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.

Long-term settlement of model rock-socketed piers

1989 ◽  
Vol 26 (3) ◽  
pp. 348-358 ◽  
Author(s):  
Robert G. Horvath ◽  
K-J. Chae
Keyword(s):  
Large Scale ◽  
Load Transfer ◽  
Creep Behaviour ◽  
Small Diameter ◽  
Soft Rock ◽  
Load Test ◽  
Creep Model ◽  
Secondary Creep ◽  
Initial Portion

Very little information is available concerning the long-term settlement behaviour of drilled pier foundations socketed into rock. This paper summarizes the results of laboratory investigations of the long-term settlement (creep) behaviour of model socketed pier foundations. The testing program included seven model piers constructed with different materials and different load-support conditions. The primary models were two small-diameter concrete piers constructed in soft shale. For all models tested the results indicated similarly shaped time–displacement curves, having two distinct regions. The initial portion of the curves represents a region of primary creep and the remaining portion represents a zone of secondary creep having a much lower rate of displacement. A comparison of short-term (1 day, which is a normal maximum duration of a full-scale load test) and long-term (200 days) settlements for the model piers showed an 84–245% increase in settlements. In addition, some information concerning load transfer with time in the model piers and available data from loading tests on large-scale socketed piers are included. Key words: socketed pier foundations, long-term settlement, creep model tests, soft rock.

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.

Hygrothermal Performance of an Engineered Clay Barrier

1990 ◽  
Vol 212 ◽  
Author(s):  
A.P.S. Selvadurai ◽  
S.C.H. Cheung
Keyword(s):  
Moisture Distribution ◽  
Experimental Simulation ◽  
Residual Moisture ◽  
Moisture Movement ◽  
Bentonitic Clay ◽  
Waste Container ◽  
Buffer Material ◽  
Deep Rock ◽  
High Level ◽  
Nuclear Fuel Waste

ABSTRACTA series of laboratory experiments was conducted to establish the heat-induced moisture movement in a bentonitic clay buffer. The buffer material is proposed as an engineered barrier to isolate a heat-emitting high-level nuclear fuel waste container from its emplacement borehole located in a deep rock repository. In the experimental simulation, the hygrothermal phenomena are initiated by a cylindrical heater placed within the compacted buffer material in a borehole centrally located in a granite block. The experimental results illustrate the time-dependent distribution of temperatures within the rock mass and the residual moisture distribution at the termination of the experiment.

Effects of Creep Deformation Model of Gr. 91 Steel at 600°C on Creep Fracture Mechanics Parameters

2017 ◽  
Author(s):  
Min-Gu Won ◽  
Nam-Su Huh ◽  
Hyeong-Yeon Lee ◽  
Woo-Gon Kim ◽  
Jae-Boong Choi
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Creep Deformation ◽  
Creep Model ◽  
Deformation Model ◽  
Secondary Creep ◽  
Creep Fracture ◽  
Reference Stress ◽  
Creep Region ◽  
Omega Model

The present paper investigates the effect of creep deformation model of Gr. 91 Steel at 600 °C on creep fracture mechanics parameters. Three types of creep deformation model were considered, i.e. Garofalo’s model and RCC-MRx model for primary-secondary creep region, and modified omega model for primary-secondary-tertiary creep region. The parameters for each creep deformation model were characterized from experiment results. Reference Stress (RS) method was used to estimate creep fracture mechanics parameters, C(t)-integral and COD rate for each creep model. Furthermore, elastic-creep finite element (FE) analyses were carried out to verify the results of RS method. Finally, the effect of creep deformation model was investigated by comparing the results of C(t)-integral and COD rate.

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.

Finite Element Simulation of Creep Deformation for Gr. 91 Steel at 600 °C Using Garofalo Model

2016 ◽  
Author(s):  
Min-Gu Won ◽  
Jae-Boong Choi ◽  
Nam-Su Huh ◽  
Hyeong-Yeon Lee ◽  
Woo-Gon Kim
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Creep Deformation ◽  
Creep Model ◽  
Deformation Model ◽  
Secondary Creep ◽  
Experiment Data ◽  
Element Simulation ◽  
Commercial Code ◽  
Creep Models

The present paper provides predictive creep deformation model for Gr. 91 steel at 600 °C. To cover primary-secondary creep regions, two types of creep models, i.e. Garofalo’s and RCC-MRx models were considered in the present study, where the parameters of Garofalo’s model were characterized based on experiment results, and the parameters of RCC-MRx model were determined by the values given in the RCC-MRx code. Furthermore, each creep model were developed based on CREEP (user creep subroutine invoked in ABAQUS) codes for applying to finite element (FE) simulations using commercial code. Then, FE analyses for creep deformation were performed by using the developed CREEP codes (for Garofalo’s and RCC-MRx models), and the results were compared with experiment data. As results, Garofalo’s model provides more accurate results than RCC-MRx model.

