Helium Cooled Lithium Lead Research Articles

Development of On-Line Tritium Monitor Based Upon Artificial Diamond for Fusion Applications

In this paper a novel on-line tritium monitor is presented. It is made with a single crystal diamond detector (SCD) covered with a thin layer of LiF 95% enriched in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li. Thermal neutrons impinging on the LiF layer produce α and T ions which are detected by the active diamond. The pulse height spectrum shows two separated peaks due to α and T ions respectively. By a proper calibration in a reference thermal flux the number of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li atoms and thus the absolute n+ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li→α+T reaction rate per unitary flux can be established. Once calibrated the detector can be used to measure the tritium production. Due to the many outstanding properties of diamond this detector could operate in the harsh working conditions of a fusion breeding blanket. A test of this detector was performed at the 14 MeV Frascati Neutron Generator (FNG). The detector was inserted inside a mock-up of the European Helium Cooled Lithium Lead (HCLL) Tritium Blanket Module (TBM), designed to validate the neutronic database for fusion application. The mock-up of the TBM was designed to perform a full set of experiments to validate tritium production code prediction comparing the experimental results with calculations. The measured tritium rates with the Li-Diamond detector are described in this paper. Comparison with calculations is in progress and will be reported in a future paper.

Test Blanket Module Pipe Forest integration in ITER equatorial port

ITER Test Blanket Modules (TBMs) will allow testing Breeding Blanket concepts for a future application in DEMO. IRFM (Institut de Recherche sur la Fusion Magnetique) contribution to this test program consists in the integration of the 2 European TBMs (Helium Cooled Lithium Lead and Helium Cooled Pebble Bed) in a dedicated equatorial port. The two Breeding Blanket concepts use Helium gas as a coolant, liquid PbLi as breeder (for HCLL process) and Helium gas for Tritium extraction (for HCPB process). These materials are passing through the cryostat interspace forming a pipe network called the Pipe Forest. The main structural function of the Pipe Forest is to absorb the thermal expansion due to the Vacuum Vessel and due to the pipe system itself. The Pipe Forest has to cope with several design issues. In this study, the different key parameters of the Pipe Forest design are identified and their relative influence is analysed. Several design options were investigated and compared based on: - Thermo-mechanical finite element calculations - Pipe Forest integration within the cryostat interspace - Interface management - Assembly and maintenance scenarios - Complex pipe routing due to the expansion bends - RCC-MR 2007 requirements The chosen thermal compensation solution (thermal expansion loops) led to a Pipe Forest design. The CAE analysis of this Pipe Forest showed that it fulfills the requirements of the RCC-MR 2007, which is the reference design and construction code selected for the European TBM.

Contact dose rates and relevant radioactive inventory in ITER TBM systems

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, already available for both the blanket modules. The possible sources of radioactive material in all the systems have been individuated and their contributes estimated.

HCLL TBM design status and development

The Helium Cooled Lithium Lead Test Blanket Module (HCLL-TBM) is one of the two European TBMs, representative of DEMO blanket technology, that shall be ready for installation in ITER starting from the first day of operation. It is developed by the CEA in the framework of the activities of the Test Blanket Module Consortium of Associates and under contract with the European Joint Undertaking Fusion For Energy (F4E). A series of 4 different HCLL-TBMs will be installed into one of the ITER equatorial ports during the experimental campaign. This paper aims at presenting the development process and design status of HCLL-TBM, with particular focus on the so-called “integral-TBM (IN-TBM)”, which will include all the main features of the corresponding DEMO blanket module. The design of such a complex component already poses considerable issues and is complicated by the peculiarities of the ITER environment (high temperature, radiation damage, pulsed plasma operation), which are not always addressed in present nuclear design codes. After recalling the main features of the HCLL IN-TBM, supporting design analyses are presented and manufacturing techniques are discussed.

