ML20214J280

Safety Evaluation Re Preliminary Design for Upgrading Present control-grade Anticipatory Reactor Trip Sys for Loss of Main Feedwater & Turbine Trip to safety-grade

ML20214J280
Person / Time
Site:	Davis Besse
Issue date:	12/20/1979
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20213D079	List: ML20213D076 ML20214J280
References
TASK-2.K.2.10, TASK-TM IEB-79-05B, IEB-79-5B, TAC-45188, NUDOCS 8705270739
Download: ML20214J280 (5)

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,~ ~' '~ do SAFETY EVALUATION B THE 0FFICE OF NUCLEAR REACTOR REGULATION

• ..s EVALUAITON OF PRELIMINARY DESIGN FOR SAFETY GRADE ANTICIPATORY REACTOR TRIPS (ARTS) ON LOSS OF MAIN FEEDWATER AND/0R MAIN TURBINE GENERATOR FOR8 AVIS-BESSE,UNITNO.l DOCKET NO. 50-346 I

I Background j Following the accident at Three Mile Island, Unit No. 2, an assessment of .feedwater transients in the Babcock & Wilcox (B&W) designed pressurized water reactors was perfomed. The results of that review were reported in NUREG-0560. This report highlighted a concern regarding the challange rate to the power-operated relief valve (PORV) in the B&W desi.gn. In response to I&E Bulletin 79-05B, Toledo Edison Company (TECO or licensee) lowered the existing setpoint for the high pressure reactor trip and raised the setpoint of the PORV. By inverting.these setpoints the challenge rate to the PORV opening, and thus the li'kGlihood of it not reseating following actuation was reduced. To provide additional margin to the automatic opening.setpoi'.t of the PORV, the licensee proposed design provisions for direct reactor trip on loss of main feedwater or turbine trip. This design modification was incorporated as part of the short-term and long-term requirements of the Commissions' May 16, 1979 Confimatory Shutdown Order. In order to achieve a timely implementation of this modification, it was determined that a control-grade design was sufficient for the short-term. This was implemented by the licensee by installing hardwired, control-grade trips for loss of main feedwater and turbine trip which were independent of the reactor protection system (RPS). For the long-term, an upgrading of this system to safety-grade is required. - The licensee submitted its proposed safety-grade design in a letter dated May 21, 1979, from J. S. Grant (TECO) to J. G. Keppler (NRC) and later supplemented the design in a letter dated October 3,1979, from L. E. Roe (TECO) to R. W. Reid (NRC). The following evaluation addresses the adequacy of the licensee's proposed preliminary design of the Anticipatory Reactor Trip System (ARTS) for D' avis-Besse, Unit No. 1. 8705270739 791220 PDR ADOCK 05000346-P P DR -- l'

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I. _Existino Reactor Prctection System The existing plan; reactor protection system includes four redundant and independent channels.

Each channel has its own independent input sensors that are physically and electrically separated from the sensors of the other channels. The present trip conditions that are monitored by these sensors and channels includeg 1. Nuclear power / flux (high) 2. Nuclear power based on flow (high) 3. Nuclear power based on reactor coolant pump status (high) ~.. 4. Reactor coolant system pressure (high) 5. Reacter cco! ant :y: tem pressure (low) 6. Reactor coolant system pressure based on temperature (low) 7. Reactor cooiant temperature (high) 8. Reactor buildin; (centainment) pressure,(high) Within the RPS caci ets each of the four channels contains a logic string of the above insu:s. Any individual input actuation will ca'ise the logic string to trip and actuate a trip relay. The trip relays of the four channels form a two-out-of-four coincident logic to open the control rod drive trip breakers. I:I. Description of Jesi:n The proposed prelic' nary design for the safety-grade anticipatory trips contains three grou:s of four redundant and independent channels. Each one of these three ;rou;s are arranged to provide automatic protective action to trip the -eac:or. 0ne group of four channels will monitor the fast acting solenoids for the turbine generator control valves. Another group of four monitar the oi.1 pressure which is associated with the control valves for both m.ain feedwater pump turbines. The remaining group of four are provided from t7e existing steam and feedwater rupture control system logic channels. The steam and feedwater rupture control system channels are designed to a:t; ate on loss of reactor coolant pumps, a low steam generator level, referse differential pressure across check valves which are located downstream of the main feedwater pumps, or low steam line pressure. Each grc,;p of four channels are ultimately connected to two out of four logic gates by way of additional logic gates and isolation devices. The ca:au: fr:m tnese two out of four logic gates are applied to four "or" gates .i:h in turn de-energize the associated undervoltage coils for the control re: crive trip breakers. Additional logic gates are also . included to provi:e tes:ing capability, operating and maintenance bypasses and manual actuatic. of the trip breakers. 1 J

r 3-IV. Evaluation a. We have reviewed the information provided by the. licensee concerning the preliminary design fcr the safety-grade anticipatory reactor trips. This review included infcmation which provided a brief description of the design, additior.al cocumentation by the licensee which responded to specific staff recuests for additional information and functional logic diagrams. The follcwing paragraphs provide the.results of this review. The licensee has identified the' applicable design bases, criteria and branch technical positions for these additional trips as outlined in column 7.2 of Table 7-1 of the Commission's Standard Review Plan.

