Civil Engineering Reference
In-Depth Information
Fig. 5.5
Reactivities and
relative power P(t)/P
0
as a
function of ramp type axial
movement of absorber
(control) rods (without and
with temperature feedbacks
of reactivity) [
3
]
5.6.2.2 Self-Regulation Characteristics of a BWR Under Required
Power Changes
BWRs have a negative Doppler coefficient of fuel temperature (Sect.
5.6.2
)
10
5
K
1
of approx
:
2
and a negative coolant void coefficient
10
3
per
of approx
:
1
:
3
%
steam volume increase
:
In this way, BWRs can be controlled directly via the speed of the internal coolant
recirculation pumps (Fig.
5.6
). When more power is needed at the turbine-generator
system or more steam is required by the turbine requiring an opening of the steam
increases the cooling water throughput, and rises the axial level of the boiling zone
in the reactor core rises. As a result of the decreasing void volume fraction in the
reactor core, a positive reactivity increase (positive contribution to k
eff
) is initiated
via the negative coolant void coefficient. The power and the fuel temperatures
