ML19345E425
| ML19345E425 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/23/1968 |
| From: | Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Morris P, Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101190187 | |
| Download: ML19345E425 (3) | |
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April 23, 1968 CGy IM,gy
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MAIL & M.cuh0S SECTION L
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Dr. Peter A. Morris Division of Reactor Licensing C.
8' US Atomic Energy Comission
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Dear Dr. Morris:
Attention:
Mr. D. J. Skovholt This letter will confirm recent telephone conversations with. F the AEC Compliance Office in Chicago regarding difficulties in with-drawing a control rod drive at our Big Rock Point Plant during a recent start-up.
Big Rock Point resumed operation on March 15, 1968 following a five-week refueling.
Due to problems with the lower be'tring in the f2 reactor recirculating pump, it was necessary to resume operation with one recirculating pump while awaiting modified repair parts.
The plant was shut down on April 4,1968 to reinstall the #2 reactor recirculating pump. After completing this work on April 6, 1968, the reactor was made critical and plant heat-up started.
Inadequate seal leak-off flow was noted from the newly inst,alled #2 pump during heat-up and did not improve when full operat!.; pressure was reached. The de-cision was then made to shut down the reactor and install a spare shaft seal cartridge. During the approach to critical followin6 this seal cartridge replacement, Drive B-b would not withdraw from its full-in position. After a check of the hydraulics system to assure that it was working properly, and.a number of attempts to withdraw the drive, the d, rive finally " broke loose" from the full-in position and then could be fully withdrawn and appeared to be functioning normally.
The drive was then, withdrawn fully to the unlatching position and the control rod drive mechanism removed from the reactor vessel and replaced with a spare mechanism.
Inspection of the removed mechanism revealed the head of a 1/2" stainless steel bolt in the upper. drive screen. The bolt head had obviously been lodged in the drive thimble and finally had been worked down through the t1}imble and into the screen, thus allowing the drive to again function normally.
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The bolt head reading was only 14 mr upon removal and only l
0.4 mr after decontamination, verifying that the bolt head could not have come from reactor vessel internals.
Subsequent gama spectrometry 1Gd
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Dr'. P:ter A. Mc i4 showed that even the 0.h mr was predominantly Zn-65, thus indicating essentially no neutron activation. There was no evidence of a tack veld on the bolt head, further substantiating that it co'ld not h' ave u
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come from reactor internals.
The bolt head probably came from early test work there torque vrenches were desi6ned to break off initially installed bolt heads prior to the new installation of 1/2" bolts in the upper grid structure.
Somehow, one of the bolt heads must have been dropped into the reactor vessel. Another possibility is that the bolt head might date back to
-the extensive modification to tne thermal shield performed in 1964 and 1965 Based upon the above investigation, Consumers Power Company concluded that the discovery of the bolt head did not indicate a problem or potential problem with the reactor or its control system and opera-tion of the plant was resumed on April 9,1968. operation of the plant
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has been norml since then.
s Yours very truly, h
RLH/ map Robert L. Haueter Asst Electric Production CC:
HThornberg Superintendent - Nuclear e
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_1 1 somf'd ay ree'd Dr. Peter A. h ris ACTION NECESSARY O
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50-155 DESCtiPflON: (Mar 6. Uncioneif d)
ElfERRED TO DAff t!CEIVED SY Daft Ltr confirming roosat teleen gABC compliance office in Chicago re Flettry 4/26 difficulties in withdrawing a sentrol g6 syo for ACTION 7gfriva-stJig _n~ h piant a.,4=c IMZg_QOfIES Th recent startup.............
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