Showing papers by "Atomic Energy of Canada Limited published in 2002"
TL;DR: It is demonstrated that doses as low as (on average) about one track per cell (1 mGy) produce the same maximum adaptive response as do doses that deposit many tracks per cell, and that the two radiations were not different in this regard.
Abstract: Broome, E. J., Brown, D. L. and Mitchel, R. E. J. Dose Responses for Adaption to Low Doses of 60Co γ Rays and 3H β Particles in Normal Human Fibroblasts. Radiat. Res. 158, 181–186 (2002). The dose response for adaption to radiation at low doses was compared in normal human fibroblasts (AG1522) exposed to either 60Co γ rays or 3H β particles. Cells were grown in culture to confluence and exposed at either 37°C or 0°C to 3H β-particle or 60Co γ-ray adapting doses ranging from 0.1 mGy to 500 mGy. These cells, and unexposed control cells, were allowed to adapt during a fixed 3-h, 37°C incubation prior to a 4-Gy challenge dose of 60Co γ rays. Adaption was assessed by measuring micronucleus frequency in cytokinesis-blocked, binucleate cells. No adaption was detected in cells exposed to 60Co γ radiation at 37°C after a dose of 0.1 mGy given at a low dose rate or to 500 mGy given at a high dose rate. However, low-dose-rate exposure (1–3 mGy/min) to any dose between 1 and 500 mGy from either radiation, de...
94 citations
TL;DR: In this article, the authors investigated how gases can break through compacted specimens of illite, bentonite, and sand-illite or sand-bentonite mixtures.
59 citations
TL;DR: Fretting tests of Zircaloy fuel sheath bearing pads in contact with zirconium alloy (Zr 2.5Nb) pressure tube specimens were conducted at temperatures varying from 25 to 315 °C as mentioned in this paper.
47 citations
TL;DR: In this paper, the suction and strength characteristics for a dense, compacted, unsaturated sand-bentonite mixture under a variety of preparation and stressing conditions were determined experimentally using thermocouple psychrometers and the filter paper method.
46 citations
TL;DR: The Canadian Shield brines are characterized by high concentrations of both stable iodine and 1 2 9 I, the former reflecting its concentrated but diagenetically modified seawater origin, and the latter its long subsurface residence time within its host shield rocks as mentioned in this paper.
Abstract: Canadian Shield brines are characterized by high concentrations of both stable iodine and 1 2 9 I, the former reflecting its concentrated but diagenetically modified seawater origin, and the latter its long subsurface residence time within its host shield rocks. Stable iodine concentrations in the Yellowknife brine are as high as 18 mg/L, requiring the contribution of iodine from an external marine reservoir. This reservoir likely comprised organic-rich marine sediments in the basin where the brine was produced. Diagenesis of these sediments released iodine to the brine during its infiltration into the subsurface. 1 2 9 I concentrations in the Yellowknife brine are as high as 3.4 x 10 8 atom/L and are due to the fission of 2 3 8 U in the rock matrix and subsequent diffusion of the radiogenic 1 2 9 I into the fracture fluids. This concentration is close to the predicted secular equilibrium concentration for a fluid in basaltic rock with a uranium concentration of 1 mg/kg after the residence time of ∼80 m.y. required for secular equilibrium has been attained. This time period is interpreted as the minimum residence time of the Yellowknife brine in the shield, but it may be much greater, possibly dating back to Middle Devonian time when most of the present-day shield was covered by seawater. Similarly high stable iodine and 1 2 9 I concentrations measured in the Sudbury brine support a generic, ancient marine hypothesis for the origin of shield brines. Stable iodine and 1 2 9 I concentrations in the shallower mine waters are the result of mixing between the brine and low-iodine modern meteoric recharge that is enriched in 1 2 9 I due to global fallout from nuclear fuel waste reprocessing activities.
46 citations
TL;DR: In this paper, the authors used U-series data to verify the finding of fast flowpaths through the tuff to ESF level, indicated by the presence of 36Cl in pore fluids.
45 citations
TL;DR: The results of a series of tests describing the vibration behavior of several rotated triangular tube bundles subjected to two-phase cross flows are presented in this paper, where tube bundles with a pitch-to-diameter ratio of approximately 1.5 were tested over a broad range of void fractions and mass fluxes.
