Shuzo Ueda

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.

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.

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.

Moment-rotation relationship considering flattening of pipe due to pipe whip loading

Abstract It is important to take flattening of pipe into consideration in order to obtain pipe deformation due to pipe whip loading. An experimental relationship between the flattening of pipe and the pipe surface strain was used to derive the moment-rotation relationship of whipping pipe. The derived moment-rotation relationship was used to calculate the pipe strain in the pipe whip tests using a simplified energy balance method. A comparatively good agreement was obtained between the analytical and experimental results.

Dust removal system using static electricity

Abstract Development of a dust removal system using static electricity has been conducted. It is envisioned that the system can collect and transport dust under vacuum. In the system, the dust is charged by dielectric polarization and floated by an electrostatic attraction force that is generated by a dc electric field. The dust is then transported by the electric curtain formed by a three-phase ac electric field. Experimental investigation has been initiated to examine the characteristics of the system. It was found that carbon and copper particles measuring 5–44 μm were successfully removed from the bottom of the chamber under a vacuum environment.

Estimation of the ductile unstable fracture of pipe with a circumferential surface crack subjected to bending

Abstract Several simple limit-load criteria have been proposed to predict in a light water reactor (LWR) pressure boundary piping the failure bending moment of a tough pipe which has a circumferential crack and is subjected to an external bending moment. However, some of those limit-load criteria give an unconservative prediction when the pipe has a short and deep circumferential surface crack. The present paper proposes a semi-empirical limit-load criterion on the basis of test results. This limit-load criterion gives a conservative prediction by choosing the optimum parameter, even if the pipe has an arbitrary circumferential surface crack. The present paper also proposes a method to calculate the tearing modulus T appL of the pipe containing the circumferential surface crack just after the ligament failure. Moreover, the compliance of a four-point bending machine is converted to an equivalent pipe length, which is used to calculate the value of T appL .

Fracture mechanics evaluation of a crack generated in SiC/SiC composite first wall

The finite element analysis was carried out for the blanket first wall made of SiC/SiC composite material for the future Tokamak fusion power reactor DREAM, which is conceptually designed in the Japan Atomic Energy Research Institute. Bending deflection and stress distribution were analyzed when the thermal expansion was constrained at the edge of the first wall. Preliminary fracture mechanics evaluation was carried out, assuming a crack in the first wall, by the finite element code ADINA. The result showed that it is necessary to find a new device for releasing thermal expansion in the design of the first wall. Effect of the fiber bridging on the crack arrest was studied in the first wall structure made of SiC/SiC composite material.

Experimental and analytical studies of four-inch pipe whip tests under PWR LOCA conditions

Abstract This paper presents experimental and analytical results of pipe whip tests performed under PWR LOCA conditions using a test pipe of 4-inch diameter and U-shaped restraints. In the tests, the effects of the overhang length on the pipe whip behavior of the pipe-restraints system were studied by measuring the strains and deformations of the test pipe and restraints, and the restraints forces. The equation for predicting the maximum strain at the outer surface of the pipe was derived using a static equilibrium condition. The calculated maximum strains at the outer surface of the pipe agree fairly well with experimental data. The dynamic response analysis of the pipe-restraints system was conducted by the finite element program ADINA. The applicability of the ADINA program to the pipe whip analysis is made clear through this analysis.

Maintenance and material aspects of DREAM reactor

A concept of a commercial fusion power reactors (Fusion Power: 5.5 GW, electric output: 2.7 GW) having high environmental safety, high thermal efficiency and high availability has been studied in JAERI. The gross reactor configuration was designed to achieve good maintainability, high performance breeding blanket, high efficient power generation system and little radwastes. Design was based on the use of low activation structural material (SiC/SiC composites) and helium as a coolant. In this paper, maintenance and material aspects of DREAM reactor design is discussed. The concluding remarks are as follows. (1) The difficulty of development of maintenance tool is alleviated by sector replacement and the radiation dose environment less than 10 Gy/h in a reactor chamber. (2) Design requirement and present status of SiC/SiC composites was investigated. (3) The SiC/SiC composite development program is planned to satisfy the requirements of DREAM reactor.

Molecular dynamics evaluation of self-sputtering of beryllium

The self-sputtering of Be was simulated by a molecular dynamics (MD) approach with the use of a newly developed 2-body Be potential. Incident angle dependence of the sputtering yield was evaluated for the incident particle energies of 50, 100, and 300 eV with respect to the (0 0 1) and (0 1 0) surfaces of the hcp crystal. The calculated sputtering yields are in good agreement with both experimental estimates and the TRIM.SP evaluations. Small but distinct dependence on the surface type is observed. The calculated reflection coefficient become at grazing angles significantly larger than the TRIM.SP evaluation.