Numerical benchmarks TRIPOLI − MCNP with use of MCAM on FNG ITER bulk shield and FNG HCLL TBM mock-up experiments

3D Monte Carlo (MC) transport codes are of first importance for the assessment of breeding blankets neutronic performances. This article supported by the EFDA Goal Oriented Training Program Eurobreed presents the difference in results between the CEA MC code TRIPOLI-4 and MCNP on two fusion neutronics benchmarks, assessing therefore TRIPOLI-4 calculation capabilities on shielding and tritium production rate (TPR). The first selected benchmark, assessing the shielding capability, is the Frascati neutron generator (FNG) ITER bulk shield experiment whereas the second benchmark, assessing the TPR calculation, is the preliminary design of the FNG helium cooled lithium–lead (HCLL) test blanket module (TBM) mock-up. To ensure the consistency of the geometry description, MCAM tool is used for automatic TRIPOLI − MCNP geometry conversions and check. A good coherence between TRIPOLI-4 and MCNP for neutron flux, reaction rates and TPR calculations is obtained. Moreover, it appears that MCAM performs fast, automatic and appropriate TRIPOLI − MCNP geometry conversions and finally that the tabulated FNG neutron source model from KIT is appropriate for TRIPOLI-4 calculations.

The TBM-CA configuration management approach for the ITER test blanket module - application to the HCLL TBS

The European Test Blanket Modules (EU-TBM) are first prototypes of a fusion reactor breeding blanket. They will be tested in dedicated equatorial ports n°16 of ITER. Technical developments are performed by a Consortium of European Associates (TBM-CA) and supported within the framework of F4E agency. Designing a complex nuclear system like TBM for ITER necessitates an organizational structure inside the consortium to manage in permanence the coherence between requirements (F4E technical and management specifications) and the TBM development through their life time. At the present stage, evolutionary nature of the design from the different teams is important. Highest priority is assigned to the Management support and Design Integration Team (MDIT) to perform an efficient control of the Configuration Management (CM). The TBM-CA CM comprises 4 main processes: a) identifying configuration of a product characteristics, including its interfaces (Configuration identification), b) controlling the evolution from agreed baseline (Configuration Control), c) creating the knowledge database in order to manage the information all along the lifecycle of the items (Configuration status accounting) and d) verifying the current configuration status of the items (Audits). CM is then a powerful tool to link the requirements for engineering, safety, quality assurance and test & acceptance activities. The application of the CM approach is illustrated through the case of TBM-HCLL (Helium Cooled Lithium Lead). The result shows that the proposed methodology and tools are suitable and provide quality solution for the items with a complex configuration such as TBM HCLL.

Numeric implementation of a nucleation, growth and transport model for helium bubbles in lead–lithium HCLL breeding blanket channels: Theory and code development

Large helium (He) production rates in liquid metal breeding blankets of a DT fusion reactor might have a significant influence in the system design. Low He solubility together with high local concentrations may create the conditions for He cavitation, which would have an impact in the components performance. The paper states that such a possibility is not remote in a helium cooled lithium–lead breeding blanket design. A model based on the Classical Nucleation Theory (CNT) has been developed and implemented in order to have a specific tool able to simulate HCLL systems and identify the key parameters and sensitivities. The nucleation and growth model has been implemented in the open source CFD code OpenFOAM so that transport of dissolved atomic He and nucleated He bubbles can be simulated. At the current level of development it is assumed that void fraction is small enough not to affect either the hydrodynamics or the properties of the liquid metal; thus, bubbles can be represented by means of a passive scalar. He growth and transport has been implemented using the mean radius approach in order to save computational time. Limitations and capabilities of the model are shown by means of zero-dimensional simulation and sensitivity analysis under HCLL breeding unit conditions.

European testing blanket modules auxiliaries design

The design of the auxiliary systems for the two European Test Blanket Modules is an important engineering task that will allow the successful integration of the two DEMO Blanket mock-ups into the ITER machine, and, through these experiments, demonstrate the technological feasibility of a blanket module for a future fusion power plant. These auxiliary systems are mainly circuits devoted to the removal of thermal power and tritium recovery from the blanket modules, as follows: • The Helium Cooling System (HCS); • The Coolant Purification System (CPS); • The Tritium Extraction System, divided in two subsystems in case of Helium Cooled Lithium Lead (HCLL), the Tritium Extraction Unit and the Tritium Removal System; • The Lead Lithium Loop (HCLL). Starting from the preliminary design developed in the past, the optimization and the engineering design of these subsystems was performed in the first year of activity of the TBM Consortium of Associates. The input parameters were reviewed and, when possible, DEMO relevant solutions were proposed. The present design takes in account both the TBM operational requirements as well the ITER operation, safety, and spatial constrains. In this paper the current loops design with accent on the integration into the ITER machine are presented.

