ML20205K441

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Proposed Tech Specs Reflecting Mod of Nuclear Instrumentation Sys Positive & Negative Rate Trip Setpoints
ML20205K441
Person / Time
Site: Zion  File:ZionSolutions icon.png
Issue date: 02/24/1986
From:
COMMONWEALTH EDISON CO.
To:
Shared Package
ML20205K435 List:
References
1344K, NUDOCS 8602270379
Download: ML20205K441 (9)
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Text

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ATTACIAIENT 2 GENERAL HISTORY AND TECHNICAL JUSTIFICATION A meeting was held in Bethesda, ND, on November 19, 1979, between Westinghouse Electric Corporation, utility representatives, and the NRC Staff. Westinghouse discussed deficiencies in the then current multiple dropped rod protection circuitry and in the reactor control circuitry.

The proposed short term solution to this problem was to immediately implement administrative controls at each facility to preclude reactor operation while power was above 90%, CBD was inserted beyond 215 steps, and the reactor control system was in automatic.

The long term solution was outlined to potentially include both analytic and hardware changes. This information would be finalized in a Westinghouse generated topical report scheduled for mid-1980. This information was formally submitted to the NRC in reference (a). Commonwealth Edison Company provided its commitment to the interim measures in reference <

(b).

Reference (e) documented the revised methodology for dealing with the rod drop issue. This document assumed that all plants would utilize a negative NIS flux rate setpoint of -5 percent /2 seconds. The NRC Staff documented its approval of this methodology in reference (f).

Zion Station did not properly implement the requirements of reference (e). The interim administrative controls were removed during January of 1985. The negative flux rate trip setpoint was not altered and remained at the Technical Specification value of 115 percent /5 seconds.

Commonwealth Edison Company became aware of this discrepancy on February 21, 1986. It was decided to re-implement the administrative controls that were originally outlined in reference (a). A detailed evaluation of the causes and corrective action was then initiated.

As part of this evaluation, Westinghouse Electric Corporation was contacted. It became evident that both the interim administrative controls outlined in reference (a) and reference (e) were based upon a trip sotpoint of -5 percent /2 seconds. Westinghouse documented its finding in reference (c). Commonwealth Edison Company had previously believed that the reduction of the trip setpoints to -5 percent /2 seconds was not part of the administrative controls outlined in references (a), (b) or (d) and at the November 19, 1979 meeting.

This information resulted in the inoperability of all four channels of the NIS negative flux rate protection due to their inability to perform the "specified functions". That is, the administrative controls were not sufficient to preclude unacceptable results for all postulated dropped rod combinations that would not result in the generation of a reactor trip signal.

The reduction of the trip setpoints besar. immediately, along with the compensatory measures discussed in Attachment 3. Item #1 will ensure that a manual reactor trip will be initiated if a multiple rod drop event should occur and an automatic trip signal not be generated. It should be noted that a reactor trip is expected to be generated for most dropped rod combinations.

Item #2 reduces the probability of experiencing a dropped event by eliminating unneeded rod movement. The movement of control rods challenges the moveable, lift and stationary coils, circuitry, and gripper mechanisms.

The maintenance of stable conditions reduces the probability of experiencing a dropped rod.

Finally, the adequacy of a flux rate setpoint of 5 percent /2 second has been previously reviewed and approved in references (e) and (f). Thus, this amer.dment request is expediting the implementation of the correct setpoints at Zion Station.

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, COMPENSATORY MEASURES TO BE IN EFFECT WHILE I

NEW TRIP SETPOINTS ARE BEING INyTALLED I

1. An extra licensed reactor operator will be assigned to observe each Units rod bottom lights and to immediately initiate a manual reactor l trip if two or more rods fall.
2. Control rod movement will be minimized throughout this time period by imposition of the following conditions.

! a. normal minor reactivity compensation for temperature variations and frequency alterations will be accomplished utilizing boration and/or dilution.

b. No load changes will be initiated.
c. The rod system will be placed in manual throughout this time period.
3. The new setpoints will be installed as soon as possible. It is estimated that the time period required to place the new setpoints into the circuitry will be less than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

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4. The act of placing the new setpoints into the circuitry requires that the protective channel be placed into the tripped mode. Therefore, for the majority of this time period the reactor protection system will be in the half-cocked mode and will actually have a 1 out of 3 trip logic for the negative flux rate trips.

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ATT M 4 IVALUATION OF SIGNIFICANT HAZARDS CONSIDERATION PROPOSED CHANGES TO ZION TECHNICAL SFECIFICATION SECTIONS 2.1.1.C AND 3.1 PASCRIPTION OF AMENDNENT REQUEST An amendment to the Zion Facility Operating License is proposed to reduce the postiv: snd n*gative NIS flux rate trip setpoints from 115 percent power /5 seconds to 15 percent /2 seconds.

BACKGROUND 10 CFR 50.92 states that a proposed amendment will involve a no significant hazards consideration if the proposed amendment does nots (1) Involve a significant increase in the probability or consequences ,

of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety. .

In addition, the Commission has provided guidance in the practical applica-tion of these criteria by publishing eight examples in 48 FR 14870.

The discussion below addresses each of these three criteria and demonstrates that the proposed amendment involves a no significant hazards conj 1deration.

BASIS FOR NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION Does the proposed amendment (1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involvo a significant reduction in a margin of safety?

  • O DISCUSSION - ITEM 1 The reduction of these trip setpoints results in more conservative operation hat was previously allowed by the Zion Technical Specifications.

It should be emphasized that 5 percent /2 seconds refers to a total power change of 5 percent reactor taking place over a total time period of not more than 2 seconds. It does not refer to a simple ramp rate of 12.5%/second.

Thus, the new setpoint of 15 percent power /2 seconds is clearly more limiting than the 115 percent /5 seconds that currently exists. This results in a reactor protection system that will produce a reactor trip signal under a wider range of dropped rod combinations than the present system. The consequences of multiple dropped rods are clearly reduced.

The setpoint change does not affect the actual operation of the control rod drive system. Thus, the probability of a dropped rod incident is unaffected.

In addition, the application of the 5 percent /2 second setpoint has been thoroughly reviewed in reference (e). The NRC Staff has previously indicated its approval in reference (f).

DISCUSSION - ITEM 2 As discussed above, the proposed amendment will impose a more conservative and restrictive flux rate trip setpoint than the existinf.

Technical Specifications. There have been no modifications to the system design. Thus, the imposition of these tighter controls will result in more conservative operation and will not create the possibility of a new or different kind of accident.

DISCUSSION - ITEM 3 The imposition of the more conservative positive and negative NIS flux rate trip setpointo will result in more conservative operation. The margin of safety will be increased because reactor trip signals will be produced earlier during a postulated rod drop accident. In addillon, reactor trip signals will now be generated for a broader range of dropped rod combinations. Thus, the margin of safety will not be adversely affected.

g Note that the proposed amendment meets and exceeds the example (ii) of the Commission guidance provided in 48 FR 14870.

(ii) A change that constitutes an additional limitation, restriction, or control not presently included in the Technical specifications: for example, a more stringent surveillance requirement.

Therefore since the application for amendment satisfies the criteria specified in 10 CFR 50.92 and is similar to examples for which no significant hazards consideration exists. Commonwealth Edison Company has made a determination that the application involves no significant hazards consideration.

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