ML18043B149

Forwards Addl Info Re SEP Topic VII-1-A,per D Macdonald 790306 Request.Discusses Isolation of Reactor Protection Sys Inputs from Plant Computer Failures

ML18043B149
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	04/18/1979
From:	Cashell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Silver R Office of Nuclear Reactor Regulation
References
TASK-07-01.A, TASK-7-1.A, TASK-RR NUDOCS 7905010488
Download: ML18043B149 (12)

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General Offices: Z12 West Michigan Avenue, Jackson,' Michigan 49201 *Area Code 517 788-0550 April 18, 1979 f<'.r Richard D Silver US Nuclear Regulatory Commission Phillips Building 7920 Norfolk Ave Bethesda, MD Enclosed is the additional information on SEP 'I'opic VII-1-A requested by Don MacDonald at the r.i.eeting between the lrRC and Consumers Power Company on [,'.arch 6, 1979. Please forward it to him.

Steve Cashell 7905010'-f gcg

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e Personal Corres-pondence SEP Topic VII l.A e

TO: Dan MacDonald, NRC/Ext 28414 FROM:* RM Ma.rusich, Consumers Power Co~any MARU 10-79 During the presentation to the NRC on ~.arch 6, 1978 concerning the isolation of RPS input signals from. non-safety signals, additional information concerni..~g the isolation of the Reactor Protection System inputs from failures in the plant computer was requested. The information req_uested and res}:lonses follow.

Attachment 1 was presented at the March 6 meeting and is attached here for background.

Note in the following discussions the following definitions are used.

"Fischer Porter" - is the :9lant computer. This machine samples and records various analog in-puts for use in process parameter monitoring. Steam Generator Pressure Channel B and Reactor Coolant Flow Channel A are the only BPS inputs to this system. Other inputs are Feedwater 'l'emperature and Flew, Prima.rJ Pressure, Loop Temperatures and Delta-T, Turbine Pressure, Steam Flow, Charging Flow, Neutron Power, Station Output and Incore Neutron Detectors.

"Tennecomp" - is the data* logger. Tb.is machine accepts analog and digital.

inputs. It is used as a post trip events recorder. The RPS inputs to the data logger are shown in Attachment 1 and additional inputs are similar to the Fischer-Porter inputs. It was recently insta.l.led as a part of the Feed~ter Purity Modifications. It has several.remote mul.tiplex/ADC stations. Only the one containing P.PS inputs/outputs is discussed here.

l. How is the input to the Tennecomp physica..lly sepera.ted?

Response: The BPS izllmt to the Tennecomp consists of digital signals (output from the bi-stable trip units) from a..11 channels *of each reactor trip a.nd a..na.log signals from channels A through D of neutron flux safety channels and reactor.

coolant flow channel A, steam generator pressure ci'.annel A, and primary coolant inlet and outlet temperature channel A.

2 The digital input from chan..~el A of the RPS trips, enters the Tennecomp through connector J1. Similar;!..¥ ,-the input from channel_ B eni;ers through connector* J4, channel C through J7 and channel D through JlO. These connectors are on the left side of the Tennecomp. Figure 1 (Drawing 105-0028o6) shows these connections.

Channels A through D of the neutron flux analog input enter through connector J2l.

and the _other analog input enters through J22. These connectors are shown on 105-0028o6 and are on the right hand side of the Tennecomp.

2. What i.s the most severe failure with respect to its affect on the RPS current loops _.which can occur in the Tennecomp and Fischer-Porter?

Response: T'aemost severe credible failure unique to the computers would be a failure in the machine multiplexer such that 2 or more inputs would be "tied" together resulting in one input feeding into another input. _ This could occur when the machine sampJ.es an input and does not "release" prior to sampling another input (Hung Mux Relay).

3. w'ha.t is the effect on the ?.PS inputs shouJ.d this failure occur?

Response: Fischer-Porter The inputs to the plant computer are described above.

AlJ. of these inputs are 850mv or less. Figure 2 (Fischer~  :?orter Drawing SC30-1545) shows a typicaJ. in'put circuit~ The failure described above could result in the con:f'iguration shown in Figure 3.

Figure 3 shows the configuration of the inputs shouJ.d the failure described in Item 2 occur. - A description of the 3 -sections follow. The top section shows the RB3 current loop. El is the power supply which supplies 80v. R6 is an internal potentiometer which is adjusted so that the sum of the load resistances plus R6 = 600ohms. - RS is the dropping resistor for the Fischer - Porter or Tennecomp. Mext to it is the dropping resistor for the RPS trip units. E4 a.nd R5 are the major portions of the forced ba.la.nce pressure transmitter. E4 is a Zener diode which removes l5v. R5*is a variable resistor used to mock up the effect of the Darlington Amplifier in the transmitter. It a.ttain.s a.

resistance that it forces the current ou~ut to be :proportional to the deflection

prcduced by the dia.~hi-am. The bottom section shows a tj-pica.l ?recess :parameter measuxement loo:p. The desc:ri:ption is the .same as for the RPS loop. Rl through R4 are the resistors wi thL"l the ma.chbe.

