ML17037B612
| ML17037B612 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 08/18/1977 |
| From: | Schneider R Niagara Mohawk Power Corp |
| To: | Lear G Office of Nuclear Reactor Regulation |
| References | |
| Download: ML17037B612 (12) | |
Text
- NRC'FDRM 195
, I1-76)
U.S. NUCI EAR REGULATORY MISSION DOCKET NUMBER
'RC DISTRIBUTION FDR PART 50 DOCKET MATERIAL FILE NUMBER TO R
Mr. Geor'ge Lear FROM:
Niagara Mohawk Power Corp'yracuse, New York Ri Ri Schneider DATE OF DOCUMENT 8/18/77 DATE RECEIVED 8/23/77
@LE ER ORIGINAL Cl COP Y DESCRIPTION ONOTOR IZED jdUNCLASS IF I E D PROP INPUT FORM o
ENCLOSURE NUMBER OF COPIES RECEIVED jP~
/%e-/4 7'++ 7 7 Consists of revision to preVious submittal concerning reactor vessel material surveillance programo
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DISTRIBUTION FOR MATERIAL ON REACTOR VESSEL DATA PER R.
INGRAM 5-26-77 CQIIW~tt
- DO>o>><XOVZ PLANT NA~IE
~ Nine Mile Point'Unit No 1
RJL 8/23/77 (1-P) (3-P)
SAFETY BRANCH CHIEF'ROJECTIfANAGER:
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Zt'IETZIG FOR ACTION/INFORMATION INTERNALD ISTRIBUTION C PDR F
2 MIPC PANLICKI EISENHUT BUTLER GRIMES HAZELTON HOGE R.
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NIAGARA MOHAWK POWER CORPORATION NIAGARA MOHAWK sos ERIE BOULKvARDWEST'((ET F[LE f August 18, 1977 Ib'g~
Director of Nuclear Reactor Regulation Attn:
Mr. George Lear, Chief Operating Reactors Branch ]f3 U.
S. Nuclear Regulatory Commission Washington, D.
C.
20555 Re:
Nine Mile Point Unit 1 Docket No. 50-220 DPR-6'3 Gentlemen:
Our letter of July 22, 1977 supplied information on reactor vessel mater'ial and weld material used in the fabri-cation of the reactor vessel'ursuant to your May 20, 1977 letter.
Subsequent to this, further information was obtained from the reactor vendor which indicated that copper'oated electrodes may have been used.
Therefore, attached is a revision to the 'July 22, 1977 transmittal.
Very truly yours, NIAGARA MOHAWK POWER CORPORATION R,.
R. Schneider Vice President-Electric Production MGM/s zd Attachment
RO 6 N K Oft LL6L LlHA OHISG330Hd IH3WA300 03AI3038
REAC~ VESSEL HATEliIAL SURVEIL CE PROGRAH The Nuclear Regulatory Commission's staff's concern is that the materials used in reactor vessel fabrication may have a wider variation in sensitivity to radiation damage than originally anticipated.
'The Nuclear Regulatory Commission has suggested that some reactor vessels may 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 material surveillance progxam.
This response provides information to show that General Electric's program of reactor vessel surveillance is completely responsive to 10CFR50, Appendix H.
- Further, the effect on adjusted reference temperature for the most adverse materials
'n 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 surveillance specimens since the beginning of its reactox pressure vessel surveillance program.
The material for base metal specimens has been taken from a plate used in the vessel beltline region or 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 vessel fabrication.
Fox vessels constructed from plate, as is the Nine Mile Point Unit 1
- vessel, the vessel longitudinal welds are represented; while
'or 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 represented in the surveillance program material.
- Thus, the surveillance specimens do represent the materials and processing of the vessel beltline region.
The procedures described above were used to select sur-veillance materials and to prepare<specimens for all oper'ating 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 surveillance specimens currently in use still provide a reasonable representation of the limiting materials in the reactor vessel beltline region.
The production of the vessel beltline region is generally
.accomplished by the welding of sevexal plates
- and, most often, several heats of steel are involved.
The vessel suxveillance specimens are produced from one of these heats.
The possible variation of the other beltline heats, however, is limited by the characteristic range of compositions resulting from the material production practices.
Consultation with the domestic heavy-section pressure vessel steel mill, Lukens Steel, concerning process capability and a survey of 10 BWR vessels
0 r>>
reveals that the residual element of major importance,
- copper, lies consistently within the 0.15 to 0.20 ~eight 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 fab'ricated.
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 BWR fluence range from 10 operating BVR's (representing copper contents in the range 0.01 to 0.30 weight percent and phosphorous contents in the range
.007 to 0.02 weight percent) reveals a minimal impact due to the possible variation in base metal composition that coul(d be present in the vessel beltline.
