Showing papers by "Atomic Energy of Canada Limited published in 2008"

Microstructure and mechanical properties of bainitic low carbon high strength plate steels

Abstract: This paper reports the results of an investigation of plates produced by the advanced thermomechanical processing (TMP) schedules, which were designed using the results of a laboratory study. There were two steel compositions that corresponded to X-80 with carbon contents 0.04 and 0.07 wt.%, respectively. The variation in microstructure, hardness, tensile properties and Charpy impact properties with TMP schedule were determined, and compared with the expected requirements for X-100 linepipe steel. The relationships between microstructure and mechanical properties were experimentally obtained and discussed.

Coplanar capacitance sensors for detecting water intrusion in composite structures

Abstract: Composite materials are becoming more affordable and widely used for retrofitting, rehabilitating and repairing reinforced concrete structures designed and constructed under older specifications. However, the mechanical properties and long-term durability of composite materials may degrade severely in the presence of water intrusion. This study presents a new non-destructive evaluation (NDE) technique for detecting the water intrusion in composite structures by evaluating the dielectric properties of different composite system constituent materials. The variation in the dielectric signatures was employed to design a coplanar capacitance sensor with high sensitivity to detect such defects. An analytical model was used to study the effect of the sensor geometry on the output signal and to optimize sensor design. A finite element model was developed to validate analytical results and to evaluate other sensor design-related parameters. Experimental testing of a concrete specimen wrapped with composite laminate and containing a series of pre-induced water intrusion defects was conducted in order to validate the concept of the new technique. Experimental data showed excellent agreement with the finite element model predictions and confirmed sensor performance.

A Lower Dose Threshold for the In Vivo Protective Adaptive Response to Radiation. Tumorigenesis in Chronically Exposed Normal and Trp53 Heterozygous C57BL/6 Mice

Abstract: Mitchel, R. E. J., Burchart, P. and Wyatt, H. A Lower Dose Threshold for the in vivo Protective Adaptive Response to Radiation. Tumorigenesis in Chronically Exposed Normal and Trp53 Heterozygous C57BL/6 Mice. Radiat. Res. 170, 765–775 (2008). Low doses of ionizing radiation to cells and animals may induce adaptive responses that reduce the risk of cancer. However, there are upper dose thresholds above which these protective adaptive responses do not occur. We have now tested the hypothesis that there are similar lower dose thresholds that must be exceeded to induce protective effects in vivo. We examined the effects of low-dose/low-dose-rate fractionated exposures on cancer formation in Trp53 normal or cancer-prone Trp53 heterozygous female C57BL/6 mice. Beginning at 6 weeks of age, mice were exposed 5 days/week to single daily doses (0.33 mGy, 0.7 mGy/h) totaling 48, 97 or 146 mGy over 30, 60 or 90 weeks. The exposures for shorter times (up to 60 weeks) appeared to be below the level necessary t...

