Excore Ni's

Question 1

Safety related functions of Excore Ni’s

Answer 1

• no failure in SR or IR can affect PR - fail in tripped condition on loss of pwr - must ranges from S/d -> 200% w/ 2 decades overlap between ranges - 2 post accident channels (transient, steady state for normal and post accident)

Question 2

Describe SR Ni’s N-31, 32

Answer 2

• BF3 gas filled proportional counter - 2000 v (voltage affects output) - surrounded by poly ( thermalize neutrons) - two detectors spaced 180 deg apart, below IR - utilizes pulse height discrimination - positively charged center electrode collects e-, and ions

Question 3

Describe IR Ni’s N-35, 36

Answer 3

• compensated ion chamber wrapped in poly (thermalize neutrons) - outer can gets pulse from n + y, inner can only signal from y => when signals combine gamma sig cancelled - only outer can lined w/ B-10 - ~ 800 v - compensating voltage applied to adjust gamma signal, => undercompensated = reading too high, b/c voltage for gamma too low and not subtracting enough from overall signal so reading too high

Question 4

Describe PR Ni’s N-41, 42, 43, 44

Answer 4

• uncompensated ion chamber lined with B-10 - 8 detectors, four corners of core - 2 detectors/ channel (top & bottom) - gamma disregarded, insignificant & proportional - ~800 v

Question 5

What region in gas amp curve does PR Ni’s operate in? IR? SR? GM?

Answer 5

PR- ionization IR- ionization SR- proportional GM- ionization

Question 6

Describe gamma metrics instrumentation N-51 & 52

Answer 6

• dual chamber unguarded fission chamber - two detectors located 180 deg apart, height of detector slightly higher than IR Ni’s - detector coated with U-235 - both chambers used (1 det) for source range (higher sensitivity to neutrons) HSDP - one chamber (1/2 det.) used for higher levels, PAMS

Question 7

Power supplies to Ni’s SR, IR, PR , GM

Answer 7

PY-11= N-31, N-35, N-41, N-51 PY-12= N-32, N-36, N-42 PY-13= N-43, N-52 PY-14= N-44

Question 8

In IR, performing Rx s/u, level Trip switch in normal, Lose control power to N-36 (IR),………..What happen?

Answer 8

Rx trips Lose control power, ssps relay not made up

Question 9

In SR, Rx s/u in progress, level Trip switch in normal, lose instrument power to N-31 (SR), ….. what happens?

Answer 9

Rx trips Lose gating circuit signal, control power can’t get to ssps relay

Question 10

In IR, performing Rx s/u, level Trip switch in bypass (N-35),lose control power on (N-35)………..what happen?

Answer 10

Rx trips If lose control power doesn’t mater if bypassed

Question 11

In IR, performing Rx s/u, level Trip switch on (N-36) in bypass, lose instrument power (N-36),…..what happens?

Answer 11

Nothing If in bypass, the gating circuit is bypassed, control power reaches ssps relay

Question 12

@ 13% power, performing Rx s/u, level Trip switches in normal, SR has been manually de-energized, IR Rod stop has not been blocked yet, lose control power to N-35 (IR)……….what happens?

Answer 12

Rx trips, IR Rx Trip not blocked yet, lose control power => Trip

Question 13

What happen if during Rx s/u below P-10, if you lose PY-11 or 12?

Answer 13

Rx trips Lose a SR and IR and therefore lose control and instrument power to applicable Ni => Rx trips

Question 14

What happens above P-10 (IR Rod stop blocked) if you lose PY-11 or 12?

Answer 14

Nothing If IR Rod stop is blocked, Trip is also blocked and won’t come in on loss of power

Question 15

How are source range Ni’s circuitry protected from faults in ; (outside SR drawer) SUR circuit, audio counts circuit, NR 45…….

Answer 15

Isolation amplifiers

Question 16

SR block/reset switches, what do they do?

Answer 16

• only work > P-6 (IR > 10^-10 amps) - blocks SR Rx Trip @ 10^5 cps SR (~5x10^-10) - de-energizes SR Ni’s - 2 switches, one for each train ssps (A & B)

Question 17

During Rx Trip when do SR Ni’s turn on? What Ni failure could prevent them from energizing?

Answer 17

When PR Ni’s < P-10 (3/4)(10%) AND When IR Ni’s < P-6 (2/2)(10^-10 amps) Ni’s automatically energize. 1 IR or 2 PR Ni’s hang up or fail high

Question 18

What is purpose of Hi-flux at s/d alarm?

Answer 18

Alert operators of inadvertent reactivity addition to core (4x stable s/d count rate), cnmt evac alarm NOT hard wired in.

Question 19

IR block switches, what do they do?

Answer 19

• only work > P-10 (2/4) - blocks C-1 IR Rod stop @ 20% equivalent - blocks IR high flux Trip @ 25% equivalent - two switches one for each train

Question 20

If one IR Ni is undercompensated too much what could happen following a Rx Trip?

Answer 20

The SR Ni’s may not energize since the IR Ni may not reach < P-6 (10^-10 amps) and automatically re-energize SR => manually energize SR

Question 21

PR block switches, what do they do?

Answer 21

• only work above P-10 (10% PR) - blocks PR hi flux Rx Trip (low set point)(25%) - 2 switches, one per train

Question 22

What is gain used for on PR drawer? What is rate mode switch used on PR drawer?

Answer 22

• adjust summing lvl amp on PR for calimetric or heat balance - used to reset lock-in feature of positive rate Trip

Question 23

Power supplies to gamma metrics

Answer 23

N-51….. PY-11 N-52…..PY-13

Question 24

What’s the difference between Delta I and axial offset?

Answer 24

Axial offset is delta I divided by total power. => @ 100% power they are equal and if AI is 0 they are equal, if maintain constant AO, delta I will change as power changes.

Question 25

Precautions and limitations with Ni’s?

Answer 25

• be cautious of accuracy of instruments following outage - only allow = 1 PR Ni at a time (de-energize SR) - if flux increases > 2x on all or > 3x on any channel suspend core alterations when s/d

Question 26

How is IR SUR affected by detector that is undercompensated (up power)? Down power?

Answer 26

Up - SUR less than actual (less positive) Down - SUR less than actual (less negative)