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Figure 8. 10 B depletion in HYPER-HBA and HYPER-OBA<br />

24<br />

HYPER-SBA<br />

HYPE R- DB A<br />

22<br />

20<br />

B-10 Mass (kg)<br />

18<br />

16<br />

14<br />

12<br />

10<br />

0 30 60 90 120 150 180<br />

Time (day)<br />

4. Conclusions<br />

A homogeneous application of the B 4 C burnable absorber can be effectively used in reducing the<br />

burn-up reactivity swing. However, it is not favourable in terms of source neutron multiplication, since<br />

a significant fraction of spallation neutrons are parasitically absorbed by B 4 C before they are<br />

multiplied. In sub-critical reactor, absorbing materials should not be placed in the neighbourhood of<br />

the target zone.<br />

Loading of 10 B burnable absorbers in the outer zones is required in order to minimise the parasitic<br />

neutron absorption by 10 B. In this application of 10 B burnable absorber, the integrated and peak proton<br />

beam powers are lower than those of the reference design. In addition, this kind use of 10 B can<br />

considerably mitigate the slanting phenomenon of the radial power distribution, which is a critical<br />

problem in TRU-loaded sub-critical reactors. Consequently, outer zone loading of B 4 C can lead to a<br />

longer cycle length, compared with the unpoisoned reference core.<br />

Finally, it is concluded that 10 B has a relatively high potential as a burnable absorbing material for<br />

fast sub-critical reactors and introduction of a burnable absorber would open a new research field to<br />

optimise the core design of ADS.<br />

791

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