ML20127K668
| ML20127K668 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/20/1992 |
| From: | James Shea NRC |
| To: | NRC |
| References | |
| NUDOCS 9211200466 | |
| Download: ML20127K668 (2) | |
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m l'NM LD STATLS GO\\T.RNMLNT Memorandum 10 THE FILES m3a h, TilRU:
Roger S. Boyd, Chief Research & Power Reactor Safety Branch, DRL IROM J. Shea, Research & Power Reactor Safety Branet Division of Reactor Licensing
$UBJirl; NSP, MONTICELLO WISCONSIN NUCLEAR P1 ANT NO. 1 - STATUS OF FIELD ERECTED REACTOR VESSEL FABRICATION REVIEW - DOCKET NO. 50-263 All of the information gathered from GE, B&W, C&E, in addition to CB61, the fabricator of the NSP vessel, is being sifted to explore what, if any, improvements can be made to further reduce the probability of reactor vessel failure over the 40 year service life. Current knowledge can be condensed in certain areas of interest:
1.
Field Erection:
Weather protection will be provided to essentially duplicate shop conditions. Vertical assembly of vessel contrasts to horizontal shop assembly but vessel rints assembled at groung level will meet template tolerance before being raised to position for final girth weld.
Hence final mechanical tolerance may be better than presently accepted in shop practice.
2.
Weldinn:
Two shaped plates will be joined together at ground level by a vertical, manual, multiple pass (inside and outside cylinder) sub-merged are type weld. Horizontal girth welds will be made in a similar manner later when tne ring is raised to its permanent position. Rigid control of weld sticks will assure no mixup of weld rod. Automatic welding in those areas is conmon in shop practice but careful super-vision and inspection of each veld pass will assure a satisfactory weld.
3.
Heat Treatment:
All weld areas are maintained at 300 +F until ultra-sonic inspections are performed.
Approximately a one hour preheat to near 1200 F is required before cooling for radiographic inspection and final 6-7 hour heat treatment at 1200 F.
Temporary flame heaters and electric heaters permit th ese operations to be performed satisf actory. At any 0
rate the metal is never allowed to cool below 200-300 F after welding until at least a one hour preheat - temporary stress relieve operation has been performed.
4.
Non Destructive Testing; Hot ultrasonic tests will be conducted upon completion of each weld (af ter surface grinding). After preheat and cooling to ambient conditions a Cobolt source radiographic inspection will be con-ducted. Current shop practices relies on cobolt source radiographic in-spection method.
Some improvements qualitatively may be possible in the n-N 9211200466 921120 PDR ADOCK 05000263 P
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THE FILES non-destructive test area. For example a portable Betation could improve by about 1/4% the capability to detect cracks. views from dif ferent angles could reduce the likelihood of undetected cracks lined up with the direction of radiation, and finally sharper images should result.
With reference to ultrasonic inspection methods automatic recorders set to operate at a preset signal would insure a permanent record and initiate written records to effectively deal with the deviation.
5.
Shop Fabrication:
CB61 will cold press reactor vessel plates into shape where others use hot rolling or pressing. Assurance that the plate developes no cracks as a result of this shaping is not yet evi-dent.
6.
Desirns Local stress concentrations calculated for the lifetime of the vessel assume no initial defects.
It would be desireable to relate crack and defect size that can be tolerated,after vessel fabrication is complete,without causing vessel failure over the vessel lifetime con-sidering crack propragation due to cycling, fatigue, vibration, etc.
Information presented in Amendment 2, " Design, Fabrication, and Erection of the Reactor Vessel" (Nov. 23, 1966) strengthens the views presented above.
Parameters Inc., consultant on the NSP reactor vessel field erection received copies of Amendment 2 on December 6, 1966 and will offer advice to the staff during the week of December 12-16, 1966.
Distribution:
DRL Reading R&PRSB Reading P. A. Morris E. G. Case R. S. Boyd M. Bolotsky A. B. Holt G. W. Reinmuth B. Grimes W. Jensen N. D. Ma son M. K. Woodard J. J. Shea II
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