workers.
The licensee has the option of substituting surface inspections (entire inside and outside wetted surfaces) of each J-groove weld for volumetric inspections below the J-groove weld to meet the current requirements. However, conducting the required surface inspections would require the guide cone to be removed, and it is believed that surface inspections could not be achieved completely due to the geometries of the threaded connections. Taking such an approach, combined with the process of performing surface inspections under the RV upper head, would result in a significant occupational radiation exposure of personnel in these high radiation and contamination areas. Therefore, the NRC staff is satisfied with the licensee's demonstration of the existing limitations that would make compliance with the specified requirements of 10 CFR 50.55a(a)(g) or portions thereof difficult and would result in hardship and personnel exposure to significant dose radiation.
The NRC staff evaluation focuses on whether there is a compensating increase in the level of quality and safety despite the hardship. The licensee has proposed to examine the subject nozzles using a combination of techniques including UT examinations, analysis and augmented inspections. The staff has evaluated the licensee's proposed alternative techniques to ensure that these alternatives provide a reasonable assurance of structural integrity for the uninspected portions of the nozzles.
3.7.1 UT Examination The licensee states that a reduced volumetric examination zone below the lowest point of the toe of the J-groove weld will be performed. This is a distance "a" above the highest point of the root of the J-groove weld down to the approximately 1.544 inches above the bottom end of the nozzle tube. This distance of 1.544 inches (i.e., 1.25-inch threaded connection + 0.094-inch chamfer + 0.2-inch acoustic uncoupling) is designated as the unexamined region by volumetric
- 12 examinations. For the unexamined region not inspected by UT, the licensee states that the analysis technique would demonstrate the adequacy of the examination volume or surface.
In addition, the licensee states that the required leak path assessment through J-groove welds will be performed to determine if leakage has occurred into the annulus between the CEDM nozzle and the RV head low-alloy steel.
3.7.2 Analysis The licensee states that an engineering evaluation has been used for the unexamined region of the nozzle and the associated J-groove weld not inspected by UT to demonstrate the adequacy of the examination volume or surface. The licensee's engineering evaluation includes an FE stress analysis and fracture mechanics based crack-growth evaluation that is detailed in Entergy Engineering Report M-EP-2003-002, Revision 1 (Reference 5). The intent of the engineering evaluation is to study the behavior of various postulated cracks that could have potential to grow to the J-groove weld and might lead to pressure boundary leakage. The analysis would predict the time for a potential crack to grow from the unexamined region to the pressure boundary. The desirable safe time would be greater than one cycle of operation. The NRC staff has reviewed the licensee's engineering evaluation and the results documented in the previous relief request #5 dated September 9, 2005 (Reference 2), and noted that the engineering evaluation and the associated results had been authorized by the NRC for the fall 2003 refueling outage (Reference 6) and the fall 2006 refueling outage (Reference 3) at ANO-2.
The licensee's predicted time for a potential postulated crack to grow from the unexamined region to the pressure boundary are presented in Table 1 and reviewed by the NRC staff. It is noted that the downhill location of the nozzles is the critical location at which a crack could potentially grow to the bottom of the weld in less than one cycle of operation. The staff has noticed that the licensee's analysis could not be performed for two cases, 00 part through-wall and through-wall cracks, at the downhill location due to the extension of the weld into the unexamined region.
Furthermore, the NRC staff has reviewed data presented in Table 3 by the licensee. It is noted in Table 3 that the analytically predicted crack-growth length for individual nozzles is compared against the available crack-growth length obtained from the 2003 UT data. The results presented in Table 3 shows that 24 nozzles have adequate available propagation lengths and, thus, meet the requirements. However, 57 of the 81 nozzles have inadequate propagation lengths and, thus, will be sUbjected to augmented inspections. The staff has reviewed footnote
- 3 of Table 3 and is satisfied with the licensee's approach as shown in Section 3.7.3 below. For those nozzles, as identified by Table 3, that do not show adequate available crack propagation length, the licensee has performed additional analysis to define the nozzle area that should be subject to an augmented inspection. The staff has reviewed the data in Table 1 and concluded that the results presented in Table 1 are consistent with the licensee's engineering evaluation and are acceptable to the NRC staff.
3.7.3 Augmented Inspections The licensee states that 57 of the 81 CEDM nozzles, as identified by Table 3, are subject to the augmented inspections. The 57 nozzles are those nozzles that do not have adequate free-span below the J-groove weld to ensure a crack growth within one operating cycle. The NRC staff
- 13 notes that the boundary for the augmented inspections has been established by the licensee's engineering evaluation and documented in Table 1. The licensee will perform the augmented inspection on the area that is identified by Table 1. Table 1 specifies the minimum 00 axial length ranging from 0.320 inch to 0.661 inch below the top of the unexamined region and the minimum circumferential extents ranging from 22.50 to 1800 that must be examined for each nozzle location. The staff notes that the licensee attained axial coverage of approximately 0.80 inch below the top of the unexamined region during the augmented inspections in the fall 2003 and the spring 2005 outages. The licensee states that it will continue to obtain the coverage of 0.80 inch for the upcoming fall 2009 refueling outage.
