ML20210T257

SER Re Util 850802 Submittal Describing Design Details of Steam Generator Blowdown & Auxiliary Steam Sys to Detect & Isolate High Energy Line Breaks.Sys Design Acceptable, However,Two Deviations from IEEE-STD-297 Criteria Apparent

ML20210T257
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	02/06/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20210R166	List: ML20210R162 ML20210R206 ML20210T257
References
NUDOCS 8702180136
Download: ML20210T257 (4)

Text

.-_ - _ -.

, ENCLOSURE 2 SAFETY EVAltfATinN REpnor

, HIGH ENFRGY LINE RREAK ISOLATInN SYSTEM STEAM GENERATOR BLownnWN AND AllXILI ARY STEAM SYSTEMS BYRON ll NITS 1 A7/RRAIDW0nD llNITS l&7 T. INTRODUCTION in a letter dated August 2,1985, Comonwealth Edison described the desien datails 1

of a systen being installed in Byron Units 1 A9 and Braidwood Units 11.9 to detect and automatically isolate high energy line breaks (NEL91 in the steam generator blowdown (SD) and auxiliary steam (AS)-systens. The intent of.the isolation system is to ensure that an HELR in either the S0 or AS system will not result in a significant temperature increase in the auxiliary buildino above the quali-fication temperatures of safety-related equipment located within the buildino.

Further desion information was provided in an April 20, 1986, letter from the licensee coverino a modification to the isolation system.

I The following documents our review and evaluation (based on Section 7.6 of I

the Standard Review Plan (SRP), NUREG-0800) of the licensee's HELR isolation system.

II. DISCllSSION A. STEAM GENERATOR BLOWOOWN SYSTEM Each steam generator blowdown line is provided with redundant, series air-operated isolation valves located in the isolation valve room. The valves are held in the open position and close when the plant instrument air supply is removed either by loss of the air source or by de-eneroization of the solenoid valves. Re-dundant electrical trains of the HELR isolation function are provided which de-energize the solenoid valves (one solenoid per valve per train).

I 8702180136 870206 <

PDR ADOCK 05000454 '

P PDR e

-?_

The HELB isolation signals for the SD system are developed from two temperature-switches per train in each of twn areas within the auxiliary building. Closure of any of the four temperature switches within a train on a high temperature (approximately 134 F) energizes a corresponding relay which, in turn, de-ener-gizes the four solenoid valves (one per blowdown line) in the train. Annunci-ation is provided in the control room upon closure of any temperature switch.

Electrical power for the isolation signals is provided from redundant safety-related sources. Appropriate surveillance and limiting conditions of operation

1. or the system will be included in the technical specifications for each Diant.

B. AlfXILI ARY STEAM SYSTEM The auxiliary steam system line is provided with two parallel flow, air-operated isolation valves in series with a redundant air-operated isolation valve located in the turbine building. These valves are held open and close when the plant instrument air supply is removed either by loss of.the air source or by da-ener-gization of the solenoid valves. Redundant electrical trains of the HELO isola-tion function are provided which de-energize the solenoid valves (one solenoid for the parallel valves for one train, another solenoid for the series valve for the other train).

The HELR isolation signals for the AS system are developed from one temperature switch per train in each of six areas within the auxiliary building. Openina of any of the six temperature switches within a train on a high tencerature

l

)

e l D

(approximately 134*F1 de-energizes a correspondino relay which, in. turn, de-ener-gizes the solenoid valve in the train. Annunciation is provided in the control upon actuation of any temperature switch. Electrical pnwer for the isolatinn signals is provided from redundant safety-related sources. Appropriate surveillanca and limitino conditions of operation for the isolation system will be included in the technical . specifications for each plant.

III. EVALUATION As stated above, OLc review and evaluation is based upon Section 7.6 of the SRp. Duotino fron that section: "The ob.iectives of the review are to-confirm that design considerations such as redundancy, independence, single failures, qualification, bypasses, status indication, and testing are consistent with the design bases of these systems and commensurate with the importance of the safety functions to be performed." Further the SRP states that specific criteria of IEEE-STD-?79 are to be used as guidance, for systems reviewed undar SRP Section 7.6 Our review indicates that the HELB isolation system design satisfies most of the considerations of IEEE-STD-279 criteria because it is a redundant, safety-related system comprised of all Class IE components which are qualified for the appropriate environment, it is automatically initiated when setpoints for the area temperatures are exceeded and there are no control / protection system interactions. The system will be tested as required by appropriate technical specifications. There are

l d-no operating or manual bypasses in the systen and no multiple setooints. Once-initiated, the system is isolated until system operation is restored by the operator ,

through the use of reset switches. Although there is no manual initiation capability for the systen, manual isolation of the SD and AS systems is-possible utilizino other solenoids for some of the isolation valves or other isolation valves in the lines. Although valve position indication is not orovided in the control room for the isolation valves, flow indication and the annunciation from the temperature switches is available to indicate that the isolation function has occurred. On the basis that the system design satisfies most of the considerations of TEEE-STD-279 as discussed above, we find it acceptable.

Although the staff finds the design acceptable, two deviations from IEEE-STO-279 criteria were apoarent. First, one annunciator is provided for each of the sys-tens (AS and SD) isolated. These annunciators are common to the system-related tenperature switches and no separate indication at the sensor level is provided.

Second, the isolction function is generated effectively by 1-out-of-P (SD system) or 1-out-of-12 (AS systen) logic. No provisinn has been provided to bypass a failed temperature switch or to orevent system isolation during testino. In l response to these twn issues, the licensee indicated that the information avail-able to the operator on system status is sufficient and that the AS and 50 systems would remain in an isolated condition until a failed temperature switch is repaired. The staff finds this acceptable.

l