Showing papers by "Atomic Energy of Canada Limited published in 1998"

A practical guide to successful outsourcing

Abstract: Studies the outsourcing phenomenon, starting with strategic analysis and working through the many practical considerations and decisions that practising managers must make. As outsourcing is not to be taken lightly, the disadvantages are discussed in some detail. Of note too, are sections concerned with managing the outsourcing relationship, post outsourcing and morale, all concerned with the human resource management aspects of outsourcing.

Calculation of radiation dose rates in a water layer in contact with used CANDU UO2 fuel

Abstract: Alpha, beta, and gamma dose rates in water, in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (i.e., Bruce A CANDU fuel, burnup 685 GJ/kg U), are calculated as a function ofcooling time. Procedures to calculate the dose rates for used CANDU fuels of different burnups from results obtained for the reference fuel are described. These procedures can be adapted to estimate dose rates for fuels other than CANDU fuel. The dose rate information is needed to compare the results of leaching and corrosion experiments, conducted by different groups, with used fuels of different burnups and/or cooling times and to predict the effects of radiolysis of groundwater on used fuel oxidation and dissolution in a disposal vault.

Geophagy: who eats soil and where do possible contaminants go?

Abstract: Geophagy describes both purposeful and inadvertent ingestion of soil. It has long been recognized as a source of essential trace metals for wild animals and livestock, and soil ingestion by humans has also been associated with nutritional disorders. The amounts ingested purposefully by some people are large, up to 50 g/day. The amounts ingested inadvertently are much smaller and very difficult to quantify. The pathways include dust adhering to plants and to hands that ultimately is transferred to the mouth and ingested. Recently, this phenomenon has been highlighted because it can be the dominant pathway for ingestion of environmentally immobile soil contaminants. Three things must be known to estimate health impacts: how much soil is ingested, are the contaminant concentrations enriched on the soil particles ingested, and how bioavailable are the soil bound contaminants in the gut? Two hypothetical scenarios are examined in detail, one is the exposure of a child playing in lead (Pb)-contaminated sand, and the other is the exposure of a hunter consuming a deer that ingested soil at a surface discharge of deep saline groundwater in the vicinity of an underground nuclear waste repository.

Fretting-wear damage: a summary of recent findings

Abstract: Flow-induced vibration of steam generator (SG) tubes may sometimes result in fretting-wear damage at the tube-to-support locations. Fretting-wear damage predictions are largely based on experimental data obtained at representative test conditions. Fretting-wear of SG materials has been studied at the Chalk River Laboratories for two decades. Tests are conducted in fretting-wear test machines that simulate SG environmental conditions and tube-to-support dynamic interactions. A new high-temperature force and displacement measuring system was developed to monitor tube-to-support interaction (i.e., work-rate) at operating conditions. This improvement in experimental fretting-wear technology was used to perform a comprehensive study of the effect of various environment and design parameters on SG tube wear damage. This paper summarizes the results of tests performed over the past 4 yr to study the effect of temperature, water chemistry, support geometry, and tube material on fretting-wear. The results show a significant effect of temperature on tube wear damage. Therefore, fretting-wear tests must be performed at operating temperatures in order to be relevant. No significant effect of the type of water treatment on tube wear damage was observed. For predominantly impacting motion, the wear of SG tubes in contact with 410 stainless steel is similar regardless of whether Alloy 690 ormore » Alloy 800 is used as tubing material or whether lattice bars or broached hole supports are used. Based on results presented in this paper, an average wear coefficient value is recommended that is used for the prediction of SG tube wear depth versus time.« less

Vibration damping in multispan heat exchanger tubes

Abstract: Heat exchanger tubes can be damaged or fail if subjected to excessive flow-induced vibration, either from fatigue or fretting-wear. Good heat exchanger design requires that the designer understands and accounts for the vibration mechanisms that might occur, such as vortex shedding, turbulent excitation or fluidelastic instability. To incorporate these phenomena into a flow-induced vibration analysis of a heat exchanger requires information about damping. Damping in multispan heat exchanger tubes largely consists of three components: viscous damping along the tube, and friction and squeeze-film damping at the supports. Unlike viscous damping, squeeze-film damping and friction damage are poorly understood and difficult to measure. In addition, the effect of temperature-dependent fluid viscosity on tube damping has not been verified. To investigate these problems, a single vertical heat exchanger tube with multiple spans was excited by random vibration. Tests were conducted in air and in water at three different temperatures (25, 60, and 90 C). At room temperature, tests were carried out at five different preloads. Frequency response spectra and resonant peak-fitted damping ratios were calculated for all tests. Energy dissipation rates at the supports and the rate of excitation energy input were also measured. Results indicate that damping does not change overmore » the range of temperatures tested and friction damping is very dependent on preload.« less

Fretting Wear Damage of Heat Exchanger Tubes: A Proposed Damage Criterion Based on Tube Vibration Response

