


CHAPTER B - B4 Emerging Technologies
4.1 Development of material science and advanced materials for DEMO
4.1.1 Magnetic properties of ODS ferritic steels
Background and Objectives: Within the Fusion Materials Topical Group in the field of the development of Oxide Dispersion Strengthened Ferritic Steels (ODS-FS) there is considerable effort in the fabrication of ODS-FS using industrial scale methods. The current activity lies within the objective of the MAT-ODSFS work-programme to create a comprehensive materials property data of non – irradiated material. The task has as objective the determination of magnetic properties of the new developed ODS-FS after being mechanically stressed.
Work performed during 2012 (Co-operation: within the Fusion Materials Topical Group, KIT):
(i) The magnetization hysteresis loop was measured for a series of Fe-Cr-W-Ti-Y2O3 steels, having different concentration of W, Ti and Y2O3 and different process of the various alloying elements, which were subject to impact tests. From the magnetization loops the saturation magnetization, the initial susceptibility and the permeability were determined for two areas of the mechanically tested specimens, the middle one that received the maximum stress during the impact test and the edge with the minimum stress. In addition the real and imaginary part of the ac magnetic susceptibility was measured for both the middle and edge parts of the impact tested specimens. The magnetic properties were correlated with the chemical composition of the alloy and the stress state of the specimen (see ANNEX 39). The accurate determination of the coercive field was not possible due to its very small value and a special home-made apparatus is under installation for its measurement during the 2013 work-programme. The coercive field is strongly dependent on the easiness of the rotation of the magnetic domain walls which is governed by the microstructure. Correlation between the magnetic and mechanical properties will be the final goal of the task to be continued in 2013. The above results were presented in the meetings of the Fusion Materials Topical Group organized by EFDA.
4.2 Materials Modelling
4.2.1 Determination of radiation damage in Fe and Fe-Cr model alloys by electrical resistivity measurements
Background and Objectives: Within the Fusion Materials Topical Group there is considerable effort in understanding and modelling radiation effects in Fe and Fe-Cr alloys, the main ingredients of EUROFER low-activation structural steels. Experimental validation of the developed modelling tools is of primary importance for the reliable prediction of radiation damage at fusion relevant dose levels. The general objective of this activity is to provide experimental data on the radiation response of Fe-Cr alloys, to assist the modelling activities and test theoretical predictions.
Work performed in 2012 (Co-operation: within the Fusion Materials Topical Group):
(i) In order to complete the experimental dataset regarding resistivity recovery of Fe-Cr alloys after low temperature irradiation, we have performed irradiations at different dose levels and measured the recovery after subsequent annealing on an alloy with 5 at. % Cr and on a pure Fe reference material. The experiments were performed at the dedicated materials irradiation facility installed at the TANDEM accelerator of NCSR-"D", using 5 MeV protons and at dose levels of 1, 3 and 10×1015 p/cm2. The results reveal the variation with dose of the various recovery stages, which is a very useful benchmark for theoretical models of radiation damage. This work will be continued in 2013 to obtain similar data for all available Cr concentrations up to 15 at. %.
(ii) A rate theory model of defect recombination kinetics has been developed for the analysis of the resistivity recovery measurements on Fe-Cr alloys. The model has been implemented as a software package in the MATLAB computing environment and allows the setting-up and solution of the system of differential equations that governs the evolution of defect concentrations during recovery experiments. The model will serve as a tool for testing possible defect recovery mechanisms and for the extraction of relevant physical parameters as, e.g., defect migration barriers, by comparison to experimental data. Application of the model to the study of the low-temperature recovery of Fe-Cr alloys reveals the trapping of interstitial defects as the Cr concentration is increased. Details of this analysis are given in ANNEX 40. The above results were presented in the meetings of the Fusion Materials Topical Group organized by EFDA.
4.2.2 Determination of short-range ordering kinetics in Fe-Cr model alloys under irradiation
Background and objectives: Ordering of solute atoms in alloys is one of the key factors determining their phase stability. Fe-Cr alloys in particular exhibit a peculiar ordering behaviour, that changes from ordering to clustering at approximately 10 at. % Cr. Thus, it is of crucial importance for the stability of Fe-Cr under irradiation, to study the changes in solute atom ordering that occur during irradiation and the associated kinetics. To study these effects we perform irradiations of Fe-Cr alloys at different temperatures and detect changes in alloy ordering by in-situ measurements of the electrical resistivity.
