I. Ricapito

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.

Tritium Extraction from Liquid Pb-16Li: A Critical Review of Candidate Technologies for ITER and DEMO Applications

Abstract Extraction of tritium from liquid lead lithium eutectic alloy is a key topic for the feasibility of any PbLi based tritium breeding blanket (BB). Particularly in DEMO, high tritium extraction efficiency will be required in order to keep low the tritium concentration in the Pb-16Li loop. This is essential to minimize tritium release into the environment and tritium permeation from BB into the primary cooling system. In addition, the tritium extraction process needs to be highly reliable in order not to impact negatively on the operation of the whole fusion reactor, ITER or DEMO. In the present paper, a critical review of the main candidate technologies for tritium extraction from Pb-16Li, particularly gas liquid contactors and vacuum permeators, is accomplished. The intrinsic limits and possible advantages of these technologies are presented and discussed, in the light of considerations coming directly from mathematical models describing their behaviour as well as from the experimental results so far achieved. Needs in terms of R&D activities are identified.

TRITIUM EXTRACTION SYSTEMS FOR THE EUROPEAN HCLL/HCPB TBMs

Abstract One of the most challenging issues for the TBM (Test Blanket Module) testing campaign foreseen in ITER is the operation of TES (Tritium Extraction Systems). This is essential not only to prove the ability to manage correctly the bred tritium but also to validate and qualify the neutronic codes for the prediction of tritium production in view of their use in future fusion plants. Two are the European candidates to be tested in ITER: the HCPB (Helium Cooled Pebble Bed) TBM and the HCLL (Helium Cooled Lithium Lead) TBM. For both these TBM concepts the following points have been addressed in this work: a) the gas stream to be processed by TES b) the TES process flow diagram c) a first assessment of the required space

Pb–17Li/water interaction in DEMO WCLL blanket: water micro-leaks

Abstract The interaction between pressurised water and liquid Pb–17Li is a topical issue for the WCLL blanket concept and needs to be studied in detail because of the potentially significant effect on the reliability and safety of the blanket. Particularly, it seems important from the design point of view to deeply investigate the consequences of coolant micro-leaks in the blanket module generated by micro-cracks with a size in the order of 10−3 mm2. This kind of interaction has been studied during an extensive experimental campaign on the RELA loops in the ENEA Research Centre at Brasimone. The results showed a reduction in the liquid metal flow-rate in the circuit and a deterioration of the heat exchange properties between breeder and coolant due to the formation and growth of solid reaction products generated by the chemical reaction between lithium and water. The molar ratio between the recovered hydrogen recovered and water injected was in the range 0.3–0.5, confirming that, in the test conditions, the main solid reaction product is lithium hydroxide (LiOH). The possible impact of these results on the TBM-ITER design is also presented and discussed.

Tritium Processing for the European Test Blanket Systems: Current Status of the Design and Development Strategy

Abstract Tritium processing technologies of the two European Test Blanket Systems (TBS), HCLL (Helium Cooled Lithium Lead) and HCPB (Helium Cooled Pebble Bed), play an essential role in meeting the main objectives of the TBS experimental campaign in ITER. The compliancy with the ITER interface requirements, in terms of space availability, service fluids, limits on tritium release, constraints on maintenance, is driving the design of the TBS tritium processing systems. Other requirements come from the characteristics of the relevant TBM and the scientific programme that has to be developed and implemented. This paper identifies the main requirements for the design of the TBS tritium systems and equipment and, at the same time, provides an updated overview on the current design status, mainly focusing onto the tritium extractor from Pb-16Li and TBS tritium accountancy. Considerations are also given on the possible extrapolation to DEMO breeding blanket.

Sensitivity study for Tritium Permeation in Helium-Cooled Lead-Lithium DEMO Blanket with the FUS-TPC Code

Abstract Hydrogen dissolves in and permeates through most materials, thus it is important to understand the permeation, diffusion and dissolution phenomena of hydrogen and its isotopes in materials. We address the problem of tritium transport in Helium Cooled Lead-Lithium (HCLL) DEMO blanket from lead-lithium breeder through different heat transfer surfaces to the environment by developing a computational code (FUS-TPC). The main features of the code are briefly described and a parametric study is performed in order to identify the most influencing parameters in terms of tritium releases into the environment and of tritium inventories. The results showed that the results are strongly affected by the tritium Sievert’s constant in Lead-Lithium and the efficiency of permeation barriers.

Overview of requirements and design integration for the ITER EU Test Blanket Systems instrumentation

The ITER project aims at building a fusion device with the general goal of demonstrating the scientific and technical feasibility of fusion power. The testing of Tritium Breeder Blanket concepts is one of the ITER missions and has been recognized as an essential milestone in the development of a future fusion reactor ensuring tritium self-sufficiency, extraction of high grade heat and electricity production. Europe is currently developing two reference breeder blankets concepts for DEMO reactor specifications that will be tested in ITER under the form of Test Blanket Modules (TBMs): the Helium-Cooled Lithium-Lead (HCLL) concept and the Helium-Cooled Pebble-Bed (HCPB) concept. The strategy for the development of the instrumentation of the HCLL and HCPB Test Blanket Systems, which include the TBMs and their Ancillary Systems, is briefly recalled in this paper, along with the overview of the requirements coming from the harsh operational environment and the main challenges related to the integration with the complex design of the TBS components.

Radioactive Safety Estimates for ITER TBM Systems

Abstract The determination of the radioactive inventory and of the contact dose rates in the different ITER Test Blanket Modules systems is carried out, both for Helium-Cooled Lithium-Lead (HCLL) concept and the Helium-Cooled Pebble-Bed (HCPB) concept. The evaluations have been carried out by means of the MICROSHIELD code, starting from the data on the neutron-induced radioactivity in the blanket materials, completely available for both the blanket modules. The possible sources of radioactive material in all the systems have been individuated and their contributes estimated. In general, for both HCLL and HCPB systems, radioactivity inventory and contact dose rates turn out to be quite moderate. No particular radioactive safety concern should arise for the examined components.