Page 72 - Dynamics and Control of Nuclear Reactors

64 CHAPTER 6 Fission product poisoning

14
100% power initally
12
75% Specific power = 30 kW/kg at 100%
10
Reactivity loss ($) 8 25% Neutron flux = 3.47e13
or
50%
6
4

2
0
0 10 20 30 40 50 60 70 80 90 100
Time after shutdown (h)
FIG. 6.4
Xe-135 poisoning of the reference reactor for four different initial power levels.

14
12 Maximum

10
Reactivity loss ($) 8 6 available
reactivity
override

2 4

0
0 10 20 30 40 50 60 70 80 90 100
Time after shutdown (h)
FIG. 6.5
Reactivity loss due to Xe-135 poisoning after shutdown from full power, with a maximum
override reactivity of 9 dollars.

6.2.8 Xe-135 poisoning after a power increase
After an increase to a higher power level, the increased flux initially causes a reduc-
tion in poisoning through removal of Xe-135 by neutron absorption. This effect
occurs because the higher flux decreases the Xe-135 concentration faster than the
production from decay of I-135. Subsequently, the poisoning grows to its new equi-
librium level as I-135 concentration increases to its new, higher level. Fig. 6.7 shows