Influence of Bore Pressure on the Creep Behaviour of Polymer Barrier Layer Inside an Unbonded Flexible Pipe

2011 ◽  
Author(s):  
Yijun Shen ◽  
Jian Zhao ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Finite Element ◽  
Polymer Material ◽  
Barrier Layer ◽  
Creep Behaviour ◽  
Polymer Materials ◽  
Creep Model ◽  
Implicit Time ◽  
Small Scale ◽  
Flexible Pipe ◽  
Creep Tests

This paper investigates the influence of bore pressure, combined with the nonlinear behaviour of the polymer material, on the creep behaviour of the polymer barrier layer inside an unbonded flexible pipe. Creep behaviour in the barrier layer may result in its reduction in thickness and is therefore an important design consideration in ensuring the structural integrity of this layer. It is meaningful to study the variation in creep behaviour in an unbonded flexible pipe under different bore pressures and temperatures, especially in high pressure pipelines for deep or ultra-deep sea applications. Creep behaviour in polymer material is complex, as it is governed by a number of variables such as the stress/strain state, temperature, and pressure for example. It is generally time-dependent and often associated with larger strains or states of deformation. Owing to the complexity of polymer material creep, an implicit time hardening creep model, based on the Maxwell viscoelastic model, has been selected to represent the creep behaviour in polymer materials and implemented into the Gap Span model, which is an in-house ANSYS based finite element model. The coefficients of this creep model were initially calibrated according to standard creep tests performed on polymer materials. The study presented in this paper focuses on the influence of bore pressure and high temperature on the creep behaviour of the polymer barrier layer. Comparisons between the simulation results of the calibrated Gap Span creep model and the corresponding small-scale creep tests demonstrate that these model predictions are overly conservative for the polymer material of the barrier layer inside an unbonded flexible pipe. Comparisons between the experimental test results and the finite element modelling results show good correlation.

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.

Analysis of the Creep Behaviour of the Polymer Barrier Layer in Unbonded Flexible Pipes Under Different Fluid Temperatures

2012 ◽  
Author(s):  
Yijun Shen ◽  
Jian Zhao ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Finite Element ◽  
Polymer Material ◽  
Barrier Layer ◽  
Creep Behaviour ◽  
Polymer Materials ◽  
Creep Model ◽  
Implicit Time ◽  
Small Scale ◽  
Flexible Pipes ◽  
Unbonded Flexible Pipes

This paper discusses the influence of different fluid temperatures on the creep behaviour of the polymer barrier inside unbonded flexible pipes. The creep behaviour of the polymer material is generally time-dependent and associated with larger, nonlinear deformation. Excessive creep deformation may lead to structural failure, due to the over-reduction of the barrier layer thickness, and is therefore an important design consideration in ensuring the structural integrity of this layer. Creep behaviour in polymer material is complex, as it is governed by a number of variables, such as the stress/strain state, temperature, and pressure for example. This paper deals with the influence of different fluid temperatures on the creep behaviour of the polymer barrier layer under pipe design pressures, particularly in high temperature fluid transportation pipelines for deep or ultra-deep sea applications. The analysis model was established using commercial finite element software ANSYS, where an implicit time hardening creep model, based on the Maxwell viscoelastic model, was selected to represent the creep behaviour of the polymer materials. The coefficients of the implemented polymer material gap span creep model are calibrated to represent the worst case of the small-scale sample gap span creep tests performed in-house. A comparison is made between the simulation results of the calibrated gap span creep model and the corresponding small-scale creep test measurements. The experimental test results and the finite element modelling results show good correlation. This demonstrates that the creep model predictions are conservative for the polymer material of the barrier layer inside an unbonded flexible pipe.

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