Spalling in a field experiment of heated boreholes in hard rock

摘要

The process of thermally-induced spalling in deposition holes for spent nuclear fuel may impact the safety of a repository if a continuous damaged zone is developed along the hole. To improve the understanding of the spalling process and examine the possibilities of reducing its impact on the safety of a repository, Swedish Nuclear Fuel andWaste Management has carried out a large field experiment during 2008-2009. The field experiment was conducted to investigate if the counterforce obtained by application of dry bentonite pellets could be sufficient to suppress thermally-induced spalling. The experiment included in total eight boreholes that were heated in a series of demonstration tests. The paper discusses the observed results of the spalling strength and its dependence on the geology and mechanical conditions of the rock. The positive effect of a small confining pressure on limiting the hydraulic conductivity of the spalled zone is also reported.