# System Studies on the Fusion-Fission Hybrid Systems and Its Fuel Cycle
### Studies on FFHS as Burner Reactor  
The majority of foreign researchers consider Pu to be a problem like MA and even more serious because of the proliferation risks. The author of [3] is not an exception: he investigates the transmutation of fuel that consists of MA and Pu in different FFHSs (with blanket thermal power from 3 to 10 GW).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Nuclide** & \(\beta\) \\ \hline \({}^{238}\)U & 0.0172 \\ \({}^{237}\)Np & 0.00388 \\ \({}^{238}\)Pu & 0.00137 \\ \({}^{239}\)Pu & 0.00214 \\ \({}^{240}\)Pu & 0.00304 \\ \({}^{241}\)Pu & 0.00535 \\ \({}^{242}\)Pu & 0.00664 \\ \({}^{241}\)Am & 0.00127 \\ \({}^{243}\)Am & 0.00233 \\ \({}^{242}\)Cm & 0.000377 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The effective fraction of delayed neutrons.  
Figure 3: Number of prompt neutrons per fission against initial neutron energy.  
FFHS do not have high requirements for plasma parameters because most of the neutrons are born inside a blanket (that contains fissile materials). For example, if \(k_{\text{eff}}\) = 0.95 then the neutron multiplication factor for a plasma source will be about 20. The fusion power of these FFHSs varies between 150 MW and 500 MW (that corresponds to ITER fusion power). The author of [3] pointed out that for FFHSs the following parameters are appropriate: fusion power <200 MW, normalized beta < 2, neutron wall loading < 1 MW/m\({}^{2}\), power amplification Q\({}_{\text{p}}\) < 2. In this case, the corresponding efficiency of burning Pu-MA fuel is 1.1 \(\times\) A, 1.65 \(\times\) A, 3.7 \(\times\) A tons annually (where A is availability factor). The original values were changed according to Pu + MA fraction in the SNF (1.1%).  
The authors of [10] point out the advantages of a FFHS for MA transmutation and investigate the utilization of a thermonuclear neutron source with fusion power less than 200 MW for the transmutation of the metal fuel consisting of MA, Pu and Zr. The proportions of fuel components are varied: the more Pu there is in the fuel the lower MA transmutation rate, but the higher blanket thermal power. It was found that the transmutation rate of MA could reach 19.4% for each irradiation cycle (that is 5 y) and about 86.5% for 25 cycles.  
Another approach for MA transmutation in a FFHS is an application of a molten salt blanket where actinide fluorides are dissolved in a molten eutectic of alkali metal fluorides. This salt also serves as a coolant. It is a very promising blanket option, having, for example, such advantages as online fuel composition control. Such an approach is addressed in [11]. In this study, the authors decided to take all transuranic elements (TRU) from SNF (i.e., Pu and MA) for fuel fabrication. The fusion power of this reactor is 250 MW and the blanket thermal power is 3 GW. In this case, it's possible to burn about 1.1 t of TRU annually. The authors also stressed that removing more than 50% of FP from the fuel after each irradiation cycle is vital.  
Finally, not only are efficiency parameters important, but also the impact of FFHSs on a nuclear fuel cycle. This impact was successfully established by research [12] for Japan's nuclear power. This paper addresses the utilization of three stellarators that have extremely high fusion powers (as for FFHS) of 1, 2 and 3 GWt. These reactors are assumed to be introduced in 2050, 2070 and 2090 respectively. The authors demonstrate that a FFHS with 1 GWt fusion power is able to burn about 350 kg of MA per year, which seems like a very small amount compared to other studies. There is a discrepancy between [11] and [12] on the impact of FPs' accumulation on the MA burning process. Thus a more detailed analysis of this question is required for new studies. The authors of [12] also show that all MA in the system could be burned by utilization of the stellarators mentioned above in approximately 200 years.