ACADs (08-006) Covered

KeywordsSteam bypass, transient overshoot, reactor coolant, main turbine, nuclear instrumentation system, pressurizer, level control system, CEDMCS, Control Element Drive Motion Control System, diagram, input signal processing, turbine load index, excore control, lag network.

Description

Supporting Material

1.1.1.9 1.1.4.6 1.1.9.1.2 1.3.8.2 2.1.15 5.4.1.2 5.4.1.8 5.4.3.9

NID20REACTOR REGULATING SYSTEM

Pre-Job Brief

• Identify critical steps• Identify error likely situations• Identify the worst thing(s) that can happen• Identify specific error prevention defenses to

be used• Identify actions to assure proper configuration

control

REACTOR REGULATING SYSTEM COURSE TERMINAL OBJECTIVE: 

Given the appropriate reference material, the I&C Technician will describe the operation and maintenance of the Reactor Regulating System. Mastery will be demonstrated by passing a written examination with a score of 80% or better.

Lesson Enabling Objectives:

EO01 Describe the method of reactor control programming used at PVNGS.

EO02 State the purpose of the RRS. EO03 List the input signals for RRS and describe

the source instrumentation for these signals.

EO04 Given a block diagram of the RRS for reference, describe how the RRS uses signal inputs to develop CEA motion demand output signals.

Lesson Enabling Objectives:

EO05 Describe the RRS outputs and the effect of these on other systems when RRS is placed in the test mode.

EO06 Given the appropriate procedures, describe how the testing of RRS is accomplished

EO07 Describe the use of Prevent Event Tools and Electrical Safe Work Practices to minimize human performance errors.

EO08 Given examples of RRS maintenance problems, determine the fault using applicable RRS prints, Tech Manual, and Setpoint Document.

EO01 Describe the method of reactor control programming used at PVNGS.

Temperature Control Programs

Ops Info Manual

100% RX Pwr

TAVG

is used to represent Reactor Power

0% RX Pwr

5.707586

TLI is scaled and biased so it can be compared to Tavg 100% Secondary Load

0% Secondary Load

5.707

EO02 State the purpose of the RRS.

Reactor Regulating System Purpose

The RRS, in conjunction with CEDMCS, forms a closed-loop control system which regulates RCS TAVG to a setpoint programmed as a function of turbine load (TLI) to satisfy 100% power Main Steam pressure requirements.

The RRS provides speed and direction signals to CEDMCS to reposition regulating CEA's to maintain RCS TAVG within a deadband of programmed reference temperature (Tref).

RRS Overview

• The Reactor Regulating System (RRS) is a non-safety related system.

• Located to the rear of control board B05 in cabinet J-SFN-C03R.

• Supplements operator manual control actions by: • Furnishing rapid response Automatic Control and

Control Element Drive Mechanism Control Withdrawal Prohibit (AWP) signals to the System (CEDMCS).

RRS Design

– The system is designed, in conjunction with SBCS, to control without significant transient overshoots, reactor power and turbine steam by-pass to counter or make adjustment for the following: Load rejection of any magnitude. Up to 10% step change in NSSS load. Up to 5% per minute ramp change in NSSS load.

EO03 List the input signals for RRS and describe the source instrumentation for these signals.

RRS INPUTS

a) Reactor Coolant System (RC)Provides TH and TC signals from both loops to RRS used to calculate TAVG

Supplies TC for AWP. An AWP is generated from any TC loop when temperature is > 575oF.b) Main Turbine (MT)Provides 1st stage shell pressure signals to RRS used as indication of turbine power and TLI signal to RRS

c) Nuclear Instrumentation System (SE)Provides signals to RRS from Control Channel Nuclear Instruments used in Power Error calculation.

RRS INPUTS

d) PLCS (SF)–The system receives from the Pressurizer Level Control System a contact closure signal indicating that the setpoint program is in Local.

e) CEDMCS (SF)–The system receives from the Control Element Drive Motion Control System a contact closure signal indicating that the CEDMCS is in `Auto -Sequential' mode (AS).

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EO04 Given a block diagram of the RRS for reference, describe how the RRS uses signal inputs to develop CEA motion demand output signals.

RRS Input Signal Processing

TH There is one RTD (RCN-TT-111X and 121X) located in each hot leg that is used in determination of TAVG.

The range of these RTDs is 500°F to 650°F. A recorder and meter for both RTDs is located on B04.

TC There is one RTD (RCN-TT-111Y and 121Y) located in RCS Cold Leg loops 1A and 2B that is used in determination of TAVG.

