Civil Engineering Reference
In-Depth Information
Fig. 5.6
Self-regulation
characteristics of reactor
power in a BWR through
changes in speed of the
internal main coolant
pumps [
3
]
increase. The raising fuel temperatures in connection with the negative Doppler
coefficient of fuel temperature cause a negative reactivity feedback which stabilizes
the process at a higher reactor power level. In this way a BWR can be controlled in a
power range above about 60 % of nominal power solely by varying the speed of the
axial coolant pumps located in the annulus between the reactor core and the inner
wall of the reactor pressure vessel [
3
].
In lower power ranges control by the recirculation pumps is supported by
movements of the absorber (control) rods.
5.6.3
Instrumentation, Control, Reactivity Protection System
(Safety Level 2)
Instrumentation implies monitoring important measured data by
- in-core instrumentation, such as the aeroball system, miniature fission chamber
detectors, continuously measuring self-powered neutron detectors [
6
,
14
-
17
];
- out-of-core neutron flux measurements covering the whole range of power from
startup to nominal power output; the out-of-core neutron flux instrumentation
furnishes important signals to the reactor protection system; it comprises the
pulse range at zero power, a medium range, and the power range [
6
];
