Nuclear Instrumentation

Question 1

What are the NI Flux ranges?

Answer 1

Question 2

What are the core quadrant locations for the NIs?

Answer 2

Question 3

What type of detectors are NI-1 and NI-2? Where are they powered from?

Answer 3

• Powered from RS-1 thru C539 and RS-2 thru C-540
• Gamma metric U-235 Fission chamber detectors. They use guarded and unguarded chambers. The unguarded are used for source range only due to their sensitivity. They are also pulse height discriminated to detect neutron pulses only.

Question 4

Where can gamma metric power be read from and where does it output to?

Answer 4

• Source range read on C03, dasey panel and SPDS. Wide range at C03 and SPDS. Power range on SPDS.
• Source range outputs to RPS and SPDS. Wide range to SPDS. Power range to SPDS and DROPS.

Question 5

What TS are associated with Source range neutron flux?

Answer 5

• LCO 3.3.9 requires 1 source range channel operable in modes 2 – 5. If the required channel is inoperable with Int range not on scale then suspend pos rx additions, insert all rods immediately and open CRD breakers and verify SD margin in 1 hour.
• If Req channel inoperable and INT range on scale then restore within 1 hour
• TS 3.9.2 requires one source range neutron monitor and additional monitor during core alts in mode 6. If required instruments inop, suspend core alts and boron changes that would be less than required for SDM immediately.

Question 6

What all instruments does gamma metrics supply?

Answer 6

NI-1/2, wide range and linear power range.

Question 7

What type detectors are the intermediate range instruments (NI-3/4)?

Answer 7

Intermediate range instruments are compensated ion chambers, powered from RS-3 and 4. One boron lined chamber to interact with neutrons and one unlined inner chamber. Current is produced by the radiation interaction with the the detector. Both neutron and gamma current flows upward thru the meter but only gamma current flows downward thru the meter thereby cancelling out the gamma current.

Question 8

Describe over and undercompensation of the intermediate range.

Answer 8

If undercompensated, the output reads higher than actual. Overcompensated reads lower than actual. Undercompensated is more conservative and how our detectors are calibrated (slightly undercompensated).

Question 9

What is the SUR for SU and INT range that feeds CRD system?

Answer 9

• Source range rod withdrawal inhibit if either SR channel reaches a 2 dpm SUR > 4 seconds (Clears when < 0.5 DPM). SR high SUR withdrawal bypassed at 10^-9 amps or NIs (5 or 6 OR 7 or 8)greater than 10%.
• INT rod withdrawal inhibit if > 3 dpm. (Bypassed > 10% power)

Question 10

How is sensitivity raised in the source range for gamma metrics and what region of gas amplificiation curve do they operate in?

Answer 10

Sensitivity is raised by using the unguarded chamber and operates in the ion chamber region.

Question 11

Where all does INT range output to?

Answer 11

RPS Channels C and D.

Question 12

What are the overlap requirements between source and intermediate range?

Answer 12

Overlap shall not be less than one decade. Typical overlap is 2 decades.

Question 13

What TS is associated with Intermediate range instruments?

Answer 13

TS 3.3.10 requires one INT range channel to be operable in modes 2 and 3,4,5 with CRD trip breaker closed and CRDs capable of withdrawal.

If inoperable, suspend pos rx changes immediately and open CRD trip bkrs in 1 hour

Question 14

What type of detectors are the power range NIs?

Answer 14

Power range instruments are uncompensated ion chambers due to the neutron population.

Question 15

Why are there two detectors per NI at the top and bottom of the core?

Answer 15

To measure imbalance

Question 16

How is quadrant power tilt calculated? What TS is associated with QPT?

Answer 16

100 * ((power in any quadrant)/(average power of all quadrants) - 1)

TS 3.2.4 requires QPT shall be maintained in limits in mode 1 > 20% power.

Question 17

How are the power range NIs auctioneered?

Answer 17

NI-5 and NI-6 are both NNI X. NI-7 and NI-8 are NNI Y. NI-5 and 6 are auctioneered to control off the highest of the 2. If NI-5 controlling and fails low then NI-6 will control. If failure of NI-5/6 occurs, then automatic swap will occur to NNI Y and control off highest of NI-7/8.

Question 18

Where all do power range NIs output to?

Answer 18

• EFIC from RPS
• ICS
• NR-514
• RPS for power indications/trips

Question 19

What is axial power imbalance?

Answer 19

Power in top half of core minus bottom half. Can be affected by rod movement, power changes, etc.

Question 20

What are the TS requirements for imbalance?

Answer 20

TS 3.2.3 requires imbalance be within limits in mode 1 > 40% power. Limits are based on RCP operation.

Reference COLR

Question 21

What is the order of preference for QPT values?

Answer 21

1) Full Incore (Plant Computer Calculation)
2) Excore (C03 readings)
3) Minimum Incore (Yokogawa)

Question 22

What would happen if compensating voltage for IR detector failed to 0 Volts?

Answer 22

Instrument would be undercompensated for gamma current would not be eliminated and IR power would read high.