ML20141P002

Safety Evaluation Supporting Amends 95 & 85 to Licenses DPR-39 & DPR-48,respectively

ML20141P002
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	03/10/1986
From:	Office of Nuclear Reactor Regulation
To:
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ML20141N995	List: ML20141N994 ML20141N998 ML20141P002
References
NUDOCS 8603180408
Download: ML20141P002 (4)

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1. o g UNITED STATES

! n NUCLEAR REGULATORY COMMISSION g .p WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PELATED TO AMENDMENT NO. 95 TO FACILITY OPERATING LICENSE PIO. DPR-39 AND AMENDMENT NO. 85 TO FACILITY OPERATING LICENSE NO. DPR-48 COMMONWEALTH EDIS0N COMPANY ZION NUCLEAR POWER STATION, UNITS 1 AND 2 DOCKET NOS. 50-?95 AND 50-304 Introduction By letter dated February 24, 1986, Commonwealth Edison Company proposed amendments to Facility Operating License Nos. DPR-39 and DPR-48, Appendix A. Sections 2.1 and 3.1. The change reflects modification of the Nuclear Instrumentation System positive and negative flux rate trip setpoints from 15 percent with a time constant of 5 seconds to 5 percent with a time constant of 2 seconds. Because the existing setpoints of 15 percent with a time constant of 5 seconds would not provide required negative flux rate protection, the Technical Specifications would require all four of the nuclear instrumentation channels to be declared inoperable due to their inability to perform their " specific functions".

This would result in a forced shutdown of both Zion units. The amendment request proposes interim measures intended to compensate for the non-conservative trip setpoints and avoid shutdown of the power plants while the trips are being reset.

Evaluation The approved Westinghouse dropped rod methodology is described in WCAP-10297A, " Dropped Rod Methodology for Negative Flux Rate Trip Plants,"

June 1983. The conclusions of the report are that there will be no violation of the DNB design basis for 1) large reactivity worth rod combinations which cause a negative rate reactor trip assuming a nominal system setpoint of 5 percent reactor power with a time constant of 2 seconds, and for 2) lower worth rods or rod combinations which show no violation of DNB limits when analyzed by the methods described in the report. The second category requires a plant and cycle specific analyses. This methodology was implemented at Zion during January of 1985, but it was not recognized that the flux rate setpoint required alteration until February 1986. The proposed Technical Specification change implements this requirement for the negative rate setpoint and since conforms with the assumptions in the ap' proved methodolgy, it is acceptable. Credit for the positiva flux rate trip is not taken in the plant safety analysis. The trip is regarded as redundant to other trips, and since the proposed change is in the conservative direction, it is acceptable.

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• As indicated above, full implementation of the Technical Specifications would lead to a shutdown requirement once the trip setpoints were found to be non-conservative. To compensate for this, the licensee implemented interim measures which had been employed in the past to ensure that DNB limits would not be violate? for dropped control rods. These measures require that the reactor be in manual control above 90% power when the control rods are inserted deeper than 215 steps. If the reactor is in automatic control when a rod drops, and there is sufficient control rod worth in the core, the power will overshoot when the controller restores full power. By limiting control rod insertion, and automatic control, the interim measures prevent a return to power and possible overshoot.

However, the licensee was informed by Westinghouse in a letter dated February 24, 1986 that the interim measures alone were not sufficient, but that for multiple dropped rods the more conservative trip setpoints were also required to ensure protection of the DNB limits. The licensee therefore proposed the following measures to be in effect during the period needed to reset the trip setpoints, which is estimated to be less than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

1. An extra licensed reactor operator will be assigned to observe each Unit's rod bottom lights and to immediately initiate a manual reactor

--- 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 variation and frequency altorations 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.

We find the proposed manual trip to be acceptable because the extra operator assigned to each unit has no other duty except to monitor the rod bottom lights and thus should be able to detect multible dropped rods with  ;

a high degree of reliability, and because the power recovery transient without control rod motion is slow enough to allow operator action.

Minimization of control rod motion will aid in reducing the probability of dropped rods, which occur most frequently during rod motion. In addition, resetting of the setpoints will take less than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, so there is little likelihood of any problem arising in the first place.

Because the proposed trip setpoint changes are in the conservativ.e direction and are acceptable because of approved methodology, and because we agree the I

measures proposed by the licensee will ensure safety until the trip setpoints have been changed, we find the proposed amendments do no involve any significant hazards consideration, and are acceptable.

Evaluation of Significant Hazards Consideration 10 CFR 50.92 states that a proposed amendment will involve a no significant hazards consideration if the proposed amendment does not:

(1) Involve a significant increase in the probability or consecuences 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.

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

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Criterion 1 The reduction of these trip setpoints results in more conservative operation that was previously allowed by the Zion Technical Specifications. It should be emphasized that 5 percent /2 seconds refers to a total a 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 22.5%/second.

Thus, the new setpoint of 5 percent power /2 seconds is clearly more limiting than the 15 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.

Criterion 2 As discussed above, the proposed amendmer.t will impose a more conservative and restrictive flux rate trip setpoint tnan the existing 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 n,ew or different kind of accident.

Criterion 3 ,

The imposition of the more conservative positive and negative NIS flux rate  !

trip setpoints will result in more conservative operation. The margin of l safety will be increased because reactor trip sianals will be produced j l

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earlier during a postulated rod drop accident. In addition, 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.

Therefore, since the proposed amendment satisfies the three criteria, the staff concli; des that the amendment does not involve a significant hazards consideration.

Finding on Existence of Emergency Situation In its submittal of February 24, 1986 Commonwealth Edison Company explains the circumstances that led to the situation where, if the existing requirements of the negative power range flux rate of the Zion Technical Specifications were fully implemented, a forced shutdown of both Zion Units would result. The staff has reviewed the submittal and concluded that the situation could not reasonably be anticipated by the Commonwealth Edison Company, the failure to act in a timely way would result in shutdown of both Zion Units, and therefore an emergency situation existed. For that reason the Commission issued the amendments under the provisions of 10 CFR 50.91(a)(5).

Conclusion These amendments involve a change in the installation or use of the facilities components located within the restricted areas as defined in 10 CFR 20. The staff has determined that these amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR Sec 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendnents.

Finding We have concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not l

, be inimical to the common defense and security or to tne health and l safety of the public. -

l Dated: March 10, 1986 -

( Principal Contributor:

M. Dunenfeld 1

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