Abstract: The results of a series of tests describing the vibration behavior of several rotated triangular tube bundles subjected to two-phase cross flows are presented. Tube bundles with a pitch-to-diameter ratio of approximately 1.5 were tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, hydrodynamic mass, two-phase damping and local void-fraction were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability lead-ing to lower than expected threshold flow velocities for instability, This effect was more pronounced in Freon two-phase flow than in air-water, and appeared well correlated to the transition between continuous and intermittent flow regimes. Generally, random turbulence excitation forces were much lower in Freon than in air-water. Although very dependent on void fraction, as expected, damping was quite similar in air-water and Freon.
45 citations
TL;DR: In this article, the steady-state thermal creep rate in the axial and transverse directions of Zr-2.5Nb of pressure tubes, used in CANDU nuclear reactors, was determined.
Abstract: The steady-state thermal creep rate in the axial and transverse directions of Zr-2.5Nb of pressure tubes, used in CANDU nuclear reactors, was determined. The data were obtained both from tensile samples having their tensile axes cut along the axial and transverse directions of the pressure tubes and from small-sized, thin-walled tubes, i.e., “mini” tubes stressed either in torsion or by internally pressurizing capsules manufactured from the mini tubes, or by additionally applying an external, axial load on these internally pressurized capsules. The temperature range of the data was from 373 to 596 K (100 °C to 323 °C) and the duration of the tests was from about 1500 hours to over 12,000 hours. The tests were carried out over a sufficiently long time for the creep rate to be measurable in the steady-state creep regime. It was found that the steady-state creep rate depends on stress in a nonlinear fashion and the stress exponent over the entire temperature range was about four. This value is consistent with the values measured earlier on other zirconium alloys. The activation energy Q was found to be about 21 and 10 kcal/mol for temperatures above and below 475 K (∼ 200 °C), respectively. These values are lower than those measured by other investigators on the same material at higher temperatures but similar to values found on other Zr alloys at low temperatures. It appears that Q is dependent on temperature and its value is consistent with the presence of dynamic strain aging (DSA). The results of this study were analyzed with a polycrystalline, nonlinear self-consistent model that take into account the crystallographic texture of the material. This model was used to derive the values of critical resolved shear stress (CRSS), which are consistent with prismatic, basal, and pyramidal glide. By using these values and the apparent temperature dependence of Q, it was shown that this model predicts well the steady-state creep rate over the entire temperature range and under very different stress states.
45 citations
TL;DR: The highly nonlinear features of the data point to a nonlinear dose-effect relationship at low doses and indicate that linear extrapolation from moderate (or high-to-low doses and dose-rates) may not be justified for in vitro studies of the cell line under consideration.
Abstract: Purpose : To test whether data that show protective effects of low doses against spontaneous neoplastic transformation of C3H 10T1/2 cells can be explained with a biomathematical model that includes radioprotective mechanisms. To link important features of the model to known biological processes. Materials and methods : The model simulates double-strand break formation in transcriptionally active and in bulk DNA, translocation of DNA segments, and the fixation of damage at mitosis; promotion is also included. The model equations were solved numerically using a stiff solver. Results : The data were successfully simulated by the model: cell transformation-reducing effects of low doses of γ-radiation delivered at low dose-rates are explained by radiation-inducible DNA repair and enzymatic scavenging. Conclusions : The model successfully simulates experimental data. The highly nonlinear features of the data point to a nonlinear dose-effect relationship at low doses and indicate that linear extrapolation from ...
36 citations
TL;DR: Iodine species released into a reactor containment building following a loss-of-coolant accident is determined by the relative timing and quantity of iodine and other fission products released from... as discussed by the authors.
Abstract: Iodine species released into a reactor containment building following a loss-of-coolant accident is determined by the relative timing and quantity of iodine and other fission products released from...
35 citations
TL;DR: In this article, area-scale fractal dimensions have been calculated from the atomic force microscopy (AFM) measurements for these oxides as a function of anodization voltage.
01 Apr 2002-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a calibration source using γ-rays from 16N (t 1/2=7.13 s) β-decay has been developed for the Sudbury Neutrino Observatory (SNO) for the purpose of energy and other calibrations.
Abstract: A calibration source using γ-rays from 16N (t1/2=7.13 s) β-decay has been developed for the Sudbury Neutrino Observatory (SNO) for the purpose of energy and other calibrations. The 16N is produced via the (n,p) reaction on 16O in the form of CO2 gas using 14-MeV neutrons from a commercially available Deuterium-Tritium (DT) generator. The 16N is produced in a shielding pit in a utility room near the SNO cavity and transferred to the water volumes (D2O or H2O) in a CO2 gas stream via small diameter capillary tubing. The bulk of the activity decays in a decay/trigger chamber designed to block the energetic β-particles yet permit the primary branch 6.13 MeV γ-rays to exit. Detection of the coincident β-particles with plastic scintillator lining the walls of the decay chamber volume provides a tag for the SNO electronics. This paper gives details of the production, transfer, and triggering systems for this source along with a discussion of the source γ-ray output and performance.
