IFMIF Test Cell Research Articles

Shielding performances analysis for the IFMIF test facility based on high-fidelity Monte Carlo neutronic calculations

The IFMIF Test Cell (TC) design was developed and optimized in the EVEDA phase, and finally the reference TC design was proposed. The present study is devoted to further investigations of open issues on the reference TC design. In order to examine the neutron streaming effect caused by pipe penetrations and gaps around removable shielding plugs, a new geometry model for neutronic analyses has been prepared directly from engineering CAD data by utilizing the McCad conversion software. All removable shielding plugs are separately described in the model and a detailed description of pipes was incorporated into the model. The calculation result suggests that the streaming effect is mitigated if the pipe penetration is designed appropriately, while the gaps around the shielding plugs above the TC have large impact on the radiation dose in the access cell. The concept of the reference TC design has been basically validated from the neutronics point of view, although the streaming effect should be compensated by the shielding capability of the test cell cover plate so that occupational workers can access to the access cell during operation.

Overview of Material Challenges in IFMIF Test Cell Design

As the core region of IFMIF, the test cell (TC) suffers intense neutron and gamma irradiations. Major material challenges of the TC faced during engineering design phase are outlined and the current key material allocations are described. Actively cooled magnetite concrete is selected as the major biological shielding material for the TC, and actively cooled closed liner made of 316L stainless steel is selected to cover the complete TC internal surfaces. Material selections for sealing gaskets and electric insulations inside the TC are preliminarily defined based on dose rate maps at different locations. Metal based sealing gaskets and glass/ceramic electric insulations are applied in the areas with high dose rate, while organic based gaskets and conventional insulation materials can only be arranged behind sufficient biological shielding. Leak tight welding seams between removable interface shielding plugs and the TC liner are located in the region with very low helium generation rate (<0.01 appm/fpy) in steel so that cutting and re-welding during the complete IFMIF life span is guaranteed.

Neutronic analysis for the IFMIF EVEDA reference test cell and test facility

The IFMIF test cell (TC) design has been further developed and optimized in the EVEDA phase, and finally the reference TC design has been proposed. In order to carry out the detailed neutronic analysis for the reference TC design, a very detailed geometrical model for Monte Carlo neutronic calculations has been prepared directly from engineering CAD data by utilizing the McCad conversion software developed at KIT. The geometrical model includes the detailed descriptions of the lithium target system proposed by Japan, all test modules based on the EVEDA phase design, and the 3-dimesional arrangement of the biological shielding. The Monte Carlo code McDeLicious, which is an enhancement to MCNP5, has been utilized in order to adequately simulate the neutron and photon productions from the 6,7Li(d,xn) reactions in the lithium target. The present analysis is focusing on the nuclear heating distribution inside the biological shielding, the nuclear property of the TC liner, and the biological dose distribution around TC during operation. Some countermeasures for reducing the He production in the liner are discussed.

Re-evaluation of the irradiation conditions in the IFMIF test cell based on the EVEDA phase design

A re-evaluation of irradiation conditions in IFMIF utilizing the new EVEDA geometry model has been carried out. The focus is on the re-assessment of the nuclear responses in the High Flux Test Module (HFTM) as well as other Test Modules. The aim of the present analysis is to provide a reliable and realistic estimate based on the latest design and knowledge. To this end, we have utilized state-of-the-art nuclear data and an updated beam footprint as prepared on the basis of deuteron beam dynamics simulations combined with the Monte Carlo code McDeLicious, an enhancement to MCNP5 developed ad hoc for IFMIF neutronics calculations. The present analysis proves that (1) the averaged DPA rate of 26 dpa/y can be achieved in HFTM with 500cm3 volume, (2) the He/DPA value for HFTM center rigs is similar as the value expected for DEMO first wall, (3) the neutron flux gradient in HFTM center rigs is less than 10%/cm.

Conceptual design of the IFMIF Start-Up monitoring module

The preliminary engineering design of the test facilities, including the various test modules to be used in the IFMIF plant is a part of the IFMIF/EVEDA (Engineering Validation and Engineering Design Activities) project from the Broader Approach to fusion.One presents the current status of the conceptual development of the IFMIF Start-Up Monitoring Module, a dedicated device used in the IFMIF test cell during the commissioning phase of the installation, in order to completely characterise the irradiation conditions behind the target on which the beam of deuterons will be focused. This STUMM embarks a lot of instrumentation to precisely characterise the neutron field, the nuclear heating and the temperatures in the test cell.One briefly describes the measuring instruments (including a specific radiation flux monitor under development), the possible layouts and the possible positioning. One also defines which types of measurements are expected by this especially dedicated commissioning module.

