Dennis LENEVEU - Academia.edu (original) (raw)

Papers by Dennis LENEVEU

Probabilistic and deterministic risk assessments were carried out by ECOMatters Inc. for the IEA ... more Probabilistic and deterministic risk assessments were carried out by ECOMatters Inc. for the IEA Weyburn CO 2 Monitoring and Storage Project (the "IEA Weyburn Project"). The objective of this work was to understand and evaluate the geological storage of CO 2 from a risk assessment perspective within the context of a large enhanced oil recovery (EOR) project being carried out in the Weyburn field, which is part of the Williston Basin that straddles the Canadian (Saskatchewan) and USA (North Dakota) borders. Probabilistic Risk Assessment (PRA) is the preferred methodology for evaluating complex, long timeframe, process-driven problems such as the geological storage of CO 2 . A unique, computationally-efficient model CQUESTRA-1 (CQ-1) was developed to rapidly assess the 1000's of cases required for a PRA, that statistically quantify the uncertainty associated with the many features, events and processes including their interactions over the long-term geological storage of...

A key supporting step in the validation of performance assessment codes for nuclear waste disposa... more A key supporting step in the validation of performance assessment codes for nuclear waste disposal is to compare verified codes developed for similar analyses. In this paper, we report on the first such comparison of system-level codes for waste package performance assessment, specifically comparison of release calculations by the AREST and SYVAC-Vault models. The purpose of this comparison is to further establish the scientific credibility of these codes for use in predictive assessment of radionuclide release, as well as to identify deficiencies and future improvements.

Greenhouse Gases: Science and Technology, 2012

ABSTRACT The potential for environmental impact from future leakage of toxic hydrogen sulfide (H2... more ABSTRACT The potential for environmental impact from future leakage of toxic hydrogen sulfide (H2S) at an enhanced oil recovery (EOR) and acid gas sequestration site near Zama Lake, Alberta, is examined. Over 800 pinnacle reefs are potentially suitable for EOR by injection of acid gas. Leakage rate as a function of time through a reference wellbore is determined for various scenarios including leakage through the annulus of the wellbore and leakage through the central plug seal of the wellbore with an intact and failed wellbore casing. Potential plumes of H2S in the air and in shallow aquifers emanating from a single reference wellbore and from 350 wellbores are modeled. Leakage rates from the 350 wellbores are calculated from randomly sampled wellbore seal failure times, reservoir permeability, and initial amounts of acid gas, and from reference values of other reservoir parameters. Results indicate that for hundreds of years after injection, the entire Zama Lake area of 12 000 km2 could have lethal concentrations of H2S over each of the leaking wellbores. The shallow aquifers over the entire Zama area and over 30 kilometres in the direction of aquifer flow could be undesirably tainted with dissolved H2S. The entire Zama Lake area and hundreds of kilometres beyond could become uninhabitable for more than 1000 years after injection due to toxic plumes of H2S in the air and in shallow aquifers. This analysis has implications for the potential use of acid gas for EOR and for subsurface sequestration in general in areas with large numbers of abandoned wells. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

MRS Proceedings, 1997

ABSTRACTCalculation of used nuclear fuel dissolution rates in a geological disposal vault require... more ABSTRACTCalculation of used nuclear fuel dissolution rates in a geological disposal vault requires a knowledge of the redox conditions in the vault. For redox conditions less oxidizing than those causing UO2 oxidation to the U3O7 stage, a thermodynamically-based model is appropriate. For more oxidizing redox conditions a kinetic or an electrochemical model is needed to calculate these rates. The redox conditions in a disposal vault will be affected by the radiolysis of groundwater by the ionizing radiation associated with the fuel. Therefore, we have calculated the alpha-, beta- and gamma-dose rates in water in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (CNFWMP) as a function of cooling time. Also, we have determined dissolution rates of UO2 fuel as a function of alpha and gamma dose rates from our electrochemical measurements. These room-temperature rates are used to calculate the dissolution rates of used fuel at 100°C, the highest t...

MRS Proceedings, 1994

A very small number of disposal containers of heat generating nuclear waste may have initial manu... more A very small number of disposal containers of heat generating nuclear waste may have initial manufacturing defects that would lead to pin-hole type failures at the time of or shortly after emplacement. For sufficiently long-lived containers, only the the initial defects need be considered in modelling of release rates from the disposal vault. Two approaches to modelling of near-field mass transport from a single point source within a disposal room have been compared: the finite-element code MOTIF (A Model Of Transport In Fractured/porous media) and a boundary integral method (BIM). These two approaches were found to give identical results for a simplified model of the disposal room without groundwater flow. MOTIF has been then used to study the effects of groundwater flow on the mass transport out of the emplacement room.

