Incores Flashcards
Describe the construction of the Incore detectors.
52 incores are comprised of 7 equally spaced flux detectors, one background detector and one temperature detector (CET). Rhodium-103 is used to detect neutrons which produces palladium and a beta particle. The beta given off is replaced from the ground and signal is read by current meter.
Where can the incore indications be read?
Plant Computer (preferred) - signals are compensated for detector efficiency, signal line loss, detector burnup and background detector reading making them the preferred reading.
C29 (Backup recorder) are used if plant computer not available. Not compensated for detector burnout. Potentiometer provide manual compensation of rhodium burnout.
Why are incores not used for control or protective functions?
Due to half life of the reactions - takes about 5 minutes of exposure for rhodium emitters to reach equilibrium (slow response).
How many CETs are there?
52
24 have a range of 50 to 2300 degrees F, 12 of which are sent to ICCMDS and SPDS and Environmentally qualified.
19 have range of 0 to 2300 deg F and sent to SPDS only.
9 are not connected.
How is axial power imbalance detected by incores?
Three detectors, one in each of three strings shall lie in same axial plane with one plan in each axial core half.
The axial planes in each core half shall be symmetrical about the core mid-plane.
Shall not have radial symmetry.
Has 9 total detectors for imbalance.
How is QPT detected by incores?
Two sets of four detectors shall lie in each core half.
Each set of four shall lie in same axial plane.
The two sets in the same core half may lie in the same axial plane.
Detectors in the same plane shall have quarter core radial symmetry.
16 Detectors for QPT.
Describe thermionic emission? Space charge release?
Thermionic Emission - The boiling off of valence electrons in the aluminum oxide insulation material surrounding the probe, resulting in valence electrons flowing to ground and negative current readings.
Space Charge Release - During normal power operation the insulation around the incore detectors builds up an electrical potential. When core temperatures are in the range of 1000 to 1400 degrees F, insulation will breakdown and the accumulated charge will be released.
What preference is used regarding limits associated with QPT?
Full incore (PMS)
Excore
Minimum Incore (Chart Recorder)
