ML20138J835

Single-Failure Analysis for Neutron Monitoring & Process Radiation Monitoring Sys

ML20138J835
Person / Time
Site:	Hope Creek
Issue date:	12/31/1985
From:	Public Service Enterprise Group
To:
Shared Package
ML20138J829	List: ML20138J826 ML20138J835
References
NUDOCS 8512180072
Download: ML20138J835 (11)

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SINGLE-FAILURE ANALYSIS FOR THE NEUTRON MONITORING AND PROCESS RADIATION MONITORING SYSTEMS HOPE CREEK GENERATING STATION PUBLIC SERVICE ELECTRIC AND GAS COMPANY

! December , 1985-l' 1

n' 8512190072 851216 PDR ADOCK 05000354 A PM L- ..

SU.GLE-FAILURE A'!tiLYSIS FOR THE NEUIR0fiICilTORIfiG

-AND PROCESS RADIATION 12ilTORI!!G SYSTEll5 Some of the safety related portions of the neutron monitoring system (liMS) and tne process radiation conitoring system (PPF.5) for the Hope Creek Generating Station (H:GS) are not designed and built to confom to the literal separation guidelines of Regulatory Guide 1.75. This analysis establishes the acceptabil-ity of these portions of the ti.' 5 and PPJ!5 by demonstrating that tney meet the single-failure criteria of IEEE Standard 279, which requires that the conse-quences of any single, design-basis failure event in a safety related portion of the systems be' tolerated without the loss of any safety function. -

Portions of NM5 and PRMS External to the NMS and PRMS Panels See Figure 7.1-1 of the HCGS FSAR for the separations concept of the reactor' protection system (RPS) and its relationship to the NM5.

Under the reactor vessel, cables from the individual, local power range conitor (LPRM) detectors and from the individual intercediate range conitor (IRM) detectors are grouped to correspond with the RPS trip channel designations.

These cable groupings are run in conduit from the vessel pedestal area to the NM5 and PRMS panels.

The radiation conitors on the main-steam lines are physically separated. The cabling from the individual sensors to the panels is run in separate cetallic conduit.

Cabling from the HMS and PRMS panels to the RPS cabinets is also run in cetal-lic conduit, providing electrical isolation and physical separation of the HMS and PRMS cabling associated with the RPS system.

It 'is concluded that the safety-related portions of the Nu.5 and PRMS external l to the HMS and PRMS panels adequately conform to the separation criteria of Regulatory, Guide 1.75.

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Single Failurn in tha NMS rnd'PRMS Panoln Figures-1 and 2 depict schematically the physical arrangement of the equipment in NMS and PRMS panels Hil-P608, Hil-P635, and Hll-P636. The designs of these panels are similar to those of NMS'and PRMS panels used in several BWR plants accepted by the NRC.

The layouts of the panels and the assignments of specific RPS trip logic circuitry provides the designs with the required tolerance to postulated single failures. The worst-case single failure-would be the loss of any combination

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of trip signals within one bay of any panel. However, the loss of any bay and its associated wiring would not prevent a scram. A valid scram signal would be transmitted via the other bays.because of the redundancy in the panel designs and the interconnections to the RPS (see Figure 7.1-1 of the'HCGS~FSAR).

The.eight IRM channels and the six average power range monitor (APRM) channels are electrically isolated and physically

- separated. Within the IRM and APRM modules, analog outputs are. derived for use with control room meters, recorders, and the process computer. Electrical isolation at the interfaces _would prevent any single failure from influencing the. trip unit output.

Physical Separation in the NMS and PRMS Panels Adequate separation in the NMS and PRMS panels is achieved

! by using the bay design depicted _in Figures 1 and 2, by using_ relay coil-to-contact as sufficient separation / isolation, and by separation between divisions / channels / wiring. Where conformation with Regulatory Guide 1.75 separation criteria cannot be achieved, the best-effort design is used.

. Circuits that provide inputs to-different divisions of the RPS are physically separated by airgaps or by the walls.

between the bays. Within the panels, where the cable and wiring runs to the different RPS divisions do not conform to the Regulatory Guide 1.75 separation criteria, fire-resistant "Sil-Temp" tape is wrapped around the cables and wires.

