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Figure 1. Configuration of the Pb-Bi-cooled HYPER core (183 fuel assemblies)
2.2 B 4
C-coated cladding
In order for a material to be an effective burnable absorber, its neutron capture cross-section
should be much larger than those of fuel elements. Also a neutron capture of a burnable absorber
should not generate nuclides with large capture cross-sections and at the same time daughter nuclides
should be naive in terms of radiotoxicity. Taking into account the above constrains on burnable
absorbers, 10 B seems to be the best candidate for the burnable absorbing material of the HYPER core.
10 B absorbs a neutron through ( , γ )
reaction, is an exothermic process:
n or ( , α)
n reaction. The ( n , α)
reaction, i.e. helium production
B +
10 1 7 4
5
+ n0
→ Li3
+ He2
Q
where Q is about 2.79 Mev for thermal neutrons and is a little larger in fast neutron systems. Table II
compares one-group effective cross-sections of boron and plutonium isotopes in the HYPER fuel
assembly. As shown in Table 2, the capture cross-section of 10 B is a little larger than the fission crosssection
of 239 Pu, the major fissile isotopes of the TRU fuel. Neutron absorptions of 11 B and Li-7 are
negligibly small. Table 2 shows that the depletion rate of 10 B is a little faster than that of 239 Pu even in
very hard neutron spectrum.
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