ML17037B619

Letter Responding to 05/20/1977 Letter Requesting Information on Reactor Vessel Material Surveillance Program

ML17037B619
Person / Time
Site:	Nine Mile Point
Issue date:	07/22/1977
From:	Rhode G Niagara Mohawk Power Corp
To:	Lear G Office of Nuclear Reactor Regulation
References
NUREG-0305
Download: ML17037B619 (12)

Text

U.S. NUCLEAR REGULATORY COMMISSION OOCKET NUMBER NRC FORM 196 12.7S I D FILE NUMBER NRC DISTRIBUTION FGR PART 50 DOCKET MATERIAL FROM: OATE OF OOCUMENT TO:

George Lear Niagaaa Mohawk Power Corp) 7/22/77 Syracuse, NY OATE RECEIVED G. K. Rhode 7/26/77 ONOTORIZEO PROP INPUT FORM NUMBER OF COPIES RECEIVEO BI ETTER ABORIGINAL $ 3UNCLASSIFI E O 0 COPY Wl OESCRIPTION ENCLOSURE Enclosed info on the reactor vessel material and weld material used in fabrication of the reactor vessel. as requested in ltr dtd 5/20/77.

1p+3p PLANT NAME! Nine Mile Point Nuclear Pwr Plt Unit No. 1 RBT 7/27/77 FOR ACTION/INFORMATION ENVIRHNMENTAL ASSIGNED AD. V~ MOORE LTR BRANCH CHIEF!

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~s71 JUL p,2 Local PDR ORB¹3 Rdg Docket No. 50-220 VStello KRGoller GLear SNowicki CParrish Niagara tlohawk Power Corporation SSheppard ATTN: Hr. Gerald K. Rhode OELD Vice President - Engineering OI8E (3) 300 Erie Boulevard West DEisenhut Syracuse, New York 13202 TBAbernathy JRBuchanan ACRS (16)

Gentlemen: File RE: TECHNICAL REPORT ON D.C. POWER SUPPLIES IN NUCLEAR POWER PLANTS (NUREG-0305}

Enclosed for your information is a copy of the subject report.

If you have any questions or comments please contact our staff.

Sincerely, Karl R. GolTer, Assistant Director for Operating Reactors Division of Operating Reactors OFFICE P ORB¹1 ORB¹3 ORB¹3 SSheppard:ar SNowi i GLear DATE > 7/ ~~

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NIAGARA MOHAWK POWER CORPORATION NIAGARA III MOHAWK 300 ERIE 80UI.EVARO, WEST SYRACUSE. N. Y. 13202 July 22, 1977

~II p aIT; Pg+iQ Director of Nuclear Reactor Regulation Attn: Mr. George Lear, Chief Operating Reactors Branch g3 U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Re: Nine Mile Point Unit 1 Docket No. 50-220 DPR'-63

Gentlemen:

Your letter dated May 20, 1977 requested infor-mation on reactor vessel material and weld material used" in fabrication of the reactor vessel. The attachment to this letter addresses itself to those concerns.

Very truly yours, NIAGARA MOHAWK POWER CORPORATION Gerald K. /bode Vice President - Engineering PEF/szd 772080305.'I

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REACTOR VESSEL MATERIAL SURVEILLANCE PROGRAM The Nuclear Regulatory Commission's staff's concern is that the materials used in reactor ves'sel fabrication may have a wider variation in sensitivity to radiation damage than originally anticipated. The Nuclear Regulatory Commission has suggested that some reactor vessels'ay incorporate more than one heat of materials, including weld materials in their beltline region.

In addition, it has been indicated that all of the heats may not be included in the reactor vessel mater'ial surveillance program.

This response provides'nformation to show that General Electric's program of reactor ves'sel surveillance is completely responsive to 10CFR50, Appendix H. Further, the effect on adjusted xeference temperature for the most adverse materials in BWR/2 through BWR/4 plants irradiated to the maximum 40-year

.fluence observed is very small.

General Electric has addressed the problem of obtaining representative survei'llance 'specimens since the beginning of its reactor pressure ves'sel'urveillance 'program. The material for base metal specimen's has been taken from a plate used in the vessel beltline region ox from a plate 'of the same heat of material. The same plate used for base metal specimens is used for production of heat-affected zone "specimens, and the weld specimens are produced by the 'identical weld practice and procedures used in the 'ves'sel fabrication. Por vessels constructed from plate, as is the 'Nine Mile Point Unit 1 vessel, the vessel longitudinal welds are represented; while for vessels fabricated from forged rings, the girth welds are represented. When widely varying weld practices such as submerged metal arc and electxoslag welding are used jointly in a vessel, both are 'repres'ented in the surveillance program matexial. Thus, the surveillance specimens do represent the materials and processing of the vessel'eltline region.

The procedures described above were used to select sux-veillance materials and to prepare specimens for all opexating BWR 2 through 4 plants. Examination of this method of selection, even in light of the most recent data, reveals that the reactor pressure vessel surveys;llance specimens currently in use still provide a reasonable 'rep'resentation of the limiting materials in the reactor vessel beltline 'region.

