RPCB: Reactor Power Cutback

Question 1

If the TEST/RESET button is depressed (backlit) and a RPCB occurs, what will happen?

Answer 1

Nothing. TEST/RESET inhibits all RPCB functionality.

Question 2

What is a Large Load Reject?

Answer 2

A signal sent to RPCB sent from SBCS. SBCS compares steam flow and TLI to PZR Pressure (specifically if TLI goes down with Ppzr going up). Need both channels to sense a load change to get a LLR.

Question 3

What happens if a selected subgroup is on the Hold Bus on a RPCB?

Answer 3

That subgroup will not fall into the core. CPCs will then trip the reactor for CEAs being out of sequence because it expected those CEAs to drop.

Question 4

What happens to the CEAs after the RPCB signal clears?

Answer 4

Rods are then able to be controlled by the RRS and/or manual operator control.

Question 5

What would happen if a Large Load Reject were initiated on a LOFP RPCB?

Answer 5

The Quick Open Block for SBCS would not work.

Question 6

When would a Turbine Setback signal clear?

Answer 6

When the Load Limit Potentiometer is dialed below 60% (Load Limit light comes on)

Question 7

What does the AUTO ACTUATE OOS button do in the RPCB System?

Answer 7

Defeats automatic only RPCB operation.

Question 8

When a Cutback is generated for a lost Main Feed Pump, what signal is sent to SBCS? Why?

Answer 8

Quick Open Block

QO is for a Main Turbine Trip. A MFP is lost, not the turbine. We’d couple a significant reduction in feed with a large increase in steam demand.

Question 9

How do you perform a manual RPCB?

Answer 9

Push the DROP SUBGRP button concurrently with the LOFP button or the LLR button on B05.

Question 10

What two events will result in a RPCB?

Answer 10

• Loss of a Main Feed Pump

- Large Load Reject (LLR)

Question 11

What happens if RRS Tave fails low on a Main Feed Pump trip?

Answer 11

CEAs drop due to RPCB and you’d get a continuous Main Turbine Runback

Question 12

What needs to work correctly to keep from tripping the Reactor on a Turbine Trip?

Answer 12

RPCB
SBCS
Fast Bus Transfer

Question 13

How long is a RPCB signal present?

Answer 13

10 Seconds

Question 14

How do you reset a RPCB?

Answer 14

Press the AUTO ACTUATE OOS and TEST/RESET buttons. Then dial the Load Limit Potentiometer counter clockwise until the Load Limit light illuminates.

Question 15

What signals are sent to the EHC System on a RPCB?

Answer 15

Setback
Runback
Increase Inhibit

Question 16

What is the purpose in the ARM signal sent to CEDMCS on a Cutback?

Answer 16

Prevents CEA re-latch before hitting the bottom of the core.

Question 17

Which signal sent to CEDMCS actually opens the circuit to the CEA coils?

Answer 17

DROP

Question 18

To de-select the CEAs for RPCB and leave RPCB in service, what buttons need to be pressed?

Answer 18

AUTO ACTUATE OOS and TEST/RESET both, twice.

Question 19

What specific parameter on a Main Feed Pump will initiate a RPCB when you lose it?

Answer 19

Main Feed Pump oil pressure <75 psig from both of 2 pressure switches (2/2 logic)

Question 20

What happens on a Turbine Setback?

Answer 20

MT Control Valves go to 60% at 480%/minute

Question 21

When is a Main Turbine Runback signal get generated?

Answer 21

When both ARM and DROP signals are present concurrent with:

• TLI > 60% OR
• sum of PT-1024 and Tave are low.

Question 22

What happens to the RPCB System if NNN-D11 is lost?

Answer 22

RPCB is totally disabled (no CEAs or turbine actions)

Question 23

To initiate a RPCB on a loss of a Main Feed Pump, what additional parameter must be met?

Answer 23

Reactor Power > 74%

Question 24

What happens to the RPCB System if NNN-D12 is lost?

Answer 24

Turbine Runback is disabled.
- On a cutback, the Main Turbine will only setback to 60% which will result in a Reactor Trip due to Secondary Power > Primary Power

Question 25

Where does the signal for a Main Turbine Runback get generated?

Answer 25

From SBCS

Question 26

What (if anything) happens to Turbine Runback capability when SBCS is placed in TEST or disconnected?

Answer 26

Main Turbine Runback is blocked

Question 27

What happens if PT-1024 fails low on a Main Feed Pump trip?

Answer 27

CEAs drop due to RPCB and you’d get a continuous Main Turbine Runback

Question 28

What is a RPCB Flag?

Answer 28

Its a signal generated by the CPCs that says its ok if a flagged CEA drops into the core because its associated with a RPCB.

Question 29

What is Turbine Increase Inhibit and when does it occur?

Answer 29

• Prevents the INCREASE LOAD button from raising Main Turbine Load until the RPCB is manually reset.
• Occurs on any RPCB

Question 30

How fast a Main Turbine Setback?

Answer 30

Moves the Main Turbine at 480%/min to 60%

Question 31

If the Main Turbine is in Standby, what features of the RPCB system pertaining to the Main Turbine don’t work?

Answer 31

Setback
Runback
Increase Inhibit

Question 32

When does a Turbine Setback occur?

Answer 32

When both ARM and DROP (1 and 2) signals exist.

Question 33

What two signals are sent to CEDMCS to drop rods for a Cutback? How long?

Answer 33

ARM and DROP

10 seconds

Question 34

What criteria must be met to get a RPCB for a Loss of a Main Feed Pump?

Answer 34

Two switches on one Main Feed Pump must read < 75psig control oil pressure

Question 35

How fast is a Main Turbine Runback?

Answer 35

Lowers load reference 130%/min due to Load Set Motor limitations.

Question 36

What does the TEST/RESET button do in the RPCB System?

Answer 36

It removes ALL auto and manual RPCB capability from service. Also deselects any selected CEAs.