ML19309G016

Technical Evaluation of End-of-Cycle Recirculation Pump Trip

ML19309G016
Person / Time
Site:	Duane Arnold
Issue date:	03/31/1980
From:	Peterson L LAWRENCE LIVERMORE NATIONAL LABORATORY
To:
Shared Package
ML19309G010	List: ML19309G009 ML19309G013 ML19309G016 ML19309G017
References
CON-FIN-A-0231, CON-FIN-A-231 NUDOCS 8005020202
Download: ML19309G016 (16)

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{{#Wiki_filter:- ATTACHMENT TO SAFETY EVALUATION 0a02 y O B006 TECHNICAL EVALUATION OF THE END-OF-CYCLE RECIRCULATION PUf# TRIP FOR THE DUANE ARNOLD ENERGY CENTER (DocketNo.50-331) L. R. Peterson s March 1980 4 A .+:e + Q O myy:.;gnp, /w.e 4.c -ygn, au m. , u scp;g. p gag <.m. x 6f + p;.> '. f;t?;.;.1,, L. vwT.5:%,, v. 3:,/.ad ;WA.gtyeem

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f ,s V_ \\ .-l ABSTRACT This report documents the technical evaluation of the 'end-of-cycle recirculation pump trip for the Duane Arnold Energy Center. The review criteria are based on IEEE Std-279-1971, IEEE Std-323-1974, IEEE Std-338-1977, and General Design Criteria 13, 20 through 24, and 29 of the Code of Federal Regulations., Title 10, Part 50, Appendix A requirements for determining the acceptability of the proposed ' system. O e e G e S e e e* e 9 e O e 9 ".en*..* * .e* y e o e a

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4 .2**- Je.' FOREWORD ~.. s. Ik This[ report is supplied as part of the Selected Electrical, Instrumentation, and Control Systems Issues (SEICSI) Program being con-ducted for the U. S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by Lawrence Livermore Laboratory, Engineering Research Division of the Electronics Engineering Department. The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled " Electrical, Instrumentation and Control System' Support," B&R 20 19 04 031, FIN A-0231. 6 --...-..:.-..---,-..--.<a.. .. l.L .a- -V-

i 1 i 5 1 l TABLE OF CONTENTS 4 v i 1 Page j s j 1. INTR 000Cf!ON. 1 j J.,! ,g 'j 1 2. DESIGN DESCRIPTION 3 . i i l 3. EVALUATION 5 . l 4. CONCLUSIONS 9 1 I REFERENCES. 11 x! j. 1 e i e. ,1 ] I - r

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TECHNICAL EVALUATION OF THE END-0F-CYCLE RECIRCULATION PUMP TRIP FOR DUANE ARNOLO ENERGY CENTER (DocketNo.50-331) } i i L. R. Peterson Lawrence Livermore Laboratory, Nevada .f . ~. E 1. INTRODUCTION Iowa Electric Light and Power Company (IEL&P) by its letter dated 22,1979 [Ref.1], applied to amend the Technical Specifications October for the Duane Arnold Energy Center (OAEC) for installation of end-of-cycle (EOC) recirculation pump trip (RPT). The design of the EOC-RPT feature for DAEC is described in General Electric Company (GE) report NED0-24220, " Basis for Installation of Recirculation Pump Trip System - Duane Arnold Energy Center," [Ref. 2], which was submitted with the proposed change to the DAEC Technical Specifications, RTS-116 [Ref. 33 c The E0C-RPT feature is installed to improve the thermal margin of a boiling water reactor (BWR) near the end of each fuel cycle by reducing the. severity of possible pressurization transients. The RPT accomplishes this objective by rapidly cutting off power to the recirculation pump motors during generator load rejection (turbine control v.alve fast closure) or turbine trip (stop valve closure). This results in a rapid reduction in recirculation flow and increases the core void content during a pressuriza-tion transient, thereby reducing the peak transient power and heat flux. s'

