Imperial College London
Job Description
Job Title: Research Associate in Modelling Behaviour of Wastes and Wasteforms from the Clean-up at Fukushima
Department: Department of Materials
Faculty: Faculty of Engineering
Job Family/Level: Academic and Research Job Family, Level B,
Contract: Fixed term appointment for up to 24 months
Location: South Kensington Campus
Responsible to: Dr Luc Vandeperre and Professor Bill Lee
Liaison with: Academics, Research Staff and Postgraduate Students
Key Working Relationships: Collaborators and colleagues internally and externally
Summary of the post:
The Research Associate will join an EPSRC-funded project (Advanced Waste Management Strategies for High Dose Spent Absorbents [HDSA]) that aims to improve the passive safety of HDSA wasteforms to assure prolonged near surface storage and disposal in an engineered facility. The post holder will be hosted by the research groups of Dr. Luc Vandeperre and Professor Bill Lee, shared between the Centre of Nuclear Engineering (http://www3.imperial.ac.uk/nuclearengineering) and the Centre for Advanced Structural Ceramics (http://www3.imperial.ac.uk/structuralceramics), both belonging to Imperial’s Department of Materials. He/she will closely collaborate with groups at: The Immobilisation Science Laboratory at the University of Sheffield (UoS, under Prof. Neil Hyatt and including Prof. Russell Hand and Dr’s Claire Corkhill and Martin Stennett), Kyushu University (Prof’s. Yaohiro Inagaki and Tatsumi Arima) and Tohoku University in Japan (Prof’s. Nobuaki Sato, Daisuke Akiyama and Akira Kirishima). As detailed below, the main responsibility is to develop a finite element model to quantify the thermal output of untreated and processed HDSA’s, which will be used to underpin assessment of wasteform storage and disposal; this model will also be used to assess the feasibility of utilising the radionuclide decay heat to drive HDSA self vitrification.
Work Package Description:
As part of an ongoing collaboration with Hitachi Ltd. on treatment of HDSAs, low temperature processing routes for alternative wasteforms are under investigation. This is considered beneficial due to the presence of Cs and Sr species that are volatile at high temperature. A glass composite material (GCM) wasteform, composed of a low melting temperature lead borosilicate or borate glass frit, has been validated for model zeolitic ion exchange encapsulation. One PhD student at Imperial is currently developing and optimising the wasteform and its processing. Because Cs and Sr have relatively short half-lives, the long-term durability of the wasteform is not as critical as typical High Level Waste applications; nevertheless, it is important to have sufficient data on the dissolution kinetics and mechanism, to underpin disposability. It is planned for a second PhD student to ascertain the long term durability of the wasteforms.
Since the lead borosilicate/borate glass can be sintered at relatively low temperatures, there is the potential that sintering could be auto-induced by the heat developing in the wasteform. This requires a careful balance of the heat generated and thermal conductivity as a function of time to ensure that, once densified, the wasteform could cool to below the glass transition temperature, avoiding a viscous wasteform. Moreover, temperature changes over time in wasteforms with non-negligible heat generation could lead to important thermal stresses and cracking at interfaces, thereby reducing the transport of heat and potentially leading to localised hot spots and severe deterioration. Within this project, the ongoing effort at Imperial, and the work proposed by the UoS, will be enhanced and expanded by the development of modelling tools capable of predicting the effect of radioactive decay on the temperature profiles of the wasteforms. This will also assist container design, so that heat extraction can be enhanced to limit wasteform core temperature. We will identify and quantify potential physical alterations to the wasteform as a consequence of the long term heat exposure, as well as aiming to model the physical processes of densification and crystallisation. Relatively easy-to-use tools for incorporation in commercial finite element software packages, which are also highly adaptable in terms of the radionuclide loading and the wasteform materials, will ensure their wider application e.g. in the UK’s clean-up of Sellafield.
