CPC/CEACS

what is the design basis and purpose of CPC/CEACS

designed to provide a reactor trip to prevent exceeding SAFDLs

what are the two digital trips in CPC/CEACS

Fuel design limits on DNBR and LPD

DNBR must be greater than 1.34

fuel centerline Melt,LPD less than 5080F (or less than 21 KW/FT)

what does the DNBR trip protect?

protects the fuel cladding

what is the lower Tcold input used for

Coolant temperature shadowing factor

Calibrates neutron flux power

determine attenuation provided by the moderator

what is the highest Tcold used for?

used in DNBR calculation

what kind of trip is the PZR out of range trip?

AUX trip

for RCP speed, what RCP failure would not affect the RCP speed input?

Sheered shaft

what would be the first trip signal for an RCP?

RCP shaft seizure

how does CPC interface with NI?

CPC gets input from associated safety channels

how does CPC compensate for NI shadowing?

uses lowest Tcold to adjust the flux signal

uses CEA position changes to adjust the flux signal

what does CEACS output to CPCs for the power distribution algorithm

rod shadowing factors

radial peaking factors

out of sequence penalties

subgroup misalignment (subgroup within a group)

excess part strength CEA insertion limits

what RCP speed will send a DNBR (less than 1.34) trip singal?

any RCP less than 95% rated speed by multiplying DNBR by a .1 factor causing a low DNBR trip

what initiates an AUX trip?

Trip sequence subroutine (TRIPSEQ)

describe the AUX trips for DNBR or LPD

trips the reactor via DNBR or LPD to PPS

AUX trips do not have pre trip alarms if aux trip occurs

what are the three outside analyzed range (operating space auxiliary trip)?

Tcold less than 505 and greater than 590 F

PZR less than 1860 and greater than 2388 PSIA

ASI greater than +.5

what will cause a flow auxiliary trip

less than 2 RCP’s running

redundant to Low DNBR trip

Flow aux trip occurs without detailed calculations

what input causes ASGT (asymmetrical SG trip) what does it protect against?

based on Tcolds (loop 1 vs loop 2)

protects agaisnt an inadvertent closure of both MSIV on a SG

what causes a variable over power trip?

trips on rate of change, step change, or max of 110%

1% per min rising

16.67% per min an lowering

8% step change

what does the variable overpower trip step change value of 8% protect us against?

protects the core during rapid positive reactivity excursions (ejected rods)

NI input to CPC VOPT is compensated for temp/CEA shadowing. RPS trip is not

which will actuate first and why? CPC VOPT or RPS trip?

CPC VOPT will first due to it being temp/CEA shadowing compensated

what is the Hot leg saturation trip?

Highest Thot reaches or exceeds saturation (based on PZR pressure) (19f to Tsat)

what is the CPC failure auxiliary trip

various internal CPC failures

what from CPC gives us a CEA Withdrawal Prohibit signal

Low DNBR pre trip

High LPD pre trip

Hi PZR pressure trip

RPCB

CPC pre penalty (CWP) (based on 4.95 deviation, reg group greater than 7.5 inches above next higher numbered reg group, or PSCEA withdrawn less than 30 inches)

how does Radial power profile use RSPT’s?

uses CEA target positions (RSPTs) to determine RPF of each node

what will cause a DNBR/LPD penalty factor?

out of range sequence

Reg groups out of sequence when not within 10in band at the top or bottom of the core

what happens to the subgroup deviation penalty factor over time and why?

penalty factor worsens over time (due to xenon) and will ramp up for 6 hours then stays at a higher value

what happens on a dropped 12 finger

trips the CPC channel on DNBR/LPD immediately, CEACs sends penalty factor to the other CPC’s

what happens on a 4 finger CEA drop

no penalty associated with a dropped 4 finger

what happens during a Rx trip during a RPCB

CEAs do not insert at the same time, instead DNBR and LPD trip is generated from penalty factors

what are Raw EXCORE NI temp shadowing corrections looking at

lowest Tcold used because it would block more neutrons

how does Raw excore NI corrections look at CEA shadowing correction

CEA position affects flux to the NI’s. Rod shadow factors checked during startup

CPC corrects the NI signal based on CEA insertions

what does a negative ASI correlate to? what about a positive ASI?

negative ASI means higher flux in the core (insert CEAs or Dilute)

positive means a lower ASI in the core (withdraw CEAs/BORATE)

which aux trip does ASI input to?

inputs to CPC AUX trip

when do CPCs shift from a canned value to a calculated value?

when power is rising and is greater than 51% (or 17% per RPT) it shifts from canned to calculated

it returns to canned when power is lowering and lowers to less than 45% (or 15% on each RTP)

how does CPCs/CEACs interface with COLSS

uses incore instrumentation to determine ASI

We also use COLSS for tech specs (more accurate)

what happens to ASI during a down power (no rod motion)

ASI goes more negative due to a lowering THOT

Thot has a greater impact than Tcold

what kind of constant is Azimuthal power tilt Tq? how is it calculated? and what alarm is associated with it?

Tilt is an addressable constant manually inserted in the CPC’s

calculated by COLSS

Alarm (Plant monitor computer) if calculated value exceeds value in CPC’s

how is DNBR calculated

CRAAP + 3

Core power distribution

Radial peaking factors

Axial peaking factors

Azimuthal Tilt

Power

Highest Tcold

PZR pressure

RCS mass flow rate

how is LPD calculated

CRAP

CEAC/PC penalty factors

Radial peaking factors

Axial peaking factors

Power level

also Azimuthal tilt and uncertainty multiplier

how does DNBR margin compare to actual DNBR?

1.34+ margin meter reading= actual DNBR

on the calibrated neutron flux power reader, what do the red and green pen indicate and why might they differ

Red pen: CPC calibrated linear power

Green pen: NI uncorrected power of VOPT

May differ slightly because of the shadowing correction applied to CPC NI power

when can we bypass the CPC DNBR and LPD?

when power is less than 1E-4 the CPC can be bypasses at the associated ROM in the control room

what does CEACS tell CPC’s

CPC receives CEA position (the 22 target rods associated with specific core quadrant)

what does CEACs receive from RSPT?

receives RSPT inputs for all CEA’s

how many CEACS are required per CPC and why?

2 are required since a single RSPT is used for 1 CEAC in all 4 channels. this means a loss of one will not cause a trip.