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s J- . -:s Operation of the EOC-RPT system reduces the change in reactor T critical power ratio (ACPR) that would be produced by a pressurization transient. Preliminary analysis by GE indicates that adding the EOC-RPT-feature will result in about 50 percent reduction in ACPR for pressuriza-tion transients involving turbine stop valve closures or turbine control valve fast closures at Duane Arnold Energy. Center. It should be noted that E0C-RPT is not related to the RPT that is associated with an anticipated transient without scram (ATWS-RPT). ,u 7 t e 9 O e 9 e l O t e l ..... w'N s mar -,

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.C 2. DESIGN DESCRIPTION 3 The design for.the EOC-RPT installation at the Duane Arnold Energy Center is described in a GE report, NEDO-24220 [Ref. 2]. The EOC-RPT is part, of the reactor protection system (RPS) because it is an essential. supplement to the reactor scram system. All components of the EOC-RPT system are Class IE. 1 The E0C-RPT is required to quickly shut down both BWR coolant recirculation pumps when closure of all four turbine stop valves occurs, or when fast closura of all four turbine control valves occurs. An EOC-RPT trip may occur, but is not required, when one turbine stop valve or one turbine control valve remains open. To mitigate pressurization transient effects, the EOC-RPT must shut down the recirculation pumps within approxi-mately 200 ms after initial closure movement of either the turbine stop valves or the turbine control valves.' 1 The EOC-RPT installation is composed of sensors that detect closugog_the turbine stop valves or fast closure of the turbine control valves a4 relays, logic circuits, and fast-acting circuit breakers that A interrupt the current from the recirculation pump motor-generator set generators to the recirculation pump motors. When the redundant RPT - breakers trip open, the recirculation pumps coast down under their own inertia. To. satisfy the reactor protection system (RPS) single-failure criterion, the EOC-RPT has two almost identical divisions that actuate RPT in a one-out-of-two configuration. Either of the two RPT divisions operates independent breakers in the supply circuits of both recirculation pumps. Turbine stop valve closure is detected by four position switches that open when the associated stop valves are less than 90 percent open. j, Turbine control valve fast closure is detected by four pressure switches in

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j the hydraulic control system for the valves. The pressure switches open when the hydraulic control fluid pressure decreases below the trip level. The stop valve position sensors and the control valve hydraulic pressure sensors for RPT are the same ones used in the reactor scram system to init.iate scram when turbine stop valve closure or turbine control valve i fast closure occurs. The actuation of any RPT sensor causes an associated electro- ~ magnetic relay [to de-energize. The contacts of these relays are. combined in logic circuits with contacts from an operating bypass and contacts from a key-controlled manual bypass switch. The logic circuits control current to the trip circuits of the RPT circuit breakers. The operatir.g bypass disables the RPT system when turbine first-stage pressure is less than that for 30 percent reactor power. The same operating bypass concurrently disables the turbine inputs to the scram system. A manual bypass switch allows each RPT division to be disabled and placed out of service for maintenance or testing. The fast-closure sensors from each of two turbine control valves provide ' inputs to one RPT division and the sensors from the other two turbine control valves provide inputs to the second RPT division. Simil ar-ly, the position switches from each of two turbine stop valves provide inputs to one RPT division and position switches from the other two stop valves provide inputs to the other RPT division. The sensor relay contacts for each RPT division are arranged to form a two-out-of-two logic for the. fast closure of control valves and a two-out-of-two logic for closure of the stop valves. The operation of either logic in a RPT division will actu, ate the E0C-RPT feature.

i 3. EVAUIATION The EOC-RPT feature is part of the. reactor protection system and is a'n essential supplement.to the reactor scram function. The EOC-RPT is required to comply with the criteria of IEEE Std-279-1971 [Ref. 4], IEEE Std-323-1974 [Ref. 5], and IEEE Std-338-1977 [Ref. 6] and with' General Design Criteria.13, 20 through 24, and 29 of 10 CFR 50, Appendix A [Ref. 7]. The E0C-RPT system at Duane Arnold Energy Center is similar to that previously approved by NRC for Browns Ferry, Unit 1. The two RPT divisions are physically and electrically independent. The sensors and relays providing inputs to the RPT systems originate from two separate Class IE scram channels. The signal channels are properly grouped and separated to provide independence between the correspcnding scram channels and the associated RPT divisions. The scram and RPT logic relays are fail-safe and will go to the tripped st' ate on loss-of-power or loss-of-input signal from each sensor. The RPT circuit breaker control and trip circuits are not fail-

