Current Status of Reduced-Activation Ferritic/Martensitic Steels R&D for Fusion Energy

Abstract

Reduced-activation ferritic/martensitic (RAF/M) steels have been considered to be the prime candidate for the fusion blanket structural material. The irradiation data obtained up to now indicates rather high feasibility of the steels for application to fusion reactors because of their high resistance to degradation of material performance caused by both the irradiation-induced displacement damage and transmutation helium atoms. The martensitic structure of RAF/M steels consists of a large number of lattice defects before the irradiation, which strongly retards the formation of displacement damage through absorption and annihilation of the point defects generated by irradiation. Transmutation helium can be also trapped at those defects in the martensitic structure so that the growth of helium bubbles at grain boundaries is suppressed. The major properties of the steels are well within our knowledge, and processing technologies are mostly developed for fusion application. RAF/M steels are now certainly ready to proceed to the next stage, that is, the construction of International Thermo-nuclear Experimental Reactor Test Blanket Modules (ITER-TBM).Oxide dispersion strengthening (ODS) steels have been developed for higher thermal efficiency of fusion power plants. Recent irradiation experiments indicated that the steels were quite highly resistant to neutron irradiation embrittlement, showing hardening accompanied by no loss of ductility. High-Cr ODS steels whose chromium concentration was in the range from 14 to 19 mass% showed high resistance to corrosion in supercritical pressurized water. It is shown that the 14Cr-ODS steel is susceptible to neither hydrogen nor helium embrittlement.A combined utilization of ODS steels with RAF/M steels will be effective to realize fusion power early at a reasonable thermal efficiency.

Surface modification and deuterium retention in reduced-activation steels under low-energy deuterium plasma exposure. Part I: undamaged steels

“…In some set of ODS-14Cr steels, Ti was replaced by Al. According to [12], an increase of Cr and an addition of Al at the same time resulted in suppression of corrosion. However, too high Cr content will cause the precipitation of Cr-enriched segregation phase, which is detrimental to the ductility of ODS ferritic steels [24,25].…”

“…Reduction of tungsten is expected to result in a higher tritium breeding ratio and a reduction of Laves phase formation which can embrittle the steel [9,10]. Oxide dispersion strengthening (ODS) by the addition of Y 2 O 3 particles has been successfully applied to improve high-temperature strength of RAFM's steels [11,12]. Dispersion of a high number density of nano-size yttria particles is also effective to reduce radiationinduced microstructural change because of the effective sink of interface between oxide particles and matrix for irradiation-induced point defects [11][12][13][14].…”

Casting technology for ODS steels - the internal oxidation approach

“…RAFM steels are very attractive structural materials but their high-temperature strength is limited and one of the effective approaches to solve this issue is oxide dispersion strengthening (ODS) method [3]. The nano-sized oxide particles with high number density can act as pinning points to dislocation movement [4].…”

“…These steels have been developed based on massive industrial experiences of ferritic/martensitic steel [1]. RAFM steels have interesting properties such as low sensitivity to irradiation-induced swelling and helium embrittlement [2].RAFM steels are very attractive structural materials but their high-temperature strength is limited and one of the effective approaches to solve this issue is oxide dispersion strengthening (ODS) method [3]. The nano-sized oxide particles with high number density can act as pinning points to dislocation movement [4].…”

Mechanical Characterization of a Nano-ODS Steel Prepared by Low-Energy Mechanical Alloying

“…www.mdpi.com/journal/metals to neutron radiation damage [8] and reduce irradiation embrittlement [9], swelling, and damage accumulation [10]. ODS steels are commonly prepared by high-energy mechanical alloying (MA) of a mixture of steel powder and Y 2 O 3 particles followed by a consolidation stage consisting of hot isostatic pressing (HIP) or hot extrusion (HE) [11,12].…”