Page 218 - Dynamics and Control of Nuclear Reactors

16.2 Sensor characteristics 217

FIG. 16.5
A gamma thermometer.

1
P ¼ ð T h θÞ, for the insulated region (16.1)
R h
1
P ¼ ð T c θÞ, for the un-insulated region (16.2)
R c
where
P¼power deposited (equal in both regions)
T h ¼temperature in the hotter insulated region
T c ¼temperature in the cooler un-insulated region
R h ¼heat transfer resistance in the insulated region
R c ¼heat transfer resistance in the un-insulated region
θ¼temperature of the fluid around the sensor.
Eqs. (16.1) and (16.2) yield the following:

ð T h T c Þ ¼ R h R c Þ P (16.3)
ð
That is, the temperature difference is proportional to the power.

16.2.1.6 Nitrogen-16 measurement
N-16 is produced in the coolant in light water reactors by neutron absorption in oxy-
gen. The N-16 flows with the coolant into the hot leg where gamma rays from N-16
decay are measured. Since N-16 production is proportional to reactor power, mon-
itoring the ex-core gamma rays from N-16 provides the N-16 concentration and,
therefore, the reactor power.