G. Benamati

Hydrogen isotopes transport parameters in fusion reactor materials

Abstract This work presents a review of hydrogen isotopes–materials interactions in various materials of interest for fusion reactors. The relevant parameters cover mainly diffusivity, solubility, trap concentration and energy difference between trap and solution sites. The list of materials includes the martensitic steels (MANET, Batman and F82H-mod.), beryllium, aluminium, beryllium oxide, aluminium oxide, copper, tungsten and molybdenum. Some experimental work on the parameters that describe the surface effects is also mentioned.

Compatibility tests of steels in flowing liquid lead–bismuth

The behaviour of steels exposed to flowing Pb–55Bi was evaluated. The materials tested are the two austenitic steels AISI 316L and 1.4970, and the six martensitic steels Optifer IVc, T91, Batman 27, Batman 28, EP823 and EM10 which were exposed to flowing Pb–55Bi for 1000, 2000 and 3000 h and at two temperatures (573 and 743 K). The corrosion tests were conducted in the non-isothermal loop of IPPE-Obninsk under a controlled oxygen level (10−6 wt%). The compatibility study showed that at a lower temperature, a very thin oxide layer (<1 μm) was formed on the steels. At higher temperature, austenitic steels also exhibited a thin oxide layer sufficient to prevent their dissolution in the melt. A thicker oxide, which grew according to a parabolic law, was observed on the surface of the martensitic steels. The oxidation resistance behaviour of the martensitic steels was correlated with their alloying elements.

Corrosion behaviour of steels and refractory metals and tensile features of steels exposed to flowing PbBi in the LECOR loop

Abstract An experimental activity has been started using the LECOR loop at the ENEA Brasimone centre to investigate the corrosion behaviour of steels and refractory metals as well as the tensile properties of steels exposed to flowing liquid lead bismuth with low oxygen activity. The oxygen content in the liquid metal was controlled and monitored by a dedicated system. The compatibility test was performed at 673 K and the corrosion and tensile results herein reported concern the first 1500-h run of the loop operation. All the materials tested suffered from liquid metal attack exhibiting a weight loss. The consequent evaluation of the corrosion rate showed that, under the given test conditions, the refractory metals are more resistant than the steels. The tensile properties of austenitic steel are not affected by the liquid metal corrosion, while the martensitic steel exhibited a mixed brittle–ductile fracture surface.

Status of Tritium Permeation Barrier Development in the EU

Abstract Tritium permeation can be significantly reduced by a suitable barrier on the structural materials of a future fusion power plant. Since alumina has the capability of tritium permeation reduction, the development of such coatings on ferritic martensitic steels by different techniques like hot-dip aluminizing (HDA) by Forschungszentrum Karlsruhe, Germany (FZK) and chemical vapor deposition (CVD) by Commissariat a l’Energie Atomique, France (CEA) was funded by the European Commission (EC) during the last 10 years. The final objective was to identify a so-called reference coating for structural components of a lithium-lead cooled blanket. This paper describes the process specifications and the results of the corresponding hydrogen permeation measurements, performed at ENEA, Brasimone, Italy. The results for CVD and HDA coating showed clearly, that Permeation Reduction Factor’s (PRF) of >1000 were sufficiently exceeded in H2 gas, but much lower values were obtained in the Pb-17Li melt. The post mortem analysis revealed that surface imperfections and spallation of parts of the coatings were responsible for the too low PRF’s. Because of shifting of priorities and changes in the blanket design from WCLL to HCLL, the EU funding of all major R&D activities was postponed in 2002 until the redesign of the European Blanket Concepts was finished.

Hydrogen and deuterium transport and inventory parameters through W and W-alloys for fusion reactor applications

The aim of this work is to measure the hydrogen/deuterium transport and inventory parameters in relevant structural and/or armour materials for the International Thermonuclear Experimental Reactor (ITER) divertor such as W and W-alloys. The W-alloys: W, W + 1% La 2 O 3 and W + 5% Re have been investigated. The materials were supplied from the Metallwerk Plansee GmbH (Austria). Measurements were conducted using a time-dependent permeation method over the temperature range 673-873 K with hydrogen and deuterium pressures in the range 10-100 kPa (100-1000 mbar). The samples were also characterized using optical microscopy, SEM and energy dispersive spectroscopy (EDS) in order to investigate the composition, microstructure and morphology of the surfaces and cross-sections through the samples.

