ML19221A408
| ML19221A408 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/17/1979 |
| From: | Ball R SPECIAL INSTRUMENT GROUP |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| TASK 11, TASK-11, NUDOCS 7905220453 | |
| Download: ML19221A408 (2) | |
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S!G DISTRIBUTION FR0ti:
R. BALL
SUBJECT:
EX-CORE MONITORING 0F CORE CONDITIONS Four groups of detectors can provide continuous information on core conditions within the pressure vessel.
g 1.
In-Core Thermocouoles - Available from computer printout and strip charts (to be put in) in Cable Room.,
2.
Resistance Thermometers - Available from computer printout - two are being read manually and recorded hourly.
These should be put on a recording bridge for continuous reading.
3.
BL Procortional Counters - These two detectors read the neutron leakage frca the pressure vessel and indicate the presence of water in the down-comer in the vessel and change in core neutron multiplication (criticality).
These detectors should be strip chart recorded continuously and be observed by the Control Room personnel.
4.
Ex-Core Power Range and Intermediate Channels - These detectors measure ganna activity distribution and shielding between source and detectors.
These detectors should be connected to an amplifier which can measure nanoamps and either be put on a strip chart recorder or on the computer printout.
DISCUSSION Neutron sources and their location:
1.
Startup sourcgs (ABC type) were in P-4 and B-12 fuel elements.
They eaca emit 1.4 x 10 neutrons per second as of April 12, 1979.
photo neutron sources - The lanthanum daghter gammas (from origen code) 2.
at 2.5 Mev on April 12,1979 were.7 x 10 ganca s/sec.
Assuming 1/3 of camas are absorbed in water and a D 0 cogcentration of 0)1M in ordigary 2
Oater - the neutron production is 15 x 10 n/sec (130 kev.
In m (volume) of primary system - The neutron production is.05 n/sec -cm.
The
" shine" from the water to the detector.
3.
Multiplication of Source Neutrons:
At 2772 MW., the flux at the power range channels near the proportional counters (Irg an average current indication of 50>>a and a calibration g
A/mv) is.312 x 10 nv The count rate of 40 c/s at the of 1.6 x 10 g
proportional counter is equivalent to' 1 n v+h.
If the source neutrons are all effective in causing, fission, the prbary fission rate would be 7 9 0 5 a g o 4 53 c'
162 0%
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3.
Multiplication of Source Neutrons (Cont.)
9 2.8 x 10 fissions /sec or about 0.1 watts.
The 1 nv neutron level at the proportional counter indic tes (if all neutrons bbme from the core) using a calibration of.3 x 10 nv/2772 MW a power level of 10 watts.
A multiplication of 100 is not credible andhthe neutron contribution must be.
4.
Proportional Counter Indications:
Normal indicagion af ter a 20-day shutdown (normal from 10 EFPD) on this plant, at 100 F, was 1 count /sec.
This could be considered a maximum direct source shine (no multiplication). A decay curve, at nearly constant temperature, of the BF counts gives about a 20 day half life between 3
April 13 and 15.
162 095
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