Managing Risk: The Human Element

Abstract: The human element is the principle cause of incidents and accidents in all technology industries; hence it is evident that an understanding of the interaction between humans and technology is crucial to the effective management of risk. Despite this, no tested model that explicitly and quantitatively includes the human element in risk prediction is currently available. Managing Risk: the Human Element combines descriptive and explanatory text with theoretical and mathematical analysis, offering important new concepts that can be used to improve the management of risk, trend analysis and prediction, and hence affect the accident rate in technological industries. It uses examples of major accidents to identify common causal factors, or echoes, and argues that the use of specific experience parameters for each particular industry is vital to achieving a minimum error rate as defined by mathematical prediction. New ideas for the perception, calculation and prediction of risk are introduced, and safety management is covered in depth, including for rare events and unknown outcomes Discusses applications to multiple industries including nuclear, aviation, medical, shipping, chemical, industrial, railway, offshore oil and gas; Shows consistency between learning for large systems and technologies with the psychological models of learning from error correction at the personal level; Offers the expertise of key leading industry figures involved in safety work in the civil aviation and nuclear engineering industries; Incorporates numerous fascinating case studies of key technological accidents. Managing Risk: the Human Element is an essential read for professional safety experts, human reliability experts and engineers in all technological industries, as well as risk analysts, corporate managers and statistical analysts. It is also of interest to professors, researchers and postgraduate students of reliability and safety engineering, and to experts in human performance. congratulations on what appears to be, at a high level of review, a significant contribution to the literatureI have found much to be admired in (your) research Mr. Joseph Fragola Vice President of Valador Inc. The book is not only technically informative, but also attractive to all concerned readers and easy to be comprehended at various level of educational background. It is truly an excellent book ever written for the safety risk managers and analysis professionals in the engineering community, especially in the high reliability organizations Dr Feng Hsu, Head of Risk Assessment and Management, NASA Goddard Space Flight Center I admire your courage in confronting your theoretical ideas with such diverse, ecologically valid data, and your success in capturing a major trend in them.I should add that I find all this quite inspiring . The idea that you need to find the right measure of accumulated experience and not just routinely used calendar time makes so much sense that it comes as a shock to realize that this is a new idea, Professor Stellan Ohlsson, Professor of Psychology, University of Illinois at Chicago

Recent progresses in Tritium radioecology and dosimetry

Abstract: In this paper, some aspects of recent progress in tritium radioecology and dosimetry are presented, with emphasis on atmospheric releases to terrestrial ecosystems. The processes involved in tritium transfer through the environment are discussed, together with the current status of environmental tritium models. Topics include the deposition and reemission of HT and HTO, models for the assessment of routine and accidental HTO emissions, a new approach to modeling the dynamics of tritium in mammals, the dose consequences of tritium releases and aspects of human dosimetry. The need for additional experimental data is identified, together with the attributes that would be desirable in the next generation of tritium codes.

The influence of curvature on membrane domains.

Abstract: An interdependence between local curvature and domain formation has been observed in both cell and model membranes. An implication of this observation is that domain formation in model membranes may be modulated by membrane curvature. In this paper, small-angle neutron scattering (SANS) is used to examine the influence of membrane curvature (i.e., vesicle size) on the formation of membrane domains. It is found that, although vesicle size and polydispersity are not significantly altered by the formation of membrane domains, the area fraction occupied by domains depends on the overall vesicle size. In particular, increasing membrane curvature (i.e., decreasing vesicle size) results in increased area fractions of membrane domains.

Supercritical Water-Cooled Nuclear Reactors (SCWRs): Current and Future Concepts — Steam Cycle Options

Abstract: One of the six Generation IV nuclear reactor concepts is a SuperCritical Water-cooled nuclear Reactor (SCWR), which is currently under development. The main objectives for developing and utilizing SCWRs are to increase the thermal efficiency of Nuclear Power Plants (NPPs), to decrease electrical energy costs, and possibility for co-generation, including hydrogen generation. Atomic Energy of Canada Limited (AECL) and Research and Development Institute of Power Engineering (RDIPE or NIKIET in Russian abbreviations) are currently developing pressure-tube SCWR concepts. The targeted steam parameters at the reactor outlet are approximately 25 MPa and 625°C. This paper presents a survey on modern SuperCritical (SC) steam turbine technology and a study on potential steam cycles for the SCWR plants. The survey reveals that by the time the Gen IV SCWRs are market-ready, the required steam turbine technology will be well proven. Three potential steam cycles in an SCWR plant are presented: a dual-cycle with steam reheat, a direct cycle with steam reheat, and a direct cycle with a Moisture Separator and Reheater (MSR). System thermal-performance simulations have been performed to determine the overall cycle efficiency of the proposed cycles. The results show that the direct cycle with steam reheat has the highest efficiency. The direct cycle with MSR is an alternative option, which will simplify the reactor design at the penalty of a slightly lower cycle efficiency.© 2008 ASME

