ML20098B305

Ro:On 840904,while Removing CRD & Orifice Assembly,Motor Overcurrent Condition on Auxiliary Transfer Cask Shutters Occurred,Preventing Full Closure.Caused by One Control Rod String Not Fully Retracted.Work Temporarily Discontinued

ML20098B305
Person / Time
Site:	Fort Saint Vrain
Issue date:	09/07/1984
From:	Gahm J PUBLIC SERVICE CO. OF COLORADO
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
P-84341, TAC-55294, NUDOCS 8409260019
Download: ML20098B305 (2)

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16805 WCR 19 1/2, Platteville, Colorado 80651 1 I

$ ~L b 7 il.y September 7, 1984 h pr n ja gg gh - Fort St. Vrain i Unit #1

! P-84341 SEP i 4 884

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C' Mr. John T. Collins Regional Administrator U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive Suite 1000 -

Arlington, TX 76011 ATTN: Eric Johnson s

SUBJECT:

Existing Condition on the Fort St. Vrain Refueling Floor

Dear Mr. Johnson:

This . letter is to provide you with a description of a situation at Fort St. Vrain that has temporarily delayed control rod drive refurbishing efforts. This situation was discussed with you and Phil Wagner during a telecon on September 4, 1984.

While removing a control rod drive and orifice assembly (CRD0A) from Region 7 for maintenance, a motor over-current condition on the auxiliary transfer cask (ATC) shutters occurred, preventing their full closure. Work was discontinued, and an investigation of the possible causes bega-The'"ATC shutters were opened, and an attempt to lower and reinstall the CRDOA into the core was made. The mechanism could not be completely seated in the penetration, so the CRDOA was again withdrawn from the core into the ATC. Once this -was completed, a radiation survey was performed around the ATC. This indicated an abnormal radiation profile for a fully retracted control rod pair in the ATC, introducing the possibility that the control rod (s) were not fully retracted. The ATC shutter drive shafts were removed, and a borescope was inserted for visual examination. These examinations revealed that one of the two control rod strings was not fully retracted.

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'O A special test was conducted- on September 5, 1984, with Messrs. Chaney and Plumlee of the NRC on-site and cognizant. This test involved lifting the ATC approximately 4 inches to verify borescope observations and to obtain radiation level data. Video tape taken during the test revealed that indeed only one control rod string was not . fully retracted. Radiation levels at the circumference of the ATC were on the order of 5 R/hr. This corresponds to approximately 80 R/hr at one foot from the control rod string.

All CRD0A work has been discontinued until it is established that the CRDOA can be removed fr,m the reactor in accordance with Fort St.

Vrain licensing -requirements and without causing unnecessary health hazards to plant personnel.

As always,- Public Service Company will keep the Nuclear Regulatory Commission abreast of the existing conditions. If you have any questions please . contact Mr. Chuck. Fuller, of my staff, at (303) 785-2224, extension 202.

Sincerely, 4 W. Gahm

,f ).

Manager, Nuclear Production JWG/dkh J