Disposal of Radioactive Waste

Grimsel's Role in Research

Its all very well to design a waste disposal system - but how do you know that it will work ?

This is where the Grimsel Test Site (GTS) comes in - with experiments to test the long term behaviour of the engineered barriers, to develop and test tools to confirm the suitability of potential geological host rocks and to test the models used to predict its performance as a long-term barrier to radionuclide release.

Many countries have plans for repositories but in order to ensure that their designs will work, they need somewhere to test out their concepts for safe waste disposal.

 
GMT Silo

These tests should be carried out in similar conditions to a repository. The GTS is a research facility several hundred metres underground which provides a relevant environment for equipment, methodology and model tests.

 
Febex bentonite backfill
The GTS is a scientific test site and not a potential repository site; although investigations may utilise a wide range of radioactive tracers, no radioactive waste will be disposed of at the GTS.

All experiments utilising a radioactive tracer are supervised by a Radiation Protection Expert (RPE) and follow very strict regulations which were set by HSK (Hauptabteilung für die Sicherheit der Kernanlagen / Swiss Federal Nuclear Safety Inspectorate - now ENSI ) and continues with BAG (Bundesamt für Gesundheit / Swiss Federal Office of Public Health). Click here for details.

Safety Barriers

A multi-barrier approach ensures the long-term isolation of radioactive waste and is the adopted solution of preference for radioactive waste management. The Engineered Barrier System (EBS) is one part of this passive multi-barrier system approach and it refers to all barriers introduced through technological (engineered) activities. It is complemented by the natural barrier, also referred to as the geological barrier or geosphere.
 

 Components of the EBS for High Level Waste (HLW) and Spent Fuel (SF)

In a deep geological repository, safe long-term containment of the waste is provided by a system consisting of three engineered barriers and one geological barrier.

In the case of spent fuel, the cladding containing the uranium pellets represents the first engineered barrier. Packaged in thick-walled metal containers (second engineered barrier), the fuel elements are placed on a bentonite plinth in the disposal tunnel and the entire tunnel is backfilled with bentonite granulate (third engineered barrier). Together with the overlying formations, the host rock forms the geological barrier.

High-level fission product solutions from reprocessing are immobilised in a glass matrix that corrodes extremely slowly. The metal containers and the bentonite backfill again represent the other two engineered barriers

The Grimsel Full-scale Engineered Barriers Experiment (FEBEX) project has been examining the emplacement of a steel canister within a bentonite backfilled tunnel. A more detailed overview from the Swiss approach is shown below:

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 Components of the EBS for Low/Intermediate Level Waste (L/ILW)

The repository for low- and intermediate-level waste has four different safety barriers - three engineered and one geological.

The waste is solidified in a matrix and enclosed in drums (first engineered barrier).

Several of these drums are placed in a concrete container which is filled with cement (second engineered barrier).

The concrete containers are stacked on top of and adjacent to one another in large caverns and the spaces between the containers are backfilled with a special mortar (third engineered barrier).

Together with the overlying formations, the host rock forms the geological barrier.

As the EBS for L/ILW waste is constructed mostly from concrete, the effect of such a large cementitous mass on the rock and water systems is being investigated directly by in situ Grimsel projects such as Gas Migration in EBS and Geosphere (GMT), Hyperalkaline Plume in Fractured Rock (HPF) and Long-Term Cement Studies (LCS).

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Deep geological disposal - Far field

A series of emplacement tunnels will be constructed deep underground to house the HLW and SF canisters. An example layout for a SF/HLW repository and an operational study (surface facilities, emplacement tunnels, pilot tunnels, rock laboratory, access ramp, ventilation tower, etc.) has been developed by Nagra.

{flv width="550" height="340" usefullscreen="true" img="videos/HLW_overview_thumb.jpg"}Overview{/flv}

Video overview of a possible tunnel layout for a SF/HLW repository, designed for a sedimentary formation

The images below are stills taken from the Nagra Die LÖSUNG DVD which outlines the procedures and methods for the remote emplacement of a HLW / spent fuel canister.  Please see the Media & Downloads section for additional videos on geological emplacement.

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Overview of Deep Geolgical Disposal - click for larger image

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Emplacement tunnels - click for larger image

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Pilot tunnels - click for larger image

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Underground rock laboratory area - click for larger image

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Access ramp - click for larger image

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Repository situated at a depth ~600m - click for larger image

 

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.
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