ML20085M552
| ML20085M552 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/02/1975 |
| From: | Hillyard H, Mathie F, Swart F PUBLIC SERVICE CO. OF COLORADO |
| To: | Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| RO-50-267-75-17, NUDOCS 8311080628 | |
| Download: ML20085M552 (7) | |
Text
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i O O P. O. Box 361, Platteville, Colorado 80651 October 2, 1975 -
i
- . \ ' .
,A ,.s Mr. E. !! orris Howard, Director '
/- 4:
02[.g Nuclear Regulatory Commission -
Region IV Office of Inspection and Enforec=ent '
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Suite 1000 .
nuington, Texas 76012 -
P.EF: Facility Operating License ,
. Nn. DFR-34 Docket No. 50-267 ,
Dear Mr. Howard:
Enclosed please find a copy of Unusual Event Report. No. 50-267/75/17, Preliminary, submitted pcr the requirements of the Technical Specifi-Cations.
Very truly'yours,
,Frederic E. Svart Superintendent, Nuclear. Production
~rort St. Vrain Nuclear -
Generating Station FES/alk Mr. Roger S. Boyd '/
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8311080628 751002 PDR ADDCK 05000267 '
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- DISTRIBtTfIONS Unusual
- Events and Abnormal Unusual Operating Monthly occurrence Occurrence ^ Cost Reports R epor *.s Report s Letter _
Addressee San Francisco Operations Office
- ERDA 1333 Broad ay '
Oakland, California 94612 2 2 2 -
Atta: Manager * * ~ 4 Pinance & Budget 1 1 - -
Calif. Patent Group Division of Reactor Research and Development ERDA - -
Washington, D. C. 20545 ,
1 1 1, ~
Atta: Director ~ ~
Asst. Dir. for UEBR Programs 2 2 2 -
Asst. Dir. for Gas Cooled teactor Project 1 - 1 1 -
Asst. Dir. for Engrg. and Technology 1 1 1 -
Asst. Dir. for Reactor Safety
- 1 1 1 1
ERDA -SCRPO-SD .
P. O. Box 81325 .
San Diego, California 92138 .
1 1 W. Soule', Project Engr.
ERDA -SCRPO .
P. O. Box 1446 Canoga Park', California _91304 1 1 1
- Wrsco
- Director * ,
bttr
- ERDA -SCRPO t2 ++ P. O. Box 1446 .
+* Canoga Park, California 91304 .
3 3 Technical Information Center
.ERDA P. O. Box 62 .. .
Oak Ridge, Tennessee 37830 10 10 , 2 John R. Zanot, Project Manager (FFLC)'
- General Atomic Company '
P. O. Box 81608 San Diego, California 92138 I"#E f,
Por Monthly Letter only: B1ick Bob Clark 1 P. O. Box 426 Platteville, CO 80651 R. Walker 1 'l 1 1 1 P. Svart 1 'l L. Brey **
D. Rodgers' 1 E. Eill 1 P. Mathie 1 1 'l
- J. Cahm D. Alexander 1 J. Liebelt 1-K. Stannard 1 (Room 526) 1 NRC, Director of Regulations, k'ashington,D.C. 20545 d NCoPy of Howard letter & xe ** g r8of
R. Boyd
= 1 1 1 (Chairman.NFSC) Oscar Lee i Control Room D. Warembourg i 1 1 (letter) copy of letter to Boyd E. Novard i P. Bronson 1
- M..J. Cooney 1 Philadelphia Electric Company 1 1 2301 Market St. PORC Committee Philadelphia, Pa.18101
O o REPORT DATE:
October 2, 1975 UNUSUAL EVENT 75/17 Page 1 of 5 OCCURRENCE DATE:
September 12, 1975 FORT ST. VRAIN NUCLEAR GENERATING STATION .
PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLAITEVILLE, COLORADO 80651 REPORT No. 50-267/75/17 Preliminary IDENTIFICATION OF .
OCCURRENCE:
At approximately 1030, September 12, 1975, the orifice valve assembly associated with control rod drive serial nomber 010 was observed to have fallen vertically
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downward from its nor=al, install'ed position on the control rod drive unit while it was positioned in a special work stand located over an equipment storage well on the refueling floor. This control . rod drive unit was in position in the work stand
- for approximately two days and ha'd not been moved prior to the orifice valve becoming disengaged.
This has been identified as an unusual event per AC 7.6', Non1 Routine' Reports, Section C.2 of the' Fort St. Vrain Technic,a1' Specifications.