Neutronic analysis for the IFMIF target and test cell using a new CAD-based geometry model

This work presents neutronic analyses to support the IFMIF target and test cell (TTC) design in the framework of the Broader Approach activities. A very detailed Monte Carlo geometry model of IFMIF TTC based on the modular TTC concept was prepared directly from a CAD model by using the McCad conversion software which has been developed at KIT. The Monte Carlo code McDeLicious, which is an enhancement to MCNP5, was utilized and nuclear heating, displacement damage and gas production rates in the TTC vessel wall were calculated. The calculation result shows that there are two prominent peaks; downstream of the test modules due to the high energy neutron contribution for gas productions and upstream due to neutron back-streaming along the beam ducts. The result suggests it is very important in the neutronic analysis to consider the detailed configuration of TTC and test modules. The dose rate distribution during operation has been assessed for the rooms adjacent to TTC across thick surrounding walls. The necessary thickness for the shielding walls has been examined. The result demonstrates the substantial improvement in the shielding capability for the top access cell with the present TTC design.

New progresses in the IFMIF target and test cell design and a proposal for the specimen flow

The development of the conceptual design of the IFMIF target and test cell (TTC) is briefly summarized by outlining the previous reference TTC design and the current modular test cell (MTC) concept. Based on the MTC concept, the latest progresses of the preliminary engineering design of the key TTC components, including the TTC vessel, the top shielding plugs, the removable intermediate ring, and the test module interface heads, are described. A specimen flow, based on handling requirements of the high flux test module, between the TTC, access cell (AC), test module handling cell (TMHC) and the post irradiation examination facilities is proposed as well as the function of the AC and TMHC is preliminary defined. The TMHC is proposed to be divided into a component handling cell and a rig handling cell regarding the dimension differences of the components to be handled inside of the cells. Re-use of irradiated specimens for another campaign of irradiation is also considered in this specimen flow.

Shutdown dose rate analyses for the IFMIF HFTM

This work contributes to neutronic support activity for the high flux test module (HFTM) designing in the framework of the IFMIF/EVEDA project. The engineering design of the IFMIF maintenance and remote handling systems is significantly affected by the radiation doses originating from radioactive materials generated during operation in the IFMIF HFTM. Two aspects of shutdown doses have been analyses for the HFTM radioactive materials removed from the IFMIF target and test cell (TTC) and then placed into the hot cell. First aspect is machine reliability expressed through absorbed gamma dose rate in the envisaged radiation-sensitive silicon-based electronics located closely to the radioactive HFTM materials. Second one is radiation protection and safety of a human being presented quantitatively as human biological dose equivalent rate around the HFTM materials. Shutdown dose rate assessments were performed for different materials subjected to the radiation by decay photons emitted from the HFTM. Three different decay radiation sources were considered in the analyses: a simple Eurofer specimen, a single HFTM rig packed with specimens and an assembly consisting of 12 rigs. The shutdown dose rate has been assessed taking into account transport of decay gammas by means of subsequent use of three computer codes: McDeLicious, FISPACT-2007, and MCNP5.

Displacement damage induced in iron by gammas and neutrons under irradiation in the IFMIF test cell

This work presents a complete comparative analysis of the radiation damage induced in iron-based materials in IFMIF by photons and neutrons. The gamma induced damage takes into account, for the first time, both photonuclear and photoatomic reaction mechanisms. The relevant cross sections were taken from available data evaluations. The gamma and neutron radiation fields were calculated by the McDeLicious Monte Carlo code using a 3-D geometry model. Finally the gamma and neutron induced damages in the iron have been assessed inside the IFMIF test cell and the surrounding concrete walls. It was found that the photoatomic mechanism dominates the photonuclear with at least one hundred times higher damage rates. The ratio of the gamma and the neutron induced displacement damage was found to be 10−3 inside the concrete wall and 10−5 in the components close to d-Li source. This fraction may increase a few times due to the uncertainty of the evaluated γ-dpa cross sections and the different surviving probabilities for defects produced by gammas and neutrons, nevertheless unlikely exceed 1%.

IFMIF target and test cell—Conceptual designs, boundary condition definitions and current status of preliminary engineering design

The reference design of the IFMIF target and test cell (TTC) which is summarized in the comprehensive design report (CDR) is reviewed and evaluated. Improved TTC conceptual designs, as well as a revision of the reference design, have been proposed in order to qualify precise and flexible positioning of test modules against the backplate in the TTC. As the result of evaluations on the existing design concepts, a referential table which addresses the design requirements and guidelines has been released and is outlined in this paper. Based on the referential table and the existing design concepts a modular TTC concept is introduced, developed, and improved aimed on providing variable in-cell operation environments, flexible accessibility for remote handling, and accurate and reliable positioning for the test modules. The current status of the preliminary engineering design based on the modular TTC concept is represented.