TL;DR: In this article, the effect of flow obstacles on critical heat flux (CHF) enhancement was investigated using a vertical 6.92 mm tube, cooled with R-134a, with a pressure range from 0.96 to 2.39 MPa, a mass flux range from 500 to 3000 kgm−m−2 ǫs−1, and an outlet (critical) quality range from −0.05 to +0.95.
TL;DR: It is concluded that radiation-induced teratogenesis reflects both Trp53-dependent and independent processes that lead to apoptosis, and these respond differently to prior adapting doses.
Abstract: Mitchel, R. E. J., Dolling, J-A., Misonoh, J. and Boreham, D. R. Influence of Prior Exposure to Low-Dose Adapting Radiation on Radiation-Induced Teratogenic Effects in Fetal Mice with Varying Trp53 Function. Radiat. Res. 158, 458–463 (2002). Teratogenesis in tails and limb digits of fetal mice with varying Trp53 status was examined after exposure of pregnant females to 4 Gy γ radiation with and without a prior 30-cGy exposure. Prior low-dose exposure modified the teratogenic effects of radiation in a manner dependent upon Trp53 status and gestation time. A 4-Gy exposure on gestation day 11 resulted in tail shortening and digit abnormalities. A 30-cGy exposure 24 h prior to a 4-Gy radiation exposure on day 11 reduced the extent of both digit abnormalities and the tail-shortening effects in Trp53+/+ fetuses and also reduced tail shortening in Trp53+/− fetuses, but to a lesser extent. However, the pre-exposure enhanced the tail-shortening effects of 4 Gy in Trp53−/− fetuses. In contrast, a 30-cGy ex...
TL;DR: The isothermal test (ITT) as discussed by the authors was used to measure the response of buffer to resaturation by groundwater over a 6.5-year period by placing ∼2.4 m 3 of clay-based buffer in a borehole at the 240 m level of AECL's Underground Research Laboratory.
TL;DR: In this paper, an iterative deconvolution method has been applied to extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen.
Abstract: X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few, if any, c-component dislocations present.
TL;DR: In this article, an experimental study of the critical heat flux (CHF) in horizontal and vertical tubes cooled with R-134a has been completed, and the effect of orientation on CHF was found to depend on mass flux, quality and pressure, as well as the limiting critical quality.
TL;DR: The observations of K lines are reported, which establish the experimental basis for direct crystallographic phasing of atomic structures containing incoherent scatterers, such as hydrogen, via thermal neutron "inside source" holography.
Abstract: In this Letter we report the observation of K lines (representing collectively, Kossel and Kikuchi lines) produced by monochromatic thermal neutrons interacting with a KDP (potassium dihydrogen phosphate) single crystal. Since K lines contain phase information, these observations establish the experimental basis for direct crystallographic phasing of atomic structures containing incoherent scatterers, such as hydrogen, via thermal neutron "inside source" holography.
TL;DR: In this article, the development of the understanding of the intergranular stresses in ZIRCALOY-2 is reviewed, and it is almost certain that tensile twinning is the explanation for the response to compressive stress and rolling that is, as yet, incompletely understood.
Abstract: The development of the understanding of the intergranular stresses in ZIRCALOY-2 is reviewed. Neutron diffraction measurements of the intergranular strains were made on rod-textured material and highly textured plate. The elastoplastic self-consistent (EPSC) model provides a sound theoretical foundation for our understanding of the behavior. The strain response of ZIRCALOY-2 to applied tensile stress is well described for two very different textures with the same slip and hardening parameters. It is almost certain that tensile twinning is the explanation for the response to compressive stress and rolling that is, as yet, incompletely understood.
01 Jan 2002
TL;DR: In this article, a cavity mounted on the wall of a duct to investigate the effect of "confinement", i.e., solid boundaries close to the cavity, on the aeroacoustic response of shallow cavities in low Mach number flow (M < 0.3).
