ML17037C104

Proposing a Supplemental Inspection Program for Sensitized Stainless Steel

ML17037C104
Person / Time
Site:	Nine Mile Point
Issue date:	03/24/1972
From:	Schneider F Niagara Mohawk Power Corp
To:	Skovholt D US Atomic Energy Commission (AEC)
References
Download: ML17037C104 (8)

Text

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MOHAWK 300 ERIE SOULEVARD WEST SYRACUSE, N.Y. 13202 Regulatorv-March 24, 1972 Flte Cy, Mr. Donald J. Skovholt Assistant Director for Reactor Operations Division of Reactor Licensing United States Atomic Energy Commission l(ashington, D. C.

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Dear Mr. Skovholt:

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Provisional Operating License DPR-17 Docket No. 50-220

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In your letter dated March 14,

1972, we.were requested to propose a

supplemental inspection program for'ensitized stainless steel on the Nine Mile Point Nuclear Station, Unit tl reactor vessel.

In a report filed May ll, 1970,."Program For Restoration. To Service Based On Reports of Primary System Investigations - Nine Mile Point Nuclear Station",

we agreed to re-examine all furnace sensitized safe ends and welds within the year and to re-evaluate the inspection program based on'he'indings.

In our report of June 10; 1971, the results of this examin-

, ation described all safe ends on the vessel proper to be in satisfactory condition, Indications were found on some of the nineteen furnace sensitized nozzles examined on the. vessel head.

Therefore, to provide a fair sampling and in the interest of minimizing exposure to personnel, our re-evaluation of the surveillance program consisted of a complete examina-

'ion of all nozzles on the vessel head (UT 5 PT) each time the head.was removed.

Should there be indications of general intergranular attack, it would be regarded as sufficient reason to re-examine the safe ends on the vessel prope'r.

Nozzles on the head were re-examined during October,

1971, with gratifying results.

However, as the program for continuing surveillance of the sensitized material over the long term is judged to be insufficient, we now propose the following based on the guide lines of the enclosure in the March 14, 1972 letter.

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Mr. Donald J. Skovholt March 24, 1972 Furnace Sensitized Safe Ends 1.

Examine 100 percent of the furnace sensitized safe ends and safe end welds by PT and UT at or within the first refueling outage.

The first refueling 'outage will take place in the spring of 1973.

All safe ends on'he vessel and head were examined by UT and 'PT in

December, 1970 and April, 1971.

Therefore, the first 100 percent examination will be accomplished within the first refueling.

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Examine 100 percent at or within the second i'efueling outage.

The second refueling outage we'll'ake place one year after the first, or during the spring ofi 1974.

I Examination of all safe ends in one outage, in addition to other in-service inspection requirements, would require excess numbers of personnel in order to hold individual exposures at a conservative level.

Examination of generous samples at regular time intervals should provide better surveillance than those performed in wholesale with irregular spacing.

Therefore, we would examine by UT and PT-a) one-third on vessel, one third on head during April, 1972 b) one-third on vessel, one third on head during Spring, 1973 c) one-third on vessel, one third on head during Spring, 1974 This then would result in 100~a being examined within the second re-fueling outage.

3.

There are no furnace sensitized safe ends welded to pipe containing non-flowing reactor coolant.

There were two core-spray safe ends in this category but they were replaced with non furnace sensitized safe ends in April, 1970.

Also provisions were made in the design to obtain an interchange of liquid within the safe end, therefore preventing stagnation.

See Niagara Mohawk report dated May 1, 1970

'Reactor Primary System Investigation at Nine Mile Point Nuclear Station" Section 7 and Appendix "D".

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One hundred percent will be re-inspected between 1973'and 1980.

One hundred percent will be re-inspected each decade of operation, thereafter in compliance with 1S-242 of Section XI of the ASME Pressure Vessel Code.

l<elds Of Field-Re laced Safe Ends 1.

All three safe ends, both core sprays and one emergency condenser

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Mr. Donald J. Skovholt March 24, 1972 were examined within the first refueling period and report filed June 10, 1971.

However, one core-spray safe end will be examined in 1974 and the emergency condenser in the following decade.

All safe end inspections by PT and UT will consist of one hundred per-cent of exterior surface.

One hundred percent of exterior circumfer-ence of welds and base metal for one wall thickness beyond edge of weld.

Severel Weld-Sensitized Heat-Affected Zones in Wrou ht 304 and 316 Pi ing without actually testing, it is not possible to ascertain whether the heat affected zone is sensitized and if so, to what degree.

During the April, 1972 outage, modified ASTM test A262 will be applied to representative heat affected'zones in welds of given procedure in piping from various suppliers'.

In conjunction, UT and PT examinations will be made.

The degree of sensitization found in the sample will determine the sensitization condition of the remainder 'of the group.

'f Of the 145 joints within the dry well 4" and over, those judged to be severely sensitized will be examined by UT and PT as follows:

April, 1972

- 10 joints

Spring, 1973 - 10 joints

Spring, 1974 - 10 joints In this way, 10~ or 15 are examined within each.the first and second refueling outage.

7 would be examined 1973 - 1980 38 would be examined over each subsequent operating decade Furnace Sensitized Com onents 1(ithin Reactor Vessel lecithin the first refueling outage, as much of the core support ring to support cone weld will be examined visually as time permits.

A high resolution TV camera will be used in the attempt.

Any remaining weld not examined'during the first refueling will be examined within the second refueling.

Four dryer support brackets and one guide rod support bracket will be examined in the same manner at or before the second refueling outage.

Anytime the vessel is opened, if the above commitments have not been

met, an attempt will be made to comply with the program.

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Mr. Donald J. Skovholt 4

March 24, 1972 This program will be repeated in approximate three year intervals.

Shou1d any of the investigations described in the entire supplemental surveillance program disclose material requiring repair, the appropriate branch of the Atomic Energy Commission will be promptly notified.

Summar of Nork To Be Done A ril, 1972 3 - Recirculation Nozzles 6 - Safety valve nozzles on head Up to 10 welds with heat-affected zones in wrought type,304 and 316 piping which may have become severely weld sensitized Ne would be pleased to discuss any part of this program at any time should questions so require.

Very truly yours, F. J. Schneider Vice President - Operations FJS:pw 1

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