Magnetohydrodynamic pressure drops in geometric elements forming a HCLL blanket mock-up

The helium cooled lead lithium (HCLL) blanket concept is one of the designs that will be tested and validated in the experimental reactor ITER. The liquid metal, which is slowly circulated in the blanket, interacts with the magnetic field that confines the fusion plasma leading to modifications of velocity and pressure distributions compared to the ones in hydrodynamic flows. Experiments have been performed to investigate magnetohydrodynamic flows in a scaled mock-up of a HCLL blanket. One of the aims is identifying the geometric elements that give rise to the main contributions to the total pressure head in the module. Parametric studies have been carried out to assess the influence of flow rate and magnetic field intensity on pressure drops.

Determination of flow distribution in a HCLL blanket mock-up through electric potential measurements

Magnetohydrodynamic experiments in a scaled mock-up of a helium-cooled lead lithium blanket module have been performed with the aim of determining the liquid–metal flow distribution inside breeder units and between sub-channels formed by the cooling plates. It has been observed that, even for strong magnetic fields, the distribution of the flow among these sub-channels is not completely uniform, i.e. inertial entrance and exit conditions still affect the flow partitioning in the breeder units. Moreover, depending on the balance between inertia, viscous and electromagnetic forces namely on Reynolds and Hartmann numbers, regions with almost stagnant or reversed flow can be observed. Since, in closed recirculation loops the accumulated tritium could represent a safety issue, their occurrence is investigated by a detailed parametric study.

Analysis of in-pile operation and modeling of tritium transport in lead-lithium irradiation experiments Libretto 4/1, 4/2 and 5

In the framework of the European R&D for the Helium Cooled Lead Lithium (HCLL) test blanket concept for ITER, NRG has designed three new Libretto irradiation experiments. Two experiments, Libretto 4/1 and 4/2, have been irradiated in HFR for 730 Full Power Days. The objective was to monitor on line the in-pile tritium production and permeation through Eurofer in contact with lead lithium eutectic. The irradiation of Libretto 4/1 and 4/2 has been conducted at 550 °C and 350 °C, respectively. Libretto 5 experiment has been irradiated for 520 Full Power Days in the temperature range of 300–500 °C with the objective to study tritium behavior in a lead lithium eutectic. The operation of the Libretto experiments included in-pile variations of hydrogen concentration in the purge gas and temperature transients. The irradiation of all three Libretto experiments has finished in 2009 and this work reports the analysis of the in-pile data. To analyze the data a model of tritium transport in lead lithium has been developed. The model incorporates two transport mechanisms: bulk diffusion and via rising tritium-helium bubbles. It was demonstrated that the bubble transport mechanism is much faster and in better agreement with the tritium residence times measured in the Libretto experiments.

System engineering approach in the EU Test Blanket Systems Design Integration

The complexity of the Test Blanket Systems demands diverse and comprehensive integration activities. Test Blanket Modules – Consortia of Associates (TBM-CA) applies the system engineering methods in all stages of the Test Blanket System (TBS) design integration. Completed so far integration engineering tasks cover among others status and initial set of TBS operating parameters; list of codes, standards and regulations related to TBS; planning of the TBS interfaces and baseline documentation. Most of the attention is devoted to the establishment the Helium-Cooled Lithium Lead (HCLL) and Helium-Cooled Pebble Bed Lead (HCPB) TBS configuration baseline, TBS break down into sub-systems, identification, definition and management of the internal and external interfaces, development of the TBS plant break down structure (PBS), establishment and management of the required TBS baseline documentation infrastructure. Break down of the TBS into sub-systems that is crucial for the further design and interfaces’ management has been selected considering several options and using specific evaluation criteria. Process of the TBS interfaces management covers the planning, definition and description, verification and review, non-conformances and deviations, and modification and improvement processes. Process of interfaces review is developed, identifying the actors, input, activities and output of the review. Finally the relations and interactions of system engineering processes with TBM configuration management and TBM-CA Quality Management System are discussed.