Abstract: Shallow cavities exposed to unbounded, low Mach number flow are generally weak aeroacoustic sources because their acoustic modes are heavily damped. This paper focuses on a cavity mounted on the wall of a duct to investigate the effect of “confinement”, i.e. solid boundaries close to the cavity, on the aeroacoustic response of shallow cavities in low Mach number flow (M < 0.3). It is found that the transverse acoustic modes of the duct-cavity combination are excited by the higher order modes of the cavity shear layer oscillations. The nature of the excitation mechanism as well as the effects of the cavity and duct dimensions are investigated by means of measurements of the amplitude and phase distributions of the acoustic pressure, complemented with flow visualization of the cavity shear layer oscillation. A method to predict the onset of resonance is also suggested. It is also shown that the acoustic resonance is effectively suppressed by a feedback control method, which generates a synthetic jet acting at the cavity upstream corner. The effect of the phase and gain of the controller transfer function is studied in some detail.Copyright © 2002 by ASME
TL;DR: The results may suggest that at later times in organ development, DNA repair is more active, allowing some cells to escape radiation-induced Trp53-dependent apoptosis, but heat may be able to significantly inhibit this active repair and increase the teratogenic effect of radiation.
Abstract: Boreham, D. R., Dolling, J-A., Misonoh, J. and Mitchel, R. E. J. Radiation-Induced Teratogenic Effects in Fetal Mice with Varying Trp53 Function: Influence of Prior Heat Stress. Radiat. Res. 158, 449–457 (2002). Teratogenesis induced by radiation in fetal mice has been closely linked to Trp53-dependent apoptosis. This study examined teratogenesis in tails and limb digits of fetal mice with varying Trp53 status after a 4-Gy radiation exposure, with and without a prior 40.5°C, 60-min heat stress. Irradiation earlier in gestation (day 11) produced greater effects than later (day 12) exposure, but in both cases the maximum teratogenic effect of radiation occurred in Trp53 normal fetuses, the minimum in Trp53 null fetuses, and intermediate effects in Trp53 heterozygotes, indicating dominance of Trp53-dependent apoptosis. Heat stress 24 h prior to irradiation on day 11 did not alter the teratogenic effects in Trp53 normal or heterozygous fetuses, but it reduced effects in the Trp53 null fetuses. Conver...
01 Jan 2002
TL;DR: In this paper, the effects of types of motion and loading conditions on the wear of PWR fuel rod cladding made of Zircaloy-4 in contact with a grid support cell were investigated.
Abstract: The objective of this study was to investigate the effects of types of motion and loading conditions on the wear of Pressurized Water Reactor (PWR) fuel rod cladding made of Zircaloy-4 in contact with a grid support cell. Fretting-wear tests, for various combinations of motion and preload, were conducted at 310°C and 11.7 MPa using primary circuit water chemistry. Wear coefficients, derived from three-dimensional profilometry, were used to assess the severity of the wear process. The types of motion and the loading conditions were found to have a significant interdependent effect on fuel rod wear coefficients. Scanning Electron Microscope (SEM) examinations were performed on the worn fuel rod cladding specimens to identify wear mechanisms.Copyright © 2002 by ASME
TL;DR: The residual intergranular strain tensors in textured Zircaloy-2 plate samples induced by cooling from 823 K to ambient temperatures were measured by neutron diffraction as discussed by the authors.
01 Jan 2002
01 Jan 2002
TL;DR: In this paper, the authors present comparative thermodynamic and economic assessments of the CANDU-X cycle options, with the ultimate goal of ascertaining which particular cycle option is the best overall in terms of thermodynamics and economics.
Abstract: Research underway on the advanced CANDU examines new, innovative, reactor concepts with the aim of significant cost reduction and resource sustainability through improved thermodynamic efficiency and plant simplification. The so-called CANDU-X concept retains the key elements of the current CANDU designs, including heavy-water moderator that provides a passive heat sink and horizontal pressure tubes. Improvement in thermodynamic efficiency is sought via substantial increases in both pressure and temperature of the reactor coolant. Following on from the new Next Generation (NG) CANDU, which is ready for markets in 2005 and beyond, the reactor coolant is chosen to be light water but at supercritical operating conditions. Two different temperature regimes are being studied, Mark 1 and Mark 2, based respectively on continued use of zirconium or on stainless-steel-based fuel cladding. Three distinct cycle options have been proposed for Mark 1: the High-Pressure Steam Generator (HPSG) cycle, the Dual cycle, and the Direct cycle. For Mark 2, the focus is on simplification via a Direct cycle. This paper presents comparative thermo-economic assessments of the CANDU-X cycle options, with the ultimate goal of ascertaining which particular cycle option is the best overall in terms of thermodynamics and economics. A similar assessment was already performed for the NG CANDU. The economic analyses entail obtaining cost estimates of major plant components, such as heat exchangers, turbines and pumps.Copyright © 2002 by ASME
TL;DR: Some of the special applications of classical microdosimetry such as the determination of kerma coefficients, differential dosimetry and aviation dosIMetry are reviewed, as well as some of the technological innovations related to the application of micro Dosimetry in operational health physics and in particular the development of multi-element proportional counters and detectors based on gas microstrip technology.