The range of these RTDs is 500°F to 650°F. A recorder and meter for both RTDs is located on B04. An Automatic Withdrawal Prohibit Signal (AWP) will be generated in

the RRS and sent to CEDMCS if either loop TC is > 575°F.

Turbine load index

• TLI is used by the RRS to develop the reference temperature for TAVG based on secondary load.

• Main Turbine first stage pressure (TFSP) is used to develop this signal because it is an approximate linear correlation to turbine load.

MTN-PT-PT11A and 11B provide this input to RRS. There is not an indicator for these two pressure

transmitters. An additional first stage pressure transmitter that DOES

NOT input into the RRS (PT-10) provides input to the EHC system and can be read on B06.

Calculation of TREF

• TLI is used to develop a reference temperature, TREF which is programmed from 0 to 100% TLI.

• TLI output to the TREF function generator is high limited to 100%.

• An AMI will occur when selected to average TLI if there is > 5% difference between TLI 1 and 2.

Excore Control Channel

• There are 2 control channel inputs for reactor power. • Either Rx power input or the average of the 2 may be

used in RRS which is selectable on the RRS test panel.• Each Rx power input is continuously compared to the

other channel and an AMI is generated at a 5% difference between channel inputs if the Rx power input is selected to average.

Lag Network

• The lag network gives higher amplification to rapidly changing inputs than for slow changing inputs.

• This provides faster response to rapidly changing inputs than for slow changing inputs and adds stability to the temperature control loop.

• Its output is sent to Total Error.

Total Error

• Total Error is generated by summing Power Error and Temperature Error.

• When TAVE is 3oF above TREF, a CEA insertion demand is generated to insert CEA's and lower TAVE.

• The insertion demand will reset at a Total Error of +2.84oF.

• Likewise, at a Total Error of -3oF, a CEA withdrawal demand is generated.

• This will reset at -2.84oF.

Gain = 0.188Bias = 4.273vdc

Vout = Vin X Gain + Bias

Out ≤ 5.773vdc

Gain = 3Bias = 5.0vdc

Vout = 3 X Ain (Tavg) – 3 X Bin (Tref) +5

TREF

Gain = 0Tau = 0.1min

Gain = 1.25Bias = 2vdcTau = 0.5 min

NC=+2vdc

Ain (ET’) has Gain 2.5Din (EB’) has Gain 2.5 + Bias(-)2vdcVout has Bias (-7.5)

NC=+5vdc

Vout = 2.5 X (Ain) + 2.5 X (Din – 2) – 7.5

ET

ET’

EB’

NC=+5vdc

Values represent U3 conditions

Different values in different units

EO05 Describe the RRS outputs and the effect of these on other systems when RRS is placed in the test mode.

RRS outputs

PLCS (SF) CEDMCS (SF) SBCS (SF) FWCS (SF)

PLCS (SF)

The system outputs to the Pressurizer Level Control System a 0 – 10V signal of TAVE used in the generation of programmed level from 0 to 100% power.

CEDMCS (SF)

The system outputs to the Control Element Drive Motion Control System as contact closures the following:

CEA Withdrawal Demand CEA Insertion Demand CEA High Rate Movement Demand Tavg - Tref High Alarm (AWP - Automatic Withdrawal

Prohibit) A High Input Deviation alarm (AMI - Automatic

Motion Inhibit) A Reactor Coolant Cold Leg High Temperature

alarm

SBCS (SF)

–Uses TAVE from RRS in generation of Quick Open Block signal and Turbine Runback Demand signal to RPCB.

–Uses Reactor Power from RRS for low power (15%) AMI generation

–Uses TLI for AMI permissive and AMI threshold determination

–CEA Automatic Withdrawal Demand is used to reset the AMI

FWCS (SF)

–Receives TAVE signal from RRS used in generation of Refill Demand signal after a Rx trip.

–Receives Reactor Power Signal from RRS which is used for the low power (15%) bistable - Economizer/Downcomer Swapover.

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3

TROUBLESHOOTING HINTS

1. Optimize the use of the Test Panel.2. Make certain that a solid understanding of the specific modules is obtained before troubleshooting.3. Never overlook switches and transfer stations. They are also susceptible to failure.4. Depress the "LIGHT TEST" pushbutton on the Test Panel to ensure that all the LEDs are operating properly.5. Always ensure that power is applied.6. Never rule out the possibility of loose wires or disconnected cables.7. Inspect for debris or tools within the cabinet.