Radiolytic heat generation tool. We will implement a database and algorithm to calculate the heat generation of the encapsulated radionuclides as a function of time. Using existing information on the heat released and the species generated during radioactive decay, we will determine values for volumetric heat generation in the finite element calculation. Although the radioactive decay chains of Sr and Cs are relatively simple, it is still necessary to understand the reduction in heat generated. Moreover, the tool will be populated with other radionuclides that might be present in limited amounts to create a generally useful tool.
Implementation of radiolytic heat in temperature distribution calculations for final state wasteforms. The next stage in the development of the tool will be to assume that the wasteform has reached a stable physical state at the onset of the calculations, e.g. a fully sintered glass-ceramic composite or a hot pressed product. Using the tool generated, material data for thermal conductivity, heat capacity, stiffness and density generated by the active PhD researchers at Imperial and the UoS PDRA, and by conducting key experiments to determine valid boundary conditions for heat exchange with environment and containers, a parametric study will be conducted to determine the effect of wasteform shape and size on the evolution of stress and temperature distributions in the wasteforms to ensure efficient design of waste packages. The benefits of higher outer surface area containers and convection on centre line temperatures will also be considered. Predictions will be validated against experimental data obtained from real encapsulated systems or from experiments in which microwaves are used to simulate volumetric heating caused by radiolytic decay at Hitachi. The latter will be carried out while on a short secondment to Japan to ensure maximum benefit of the calculations for the experiments and vice versa.
Implementation of damage predictions for the wasteforms. A key outcome of the predictions under the task above should be an ability to determine the stresses acting on the wasteform, both from containment by the waste containers as well as from temperature differences in the wasteform. Such stresses may be substantial and lead to separation between the container and the wasteform and the formation of internal cracks. Such changes may also affect the heat extraction from the wasteforms and initiate a series of events through which the entire wasteform degrades to an extensively fractured, powdered form. To account for this, failure mechanisms will be incorporated in the description so that their effect can be predicted.
Development of predictive tool for processing of glass ceramic wasteforms containing HDSAs. One of the key innovative aspects of the GCM is that the heat released from radioactive decay may be sufficient to transform the wasteform from HDSA encapsulated in glass frit, to a dense glass ceramic composite without further treatment. This requires that (i) the heat generated is sufficient to heat the glass above its glass transition temperature, Tg, allowing it to sinter and (ii) that once densified, heat loss by thermal conduction to the environment becomes sufficient to allow the glass to cool to below Tg. Since the heat generated over time decays, eventually the glass will cool sufficiently; it is important to understand at which stage of the wasteform lifetime this is likely to occur, to inform design and allow the development of methodologies to influence this decay. The aim of this phase of the research is therefore to model the sintering and crystallisation of the waste form and the resulting changes in thermo-mechanical and thermo-physical properties. This will be carried out in bespoke routines coupled to commercial finite element software via updating of the properties using representative volumes.
Data generation for prediction of processing of GCM wasteforms. Although to some extent literature information on the effect of porosity on mechanical and thermal properties can be used to generate generic descriptions of the sintering, crystallisation is always highly system-specific and can be influenced by the presence of otherwise inert phases (e.g. the effect of fibres on the crystallisation of glass-ceramic matrices). Hence a range of measurements on the properties and evolution of crystallisation during densification are required.
Key Responsibilities:
· To readily and autonomously implement database and algorithm to calculate decay heat from immobilised radionuclides; develop finite element models to calculate heat generation by conceptual waste packages; elaborate in parametric study effect of waste package dimensions on evolution of stress and temperature distributions.
· To investigate effect of temperature gradients on waste package thermal stresses and potential failure scenarios; use model to evaluate feasibility of self vitrification using HDSA radiogenic decay heat and glass encapsulant; investigate glass crystallisation kinetics to assist refinement of heat flux model.
· To respect as much as possible deliverable dates and keep collaborators informed of your progress.
· To analyse results, determine their scientific meaning, and disseminate them through journal publications, conference presentations and research sponsors and collaborators – both informally and formally.
· To maintain accurate and complete records of all experiments and calculations.
