Euradwaste '08 - EU Bookshop - Europa

Summary
NF-PRO – Mechanical and permeability properties
of highly pre-compacted granular salt bricks
Klaus Salzer, Till Popp, Heinz Böhnel
Institut für Gebirgsmechanik GmbH Leipzig (IfG), Germany
In the salt concept for the disposal of high level radioactive waste in deep geological rock
formations granular salt is the favorite for backfilling of remaining openings because of its
advantageous physical properties. However, its initial sealing capacity is low due to the high
porosity. Besides others, the usage of pre-compacted blocks of crushed salt offers an alternative
sealing concept. Our investigations are aiming to investigate both the mechanical compaction
behaviour and the evolution of transport properties in salt bricks (artificial pressed
granular salt with a porosity of ~8%), as a prerequisite to develop mechanism-based constitutive
models describing these processes in the low porosity region (10 - 1%). A key factor is
the role of water, since it affects in a complex manner the coupled hydraulical/mechanical
properties of granular salt.
1. Introduction
In the salt concept for the disposal of high level radioactive waste in deep geological rock formations
granular salt is the favourite for backfilling of remaining openings because of its advantageous
physical properties because (1) it has good compacting properties, (2) its thermal and mechanical
properties after compaction are similar to the surrounding rock salt, and (3) it is easy available.
Nevertheless a limiting factor for the use of backfill saliferous granulates is their initially high porosity
and permeability, resulting in a low sealing capacity and mechanical integrity just after emplacement.
In the framework of NF-PRO considerable efforts have been obtained regarding the
knowledge about compaction of granular salt, not only with respect to the acting fundamental densification
processes but also to improve its compaction behaviour.
Besides adding bentonite to enhance compaction and to reduce permeability, an alternative concept
is the use of pre-compacted salt stones, e.g. bricks, which are characterized by porosities