ML073300272

(HNP) Request for Additional Information (RAI) Regarding Core Shroud Stabilizer Assemblies

ML073300272
Person / Time
Site:	Hatch
Issue date:	11/29/2007
From:	Martin R NRC/NRR/ADRO/DORL/LPLII-1
To:	Madison D Southern Nuclear Operating Co
Martin R, NRR/DORL, 415-1493
References
TAC MD6396
Download: ML073300272 (6)

Text

November 29, 2007 Mr. Dennis R. Madison Vice President - Hatch Edwin I. Hatch Nuclear Plant 11028 Hatch Parkway North Baxley, GA 31513

SUBJECT:

EDWIN I. HATCH NUCLEAR PLANT, UNIT NO. 1 (HNP 1), REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING CORE SHROUD STABILIZER ASSEMBLIES (TAC NO. MD6396)

Dear Mr. Madison:

By letter to the Nuclear Regulatory Commission (NRC) dated August 14, 2007, Southern Nuclear Operating Company, Inc., submitted a request for authorization under the provisions of Title 10 of the Code of Federal Regulations, Part 50, Section 50.55a(a)(3)(i) for modification of the core shroud stabilizer assemblies (tie rods) for HNP1. We have reviewed the information and have identified that additional information is needed to complete the review. Our request for additional information is enclosed.

We discussed this issue with your staff on November 21, 2007. Your staff indicated that it plans to submit a response to this issue within thirty (30) days of receipt of this letter.

Sincerely,

/RA/

Robert E. Martin, Senior Project Manager Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-321

Enclosure:

RAI cc w/encl: See next page

- ML073300272 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/LPL2-1/BC NAME RMartin:nc MOBrien EMarinos DATE 11/29/07 11/29/07 11/29/07 REQUEST FOR ADDITIONAL INFORMATION CONCERNING MODIFICATION OF CORE SHROUD STABILIZER ASSEMBLIES By letter dated August 14, 2007, Southern Nuclear Operating Company, Inc. (SNC),

submitted a request for authorization under the provisions of Title 10 of the Code of Federal Regulations, Part 50, Section 50.55a(a)(3)(i) for modification of the core shroud stabilizer assemblies (tie rods) for the Edwin I. Hatch Nuclear Plant, Unit 1 (HNP 1). The licensee proposes to replace tie rod upper support with a modified upper support design capable of operation through the end of the renewed operating license term. The staff has reviewed the information the licensee provided that supports the proposed request and requires information from the licensee related to the following issues to complete its review.

1. Section 6.3, Materials Fabrication, in Enclosure 1 to the August 14, 2007, letter indicates that the replacement hardware conforms specifically to the conditions described in Sections 3.5.2, 3.6.2 and 3.6.3 of the Nuclear Regulator Commission staffs safety evaluation for BWRVIP-84, BWR Vessel and Internals Project Guidelines for Selection and Use of Materials for Repair to BWR Internal Components (BWRVIP-84), dated September 6, 2005. These sections of the staffs safety evaluation describe requirements for surface preparation techniques to reduce susceptibility to intergranular stress corrosion cracking (IGSCC) and fatigue in cold worked austenitic stainless steel and Alloy X-750 material and to reduce the susceptibility to cracking of electrical discharged machined Alloy X-750 material.

The licensee is requested to provide a description of the surface preparation techniques used to reduce the susceptibility to IGSCC and fatigue in cold worked austenitic stainless steel and Alloy X-750 material in the replacement hardware.

The licensee is also requested to provide a description of the surface preparation techniques and qualification tests performed to reduce the susceptibility to cracking of electrical discharged machined Alloy X-750 material in the replacement hardware.

2. Section 5.3.1 of GE-NE-0000-0061-6346-R2-P indicates that the bearing interface of the horizontal arm of the upper support and the contact between the threads in the tie rod nut and the tie rod were modeled using contact elements with a particular coefficient of friction value. Describe the impact of lower or higher coefficient of friction values on the total stress (Pm + Pb + Q + F) due to sustained normal operation and whether different coefficient of friction values could cause the total stress to exceed the threshold for IGSCC susceptibility in BWRVIP-84. How was the coefficient of friction used in the GE-NE-0000-0061-6346-R2-P report determined?

