Underground Storage - Hydrogeology: Objectives, Methods, Applications - page 305

LLFPs making up category C are vitrifi ed and cooled for approximately 50
years while awaiting their fi nal underground storage site, but other waste
products are generated by their treatment (cement and concrete), which
also await a fi nal storage location. The total volume for 2030 is estimated
at 95,000 m 3 . In most countries, deep geological repositories are being
considered, in deep geologic structures far from tectonically active zones.
The two sought-after characteristics are the absence of risk of accidental
human intrusion in the future, and the absence of water circulation. This
therefore implies a precise understanding of the hydrogeologic mechanisms
of potential sites.
The waste is stabilized and placed in a container; the whole makes up
a package which must obey very strict standards in order to allow its long-
term storage. The goal of burial is to create a subterranean barrier around
the containers. At least one of the elements of the packaging-constructed
barrier-geologic formation system must remain stable for thousands of
years. However, no one today can predict the interaction of groundwater
with the containment systems over such a length of time. Geothermal sites
and the discovery in Oklo (Gabon) of natural nuclear reactors 2 billion years
old fortunately offer natural laboratories under study, which can provide
nuclear storage site designers with inspiration (Alexandre, 1997).
2.2 Hydrogeologic context of storage sites
2.2.1 Surface storage
The waste must be deposited on a draining formation, above an aquifer that
is blocked at depth by a perfectly impermeable substratum, with no risk
of the aquifer reemerging at the surface. The aquifer must have a single,
well-understood outlet, in order to enable water quality monitoring.
The Aube site is set up in Soulaynes Dhuys on Albo-Aptian sand, above
the impermeable clays of the Upper Aptian.
2.2.2 Burial
On the global scale, no site is yet operational, and laboratories are currently
studying the feasibility of storage (Table 23). The sites must follow the
following constraints:
• lack of valuable resources below ground,
• absence of any water circulation,