Transmutation Calculation
Transmutation performances of the hydride MA target and related core features in FBRs have been evaluated with the method shown in Table 16.2. A threedimensional continuous energy Monte Carlo Code MVP [9] and MVPBURN [10] are used as burnup calculations for evaluating the transmutation of MAs. The crosssection library applied in the calculations is JENDL4.0, which is processed to be adjusted to the MVP code. In the burnup calculation, the predictioncorrection method is employed to improve accuracy with millions of neutron histories for the criticality calculation, where the accuracy of Eigen value is about 0.04 %.
Table 16.2 Calculation method for MA transmutation

Table 16.3 Comparison of reduction ratio of MAs
aValues in parentheses are reduction masses by fissions 
Calculations have been done for two kinds of transmutation target. In case 1, the transmutation target was the MA hydride of (MA01, Zr09)H16. Calculation with metal MA0.1Zr0.9 target without H was done in case 2. The results of calculations are summarized in Table 16.3, where effective halflife is defined as the time such that the residual amount of MA is decreased to half of the MA loaded during the burnup. The effective halflife is calculated to be 2.19 years in case 1 and
8.7 years in case 2, mainly because of the softened spectrum effect induced by the MAhydride. The transmutation rate of the MAhydride target is about three times higher than that of the MAmetal target. Figure 16.4 shows the change of total MA and each element of MA in the MAhydride target with increase of time. Major elements in MA, that is, Np and Am are decreased simultaneously during the burn — up. The contribution of longlived Cm (245Cm and 246Cm) is much smaller than that of Np and Am. The change of total MA in the MAmetal target is also shown in Fig. 16.4 for comparison.
The major mode of the transmutation in the present method is not fission but neutron capture (see Table 16.3). As shown in Fig. 16.5, Am and Np are mainly transmuted to Pu because of neutron capture, beta decay, and alpha decay. Recycled Pu is used as a driver fuel in this reactor.







































