Excore NIs

Question 1

Which Detector is used for SR?

Answer 1

• Boron Trifluoride (BF3) detector ** (Proportional Region)

Question 2

Which Detector is used for IR?

Answer 2

• Compensated Ion Chamber* (Ionization Region)

Question 3

Which Detector is used for PR?

Answer 3

• Uncompensated Ion Chamber* (Ionization Region)

Question 4

Which Detector is used for Gammametrics?

Answer 4

• Fission Chamber*** (U235)

Proportional Region

Question 5

Where is gammametrics SR N-23 powered from?

Answer 5

• Opposite Units CRID 3

Question 6

What is the definition of QPTR?

Answer 6

• Ratio of maximum upper (lower) excore detector calibrated output to the average of the upper (lower) detectors ***
• Normalized currents

Question 7

What does a channel comparator do?

Answer 7

• Compares total power from each channel to total power from any other channel and generates alarm at 2% (3%) difference***

Question 8

What do Instrument Power fuses do for excore NIs?

Answer 8

• Power Instrument Power Supplies

- IP fuses always trips unless switch is in bypass (does not block trip input from ctrl power fuses)

Question 9

What do Ctrl Power fuses do for excore NIs?

Answer 9

• Powers the Bistables
• CP Fuses removed always causes a trip to SSPS unless blocked for SR and IR NIs
• Ctrl Pwr provides power to the “level trip bypass” switch, so if power is lost to ctrl power with the switch in “level trip bypass” the channel will trip for IR and SR NIs

Question 10

If you are coming down in power and you are undercompensated, what can happen?

Answer 10

• P-6 may not auto clear to re-energize SR (IR 6e-11 (2/2)).
• Will have to Unblock SR manually

Question 11

How will the Instrument Power fuses output signal fail if the fuse is removed?

Answer 11

• Output signal fails high

Question 12

Given the following plant conditions:
• A Unit 1 startup is in progress
• The reactor is critical in the source range
• N41 Power Range channel is removed from service (all bistables placed in the trip condition) for surveillance testing
• A loss of power to the CRID 2 bus occurs
Which of the following actions will occur?

a. Reactor trips and BOTH source range channels are de-energized
b. The reactor is critical and BOTH source range channels are de-energized.
c. Reactor trips and N32 Source Range channel is de-energized. N31 Source Range channel is still in operation.
d. The reactor is critical and N32 Source Range channel is de-energized. N31 Source Range channel is still in operation.

Answer 12

• a. Reactor trips and BOTH source range channels are de-energized

Question 13

On a BF3 Source Range Detector, how are the gamma pulses sorted out from Neutron pulses?

Answer 13

• Uses Pulse Height Discriminator ***

sorts neutron pulses from gamma pulses

Question 14

On a Compensated Ion Chamber IR Detector, how do Neutrons create pulses?

Answer 14

• Boron gives neutron interactions in outer can ***

Question 15

On a Compensated Ion Chamber IR Detector, how are the gamma pulses sorted out from Neutron pulses?

Answer 15

• Gamma interactions are set to oppose each other from inner to outer can ***
• Cancels out gamma output leaving only neutron

Question 16

On a Uncompensated Ion Chamber PR Detector, how are the gamma pulses sorted out from Neutron pulses?

Answer 16

• Neutron to Gamma ratio is 1000:1 and are proportionally the same throughout the power range *** (No differentiation is needed nor provided)

Question 17

Why are gammametrics used?

Answer 17

• Used for post accident indication of power **

Question 18

What range of indications do gammametrics provide?

Answer 18

• Source Range and Wide Range power indications **

Question 19

Where are IR NIs (NI-35/36) powered from?

Answer 19

• IR N-35 CRID 1

- IR N-36 CRID 2

Question 20

In PR NIs, compensation is?

Answer 20

• Negligible

Question 21

Unit 1 is conducting a reactor startup following a refueling outage.
The following conditions exist:
- Source Range Instrument N-31 indicates 2.1e4 cps.
- Source Range Instrument N-32 indicates 2.0e4 cps.
- IR Instrument N-35 indicates 2.5e-11 amps.
- IR Instrument N-36 indicates 1.0e-9 amps.
- Rods are in manual with no rod motion.
- Source Range and Intermediate Range Nuclear Instruments are slowly rising.

Which ONE of the following best explains the indications?

A. N-35 compensating voltage is set too high

B. N-35 compensating voltage is set too low

C. N-36 compensating voltage is set too high

D. N-36 compensating voltage is set too low

Answer 21

• A. N-35 compensating voltage is set too high

Question 22

What lower flux deviation will give you an alarm?

Answer 22

• alarms when pwr is < 50%
  OR
• a lower detector is +/- 2% avg from all the others

Question 23

What PR flux deviation will give you an alarm?

Answer 23

• PR NI channel +/- 3% from any other

Question 24

What is powered by the Opposite Units CRID III?

Answer 24

• SR NI N-23
• Flux Panel log power
• SUR Meter
• LSI-4 Neutron Flux Meter
• NI Panel SR Neutron Flux Meter

Question 25

What happens if the Audible count rate is lost?

Answer 25

• Prompt and definite indication of a boron dilution event is lost
• The boron dilution event may not be detected quickly enough to stop the dilution prior to the loss of SDM
• Isolate any dilution flowpath to the RCS immediately ***

Question 26

What are the alt power indications that are compared to NIs?

Answer 26

• Thermal power
• RCS ΔT
• MPC-253

Question 27

What cools the Excore NI detectors?

Answer 27

• CRDM Fans