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Table 12. 135 Cs transmutation efficiency when using different moderators
Moderator
Radial blanket Axial blanket
%/cycle kg/TWh %/cycle kg/TWh
CaH 2 44.7 0.40 16.2 0.72
MgH 2 44.8 0.40 16.2 0.72
TiH 2 33.6 0.30 11.5 0.51
CeH 3 39.0 0.35 13.7 0.61
ZrH 2 40.2 0.36 14.2 0.64
Be 40.3 0.36 14.2 0.64
C 41.3 0.37 14.7 0.65
Be 2 C 47.3 0.42 17.4 0.78
NbBe 17 42.7 0.39 15.3 0.68
Besides, other caesium isotopes ( 133 Cs, 137 Cs etc.) are accumulated in power reactor spent fuel and
the Cs 135 fraction is ~10% only. When transmuting caesium without chemical isotope separation, the
transmutation efficiency decreases one order due to creation secondary 135 Cs.
Thus, the results presented show that the issue on advising to transmutate 135 Cs in reactor
conditions remains open.
The transmutation of 93 Zr (T 1/2 = 1.53 × 10 6 years, production 1.74 kg/TWh for fast reactors
2.8 kg/TWh for thermal reactors) was not considered in detail in this report due to large uncertainties
in its nuclear data.
The transmutation of such elements 79 Se (T 1/2 = 65 000 years) and 126 Sn (T 1/2 = 10 5 years) is not
considered because of their low transmutation rate.
The analysis results allow forming the final Table 13.
Table 13. A comparison of transmutation rate
for different FP and their production in power reactors.
Isotope T 1/2 Production in reactors,
kg/TWh
Transmutation efficiency
kg/TWh
without moderator with moderator
99 Tc 2.13 × 10 5 3.0/3.2 10.6 5.3
107 Pd 6.5 × 10 6 1.54/0.78 5.5 3.0
135 Cs 2.3 × 10 6 3.70/1.4 5.1 0.8
129 I 1.57 × 10 7 0.70/0.66 5.3 0.7
79 Se 6.5 × 10 4 0.03/0.02 0.09 0.01
126 Sn 10 5 0.15/0.08 0.2 0.04
93 Zr 1.53 × 10 6 1.74/2.8 2.3 1.4
233