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Similar calculations were made for 129 I and 99 Tc in the Belgian High Flux Reactor (BR2)
which has a neutron flux of 3×10 14 n/(cm 2·sec) [158]. For iodine the target was CaI 2 and for Tc the
metal form. The calculated annual transmutation ranged between 6 and 9% for 129 I and 3 to 6% for
99 Tc. The major problem is the chemical stability of the CaI 2 target during irradiation and the very long
transmutation half-life for both 129 I and 99 Tc of about 12 years or more.
2.4.1.6 Conclusion
A ranking of some reactor types with respect to transmutation rates and half-lives is given for
99 Tc in Table II.15. The transmutation rates should be compared with the production rate in a 1-GWe
PWR, which is 21 kg/year or about 0.02 kg/MWe·year. Fast reactors with target pins loaded in a core
sub-assembly (with or without moderation) seem best, as they would burn the 99 Tc production of up to
five PWRs. The second best option would be to load targets in the moderator of a HWR. Transmutation
rates in standard PWRs are much lower.
Generally, transmutation of 99 Tc or 129 I in present reactors is not encouraging because of the
long transmutation half-lives and the huge inventories of fission products required. Special-purpose high
flux reactors could improve the prospects.
2.4.2 Nuclear data on fission products
The thermal neutron capture cross-section and resonance integral have been measured for
99 Rc, 129 I and 135 Cs using the TRIGA Mark-II reactor at Rikkyo university. For some nuclei, these data
differ very much from previous values [159].
Table II.15 Ranking of reactors with respect to 99 Tc transmutation capability
Reactor Configuration Inventory
99 Tc
(kg)
Transmutation
99 Tc
(kg/year)
Transmutation
99 Tc
(kg/MWe-year)
Half life
(year)
FR
FR
Moderated S/A
in inner core
Non-moderated S/A
in inner core
LWR Pin in guide tube UO 2
fuel
LWR
Pin in guide tube
MOX fuel
2 741 122 0.11 15
2 662 101 0.09 18
3 633 64 0.07 39
1 907 17 0.02 77
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