ML20064C509

Responds to Request for Info Re Engineered CEA Position Indication Sys to Be Used on CEA A-42 to Enable Fuel Rod Position to Be Displayed & to Comply W/Operating Requirements of Spec 3.1.3.3

ML20064C509
Person / Time
Site:	Millstone
Issue date:	10/12/1978
From:	Counsil W NORTHEAST UTILITIES
To:	Reid R Office of Nuclear Reactor Regulation
References
TAC-30201, TAC-49061, NUDOCS 7810200060
Download: ML20064C509 (2)

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October 12, 1978 Docket No. 50-336 L s

Director of Nuclear Reactor Regulation Attn: Mr. R. Reid, Chief Operating Reactors Branch #4 U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1) D. C. Switzer letter to R. Reid dated April 20, 1978.

(2) R. Reid letter to D. C. Switzer dated April 20, 1978.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 CEA Position Indication As described in Reference (1), just prior to startup following the first refueling outage, it was discovered that the reed switch position indicator for CEA #A-42 was inoperable. Subsequent investigation revealed that one pair of the reed switch con-tacts for a position between 0 and 4 steps was welded closed. Attempts to fail open the welded contact by current injection may not have been successful; however, the attempt did inadvertently create an open circuit in the negative supply lead to the resistor chain.

In Reference (2), an amendment was issued for unit operation without the reed switch indicator channel for CEA #A-42, under certain special conditions imposed as an addendum to Specification 3.1.3.3. These special provisions will be sus-pended at midnight on October 20, 1978, and Specification 3.1.3.3 will return to 1 % original format.

In response to the Staff's verbal request, this letter is submitted to describe a recently engineered CEA position indication system which will be used for CEA

1. A-42 enabling full rod position information to be displayed and fully complying with the operability requirements of Specification 3.1.3.3.

System Description

The original design of the reed switch CEA position indicator system consists basically of a three-wire voltage divider, resistor ladder network. A magnet attached near the top of the CEA upper extension actuates reed switch contacts for every two 3/4" step positions of the CEA between upper and lower limits.

l The closing of the reed switch contacts varies a 0-5 volt signal in 90 equal increments supplying information to the position display indicator.

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' Although an open circuit in the negative supply lead exists, the operable part of the circuit remaining acts as a two-vire resistance chain capable of providing an equal l change in resistance for every two 3/4" step positions of the CEA.

l' Using this concept, a resistance to voltage transducer with 0-5 volt output has been temporarily installed outside the containment to provide information to the Metrascope for CEA #A-42 position display. In order to effect the necessary voltage reversal required (minimum resistance-maximum voltage) to drive the Metra-scope a series " bucking" voltage is applied in the transdu~cer output circuit.

This sytem has been calibrated to provide full span indication (90 reed switch /

resistor positions) between the upper and lower CEA limits and the total system

! inaccuracies inherent in the equipment employed, including long-term stability and drif t, will not compromise the ability of the indicating system to be capable of determining absolute CEA position within the required 13 step positions.

We have demonstrated during periodic exercising of CEA #A-42 that the modified reed switch indication system will track with the pulse counting system and a test over the full range of steps (withdrawal and insertion) has been performed.

Although it is the intention of NNECO to replace the entire reed switch assembly for CEA #A-42 during the next long-term cold shutdown, it has been concluded

' hat the temporary indication system described completely fulfills the require-ments for the CEA position indicator channels as detailed in Specification 3.1.3.3, and, as such, full compliance with the applicable LCO is achieved.

NNECO has reviewed this inforention pursuant to the requirements of 10CFR170 and has determined that no fee is applicable in this instance. The license amendment requested in Reference (1) was determined to be a Class 3 amendment, and this letter forwards additional information on this subject at your request. Please note that this letter does not constitute a request for license amendment, and formal review of the above described system is not requested.

We trust this information is responsive to your verbal request.

Ve.ry truly yours, NORTHEAST NUCLEAR ENERGY COMPANY

]!N M W. G. Counsil Vice President

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