The goal of the work of the Special Group is the study and analysis of the changes in the properties of materials and the construction of models of materials subject to irradiation that is typical in fusion or in spallation. Since intensive sources of high energy neutrons are not available, the effects of bombardment are simulated using low mass ions from a cyclotron. In the case of spallation materials, information can also be gained by studying targets of existing weak sources (ISIS, LANSCE) that have been taken out of service. We have succeeded in collecting all existing available highly-dosed components from these sources in the Hot Cells of the FZJ. The results of mechanical tests yield valuable information about the servicable lifetime of targets in the High-Performance Sources ESS (European Spallation Source) and SNS (US-Spallation Neutron source) that are currently planned. In addition, theoretical models are used in an attempt to translate know-how gained via the development of materials for fission and fusion to the case of spallation. As in previous years, the group has enjoyed a close working relationship with Institute Theory II (H. Trinkhaus), which is a pre-requisite for an analysis of the experimental results that is meaningful and suggestive of further work.

• Samples of the `low activation' steel F82H subject to implantation of more than 10 wt ppm hydrogen showed strong variations in their strength and ductility. This may possibly point to the creation of micro-cracks (hydrogen embrittlement).

• A model for the creation of lens-shaped helium bubbles in alpha-SiC was developed. The model also describes the growth of dislocation loops around the bubbles.

• Measurements on irradiated beta-SiC showed recovery behaviour that was only slightly different from that of alpha-SiC. The healing out of defects is shifted to slightly higher temperatures (see detailed report).

• Thermal recovery from radiation-induced dimensional changes in oxide ceramics (Al2O3, MgO, MgAl2O4) correlated with the recovery behaviour of defects observed by optical absorption and ESR.

• Segregation at grain boundaries (gb) induced in NiSi by radiation showed unusual morphologies which varied from gb to gb. For coherent and incoherent twin-boundaries, the different morphologies could be correlated with the character of the gb. In general such a correlation could not be established.

• The ductility and strength of the light metal beryllium was shown to be strongly influenced by its helium content.

• Via conclusive measurements using electron bombardment, we showed that the radiation induced electrical degradation in ceramics that has been found to follow electron- ion- and neutron-bombardment is an artefact caused by the formation of cracks and by surface contamination.

• Of the materials that were radiated by the 800MeV proton beam of the LAMPF-facility in Los Alamos, martensitic steels showed the least embrittlement in bending tests in the hot cells at FZJ. These materials are now regarded as the favoured candidate materials for the Hg-target container of ESS.

In 1997, the work of the special group was again an essential part of the Eurpoean Fusion Programme. This is now partly integrated within the ITER Programme. 25% of the total costs (45% for irradiation) were financed via the Association FZJ/EURATOM by the EU in Brussels. In 1998, this translated into a net income of 600,000 DM for the FZJ. The areas of work are determined in consultation with the other partners in the Programme. The group has particularly close collaborations with the Riso National Lab, the University of Ancona, the Institute for Physical Chemistry of the Russian Academy of Sciences, Moscow and the Kurchatov Institute in Moscow. The main partners in connection with the ESS-related work are the National Laboratories Los Alamos and Oak Ridge, the Paul-Scherrer Institute, Villigen and the Rutherford Appleton Laboratory, Didcot. This work is supported via an EU-TMR contract (Leading Institution FZJ; 1.6M Euro for 13 participants from 9 countries, of which 280,000 Euro devolves to FZJ as the largest partner).

A cooperative project without transfer of funding is the STIP-Cooperation (an international Radiation Programme at the Swiss 0.9 MW Spallation-Source SINQ, with follow-up examination of the samples in the Hot-Cell Laboratories in Jülich, Oak Ridge, Saclay and Villigen).

All ESS-related work is part of the HGF Strategic-Fund Project ‘Research and Development related to the construction of the pulsed European Spallations Neutron Source ESS' with the Hahn-Meitner Institute as partner. (Duration mid 1998 - mid 2001).