Development of the EU water-cooled Pb-17Li blanket

The reference concept of the EU water-cooled Pb-17Li DEMO blanket is essentially formed by a directly-cooled steel box having the function of Pb-17Li container and by a double-wall U-tube bundle, immersed in the liquid metal, in which the pressurised water-coolant flows. The structural material is martensitic steel. All blanket performances satisfy DEMO requirements, such as tritium breeding self-sufficiency, capability of the box-structures to withstand water-coolant pressure under faulted conditions, limitation of the Pb-17Li/steel interface temperature to 480°C, power conversion efficiency of about 35%, and acceptable increase of temperature in case of out-of-vessel LOCA. A preliminary design of the test module and of the associated circuit components to be tested in ITER has been performed taking into account ITER specifications for test ports and ITER pulsed working conditions. Test-module DEMO-relevance has been one of the leading criteria for the module design. Preliminary module manufacturing sequences have been defined. The paper recalls the associated R and D activities which have to be finalised prior to the ITER testing and mainly involve tritium permeation barrier development, tritium extraction from Pb-17Li, advanced manufacturing techniques, definition of water/Pb-17Li interaction counter-measures, and Li-concentration control techniques.

Hydrogen isotope permeation through and inventory in the first wall of the water cooled Pb–17Li blanket for DEMO

The hydrogen isotope transport through the first wall between plasma and first wall coolant has been investigated. The time dependence of hydrogen isotope permeation through the first wall from plasma into water coolant has been calculated. The hydrogen isotope inventory (both mobile and trapped hydrogen isotopes) in the first wall has been evaluated. The influence of temperature gradient, surface conditions, isotopic effect and trapping in the ion- and neutron-induced defects on the hydrogen isotope permeation and inventory has been considered.

Hydrogen Isotopes Permeability in Eurofer 97 Martensitic Steel

ABSTRACT In considering structural materials for fusion reactors a detailed understanding of the transport parameters and solubility of hydrogen and its isotopes is an important issue which deal with safety and blanket performance aspects. The experimental activities were focused on the determination of hydrogen/deuterium transport parameters through Eurofer 97 in the temperature range 423+723K using a time dependant permeation technique The hydrogen permeation and diffusivity at room temperature and density of trapping sites were also evaluated using Devanathan’s technique. Hydrogen / deuterium permeation experiments on Eurofer 97 showed a non-negligible decrease in permeability with respect to other fusion oriented martensitic steels, even if it remains about one order of magnitude higher compared with that of austenitic AISI 316L steel.

Qualification of tritium permeation barriers in liquid Pb–17Li

Abstract The reduction of tritium permeation from the Pb–17Li, or plasma, into the coolant is of crucial importance in order to reduce the radiological hazard in the steam generator vault as well as in the turbine/condenser area and to optimise the tritium balance in the reactor. The use of aluminium rich coatings has been selected as reference solution for the water cooled lithium lead (WCLL) blanket in order to produce reliable tritium permeation barriers (TPB). TPB qualification activities performed in the past allowed the selection of two reference deposition techniques, the chemical vapour deposition (CVD) process developed on laboratory scale by CEA, and the hot dipping (HD) process developed by FZK. On the basis of the results obtained in the past with the Corelli I–II devices, a new apparatus named Vivaldi was designed to perform comparative tests on two hollow cylindrical specimens in the same operating conditions. The performance of alumina coating on EUROFER 97 steel has been tested in gas and liquid metal phase. The obtained results in terms of permeated fluxes and permeation reduction factors (PRF) are herein presented and discussed. A post experiment examination of coatings was performed by use of optical and SEM microscopy.

Hydrogen permeation through tritium permeation barrier in Pb-17Li

One of the main problems in the development of water cooled lithium lead (WCLL) DEMO fusion reactor is the reduction of the tritium permeation from the Pb–17Li, or the plasma, into the cooling water. The control of tritium losses is an important issue in fusion technology because of its safety and operational implications. This goal can be achieved using a tritium permeation barrier (TPB). The use of aluminium rich coatings, which forms Al2O3 at their surface, has been selected as reference solution for WCLL blanket in order to produce reliable TPB. The hot dipping process is one of the two candidates for the production of coatings on large blanket segments. The effectiveness of hot dipped aluminium coating on MANET II steel has been verified in gas phase and in liquid Pb–17Li, using a test apparatus named Corelli II. The permeation rate measured in gas phase is one order of magnitude lower than the one in liquid metal phase. Performing SEM-EDS analysis on the specimen, it was observed that micro cracks on the coating surface were present. The permeation curves in gas and Pb–17Li are reported and discussed. The characteristics of the new experimental device Vivaldi will be briefly described.