J. Sanz

The threshold energy for defect production in SiC : a molecular dynamics study

Abstract We discuss the results of molecular dynamics computer simulation studies of the threshold energy for defect production in β-SiC. The simulations are performed with the Tersoff potential for SiC which provides accurate values of many of its defect properties. In addition, we show that it properly describes the melting behavior of SiC. Simulations were carried out for Si and C recoils in three-dimensional cubic computational cells with periodic boundary conditions and up to 4096 atoms. The results show anisotropy in the threshold for Si and C recoils as well as for the recoil direction. The lowest threshold is 25 eV for C recoils along [111] and the highest is 85 eV for Si recoils along [110]. Details of the defect configurations obtained will be discussed.

Selection of IFE target materials from a safety and environmental perspective

Target materials for inertial fusion energy (IFE) power plant designs might be selected for a wide variety of reasons including wall absorption of driver energy, material opacity, cost, and ease of fabrication. While each of these issues are of great importance, target materials should also be selected based upon their safety and environmental (S and E) characteristics. The present work focuses on the recycling, waste management, and accident dose characteristics of potential target materials. If target materials are recycled so that the quantity is small, isotopic separation may be economically viable. Therefore, calculations have been completed for all stable isotopes for all elements from lithium to polonium. The results of these calculations are used to identify specific isotopes and elements that are most likely to be offensive as well as those most likely to be acceptable in terms of their S and E characteristics.

Low activation structural materials for ICF reactors: differences with MCF environments☆

Abstract Activation calculations considering the neutron flux and spectrum of a first structural wall (FSW) in an inertial confinement fusion reactor (ICF) are performed for all stable elements, using a recently upgraded data base. Surface γ dose rate and waste disposal rating (WDR) are employed as indices to compare the merit of elements and compute the concentration limits corresponding to hands-on processing, remote recycling and shallow land burial (SLB). The performance of steels, vanadium alloys and silicon carbide, as candidate structural materials has also been explored. The materials with less waste/recycling concerns are identified, and the influence that impurities can exert in their radiological performance is analyzed. Critical radionuclides, dominant reactions, and isotopes originating critial transmutation/decay sequences are indicated. In addition, calculations for magnetic confinement fusion (MCF) conditions are made to perform ICF/MCF comparisons, finding that some important elements and materials respond very differently in the two environments.

Activation analysis and materials choice in the laser fusion reactor KOYO

Abstract The laser fusion conceptual reactor KOYO, developed by the ILE Osaka, is presented and analyzed from the activation perspective. The reactor is driven by a laser diode pumped solid state laser which dramatically increases the efficiency of the system, and uses liquid LiPb film protection flowing through ceramic SiC porous tubes in the blanket. Neutron fluxes have been computed using 2/3D models and compared with spherical approaches. Two blanket areas with different packing fractions are considered, and we show the availability of a large fraction of the SiC with impurities to be considered as shallow land burial (SLB). We propose a more complete solution for SLB through the use of porous woven graphite (C) fabric tubes. A graphite reflector is included with important effect in the activation of the chamber wall. Ferritic HT-9 is considered as the structural material for the chamber wall, allowing its SLB and different recycling options. Releases of 1 kg of target-emissions-facing SiC tubes and HT-9 materials have also been simulated with optimum performances.

Accidental release characteristics of activated materials in inertial and magnetic fusion reactors

Abstract The short-term radioactivity of some candidate structural materials for fusion reactors (reference steels and non-ferrous “low activation” materials) has been analyzed in power relevant conditions of inertial and magnetic fusion energy (IFE and MFE) reactors. Materials are assessed with regard to accident safety, using an offsite dose-related criterion. It turns out that the best option for IFE differs from that of MFE. For some materials in IFE conditions, the potential off-site dose can be largest when radioactivity release occurs sometime during reactor operation rather than at the end of its lifetime.

Option for Spallation Neutron Sources

Spallation reactions are a very important option for efficient neutron sources appropriate for fusion materials testing. An “option of this option” is the EURAC concept, which makes use of short-term accelerator technology in the cheapest way and is proved to provide the needed neutron flux to verify fast experiments on fusion materials performance. Its flexible conception allows an optimum combination of very high fluxes of about 1016 n/cm2/s, with decreasing fluxes along the testing zones in enough volume to perform the correct irradiations. With this assumption, the rate effect can be perfectly analyzed together with the end-of-life conditions assumed in the structural material of the future fusion environments. The possible negative effects of the high-energy neutrons in the Spallation spectrum have been taken into account, concluding their non-significance in the desired damage parameters. The EURAC concept can also be considered in light of other purposes like incineration processes,μ production, and, with the appropriate booster, high-flux cold neutron source.

European fusion target work

Abstract Target concepts developed in the context of the HIDIF project (Heavy Ion Driven Inertial Fusion) are presented. Target design has evolved, from the beginning of the study in 1993, in parallel with the evolution of accelerator parameters. Two different phases can be distinguished: (a) up to 1998 the goal was just demonstration of ignition with heavy ions, (b) from 1998 target and driver are being upgraded to high-gain designs able to be used for energy production. Analytical models and numerical tools developed in this context are summarized, and future research directions are discussed.

Safety Issues of Hg and Pb as IFE Target Materials: Radiological Versus Chemical Toxicity

Abstract We have performed a safety assessment of mercury and lead as possible hohlraum materials for Inertial Fusion Energy (IFE) targets, including for the first time a comparative analysis of the radiological and toxicological consequences of an accidental release. In order to calculate accident doses to the public, we have distinguished between accidents at the target fabrication facility and accidents at other areas of the power plant. Regarding the chemical toxicity assessment, we have used the U.S. DOE regulations to determine the maximum allowable release in order to protect the public from adverse health effects. Opposite to common belief, it has been found that the chemical safety requirements for these materials appear to be more stringent than the concentrations that would result in an acceptable radiological dose.

Neutron damage in reduced activation martensitic alloys in inertial and magnetic fusion reactors: Comparison with fission reactors

Abstract Neutron irradiation damage in terms of displacement and transmutant production, is assessed in inertial (ICF) and magnetic (MCF) confinement fusion reactors, for the reduced activation martensitic steel, B-TAHF. These results, along with current experimental and theoretical information available on ferritic/martensitic steels, have been used to infer irradiation responses, such as swelling and ductile to brittle transition temperature (DBTT). The ICF approach can lead to concepts with a first structural wall (FSW) able to last the power plants entire lifetime. In MCF, the material at end of life does not fulfill the technological requirements. Damage calculations have also been carried out in the HFIR and the FFTF reactors, for purposes of planning and assessing irradiation experiments in fission reactors in the light of fusion reactor needs. Fission irradiations can be very useful for assessing ICF reactor materials, but appear to have little engineering relevance for MCF commercial applications.

Effect of activation cross-section uncertainties in the assessment of primary damage for MFE/IFE structural materials

The primary damage behaviour of the low activation steel Eurofer was studied under irradiation in the high flux test module of IFMIF and in the first structural wall of the magnetic (ITER and DEMO) and inertial (HYLIFE-II and HAPL) fusion energy (MFE/IFE) reactors. We have calculated the damages, gas production rates and gas to dpa production ratio with ACAB code. The effect of activation cross section uncertainties in the assessment of hydrogen and helium production is also analysed.