M. R. ANSARI ET AL.
374
0510 15
0
1000
2000
3000
4000
5000
6000
7000
8000
time (s)
T (C)
Tra nsient Response to Reactivity Step Disturba nce
T
f
T
c
T
m
Figure 24. Transient behavior of fuel, coolant and modera
tor to symmetric reactivity disturbance at early time. 
15 20 25 30 35 40 45 50
0
1000
2000
3000
4000
5000
6000
7000
time (s)
T (
C)
Perm anent Response to Re activity Ste p Disturba nce
T
f
T
c
T
m
VVE
Figure 25. Transient behavior of fuel, coolant and modera
tor to symmetric reactivity disturbance at long period o
nd Figure 25 for a longer period of time.
ime representative equations
ped for future power generation. The model be
ha
ough the vari
ab
showed that the
te
jor Systems Codes, Capabilities and Limi
tations,” EPRI, WS8212, 1981.
hase Flow Fundamen
.2 Model on Trip off One Main Coolant Pump for

f
time.
time a
5. Conclusions
wodimensional tT
a
were
nalyzed for nuclear power reactor kinetics and thermo
hydraulic behavior for large AGR nuclear power genera
tion. The governing equations used in modeling of the
reactor included neutron diffusion, delayed neutron pre
cursor concentration and thermohydraulic equations for
fuel, moderator and cooling temperatures. The equations
were solved numerically using the finite difference
method. The reactor transient response was demonstrated
for reactivity disturbances in different conditions. For
this reason, the initial reactivity was established for the
steadystate condition. The initial reactivity values are
the reactivity amounts that do not change the reactor
power and maintain all the variables at steadystate val
ues. Higher values of the reactivity were imposed as fol
lows.
1) A nuclear reactor AGR type with 2000 MWe was
develo
ved well physically (qualitatively) and numerically
during critical conditions without failure.
2) The reactivity of all nodes was increased by 0.01.
The reactor response showed that even th
les increased, however, the negative feedback coeffi
cient and delayed neutron generation prevented the reac
tor system from the critical condition. Nevertheless, if
this condition were continued, for a reactor without a
control system, the fuel rod temperature would increase,
and the reactor would end with crisis.
Only the center node reactivity disturbance increased
to a value of 0.1. The reactor response
mperature increased to very high values. This behavior
could lead to fuel rod melting and explosion, even
though this model is not prepared to predict these crises.
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