Measurement of Rates of Delayed Hydride Cracking (DHC) in Zr-2.5Nb Alloys—An IAEA Coordinated Research Project

Abstract: Values of DHC rates in Zr alloys are sensitive to measurement procedures. A standard method has been developed at the laboratories of AECL and evaluated in a round-robin involving ten IAEA member states. Two test materials were used—Zr-2.5Nb pressure tubes in the cold-worked (CANDU™) and heat-treated (RBMK) conditions. Cracks were grown from fatigued starter cracks in the axial direction on the axial-radial plane of the original tubes. To obtain the maximum value of Vc, specimens were heated to dissolve all their hydrogen, then cooled at 1 to 3°C/min to the test temperature before loading at 15 MPa√m. Although the start of cracking was detected by potential drop, the extent of cracking was measured directly on the crack faces. The values of incubation time to the start of cracking were highly variable but Vc was well behaved. The values of Vc were normally distributed with a range varying from a factor of 1.2 to 5.2. At 250°C the mean value of Vc from 80 specimens of cold-worked material was 8.9(±1.12)×10-8 m/s and from 41 specimens of heat-treated material the mean value of Vc was 3.3(±0.64)×10-8 m/s. Tests were also done at six other temperatures between 144 and 283°C, using up to 22 specimens at each temperature. Both materials had an Arrhenius-type temperature dependence, Vc= A exp(-Q/RT). The use of strictly defined and coordinated experimental procedures gave a consistent set of Vc values, allowing effective comparison of results obtained in different national laboratories and resulting in good correlations between the DHC velocity values and differences in strength, crystallographic texture, and distribution of β-phase in the test materials.

Age-dependent changes in oxygen tension, radiation dose and sensitivity within normal and diseased coronary arteries-Part C: oxygen effect and its implications on high- and low-LET dose.

Abstract: Purpose: The aim is to study the implications of the decrease in oxygen concentration in the coronary artery walls with age and atherosclerosis, particularly with regard to an associated reduction in the radiosensitivity to high-and low-linear-energy-transfer (LET) irradiation.Materials and methods: In accompanying papers, the age-dependent morphology and composition for the wall layers of normal and diseased coronary arteries were developed in Part A from published data. In Part B, the oxygen concentration in the coronary artery walls was evaluated taking account the diffusion of oxygen from blood and the solubility of oxygen in tissues. In this part the oxygen effect was evaluated using published experimental data.Results: Based on simulation results from the one-dimensional diffusion model, the oxygen enhancement ratio (OER) is lower in the hypoxic vessel walls of aged and atherosclerotic arteries. Consequently the high-LET radiation damage arising from both the radon (222Rn) and thoron (220Rn) decay c...

Advanced Concepts for Pressure-Channel Reactors: Modularity, Performance and Safety

Abstract: Based on an analysis of the development of advanced concepts for pressure-tube reactor technology, we adapt and adopt the pressure-tube reactor advantage of modularity, so that the subdivided core has the potential for optimization of the core, safety, fuel cycle and thermal performance independently, while retaining passive safety features. In addition, by adopting supercritical water-cooling, the logical developments from existing supercritical turbine technology and “steam” systems can be utilized. Supercritical and ultra-supercritical boilers and turbines have been operating for some time in coal-fired power plants. Using coolant outlet temperatures of about 625°C achieves operating plant thermal efficiencies in the order of 45-48%, using a direct turbine cycle. In addition, by using reheat channels, the plant has the potential to produce low-cost process heat, in amounts that are customer and market dependent. The use of reheat systems further increases the overall thermal efficiency to 55% and beyond. With the flexibility of a range of plant sizes suitable for both small (400 MWe) and large (1400 MWe) electric grids, and the ability for co-generation of electric power, process heat, and hydrogen, the concept is competitive. The choice of core power, reheat channel number and exit temperature are all set by customer and materials requirements. The pressure channel is a key technology that is needed to make use of supercritical water (SCW) in CANDU®1 reactors feasible. By optimizing the fuel bundle and fuel channel, convection and conduction assure heat removal using passive-moderator cooling. Potential for severe core damage can be almost eliminated, even without the necessity of activating the emergency-cooling systems. The small size of containment structure lends itself to a small footprint, impacts economics and building techniques. Design features related to Canadian concepts are discussed in this paper. The main conclusion is that development of SCW pressure-channel nuclear reactors is feasible and significant benefits can be expected over other thermal-energy systems.

