Modeling internal deformation of salt structures targeted for radioactive waste disposal

Notícia | 05-03-2014

A càrrec de: Zurab Chemia
Department of Geosciences and Natural Resource Management,
Universitat de Copenhaguen, Dinamarca

Dia: Dimecres 5 de març
Hora: 11:00 h
Lloc: Sala d'actes de l'Institut Jaume Almera

Systematic numerical models are used to argue that externally inactive salt structures, which are potential targets for radioactive waste disposal, might be internally active due to the presence of dense layers or blocks within a salt layer. Gorleben salt diapir (NW Germany), which was targeted as a future final repository for high-grade radioactive waste is used as a general guideline in studies of the parameters that control the development of a salt diapir and how it entrains a dense inclusion. Results from these numerical models show that in order to assess the potential importance of sinking or mobility of entrained blocks within a diapir, it is important to understand how a dense layer was initially entrained into a diapir. Two time-scales have to be considered: the time scale of diapiric growth t1 (e.g. by down-building) and the time scale of sinking of the blocks, t2. Keeping all material parameters the same, entrainment of dense blocks requires that t1 < t2, i.e. during diapiric rise, the blocks do not sink faster than the diapir grows. The time scale of the diapiric growth (t1) is governed by four main parameters (sedimentation rate, salt viscosity, perturbation width and stratigraphic location of dense layer. The time scale of sinking of dense blocks (t2), which controls the mobility of the blocks, depends on salt viscosity. If the effective viscosity of salt falls below the threshold value of around 1018-1019 Pa s, the mobility of embedded blocks might influence any repository within a diaper. Thus, the mobility of dense blocks strongly depends on redistribution of stresses at boundary between salt rocks with distinctly different creep properties