Yasushi Seki

Results of an International Study on a High-Volume Plasma-Based Neutron Source for Fusion Blanket Development

AbstractAn international study conducted by technical experts from Europe, Japan, Russia, and the United States has evaluated the technical issues and the required testing facilities for the develo...

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.

Numerical calculations of helium ash enrichment and exhaust by a simple divertor

A simple poloidal divertor able to enrich and exhaust helium ash has been proposed for an INTOR-size reactor. Monte-Carlo simulations are carried out to investigate the motion of DT-fuel and He-ash particles after they have been re-injected from the divertor neutralizer plate. Helium-ash exhaust is shown to be feasible with a modest pumping speed of about 5 × 105 litre s−1 for most of the conceivable conditions of plasma particle containment.

Fusion reactor design studies

Abstract This paper is a summary of fusion reactor design studies presented and discussed at the IAEA Technical Committee Meeting and Workshop on Fusion Reactor Design and Technology, held in September 1993 at the University of California, Los Angeles. This summary does not represent all the reactor design studies carried out in the world since the last meeting in Yalta in 1986. The reactor designs presented are mostly D–T fuel cycle with both magnetic confinement and inertial confinement. As a D–3He, only the ARIES-III was presented. Steady state and pulsed tokamak studies, stellarator and reversed field pinch reactor studies are summarized. Six recent D–T inertial confinement fusion reactors presented at the meeting are summarized. A short summary on D–3He reactors and fusion-fission hybrid reactor designs is given.

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.

Recent directions in plasma physics and its impact on tokamak magnetic fusion design

Abstract Steady progress has been made in recent years towards achieving fusion breakeven and reactor-relevant plasma conditions in the largest tokamak experiments. In particular, the experimental observation of a large self-sustaining bootstrap current in the plasma permits development of steady-state reactor concepts with modest current drive power and relatively high plasma energy gain ( Q ). The SSTR (Japan) and ARIES-I (USA) designs reported in this paper are first-stability, steady-state tokamak reactors based on “modest” extrapolations from the present tokamak physics database. The plasma is characterized by a high edge safety factor ( q a ) and a high poloidal beta ( β p ) in order to increase bootstrap current fraction (∼70%). This mode of operation is achieved by selecting high values of both aspect ratio ( A = R / a = 4−4.5) and toroidal magnetic field on axis (9–11 T) in these reactors. Both reactor studies suggest that the tokamak system can be a steady-state power reactor with net electricity of ∼1 GW and with plant efficiency 30–40%. The SSTR is characterized by its technical feasibility in the near future. On the other hand, the ARIES-I focuses on better safety and environmental aspects and a longer time frame. The SSTR and ARIES-I studies show that, with proper R&D programs, tokamak fusion reactors can be developed that will have acceptable cost of electricity.

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.

Radioactivation of structural material of the superconducting magnet for a fusion reactor

Radioactivation of five types of candidate steel alloys for the structural materials of superconducting toroidal field coils (TFC) of a D-T fusion reactor has been comparatively studied. As a result, the use of a high Mn steel in place of 316 SS is shown to reduce the dose rate at the He vessel of the TFC to ∼ 1/3 the value with 316 SS at 1 day after shutdown, and to ∼ 1/1000 at 10 years after shutdown. These reductions are mostly caused by the 0.28 wt% Co assumed to be included in 316 SS but none in the high Mn steel. Newly defined dose rate sensitivities of constituent elements are shown to be useful in identifying the cause of dose rate change brought on by the steel composition change. They can also be utilized in estimating the dose rate change brought on by the replacement of 316 SS with any new steel alloy with similar composition.

The advanced SSTR

Abstract A reactor concept is proposed to improve economical competetiveness of the tokamak fusion reactor with agressive physics and engineering assumptions. Key elements are high field magnets with B max =21 T with high normalized beta β N =4.2 with 80% bootstrap current fraction and short throat radiative divertor. The power plant should have large net electric power of 3.4 GWe with twin tokamak reactor. Significant simplification of tokamak auxiliary system is also required.

Nuclear Characteristics of D-D Fusion Reactor Blankets, (I) Survey Calculation

In this paper, neutronic and photonic calculations are undertaken covering several blanket models of the D-D fusion reactor, using presently available data, with a view to comparing the nuclear characteristics of these models, in particular, the nuclear heating rates and their spatial distributions. Nine models are taken up for the study, embodying various combinations of coolant, blanket, structural and reflector materials. About 10 MeV is found to be a typical value for the total nuclear energy deposition per source neutron in the models considered here. The realization of high energy gain is contingent upon finding a favorable combination of blanket composition and configuration. The resulting implications on the thermal design aspect are briefly discussed.