3. Section 2, Background, in Enclosure 1 to the August 14, 2007, letter indicates that the cause of the cracking in the upper supports in the shroud stabilizer assembly was IGSCC of the Alloy X-750 material. Alloy X-750 material is susceptible to IGSCC if subjected to sustained, large peak stress conditions.

The BWRVIP issued letters dated March 29, 2006, and April 3, 2006, requiring Enclosure

plants with core shroud tie rod repairs to inspect their repairs at their next scheduled refueling outage. These letters indicated that inspections should include all the same or similar locations where the indications were observed and that consideration should also be given to other locations in the tie rod repair where X-750 material is used and which may experience high-sustained stresses.

a) The licensee is requested to identify all Alloy X-750 components, excluding the replacement tie rod upper support and nuts, in the primary vertical and horizontal load paths of the core shroud stabilizer assembly.

b) What design changes are proposed to reduce the total stress in the Alloy X-750 components, excluding the replacement tie rod upper support and nuts, to reduce their sustained, peak stresses to a value below the IGSCC susceptibility criteria.

c) When were the components identified in response to RAI-3b last inspected for IGSCC? What were the results from the inspection?

d) What is the proposed frequency of inspection for the Alloy X-750 components and what type of inspection will be performed to ensure that the Alloy X-750 components have not had IGSCC ?

4. Section 7.2.2, Inspections During Subsequent Refueling Outages, of Enclosure 1 to the August 14, 2007, letter indicates that the licensee will work with General Electric and the BWRVIP to establish the appropriate reinspection criteria for X-750 components. Provide a plan and schedule for determining which X-750 components need to be reinspected to verify that they are not susceptible to IGSCC.

5. Identify the water chemistry (i.e., hydrogen addition, noble metal addition, etc.)

controls that have been instituted or will be instituted at HNP 1 to reduce the susceptibility of Alloy X-750 and austenitic stainless steel to IGSCC. What impact does this water chemistry have on the susceptibility to IGSCC of the replacement tie rod upper support and nuts?

6. By letter dated February 20, 1996, the licensee proposed to increase the shroud stabilizer tie rods mechanical preload to prevent shroud horizontal weld separation during normal operation. The additional mechanical preload assures that no gaps exist during normal operation while satisfying allowable stress limits.

Explain how the shroud stabilizer tie rods mechanical preloads have been incorporated into the structural analyses performed in GE-NE-0000-0061-6346-R2-P report.

Edwin I. Hatch Nuclear Plant, Units 1 & 2 cc:

Laurence Bergen Mr. Jeffrey T. Gasser Oglethorpe Power Corporation Executive Vice President 2100 E. Exchange Place Southern Nuclear Operating Company, P.O. Box 1349 Inc.

Tucker, GA 30085-1349 P.O. Box 1295 Birmingham, AL 35201-1295 Mr. R. D. Baker Manager - Licensing General Manager Southern Nuclear Operating Company, Edwin I. Hatch Nuclear Plant Inc. Southern Nuclear Operating Company, P.O. Box 1295 Inc.

Birmingham, AL 35201-1295 U.S. Highway 1 North P.O. Box 2010 Resident Inspector Baxley, GA 31515 Plant Hatch 11030 Hatch Parkway N. Mr. K. Rosanski Baxley, GA 31531 Resident Manager Oglethorpe Power Corporation Harold Reheis, Director Edwin I. Hatch Nuclear Plant Department of Natural Resources P.O. Box 2010 205 Butler Street, SE., Suite 1252 Baxley, GA 31515 Atlanta, GA 30334 Steven M. Jackson Senior Engineer - Power Supply Municipal Electric Authority of Georgia 1470 Riveredge Parkway, NW Atlanta, GA 30328-4684 Mr. Reece McAlister Executive Secretary Georgia Public Service Commission 244 Washington St., SW Atlanta, GA 30334 Arthur H. Domby, Esq.

Troutman Sanders Nations Bank Plaza 600 Peachtree St, NE, Suite 5200 Atlanta, GA 30308-2216 Chairman Appling County Commissioners County Courthouse Baxley, GA 31513