MRS Proceedings, 1993

ABSTRACTThe corrosive environment around the containers in a Canadian nuclear fuel waste disposal... more ABSTRACTThe corrosive environment around the containers in a Canadian nuclear fuel waste disposal vault will change over time from “warm and oxidizing” to “cool and anoxic”. As the conditions change, so too will the corrosion behaviour of the containers. For copper containers, uniform corrosion and, possibly, pitting will occur during the initial aggressive phase, to be replaced by slow uniform corrosion during the long-term anoxic period.The corrosion behaviour of copper has been studied over a range of conditions representing all phases in the evolution of the vault environment. The results of these studies are summarized and used to illustrate how a model can be developed to predict the corrosion behaviour and container lifetimes over long periods of time. Lifetimes in excess of 106 a are predicted for 25-mm-thick. copper containers under Canadian disposal conditions.

MRS Proceedings, 1988

ABSTRACTA series of calculations of radionuclide release was performed with the AREST and SYVAC-V... more ABSTRACTA series of calculations of radionuclide release was performed with the AREST and SYVAC-Vault models (SVM) in order to assess concurrance. Specifically, the effects of precipitation and decay chain in-growth on the predicted release of nuclides from waste packages containing spent nuclear fuel were compared between each code. The results for maximum release rates generally agreed within a factor of 10. The differences in results can be explained based on the differences in geometry and boundary conditions between the two codes. Both codes showed nearly identical enhancement factors in release rates of uranium-series nuclides (U-238, U-234, Th-230, Ra-226) arising from the effect of decay-chain in-growth. Calculated enhancement factors in release rates for precipitation of a new uranium-bearing solid within the waste package were also in good agreement between AREST and SVM.

MRS Proceedings, 1989

ABSTRACTThe Vault Model has been developed to assess the performance of engineered barriers in a ... more ABSTRACTThe Vault Model has been developed to assess the performance of engineered barriers in a conceptual geological disposal vault for used nuclear fuel. It represents container failure, release of radionuclides from used fuel and mass transport of released radionuclides through the clay-based sealing materials surrounding the waste containers. This paper focusses on mass-transport processes represented by the Vault Model, including diffusion, convection and retardation.In particular, we present results of several scoping calculations carried out with the Vault Model. We consider cases where the clay-based barriers are represented by either a one- or a two-layer system adjacent to an intact rock and a case where the two clay-based barriers are adjacent to a highly fractured rock. These calculations provide insight into the model and produce test cases for comparison with both relatively simple analytical estimates and similar computer codes, as they become available. The analytic...

MRS Proceedings, 1987

Sensitivity surfaces have been developed to analyse the performance of engineered barriers of an ... more Sensitivity surfaces have been developed to analyse the performance of engineered barriers of an underground nuclear fuel waste disposal vault. The major engineered barriers are the waste form, the containers and the buffer surrounding the containers. A modular computer code has been developed that calculates the release rate from each barrier. The modules are linked together through the use of time-series-management routines. By systematic variation of the model input parameters, sensitivity surfaces are constructed that illustrate the behaviour of an objective function such as maximum fractional release rate in response to the changes in the input parameters.

Journal of Nuclear Materials, 1997

Dissolution rates of UO fuel are determined as a function of alpha and gamma dose rates. These ro... more Dissolution rates of UO fuel are determined as a function of alpha and gamma dose rates. These room-temperature rates 2 are used to calculate the dissolution rates of used fuel at 1008C. Also, the alpha, beta and gamma dose rates in water in contact with the reference used fuel are calculated as a function of cooling time. These results are used to calculate used CANDU fuel dissolution rates as a function of time since emplacement in a defective copper container for the Canadian Nuclear Fuel Waste Management Program. It is shown that beta radiolysis of water is the main cause of oxidation of used CANDU fuel in a failed container and that the use of a corrosion model is required for ; 1000 a of emplacement in the waste vault. The results obtained here can be adopted to calculate used nuclear fuel dissolution rates for other waste management programs. q 1997 Elsevier Science B.V. h 4 93 7 w x 17 . However, any model of fuel dissolution within a 0022-3115r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved. Ž . PII S 0 0 2 2 -3 1 1 5 9 7 0 0 2 7 2 -9

