Sustainability and Economy of Energy Supply with HTGR Fueled by Uranium from Seawater

摘要

Sustainability and economy of energy supply with High Temperature Gas cooled Reactor (HTGR) fueled by uranium from seawater have been investigated and discussed. To sustain the nuclear energy safely by electricity generation with HTGR, the uranium resources must be inexhaustible. Generally, the abundance of resources is measured by a duration period which is defined as the ratio of available resources to consumption rate. The seawater uranium, which exists in seawater as a solute of huge amount, is expected to be alternative resources. It is said that 4.5 billion tons of uranium is dissolved in the seawater, which corresponds to a duration period of approximately 70 thousand years. The uranium dissolved in seawater is in an equilibrium state with the uranium on surface of sea floor, which is approximately a thousand times of the amount dissolved in seawater. This suggests that almost all of the uranium dissolved seawater and contained in the rock on the surface of sea floor, which is 4.5 trillion tU and corresponds to the duration period of 70 million years, can be recoverable. In other words, the uranium from seawater is almost inexhaustible natural resource. The cost of extracting uranium from seawater with current technology is still expensive compared with that of conventional uranium. However, the economy of nuclear power generation fueled by seawater uranium should be assessed for entire electricity generation cost. In the present study, the economy of electricity generation using uranium from seawater is assessed using a commercial HTGR. Compared with ordinary LWR using conventional uranium, HTGR can realize lower cost of electricity owing to small volume of water and steam systems, rationalization by modularizing, and high thermal efficiency, even if fueled by seawater uranium. It is concluded that the HTGR fueled by seawater uranium with the current technology enables the energy sustainability to be maintained for a long term approximately 70 million years with superior inherent safety features and low cost of 3.92 cents/kWh (4.70 yen/kWh), which is lower than the 4.66 cents/kWh (5.59 yen/kWh) cost of LWR using conventional uranium.