Satoshi Nishio

DEMO plant design beyond ITER

A conceptual design of a DEMO reactor for the first integrated demonstration of generating fusion plant is made under the assumption that its design and construction would be started in 2020s and its operation in 2030s. A steady-state tokamak is minimized to have 5.8 m of major radius with 2.3 GW of fusion power with energy amplification Q exceeding 30. Modest extrapolation of improved plasma physics as well as technology development such as superconducting magnet, blanket and reduced activation material are assumed. It is suggested that demonstrating the fusion as a viable source of energy in plant scale will be possible based on the successful operation of ITER, while a number of technical issues must be solved in coherent programs paralleling ITER.

A fusion power reactor concept using SiC/SiC composites

JAERI studied a concept of a commercial fusion power reactor (5.5 GW, electric output: 2.7 GW) having high environmental safety, high thermal efficiency and high availability. The reactor configuration was designed to achieve good maintainability, high performance breeding blanket, high efficiency power generation system and less radwastes. The design was based on the use of low activation structural material (SiC/SiC Composites) and helium as a coolant. (1) Easy maintenance is attained by sector replacement with the radiation environment less than 103 R/h in a reactor chamber. (2) The net thermal efficiency over 45% is attained by high temperature helium gas Brayton cycle. (3) Most of radwastes of DREAM reactor can be disposed in shallow land burial as a low level radwaste after cooling of several tens of years.

Blanket and divertor design for the Steady State Tokamak Reactor (SSTR)

Abstract The tritium breeding blanket and plasma facing components (first wall and divertor) have been designed for the Steady State Tokamak Reactor (SSTR). Low activation ferritic steel (F82H) was chosen for the structural material of the first wall and the blanket. The ceramic breeder pebble bed concept with beryllium neutron multiplier was adopted. The blanket is divided into two parts; a replaceable blanket and a permanent blanket. Electrical insulation made of functionally gradient material (FGM) was introduced in the blanket box structure to drastically reduce electromagnetic loads during a plasma disruption and to simplify the attaching mechanism of the blanket. Low-temperature and high-density divertor plasma conditions and a radiative cooling concept lower the heat flux to the divertor plate to below 3 MW/m2 and enable us to adopt the same cooling conditions as the blanket coolant. Puffing mechanisms of gas (deuterium) and iron are installed for the radiative cooling of the divertor plasma.

Impact of low activation materials on fusion reactor design

The following impact of low activation materials to the fusion reactor design are described based on the design of five fusion power reactors with different structural material/coolant combinations. (1) Reduce the radioactive impact to the environment in case of severe accidents. (2) Reduce the radioactive impact to the environment during normal operation. (3) Reduce the decay heat during the maintenance and in case of loss of cooling accidents. (4) Reduce the gamma-ray dose during the maintenance. (5) Reduce the amount and lower the level of radioactive waste from replaced components and at the decommissioning of a fusion reactor. In order to reduce environmental impact in case of severe accidents to the level such as to enable construction of a fusion reactor near big cities, the low activation material must be of very low activity such as may only be achievable by SiC/SiC composites.

First wall issues related with energetic particle deposition in a tokamak fusion power reactor

Abstract Energetic particle deposition to the wall due to toroidal magnetic field (TF) ripple was assessed for a 2 GW fusion power reactor. When the present allowance for the loss is applied, the alpha particle flux to the wall can be as high as 2×10 18 m −2 s −1 in the reactor, eroding tungsten by ∼20 μm per year. The peak particle fluence over a 2-year operation cycle can reach 10 26 m −2 , probably being larger than a critical fluence for blister formation. The result suggests that, for the steady-state tokamak fusion reactor, we should introduce a new design methodology of determining an acceptable level of TF ripple on the basis of particle fluence to the wall, instead of the present one based on a tolerable heat flux.

Studies of breakeven prices and electricity supply potentials of nuclear fusion by a long-term world energy and environment model

