ML20094E576

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Rev 0 to SEP Topic VII-1A,Isolation of Reactor Protection Sys from Nonsafety Sys,Including Qualifications of Isolation Devices, Failure Mode & Effects Analysis
ML20094E576
Person / Time
Site: Oyster Creek
Issue date: 08/03/1984
From:
GENERAL PUBLIC UTILITIES CORP.
To:
Shared Package
ML20094E573 List:
References
TASK-07-01.A, TASK-7-1.A, TASK-RR TDR-481, TDR-481-R, TDR-481-R00, NUDOCS 8408090257
Download: ML20094E576 (11)
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..:, , JSEP-Topic No. VII;1A' Isolation of Reactor Protection' System From Nonsafety Systems,

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J .; . . ' Including-Qualifications of Isolation P _ _

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. Failure Mode and Effects Analysis q,w yI ~ ~ 0yster-Creek Nuclear Generating Station

- dy . Docket.No. 50-219.

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TDR 481 Rev. O Page 2 of 11 j_'

TABLE OF- CONTENTS

~ 1.0~ . Introduction

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'2.0 . Method -

3.0- Results 4.0 - . Conclusion 5.0 Recommendation Fig. 'l - APRIMIRil Interface with Recorders-

-Fig. 2 - Recorder Input Buffer Circuit Fig. 3 - RPS Logic m- Fig. 4 - Nuclear lionitoring System Interface widi RPS Channel 1 Fig. 5-- Nuclear Monitoring System Interface widi RPS Channel 2 t

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1.0' INTRODUCTION

  • ' The' integrated Plant Safety Assessment - Systematic Evaluation

' Program _(SEP) was initiated by US Nuclear Regulatory Conaission (NRC) to review the designs-of older operating nuclear reactors to

-reconfirm-and document their safety. The results of SEP for Oyster

. Creek Nuclear Generating-Station (OCNGS) are published by liRC in

NUREG-0822 in January 1983..

Item 1.27. Topic VII' A in.IlVREG 0822 " Isolation of Reactor e Protection System From Nonsafety Systems, Including Qualification of Isolation Devices" identifies that there are no isolation devices between the Nuclear flux monitoring system IR!ts and APR!!s and their Lprocess recorders..

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[ GPUll has agreed to perfona a Failure Mode and Effects Analysis to

- . evaluate the need for isolation devices between,these systems and their recorders.. ~ This TDR documents the FMEA and its results.

2.0 IETH005-The analysis considers the worst case failure of the Recorders and the consequences.of the failures to the- APRMs and IRM trip functions which trip the Reactor Protection System.

. The consequences of the Recorder failure are considered to be

11. . Open circuit at the Recorder input teruinals
2. :Short circuit at the Recorder input tenainals
13. Recorder Power Supply voltage (115 VAC) applied to recorder input-teminals.

The APRlt/IR!l interface with their process recorders is shown in

_ figure 1.

- 2.1 References

-Following Gancral Electric docuuents show the Elementary Drawings of_ the system and its component parts.

._2.1.1 .GE237E645 Average Power Range Ilonitor (Dual) 2.1.2 GE237E650 . Wide Range !!onitor (Mean Square Voltage) 2.1.3 GE107C4818 Direct Current Araplifier 2.1.3 GE 706E812 Neutron Monitoring System m

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TDR 481 Rev. 2 g Page 4 of 11 gw; ,

2.2 Analysis 4~ The high impedance buffer circuit between IRM/APRM recorders and the associated DC amplifiers is shown in Figure 2.

The DC amplifier circuit is given in reference 2.1.3.

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The outputs from DC amplifiers is 0-10 VDC. This 0-10 VDC output is fed to IRi?/APRM trip units that provide Reactor

, Protection System scram under Hi. Flux conditions. The same

. output through a high impedance potential divider circuit is T stepped down to 0-1 Vdc signal, and is used to record the

, reactor' core flux level on the IRM/APRM process recorders.