Data at the upper end of the copper range (0.30%)
was obtained from an atypical~ source.
't represents a foreign plant with a forged ring produced by foreign practice.
It does, ho~ever, provide additional support for predicting the maximum effect of elevated copper contents.
The predicted end of 40-year j.j,fe fluence't the vessel wall 1/4T location is below 2 x 10~~ nvt') 1.MeV) as indicated in the FSAR Volume 1 Section V.
For this fluence range, an estimated end of life variance of approximately 15oF in transition temperature shift would be indicated for a copper composi;tion range of 0.15 to 0.20 weight percent copper.
This variance represents'he'xpected deviation in predicted transition temperature shift due to compositional differences.
That is, at the end of life fluence, the predicted shift in transition temperature could vary by 15 F depending on the composition of the heat of plate material in question.
- Thus, even with the maximum predicted variability of copper content for the belt-line plate material, a minimal variation in predicted transition temperature shift is expected'
'imilarly, the variability of weld 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 residual element compositions present in weld metal'falls within several major bands determined by weld process, electrode
- coating, and flux type.
This variability inherent to process characteristic is already taken into account by the fact that the identical weld process and procedures
'used in vessel manufacture are used to produce the surveillance weld specimens.
If the copper content range resulted strictly from he'at to heat variations of filler metal composition within a given process, the surveillance specim'ens still adequately represent a limited range of weld metal composition.
In the vessel beltline region one heat of filler metal was used. for fabrication.
law
H A surv'ey of weld practices used in 10 BWR pressure vessels has characteri'zed 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 an'alysis of extensive GE data) the copper variations within a given process contribute only a minimal estimated variance in the predicted transition temperature shift.
For submerged metal arc and electroslag welds made without copper-coated electrodes, the expected copper content range is 0.15 to 0.20 weight percent.
For shielded metal arc welds, copper content of less than 0.15 weight percent should result; while submerged metal arc welds made with copper'-coated elec-trodes exhibits a typical range of 0.25 to 0.30 with a maximum outside limit of 0.20 to 0.40 weight percent copper.
- For, shielded metal arc, electroslag, and submerged metal arc welds made without copper-coated electrodes, a 10 to 15 F variation in trans'ition temperature response due to residual elemental composition at the maximum 1/4T end-of-life fluence is expected.
For submerged metal arc welds made with copper-coated electrodes, a
larger variation is expected.
The typical copper content of 0.25 to 0.3 weight percent exhibited by these welds w'ould result in a 25 F variation in transition temperature shift at 2 x 1018 nvt
( g 1 mev).
The maximum range of copper contents, 0.20 to 0.40 weight percent, exhibited by this process would result in approxi-ma ~ly a 50 p variation in transition temperature shift at the 2 x 10 nvt 1/4T end-of-life fluence value.
Because of the steps taken to assure duplication of the exact vessel weld procedure and welding parameters in making the surveillance weld, however, the typical range. of 0.25 to 0.30 weight percent rather than the maximum range of 0.20 to 0.40 weight percent should be expected to characterize the variation between surveillance samples and vessel welds for any given vessel.
- Thus, a variation of approximately 25 F in transition temperature response for submerged metal arc welds made with copper-coated filler wires at end-of-life due to compositional variations between the weld metal in the surveillance samples. and the actual welds in the pressure vessel.
Based on the preceding discussion, the selection of ma-.
terials for the reactor pressure vessel surveillance programs in BWR 2, 3 and 4's does'easonably represent the materials in the beltline region of the vessel.
The steps taken by General Electric to assure adequate representation of the weld process and all subsequent material processing steps seen by the vessel materials limi*ts'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 by only 10 F to 25 F variability in the predicted transition temperature shift for the BWR'luence range.
Included in the analysis
~
s
4-of the behavioral variations due to compositional variations is a major factor of conservatism.
The maximum expected composition range for each material condition is used as a
basis for the estimated effects of composition.
Rarely will the heat of surveillance sample material happen to fall.at the exact bottom of the expected copper content range while the vessel materials from the other heats in the beltline fall at the top of the same copper range.
- Thus, the estimated effects projected will tend to be minimized by the actual field conditions.
Although it is still important to know the residual element composition of the vessel steel and surveillance'e specimens for complete analysis of surveillance test results,
..<his information can easily be obtained by chemical an/lysis of archive material and analysis of specimens at the time of testing.
General Electric believes that the steps taken during the production of BWR pressure vessel surveillance specimens adequately assure reasonable representation 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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