Development and qualification of functional materials for the EU Test Blanket Modules: Strategy and R&D activities

Europe has developed two reference tritium breeder blankets concepts for a DEMO fusion reactor: the Helium-Cooled Lithium–Lead and the Helium-Cooled Pebble-Bed. Both will be tested in ITER under the form of Test Blanket Modules (TBMs). The paper reviews the current status of development and qualification of the EU TBMs functional materials; i.e. ceramic solid breeder materials, beryllium/beryllides multiplier materials and Lithium–Lead liquid metal breeder material Pb–15.7Li. For each functional material the main functional/performance requirements with key qualification issues, current status of the R&D activities and the EU development strategy are presented. In the development strategy major steps considered are listed pointing out importance of the ‘Development/qualification/procurement plan’, currently under elaboration, for definition of a roadmap of further activities aiming at delivery of qualified functional materials to be used in the European TBMs in ITER.

Aluminum-Based Barrier Development for Nuclear Fusion Applications

Abstract In the helium-cooled lead-lithium (HCLL) design concept for blanket structures of a future fusion power plant, the eutectic Pb-15.7Li alloy is used as a liquid tritium breeder and is in direct contact with the structural material, e.g., ferritic-martensitic steels. Compatibility tests showed that a high corrosion attack appears and that the dissolved steel elements like Fe and Cr form precipitates, with a high risk of system blockages. Therefore, coatings as corrosion barriers are required for a reliable plant operation. Because of safety reasons, a distinct permeation reduction of the tritium, produced in the Pb-Li alloy by nuclear reactions, into the environment has to be limited, too. Previous developments already showed that Al-based coatings can perform very well as anti-corrosion and tritium permeation (T-permeation) reduction barriers in a PbLi environment. However, industrially relevant coating technologies for fusion application are still missing and/or cannot fulfil low activation criteria. Electrochemical deposition processes are highly flexible and used widely for the production of functional coatings, e.g., for corrosion protection. Nevertheless, because of its unique electrochemistry, Al cannot be deposited from water-based systems. Therefore, the development of two different Al coating processes from nonaqueous systems was initiated and proofed by the successful generation of protective and reproducible scales after heat treatment.

Studies on additional electrical heating of the HCLL TBM breeder zone

Among the test blanket modules (TBMs) to be tested in the successive ITER phases, European design activities have focused on the electromagnetic (EM) TBM to be tested in ITER first phase (H-H), and on the integral (IN) TBM to be tested in the full duty D-T phase. The scope of the present contribution is to report activities performed on the helium cooled lithium lead (HCLL) TBM, in its EM version for the H-H phase. This phase is characterized for the TBM by relevant D-T phase magnetic field, surface heat flux and disruption induced loads, and the lack of nuclear volumetric heating. On one hand, H-H phase gives the opportunity of experiments and use of instrumentation which will not be possible in the irradiated environment of D-T phase. On the other hand, H-H phase specificity is a temperature level in the breeder zone much lower than that in the D-T phase. Main EU objectives assigned to TBM testing in H-H phase for design validation and for the build-up of a reliability database can be fulfilled at this temperature level, which is not the case for the scientific experimental program (MHD, corrosion and tritium permeation). Hence, partial heating of the TBM is foreseen. A technical solution for an electrically heated configuration of the breeder zone has been investigated. Finite element (FE) analyses were performed to assess the thermal behaviour of the TBM for the non-heated and heated cases.

