Formulation of backfill material for a nuclear fuel waste disposal vault

1986 ◽  
Vol 23 (2) ◽  
pp. 216-228 ◽  
Author(s):  
Raymond N. Yong ◽  
Prapote Boonsinsuk ◽  
Gary Wong
Keyword(s):  
Hydraulic Conductivity ◽  
Nuclear Fuel ◽  
Clay Content ◽  
Potential Candidate ◽  
Lake Agassiz ◽  
Backfill Material ◽  
Buffer Material ◽  
Swelling Capacity ◽  
Crushed Granite ◽  
Nuclear Fuel Waste

The Canadian concept for disposing of nuclear fuel waste, currently being studied by Atomic Energy of Canada Limited (AECL) and Ontario Hydro, is to permanently place the waste in an underground vault located in plutonic rock of the Canadian Shield at a depth of 500–1000 m. The waste will be in containers surrounded by a buffer material. Following waste emplacement, the vault will be backfilled. The quantity of backfill material required will be between 5 and 10 million cubic metres.The development of backfill material for a nuclear fuel waste vault is directed at determining the appropriate composition of backfill material that will meet the stringent criteria to be set by AECL to ensure its successful performance. The criteria, with respect to engineering behaviour, include low hydraulic conductivity, sufficient swelling capacity upon wetting, low shrinkage upon drying, and low segregation tendency. The methodology adopted and the results obtained are described in this paper. Using a mixture of crushed granite aggregate and glacial Lake Agassiz clay, a potential candidate for backfill material would have a maximum grain size of 19.1 mm and a clay content of at least 25% by weight. Such a backfill material will yield low hydraulic conductivity (close to that of the pure clay) and other properties well within the acceptable range. Key words: aggregate–clay mixture, swelling clay, hydraulic conductivity, backfill, waste management.

Thermal and physical properties of candidate buffer–backfill materials for a nuclear fuel waste disposal vault

1989 ◽  
Vol 26 (4) ◽  
pp. 629-639 ◽  
Author(s):  
H. S. Radhakrishna ◽  
H. T. Chan ◽  
A. M. Crawford ◽  
K. C. Lau
Keyword(s):  
Hydraulic Conductivity ◽  
Nuclear Fuel ◽  
Waste Disposal ◽  
Management Program ◽  
Buffer Material ◽  
Backfill Materials ◽  
And Performance ◽  
Nuclear Fuel Waste ◽  
Clay Barriers ◽  
Ontario Hydro

As part of the Canadian Nuclear Fuel Waste Management Program, Ontario Hydro has, over several years, conducted research into the behaviour and performance of buffer–backfill for the proposed nuclear fuel waste disposal vault. In this paper, a review has been made of laboratory studies made at Ontario Hydro on the thermal properties, strength, hydraulic conductivity, and compactability of clay-based buffer materials. The results of this work have enabled the formulation of selection criteria for the buffer material mix for the prototype Canadian nuclear fuel waste disposal scheme. Key words: bentonites, buffer, backfill, nuclear waste disposal, thermal conductivity, clays, hydraulic conductivity, compaction, clay barriers, clay seals, shrinkage.

Lifetimes of Titanium and Copper Containers for the Disposal of Used Nuclear Fuel

1991 ◽  
Vol 257 ◽  
Author(s):  
Lawrence H. Johnson ◽  
D.W. Shoesmith ◽  
B.M. Ikeda ◽  
F. King
Keyword(s):  
Nuclear Fuel ◽  
Bulk Solution ◽  
General Corrosion ◽  
Compacted Clay ◽  
Used Nuclear Fuel ◽  
Buffer Material ◽  
Using Data ◽  
Long Term Performance ◽  
Term Performance ◽  
Nuclear Fuel Waste

ABSTRACTTitanium and copper have been proposed as suitable container materials for disposal of nuclear fuel waste in plutonic rock of the Canadian Shield. Studies of the corrosion of these materials have led to the development of container failure models to predict long-term performance. Crevice corrosion and hydrogen-induced cracking of titanium have been identified as potential failure mechanisms, and these two processes have been studied in detail. Using data from these studies as well as a number of conservative assumptions, titanium container lifetimes of 1200 to 7000 a have been estimated. For copper, general corrosion has been studied in detail in bulk solution and in compacted clay-based buffer material. Results indicate that the copper corrosion rate is likely to be controlled by the rate of transport of copper species away from the container surface. An assessment of copper pitting data suggests that pitting is an extremely improbable failure mechanism. The copper container failure model predicts minimum container lifetimes of 30 000 a. The results demonstrate that long lifetime containment can be provided, should performance assessment studies indicate the need for such an option.

Modelling the Consumption of Oxygen by Container Corrosion and Reaction with Fe(II)

1995 ◽  
Vol 412 ◽  
Author(s):  
M. Kolář ◽  
F. King
Keyword(s):  
Nuclear Fuel ◽  
Waste Disposal ◽  
Corrosion Reaction ◽  
Crushed Granite ◽  
Backfill Materials ◽  
Nuclear Fuel Waste ◽  
Oxidation Of Organics

AbstractA model is described that predicts the rate of O2 consumption in a sealed nuclear fuel waste disposal vault as a result of container corrosion, reaction with biotite and the oxidation of organics and other oxidizable impurities in the clay. The most important reactions leading to the consumption of O2 for Cu containers in a conceptual Canadian disposal vault are container corrosion, the oxidation of dissolved Cu(I) and the oxidation of organics and other impurities in the clay. Consumption of O2 by the oxidation of dissolved Fe(II) from biotite is significant in backfill materials containing crushed granite and in the rock itself. The O2 initially trapped in the disposal vault is predicted to be consumed in between 50 and 670 a.

