ML20002C867
| ML20002C867 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/01/1974 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101120221 | |
| Download: ML20002C867 (4) | |
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General Offices: 212 West Michigan Avenue. Jackson, Michigan 49201. Area Code 517788-0550 k
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. John F. O' Leary, Director Re: Docket 50-155 Directorate of Licensing DPR-6 US Atomic Energy Commission Big Rock Point Washington, DC 20545
Dear Mr. O' Leary:
This letter is written to inform you of a minor modification that vill be performed on one control rod bla @ st the Big Rock Point Plant during the refueling outage that is presently in progress.
This modification involves remrcal of the four lover rollers from one control rod blade and is part of
,ffort to achieve a long-term solution to operating problems that he - 5een experienced in the past. These prob-lems were involved with the ass of four rollers from a total of three peripheral control rod blades in the Big Rock Point reactor and were previously described in our letters to the Director of Licensing dated April 25,1972 and May 1, 1973 In an attempt to determine a long-term solution to the problems reported in the above-referenced letters, an analysis was undertaken of several possible modifications to the rollers on the lower portions of th? peripheral control rod blades.
This analysis considered removal of rollers as well as repair to the original design, velding the existing rollers to the control rod blade and installation of a device on the con-trol rod blade that would disturb the flow conditions in the vicinity of the lover rollers.
The analysis concluded that removal of the bottom rollers from a peripheral control rod blade was the most feasible course of action.
The weight of the control rod blade is 113 pounds and the maximum frict ~
force that can be exerted with the rollers removed is calculated to be approximately 95 pounds; thus, a total maximum downward force of 208 pounds exists to retard insertion of the control rod blade into the core. The total upward hydraulic fore ' Mist is exerted when inserting the control rod blade is approximately 1800 pounds; thus, a minimum upward force of approxi-mately 1600 pounds exists to move the control rod blade.
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- Mr. John F. O' Leary, Director '
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. Docket 50-155 l
April 1,1974 ~
Restoration of. the rollers to their original design was rejected because it was likely that if this course of action were taken the problem i
would recur. The possibility of affixing a device to the control rod blade
' that would disturb the flow conditions in the vicinity of the rollers (to' eliminate roller vibration and subsequent failure) was rejected on the basis of the complexity of the analysis and critical positioning of the de-vice. Rigidly velding the existing rollers to the control rod blade was rejected because the frictional forces would.be only slightly reduced' (approximately 13 pounds less) when compared to the analysis with the rol-1ers removed. Also, welding of the rollers would be costly in terms of plant personnel radiation exposure.
The analysis was reviewed by the NSS vendor (General Electric-Company). 'GE agreed with our recommendation to remove the lower rollers on a peripheral control rod blade. The purpose of the rollers is to reduce friction and prevent galling under heavy side loads-Heavy side loads are not expected to occur in the region below the core. GE recommended that any testing ' performed following removal of the lower rollers include a con-trol rod drive settling friction test. This test provides a sensitive measurement of the' drive line friction and will verify the results of the
- analysis, GE assessed the mechanism a failure to be most likely caused by a lateral vibration of the impaired roller (Stellite 3) wearing down the j-soft pin (Haines 25). The 0.125 inch diameter pin is a wrought alloy with hardness ranging from Rockwell C c-46. They attributed the cause to be flow' induced.
Local flow turbulences are created in the lower regions of the core (in the vicinity of the lower bottom rollers when the peripheral con-
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trol rod blades are fully withdrawn) as flow sweeps across the cor' support plate. The upper ends of the peripheral control rod blades and both ends of the inner 16 control rod blades are in an area that experiences far less -
flow turbulence. GE also considered that simple spinning of the roller on the pin due to the flow conditions was a possibility.
However, this was not considered as likely as a lateral vibration mechanism.
The Big. Rock Point's Safety Audit Review Board (SARB) has reviewed the analysis performed including all alternatives and GE recommendations.
SARB recommended that the bottom rollers be removed from one peripheral con-trol rod-blade during 'he present refueling outage and that this blade be operated for one cycle with the rollers removed. SARB further recommended that prior to resuming operation with the lower rollers removed that test-ing (settling friction, scram time and notching) be performed to confirm that there is ne significant effect with regard to control rod drive opera-4 i
tion. TheEe recomw:ndations are being implemented by the plant staff during the present refueling outage.
Based on the outcome of the testing and operation of the control rod blade with the lower rollers removed for one-cycle, SARB will make further recommendations with regard to permanent corrective' action for the remaining 15 peripheral control rod blades.
If it is deemed desirable to t
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MrL John'F. O' Leary,. Director 3
- Docket 50-155 April'1, ~.1974 '
. remove-the ' lower rollers from the remaining 15 -peripheral control rod 4
- blades, a Technicial Specificetion change. vill be proposed to appropri-ately modify a descriptive portion of the Technical-Specifications.
. Based on a review of the data as ' summarized above, SARB con-cluded that removal of the lower rollers from one peripheral control rod blade did not require a change-to the descriptive portion of the Technical Specifications concerning control-rod guidance and did not involve an un-
- reviewed safety question or increase the probability or the consequences
. of a previous' analyzed accident.
Yours very truly, LLA ?b MC y
RBS/pb Ralph B. Sewell Nuclear License Adminisrator CC: JGKeppler, USAEC r
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6 AEC DIf IBUTION FO'1 PART 50 DOCKET MAT' 3L_
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CONTROL NO:
FILE:
C N niers Power Company J:ckson, Mich. 49201 Mr. R.B. Sewell 4-1-74 4-4-74 x
55 ORIG CC OTHER SENT AEC PDR XXX SENT LOCAL PDR XXX J.F. O' Leary 1 signed CLASS UNCLASS PROP INFO INPUT NO CIS REC'D DOCi:ET NO:
XXX 40 50-155 ENCLOSURES:
DESCRIPTION:
Ltr adv AEC of a minor modification involving ramoval of the four lower rollers from one AC_1'.-:.
-J control rod blade.........
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PLANT NAME?
Big Rock Point FOR ACTIO"/INFORMATION 4-4-74 JB BUTLER (L)
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W/ Copies W/ Copies W/ Copics W/ Copies INTERNAL DISTRIBUTION TECH REVIEW DENTON A/T I"D REGFIL]E AEC-PDR HENDRIE GRIMES LIC ASST BRAI'n'.A'i SALTZPA';
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B. WRT MUNT4ING/ STAFF MACCARY KASTNER GEARIN (L)
CASE KNIGHT BALLARD GOULBOURNE (L)
PLANS GIAMBUSSO PAULICKI SPANGLER LEE (L)
MCDCNALD BOYD SHA0 MAIGRET (L)
DUBE v/ Input MOORE (L)(EWR)
STELLO ENVIRO REED (E) 0 DEYOUNG(L)(PWR)
HOUSTON MULLER SERVICE (L)
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NOVAK DICKER SHEPPARD (L)
B. M G P. COLLINS ROSS KNIGHTON SLATER (E)
DENISE IPPOLITO YOUNGBLOOD SMITH (L)
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FILE & REGION (3)
LONG PROJECT LDR WADE (E)
MORRIS LAINAS WILLIAMS (E)
STEELE BENAROYA HARLESS WILSON (L)
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