The production of the vessel'eltline region is generally accomplished by theweXding of sev'ex'al plates and, most often, several heats of steel are involved. The 'vessel surveillance specimens are produced from one 'of the'se 'he'ats. possible variation of the other'eXtline heats,-'o'wever', isThelimited the characteristic range 'of .compositions resulting from the by material production practices'. Consultation with the domestic heavy-section pressure ves'sel steel mill, Lukens Steel, concerning process capability and a survey'f 10 BWR vessels

t reveals that the residual element of major importance, copper, lies consistently within the 0.15 to 0.20 weight percent range when special low-copper scrap selection procedures are not invoked in the mill process. This was the case when the Nine Mile Point Unit 1 vessel was fabricated.

Examination of the predicted effect of residual element composition on the irradiation behavior of pressure vessel steels is discussed in Regulatory Guide '1.99. A preliminary analysis of GE data in'the 'BUR fluence "range from'0 operating BWR's (representing copper'ontents in the 'range 0.01 to 0.30 weight percent and phosphorous contents in the range .007 to 0.02 weight per'cent) rev'eals a minimal impact due to the possible .variation in'base 'metal composition that could be present in the ves'seX beltline.'" Data at the upper end of the copper range (0.30%) was obtained from an atypical source.

Xt represents a foreign. plant with a forged ring produced by foreign practice. Xt does, howev'er, .provide additional support for predicting the 'maximum effect of"elevated copper contents.

The predicted end of 40-year .$ j,fe 'fluence at the vessel wall 1/4T location is b'elow 2 x 10~o nvt (> 1 MeV) as indicated in the FSAR Volume 1 Section V. For thi.'s fluence 'range, an estimated end of life "variance 'of approximately 15oF in transition temperature shift would be 'indicated for a copper'omposition range of 0.15 to 0.20'eight'er'cent copper. This variance represents the expected dev'iation in predicted transition temperature shift due to compositional differences. That is, at the end of life fluence,'he:predicted shift in transition temperature could vary by 15oF depending on'he composition of the heat of plate 'material in ques'tion. Thus, even with the maximum predicted variability'f copper conten't for the belt-line plate mater'ial, a minimal variation in predicted transition temperature shift is e'xpected.'imilarly, the variability of wel'd metal properties within the beltline region does not present a major obstacle 'to their effective representation'by the 'current surveillance specimens.

Typically, the 'range 'of'res'idual element compositions present in weld metal falls.;within sever'al major bands determined by weld proces's, el'ectrod'e 'co'ating, and flux type. This variability inherent to process characteristic is already taken into account by .the 'fact that theidentical weld process and procedures used in 'ves'sel manufacture are 'used to produce the surveillance 'weld specimens. Xf the copper'ontent range resulted strictly from h'eat to heat variations of filler metal composition withi'n a given proc'e's's,, the 'surveillance specimens still adequatel'y repres'ent a limited range 'of weld metal composition. Tn the 'ves'sel'beltline 'region one heat of filler metal was used for fabr'ica'tion'.-

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A survey of weld practices used in 10 BWR pressure vessels has characterized the ranges of copper contents expected for the weld metal in the vessel beltline. When compared in the fluence region of the BWR (based on the predications of Regulatory Guide 1.99 and a preliminary analysis of extensive GE data) the copper variations within a given process contribute only a minimal estimated variance in the predicted transition temperature shift. For, standard submerged metal arc and electroslag welds a range of 0.15 to 0.20 weight percent copper result in approxi-mately a 15 F variation in transition temperature shift at the end of a 40-year vessel life. For shielded metal arc welds a copper content less than 0.15 weight percent and an estimated end of 40-year life variation of 5o to 10 F in predicted transition temperature shift is expected. For the extreme case of submerged metal arc welds made with copper-coated electrodes used for circumferential welds in 6 BWR's, a range of 0.2 to 0.4 weight percent copper result in a projected end of life variability of approximately 25 F in transition temperature shift. The analysis of the effect of elevated copper in these welds produced with copper-coated e ectrodss is based on a maximum predicted fluence of 6 x l0 nvt () l Mev) at the 1/4T wall location for the six plants affected.

Based on the preceding discussion, the selection of materials for the reactor pressure 'vessel survei'llance programs in BWR 2, 3 and 4's does reasonably represent the materials in the beltline region of the vessel. The steps taken by General Electric to assure adequate representation of the welds process and all subsequent material proces'sing step's seen by the vessel materials limits the only possible 'variation between surveillance specimens and vessel material to the heat-to-heat variability of base metal and weld metal. The net, end of 40-year life effect of these possible variations, is projected to be only 10o to 25oF variability in the 'predicted transition temperature shift for the BWR fluence range.

Although it is still important to know the residual element composition of the vessel steel and surveillance speci-mens for complete 'analysis of survei;llance test results, this information can easily be 'obtained by chemical analysis of archive material and analysis of specimens at the time of testing. General Electric believ'es that the steps taken during the production of BWR pres'sure 'ves'sel surveillance specimens adequately assure reasonable 'rep'res'entation of the vessel material and that any. variations in irradiation behavior between the surveillance materials and additional heats of vessel materials would be 'minimal in the BWR fluence range.

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