**Author details**

Yuji Fukaya

dissolved in groundwater congruently with glass form dissolution. On the other hand, the concentration of 237Np is limited by solubility. Then, the inventory of 237Np should be reduced lower than the amount corresponding to the solubility. The MA recycling may not contribute

Furthermore, MA recycling increases working environment burden like the concept of PPP. MA recycling makes difficulty not only for spent fuel but also for fuel fabrication. **Table 7** lists the feasibility of fuel fabrication in globe box (GB) [43]. MOX fuel and neptunium-doped MOX fuel with high decontamination can be fabricated in GB with the current technology. However, for americium- and/or curium-doped fuel, automation is necessary, or fuel fabrication in GB is impossible. Fuel with low decontamination cannot be fabricated in GB. In this context, there is the opinion that MA recycling should not be performed [45]. For nuclear proliferation, safeguard should be enhanced by increasing the transparency of society instead of MA recycling [45].

Safety and economics of uranium utilization for nuclear power generation were investigated and discussed. To compare the alternative candidate of plutonium breeding by FBRs, P&T tech-

For the safety of reactor, to remain inherent safety feature for "shutdown" function, uranium utilization in thermal reactor is necessary. The safety feature is lost in fast reactor. The core performance, breeding ability, and economy are related to a transaction in fast reactor.

The amount of conventional uranium corresponds to consumption of approximately 290 years, and it is not much enough to sustain the energy supply eternally. On the contrary, the amount of seawater uranium, which is 4.5 billion tU corresponding to 72,000 years and 4.5 trillion tU including the uranium at the surface of the seafloor corresponding to 72 million years, is

Furthermore, by utilization plutonium in spent fuel in thermal reactor, the duration period of uranium can be increased. By once-through utilization, that can be increased to 1.6 times. By

With seawater uranium, the electricity generation cost increases by mere 3%. With HTGR, the cost with seawater uranium is cheaper than the cost of existing LWR with conventional uranium. The cost of FBR with multi-recycling increases by 40% compared with the cost of LWR. From the viewpoint of energy security, conventional uranium has problems, i.e., geology and concession. Therefore, seawater uranium should be recovered before exhaustion of conventional uranium from the viewpoint of energy security because the uranium mining concession, which is necessary to supply the uranium resources sustainably, is difficult to fulfill the entire require-

ment. Moreover, seawater uranium should be recovered by the countries facing ocean.

Plutonium utilization has problems of energy security due to the decay of <sup>241</sup>Pu. When fuel loading and/or reactor operation would significantly delay, the fuel should be refabricated and reloaded. Moreover, weapon-grade plutonium is generated in the blanket of FBR. There

multi-recycling, which can by HMLWR, that can be increased to 2.5 times.

to reduce public dose with the recovery ratio of 99.9%.

44 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

nology, one of the advantages of FBRs, was also discussed.

**7. Summary**

almost inexhaustible.

is a threat for the spent fuel to be seized.

\*Address all correspondence to: fukaya.yuji@jaea.go.jp

Japan Atomic Energy Agency, Japan
