2CAN020901, Request for Alternative to 10 CFR 50.55a(g)(6)(ii)(D) Examination Requirements
| ML090400962 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/09/2009 |
| From: | David Bice Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN020901, EA-03-009, TAC MC8282 | |
| Download: ML090400962 (11) | |
Text
Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4710 David B. Bice Acting Manager, Licensing Arkansas Nuclear One 2CAN020901 February 9, 2009 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
Request for Alternative to 10 CFR 50.55a(g)(6)(ii)(D)
Examination Requirements Arkansas Nuclear One, Unit 2 Docket No. 50-368 License No. NPF-6
REFERENCES:
- 1. Entergy Letter to the NRC dated September 9, 2005, ANO-2 Relaxation Request #5 to NRC First Revised Order EA-03-009 for the Control Element Drive Mechanism Nozzles
- 2. NRC Letter to Entergy dated May 17, 2006, 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)
Dear Sir or Madam:
Effective October 10, 2008, the Nuclear Regulatory Commission (NRC) amended 10 CFR 50.55a to include 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 Once a licensee implements the code case, the First Revised NRC Order EA-03-009 (the Order) is no longer applicable and shall be deemed to be withdrawn.
Arkansas Nuclear One, Unit 2 (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 Reference 1, Entergy Operations, Inc. (Entergy) requested relaxation from Section IV.C.(5)(b) of the Order for ANO-2. Specifically, the bottom of the ANO-2 control element drive mechanism (CEDM) nozzles contain threads that could not be effectively examined in accordance with the Order. In Reference 2, the NRC granted the relaxation.
2CAN020901 Page 2 of 3 The conditions that required Entergy to submit a relaxation request to the Order remain with the amendment to 10 CFR 50.55a. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), Entergy hereby requests approval of the proposed alternative to the requirements of the Code Case N-729-1 for the upcoming ANO-2 refueling outage, currently scheduled for Fall 2009.
The request is provided in Attachment 1 to this letter. It should be noted that the request is actually a summary of the request made in Reference 1. The NRC has previously noted that there was no need to reproduce all of the detailed information that has already been provided in a relaxation request in a new relief request.
The assumptions and technical basis used in the previous relaxation request under the Order were reviewed by Entergy, as discussed in Attachment 1 to this letter. It was determined that the assumptions and technical basis used in the previous Relaxation Request remain valid with regard to the requirements of Code Case N-729-1 as conditioned by 10 CFR 50.55a.
In accordance with 10 CFR 50.55a(a)(3)(i), the proposed alternative to the referenced requirements may be approved by the NRC provided an acceptable level of quality and safety are maintained. Entergy believes the proposed alternative meets this requirement.
This relief request includes one new regulatory commitment. Attachment 2 contains a copy of the commitment for completeness.
Entergy requests approval of the proposed alternative by August 27, 2009, in order to support the Fall 2009 refueling outage. Although this request is neither exigent nor emergency, your prompt review is requested.
If you have any questions or require additional information, please contact me.
Sincerely, DBB/rwc Attachments:
- 1. Request for Alternative ANO2-ISI-002
- 2. List of Regulatory Commitments
2CAN020901 Page 3 of 3 cc: Mr. Elmo E. Collins Regional Administrator U. S. Nuclear Regulatory Commission Region IV 612 E. Lamar Blvd., Suite 400 Arlington, TX 76011-4125 NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. Alan B. Wang MS O-7 D1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Arkansas Department of Health Radiation Control Section 4815 West Markham Street Slot #30 Little Rock, AR 72205
Attachment 1 2CAN020901 Request for Alternative ANO2-ISI-002 to 2CAN020901 Page 1 of 5 REQUEST FOR ALTERNATIVE ANO2-ISI-002 I. ASME COMPONENTS AFFECTED Arkansas Nuclear One, Unit 2 (ANO-2) has ninety (90) ASME Class 1 reactor pressure vessel (RPV) head penetration nozzles comprised of eighty-one (81) Control Element Drive Mechanism (CEDM) nozzles, eight (8) Incore Instrument (ICI) nozzles, and one (1) vent line nozzle. This request pertains to the CEDM nozzles only.
II. APPLICABLE CODE EDITION AND ADDENDA ASME Code,Section XI, 2001 Edition with the 2003 Addenda is the current code of record for ANO-2.
III. CODE CASE N-729-1 REQUIREMENTS The Code of Federal Regulations 10 CFR 50.55a(g)(6)(ii)(D)(1) requires that examinations of the reactor vessel head be performed in accordance with ASME Code Case N-729-1 (Reference 1), subject to the conditions specified in paragraphs 10 CFR 50.55a(g)(6)(ii)(D)(2) through (6).
