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3.1.7.1 Material reactivity wsrths
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The reactivity worths sf the major fuel co~stituents are shown in
Table 19. The total worth is negative because the effects of fertile
thorium and 238~ overcone the positive effects sf the fissile materials.
This means that the reactivity could be made significantly higher by re-
moving fuel salt, although the breeding performance would be reduced.
Table 19. Material concentration
coeffielent of reactivity
0.00026
-0* 08691
-9- 0001 1
-0.0023
0.0048
-0.8015
0.0025
-0 e 00050
-0.00019
-0.14
0.15
0. 010
4.29
-0.0626
0.20
4.014
4- 063
4.0079
4.092
Removing lX of the uranium would have a reactivity effect of -0.0015
~k/k, and reinserting it would have a comparable positive effect.
parable result for plutonium would be only 8.0001 Akbk. If 1% of the
A com-
fuel salt could be replaced suddenly by bubbles, the effect would be an
increase of 0.00114 in reactivity, which is sufficient to induce a signifi-
cant system transient. In practice, no likely mechanism exists that could
bring about such an effect suddenly.
~ ~ aspecific e coefficients S~QW that, atom for atom, 233~ is a much
more reactive fuel than 2 3 5 ~ or plutonium in the reference isotopic mix
and that 23% is a greater depressant than thorium.
3.1.7.2 Temperature effects on reactivity
Temperature affects the reactivity of the core by (1) broadening
narrow ~ros~-se~tion resonances, thus increasing their capture rate