ML19257A217

Responds to IE Bulletin 79-17, Pipe Cracks in Stagnant Borated Water Sys at PWR Plants. Visual Examination of All Normally Accessible Welds at Svc Pressure Performed Per IWA 5240

ML19257A217
Person / Time
Site:	Millstone
Issue date:	11/28/1979
From:	Counsil W NORTHEAST UTILITIES
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
IEB-79-17, NUDOCS 8001030077
Download: ML19257A217 (3)

Text

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) h RTFOAD CONNECTICUT 06101 g (203; 666 6911 k L J November 28, 1979 Docket No. 50-336 Mr. B. H. Grier, Director Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406

References:

(1) B. H. Grier letter to W. G. Counsil dated July 26, 1979, forwarding I&E Bulletin No. 79-17.

(2) B. H. Grier letter to W. G. Counsil dated October 29, 1979, forwarding I&E Bulletin No. 79-17, Revision 1.

(3) W. G. Counsil letter to B. H. Grier dated August 24, 1979.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 I&E Bulletin No. 79-17 Reference (1) requested that Northeast Nuclear Energy Company (NNECO) conduct a review of the safety-related stainless steel piping systems to identify systems and portions of systems which contain stagnant oxygenated borated water. The NRC Staff requested that NNEC0 provide specific information regarding these systems within thirty (30) days and to examine the systems by visual, liquid penetrant and ultrasonic techniques within ninety (90) days to verify system integrity.

In Reference (3), NNEC0 submitted the thirty (30) day response to Items 1(a)-1(d) of Reference (1). The Reference (3) response identified the systems and portions of systems which NNECO had determined to contain stagnant oxygenated borated water.

In response to Item 2 of Reference (1), NNECO provides the following:

Item 2(a)

Perform ASME Section XI visual examination (IWA 2210) of normally accessible welds of all engineered safety systems at service pressure to verify system integrity.

Response

NNECO noted in Reference (3) that guidance for the visual examination to verify system integrity will be drawn from IWA 5240. This guide states that insulation 1666 067 F06(038o77 ,

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. will be removed only if evidence of leakage is found at a low point or under a pipe. This definition was selected as it most appropriately addresses the in-tent of the inspection.

Accordingly, NNEC0 has performed a visual examination of all normally accessible welds at service pressure in accordance with IWA 5240. The results of these visual examinations indicate no observed through-wall leakage in any of the systems identified in Reference (3).

Item 2(b)

Conduct ultrasonic examination and liquid penetrant surf ace examination on a representative number of circumferential welds in normally accessible portions of systems identified by 1 above. It is intended that the sample nunber of welds include all pipe diameters in the 2-1/2 inch to 24-inch range with no less than a 10 percent sample by system and pipe wall thickness. It is also intended that the UT examination cover the weld fusion zone and a minimum of 1/2-inch on each side of the weld at the pipe ID. The examination shall be in accordance with the provisions of ASME Code Section XI-Appendix III and Supplements of the 1975 Winter Addenda except all signal responses shall be evaluated as to the nature of the indications. Thase code methods or alternative examination methods, ccmbination of methods, or newly developed techniques may be used provided the precedures yield a demonstrated effectiveness in detecting stress corrosion crack-ing in austenitic stainless steel piping.

Response

A liquid penetrant (PT) surface examination and ultrasonic examination have been completed on ten percent (10%) of the welds including all pipe diameters in the two and one-half inch (2-1/2") to twenty-four inch (24") range of stagnant oxy-genated borated water systems. The liquid penetrant surface examination was completed in accordance with Section V, Article 6, of the ASME Code up to and including the sunmer of 1975 addenda. The liquid penetrant examination indicated no surface cracks were present in the examined welds.

The ultrasonic (UT) examinations have been completed in accordance with NUSCO UT procedure NU-UT-2, Revision 1, which exceeds the requirements of Appendix III,Section XI, and Supplements of the 1975 Winter Addenda, in that a zero degree scan as well as an angle beam examination was completed. The ultrasonic exami-nations indicated no cracking in the fifty-four (54) welds which were examined.

In Reference (2), the NRC Staff revised Reference (1) to include systems or portions of systems where dynamic flow conditions do not exist on a continuous basis. In Reference (3), NNEC0 defined piping not flushed at least once per month as stagnant. This definition was based on the fellowing:

(1) No cracks were found in the high pressure injection lines at three Mile Island, Unit No.1 (TMI-1) which were occasionally flushed.

(2) This definition results in examination of a sufficiently large sample of welds to produce a statistically meaningful inspection.

(3) The class of piping is subjected to the more adverse environment with respect to this concern, as the fluid is motionless for the longer period of time than the piping defined as non-stagnant.

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NNECO maintains that the definition of stagnant noted above adequately addresses the concerns of Reference (1), based on the following:

(1) The visual examinataon required by Item 2(a) has indicated no through wall leakage exists.

(2) Completion of liquid penetrant and ultrasonic examination of ten percent (10%) of the accessible welds in the stagnant oxygenated borated water systems identified in Reference (3) has not revealed any crack indications.

(3) NNECO maintained a chemistry sampling monitoring program from August 30, 1975 through February, 1979, to assure the integrity of the safety-related piping containing boric acid. Under this program, the piping in the safety injection system, containment spray system, which are not flushed at least once per month, and two lines from the boric acid storage tanks in the CVCS were monitored. The maximum allowable chloride concentration in these systems is .15 ppm. This monitoring program was concluded in February, 1979. An augmented Inservice In-spection Program, which includes the piping systems in the above mentioned chemistry monitoring program, was implemented on April 26, 1979.

(4) The weld joint design used at Millstone Unit No. 2 differs significantly from that employed at Three Mile Island Unit No.1 (TMI-1). The geometry of the TMI-1 weld joint is judged to increase the susceptibility of the subject welds to the IGSCC phenomena.

(5) No problems of this nature have been identified in safety related systems at Millstone Unit No. 2 during its four (4) years of operation.

Lastly, please be advised that the monthly visual examination described in Item 2(a) of Reference (2) will not be performed as the examinations required by References (1) and (2) have been completed under NNEC0's interpretation. NNEC0 has not identified cracking in any of the welds examined at Millstone Unit No.

2 by any of the methods required by Reference (1) as revised by Reference (2).

We trust you find this information satisfactory to disposition the Reference (1) and (2) concerns. We remain available should the Staff require clarification of any of the above information.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY 7 -

i $lk W. G. Couilsil Vice President 1666 069