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equires irradiation times beyond 10 years, which, in turn, will require the structure material<br />

performing at high damage doses.<br />

The second aspect of long-time irradiation is the dependence of actinide cross-sections and burning<br />

efficiency on cycle number. Taking into account that the irradiation time is more than 10 years and core<br />

lifetime is approximately one and half a year it is necessary to have ~10 cycles of moderated<br />

subassembly irradiations. Dependency of actinide cross-sections on cycle number for two type of subassemblies<br />

are shown on Figures 5a and 5b.<br />

Figure 5a. Dependency of cross-sections on cycle number<br />

(without moderator)<br />

<br />

σEDUQ<br />

σ I<br />

$P P<br />

σ F<br />

$P <br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

&\FOHÃQXPEHU<br />

Figure 5b. Dependency of cross-sections on cycle number<br />

(with moderator)<br />

<br />

σÃEDUQ<br />

σ F $P <br />

σ I $P P<br />

<br />

<br />

<br />

<br />

<br />

<br />

<br />

&\FOHÃQXPEHU<br />

This dependency shows the cross-sections in moderated sub-assembly reach the maximum value<br />

that after approximately 8 cycles. For the non-moderated sub-assembly the cross-sections do not<br />

practically depend on cycle number.<br />

3. Influence of moderated sub-assembly on core parameters<br />

To check the influence of moderated sub-assembly with americium on core parameters we<br />

investigate the dependency of multiplication factor, target burn-up and sub-assembly power on cycle<br />

number.<br />

223

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