ASME Message

Abstracts
hydrochemical conditions at coastal sites. It is thus of great importance in the Japanese disposal programme to establish
comprehensive techniques for characterising the overall evolution of coastal sites over geological time with focus very
much on the persistence of the key safety functions throughout episodes of uplift/subsidence and climatic and sea-level
changes.
To this end, based on practical experience from the ongoing underground research laboratory projects of JAEA, a
transparent and traceable roadmap for planning and implementing a sequence of field investigations at any coastal site
has been formulated. Known as a “Geosynthesis Data Flow Diagram (GDFD)”, this system illustrates linkages between a
range of parameters, including investigations of key aspects to be addressed, interpretation of data acquired, synthesis of
the results of different studies and analyses and final clarification of the key properties and processes of the geological
environment. In particular, the GDFD defines a geosynthesis methodology for describing temporal and spatial changes of
various characteristics and processes, with particular focus on the site palaeohydrogeology.
Such a geosynthesis methodology has been introduced in an ongoing collaborative programme for characterising
the coastal geological environment around Horonobe in northern Hokkaido, Japan. A basic strategy for stepwise
investigations has been proposed, which incorporates the geosynthesis methodology in an effective manner in each step
from initial survey/review of existing information, through aerial, terrestrial and marine exploration, to the final borehole
programme. This technique has now been tested and optimised based on technical findings and experience that have been
accumulated with the progress of the investigations.
5) 40052 – Development of comprehensive techniques for coastal site characterisation: (3) Conceptualisation of
long-term geosphere evolution
Tadafumi Niizato, Kenji Amano, Kunio Ota, Takanori Kunimaru, JAEA (Japan);
Lanyon Bill, Nagra (Switzerland);
W Russell Alexander, Bedrock Geosciences (Switzerland)
A critical issue for building confidence in the long-term safety of geological disposal is to demonstrate the stability
of the geosphere, taking into account its likely future evolution. This stability is broadly defined as the persistence of
Thermal-Hydrological-Mechanical-Chemical conditions considered favourable for the long-term safety of a geological
repository. The geosphere is slowly but constantly evolving, and then the stability, in this case, does not imply that
steady-state conditions exist. What is important is that the evolution of the geosphere can be understood. In general, an
understanding of the evolution is gained by studying the palaeohydrogeological evolution of a site, defining temporal and
spatial changes of various characteristics, events, and processes over geological time. The site palaeohydrogeology refers
to natural events and processes that have occurred in the past and contributed to the present state of the geosphere, which
include sub-surface processes (e.g. crustal movement, diagenesis, etc.) and earth-surface processes (e.g. climatic and
sea-level changes, geomorphological processes, etc.). An understanding of the palaeohydrogeological evolution of the
site provides the firm foundation to describe the likely future evolution of the site. An ongoing collaborative programme
aims to establish comprehensive techniques for characterising the overall evolution of coastal sites through studying the
palaeohydrogeological evolution in the coastal system around the Horonobe area, Hokkaido, northern Japan. In this study,
the current status for the conceptualisation of the long-term geosphere evolution in the coastal area, is based on data from
the JAEA’s underground research laboratory project. Information on surface and sub-surface processes has been
integrated into a chronological conceptual model which indicates space-time sequences of the events and processes in the
area over geological time. Spatial scale for the conceptualisation is ca. 100 km in the East-West direction through the
locations of the underground research laboratory and of the borehole investigations on the coast in the Horonobe area.
Temporal conceptualisations over the last few million years are focused on the spatial and temporal changes of the
geosphere caused by sub-surface processes and over the last several hundred thousand years focused on the changes
caused by earth-surface processes. The methodology for conceptualisation of the geosphere evolution will be applied to
other analogous coastal areas on Japan’s western seaboard to produce comprehensive techniques to support
understanding the geosphere evolution of potential coastal sites for deep geological repositories.
6) 40048 – Development of Comprehensive Techniques for Coastal Site Characterisation (2) Integrated
Palaeohydrogeological Approach for Development of Site Evolution Models
Kenji Amano, Tadafumi Niizato, Hideharu Yokota, Kunio Ota, JAEA (Japan);
Bill Lanyon, Nagra (Switzerland);
W Russell Alexander, Bedrock Geosciences (Switzerland)
Radioactive waste repository designs consist of multiple safety barriers which include the waste form, the canister,
the engineered barriers and the geosphere. In many waste programmes, it is considered that the three most important
safety features provided by the geosphere are mechanical stability, favourable geochemical conditions and low
groundwater flux. To guarantee that a repository site will provide such conditions for timescales of relevance to the
safety assessment, any repository site characterisation has to not only define whether these features will function
appropriately today, but also to assess if they will remain adequate up to several thousand to hundreds of thousand years
into the future, depending on the repository type.
In general, this is done by studying the palaeoKHNPgeological evolution of a site, defining temporal and spatial
changes of various characteristics and processes. These may include hydrogeology, geology, groundwater flow
-87-