ML20127P053

Safety Evaluation Supporting Amend 88 to License DPR-40

ML20127P053
Person / Time
Site:	Fort Calhoun
Issue date:	05/09/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20127P019	List: ML20127P014 ML20127P032 ML20127P053
References
NUDOCS 8505230683
Download: ML20127P053 (7)

Text

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1. k 4* UNITED STATES p t, NUCLEAR REGULATORY COMMISSION

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• WASHINGTON, D. C. 20555 e

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. TO FACILITY OPERATING LICENSE N0. DPR-40 OMAHA PUBLIC POWER DISTRICT FORT CALHOUN STATION, UNIT NO. 1 DOCKET NO. 50-285

Background

The staff originally reviewed and accepted the Ft. Calhoun design as a four (4) channel (two-out-of-four logic) protection system. However, the Ft. Calhoun plant is presently operating with Technical Specifications (TSs) which allow the operation of a four (4) channel protection system with one of the four channels of a given process variable in bypass for an indefinite period of time. The system would then function for the given process variable as a two-out-of-three protection system rather than a two-out-of-four protection system. Upon further review, the staff has concluded that insufficient information is available on the effects of single failures within the Ft. Calhoun protection system to warrant the loss of conservatism incurred by operation for a lengthy period of time with one channel of a given parameter in bypass.

Subsequently, the NRC informed the licensee by letter dated March 31, 1982 that one of two methods would be acceptable to the staff regarding the bypassing and tripping of inoperable channels associated with plant protection systems.

One method (Option 1) requires the incorporation of TSs which will not allow an RPS/ESFAS inoperable channel to be bypassed for greater than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> unless active maintenance is being performed after the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> limit. Option 2 allows an inoperable channel to be bypassed for a lengthy period of time (beyond 48 8505230683 850509 PDR ADOCK 05000285 P PDR

hours regardless of whether active maintenance is being performed or not; typically until the first cold shutdown after channel failure)'if it can be .

verified .that the remaining protection system channels in a two-out-of-three logic are sufficient to satisfy all requfred protection system criteria.

The licensee elected to pursue Option 1 and submitted support information by letters dated June 15 and October 27, 1982. Upon review of the licensee's letters, the staff found unsupported evceptions related to Option 1. The exceptiens will allow the licensee to bypass various protection channels for

. extended periods (beyond 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />) regardless of whether active maintenance is being performed or not and to use jumpers or blocks to place ESFAS channels in the bypassed or tripped condition. The licensee, upon notification of the staff's concerns and proposed TSs by letter dated May 23, 1983, responded by letter dated April 6,1984. The staff's evaluation of this information follows.

EVALUATION The TSs submitted in the licensee's April 6,1984 letter are consistent with those delineated by the staff (May 23, 1983 letter) with exceptions as noted above. The detailed description and evaluation of each exception follows.

Exception fio. 1 - The licensee proposes to bypass for up to seven (7) days an inoperable channel associated with high power level, thermal-margin / lou l

pressurizer pressure, or axial power distribution if the failure results fron-malfunctioning resistance temperature detectors (RTDs) or nuclear detectors.

-If the inoperable channel is not returned to operable status within seven

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days, the plant will be placed in a hot shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> so that the defective channel can be repaired.

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The licensee has requested this additional channel bypass time because the nomally inaccessible RTDs and nuclear detectors require a reasonable amount

-of time to repair (including scheduling and planning) and because of a concern regarding the increased probability for spurious plant trips by placing the system in a one-out-of-three trip logic. The licensee fias verified that tfie failure of tiiese components occurs infrequently and that the RPS and ESFAS

.are designed with sufficient redundancy and separation to ensure performance of their intended function with one inoperable channel in bypass for seven

-days.

Exception No. 2 - The steam generator low pressure and steam generator differ-ential pressure channels of the auxiliary feedwater (AFW) automatic initiation circuitry are used to detect and prevent delivery of AFW to a " faulted" steam generator. The licensee proposes to place one inoperable channel of the

' four. steam generator pressure and/or steam generator differential pressure signals on one of the steam generators in the bypassed condition for a pro-longed period of time (beyond the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> limit until the next cold shutdown).

If another failure then occurs in one of the four channels on the other steam

. generator (i.e., the one without a previously bypassed channel), one of the two' inoperable channels must be fixed within seven days or the unit will be placed in.. hot shutdown for repair. It should be noted that the prolonged bypass will be allowed only after the Plant Review Comittee has. reviewed and documented their judgment concerning operation with a defective channel in bypass..

