RS-11-063, Regarding Supplement to Inservice Inspection Relief Request 13R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations
| ML111010202 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 04/10/2011 |
| From: | Benyak D Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-11-063 | |
| Download: ML111010202 (4) | |
Text
n Nuclear RS-11-063 10 CFR 50.55a April 10, 2011 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station Unit 1 Facility Operating License No. NPF-3?
NRC Docket No. STN 50-454
Subject:
Supplement to Byron Station Unit 1, Inservice Inspection Relief Request 13R-19:
Alternative Requirements for the Repair of Reactor Vessel Head Penetrations
References:
(1) Letter from J. Hansen (Exelon) to U. S. NRC, "Byron Station Unit 1 Inservice Inspection Relief Request 13R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations," dated March 24, 2011 (2) Letter from D. M. Benyak (Exelon) to U. S. NRC, "Additional Information Related to Byron Station Unit 1, Inservice Inspection Relief Request 13R-19:
Alternative Requirements for the Repair of Reactor Vessel Head Penetrations," dated March 25, 2011 (3) Letter from D. M. Benyak (Exelon) to U. S. NRC, "Additional Information Related to Byron Station Unit 1, Inservice Inspection Relief Request 13R-19:
Alternative Requirements for the Repair of Reactor Vessel Head Penetrations," dated March 31,2011 (4) Letter from J. Hansen (Exelon) to U. S. NRC, "Supplement to Byron Station Unit 1, Inservice Inspection Relief Request 13R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations," dated April 8, 2011 (5) Email from N. DiFrancesco(U.S. NRC)toR. Mcintosh (Exelon), "Request for Additional Information for Repair of Reactor Vessel Head Penetration Numbers 64 and ?6 (ME58??), Repair of Reactor Vessel Head Penetration Numbers 31 and 43 (ME5948), Alternative for Repair of Reactor Vessel Head Penetrations (ME5961)," dated April 9, 2011 In Reference 1, in accordance with 10 CFR 50.55a, "Codes and standards," paragraph (a)(3)(i),
Exelon Generating Company, LLC (EGC), submitted the Relief Request 13R-19 from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," on the basis that the proposed alternatives would provide an acceptable level of quality and safety.
Specifically, Reference 1 proposed to perform an alternative repair technique using an imbedding seal weld methodology on the reactor Vessel Head Penetration (VHP) housings and
April 10, 2011 U. S. Nuclear Regulatory Commission Page 2 J-groove welds of Byron Station, Unit 1. The performance of the imbedded flaw seal weld technique in accordance with the Relief Request 13R-19, in Reference 1, essentially uses the non-structural seal weld to isolate the Primary Water Stress Corrosion Cracking (PWSCC) susceptible material, alloy 600 and its weld materials alloy 182/82, from primary coolant with highly PWSCC resistant weld material Alloy 52 or 52M. There are four penetration nozzles, 31, 43, 64 and 76, that require this repair method during the ongoing Byron Station, Unit 1, Refueling Outage B1 R17. During performance of the repairs in B1 R17, EGC has supplemented the request with letters dated March 25, March 31 and April 8, 2011, by References 2, 3 and 4.
On April 9, 2011, in Reference 7, the NRC provided a Request for Additional Information (RAI).
EGC has included a response to the RAI in Attachment 1 of this letter.
To achieve As Low As Reasonably Achievable dose and produce a technically acceptable repair of nozzles 31 and 64, Reference 4 added a provision for approval under 10 CFR 50.55a(a)(3)(ii), to use these additional alternative requirements in eliminating mechanical discontinuities detected in the seal welds during performance of the repairs. EGC requests an expedited verbal approval by noon on April 10, 2011, to use the Relief Request 13R-19 as amended, with the additional information that is provided in Attachment 1.
There are no new regulatory commitments in this submittal. More specifically, the regulatory commitment from EGC's recent response to an RAI (Le., Reference 2) will remain applicable to Relief Request 13R-19.
