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14 декабря, 2021
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Short-term reactivity excursions
Short-term fuel evolution as well as temperature changes may lead to reactivity changes. For thermal reactors the very large capture cross-section of 135Xe
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Figure 8.1. Variations of kx for (1) (KMTh + U) a mixture of 232Th (90%)-233U (10%); (2) (KmPu) a mixture of 238Pu (2.5%), 239Pu (60.8%), 240Pu (24.9%), 241Pu (11.7%), as considered by Rubbia et al. [45]; (3) (KMA. M.) a mixture of minor actinides of 237Np (33.3%), 241Am (21.6%), 243Am (40%), 242Cm (2.1%), 243Cm (0.032%), 244Cm (1.4%), 245Cm (0.9%) [45]. The flux assumed in the calculations was 4 x 1015 n/cm2/s. |
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Figure 8.2. Evolution of the fission rates for the minor actinide fuel, as a function of time, and according to the fissioning nucleus. The neutron flux assumed was 4 x 1015 n/cm2/s. |
and 149Sm lead to such effects. In the case of the Th-U cycle, a specific effect arises, both for thermal and fast reactors, due to the 27 day half-life of 233Pa. We first examine this effect.