Age-dependent changes in oxygen tension, radiation dose and sensitivity within normal and diseased coronary arteries-Part A: dose from radon and thoron.

Abstract: Purpose: There is mounting evidence that a significant fraction of radiation-induced mortality and years-life lost are non-cancerous in nature This study quantifies the radon dose to the coronary artery walls, especially the intimal layer, vunerable to the development of atherosclerosis, and associated cardiovascular disease (CVD) Two accompanying papers determine the oxygen levels (Part B) in coronary arteries and the oxygen effect for radon and other exposures (Part C)Materials and methods: The alpha-radiation dose to coronary artery walls was calculated from the proportion of inhaled radon (222Rn), thoron (220Rn) and their short-lived progeny, which was not deposited in the lung and passed into blood Age- and gender-dependent morphology and composition for the wall layers of coronary arteries were developed from published data for a normal population and also for individuals with cardiovascular disease The alpha particle dose to the coronary artery walls was evaluated taking account the diffusion

Effect of CANDU Bundle-Geometry Variation on Dryout Power

Abstract: Dryout powers have been evaluated at selected inlet-flow conditions for two proposed designs of CANDU® bundles and compared to those of the 37-element and CANFLEX® bundles. These proposed designs consist of a large centre element (18 mm for one design and 20 mm for the other) and three rings of elements of 11.5 mm in outer diameter. The critical heat flux for each bundle design has been predicted using the correlation derived with Freon data obtained from the corresponding full-scale bundle test. An improvement in dryout power has been shown for the proposed design having a 20-mm centre element with a radial power profile corresponding to the natural-uranium fuel as compared to other bundles, particularly the natural-uranium 37-element bundle, with a symmetric cosine axial power profile. The dryout power improvement is further enhanced for the upstream-skewed axial power profile.© 2008 ASME

Laboratory bentonite colloid migration experiments to support the Äspö Colloid Project

Abstract: One of the objectives of the Aspo Colloid Project is to evaluate the potential of bentonite colloids to facilitate radionuclide transport Since bentonite colloids are not stable in Aspo groundwaters, the field-scale experiments performed at Aspo needed to be limited to using latex colloids To support the Aspo Colloid Project, laboratory scale colloid migration experiments, using both bentonite and latex colloids, were performed in the Quarried Block (QB) sample, a 1 m × 1 m × 07 m block of granite containing a single, well characterized, through-going, sub-horizontal, variable aperture fracture The main purpose of this laboratory program was to provide additional information that cannot be obtained on the field-scale regarding bentonite versus latex sphere colloid transport, particularly at low flow rates Tracer tests were performed as dipole experiments within the fracture plane using a borehole pair with a separation distance of 380 mm Flow rates and ionic strength were varied between tests With low ionic strength water, results showed that at high flow velocities typical of forced-gradient field-scale tracer tests (10’s cm/h), bentonite colloids and 100 nm latex colloids were mobile and had similar transport behaviour Differences in transport behaviour between the two colloid types became evident as flow velocity was reduced to centimeter per hour and then millimeter per hour, the latter being more typical of certain natural flow conditions Bentonite colloid recoveries were reduced by up to a factor of three and eluted colloid sizes were predominately in the smallest particle size range (4–15 nm), particularly at low flow velocities With high ionic strength, Aspo-type, water, bentonite colloids were not mobile in the QB fracture and could not readily be re-mobilized by subsequent injection of low ionic strength water