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A New Approach to the RN Source Term for Spent Nuclear Fuel under Geological Disposal Conditions

Published online by Cambridge University Press:  21 March 2011

Christophe Poinssot ,
Christophe Jegou ,
Pierre Toulhoat ,
Jean-Paul Piron  and
Jean-Marie Gras
Christophe Poinssot
Affiliation:
Commissariat à l'Energie Atomique CEA, Fuel Cycle Division, Department for Waste Storage and Disposal, CEA-Saclay, BP11, F-91191 Gif-sur-Yvette Cedex
Christophe Jegou
Affiliation:
Commissariat à l'Energie Atomique CEA, Fuel Cycle Division, Department for Reprocessing and Vitrification, CEA-Marcoule, BP171 30207 Bagnols sur Cèze
Pierre Toulhoat
Affiliation:
Commissariat à l'Energie Atomique CEA, Fuel Cycle Division, Department for Waste Storage and Disposal, CEA-Saclay, BP11, F-91191 Gif-sur-Yvette Cedex
Jean-Paul Piron
Affiliation:
Commissariat à l'Energie Atomique CEA, Nuclear Reactor Division, Department for Fuel Studies, CEA-Cadarache, 13107 Saint Paul lez Durance
Jean-Marie Gras
Affiliation:
Electricité de France EDF, R&D Division, EDF, Les Renardières, Route de Sens, F-77250 Moret-sur-Loing, France
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Abstract

Under the geological disposal conditions, spent fuel (SF) is expected to evolve during the 10,000 years while being maintained isolated from the biosphere before coming in contact with water. Under these circumstances, several driving forces would lead to the progressive intrinsic transformations within the rod which would modify the subsequent release of radionuclides. The major mechanisms are the production of a significant volume of He within the UO2 lattice, the accumulation of irradiation defects due to the low temperature which avoids any annealing, the slow migration of radionuclides (RN) within the system by (i) the α self-irradiation-induced athermal diffusion and (ii) locally the building-up of internal mechanical stresses which could turn the pellets into powder. However, the current RN source terms for SF have never accounted for this evolution as they are based on existing knowledge of the fresh SF. Two major mechanisms were considered, the leaching of the readily available fraction (one which was supposed to be instantly accessible to water), and the release of RN through alteration of the UO2 grains. We are now proposing a new RN source term model based on a microscopic description of the system in order to also take account of the early evolution of the closed system, the amplitude of which increases with the burnup and is greater for MOX fuels.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 469
Copyright
Copyright © Materials Research Society 2001

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References

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