, The effects of the various failure model of the IRM/APRM recorders on the RPS trip functions are analyzed below.

. 2.2.1- Open Circuit At the Recorder Input Terminals In this failure mode,' recorder signal input circuit is-assumed to be opened due to recorder failure.

This open circuit will ~not. degrade the 0-10Vdc signal that

drives the Scram Trip Unit, therefore, the integrity of the RPS system will not be compromised.

" .- '2.2.2 . Short Circuit at the Recorder Input Terninals x ,

In this failure mode, a short circuit across 0-1 Vdc signal resistor (R18 in fig. 2), is assumed.

, The short circuit across resistor R18 will not be able to degrade the Scram Trip Unit signal. The 9K resistor (R17) prov_ ides isolation to 0-10Vdc Scram Trip Unit signal against such faults. Therefore, this type of fault will not

, compronise RPS integrity.

2.2.3 Recorder Power Supply Voltage (115 AC) Applied to Recorder Input Signal Termina"s I This' type of failure mode can be further divided into two

types. One where 115 VAC is applied to one of the input signal terninals and the other where 115 VAC is applied across the recorder input signal terminals (or across resistor R18, Fig. 2).

2.2.3.1 The reference point of the DC amplifier is floating, therefore, applying 115 VAC to one of the recorder input signal- terminals will just change the reference and the

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TDR 481 Rev. 2 Page 5 of 11 v input signal to Scram Trip Unit (with respect to reference) will still remain 0-10 Vdc. Therefore, in this type of failure mode the input to Scram Trip Unit will not be degraded and the integrity of the RPS will not be compromised.

2.2.3.2. The Reactor Protection System (RPS) logic is wired in l 4

one-out-of-two-twice logic, as shown in Figure 3. !ne RPS consists of two logic channels and each logic channel has two subchannels. At least one subchannel in each of the logic channels must trip to provide reactor scram.

Figures 4 and 5 show the IRit/APRit interface with the RPS logic channels 1 and 2, respectively. The RPS

. circuit is normally energized, i.e., the logic subchannels deenergize relays 1K1, 1K2, 2K1 and 2K2, by opening trip contacts, to provide reactor scram. Each RPS subchannel can be tripped by two IRMs or two APR!!s under abnormal core flux conditions. Therefore, to fail one RPS subchannel its associated IR!!/APRM scram trips have to fail. But due to nature of the RPS logic failure of one subchannel cannot prevent reactor trip when the safety limits are exceeded. The RPS will fail to scram the reactor, under unsafe flux conditions, only if one entire RPS channel fails (i.e., both the subchannels in one channel fail). With respect to Nuclear lionitoring system interface with RPS, the above condition will occur when channels 1, 2, 3, and 4 of APRi1 system (11,12,13 and 14 of IRM system in start

- up mode) fail simultaneously or channels 5, 5, 7, and 8 of ARPM system (15,16,17, and 18 of IRit system in startup mode) fail simultaneously. Furthermore considering the allowable by-pass conditions of the

, . APRM/IRil, three of these four APRM/IRMs have to fail simultaneously to defeat the safety functions.

The probability of the second type of recorder failure (described in this section) degrading the scram trip signals in the above cocbinations of the APR!iS or IRMs is very low (almost negligible).

[ 3.0' RESULTS The above analysis shows that the failure of IRit/APRM process recorders,. in any mode, will not compromise the integrity of the RPS system and would, therefore, not create a safety concern.

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l 4.0 C0tlCLUSI0ft -

'it The APRit/IRtb will not fail to initiate a sceau signal in the event

'1 'of.any' credible failure in their process recorders. Therefore, in the existing conf.iguration, the RPS integrity will not be coupromised due to any failures in the APRit/IRM process recorders. Therefore, isolation: devices between APRit/IRll electronics and their process recorders are not required.

5.0 REC 0lfENDATI0fl.

The analysis-indicates diat the isolation device, between the IR?t/APRiis and their process recorders are not required.

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