Further, the licensee has prcvided documentation which indicates that the design will conform to these items.,However, details of the design are not sufficiently conplete to make a determination that the design satisifies all these items.

Acccrdingly.,as desien details are developed prior to . operation of the ad:itional trip circuitry and equipment, we will require that the licensee si.r.it details of the final design for our review. The final design su:'mit:al should include the final logic diagrams, elementary electrical schemat'es, applicable piping and instrumentation diagrans, appropriate cab e rcutir.g and physical layout drawings and detailed test and installation checkout procedures. In addition, the seismic and environmental gaalification information for this equipment is required to be submitted when tre vendor (s) is determined. Another important area which our review concentrated on the adequacy of the design approach for these anticipatory trips as it relaus to the existing reactor prctection system. That is, it is imperative that this added equipment and circuitry not degrade in any way the existing reactor protection system. Based on the information presently available, we believe that this is the case for this design. However, we will require additional confimatory review effort following the submission of the final design. The design requiremsn:s for these anticipatory trips,.as required by IEEE Standard 279-1971, are to be equivalent to those of the reactor protection system with the exception that certain sensor equipment and associated circuitry will not confonn to seismic requirements. We conclude that this is acceptable for tr.ese items based on the anticipatory nature of these trips and the fact that other fully qualified, presently existing, reactor trips serve as a ba:kup to these trips. However, we have identified a related concern whi:h needs to be addressed in more detail by the licensee. Specifically, tnis :encern relates to the isolation devices and related routing circuitry used to transfer the associated initiating signal from a non-seismic area :o a seismic area su:h that the effects of credible fau.lts (i.e., crour. ding, shorting, application of high voltage, or electromagnetic inter #erence) or failures in these areas will not be propagated back to :ne reactor protection system such that this system is degraded below ar. a:cep:able level. Accordingly, we will require, prior to the operaticn of these anticipatory reactor trips, that the licensee submit an analys~is #or~:hese isolation devices and related circuitry which demonstrates : hat this acceptable level is maintained.

4- -for us to conclude that adequate provisions are being inc accomplish the required tests for reactor protection system. trip functions. Accordingly, we will require that the licensee include provisions to perform complete functional:ests at power on an appropriate periodic basis (i.e., every 30 days). Further, we will require that response time testing of these trip functions be. performed gs required by the Standard Technical Specifications V. Conclusion The licensee has identified the design bases and design requirements for the " Anticipatory Reactor Trips" and has also provided a preliminary design description. We have concluded that this identification along with the preliminary design description provides sufficient bases for approval _of the preliminary design. However, we note thIt in order to approve the final design as soon as possible, we will require the licensee to submit the above identified information as soon as it is available. Also, a site visit coordinated with our Office of Inspection and Enforcement may be required preceding final approval of t e design. 4

Attachment:

Summary of Inforration Needed ' e-for Final Design Approval for the ARTS 5 e 9 i l W

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SUMMARY

OF INFORMATION NEEDED.FOR FINAL DESIGN APPROVAL FOR THE ARTS Page No. Requirement in SER 3 The final design submittal should include the final logic diagrams, elementary electrical. schematics, applicable piping and instrumentation diagrams, appropriate cable routing and physical layout drawings and detailed test and installation checkout procedures. In addition, the seisric and environmental qualification information for this equipment is required. 3 Include in the final design submittal the necessary documentation to demonstrate that the added equipment and circuitry does not degrade in any way the existing RPS. 3 For tne isolation devices and related routing circuitry used to transfer the associated initiating signal from a non-seistic qualified area to a' fiismic Category I area, submit an analysis which demonstrates that the effects of credible faults or failures in these-areas will not be cropagated back to the RPS such that this system is -degraded below an acceptable level. 4 Assure that the ARTS design and testing requirements include

he provision to perform complete functional tests at power en a seriodic basis (i.e., every 30 days).

In additior:, resocnse time testing of these trip functions shall be per-formed as required by the Standard Technical Specifications. 1

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