Code Case N-729-1 Requirements Code Case N-729-1 requires that components shall be examined as specified in Table 1 of the code case. Table 1, Item B4.20 requires examination of all nozzles. Paragraph 2500 of Code Case N-729-1 states, in part:
If there are obstructions or limitations that prevent the examination of the volume or surface required by Fig. 2 of the code case for one or more nozzles, the analysis procedure of Appendix I of the code case is to be used to demonstrate the adequacy of the examination volume or surface for each such nozzle. If Appendix I is used, the evaluation shall be submitted to the regulatory authority having jurisdiction at the plant site.
One of the conditions listed in the amended 10 CFR 50.55a for the use of this code case states that if Appendix I is to be implemented, prior NRC approval is required. This request is not to implement Appendix I.
IV. REASON FOR REQUEST Pursuant to 10 CFR 50.55a(a)(3)(i), Entergy Operations, Inc. (Entergy) requests an alternative to the requirements of Code Case N-729-1 for the remainder of the current (3rd) 10-year inservice inspection (ISI) interval and the fourth (4th) ISI interval until the head is replaced for ANO-2. Entergy plans to inspect the RPV head CEDM penetration nozzles at ANO-2 using the ultrasonic testing (UT) method to the extent possible. However, a UT inspection from the inside diameter (ID) of the CEDM nozzles at ANO-2 can only be to 2CAN020901 Page 2 of 5 performed from 2 inches above the root of the J-groove weld down to a point approximately 1.544 inches above the bottom of the nozzle. This 1.544 inch blind zone is due to limitations resulting from CEDM nozzle configuration (1.344 inches) and inspection probe design (0.200 inches). These limitations are discussed below. The hardships associated with these limitations are discussed in Reference 2.
Nozzle Configuration Limitation Guide cones are attached to the bottoms of the ANO-2 CEDM nozzles via threaded connections. Specifically, the guide cone screws into the end of the CEDM nozzle with a welded set screw and two tack welds at the cone-nozzle interface to secure the guide cone to the nozzle. The length of the threaded connection region is 1.25 inches. Additionally, a 45 chamfer exists immediately above the threaded connection region. The length of the chamfer region is 0.094 inches.
Due to the threaded connection and chamfer region at the bottom of each CEDM nozzle, a meaningful UT examination in that area cannot be performed. Specifically, the chamfer region geometry causes sporadic signals while, once the guide cone is reached, sound cannot pass into the CEDM nozzle base material because of the gap that exists between the guide cone and the nozzle at the threaded connection. Therefore, UT of the bottom 1.344 inches (1.25 + 0.094) of the CEDM nozzles is not possible.
Inspection Probe Design Limitation The inspection probe to be used to inspect the ANO-2 CEDM nozzles typically consists of multiple individual transducers. Various probe configurations may be utilized to perform the inspections.
The inspection probe is designed so that the ultrasonic transducers are slightly recessed into the transducer holder. This recess must be filled with water to provide an acoustic coupling between the transducer and the nozzle wall. Because of this design, the complete diameter of the transducer must fully contact the inspection surface before ultrasonic information can be collected. Because UT probes have a diameter of 0.250 inch, these transducers, in theory, are able to collect meaningful UT data down to a point approximately 0.125 inch (1/2 diameter) above the chamfer. However, when the lower edge of the transducer recess drops below the chamfer, the water between the transducer and the nozzle cannot be maintained, and the acoustic coupling is lost. Based on prior UT inspection experience and a review of UT data from previous inspections, meaningful data down to a point 0.200 inches above the chamfer can be collected.
V. PROPOSED ALTERNATIVE AND BASIS FOR USE UT Examination The ID of each CEDM nozzle (i.e., nozzle base material) will be ultrasonically examined from the applicable point above the root of the J-groove (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 to 2CAN020901 Page 3 of 5 incidence angle greater than 30 on a horizontal plane perpendicular to the nozzle axis) to 1.544 inches above the bottom of the nozzle.
The data acquisition techniques used are expected to be essentially the same as those used in previous examination activities.
In addition, an assessment to determine if leakage has occurred into the interference fit zone will be performed.
Analysis For the blind zone portions of the CEDM nozzle not examined by UT, analysis has been performed to:
a) Determine if sufficient free-span exists between the blind zone and the weld to facilitate one (1) operating cycle of crack growth without the crack reaching the weld, and b) For nozzles or portions of nozzles not meeting the item above, determine how much propagation length 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 blind zone plus some additional distance into the blind zone. The additional distance into the blind zone has previously been defined and is subject to augmented inspection as described below. This area to be inspected may include a portion of the weld.
Augmented Inspections CEDM 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 will be inspected.
These nozzles and their associated augmented inspections were identified in Reference 1.
Specifically, an augmented inspection of the applicable outside diameter (OD) surface of the nozzle and applicable surfaces of the J-groove weld fillet cap will be performed on that portion of the nozzle and weld fillet cap that has been determined by analysis as necessary to prevent a crack from reaching the J-groove weld in less than one operating cycle.