Radiation deep penetration calculations for the IFMIF test cell wall

Deep radiation penetration calculations were performed for the IFMIF test cell wall on the basis of two different approaches employing the Monte-Carlo technique and a coupled Monte-Carlo/deterministic computational scheme called MCDO. For the Monte-Carlo calculations, the McDeLicious code was used which is an extension to MCNP-5 with the capability to simulate the d-Li neutron source on the basis of tabulated d-Li cross-section data. Use was made of a three dimensional geometry model of the IFMIF test cell representing in detail its interior and the shielding 3 m thick heavy concrete walls. The interface program MCDO, which couples McDeLicious and the 3D discrete ordinate code TORT, was used to transport the neutrons and photons through the wall and to obtain spatial distributions of the doses in the adjacent rooms. These coupled calculations have revealed hot spots of the radiation doses in the access room neighbouring the test cell in the d-beam downstream direction. The dose rate there exceeds several times the limit of 100 μSv/h for the work personnel.

Proposal of an improved design of IFMIF Test Cell components for enhanced handling and reliability

An adequate design of components to be manipulated by remote handling is a key factor in the success of any activated facility, having a decisive impact on availability, prompt and safe maintenance, occupational exposures and flexibility of the facility. Such components should satisfy at least the basic remote handling requirements of simplicity, accessibility, modularity, standardization and assembling adequacy. Highly activated components in the IFMIF facility are found in the Test Cell, a pit closed by stepped shielding plugs. The Test Cell confines the Test Modules which contain the samples and experiments. The present reference design of the IFMIF Test Cell shows some drawbacks, in particular the jamming tendency of the shielding plugs, slow and complex access to the Backplate, a low lifetime component, and difficult positioning of the Test Modules. This paper summarises several modifications aiming at improving, under such remote handling requirements, the present reference design of the Test Cell shielding plugs and aspects of the geometrical structure of the Test Cell. A functional modularization of the present shielding plugs has been carried out and positioning guides for the Test Modules have been devised.

Feasibility of fission chambers as a neutron diagnostic in the IFMIF—Test Cell

A diagnostic based on a set of fission ionization chambers is proposed for the IFMIF Test Cell in order to achieve on-line control of the irradiation parameters. These chambers are widely used in fission reactors; however the IFMIF environment (neutron spectrum, high neutron fluxes, gamma doses, reduced space, etc. …) requires a careful design of the whole diagnostic. This work shows the current status of the diagnostic development, which is being performed in the framework of the Broader Approach activities. The definition of the diagnostic strategy is addressed to establish the main specifications and requirements of the IFMIF fission chambers and their deployment. The map that the signal of a set of fission chambers will supply has been assessed by taking into account their sensitivity, their positioning inside the Test Cell and the IFMIF neutron flux. The results show that this experimental system will be capable of measuring and characterizing the high neutron fluxes expected for IFMIF.

Tritium permeation experiment at IFMIF Medium Flux Test Module

Tritium release experiments using different breeding material candidates are planned for the medium flux region of the IFMIF Test Cell. Nowadays, only ceramic breeder materials have been suggested to be tested in the Tritium Release Module located in the Medium Flux Test Module of IFMIF. Liquid breeder blankets are very promising and for that reason, several concepts will be tested in ITER. One of the main problems concerning the liquid blankets is the permeation of the generated tritium in the breeder throughout the walls. Since tritium permeation is highly influenced by irradiation conditions, IFMIF is a suitable scenario to perform tritium permeation related experiments. In this paper, a preliminary design of a tritium permeation experiment for the Medium Flux Test Module of IFMIF is proposed, in order to contribute to the progress of the liquid breeder blanket concept validation. The conceptual design of the capsule in which the experiment will be performed is carried out, taking into consideration the experiment necessities and its implementation in the Tritium Release Module. In addition to this, some thermal hydraulic calculations have been performed to evaluate the thermal behaviour of the irradiation capsule.

Radiation transport analyses for IFMIF design by the Attila software using a Monte-Carlo source model

Accurate calculation of the neutron transport through the shielding of the IFMIF test cell, defined by CAD, is a difficult task for several reasons. The ability of the powerful deterministic radiation transport code Attila, to do this rapidly and reliably has been studied. Three models of increasing geometrical complexity were produced from the CAD using the CADfix software. A fourth model was produced to represent transport within the cell. The work also involved the conversion of the Vitenea-IEF database for high energy neutrons into a format usable by Attila, and the conversion of a particle source specified in MCNP wssaformat to a form usable by Attila. The final model encompassed the entire test cell environment, with only minor modifications. On a state-of-the-art PC, Attila took approximately 3 h to perform the calculations, as a consequence of a careful mesh ‘layering’. The results strongly suggest that Attila will be a valuable tool for modelling radiation transport in IFMIF, and for similar problems.