Creep behaviour of a buffer material for nuclear fuel waste vault

1985 ◽  
Vol 22 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Raymond N. Yong ◽  
Prapote Boonsinsuk ◽  
Demos Yiotis
Keyword(s):  
Finite Element ◽  
Nuclear Fuel ◽  
Host Rock ◽  
Creep Behaviour ◽  
Creep Model ◽  
Secondary Creep ◽  
Full Size ◽  
Waste Container ◽  
Buffer Material ◽  
Nuclear Fuel Waste

In the Canadian nuclear fuel waste disposal concept currently under study, one of the prime candidate procedures is the borehole emplacement technique. Each fuel waste container will be placed in a 1.1 m diameter hole in the floor of a disposal vault in deep plutonic rock. The container will be surrounded by buffer material consisting of a mixture of clay and sand. This study examines the creep behaviour of the buffer material in the borehole during interaction with the waste container and the host rock. It simulated the buffer – container – host rock interaction through a small-scale physical model using the loading pressures anticipated in the full-size system. The results from the model tests were compared with those predicted by a finite element analytical model. The creep behaviour of the full-size system was then predicted using the analytical model.From the results, it is evident that the creep behaviour of the buffer material depends significantly on interaction within the container – buffer – host rock system, overburden pressure, and water uptake. At relatively low overburden pressures, the waste container might settle, causing a separation between the buffer material and the container top. However, this could be alleviated by the swelling properties of the buffer material. The secondary creep rates are negligible, and creep in the buffer material is primarily governed by the primary creep stage. Key words: creep, model test, swelling soil, soil deformation, unsaturated soil, finite element analysis.

Occurrence and identification of microorganisms in compacted clay-based buffer material designed for use in a nuclear fuel waste disposal vault

1997 ◽  
Vol 43 (12) ◽  
pp. 1133-1146 ◽  
Author(s):  
Simcha Stroes-Gascoyne ◽  
Shelley A. Haveman ◽  
Connie J. Hamon ◽  
Terri-Lynn Delaney ◽  
Karsten Pedersen ◽  
...  
Keyword(s):  
16S Rrna ◽  
Moisture Content ◽  
Nuclear Fuel ◽  
Dry Weight ◽  
Buffer Layers ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
Buffer Material ◽  
Nuclear Fuel Waste

A full-scale nuclear fuel waste disposal container experiment was carried out 240 m below ground in an underground granitic rock research laboratory in Canada. An electric heater was surrounded by buffer material composed of sand and bentonite clay and provided heat equivalent to what is anticipated in a Canadian nuclear fuel waste repository. During the experiment, the heat caused a mass transport of water and moisture content gradients developed in the buffer ranging from 13% closest to the heater to 23% at the rock wall of the deposition hole. Upon decommissioning after 2.5 years, microorganisms could be cultured from all samples having a moisture content above 15% but not from samples with a moisture content below 15%. Heterotrophic aerobic and anaerobic bacteria were found in numbers ranging from 101to 106cells/g dry weight buffer. Approximately 102, or less, sulphate-reducing bacteria and methanogens per gram of dry weight buffer were also found. Identification of buffer population members was performed using Analytical Profile Index (API) strips for isolated bacteria and 16S rRNA gene sequencing for in situ samples. A total of 79 isolates from five buffer layers were identified with API strips as representing the beta, gamma and delta groups of Proteobacteria and Gram-positive bacteria. Sixty-seven 16S rRNA clones that were obtained from three buffer layers were classified into 21 clone groups representing alpha and gamma groups of Proteobacteria, Gram-positive bacteria, and a yeast. Approximately 20% of the population comprised Gram-positive bacteria. Members of the genera Amycolatopsis, Bacillus, and Nocardia predominated. Among Gram-negative bacteria, the genera Acinetobacter and Pseudomonas predominated. Analysis of lipid biomarker signatures and in situ leucine uptake demonstrated that the buffer population was viable. The results suggest that a nuclear fuel waste buffer will be populated by active microorganisms only if the moisture content is above a value where free water is available for active life.Key words: 16S rRNA, bacteria, bentonite, nuclear fuel waste, phospholipid fatty acids, water activity.

Thermal Behaviour of Backfill Material for a Nuclear Fuel Waste Disposal Vault

1989 ◽  
Vol 176 ◽  
Author(s):  
R.N. Yong ◽  
A.M.O. Mohamed ◽  
S.C.H. Cheung
Keyword(s):  
Mechanical Properties ◽  
Nuclear Fuel ◽  
Thermal Response ◽  
Management Program ◽  
Thermal And Mechanical Properties ◽  
Used Nuclear Fuel ◽  
Backfill Material ◽  
Rock Formations ◽  
Pressure Development ◽  
Nuclear Fuel Waste

ABSTRACTThe concept of disposing of used nuclear fuel in engineered rock formations is being studied in the Canadian Nuclear Fuel Waste Management Program. After the used fuel is emplaced in the vault, the vault would be backfilled. The backfill has to satisfy a number of engineering requirements. A reference backfill with satisfactory hydraulic, thermal and mechanical properties has already been selected.As the used fuel in the waste containers decays, heat will be generated and this heat will raise the temperature of the backfill material. The performance of the reference backfill material was evaluated over the temperature range 20–100°C. This paper addresses the results of experiments on thermal response and pressure development in the backfill for the period shortly after vault closure.

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