Understanding the role of helium in tritium breeder materials for fusion
Lead Research Organisation:
University of Sheffield
Department Name: Materials Science and Engineering
Abstract
The aim of this project is to determine the effect of helium on the diffusion of tritium in Li-containing ceramic materials. Li-ceramics are candidates for the tritium breeder blanket material surrounding a fusion reactor core. In the breeder blanket, tritium will be produced by the transmutation of lithium following capture of a fusion neutron. The production of tritium also results in the formation of helium atoms. Little is known experimentally about how tritium and helium will interact at predicted breeder blanket operating temperatures, specifically, whether helium atoms will trap tritium and consequently reduce tritium diffusion/extraction out of the blanket. Reduction in tritium diffusion/extraction would reduce reactor efficiency and affect the life-time of the breeder blanket.
A programme of experiments, including irradiation experiments and state of the art characterisation techniques, will be employed to determine the dependence of breeder blanket composition and microstructure on helium-tritium interactions.
A programme of experiments, including irradiation experiments and state of the art characterisation techniques, will be employed to determine the dependence of breeder blanket composition and microstructure on helium-tritium interactions.
Organisations
People |
ORCID iD |
| Amy Gandy (Primary Supervisor) | |
| Samuel Waters (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509735/1 | 01/10/2016 | 30/09/2021 | |||
| 1816101 | Studentship | EP/N509735/1 | 01/10/2016 | 25/03/2020 | Samuel Waters |
| Description | Lithium containing ceramics such as lithium metatitanate (Li2TiO3) are leading candidates for application as tritium breeder blanket materials in fusion reactors, Li2TiO3 is also used extensively as a cathode material in lithium ion batteries. We report the discovery of inherent, nanoscale vacancy-type defects in Li2TiO3 prepared by solid state synthesis (to be published in scientific literature imminently). These defects are shown to evolve into much larger voids and cavities upon thermal annealing (heating), to breeder blanket operating temperatures, this could impact both the mechanical integrity of the material, and its tritium transport properties; as far as the authors are aware, there has been no previous report of any such defects or the thermal evolution behaviour thereof. Helium is produced as a by-product of tritium production as a result of transmutation of lithium following neutron capture; In addition to the discovery examination of the thermal evolution of these inherent defects, we have demonstrated that helium accumulates significantly in Li2TiO3 at room temperature in the form of gas bubbles. The number density of helium bubbles is generally shown to increase with ion fluence, and experiments so far suggest that the extent of helium accumulation may be dependant on microstructural properties such as grain size and porosity (TBC in further experiments). There is also evidence to suggest that the presence of helium accelerates the growth of defects at elevated temperature.He implantation also appears to affect the thermal behaviour of the material, with melting-like behaviour (possibly attributable to the presence of lithium carbonate (Li2CO3), formed by surface reaction with atmospheric air under ambient conditions) observed at 600-700°C in He implanted samples. Thermal desorption spectroscopy (in which the quantities of off-gas species are measured as a function of temperature) confirms the release of CO2, peaking at temperatures correlating to the onset of void evolution and localised melting; this suggests that the decomposition of Li2CO3 may be responsible for the observed void evolution and melting-like behaviour. In a separate study there is preliminary evidence (in the form of Raman spectra and glancing angle XRD patterns of Ti+ ion implanted samples) that there may be a correlation between ceramic grain size and radiation damage resistance in Li2TiO3, the be investigated further in future experiments. There is also some evidence of crystallographic disorder in Li2TiO3 as a function of sintering temperature. This is currently being investigated using a combination of x-ray and neutron diffraction techniques and Rietveld refinement. |
| Exploitation Route | The observation of lithium carbonate formation under ambient conditions, and the discovery of inherent vacancy type defects and their thermal evolution at breeder blanket operating temperatures should be recognised and accounted for in terms of determining the material suitability of Li2TiO3 prepared by solid state synthesis for use as a breeder material and other applications. Measures should be taken to avoid the formation of unwanted secondary phases during storage and transport, and efforts should be made to understand the impact of the discovered vacancy type defects on (i) mechanical integrity and tritium transport properties in the context of ceramic breeder applications; (ii) Material properties relevant to electroceramic applications. Following further experiments to confirm the effects of ceramic microstructure and/or processing conditions on helium accumulation characteristics and radiation damage resistance, the properties of candidate ceramic breeder materials proposed for industrial application should be engineered to achieve optimum performance (i.e. minimum helium accumulation, maximum radiation damage resistance) where possible. |
| Sectors | Electronics,Energy,Manufacturing, including Industrial Biotechology,Other |