International Journal of Greenhouse Gas Control, 2011

A -area of the free phase pool (m 2 ) a b -bubble radius (m) Co -solubility of free phase in form... more A -area of the free phase pool (m 2 ) a b -bubble radius (m) Co -solubility of free phase in formation fluid (kg/m 3 ) C b -concentration of free phase in wellbore (kg/m 3 ) CC -the concentration of dissolved CO2 (kg/m 3 ) CD -bubble drag coefficient C pA -the heat capacity of the acid gas (kJ/kg/K) D -molecular diffusion coefficient of free phase in formation fluid (m 2 /a) DT -the thermal diffusivity of the formation (m 2 /a) g -acceleration due to gravity (ms −2 ) FD -steady state dissolution rate of free phase (kg/a) Gp -the fluid pressure gradient (bar/m) hs -height of free phase (m) ho -initial height of free phase (m) h d -thickness of the stagnant layer (m) hr -reservoir thickness (m) H -total head difference across the radius of influence of the well (m) H b -buoyancy head difference (m) k -permeability (m 2 ) k b -bubble mass transfer coefficient (m/a) krs -relative permeability of free phase KF -the thermal conductivity of the formation (W/m/K) Ks -hydraulic conductivity of the free phase in the reservoir (m/s) L b -length of wellbore (m) Mo -initial mass of free phase (kg) M -mass of free phase (kg) MC -the molecular weight of CO2 (a.m.u.) Nw -number of leaking wellbores in the free phase pool NL -number of bubbles per unit length of wellbore Pc -capillary entry pressure (MPa) Pa -atmospheric pressure (MPa) Pw -fluid pressure (MPa) Qs -leakage rate of free phase up the wellbore (kg/a) w -mass transfer coefficient (m/a)

Energy Conversion and Management, 2008

ABSTRACT A computationally efficient semi-analytical code, CQUESTRA, has been developed for proba... more ABSTRACT A computationally efficient semi-analytical code, CQUESTRA, has been developed for probabilistic risk assessment and rapid screening of potential sites for geological sequestration of carbon dioxide. The rate of dissolution and leakage from a trapped underground pool of carbon dioxide is determined. The trapped carbon dioxide could be mixed with hydrocarbons and other components to form a buoyant phase. The program considers potential mechanisms for escape from the geological formations such as the movement of the buoyant phase through failed seals in wellbores, the annulus around wellbores and through open fractures in the caprock. Plume animations of dissolved carbon dioxide in formation water around the wellbores are provided. Solubility, density and viscosity of the buoyant phase are determined by equations of state. Advection, dispersion, diffusion, buoyancy, aquifer flow rates and local formation fluid pressure are taken into account in the modeling of the carbon dioxide movement.Results from a hypothetical example simulation based on data from the Williston basin near Weyburn, Saskatchewan, indicate that this site is potentially a viable candidate for carbon dioxide sequestration.Sensitivity analysis of CQUESTRA indicates that criteria such as siting below aquifers with large flow rates and siting in reservoirs having fluid pressure below the pressure of the formations above can promote complete dissolution of the carbon dioxide during movement toward the surface, thereby preventing release to the biosphere. Formation of very small carbon dioxide bubbles within the fluid in the wellbores can also lead to complete dissolution.

Corrosion, 1997

ABSTRACT A model was developed to predict the failure of Grade-2 titanium (Ti-2) nuclear waste co... more ABSTRACT A model was developed to predict the failure of Grade-2 titanium (Ti-2) nuclear waste containers. Two major corrosion modes were included: failure by crevice corrosion (CC) and failure by hydrogen-induced cracking (HIC). A small number of containers were assumed to be defective and to fail within 50 years of emplacement. The model is probabilistic in nature, and each modeling parameter was assigned a range of values, resulting in a distribution of corrosion rates and failure times. The crevice corrosion rate (R{sub cc}) was assumed to be dependent only upon properties of the material used and the temperature of the vault. CC was assumed to initiate rapidly on all containers and to propagate indefinitely without repassivation. Failure by HIC was assumed to be inevitable once container temperature (T) fell to â¤ 30 C. Depending upon the rate at which they were expected to cool, temperature-time profiles for individual containers were approximated by two-step or single-step temperature-time functions. These functions then were used with experimentally measured corrosion rates to compute the fractional failure rates and cumulative fractions of containers failed as a function of time. Approximately 97% of all containers were predicted to fail by CC. Only â¼ 0.025% were predicted to fail before 500 years, the time considered a minimum for containment of nuclear waste. The majority of containers were predicted to fail between 1,200 years and 7,000 years.

Corrosion Science, 1995

ABSTRACT Steady-state corrosion potentials of copper in O2-containing NaCl solution have been mea... more ABSTRACT Steady-state corrosion potentials of copper in O2-containing NaCl solution have been measured using three types of electrode: a rotating-disc electrode, an electrode covered by a porous nylon membrane and an electrode covered by a layer of compacted Na-bentonite clay. Mass-transfer coefficients for these electrodes vary from 10−2 cm s−1 in bulk solution to 10−7 cm s−1 for the clay-covered electrode. Solutions were equilibrated with atmospheres of air, 2% O2/N2, 0.2% O2N2, or were nominally deaerated. In aerated bulk solution, the anodic reaction is mass-transfer limited and the cathodic reaction is kinetically controlled. With decreasing [O2], the cathodic reaction becomes partially mass-transfer limited. Both reactions are essentially mass-transfer controlled for the membrane- and clay-covered electrodes. A mixed-potential model is developed for predicting ECorr over a wide range of mass-transfer conditions and [O2], under circumstances where either reaction may be under joint kinetic/mass-transfer control.