Work performed in 2012 (Co-operation: Within Fusion Materials Topical Group, SCK-CEN)
(i) A Fe-Cr alloy with nominal Cr concentration of 5.8 at. % and a reference sample of pure Fe have been irradiated with 5 MeV protons at the dedicated materials irradiation facility installed at NCSR-"D" TANDEM accelerator. Irradiations were performed at two different temperature regimes: a cryogenic one at 40 K and a relatively higher one at 400 K. At cryogenic temperature the radiation damage created in the form of lattice defects remains "frozen" in the material, resulting in a continuous increase of the electrical resistivity of both the Fe-Cr alloy and pure Fe. In contrast, at the high irradiation temperature the alloy exhibits a totally different behaviour with respect to the pure metal. Namely, no measurable changes are observed in the resistivity of pure Fe, since irradiation defects migrate and annihilate almost instantly. In the alloy the resistivity displays a transient behaviour as a function of dose, which is attributed to changes in Cr solute ordering. The experimental results are detailed in ANNEX 41. This task will be continued with irradiations at different Cr concentrations and temperatures. Theoretical modelling of the observed effect will be conducted in collaboration with the Belgian Association (SCK-CEN). The above results have been presented in the meetings of the Fusion Materials Topical Group organized by EFDA.
4.2.3 Effect of iron ion irradiation on the structural and magnetic properties of thin Fe layers
Background and objectives: For Fusion energy applications FeCr steels are the candidate structural materials. Understanding the neutron irradiation effects on Fe and FeCr steels is of paramount importance for the development of radiation resistance materials. The energy of the incident fusion neutrons is 14 MeV. However, as the neutrons penetrate within the material they lose energy and thus the primary knock-ons of Fe have a range of energies with a maximum energy of around 1 MeV. Thus, the main part of the damage arising from neutron or other ions irradiation is due to energetic Fe atoms which create the radiation damage cascades. This phenomenon can be studied by employing Fe ion irradiation of Fe or FeCr alloys. Iron irradiation also has the advantage that this phenomenon can be studied by selecting the specific incident energy in contrast to neutron irradiation in which the primary knock-ons have a range of energies. Since the penetration of energetic Fe ions is of the order of few nm to μm depending on the incident Fe energy, thin films need to be investigated.
Work performed in 2012 (Co-operation: Within Materials and Modelling group (TG-M), CEA-JANNUS)
(i) Fe+ ion having having an energy 490 keV were used to irradiate different thickness Fe thin films at JANNuS laboratory at CEA, Saclay, at different ion doses. The irradiation induced changes in the crystalline structure and in the magnetic properties of the 50 nm thick iron samples and for two different ion doses, namely 5.4 and 57 dpa, were investigated employing magnetization hysteresis loop measurements, grazing incidence X-ray diffraction, X-ray reflectivity and polarised neutron reflectivity measurements. The results up to now show drastic changes with irradiation in the magnetic properties, whereas the bcc crystalline structure remains after irradiation presenting an increase of the lattice constant and increase of the grain size and or stress relief (see ANNEX 42). The above results were presented in the meetings of the Fusion Materials Topical Group organized by EFDA.
4.2.4 Determination of agglomeration and/or short range order phenomena in thermally aged FeCr alloys
Background and objectives: The general objective of this activity is investigate agglomeration phenomena in thermally aged FeCr alloys using Small Angle Neutron Scattering (SANS) measurements and to provide experimental data for the testing of the different theoretical predictions.
Work performed in 2012 (Co-operation: Within Materials and Modelling group (TG-M), TEKES (University of Helsinki)):
(i) Due to technical problems during the performance of the SANS measurements on thermally aged FeCr specimens, in 2011 no extensive experimental activity was carried out in 2012. A beam time application was submitted to Helmholtz Association for repeating the SANS measurements on the thermally aged samples. The application was successful and 4 beam days were allocated. The experiments are to be carried out end of June 2013.
