ML20023B828

Responds to 830316 Request for Plans for Cycle 6 Reload Outage Steam Generator Insp.Tube Defect Assessment & Supplementary Steam Generator Testing Program Tables Encl

ML20023B828
Person / Time
Site:	Millstone
Issue date:	04/29/1983
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	Clark R Office of Nuclear Reactor Regulation
References
A03124, A3124, TAC-51351, NUDOCS 8305060424
Download: ML20023B828 (5)

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g , , cw-sv ca a s.:anov ,, (203) 666-6911 April 29,1983 Docket No. 50-336 A03124 Director of Nuclear Reactor Regulation Attn: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1) R. A. Clark letter W. G. Counsil, dated March 16,1983.

(2) W. G. Counsil letter to R. A. Clark, dated February 12,1982.

(3) E. L. Conner letter to W. G. Counsil, dated March 5,1983.

(4) W. G. Counsil letter to R. A. Clark, dated January 22,1982.

Millstone Nuclear Power Station, Unit No. 2 Cycle 6 Refueling Outage Steam Generator Inspection Plans in Reference (1), the NRC Staff issued license Amendment No. 83 and the supporting Safety Evaluation to Facility Operating License No. DPR-65, for Millstone Unit No. 2. Documented in Reference (1) was a request for Northeast Nuclear Energy Company (NNECO) to provide the plans for the Cycle 6 reload outage steam generator inspection, thirty (30) days prior to the outage.

In response to that commitment, NNECO provides the following information.

The Millstone Unit No. 2 steam generators (SG) will be inspected during the May 1983 Refueling Outage using advanced multifrequency eddy current inspection techniques in accordance with Technical Specification Requirements. The inspection plan which will be implemented will be in excess of the required 3

\ percent sample and will include at least 10 percent of the unplugged tubes in the hot legs of each of the two SGs. The areas to be inspected are out. lined in the attached Table 1.

Approximately 40 percent of the tubes included in the inspection plan will be inspected fulllength (from the hot-leg tubesheet to the cold-leg tubesheet). The 8305060424 830429 PDR ADOCK 05000336 G pon

remaining tubes to be inspected will be from the hot-leg tubesheet completely around the U-bend to the top tube support plate on the cold-leg side.

Above and beyond the Technical Specification Requirements, the following actions are planned for this inspection:

1. Thirty-three tubes in SG No.1, and 21 tubes in SG No. 2 which were not inspected during the December 1981 Refueling Outage, (as identified in Reference (2)) in fulfillment of the Reference (3) commitment.

2. A representative sample from each SG of tubes typifying the leaking tube found during the March 1983 plant shutdown.

3. A representative sample from each SG of the accessible outer peripheral tubes.

In addition to inspecting for tube defects, a Supplementary Program for denting assessment will also be performed on a best effort basis. Advanced multifrequency eddy currt.at and profilometer methods will be used to assess the status of and progression of SG tube denting in this Supplementary Program. The techniques represent an advanced level of nondestructive testing technology and should provide results with optimum definition.

Table 2 of the attachment outlines the Supplementary Steam Generator Testing Program and includes a tube plugging criterion which represents a gauging criteria in combination with tube strain based on profilometer data. Since the profilometer measurements represent the actual tube shape, the strain computed from the measurement represents optimum definition of tube strain.

NNECO concludes that the planned steam generator inspections outlined in the attached Tables 1 and 2 will provide the necessary information to ensure the probability of a SG tube failure remain acceptably low during Cycle 6 operation of Millstone Unit No. 2.

We trust you will find this information responsive to the Reference (1) request.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY f(V17& ~

W. G. Counsil Senior Vice President

e Definitions Accessible Tube: A tube that is accessible to remote, manipulator type of devices used for conducting eddy current examinations.

Affected Areas: These areas of the steam generator where tube pitting has been concentrated (Reference 4).

Blockage: Tube condition that prevents passage of a probe of the nominal diameter indicated.

Denting: Constriction of the Inconel tubing that occurs at the tube / tube support junctions as a result of magnetite build-up in these regions.

Profilometer: Device for measuring eight or more internal tube radii as a function of axial position.

Unaffected areas: Those areas of the steam generator where no tube pitting has been found (Reference 4).

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TABLE 1 Inspection Program for Tube Defect Assessment Approximate Sample Size (Percent of Unplugged Tubes) Sample Location

• 10% Hot-Leg Tubes in Affected Areas of each SG 6% Cold-Leg Tubes in Affected Areas of each SG 10% Hot-Leg Tubes in Unaffected Areas of each SG 3% Cold-Leg Tubes in Unaffected Areas of each SG

• Includes tubes where flaws have been identified previously.

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TABLE 2 SUPPLEMENTARY STEAM CENERATOR TESTING PROGRAM (EDDY CURRENT TESTS Sample Size / Location Result Action Requirements 1.0 10 percent of the tubes 1.1 of each steam generator, Blockage of .540* diameter probe 1.1.1 Perform profilometer test and at support elevation, hot-leg side.

determine maximum tube strain' or plug tube.

1.1.1.1 If maximum strain is less than 14%, no action is required.

1.1.1.2 If maximum strain is greater than 3 or equal to 14%, plug tube.

1.1.2 An adjacent tube shall be selected and subjected to a tube inspection.

1.2 Blockage of .540* inch diameter 1. 2. l' 'None, provided that no blockage probe at cold-leg side.

is found on hot-leg side in 10%

sample population.

8 "

1.2.2

' Retest from cold-leg side, if blockage is encountered.

1.2.2.1 If blocked, perform profilometer test and determine maximum tube strain, or plug tube.

1.2.2.1.1 If maximum strain is less than 14%, no action is required.

1.2.2.1.2 If maximum strain is greater than or equal to 14%, plug tube.

1.3 Nonblockage of .540* inch diameter probe at support 1.3.1 None elevations hot-leg and cold-leg iay be changed to .460 inch diameter probe depending on the outcome of a study comparing minimum ediam t

>ased on ' profilometry data from previous M111 stone' 2 outages. er to strain,