It is evident from controversial statements in the literature that the effects of the δ-ferrite phase on the impact properties of martensitic Cr-steels are not fully understood, especially with respect to the development of martensitic low-activation steels. An investigation has been started to clarify this situation using instrumented impact testing and SEM investigations. By analyzing the fracture behaviour of alloys exhibiting between 0 and 25% δ-ferrite it could be shown that small amounts of this phase (about 1%) improve the toughness. On the other hand, higher amounts of the δ-phase significantly favour cleavage fracture. As SEM investigations revealed, these opposing effects are caused by the formation of a brittle M23C6 layer in the interface between larger δ-ferrite grains and the martensitic matrix. If this interface layer is avoided, δ-ferrite containing alloys show a somewhat better behaviour in the transition region than fully martensitic heats. The possible fracture mechanisms are discussed.

The loading of the First Wall by neutrons, plasma particles and wave radiation is reviewed. For a First-Wall concept proposed by the NET-team, the cyclic thermomechanical loading conditions of austenitic (316 L) and martensitic (MANET, 1.4914) steels are compared. Due to its more favorable thermo-physical properties, the secondary stresses are lower in the martensitic steel so that its fatigue resistance should be superior. The effect of high neutron fluences has, however, yet to be determined. The ductile-brittle transition temperature of martensitic steels may limit the operational temperatures to a lower limit of about 250 ° C. Finally consideration is given to the concept of low-activation materials.

The relevance, the testing needs and the evaluation methods for the dynamic material properties essential for structural design analysis with respect to the abnormal high-rate loading conditions in a fusion reactor are discussed. Emphasis is given to the dynamic fracture toughness and to bcc materials (like ferritic/martensitic steels, Mo or V-alloys) which exhibit brittle/ductile fracture transition temperatures. These increase with n-fluence and loading rate, as well as, in general, also with increasing specimen size and notch acuity. Aiming at realistic transition temperatures it is proposed therefore to systematically investigate the correlation between the results of pre-fatigued impact specimens (of standard and sub-size) and of dynamic fracture mechanics samples of proper dimensions instead of carrying out extensive standard Charpy impact tests.

This paper presented a review on the past, present and the future of thorium fuel cycle. The aim of this study is to evaluate the developments in thorium fuel cycle, looking at the prospects and drawbacks on the possibility of thorium-based nuclear fuel for commercial reactors realising the increasing challenges of uranium-based nuclear fuel. The initial interest on thorium-based nuclear fuel and why it was abandoned at the early stage of nuclear technology were considered. Also, the reasons behind the present renewed interest on the viability of thorium fuel cycle as a valuable alternative to the conventional uranium-based fuel were studied. Thorium abundance, its physical, chemical and neutronic properties were evaluated in comparison to the uranium fuel cycle to determine thorium fuel sustainability for next generation nuclear industry. In this study, it was found that thorium fuel is three to four times more abundant, has higher conductivity, high melting temperature, low expansivity and more proliferation resistant compared to uranium fuel. The possible application and related challenges of thorium fuels in different reactor types and designs such as light water reactors (LWRs), high temperature gas-cooled reactors (HTGRs), heavy water reactors (HWRs), molten salt reactors (MSRs) and accelerator driven system reactors (ADSRs) were reviewed. The findings indicate that thorium fuel cycle can be used in the currently dominant LWRs designs in the nuclear industry with little technical modification, and also in other reactor types under investigation for future application especially molten salt breeder reactors, fast reactors and accelerator driven system reactors. Finally, this review made some recommendations on the short-term and long–term applications of thorium-based nuclear fuel cycle, and the issues that must be addressed before using thorium fuel for commercial reactor operations.

This paper reports on the results of development work done at Kernforschungszentrum Karlsruhe in cooperation with Interatom and ARBED-Saarstahl on materials for LMFBR fuel elements of high burn-up. The swelling resistance of the reference material for the prototype reactor SNR-300, the austenitic steel 1.4970, has been optimized by variation of minor alloying elements. An even higher swelling resistance has been found in heavy ion irradiations for a new class of austenitic steels, characterized by chromium and nickel contents of around 9 and 25 wt%, respectively. Finally, very promising results have been obtained with an optimized 12% CrMoVNb martensitic steel intended for wrapper application.

The susceptibility of tempered martensitic and of austenitic steels to high temperature (helium) embrittlement has been analyzed by considering the temperature dependence of grain strength and grain boundary strength.

With the aid of various and complementary metallurgical investigations the precipitation behaviour of a 15% Cr-15% Ni-Mo-Ti-B austenitic stainless steel was studied over prolonged periods of time (2 min-12000 h) and within the temperature range of 823–1653 K (550–1380°C). Three heats with varying boron content (30–100 ppm) and varying TiC-ratio (3.7−5.1) were investigated.

Heat-resisting martensitic 12% chromium steels are considered as alternative materials for application as fuel-element components such as wrappers in the liquid sodium cooled fast breeder reactor. This type of steel appears to have certain important advantages in comparison with austenitic stainless steels as far as the response to heavy neutron irradiation is concerned.