This eliminates the possibility of fault propagation between the RPS divisions. In accordance with paragraph 5.6.2 of IEEE: Standard 384,_this; tape has been demonstrated to be acceptable.

' All safety related cabling and wires within these panels

. either meet Regulatory Guide 1.75 or are wrapped 'in Sil-Temp tapefwith the. exception of the Redundant Reactivity Control System _(RRCS) inputs which are electrically isolated at

. the RRCS panels.

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Separated ducts are provided in the panel for the incering circuit wires frcm

_ tne sensors that belong to UPS Bus I cr Bus 2.

As shown in Figure 3, the isolation / separation precludes the propacation fro:

outside the tiMS cabinets of failures that coulo cause the loss of any safety function.

liMS/PRMS Interface to RP5 Althouch the LPPJi sensors are not recuired to ceet Class 1E recuirecents, the design bases of the APFJis specify that the LPPJi signals used for the APFJ!s be so selected, powered, and routed that the APPJis do ceet applicable safety

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criteria. The LPRM signal conditioners and associated power supplies are isolated and separated into groups.

The logic circuitry for the lim 5 and PFJ45 scra:n trip signals conforcs to the single-failure criteria. The contact configurations and failure consequences associated with IRM A (see Figure 4) and APPJi A (see Figure 5) are typical of

- the other trip channels and are described in what follows.

• With the reactor scram mode switch in the " Shutdown," " Refuel," or "Startup" positions, IRM A upscale or inoperating signals (unless bypassed) or APRM A upscale or inoperative signals (unless bypassed) would produce a channel trip of the output relay.

• With the reactor system code switch in the "Run" position, IRM A upscale '

or inoperative signals (unless bypassed) and an APRM A downstale signal (unless bypassed) or APRM A upscale neutron trip or upscale thermal trip or inoperative signals (unless bypassed) would produce a channel trip of the output relay.

• A trip of the channel output relay for IRM A and APRM A or a trip of the channel output relay for IRM E and APRM E would produce an RPS Al channel trip. In PRMS, the log radiation conitor A would produce an RPS Al channel trip (see Figure 6).

a for Mis, one tripped (urbypassed) channel on the RPS trip system would cause a l

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,. half scra- If one APPJi bev were to fail in an entripoed condition, the i

remaining bays would be capaele of sending RPS sufficient scra signals to j produce a full scram, even if cne of tnem were bypassed.

As shown in Figures 2 and 7, if one bay of panels H11-P635 or H11-P636 were te fail in an untripped condition, the remaining bays would be capable of sending sufficient RPS signals even if one of the IFR channels were bynassed. The IPJi

bypass switches can bypass one IRM channel at a tics.

Similarly for PPRS, if one bay were to fail in an untripped condition, the

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remaining bays would be capable of sending sufficient RPS trip signals to produce a full scrat.

' Common Power Sucoly Justification The fiM5 is supplied with 120-Vac, 60-Hz power from UPS busses 1 & 2. A design change has been authorized for the installation on each bus of redundant

? electrical protection assemblies (EPKs), which will conitor the incoming voltage and frequency.

Any fault in one lim 5 channel could not cause an unsafe failurt in another channel sharing the same low voltage power supply because 10-acp fuses are installed.for wire protection, and the power supplies are designed with i over-voltage and over-current protection circuitry at their output.

The PPRS is supplied with 120-Vac, 60-Hz power from RPS busses A and B. EPAs are already installed on each bus to provide voltage and frequency protection.

Any fault in one PPRS channel could not cause an unsafe failure in another channel sharing the same power supply because 5-a:p fuses are installed for wire protection, and the power supplies are designed with over-voltage and over-current protection circuitry at their output.

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Because of'the'fai1-safe HMS/FEMS logic configuration, a loss of one supply would result'in a half scra: signal to RPS. Loss of both supplies would result t

- in'a full scrat.

Common Associated Circuit Interfaces Nonessential (associated) circuits to common information equipment are current limited 'and protected such that their failure cannot jeooardize an adjacent circuit.

Figure 8 provides an example of an associated circuit interface on LPRi card Z11. - At the zera'to-160 mV computer output, the card is protected with q 30-MA ~

fuse. The zero-to-10-V output to the rod block monitor has an additional ^

isolator protection for the card.

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