ML20151P101

Discusses long-term Action Re CRD Mechanism Position Indication Proposed by NRC Preliminary Rept Restart & Continued Operation of Fort St Vrain Nuclear Generating Station, Per 841016 Ltr

ML20151P101
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/27/1985
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Berkow H Office of Nuclear Reactor Regulation
References
P-85484, TAC-61601, NUDOCS 8601030301
Download: ML20151P101 (2)

Text

1. ,

i i (0 h I,

\

PubliC SerVICO~ -

reno s.,*.

Company of Colorado s

, N

' 2420 W. 26th Avenue, Suite 100D,. Denver, Colorado 80211

c. <

g > --

'\ \

December 27, 1985 Fort St. Vrain Unit No. 1 s~

P-85461 p,' (

\

\ ' Director of Nuclear Reactor Regulation ,

U.S. Nuclear Regulatory Commission Washington, DC 20555

' Attn: Mr. H.N. Berkow, Projedt Director '-

Standardization and Special ,

. Projects Directorate ,

L ', Docket No.59-267 ,

N

SUBJECT:

CROM Position Indication Long-Term Actions ,

- t-N

REFERENCES:

1) NRC Ldtter Dat'ed October.16, 1984, flenton to Walker (G-84392) i 2),PSC Letter Dat'ed

, q January 4,1985, Lee to Johnson

, 1 (P-85003) 4,

Dear Mr. Berkow:

s s y

This letter. is to address one of the long-term actions proposed by your " Preliminary \,3 port Related to the Restart and Continued Operation of Fort St. Vrain Nuclear Generating Station" under cover letter of October 16, 1984 (Ref. 1). In Section.3.5, part 1 of Ref.

1 under long-term s says "1. Damage'pue,Qo overtravel should be precluded e/her by the installation of a posltive mechanical stop or

' dby providing sufficient clearance to prevent damage."

\ I.

'Our response to this concern was addressed in Ref. 2 and reads as

, follows:

"Ve NRC Finding: Investigate a design change to provide a positive

, stop on the CRDM position indicator potentiometer shaft to prevent over travel and provide the results to the NRC.

J AD - D. CHliTCHF I F l.D (l t r only) 86c1030301 851227 y . ,, ,,,m,,,

PDR ADOCK 05000267 gp . ,so nn,,us ,

PDR ness tro,,

P g a n,o < ,, ,,.cu i h \ j

.. d4 e PSC Response: The concept of either a positive stop or an alternate type of position pctentiometer is being considered.

The problem is that overtravel of the control rod damages the existing position potentiometers resulting in loss of position indication. Preliminary results favor an alternate potentiometer rather than a positive stop. Investigations and design efforts are targeted for completion by January 1, 1986. Installation of modifications will be accomplished during future preventive maintenance activities."

Our investigations and design analysis indicates that the new potentiometer design is the only achievable option. This new potentiometer is designed to allow 150% mechanical rotation as compared to the existing potentiometer. The possibility of damage to the new potentiometer is considered incredible because of the degree of overtravel required before the damage would occur.

A potentiometer of the new design has been procured, and testing has been scheduled following the CRDM temperature requalification tests which are currently being done at GA Technologies. The new potentiometers are designed to better withstand their environment as well as allow for overtravel that in the past has been destructive to the potentiometers. '

If you have any questions on this subject, please contact Mr. M.H. Holmes at (303) 480-6960.

Very truly yours, fa/t.

D. W. Warembourg, Manager Nuclear Engineering Division DWW/JGH:pa 4