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The licensee has performed an analysis of the prolonged bypass of a $1rigle steam generator low pressure and/or steam generator differential pNssure channel as it relates to the design' basis events that rely on AFP initiation.

The results of the licensee's analysis cunfirm that sufficient fedundancy and separation exists such that no degradation of safety margin occurs with a channel in prolonged bypass. Moreover, with any one of the subject channels in the actuation permissive state, a single failure within the AFW actuation circuitry will not preclude the feeding of the incapacitated steam generator.

Exception No. 3 - The licensee proposes that the TSs allow eight hours (instead of one hour) to place certain inoperable ESFAS channels in the bypass or trip condition since the-present Ft. Calhoun Station (FCS) design requires that jumpers or blocks be used for those ESFAS channels which do not have built-in bypass capabilities. The staff informed the licensee that such modifications are not normally allowed based on IEEE 279 requirements. Subsequently, upon our request, the licensee provided information to justify the FCS design.

The ESFAS consists of four sensing channels and normally operates as a two-out-of-four logic for system actuation. The use of jumpers or blocks for inoperable ESFAS channel bypass or trip is part of the original FCS design which has been reviewed and approved by the staff. The new TSs require that should a channel become inoperable, that channel must be placed in the bypassed or tripped condition within eight hours. If placed in bypass, the affected system would then be allowed to operate as a two-out-of-three system for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The time limit for this configuration applies to all of the ESFAS except for the AFW systen (See Exception f;a. 2 above). If not returned to operable status vrithin the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> tirre limit and active maintenance is not

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being performed on the subject channel, the operator would then be required to' place the inoperable channel in the tripped condition which would put the ESFAS in a one-out-of-three logic. ,The licensee has verified that there is sufficient redundancy and separation to allow such bypass conditions. Also, it shculd be noted that the TSs allow only one inoperable channel of a given parameter to be bypassed at any given time.

FCS operating experience has shown that the use of jumpers or blocks to bypass or trip the various inoperable ESFAS channels is infrequent (typically 2 to 3 times a year). The licensee has verified that strict administrative pro-cedures are in use at the FCS to control such circuit modifications. For example, the status of a jumpered or blocked channel is indicated in the con-trol room by placing a " Hold for Inspection" sticker on the associated indi-cator(s). When the inoperable channel has been repaired and the jumper or block removed, testing is performed on that channel to ensure operability.

Also, the licensee has verified that jumpers and blocks are not and will not be used for routine surveillance testing of the systems governed by the proposed TSs.

CONCLUSION It should be reiterated that the TSs currently in use at the FCS allow plant operation with one inoperable channel of a given process variable in bypass for an indefinite period. Overall, the newly proposed TSs (licensee's April 6, 1984 letter) which were developed in accordance with Option 1 impose a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> time limitation for the bypass of an inoperable protection channel.

Ootien 1 also allows bypass beyond the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> limit only if active tainter.ance

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. is'being performed on that channel. Although th'e proposed method to bypass an inoperable channel is not the praferred alternative as related to current regulatory requirements on this subject, the staff considers the implementation of Option 1 to be a considerable improvement over the existing TSs since it limits the use of protection channel bypasses. Option 1 also aids in the prevention of inadvertent protection system actuation and provides sufficient flexibility for the performance of maintenance on the inoperable channel.

- As discussed above, however, the licensee has taken some exceptions to Option 1. The staff has concluded, based on the above evaluation, that the licensee has provided sufficient information to confirm that the exceptions do not cause a degradation in plant safety. Thus, the staff finds the TSs proposed by the licensee in their April 6,1984 letter which are unique to the FCS to be satisfactory for implementation.

ENVIRONMENTAL CONSIDERATION This amendment involves a change'~ in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.

The staff has determined that the amendment involves 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 published a proposed finding that the amendment involves no significant hazards consideration and.there has been no public

. coment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR !51.22(c)(9).

Pursuant to 10 CFR 651.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance'of the amendment.

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.. CONCLUSION cc 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 bo endangered by operation in the proposed manner, and (2) such activities'will

.be conducted .in compliance with the Commission's regulations, and the issuar.co

,cf.the amendment will not be inimical to the ccmmon defense and. security or to.

the health and safety of the public.

Date: .May 9, 1985 Principal Contributor:

R.~'Stevens O

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