The augmented inspections will be performed using ECT, PT, or a combination of both inspection methods. ECT and/or PT inspection methods are an effective means in detecting surface opening flaws. The NRC staff notes that through-wall and 00 part through-wall cracks are the limiting flaws as established by the licensee's analysis, it is highly likely that ECT and/or PT will detect these types of flaws in the inspection area, if present.
The NRC staff has reviewed the licensee's fracture mechanics analysis results regarding the 10-initiated cracks. It was shown that the 10-initiated cracks would not grow through-wall and reach into the weld establishing a leak path within one cycle of operation for any of the nozzle locations. The staff concluded that this analysis is acceptable.
In summary, the NRC staff concludes that the licensee's proposed alternative (UT examination, analysis and augmented inspections) provides reasonable assurance of structural integrity and public health and safety. With these considerations, compliance with the requirements of 10 CFR 50.55a(g)(6)(ii)(O)(3) would result in hardship without a compensating increase in the level of quality and safety.
3.8 COMMITMENTS In its letter dated February 9, 2009, the licensee made the following commitment:
The alternative examination proposed by the Relief Request will be completed each ANO-2 refueling outage until the reactor vessel head is replaced.
The NRC staff concluded that the proposed commitment satisfies the need for continuing compliance and is, therefore, acceptable.
4.0 CONCLUSION
The NRC staff has reviewed the licensee's bases for AN02-ISI-002 and concludes that the licensee's proposed alternative provides reasonable assurance of structural integrity and public health and safety; and that compliance with the requirements of 10 CFR 50.55a(g)(6)(ii)(O)(3) would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Therefore, while the licensee requested the authorization of this alternative pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes this alternative pursuant to 10 CFR 50.55a(a)(3)(ii), for the remainder of the current (third) 10-year lSI interval and the fourth lSI interval until the RV head is replaced for ANO-2.
- 14 All other requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
5.0 REFERENCES
- 1.
Bice, D. B., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Request for Alternative to 10 CFR 50.55a(g)(6)(ii)(D), Examination Requirement, Arkansas Nuclear One, Unit 2," dated February 9, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML090400962).
- 2.
Buford, F. Goo, Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "ANO-2 Relaxation Request #5 to NRC First Revised Order EA-03-009 for the CEDM Nozzles," dated September 9,2005 (ADAMS Accession No. ML052560109).
- 3.
Terao, D., U.S. Nuclear Regulatory Commission, letter to J. Forbes, Entergy Operations, Inc., "Arkansas Nuclear One, Unit 2 (ANO-2) - Relaxation Request from U.S. Nuclear Regulatory Commission (NRC) Order EA-03-009 for the Control Element Drive Mechanism (CEDM) Nozzles (TAC No. MC8282)," dated May 17, 2006 (ADAMS Accession No. ML060750482).
- 4.
Borchardt, R. W., U.S. Nuclear Regulatory Commission, letter to Holders of Licenses for Operating Pressurized-Water Reactors, "Issuance of First Revised NRC Order (EA-03-009) Establishing Interim Inspection Requirements for Reactor Pressure Vessel Heads at Pressurized Water Reactors," dated February 20,2004 (ADAMS Accession No. ML040220181).
- 5.
Entergy Operations, Inc., "Fracture Mechanics Analysis for the Assessment of the Potential for Primary Water Stress Corrosion Crack (PWSCC) Growth in the Uninspected Regions of the Control Element Drive Mechanism (CEDM) Nozzles at Arkansas Nuclear One Unit 2," Entergy Engineering Report M-EP-2003-002, Revision 1, dated August 26, 2003 (ADAMS Accession No. ML032690649).
- 6.
Berkow, H., U.S. Nuclear Regulatory Commission, letter to M. Krupa, Entergy Operations, Inc., "Arkansas Nuclear One, Unit 2 (ANO-2) - Relaxation Request from U.S. Nuclear Regulatory Commission (NRC) Order EA-03-009 for the Control Element Drive Mechanism (CEDM) Nozzles (TAC No. MB9542)," dated October 9,2003 (ADAMS Accession No. ML032820552).
- 7.
Electric Power Research Institute (EPRI), "Materials Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Material (MRP-55)," EPRI Report, dated July 18, 2002 (ADAMS Accession No. ML023010510).
Principal Contributor: A. Rezai Date: August 27, 2009
- 2 10 CFR 50.55a(a)(3)(ii), for the remainder of the current (third) 10-year lSI interval and the fourth lSI interval until the RV head is replaced for ANO-2.
All other requirements for which relief has not been specifically requested remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
The NRC staffs safety evaluation is enclosed.
Sincerely, IRA!
Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-368
Enclosure:
Safety Evaluation cc w/encl.: Distribution via ListServ DISTRIBUTION:
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