In response to social demand, this paper investigates the breakeven price (BP) and potential electricity supply of nuclear fusion energy in the 21st century by means of a world energy and environment model. We set the following objectives in this paper: (i) to reveal the economics of the introduction conditions of nuclear fusion; (ii) to know when tokamak-type nuclear fusion reactors are expected to be introduced cost-effectively into future energy systems; (iii) to estimate the share in 2100 of electricity produced by the presently designed reactors that could be economically selected in the year. The model can give in detail the energy and environment technologies and price-induced energy saving, and can illustrate optimal energy supply structures by minimizing the costs of total discounted energy systems at a discount rate of 5%. The following parameters of nuclear fusion were considered: cost of electricity (COE) in the nuclear fusion introduction year, annual COE reduction rates, regional introduction year, and regional nuclear fusion capacity projection. The investigations are carried out for three nuclear fusion projections one of which includes tritium breeding constraints, four future CO2 concentration constraints, and technological assumptions on fossil fuels, nuclear fission, CO2 sequestration, and anonymous innovative technologies. It is concluded that: (1) the BPs are from 65 to 125 mill kW−1 h−1 depending on the introduction year of nuclear fusion under the 550 ppmv CO2 concentration constraints; those of a business-as-usual (BAU) case are from 51 to 68 mill kW−1h−1. Uncertainties resulting from the CO2 concentration constraints and the technological options influenced the BPs by plus/minus some 10–30 mill kW−1h−1, (2) tokamak-type nuclear fusion reactors (as presently designed, with a COE range around 70–130 mill kW−1h−1) would be favourably introduced into energy systems after 2060 based on the economic criteria under the 450 and 550 ppmv CO2 concentration constraint, but not selected under the BAU case and 650 ppmv CO2 concentration constraint, and (3) the share of electricity in 2100 produced by the presently designed tokamak-type nuclear fusion reactors (introduced after 2060) is well below 30%. It should be noted that these conclusions are based upon varieties of uncertainties in scenarios and data assumptions on nuclear fusion as well as technological options.

Prototype tokamak fusion reactor based on SiC/SiC composite material focusing on easy maintenance

If the major part of the electric power demand is to be supplied by tokamak fusion power plants, the tokamak reactor must have an ultimate goal, i.e. must be excellent in construction cost, safety aspect and operational availability (maintainability and reliability), simultaneously. On way to the ultimate goal, the approach focusing on the safety and the availability (including reliability and maintainability) issues must be the more promising strategy. The tokamak reactor concept with the very high aspect ratio configuration and the structural material of SiC/SiC composite is compatible with this approach, which is called the DRastically Easy Maintenance (DREAM) approach. This is because SiC/SiC composite is a low activation material and an insulation material, and the high aspect ratio configuration leads to a good accessibility for the maintenance machines. As the intermediate steps along this strategy between the experimental reactor such as international thermonuclear experimental reactor (ITER) and the ultimate goal, a prototype reactor and an initial phase commercial reactor have been investigated. Especially for the prototype reactor, the material and technological immaturities are considered. The major features ofthe prototype and commercial type reactors are as follows. The fusion powers of the prototype and the commercial type are 1.5 and 5.5 GW, respectively. The major/minor radii for the prototype and the commercial type are of 12/1.5 m and 16/2 m, respectively. The plasma currents for the prototype and the commercial type are 6 and 9.2 MA, respectively. The coolant is helium gas, and the inlet/outlet temperatures of 500/800 and 600/900°C for the prototype and the commercial type, respectively. The thermal efficiencies of 42 and 50% are obtainable in the prototype and the commercial type, respectively. The maximum toroidal field strengths of 18 and 20 tesla are assumed in the prototype and the commercial type, respectively. The thermal conductivities of 15 and 60 W/m per K are assumed in the prototype and the commercial type, respectively.

A computer program system for transient electromagnetic analysis on a tokamak device

A description is given of EDDYTOR, an eddy-current analysis and evaluation code system for tokamak reactors. The EDDYTOR system is able to calculate eddy currents, electromagnetic forces, stress and deformation, and plasma position and control properties. The program was designed to operate on an engineering work station utilizing a commercial CAE (computer-aided engineering) package. It has been shown to save on design time and to maintain overall design consistency, since a comprehensive design analysis can be performed within the same system. >

Engineering aspects of a steady state tokamak reactor (SSTR)

Abstract A steady-state tokamak power reactor based on a bootstrap current drive is an engineering feasibility. This paper describes the basic engineering design philosophies and aspects of the steady-state tokamak power reactor. The most important conclusion is that the steady-state tokamak power reactor design is based on a mere extension of the present technology. The electric-power-producing tokamak reactor can be scoped within our present engineering knowledge.

Conceptual design of the steady state tokamak reactor (SSTR)

Abstract A conceptual design study of the Steady State Tokamak Reactor (SSTR) has been performed in order to provide a realistic goal for the fusion research. The SSTR is designed as a DEMO or power reactor to be built in the near future [Y. Seki et al., Proc. 13th Int. Conf. Plasma Phys. and Contr. Nucl. Fusion Res., Washington, USA, IAEA-CN-53/G-1-2]. The major feature of the SSTR is the maximum utilization of bootstrap current in order to reduce the power required for steady state operation [M. Kikuchi, Nucl. Fusion 30 (1990) 265]. This requirement leads to the choice of moderate plasma current (12 MA) and high poloidal beta (βp = 2) for the device, which are achieved by selecting moderate aspect ratio (A = 4) and high toroidal magnetic field (Bt = 16.5 T). A negative-ion-based NBI system is used for central current drive to realize steady state operation. It is shown that a tokamak system based on the small extension of the present physics and technologies can produce net electricity of ∼ 1 GW if the proper physics and engineering R&D are conducted.