Scientific basis of the nuclear fuel cycle IV

Introduction and scope:

Nuclear fuel cycle materials are studied for under demanding temperature, pressure and irradiation environments. These materials act as barriers and their properties are investigated with emphasis on mechanical performances, durability, plasticity and stability. Symposium includes sessions dealing with energy vector materials or processes ranging from fuels for thermal or fast reactors, their analysis after irradiation, their reprocessing for recycling and the waste forms. Macro-properties such as thermodynamic, thermophysical and mechanical as well as microstructural analysis of these materials are discussed for example comparing properties prior and after irradiation.

The nuclear fuel cycle includes materials that enable the nuclear energy vector to be used after conversion from heat to electricity and proceeds through processes that allow fuels to be reused after reprocessing and recycling. Fuel materials include oxides, nitrides, carbides or metals in homogeneous form or as composites such as cercer, cermet or metmet that can be used either as fuel or as target for transmutation. Currently the main challenge for fuel studies is to deliver the basis for the scientific understanding of fundamental properties, mainly at the atomic and microstructural level, which determine the evolution of macroscopic properties during irradiation. It is needed to develop predictive tools (models, codes) which allow optimizing the effort for the development of safe and innovative fuel concepts.

The FUEL PROPERTIES session aim at introducing the research for fuel production optimization prior to irradiation.Accident Tolerant Fuel (ATF) includes both cladding specific material and fuel meat targeting lower reactivity between fuel assemblies and water. The cladding concerns coating for zirconium cladding or silicon carbide cladding development. Other cladding concepts such as hybrid designs (SiC protected Zircalloy cladding) or other high temperature material are also studied together with cladding – pellet chemical interactions. Synthesis and characterization of specific fuel starting material such as uranium nitride and silicide powder as pellets and composites, including conventional and advanced processes. Thermal dynamic calculations for investigating routes to fabricate uranium nitride and silicide from hexafluoride are performed together with the study of reactions between these fuels and air or steam. Others high density fuel manufacturing and characterization are also discussed. A specific ATF discussion is foreseen. Post-Irradiation Examination (PIE) provides most valuable data to assess the safety of nuclear fuel and materials during in-pile irradiation. During its operational life, nuclear fuel must retain its function within adequate safety margins while being subjected to lattice alteration due to neutron and fission damage, compositional change due to the accumulation of fission products, significant temperature gradients and mechanical constraint conditions. Relevant fuel properties affecting thermal transport efficiency as well as chemical and mechanical integrity can be investigated by PIE techniques carried out in shielded facilities. In the past, systematic irradiation campaigns followed by PIE have established the basis for the safe operation of commercial nuclear reactors worldwide.

The FUEL POST IRRADIATION EXAMINATION session aims at providing an overview of advanced PIE tools and procedures available, and of the main achievements obtained or expected by applying such techniques.For optimal performance of the nuclear fuel cycle reprocessing and recycling is a must prior reuse of the fissile vectors. After then success of PUREX process other partitioning techniques have been profiled to also make use of the actinides as potential fertile elements, and to reduce by re-irradiation the radiotoxicity of the final waste material. The partitioning and transmutation approach allows utilization of the actinides. This process is the topic of an important R&D challenge that could yield to a strong reduction of neptunium, americium or curium in dedicated transmutation units or in thermal or fast reactors.

The REPROCESSING session will address these key issues opening the strategy from single to multi-recycling based on the partitioning and transmutation strategies. The disposal of high-level nuclear waste in deep geological formations poses major scientific and social challenges to be met in the next decades. One of the key issues is related to the long term safety of a waste repository system over extended periods of time (up to 10⁶ years). Innovative waste forms in particular regarding actinide elements and some long-lived fission and activation products can help to improve this long-term safety aspect of deep geological disposal. Some of the relevant materials have been studied for several decades and have clearly demonstrated some of their superior properties. Furthermore, recent publications clearly show exciting and unexpected results. Also, new materials have been discovered in recent years to have very promising properties - such as murataite.

The WASTE FORM session is intended to provide an overview of recent advances and developments in related research areas including new synthesis routes, radiation damage and related structure - property relations as well as performance under repository conditions using both, experimental as well as computational approaches.

Hot topics to be covered by the symposium:

• New challenges
• Fissile: Green Fuel production
• Fuels: Accident Tolerant Fuels
• Waste: from Wet to Dry Storage
• Cycles: sustainable aspects.

Tentative list of invited speakers:

• Rod Ewing Professor in the Department of Geological and Environmental Sciences in the School of Earth Sciences at Stanford University. rewing1@stanford.edu
• Melisa Denecke, Professor and co-director Dalton Nuclear Institute, The University of Manchester. melissa.denecke@manchester.ac.uk
• Sergey Stepanovsky, Physical Institute of the Russian Academy of Sciences RAS Moscow. serge.stefanovsky@yandex.ru
• Eugene Kotomin, Institute of Solid State Physics, Latvian State University, Riga. kotomin@latnet.lv
• Peng Xu, Westinghouse Electric Company, Vasteros, Sweden. xup@westinghouse.com
• Malcolm Joyce, Nuclear Engineering, Head of the Engineering Department, Lancaster University, UK. m.joyce@lancaster.ac.uk
• Motoyasu Kinoshita, vice president of the International Thorium Molten Salt Forum, Uni Tokyo. moto@butsuri.net
• Gu Long, Director Institute of Modern Physics, Lanzhou, China. Gulong@impcas.ac.cn
• Grzegorz Wrochna, Director, National Centre for Nuclear Research, Swierk, Poland. G.Wrochna@ncbj.gov.pl
• Urszula Woźnicka, Institute of Nuclear Physics, Kraków. Urszula.Woznicka@ifj.edu.pl
• Horváth Ákos, Centre for Energz Research, Budapest, Hungary. akos.horvath@energia.mta.hu
• Jan Uhlir, Research Centre Rez, Czech Republic. jan.uhlir@cvrez.cz
• Ville Tulkki, VTT, Finland. ville.tulkki@vtt.fi
• Olivia Roth, Studsvik, Sweden. olivia.roth@studsvik.se
• Thierry Wiss, ITU, JRC, Karlsruhe, Germany. thierry.wiss@ec.europa.eu
• Manuel Pouchon, Head of LNM, PSI, Villigen, Switzerland. manuel.pouchon@psi.ch