Basis The background and basis for the proposed alternative is provided in Reference 2, with regard to the requirements of the Order. There are some differences between the requirements of the Order and the requirements of Code Case N-729-1 as conditioned by 10 CFR 50.55a.
a) Differences in the Required Examination Volume The examination volume required by the Order specified ultrasonic testing of the reactor pressure vessel (RPV) head penetration nozzle (i.e., nozzle base material) to 2CAN020901 Page 4 of 5 from 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 2 inches below the lowest point at the toe of the J-groove weld on a horizontal plane perpendicular to the nozzle axis (or the bottom of the nozzle if less than 2 inches); OR from 2 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 1.0 inch below the lowest point at the toe of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) and including all RPV head penetration nozzle surfaces below the J-groove weld that have an operating stress level (including all residual and normal operating stresses) of 20 ksi tension and greater.
The examination volume required by Code Case N-729-1 specifies ultrasonic testing of the RPV head penetration nozzle (i.e., nozzle base material) from 1.5 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 1.5 inches below the lowest point at the toe of the J-groove weld on a horizontal plane perpendicular to the nozzle axis (or the bottom of the nozzle if less than 1.5 inches) for nozzles with an incidence angle less than or equal to 30; and from 1.0 inches above the highest point of the root of the J-groove weld (on a horizontal plane perpendicular to the nozzle axis) to 1.0 inches below the lowest point at the toe of the J-groove weld on a horizontal plane perpendicular to the nozzle axis (or the bottom of the nozzle if less than 1.0 inches) for nozzles with an incidence angle greater than 30.
The proposed alternative provides a combination of UT examination to the extent possible, plus augmented surface examination as required to ensure that a postulated flaw in the lower portion of the nozzle that cannot be volumetrically (UT) examined will not propagate into the weld during one cycle of operation. The basis for the proposed alternative does not require that the specified UT examination volume be met; therefore, the basis for the proposed alternative remains valid with regard to the differences between the examination volumes specified in the Order and in Code Case N-729-1.
b) Differences in the Specified Examination Frequency The frequency of examination specified by the Order for high susceptibility heads required that the proposed alternative be completed each refueling outage.
The frequency of examination specified by Code Case N-729-1 requires that the volumetric examination be completed prior to a head accumulation of 2.25 RIY (Re-Inspection Years) of operation.
The length of operating time that translates into an RIY value of 2.25 years is calculated as a function of the operating temperature of the head. Based on the temperature of the ANO-2 head during normal operation, the volumetric examination will have to be performed each refueling outage to prevent exceeding an RIY value of 2.25 between successive examinations. However, because the RIY value is subject to calculation variables, and since the examination frequency is a critical criterion in the basis for the proposed alternative, Entergy is adding a specific commitment that the proposed alternative examination will be completed each refueling outage.
to 2CAN020901 Page 5 of 5 VI. CONCLUSION 10 CFR 50.55a(a)(3) states:
Proposed alternatives to the requirements of paragraphs (c), (d), (e), (f), (g) and (h) of this section or portions thereof may be used when authorized by the Director of the Office of Nuclear Reactor Regulation. The applicant shall demonstrate that:
(i) The proposed alternatives would provide an acceptable level of quality and safety, or (ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Entergy believes the proposed alternative provides an acceptable level of quality and safety by utilizing inspections and supplemental analysis to determine the condition of the ANO-2 CEDM nozzles. This request is the same as the request for relaxation documented in Reference 2 and approved by the NRC in Reference 3. Therefore, Entergy requests authorization to perform the proposed alternative to the Code Case requirement pursuant to 10 CFR 50.55a(a)(3)(i) for implementation beginning with the ANO-2, 2R20 refueling outage scheduled for the Fall of 2009 and continuing into the fourth (4th) 10 year inservice inspection interval until the head is replaced. It should be noted that the 2R20 outage is the last refueling outage in the third (3rd) 10 year inservice inspection interval.
VII. REFERENCES
- 1. 10 CFR 50.55a, Codes and Standards
- 2. Entergy Letter to the NRC dated September 9, 2005, ANO-2 Relaxation Request #5 to NRC First Revised Order EA-03-009 for the Control Element Drive Mechanism Nozzles
- 3. NRC Letter to Entergy dated May 17, 2006, 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)
Attachment 2 2CAN010901 List of Regulatory Commitments to 2CAN020901 Page 1 of 1 List of Regulatory Commitments The following table identifies those actions committed to by Entergy in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
TYPE (Check one) SCHEDULED ONE-TIME CONTINUING COMPLETION DATE COMMITMENT ACTION COMPLIANCE (If Required)
The alternative examination proposed by X N/A the Relief Request will be completed each ANO-2 refueling outage until the reactor vessel head is replaced.