Toshiya Nanahara

Development of a Frequency-stabilizing Scheme for Integrating Wind Power Generation into a Small Island Grid

Abstract Integrating wind power generation into small islands has been one of the demonstration projects in Okinawa Prefecture, Japan. Since such integration could deteriorate power quality, including frequency, in an island grid, a frequency-stabilizing system using flywheels has been integrated into a small island. In order to establish a proper frequency-stabilizing scheme for a small island, an accurate model of a diesel generator including a governor is vital. Therefore, a model was developed through generator dump tests. A new frequency-stabilizing scheme was also developed through the time-domain simulation of the island grid model, which consists of the above mentioned diesel generator model and negative load change representing wind power variation. The developed stabilizing scheme was applied to the flywheels in the island grid and revealed great performance for mitigating frequency variation.

Parametric study on blanket neutronics and economics of fusion—fission hybrid reactors

Abstract A parametric study has been performed for the blanket neutronics and economics of fusion—fission hybrid reactors. Optimum blanket designs were sought for both the electricity-producing hybrid reactor and the fissile fuel-producing hybrid reactor. Comparisons of the nuclear performances and economics between these two hybrid reactors were also conducted. A tokamak-type fusion reactor was selected as the base reactor. It was assumed that natural uranium oxide is fed to the blanket as the fertile material with lithium oxide as the tritium breeding material. In the neutronics design of the electricity-producing hybrid reactor, blanket fuel composition and arrangement were surveyed to attain high energy multiplication in the blanket. Moreover, efforts were made to suppress the blanket thermal power increase due to plutonium buildup, because it determines the frequency of blanket fuel exchange and limits the reactor load factor. On the other hand, the blanket for the fissile fuel-producing hybrid reactor was designed so that the amount of the fissile fuel bred per unit blanket thermal power is maximized. Economic analysis shows that the electricity from the symbiotic system composed of the fissile fuel-producing hybrid reactor and light water reactors costs about 30% less than that from the electricity-producing hybrid reactor. However, the large energy multiplication in the blanket of the electricity-producing hybrid reactor makes the neutron wall loading 40% lower than that of the fissile fuel-producing hybrid reactor. Therefore, the electricity-producing hybrid reactor can make its requirement for fusion technology less demanding than the other .

Economic Assessment of Tokamak Fusion Reactor Plants

Abstract As the R&D of nuclear fusion technology makes steady progress, it becomes important to examine with what perspective and toward what direction further steps should be taken. This paper discusses the prospect of commercial nuclear fusion power reactors principally from the viewpoint of electric utilities, namely its potential users. Based upon conceptual designs of pure fusion reactors and fusion fission hybrid reactors, generation costs (cost of electricity) of the reactors are evaluated. Two different approaches are employed in the design because much uncertainty still remains in the future characteristics of fusion power reactors. The generation costs for the above two approaches show a fair similarity. The evaluated costs of the hybrid reactors are significantly lower than those of the pure fusion reactors.

Approach to Evaluation of Flexibility of Generation Mix

Abstract So far, generation system planning has generally been conducted so as to achieve minimum production cost, but not to make the plan flexible to cope with uncertainty of the situation. Under the current competitiveness of energy industry and uncertain factors of price, demand, etc., in power systems, planners are asked to indicate quantitatively the flexibility of the developed plan and to propose it to the decision makers. The paper shows the way to take uncertain factors into consideration in power systems planning, proposing a new evaluating index of “Maximum Regret” to indicate the flexibility of the power system (generation mix) quantitatively. The maximum regret exhibits how much the production cost increases in the worst case compared with the optimum cost. Flexibility against changing factors is higher in a system with a lower index of maximum regret, as shown in the sample model study.