Excore Ni's Flashcards
Safety related functions of Excore Ni’s
- 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)
Describe SR Ni’s N-31, 32
- 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
Describe IR Ni’s N-35, 36
- 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
Describe PR Ni’s N-41, 42, 43, 44
- uncompensated ion chamber lined with B-10 - 8 detectors, four corners of core - 2 detectors/ channel (top & bottom) - gamma disregarded, insignificant & proportional - ~800 v
What region in gas amp curve does PR Ni’s operate in? IR? SR? GM?
PR- ionization IR- ionization SR- proportional GM- ionization
Describe gamma metrics instrumentation N-51 & 52
- 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
Power supplies to Ni’s SR, IR, PR , GM
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
In IR, performing Rx s/u, level Trip switch in normal, Lose control power to N-36 (IR),………..What happen?
Rx trips Lose control power, ssps relay not made up
In SR, Rx s/u in progress, level Trip switch in normal, lose instrument power to N-31 (SR), ….. what happens?
Rx trips Lose gating circuit signal, control power can’t get to ssps relay
In IR, performing Rx s/u, level Trip switch in bypass (N-35),lose control power on (N-35)………..what happen?
Rx trips If lose control power doesn’t mater if bypassed
In IR, performing Rx s/u, level Trip switch on (N-36) in bypass, lose instrument power (N-36),…..what happens?
Nothing If in bypass, the gating circuit is bypassed, control power reaches ssps relay
@ 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?
Rx trips, IR Rx Trip not blocked yet, lose control power => Trip
What happen if during Rx s/u below P-10, if you lose PY-11 or 12?
Rx trips Lose a SR and IR and therefore lose control and instrument power to applicable Ni => Rx trips
What happens above P-10 (IR Rod stop blocked) if you lose PY-11 or 12?
Nothing If IR Rod stop is blocked, Trip is also blocked and won’t come in on loss of power
How are source range Ni’s circuitry protected from faults in ; (outside SR drawer) SUR circuit, audio counts circuit, NR 45…….
Isolation amplifiers
SR block/reset switches, what do they do?
- 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)
During Rx Trip when do SR Ni’s turn on? What Ni failure could prevent them from energizing?
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
What is purpose of Hi-flux at s/d alarm?
Alert operators of inadvertent reactivity addition to core (4x stable s/d count rate), cnmt evac alarm NOT hard wired in.
IR block switches, what do they do?
- 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
If one IR Ni is undercompensated too much what could happen following a Rx Trip?
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
PR block switches, what do they do?
- only work above P-10 (10% PR) - blocks PR hi flux Rx Trip (low set point)(25%) - 2 switches, one per train
What is gain used for on PR drawer? What is rate mode switch used on PR drawer?
- adjust summing lvl amp on PR for calimetric or heat balance - used to reset lock-in feature of positive rate Trip
Power supplies to gamma metrics
N-51….. PY-11 N-52…..PY-13
What’s the difference between Delta I and axial offset?
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.
Precautions and limitations with Ni’s?
- 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
How is IR SUR affected by detector that is undercompensated (up power)? Down power?
Up - SUR less than actual (less positive) Down - SUR less than actual (less negative)