To analyze the effect of the failuxe the following assumptions are made:

1. Plant condi ti ans are such that there is a lbma. current wi thL"l the :rtr-rs loop and 50ma L"l the process parameter loop.

2. The failure occurs so that R4 and R3 are connected and Rl and R2 are connected.

The values of the parameters are:

R8 = 16obms R6 = 600 - (16 + 100 ) = 484ohms R5 achieves a resistance so that lOma flows through loop

= 80 600 = 5900obms 0.01 Rl through R4 = lOOobms R9 = 16obms R7 = 600 - 16 =*584ohms R4 achieves a resistance so that 50ma. flows thxoug_~ loop

= So ~ 15 - 600 = 700ohms 0.05 The equations for this configuration are:

I Sum of currents at A=O I Il = I2 + I3 Sum of currents at B=O I + I =I 3 4 5 Sum of voltage drops around top section =O 80 - I R6 + I R8 + I 100 + I R5 - 15= 0 1 2 1 l .

Sum of voltage drops around middle section =0 L R4 + I R3 - I R9 + I R2 + I Rl - I R8 =O

-i l 4 1 l 2 Sum of voltage drops around bottom section =0 80 + r R7 + r R9 + I R4 - 15 5 4

=0 5

These equations are solved for r (the cuxrent across the ?.PS trip '.lnit dropping 1

resistor) which is found to be 9.97ma.. The efi'ect of the fa.iluxe is therefore minimal since prior to the failure the current was lCma and R5 (t):ie Darl:i:lgton) rill quickly readjust it to 10.Cnia. since the 9.97m.a. would also be going th--.oough the feedbac~ coil.

4 Tennecomp - Analog Inputs The analog il!puts are described above. Figure 4 shows the analog input to the Tennecomp. The failure described in Item 2 could result in a coni'iguration similar to the one shown in Figure 3. The only differences is :Chat the values of some of the resistors are different. Using the same assumptions as previously a.nd the following.data changes, the configuration can be analyzed to obtab the effect on current JJ_*

Data changes:

Rl through R4 = lOOOobms RS = lOOohms R9 = 200obms (used to simulate a 0-lOv il!put)

The analysis shows that I 1

= 11.lma a small change from*the i..'litial valve of lOma and a change which can be easily ma.de up in R5. Figure 4 also shows how the l0-120v inputs are accepted. It is possible to "tie" one of these inputs to a RPS current loop. The confi@.il"ation after the faili.ire which tied a l20v and RPS loop together is shown in Figure 5. Analyzing this coni'igura.tion to determine the change in 1i shows that r 1

= 9.85ma. after the failure vs lOma prior to the failur~. This is a minimal effect and can easily be compensated by R5.

Tennecomo - Di;:i:ital Inouts The digital inputs, wb.icll m the case of the RPS inputs come from bistable trip unit output, are isolated by optical isolators (shown in Figure 6, Tennecomp d_""a.wing 161-002811) and by the bistable trip units within the R...-OS.

Therefore there is no eff'ect on the RPS from the failure described in item 2.

Attachment l Ties To Comouter The following RPS in-put signals also in-put to. the Tenneccmp Drawt.'lg Tennecomp 114-002815, 141-002815 shows that isolation is achie*red by resistors:

Steam C-ene::-ator Pressure Channel A only Prima.rJ Coolant Flow Channel A only Steam Genera.tor Water Level Channel A only Pri~r/ Coolant Outlet Temp Channel A only Primary Coolant Inlet Temp Channel A only Neutron Flux Safetv Channels A through D The following RPS outpui sign.a.ls a.re a.lso i.11put to the data logger:

Neutron Flux Sa.f ety Channel A through D Reactor Trip Channels A through D frOlll:

Thennal ~.a.rgin Steam Generator Pressure Steam Generator Water Level Primal"'/ Coolant Flew High Flux Clutch Power De-energized Pressurizer Pressure (Ei)

P.PS out-put shewn on d..-..a.~...n~ ~615 and in detail on 2966-E-2858 and 2<;66-D-3198 (Bistable Output Terminals W, X, Y). Tenno=ccmp drawi...,g 161-002812 shows that isolation is achieved by the optical isolator, ther:nistor and resistors.

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