Abstract: Classical microdosimetry concerns the measurement and analysis of the spectrum of radiation energy deposition events in simulated microscopic tissue-equivalent sites. Over the past three decades, classical microdosimetry has been extensively applied for the direct measurement of dosimetric quantities, such as the ambient dose equivalent, and for the spectroscopic properties of tissue-equivalent proportional counters that have led to methods of mixed-field analysis and particle identification. This paper reviews some of the special applications of classical microdosimetry such as the determination of kerma coefficients, differential dosimetry and aviation dosimetry. Also reviewed are some of the technological innovations related to the application of microdosimetry in operational health physics and in particular the development of multi-element proportional counters and detectors based on gas microstrip technology.
01 Jan 2002
TL;DR: An overview of vibration analysis procedures and recommended design guidelines is presented in this paper, which pertains to liquid, gas and two-phase heat exchanger such as nuclear steam generators, reboilers, coolers, service water heat exchangers, condensers, and moisture-separator-reheaters.
Abstract: Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heat exchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heat exchangers such as nuclear steam generators, reboilers, coolers, service water heat exchangers, condensers, and moisture-separator-reheaters. Generally, a heat exchanger vibration analysis consists of the following steps: 1) flow distribution calculations, 2) dynamic parameter evaluation (i.e. damping, effective tube mass, and dynamic stiffness), 3) formulation of vibration excitation mechanisms, 4) vibration response prediction, and 5) resulting damage assessment (i.e., comparison against allowables). The requirements applicable to each step are outlined in this paper. Part 1 of this paper covers flow calculations, dynumic parameters and fluidelastic instability.Copyright © 2002 by ASME
TL;DR: With the inclusion of inducible radioprotective mechanisms in a radiobiological state-vector model it was possible to explain plateaus in dose-response relationships for neoplastic transformation produced by in vitro irradiation of different cell lines with low-LET irradiation at high dose rates.
Abstract: With the inclusion of inducible radioprotective mechanisms in a radiobiological state-vector model it was possible to explain plateaus in dose-response relationships for neoplastic transformation produced by in vitro irradiation of different cell lines with low-LET irradiation at high dose rates. The current study repeated the simulation of one data set that contains a plateau at mid doses. In contrast to earlier studies, the new one did not model the repair of double-strand breaks (DSBs) located in bulk DNA (likely via non-homologous end joining) as being inducible. Repair of specific DSBs located in actively transcribed genes was assumed to occur via homologous recombination and was considered to be inducible. This reduced the number of parameters that have to be determined by fitting the model to data. In addition, all types of radical scavengers were formerly considered to be inducible by radiation. This was redefined in the current work and the effectiveness of scavengers was implemented in a refined way. The current work investigated whether these and other model adjustments lead to an improved fit of the data set.
01 Jan 2002
TL;DR: The data suggest that Trp 53-dependent or independent apoptosis may not be directly involved in heat-induced teratogenesis, but that the primary teratogenic effect of heat results from the disruption of another tail length-regulating process that is independent of Trp53.
Abstract: Boreham, D. R., Dolling, J-A., Misonoh, J. and Mitchel, R. E. J. Teratogenic Effects of Mild Heat Stress during Mouse Embryogenesis: Effect of Trp53. Radiat. Res. 158, 443–448 (2002). Hyperthermia can be teratogenic in fetal mice exposed during organogenesis, an effect considered to be due to heat-induced apoptosis of cells in the developing organs. We exposed pregnant mice carrying Trp53+/+, Trp53+/− and Trp53−/− fetuses to mild whole-body hyperthermia that raised their core temperature to 40.5°C for 60 min on either day 10 or 11 of gestation. On day 18 of gestation, the fetuses were removed from control and hyperthermia-treated mice and genotyped, and tail length was measured. Limb digits were examined for abnormalities. Tail length in unheated control fetuses was influenced by Trp53 status. A complete lack of functional Trp53 (Trp53−/−) but not partial lack of function (Trp53+/−) resulted in shorter tails compared to Trp53+/+ fetuses, indicating a role for Trp53 in the regulation of tail lengt...