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The RPT circuit breakers that interrupt the current to the recirculation pumps require power to actuate. For this reason, the RPT logic circuits, control circuits, and trip cir-. cuits operate on 125 Vdc. Each RPT division is supplied by a separate Class 1E-rated 125 Vdc battery power supply with 30 amp inline fuses for the, positive and negative lines from the battery supply. Separate 10 amp branch fuses protect the RPT circuit breaker elevating-mechanism circuits; 15 amp branch fuses protect the local breaker closing circuits, the control room breaker closing circuits, and the indicator light circuits. These branch fuses isolate the circuits from the l breaker trip circuits so that a short circuit in the elevating or closing l functions of the breaker will not disable breaker trip actuation. A relay .a". 9, J

in each RPT division senses loss of power to the trip circuit in that division and actuates an "RPT Power. Not Available" annunciator in the control room. In addition, indicating lights are provided in the control room to monitor the trip coil circuits and the position of the trip breakers. The iGC has previously found that this departure from fail-safe design is acceptable. There is one interconnection between each E0C-RPT division and a ~ non-safety system. When each RPT breaker trips, auxiliary relay contacts in the RPT bre'aker actuate a control' circuit for the recirculation pump motor-generator (M-G) set to de-energize the M-G set after the RPT breaker interrupts the current from the M-G set to the recirculation pump motor. This interlock is adequately isolated so that no credible failure can prevent proper RPT action. An operating bypass automatically disables the RPT system when the reactor is operating at less than 30 percent power. The operating bypass is annunciated automatically in the control room. Each RPT division can be bypassed manually by use of an out-of-service keyswitch which is administratively controlled. Use of the out-of-service keyswitch bypass produces a suitable annunciator indication in the control room when the keyswitch is turned to the "RPT SYS INOP" position. The proposed technical ' specifications for the Ouane Arnold Energy Center provide suitable restrictions to limit operating power when one or both of the E0C-RPT divisions are inoperable. Capability to check the RPT sensors and logic is provided by operating each valve, one at a time. Lights across the relay contacts in the logic indicate proper operation at that point. The RPT divisions do not need to be bypassed to. conduct such. tests. During periodic testing of th,e. scr,am 1.ogic,,when. two turbine..s op yalves are. ope. rated.,s.imulta.neous.ly, .e .e. t,,y,affec,ted RP,T. division. gust, b.eJypasgd.briefly tyrgent.R,PT, actua.- h ~ ~* tion. The bypase, is accomplished by use of the E0C-RPT system out-of-servica keyswitch during the scram-logic test. ,,6 - 6we e

. 4 .a l The proposed technical specifications for Duane Arnold Energy Center specify monthly functional checks of both the EOC-RPT initiate logic and scram logic. We consider monthly testing of the EOC-RPT input sensors and logic circuits to be adequate for providing timely indications of system failure. Although the purpose of the RPT is to mitigate a core-wide pres-a surization trans,ient, the desired thermal margin advantage can be realized only if the initiating, events are sensed on an anticipatory basis, rather than by monitoring reactor pressure directly. The use of pressure' switches to sense the loss of hydraulic control fluid pressure to each turbine ~ control valve is adequate to anticipate fast closure of those valves. Similarly, position switches set to trip at 90 percent open will adequately ~ anticipate closure of the turbine stop valves. The EOC-RPT is not given credit for any other initiating events. To be effective, the RPT must be initiated almost immediately. GE states that their analysis shows that manual initiation of a prompt trip 7 of the recirculation pumps, at any ' reasonable point after the time when automatic action should have occurred, will not produce a significant improtement on the situation. The power to the ceirculation pump motor-h generator sets can be tripped manually from the w.ol room. Therefore, y provisions for manual initiation of the EOC-RPT feature are unnecessary. 2 } The RPT feature is required to reduce recirculation-pump flow. after either the turbine control valves or the stop valves start closing, and within a delay time assumed in the transient calculations for that operating cycle. The licensee and GE have specified that the RPT circuit breakers will have a maximum interrupting time of 135 ms. The remainder of the shutdown time will include system action, sensor response, logic response, and pump coastdown. The licensee and GE include time-response tests during initial . testing of the E0C-RPT installation to confirm that the system time ' ~ " *' ~ ~ 'r'eiponse, consisting of coastdown time and delay time, is less than that' --.,.--. - r n. m -..-. m -