· To actively participate in project meetings and liaise when appropriate with the project industrial sponsors.
· To travel, when appropriate, in the UK, to Japan or elsewhere to attend international conferences and present research results.
· To ensure the validity and reliability of data at all times.
· To engage proactively with the other project researchers.
· To monitor new progress published in the open literature in the field of the project.
Other Duties:
· To assist in the supervision of MSc and PhD students.
· To undertake appropriate administration tasks.
· To maintain safe workplace practice and procedures in accordance with the requirements of Health and Safety legislation.
· To maintain up-to-date knowledge of relevant statutory Health and Safety legislation as well as recommendations and attend safety training as required.
· Any other duties commensurate with the grade of the post as directed by line manager / supervisor.
· To develop contacts and research collaborations within the College and the wider community.
· To take responsibility for organising resources and effective decision making in support of research.
· To contribute to the Department’s teaching activities up to approximately half a day per week during the academic year, as appropriate.
· To undertake any necessary or useful training and/or development.
To observe and comply with all College policies and regulations, including the key policies and procedures on Confidentiality, Conflict of Interest, Data Protection, Equal Opportunities, Financial Regulations, Health and Safety, Imperial Expectations (for new leaders, managers and supervisors), Information Technology, Private Engagements and Register of Interests, and Smoking.
To undertake specific safety responsibilities relevant to individual roles, as set out on the College Website Health and Safety Structure and Responsibilities page (http://www3.imperial.ac.uk/safety/policies/organisationandarrangements).
Job descriptions cannot be exhaustive and the post-holder may be required to undertake other duties, which are broadly in line with the above key responsibilities.
Imperial College is committed to equality of opportunity and to eliminating discrimination. All employees are expected to adhere to the principles set out in its Equal Opportunities in Employment Policy, Promoting Race Equality Policy and all other relevant guidance/practice frameworks.
Person Specification
Applicants are required to demonstrate that they possess the following attributes:
Imperial Expectations
These are the 7 principles that Imperial leaders, managers and supervisors are expected to follow:
1. Champion a positive approach to change and opportunity
2. Communicate regularly and effectively within, and across, teams
3. Consider the thoughts and expectations of others
4. Deliver positive outcomes
5. Encourage inclusive participation and eliminate discrimination
6. Support and develop staff to optimise talent
7. Work in a planned and managed way
Education and Qualifications:
· A PhD degree (or equivalent) in an area pertinent to the research subject, e.g. Physics and/or Chemistry of Materials.
Knowledge or Experience:
Essential:
· Research, as evidenced by peer-reviewed journal publications.
· Experience of communicating research in English (international conference oral presentations).
· Experience of multi-scale modelling including finite element methods.
· Understanding of microstructural development in materials systems.
· Understanding of materials thermo-mechanical behaviour.
Desirable:
· Experience of multiphase materials systems.
· Experience of the nuclear sector and/or radionclude behaviour.
· Glass/ceramic processing and simple thermal and/or mechanical properties measurements.
· Experience of student supervision.
· Experience of working with experimental and theoretical materials scientists.
Skills and Abilities
· Good written communication skills and the ability to write scientifically, clearly and succinctly for publication in English.
· Excellent verbal communication skills
· Ability to relate to other researchers and students in an academic context, together with industrial collaborators and funders and work as part of a team.
· Ability to organise and prioritise own work.
· Ability to work with minimal supervision and as a part of a research team.
· Ability to interact successfully with others and to learn new skills.
· Ability and willingness to share knowledge with co-workers.
· Independent ability to perform lattice parameter refinement or willingness to attend a dedicated course.
· Good organisational and multi-tasking abilities
· Ability to exercise initiative and judgment in carrying out research tasks
Personal Attributes:
· Willingness to undertake any necessary training for the role
· Willingness to work as part of a team and to be open-minded and cooperative
· Willingness to travel both within the United Kingdom and abroad to conduct research and attend conferences
· An open, flexible and positive approach to working in a constantly changing environment