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DISPOSAL OF CONDITIONED HLW AND LONG LIVED WASTE IN A CLAY FORMATION. DEVELOPMENT OF EFFECTIVE CONCEPTS FOR ATTENUATING THE NEAR FIELD EFFECTS OF HLW IN ARGILLACEOUS ROCKS.

Objective

IN THE EARLIER DESIGNS AND CONCEPT DEVELOPMENTS OF MINED REPOSITORIES OF HLW IN ARGILLACEOUS FORMATIONS, THE MAIN POST-CLOSURE FUNCTIONS OF THE BACKFILLING OF DISPOSAL GALLERIES ARE TO PROVIDE MECHANICAL STABILITY OF THE SYSTEM AND TO OBSTRUCT PREFERENTIAL PATHWAYS FOR RADIONUCLIDE RELEASE.
IN THE RECENT YEARS REALISTIC AND ACTUAL DATA ABOUT WASTE CHARACTERISTICS, WASTE ARISINGS AND POTENTIALLY FAVOURABLE ARGILLACEOUS FORMATION BECOMING AVAILABLE, AND ALSO IN VIEW OPTIMIZATION A NEED ARISES TO DEVELOP MORE SPECIFIC CONCEPTS WHICH PROVIDE A LIMITATION OF THE NEAR-FIELD EFFECTS AND THUS IMPROVE THE PERFORMANCES OF THE INDIVIDUAL STRUCTURAL AND BARRIERS COMPONENTS.
THE AIM OF THE STUDY IS TO DEVELOP BACKFILLING CONCEPTS SPECIFIC FOR MINED REPOSITORIES IN A STRATIFORM ARGILLACEOUS FORMATION, WHICH ALSO PARTICIPATE IN THE ATTENUATION OF THE EFFECTS OF HEAT RELEASE, RADIATION, OXIDATION, WETTING AND CORROSION, AND PROVIDE ALL AT THE SAME TIME MECHANICAL STABILITY, CHEMICAL COMPATIBILITY AND EMPLACEMENT FEASIBILITY.
A test design has been developed for determining the in situ permeability of an argillaceous formation (Boom clay) on a large scale.
The proposal is an in situ macropermeability test with a set up comprising a central borehole (metric scale in length) designed as to allow various types of control of the water level, surrounded by a lattice of piezometers installed in the clay mass for the monitoring of the interstitial water pressure changes in function of the various water level controls.

3 measuring series may be distinguished:
measurement (from the moment of filter installation onwards) of the rise of water level in the filter as a function of time;
a measurement involving closing the filter, or part of it, with a packer for instance and putting a sudden pressure on the closed part;
a variation on the previous test which consists of maintaining theclosed filter part under constant pressure and measuring the inflowing water volume.

On the basis of theoretical developments a feasible test set up has been developed allowing the performance of 3 different hydraulic tests in view of determining the local hydraulic conductivity of the Boom clay. The basis for it is derived essentially from the methods for hydraulic testing of low permeability formations as developed by Bredehoeft and Papadopulos (1980).

The appropriateness and feasibility of the proposed method to serve the objectives of demonstrating if their exists another hydraulic conductivity on the very local scale in the Boom clay have been shown by calculation. In these calculations they hydrological data about the Boom clay from other research activities have been applied. The final conclusion about the value of the local hydraulic conductivity of the Boom clay and the reliability of the proposed method can only drawn when the tests are eventually run.

The aim of the study was to develop backfilling concepts with capabilities to attenuate near field effects of mined repositories in argillaceous host rocks by examining the characteristics and the performances of a clay host rock and potentialy favourable engineered barriers and assessnig system components which contribute their durability.

The main results are:
the HLW canister, used as refernce cannot be considered as a preventative barrier due to its collapse at an outside pressure of 2.5 MPa and to the sensitivity od austenitic steel at the stress corrosion cracking;
sulphate resistant concrete can be used as backfill material or as lining if it is sufficiently matured before being solicited by the thermal loading generated by the HLW packages;
excavated Boom clay can be used as buffer material but future research is necessary to determine the appropriate processing to be used and the eventual adjuvent(s) to be considered;
a program called TEMPRES is now available to compute the temperature, pore water pressure and stresses around heating sources in clay host rock, the validation is not yet complete but results look promising;
a program calle SOURCE was developed to approximate pore water pressure response at digging and drilling works performed in a isotropic medium where the pore fluid flow can be related to the pore water pressure by Darcy's Law.
1. DEFINITION AND QUANTIFICATION OF NEAR-FIELD EFFECTS AROUND HLW-PACKAGES IN A CLAY ENVIRONMENT FOR SELECTIVE REPRESENTATIVE EMPLACEMENT CONFIGURATIONS OF MINED REPOSITORIES (IN-GALLERY AND IN-FLOOR CONCEPT).
2. SETTLING OF DISTURBANCE ALLOWANCES FOR THE VARIOUS COMPONENTS IN THE NEAR-FIELD, GLASS MATRIX, CONTAINER MATERIAL, CONCRETE AND IN SITU SURROUNDING CLAY).
3. ON THE BASIS OF THE RESULTS OF 1 AND 2, DEFINITION OF THE ATTENUATION FACTOR TO BE ACHIEVED BY ENGINEERED BARRIERS WITH A PARTICULAR ATTENTION TO THE THERMAL EFFECTS THE RADIATION DOSE AND THE OXIDATION EFFECTS.
4. DEFINITION OF COMPLEMENTARY REQUIREMENTS OF THESE INTERFACE MATERIALS REGARDING THEIR CHEMICAL COMPATIBILITY WITH THE WASTE PACKAGES AND THE CLAY ENVIRONMENT, THEIR MECHANICAL STABILITY, THEIR PERMEABILITY, WATER SATURATION LEVEL AND THEIR EMPLACEMENT FEASIBILITY.
5. SELECTION OF APPROPRIATE MATERIALS ON THE BASIS OF HEAT TRANSFER AND SHIELDING PROPERTIES, RADIATION RESISTANCE HYDRAULIC PROPERTIES, CHEMICAL BUFFERING, AND RADIONUCLIDE RETENTION CAPABILITIES, MECHANICAL CHARACTERISTICS, LONGEVITY, AVAILABLE METHODS OF APPLICATION AND COSTS.
6. DESIGN AND DIMENSIONING CONCEPT WHICH MEET THE ABOVE SET OF REQUIREMENTS AND ETABLISHMENT OF APPROPRIATE EMPLACEMENT TECHNIQUES AND PROCEDURE FOR THE SELECTED EMPLACEMENT CONFIGURATIONS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

BELGIAN NUCLEAR RESEARCH CENTRE
Address
200,Herrmann Debrouxlaan 40-42
1160 Bruxelles
Belgium

Participants (1)

École Nationale Supérieure des Mines de Paris
France
Address
60 Boulevard Saint-michel
75272 Paris