ML20002C484
| ML20002C484 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/28/1974 |
| From: | Sewell R, Youngdahl R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20002C485 | List: |
| References | |
| NUDOCS 8101100358 | |
| Download: ML20002C484 (5) | |
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- Area Code S17 7HB OSSO June 28, 1974 Mr. John F. O' Leary, Director Re: Docket 50-155 Directorate of Licensing License DPR Proposed US Atomic Energy Commission Technical Specifications Washington, DC 20545 Change - Amendment to License DPR-6
Dear Mr. O' Leary:
Transmitted herewith are three (3) executed and thirty-seven (37) conformed copies of a Request for Change to the Technical Specifi-cations of License DPR-6, Docket 50-155 issued to Consumers Power Company on May 1,196h for the Big Rock Point Plant.
This proposed change will involve the removal of the four (4) lower r711ers from the remaining fifteen (15) peripheral control rods.
One peripheral control rod with the four lower rollers removed was test-operated during the last power cycle. The test operations conducted during this cycle showed that the removal of these lower rollers will not alter the performance of the control rods. The removal of these rollers will al-o eliminate the problems associated with the loss of these rollers.
'See letters to Directorate of Licensing, April 26, 1972, May 1, 1973 and April 1, 1974.)
Your expeditious review and approval of this Technical Speci-ficat3ons change would be most appreciated since this modification could be accomplished during the present refueling outage which is scheduled for completion July 21, 1974.
Yours very truly, b
'.x RBS/mel Ralph B. Sewell Nuclear Licensing Administrator CC: JGKeppler, USAEC
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CONSUMERS POWER COMPANY I
Docket No 50-155 Request for Change to the Technical Specifications License No DPR-6 For the reasons hereinafter set forth, the following changes to the Technical Specifications of License DPR-6 issued to Consumers Power Company on May 1, 1904, for the Big Rock Point Plant, are re-quested:
Change k.l.l(g) To Read as Follows The 32 cruciform-shaped control rods shall be guided and supported by the " fuel channel and support tube" assemblies. Each control rod shall contain a maximum of eight (8) rollers to a minimum of four (4) rollers of either a nominal 0.h85-inch diameter or each control rod shall contain a maximum of eight (8) rollers to a minimum of four (h) rollers of a nominal 0 567-inch diameter. The bottom four (4) rollers which can be eliminated shall move in a minimum interfuel channel space of 0.628 inch.
Bases for Technical Specifications Change Lower rollers have become detached from several outer periphery control rods ee described in our previous letters to the Directorate of Licensing dated April 26, 197P, May 1, 1973 and April 1, 197h. As de-scribed in our April 1, 1974 letter (attached), General Electric has assessed that the most likely mechanism of failure is one caused by a flow-induced lateral vibration of the impaired roller (Stellite-3) wearing down the soft pin (Haines 25). Local flow turbulences are created in the lower regions of the core in the vicinity of the lower rollers when the peripheral control rods are fully withdrawn, as flow sweeps across the core support plate. The upper ends of the 16 peripheral control rods and both ends of the inner 16 control rods are in an area where far less flow turbulences are experienced.
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2 As a result of this analysis, a modification was performed during the refueling outage of April 197h which involved the removal of the four (k) lower rollers from one oontrol rod (C-6). It was re-quested that this control rod be operated for one cycle with the lower
-rollers removed to gain operating experience to justify removal of the lower rollers from the remaining outer peripheral control rods. Prior to resuming operation with the lower rellers removed, a series of tests were performed which included settling friction, scram timing snd notching to confirm that proper control rod drive operation was not hindered. Based on the outcome of the testing and operation of the control rod with the lower rollers removed for cne cycle, SARB was to make further recommendations with regard to permanent corrective action for the remaining peripheral control rods. This cycle was intended to last approximately one (1) year until the refueling outage scheduled in 1975 However, since a considerable number of operations of Control Rod C-6 (from which the four lower rollers have been removed) has been conducted since the test began, it is now desired to remove the rollers from the remaining 15 peripheral control rods during this present out-age.
The following describes the number of operations performed on Control Rod C-6 with the four (h) lower rollers removed. At the begin-ning of Cyc3e 12 on May 5,1974, one scram time test (two full-length trip tests) was performed, one friction test was performed, at least, and four (h) insert withdrawal timing tests were performed as well as three (3) critical approaches. At the end of Cycle 12, on June 2,1974, one scram test (two full-length trip tests) was performed plus three (3) withdrawal insert timing tests, one critical approach and two (2) full incertions of Control Rod C-6 were performed. No abnormalities were noted in any of the tests or operating cycles of Control Rod Drive C-6 nor was there any evidence of impaired operation caused by the removal of the four (4) lower rollers. In addition, the support-tube-and-channels surrounding Control Rod C-6 were inspected with no wear noted on any of the support-tube-and channels as documented in the Big Rock Point logbooks.
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3 Further testing vill be performed during the next operating cycle. At each cold shutdown, all blades with rollers removed will be friction tested and the results compared with previous test results to determine if trends exist. At the next refueling outage, at least blades and their surrounding channels will be inspected for signs of wear.
During the recent attempt to start up for power operation on June 5,1974, Control Rod C h became stuck in the fully inserted position in the core. An inspection disclosed that a roller was lodged between the index tube and housing extension of Control Rod Drive C 4.
Further inspection determined that the roller came from Control Rod D-6.
Control Rod D-6 was one of the control rods which had a lower roller previously missing and is located adjacent to Control Rod C-6.
This is the area apparently which sees tho highest local flow turbulence since a number of lower rollers have been lost from these two control rods in the past.
It was also noted through the inspection of Control Rod D-6 that a third roller was loose and ready to fall out.
Further inspection of the control rods disclosed a lower roller missing from Control Rod B-1.
The roller was retrieved from the bottom of the reactor vessel.
Since the number of operations that has occurred on Control Rod C-6 since the beginning of Cycle 12 closely approximates the number of cycles anticipated through the end of the cycle scheduled to end in 1975, and no abnormalities were noted, it is requested that the lower rollers on the remaining outer periphery control rods be removed during this outage. The loss of a roller does not cause any safety implica-tions since it cannot prevent the insertion of a control rod. However, should a loose roller become lodged between the control rod drive housing extension and index tube, it would prevent withdrawal of the control rod 4
and could severely limit power output.
Conclusions Based on the foregoing, both the Big Rock Point Plant Review Committee and the Safety Audit and Review Board have concluded that l
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thic proposed change does not involve a significant hazards consideration.
CONSUMERS POWER COMPANY
'/G%um (l/1 l By R. C. Youngda Senio Vice Pkesident Date: June 28, J. 74 Sworn and subscribed to before me this 28th day of June 1974.
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LA.n d M Lois E. Barnes, Notary Public Jackson' County, Michigan My commission expires June 20, 1976.
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