assumed in the applicable transien,t calculations. However, the licensee has not included any provisions in the technical specifications for subse-quent time-response testing that would detect any degradation of system time response. We concur with the proposed surveillance requirement in the Duane Arnold Energy Center' Technical Specifications that functional tests of the E0C-RPT circuit breakers be conducted once per operating cycle. We further recomend testi'ng the EOC-RPT system' response time from initial closure movement of the turbine stop valves or control valves until recirculation ptanp shutdown or, alternatively, measuring the RPT circuit breaker inter-rupting time with suitable correlation of that measurement to the E0C-RPT system response time. To better meet the criteria of IEEE Std-338-1977, Section 6.3.4, these time-response tests should be made prior to each op-erating cycle for both E0C-RPT divisions as part of the RPT circuit breaker functional checks. b ~ y. b: h-tes:in; f un .x.. .w.. e l l - 1 (

..e _.v 4. CONCLUSIONS Considering the separation, independence, and isolation of the } two EOC-RPT divisions and their respective inputs,. circuits, and power supplies, the EOC-RPT feature for the Duane Arnold Energy Center meets the criteria of IEEE Std-279-1971, IEEE Std-323-1974 and General Design Criteria 13, 20 through 24, and 29 of 10 CFR 50, Appendix A. We recomend approval of the EOC-RPT system design as submitted by the licensee. We also recomend approval of the proposed change for the addition of an EOC-RPT feature at Duane Arnold Energy Center to DAEC Technical Specifica- ~ tions (RTS-116). To better fulfill the criteria of IEEE Std-338-1977, we recommend that suitable requirements for time-response tests of the EOC-RPT system prior to each operating cycle be included in the Surveillance Requirements of the Technical Specifications. Such time-response tests should be designed to verify that the E0C-RPT system response time is less than the response time assumed in the applicabic transient calculations for the corresponding operating cycle. f .....-- e. J....~ ..2.u-.__... ~. ,,c......... ........;_..,,.~,. .-w.~ ~ ~.w w.- ,y w ~w.v-...e-en, m..._,,,,,

~ REFERENCES j 1. Iowa Electric Light and Power Company letter (L. D. Root) to NRC/NRR (H. Denton) dated October 22, 1979. 2. General Ele'ctric Company, Nuclear Power Systems Division, " Basis for Installati6n of Recirculation Pump Trip System - Duane Arnold Energy Center," report NEDO-24220, 79 NED306, Class I, September 1979. 3. Iowa Electric Light and Power Company, "Froposed Change RTS-116 to DAEC Technical Specifications," enclosure to IEL&P letter dated Oct-ober 22, 1979. 4. IEEE Std-279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations." 5. IEEE Std-323-1974, " Qualifying Class 1E Equipment for Nuclear Power Generating Stations." 6. IEEE Std-338-1977, " Standard Criteria for the Periodic Testing of ~ Nuclear Power Generating Station Class 1E Power and Protection Systems." 7. Code of Federal Reaulations, Title 10, Part 50, Appendix A, " General Design Criteria for Nuclear Power Plants." e8 e = . om .,,, p ,11 - l l

ATTACHMENT TO LICENSE AMENDMENT NO. 58 FACILITY OPERATING LICENSE NO. DPR-49 DOCKET NO. 50-331 Replace the following pages of the Appendix "A" Technical Specifications with the enclosed pages. The revised pages are identified by Amendment Number and contain vertical lines indicating the area of change. 3.2-4 3.2-14 3.2-15 3.2-23 3.2-26 3.2-34 3.7-14 3.7-41 3.8-2

• 3.8-11 3.8-12
• No change.

Provided for convenience J l 4 ,.,._}}