Nuclear engineering and design/fusion : an international journal devoted to the thermal, mechanical, materials, structural, and design problems of fusion energy最新文献

The interaction of 52 MeV deuterons with lithium was investigated, in view of the optimization of a lithium target for an intense neutron source based on the d-Li stripping reaction. The experimental results are compared with theoretical calculations obtained from an updated version of the Bragg code. This code describes in detail the interaction of charged particles with matter. Within the experimental uncertainties the theoretical results are well reproduced by the experiments.

Cascade damage and high helium production rate are major characteristic features of fusion neutron radiation effects. Experimental as well as computational studies of these two factors which have been performed by the authors are presented and discussed from the standpoint of microstructural evolution. The experimental work has been performed using a facility comprising two small ion accelerators and an electron microscope, capable of observing cascade damage during heavy ion bombardment, and of carrying out dual beam irradiations to study the effect of simultaneous injection of helium atoms with displacement cascades. It has been shown that the evolving microstructures depend strongly on the nature of the cascade, type of materials, irradiation temperature, and amount and mode of helium implantation. The implication of these microstructural studies to the radiation effects relevant to fusion reactor design is discussed.

Four distinct operating modes have been proposed for tokamaks, and consequently a variety of thermal environments can be postulated for future reactor subsystems. Our study concentrates on lifetime limitations associated with fluctuating thermal loads on the first wall, limiter or divertor plates, and in the breeding blanket. Simultaneous failure from thermal fatigue, radiation damage, and disruption-induced erosion is considered, and burn length goals are calculated in order to help achieve high availability for a commercial reactor. In addition, the cost of thermal storage is found as a function of the dwell period between burns of a pulsed cycle; thermal storage is shown to be an expensive requirement for pulsed reactors.

The influence of primary blanket coolant leaks through flaws in the first wall on Tokamak fusion plasma performance is investigated. A one-dimensional, three region radial diffusion model of impurity transport in the plasma is developed. The model includes plasma removal and recycling in the boundary layer and is used to correlate plasma performance with coolant leakage rates. In turn, coolant leak rates are estimated via molecular or viscous flow, as appropriate through both elastically loaded cracks and cracks opened by creep. Fatigue and environmentally induced subcritical crack growth and unstable crack growth flaw sizes are estimated for austenitic and ferritic stainless steels and compared to the coolant leak rate flaw sizes. The materials and plasma analyses are combined to yield estimates of the critical leak rate for three coolant candidates: helium, water, and lithium. The results indicate that the maximum-leak-rate (MLR) flaw sizes for helium, water and lithium are 5 to 8 mm, 6 to 8 mm and 1.5 to 3 × 10⁴ mm, respectively, for elastically loaded cracks and 0.1 to 0.3 mm, 0.2 to 0.3 mm, and 700 to 1500 mm, respectively, for cracks opened by creep. The threshold flaw sizes for fatigue and corrosion fatigue subcritical crack growth of Type 316 stainless steel and HT-9 range from 0.2 to 2 mm and the flaw sizes for unstable crack growth of irradiated 316 stainless steel and HT-9 are 4 mm and 50 mm, respectively. These results suggest that the MLR sizes for helium and water are among the smallest flaws that may affect reactor performance and that the threshold for subcritical crack growth in fatigue is a critical material property. Also, creep processes are shown to have a significant effect on the MLR flaw size.

The design and installation of a protective inner wall for a tokamak vacuum vessel is described. This wall is a series of small rectangular plates attached to the existing walls with threaded fasteners. The design effectively conceals and protects all mounting hardware beneath the plate array, while providing a substantial surface area that will absorb plasma energy.

The CrMo ferritic (martensitic) steels are leading candidates for the structural components for future fusion reactors. However, irradiation of such steels in a fusion environment produces long-lived radioactive isotopes that lead to difficult waste disposal problems once the structure is removed from service. One method proposed to alleviate such problems is the development of steels that contain only elements that produce radioactive isotopes that decay to low levels in a reasonable time (tens of years instead of hundreds or thousands of years). For such a solution for the CrMo steels, molybdenum must be eliminated. In addition, niobium must be maintained at extremely low levels. Tungsten is proposed as an appropriate substitution for molybdenum, and the procedures for developing CrW steels analogous to the CrMo steels are discussed.

A study is reported of uniaxial tensile properties over a wide temperature range (293–1173 K) and at different strain rates between 4 × 10⁻⁵ to 4 × 10⁻²s⁻¹ for a high manganese content austenitic steel (Fe-17Mn-10Cr-0.1C) which is an alternative to AISI 316 stainless steel in the material selection for the conceptual tokamak fusion reactor designs. The behaviour of this alloy is similar to that of other high manganese steels, including a strain induced γ(fcc) → ϵ(hcp) martensitic transformation which considerably increases the strain hardening rate and leads to a maximum in ductility near 470 K. Moreover, non-linear statistical analysis of the true stress—true strain data, fitted to several constitutive equations, shows that the best description of plastic flow is given, for the present material, by the Ludwigson law (1971): $\text{σ = A}{}_{\mathrm{<mtext>LU</mtext>}}\text{exp}\text{(C}{}_{\mathrm{<mtext>LU</mtext>}}\text{ϵ) + B}{}_{\mathrm{<mtext>LU</mtext>}}\text{ϵ}{}^{\mathrm{n}}{}_{\mathrm{<mtext>p</mtext>}}\text{LU}$ or by the Matteazzi—Petrone—Piatti law (1982) if the strain rate effect is also considered: where σ = true stress, ϵ_p = true plastic strain, ϵ_p = true strain rate, ϵ_p = reference strain rate and the other parameters are material constants.

In the HIBALL heavy ion beam fusion reactor design, the INPORT concept is used to protect the first surface of the reactor from damage by the high energy X-rays, ion debris and fast neutrons from the exploding target. Liquid Li₁₇Pb₈₃ flows through porous SiC tubes and wets outside of the tubes with a layer of Li₁₇Pb₈₃. This Li₁₇Pb₈₃ film is evaporated on each shot by the target X-rays and ion debris. The mechanisms that control the vapor pressure of the chamber are: gas radiation, Li₁₇Pb₈₃ evaporation from the INPORT tubes, and gas condensation back onto the INPORT tubes. From the beam stripping cross section for Bi²⁺ ions on Pb the gas pressure (evaluated at 0°C) inside the chamber must be at or below 10⁻⁴ torr in order for the ion beam to reach the target and ignite it. The repetition rate is therefore determined by the time required to reestablish this pressure after a shot. Calculations are presented that indicate that this time is short enough to allow a 5 Hz repetition rate for a wide range of parameters.

A simple comparative study of fissile breeding economics of fusion-fission hybrids, spallators, and also of fast breeder reactors, has been carried out. In spite of the uncertainty of present projections into the future and of discrepancies in available data, even with quite conservative assumptions it is shown that hybrids and spallators can become economic at a realistic uranium price increase, successfully competing against fast breeders.