Development of welding technologies for the manufacturing of European Tritium Breeder blanket modules

Europe has developed two reference Tritium Breeder Blankets concepts for a DEMO fusion reactor: the Helium-Cooled Lithium–Lead and the Helium-Cooled Pebble-Bed. Both are using the reduced-activation ferritic–martensitic EUROFER-97 steel as structural material and will be tested in ITER under the form of test blanket modules. The fabrication of their EUROFER structures requires developing welding processes like laser, TIG, EB and diffusion welding often beyond the state-of-the-art. The status of European achievements in this area is reviewed, illustrating the variety of processes and key issues behind retained options, in particular with respect to metallurgical aspects and mechanical properties. Fabrication of mock-ups is highlighted and their characterization and performances with respect to design requirements are reviewed.

Tritium breeder blankets design and technologies in Europe: Development status of ITER Test Blanket Modules, test & qualification strategy and roadmap towards DEMO

Europe has developed two reference tritium breeder blankets concepts that will be tested in ITER under the form of Test Blanket Modules: (i) the Helium-Cooled Lithium–Lead which uses the liquid Pb–15.7Li as both breeder and neutron multiplier, (ii) the Helium-Cooled Pebble-Bed with lithiated ceramic pebbles as breeder and beryllium pebbles as neutron multiplier. An extensive development program has been carried-out over the last decade combining experimental and numerical simulations aimed at identifying and quantifying physical phenomena occurring in breeder blankets and at optimizing their design and technologies accordingly. On this basis, sound guidelines for the design and technological choices of Test Blanket Modules can be derived. In addition, regulatory and ITER project requirements, which prefigure the future DEMO blanket ones, are now integrated in the development and qualification program of the Test Blanket Modules. Their scope and implication are analyzed.

Mock-up testing facilities and qualification strategy for EU ITER TBMs

European test blanket modules (TBM) for both European blanket concepts, namely the Helium Cooled Lithium Lead (HCLL) and the Helium Cooled Pebble Bed (HCPB), and their auxiliary systems have been designed in the last years. This paper presents the experimental facilities available in Europe for the qualification tests of European TBMs. In particular, devices designed to analyze specific technological issues, for example corrosion under strong magnetic fields or tritium management and extraction, as well as large scale facility to perform integral tests are described. A preliminary overview on the qualification strategy is presented and discussed.

The coolant purification system of the European test blanket modules: Preliminary design

The HCPB (Helium Cooled Pebble Bed) and HCLL (Helium Cooled Lithium Lead) Test Blanket Modules (TBMs), developed in EU to be tested in ITER, adopt helium at 80 bar as primary coolant. This paper contains a conceptual design of the TBMs Coolant Purification System (CPS) based on the need to remove permeated tritium and gas impurities. The following steps have been considered: identification of CPS design requirements; review of the purification systems developed for Helium Cooled Fission Reactors and proposed for DEMO Fusion Reactor; selection of the most promising technologies for CPS; indications on instrumentation and procedures for tritium balance. The proposed solution is a three-stage process constituted by an oxidiser to convert Q 2 and CO to Q 2O and CO 2, an adsorption step, performed on molecular sieve at room temperature to remove Q 2O and CO 2, and a final step performed on a heated getter to remove residual impurities.

Measurement and analysis of neutron flux spectra in a neutronics mock-up of the HCLL test blanket module

Fast neutron and gamma-ray flux spectra and time-of-arrival spectra of slow neutrons have been measured in a neutronics mock-up of the European Helium-Cooled Lithium–Lead Test Blanket Module with the aim to validate nuclear cross-section data. The mock-up was irradiated with fusion peak neutrons from the DT neutron generator of the Technical University of Dresden. A well characterized cylindrical NE-213 scintillator was inserted into two positions in the LiPb/EUROFER assembly. Pulse height spectra from neutrons and gamma-rays were recorded from the NE-213 output. The spectra were then unfolded with experimentally obtained response matrices of the NE-213 detector. Time-of-arrival spectra of slow neutrons were measured with a 3He counter placed in the mock-up, and the neutron generator was operated in pulsed mode. Monte Carlo calculations using the MCNP code and nuclear cross-section data from the JEFF-3.1.1 and FENDL-2.1 libraries were performed and the results are compared with the experimental results. A good agreement of measurement and calculation was found with some deviations in certain energy intervals.