CONDITIONS PRIOR Routine Shutdown TO OCCURRENCE:
Steady State Power
- ' Routine Load Change Hot Shutdown X
Cold Shutdown Other (specify)
Reft $eling Shutdown Routine Startup The major plant parameters at the time of the event were as follows:
RTR ~* Wth Power E E'CT
- We Pressure
- psig Secondary Coolant Temperature * 'F Flow
- f/hr.
Pressure
- psig Primary Coolant Temperature *- *P Core Inlet-
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O o IMUSUAL EVENT 75/17 Page 2 of 5 CONDITIONS PRIOR
- TO OCCURRENCE (continued):
Temperature
- 'F Core Outlet Primary Coolant (continued) F16w
- f/hr.
- No bearing on this event.
DESCRIPTION OF OCCURRENCE:
Vrain are in the process of modifica-All of the control rod drives at Fort St.
tion to eliminate internal gas flow leakage paths (CWP-51). Control rod. drive serial number 010 had been removed from region five of the PCRV and placed in a special work stand on the refueling floor for implementation of the necessary modifications. All operations and handling associated with this control rod drive were routine and normal.
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a functional Upon completing the prescribed approved modifications to this unit,All tests resulted.
operating test was performed using established procedures.Just prior to preparing in normal response from the control rod drive unit.
this unit for return to the PCRV, the orifice valve was observed to have fallen from its normal position at the lower end of the control . rod drive unit.
The dust cover (6) which protects the bolted support assembly for the orifice -
All of the parts were re-valve and actuator shaft was removed for inspection.
covered in tact: 1 self-locking. nut (42), 6 belleville washers (41),.1 bearing w:asher (49), and 1 stop plate (15) (see drawing SLR D1201-400G attached). The
control rod drive unit was then further disassembled as required to allow addi-tional internal inspection of the orifice drive mechanism.
APPARENT CAUSE Design Unusual Service Cond.
OF OCCURRENCE: Including Environ.
Manufacture Component Failure.
Installation /Const. X Other (specify)
Operator Improper final assembly of the Procedure . control rod drive unit at time _
of manufacture.
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The apparent cause of this occurrence is failure to fully eng ge the lock nut with the threaded portion of the support shaf t'. The locking action of _ the
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lock nut requires full engage.ient so that this improper assembly allowed the lock nut to disengage from the shaft.
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O o UNUSUAL EVENT 75/17 Page 4 of 5 ANALYSIS OF
- OCCURRENCE:
All of the bolted support parts (12, 42, 49, 41, and 15) (SLR-D1201-400) were No' abnormal indi-removed from the control rod drive and closely inspected. cations of any kind could be found. The orifice valve support shaf t and ac-tuator were removed from the control rod drive unit and carefully inspected, with considerable emphasis being given. to the threaded end of the stiaft to which the bolted support is attached. All threads looked normal; no signs of distress or abnormality could be seen. All of the parts were then reassembled This was done to determine that the physical mating of all parts was normal. Further, tihe self-satisfactorily and 'all parts fit properly and smoothly. locking nut (42) threaded down to its proper position and tightenedThis snugly, is nor-was in fact locked such that a wrench was required to remove it. . ' mal and proper. . ' The only conclusion which can be drawn in view of the observed facts is that - the self-locking nut had never been tightened down properly during initial assembly of the unit. Because the nut was not properly tightened, vibrations and pulsing of the nearby orifice drive motor could have caused the nut to back off sufficiently to release the orifice valve. This threaded support is essentially unstressed during normal installation and operation of.the control rod drive which would allow the nut free movement if it were,not preperly tightened. , CORRECTIVE ACTION: < Seven spare control rod drives plus the 25 units still to be removed from the PCRV will be inspected to verify that the orifice valve support bolt is properly assembled, and that the retaining nut is tightened to the proper It is felt that this unusual event is an position on the isolated case. mating threads.If any additional discrepancies are found, the additional units, presently installed in the PCRV, will be removed for inspection. FAILURE DATA /SIMILAR REPORTED OCCURRENCES:
- None PROGRAMfATIC IMPACT:
None .
,0DE IMPACT:
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O O . UNUSUAL EVENT 75/17 Page 5 of 5 Submitted By: kav C. # a _/'n- - Harvey W. Hillyard, Jr/ Technical Services Supervisor , l-Reviewed By: . Frank M. Mathie Superintendent Maintenance f? Approved By: / e ' . I pederic E. Swart Superintendent, Nuclear Production 9 e S
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