IFMIF high flux test module and test cell—Design and design validation

The present paper summarizes work devoted to design and design validation of the HFTM and improvements obtained by neutronics, thermohydraulic and mechanical analyses. The HFTM design requirements and its main features will be described. Remarkable progress has been achieved in the development of appropriate computational tools, data and methods for IFMIF neutronics and activation analysis. Similarly, the thermohydraulic simulations have been validated against experimental data obtained in the ITHEX facility to test turbulence models of gas flow in narrow channels. Iterative analyses lead to several design optimizations of container and helium supply. Crucial manufacturing techniques for the parts of the HFTM have been tested extensively to assure a reliable and reproducible manufacturing route for the final procurement of the HFTM. Finally, the integrated design of the Target and Test Cell has been initiated with contributions from several international design teams.

Development of activation foils method for the IFMIF neutron flux characterization

This work proposes to use the activation foil method for the neutron spectrum determination in the IFMIF facility. Suitable elements were selected to this end with dosimetry reactions having thresholds and effective cross sections covering the whole IFMIF energy range up to 55 MeV. The available evaluated nuclear data libraries and experimental data were carefully screened to select appropriate dosimetry cross sections with uncertainties as low as possible. For the determination of the neutron spectra from the induced γ-activities the unfolding code SAND-II was applied after having it modified for the use of the selected dosimetry cross sections above 20 MeV. This approach was tested by measuring the white neutron spectrum at the cyclotron of Nuclear Physics Institute (Řež), where neutrons up to 35 MeV energy were generated by a 37 MeV proton beam impinging on a heavy water target. The paper concludes with recommendations for the procedure for determining the neutron energy differential flux in the IFMIF test cell with respect to the size of the dosimetry foils, the irradiation time and the expected induced activities.

Natural convection cooling of the IFMIF target and test cell

The present work summarizes efforts on the simulation of natural convection cooling within the IFMIF target and test cell. The simulations have been performed with the STAR-CD code using the k– ω high-Reynolds number turbulence model. A dedicated thermohydraulic model has been devised including Lithium loop components. Nuclear heat production has been calculated by the Monte-Carlo code McDeLicious for different parts of the target and test cell walls and was used as input for the STAR-CD simulations. Helium atmospheres at several pressures from 0.1 to 10 −5 MPa have been investigated. In order to limit the maximum temperature of the concrete walls to 80 °C it was necessary to add thermal insulation layers to the hot Lithium loop surfaces and a conceptual system of two cooling layers in different depths of the concrete walls.

Shielding analyses of the IFMIF test cell

Full 3-D shielding calculations of the IFMIF test cell were performed using a computational scheme for coupled Monte Carlo/deterministic transport calculations that enables the use of a detailed geometry model of the test cell in the Monte Carlo calculation and is suitable, at the same time, to handle the deep penetration transport through the thick surrounding concrete walls. Calculations for the test cell cover, which includes numerous penetrations through which neutrons stream, were performed by the Monte Carlo method. The results demonstrate that the dose rate limit for work personnel access to the access/maintenance room can be safely met during IFMIF operation assuming the test modules are surrounded by a horseshoe shield and the back heavy concrete wall is no less than 250 cm thick. No work personnel access to the room above the cover will be permitted during IFMIF operation due to the strong neutron streaming through the cover penetrations.

Neutronics and activation characteristics of the international fusion material irradiation facility

A neutronics and activation characterization of the main IFMIF test cell components has been performed by using a newly developed global geometry model for the Monte Carlo calculations, which describes in detail the IFMIF sub-systems. The neutron fluxes and displacement damage rates in different materials have been assessed by the McDeLicious code, which simulates the IFMIF neutron source extending up to 55 MeV and uses cross-sections from suitable evaluated libraries for neutron transport. The induced radioactivities and γ-ray contact dose rates were calculated by the ALARA inventory code on the basis of the IEAF-2001 activation library. The displacement damage rates in steel vary from 60 to 0.004 dpa/year and the induced radioactivity after 1 year IFMIF operation 10 15–10 11 Bq/kg as one moves from the lithium target back plate to the test cell walls. Comparative activation analysis of the SS-316 and Eurofer steels has shown that latter one will have γ-ray dose rate an order of magnitude less for the cooling period 10–1,000,000 years.