If you have any questions about this letter, please contact Mr. Richard W. Mcintosh at (630) 657-2816.
Respectfully,
~'M~L Darin M. Benyak Director, Licensing and Regulatory Affairs
Attachment:
- 1. Additional Information Related to Alternative Requirements for the Repair of Reactor Vessel Head Penetrations, 13R-19
ATTACHMENT 1 ADDITIONAL INFORMATION RELATED TO THE ALTERNATIVE REQUIREMENTS FOR THE REPAIR OF REACTOR VESSEL HEAD PENETRATIONS, 13R-19 (Page 1 of 2)
NRC QUESTION RAI-1:
By letter dated March 25, 2011, the licensee noted for penetration nozzle number 64 the fol/owing; For the 151 NOE of the repair for Penetrations 64 and 76 starting with refueling outage B1R18, Note 3 does not apply since the repair location is in the "VHP Nozzle 00 below J-groove weld." Therefore, 151 NOE of the repair for Penetrations 64 and 76 will be performed in accordance with Code Case N-729-1, as amended by 10 CFR 50.55a(g)(6)(ii)(0).
By letter dated April 8, 2011, the licensee requests relief from NB-4450 for the repair of six rejectable liquid dye penetration surface indications in the seal weld of head penetration nozzle number 64.
The Table of Item 3 of Section 5.0, "Conditions and Limitations" of Reference 2 of the March 24, 2011 submittal requires only a volumetric or surface examination for the 151 inspection of a penetration with a flaw in the nozzle below the J-groove weld.
In addition to the volumetric examination of the nozzle, will a surface examination be performed on wetted surface of the entire seal weld for penetration number 64 at the same frequency requirement of the volumetric examination of penetration number 64 in accordance with 10 CFR 50.55a(g)(6)(ii)(0)?
(
I RESPONSE TO RAI-1 :
\\
In addition to the volumetric examination required of the penetration number 64 in accordance with 10 CFR 50.55a(g)(6)(ii)(D), EGC will perform a surface examination on the wetted surface of the seal weld repair areas that are subject to the alternate repair rules to NB-4450 during
\\ B1 R18. The acceptance standards for this surface examination will be in accordance with I.. 10 CFR 50.55a(g)(6)(ii)(D).
NRC QUESTION RAI-2:
For aI/ unacceptable linear indications in the seal weld, provide each new second seal weld's minimum area of coverage? Will this area of coverage be based on a distance beyond each indication's dye penetrant length and width result? Provide a description of application and the number of the weld beads applied to address Indications #2 and #3 of Penetration number 31.
RESPONSE TO RAI-2:
Each new seal weld's area of coverage will extend at least 1/8-inch in width and nominally 1/4-inch or more in length beyond each existing linear indication to be sealed. One exception will be indication number 1 on penetration 64 (the indication near the toe of the J-groove weld repair weld); this repair will extend approximately 1/16-inch to 1/8-inch beyond the indication in
ATTACHMENT 1 ADDITIONAL INFORMATION RELATED TO THE ALTERNATIVE REQUIREMENTS FOR THE REPAIR OF REACTOR VESSEL HEAD PENETRATIONS, 13R-19 (Page 2 of 2) the direction of the weld toe. Note that prescriptive verification of these coverage dimensions is not feasible, because measurements would result in substantial dose increases; alternatively, the final liquid penetrant examination of each repair (which will include the repair itself and an adjacent 1/2-inch) will be used as verification of acceptable seal weld coverage.
The specific location and orientation of each indication will be used in determining the dimensions of the indication-specific weld repair.
Repair of indications 2 and 3 in penetration 31 will be accomplished using a series of axially oriented, side by side weld beads. This series of weld beads will, when completed, completely cover indications 2 and 3. A preliminary estimate indicates approximately 9 to 12 weld beads will be required for this repair; the exact number of beads may be different as necessitated by actual field conditions.