Disposal of Radioactive Waste

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.
 

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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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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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.

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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.

Overview of Deep Geolgical Disposal - click for larger image

Emplacement tunnels - click for larger image

Pilot tunnels - click for larger image

Underground rock laboratory area - click for larger image

Access ramp - click for larger image

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

Different types of radioactive waste and their sources in Switzerland

The Nuclear Energy Ordinance in Switzerland distinguishes the following categories of waste.

Art. 51 Categories of radioactive waste
For the purpose of disposal, radioactive waste is divided into the following categories:
 

• high-level waste (HLW):
  • spent fuel (SF) not destined for reprocessing;
  • vitrified fission product solutions from reprocessing of spent fuel;
• alpha-toxic waste (ATW): waste with a content of alpha-emitters exceeding a value of 20,000 Becquerels per gram of conditioned waste;
• low- and intemediate-level waste (L/ILW): all other radioactive waste.

For disposal, Nagra allocates the waste to different repository types:







Deep geological repository for HLW/SF for spent fuel and vitrified fission product solutions from reprocessing.

Deep geological repository for low- and intermediate-level waste (L/ILW). 

Radioactive waste materials are generated from medicine, industry, research and power generation.

We consume raw materials and energy on a daily basis. This produces gaseous, liquid and solid wastes. Some of this waste can be recycled and the remainder has to be disposed of safely. Respect for the environment, mankind and biota demands that we find and implement waste management solutions. Radioactive wastes have to be isolated from the human environment for the duration of their toxicity and managed safely. Carefully implemented procedures and proper practices can ensure that no adverse effects will result.

Different types of radioactive waste and their sources in Switzerland

Based on current understanding, many countries, including Switzerland, have concluded that deep geological disposal is the only method for managing radioactive waste that meets the strict requirements relating to long-term safety. Concepts in which safety relies on continuous monitoring by human institutions are not capable of fulfilling these requirements, for long times.

Underground laboratories (URLs), such as Grimsel,  serve an important role in the overall investigation into the long-term disposal of radioactive waste. Together with site-specific tests, laboratory studies and studies of natural analogues, they can assist in developing rigorous databases for the assessment of long-term safety and engineering feasibility of proposed disposal concepts.

The Swiss Federal Council and Parliament have decided that all waste arising in Switzerland will undergo deep geological disposal.