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Engineered Barriers and Their Interaction with Rock
3.1 Engineered Barriers The multibarrier principle has been used by all the Organizations in designing their HLW concepts since the redundance gives an apparent and partially true back-up of the safety, which is basically the ratio of the allowed and predicted concentrations of major long-lived radionuclides in wells with drinking water. The barriers are: 1. 2. 3. 4.
The waste itself (“HLW”) Containers of metal in which the waste is confined (“canisters”) Low-permeable clay embedding the containers (“buffer”) Seals and fills in holes and tunnels (“plugs and backfills”)
The waste has a very low solubility and hence offers resistance to release of radionuclides. The canisters can be made of chemically very stable material and be made tight by appropriate closure. The low-permeable clay minimizes percolation of groundwater and offers ductile environment of the canisters and hence moderation of the impact of external forces. The plugs serve to separate permeable and tight backfills in holes and tunnels. We will examine the four barriers here, focusing on the three firstmentioned and their mutual interaction and leaving the last one to be treated in greater detail in the next chapter.
3.2 HLW The international Atomic Energy Agency (IAEA) has defined five categories with respect to final disposal as given by Table 3.1. The international committee for radiation protection (ICRP), which introduced the ALARA principle implying that all radiation doses shall be kept as “low as reasonably achievable” with respect to economic considerations and to society, has defined a number of criteria concerning exposure of the whole body or part of it to radiation. National radiation protection R. Pusch, Geological Storage of Highly Radioactive Waste, C Springer-Verlag Berlin Heidelberg 2008 DOI: 10.1007/978-3-540-77333-7 4,
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3 Engineered Barriers and Their Interaction with Rock
Table 3.1 Definition of radioactive waste for final disposal Waste classes
Typical characteristics
Disposal options
1. Exempt waste (EW)
Activitiy levels at or below clearance levels representing an annual dose of members of the public of less than 0.01 mSv Activity levels above clearance levels as for 1) and thermal power below about 2 kW/m3 Restricted long-lived radionuclide concentrations Long-lived radionuclide concentrations exceeding limitations for short-lived waste Thermal power above about 2 kW/m3 and long-lived radionuclide concentrations exceeding limitations for short-lived waste
No radiological restrictions
2. Low and intermediate waste (LILW) 2.1 Short-lived waste (LILW-SL) 2.2 Long-lived waste (LILW-LL)
3. High-level waste
No radiological restrictions
Near surface or geological disposal facility Geological disposal facility
Geological disposal facility
IAEA Safety Guide, Classification of radioactive Waste, Safety series No. 111-G-1.1, Vienna (1994).
requirements are established for purposes broader than radioactive waste management. In the establishment of acceptable le
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