4.2.5 Determination of thermal properties of FeCr alloys as a function of temperature
Background and objectives: The general objective of this activity is to investigate and determine the thermal properties of FeCr alloys as a function of the temperature
Work performed in 2012:
(i) The determination of the thermal properties of FeCr as a function of temperature in the temperature range 4 to 300 K was completed in 2011. The experimental results concerning specific heat were compared to those obtained from existing theoretical models and the results were presented in both the 2011 Annual Report of the EURATOM-Hellenic Association and in a report sent to EFDA. Effort was made in 2012 to extend the measurements in the temperature range 300 to 1200 K using a Differential Scanning Calorimetry but the accuracy of the measurements was limited to 20-30% due to limitations of the apparatus available at NCSRD.
4.7 Fusion safety issues
4.7.1 Validation of calculations of neutron streaming through ducts
Background and Objectives: Neutron streaming through penetrations of ITER structural and shielding materials is important to be investigated for assessment of the efficiency of the biological shield. In particular, evaluation of neutron streaming through ducts is a major safety task involving radiation transport computations along long paths and in complex geometries. Therefore, a study performed at JET aiming at validating the calculation of neutron streaming through ducts and of the dose rates outside of the JET torus hall is of outmost importance, since it enables validation of the safety assessment calculations used for ITER. Objective of the present work was the evaluation of the neutron fluence and dose along the SW entrance maze and the SE ventilation duct.
Work performed in 2012 (Co-operation: IPPLM-IFJ, CCFE):
(i) Development of a computational model of the JET Hall SW entrance labyrinth and evaluation of the streaming neutrons fluence and ambient dose equivalent along the labyrinth. The model was based on “as-built” geometric and material composition data. The input neutron source was provided by CCFE.
(ii) Neutron fluence and dose was predicted at a set of locations within the JET torus hall (at the area of the SW labyrinth).
(iii) The results of the simulations were compared against experimental measurements. The measurements were performed by CCFE using thermoluminescent detectors (TLDs) positioned at the centre of polyethylene moderator cylinders. MCP and MTS-type TLDs were used developed and calibrated by IPPLM-IFJ. The MCNP model of JET torus Hall SW entrance maze (duct) and the results of MCNP calculations for the selected locations are presented in ANNEX 43. The results were presented at Task Force Fusion Technology 2012 Semi-Annual Monitoring Meeting, JET Culham Science Centre, 11-14 December 2012. This work will be continued in 2013.
4.7.2 Neutron Streaming Calculation – Blanket
Background and Objectives: Results of neutronic analyses are a major design driver for most tokamak components, in particular breeding blanket, divertor, shielding, magnets, ports, remote handling tools, and the hot cell. The DTM neutronic studies carried out in 2012 are focussed on an early availability of important DEMO design driving parameters and on improving the integration of neutronic analyses in the design and analysis process of tokamak components. This will be achieved by evaluation of available neutronic tools that are best suited for the DEMO design phase, development of a DEMO model for scoping studies and performing neutronic scoping studies for DEMO. Objective of the task undertaken was the evaluation of neutron streaming through the DEMO blanket. Scope of the assessment was to understand the nuclear loads that would act on components inside DEMO blanket gaps, e.g. diagnostic devices or bolts accessible for Remote Handling tools through the gaps.
Work performed in 2012 (Co-operation: CCFE, CEA, IPPLM, CIEMAT, KIT, ENEA_Frascati, MHEST, HAS):
(i) This work was initiated on April 2012. Calculations were employed aiming to assess the neutron heating peaking factor due to streaming through the horizontal gaps between single blankets and streaming through the vertical gaps between adjacent multi-module segments. The revised provisional model of HCLL DEMO and a routine describing the plasma neutron source prepared under task WP12-DTM04-T02 were provided. Preliminary MCNP runs were performed. However, technical difficulties were encountered regarding the modifications of the complex DEMO geometry input file and therefore the task could not be completed within the time schedule. The work done and problems encountered are presented in ANNEX 43.
Last Updated (Thursday, 27 February 2014 14:12)