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Workreport 2008-56

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Name:

Backfilling Techniques and Materials in Underground Excavations: Potential Alternative Backfill Materials in Use in Posiva’s Spent Fuel Repository Concept

Writer:

Dixon, D. A. & Keto, P.

Language:

English

Page count:

74

Summary:

A variety of geologic media options have been proposed as being suitable for safely and permanently disposing of spent nuclear fuel or fuel reprocessing wastes.  In Finland the concept selected is construction of a deep repository in crystalline rock (Posiva 1999, 2006; SKB 1999), likely at the Olkiluoto site (Posiva 2006).  Should that site prove suitable, excavation of tunnels and several vertical shafts will be necessary.  These excavations will need to be backfilled and sealed as emplacement operations are completed and eventually all of the openings will need to be backfilled and sealed. Clay-based materials were selected after extensive review of materials options and the potential for practical implementation in a repository and work over a 30+ year period has led to the development of a number of workable clay-based backfilling options, although discussion persists as to the most suitable clay materials and placement technologies to use.  

As part of the continuous process of re-evaluating backfilling options in order to provide the best options possible, placement methods and materials that have been given less attention have been revisited.  Primary among options that were and continue to be evaluated as a potential backfill are cementitious materials. These materials were included in the list of candidate materials initially screened in the late 1970’s for use in repository backfilling. Conventional cement-based materials were quickly identified as having some serious technical limitations with respect their ability to fulfil the identified requirements of backfill. Concerns related to their ability to achieve the performance criteria defined for backfill resulted in their exclusion from large-scale use as backfill in a repository. Development of new, less chemically aggressive cementitious materials and installation technologies has resulted in their re-evaluation. Concrete and cementitious materials have and are being developed that have chemical, durability and mechanical properties that should allow their use in limited quantities in a repository (e.g. grouts, shotcrete or concrete plugs/seals). Widespread use of cemented backfill materials is still not a viable option for backfilling of Posiva’s repository although some of the technologies developed for materials placement in the mining industry have potential for repository application.

Extensive work has been done in order to identify a range of potentially suitable clay-based backfilling materials and technologies that could be used to install them in a repository environment. As a result of these efforts a suite of materials and technologies are available for backfilling of repository openings and although many have not yet been demonstrated at full-scale in an underground environment there is considerable confidence that one, or more of these options will prove suitable.

Keywords:

spent nuclear fuel, disposal, backfill, assessment, concept

File(s):

Backfilling Techniques and Materials in Underground Excavations: Potential Alternative Backfill Materials in Use in Posiva's Spent Fuel Repository Concept (pdf) (1.7 MB)


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