Abstract: A simple criterion is proposed to estimate fretting wear damage in heat exchanger tubes with clearance supports. The criterion is based on parameters such as vibration frequency, midspan vibration amplitude, span length, tube mass, and an empirical wear coefficient. It is generally accepted that fretting wear damage is proportional to a parameter called work rate. Work rate is a measure of the dynamic interaction between a vibrating tube and its supports. Due to the complexity of the impact-sliding behavior at the clearance supports, work rate calculations for heat exchanger tubes require specialized nonlinear finite element codes. These codes include contact models for various clearance support geometries. Such nonlinear finite element analyses are complex, expensive and time consuming. The proposed criterion uses the results of linear vibration analysis (i.e., vibration frequency and mid-span vibration amplitude due to turbulence) and does not require a nonlinear analysis. It can be used by nonspecialists for a quick evaluation of the expected work rate, and hence, the fretting wear damage of heat exchanger tubes. The proposed criterion was obtained from an extensive parametric study that was conducted using a nonlinear finite element program. It is shown that, by using the proposed work rate criteria, work rate can be estimated within a factor of two. This result, however, requires further testing with more complicated flow patterns.

Two-Phase Flow From a Stratified Region Through a Small Side Branch

Abstract: Experimental data are presented for the mass flow rate and quality of two-phase (air-water) discharge through a small branch (6.35 mm i.d.) located on the side of a large reservoir under stratified conditions. These data correspond to different values of the interface level between the onsets of gas and liquid entrainments for test-section pressures ranging from 316 to 517 kPa, test-section-to-separator pressure differences ranging from 40 to 235 kPa, and different hydraulic resistances of the line connecting the test section and separator. Influences of these independent variables on the mass flow rate and quality are discussed and normalized plots are presented showing that the data can be collapsed for a wide range of conditions. Comparisons are made with previous investigations and new empirical correlations are formulated and shown to be capable of predicting the present data with good accuracy.

Decreasing Collectivity in Smoothly Terminating Bands in the A ∼ 110 Region

Abstract: Lifetimes of states in two rotational bands in ${}^{108}\mathrm{Sn}$ and one in ${}^{109}\mathrm{Sb}$ have been determined using the Doppler shift attenuation method. The deduced quadrupole moments for the states are in excellent agreement with cranked Nilsson model predictions, which imply a gradual change in the nuclear shape from collective near-prolate at medium spin to noncollective oblate at high spin. This change results from the gradual alignment of the spin vectors of the valence particles and holes in a specific configuration. These data provide crucial evidence in support of the phenomenon of smooth band termination.

Radiation exposure and dose to small mammals in radon-rich soils.

Abstract: Protection of the environment from radionuclide releases requires knowledge of the normal background levels of radiation exposure in the exposed biotic community and an estimate of the detriment caused by additional exposure. This study modeled the background exposure and dose to the lungs of small burrowing mammals from 222Rn in artificial burrows in radon-rich soils at a site in southeastern Manitoba. E-PERM chambers used to measure 222Rn in soil showed good reproducibility of measurement, with an average coefficient of variance (CV) of about 10%. Geometric mean (GM) 222Rn concentrations at nine randomly selected sites ranged from 5,490 Bq/m3 (GSD = 1.57, n = 7) to 41,000 Bq/m3 (GSD = 1.02, n = 5). Long-term monitoring of 222Rn concentrations in artificial burrows showed large variation within and between burrows and did not show consistent variation with season, orientation of the burrow opening, or levels of 226Ra in the soil. Annual GM concentrations in individual burrows ranged from 7,480 Bq/m3 (GSD = 1.60) to 18,930 Bq/m3 (GSD = 1.81) in burrows several meters apart. A grand GM of 9,990 Bq/m3 (GSD = 1.81, n = 214) was measured over the site for the year. An exposure model was constructed for five small mammal species based on their respiration rates and the number of hours spent in the burrow, active or hibernating, exposed to soil gas 222Rn, and the time spent out of the burrow exposed to atmospheric 222Rn. A background dose of 0.9 mGy/a from atmospheric 222Rn (40 Bq/m3) was estimated for a large-bodied (80 kg), nonburrowing animal living on the soil surface. The highest exposures (mJ/a) in burrowing mammals occurred in those species with the highest respiration rates. Hibernation accounted for a small fraction of total annual exposure (<5%) because of very low respiration rates during this period. Absorbed dose to lung (mGy/a) was highest in the pocket gopher and decreased in the larger animals because of larger lung mass. Using mean 222Rn concentrations from the field studies and an equilibrium factor (F) of 0.5, doses to lung ranged from 90 mGy/a in the badger to 700 mGy/a in the pocket gopher. These doses closely correspond to those estimated from published dose conversion factors (DCFs) of 1.4 mGy per mJ · h/m3 for whole lung. For the ground squirrel, the DCF approach gives an estimated dose of 300 mGy/a versus 270 using the respiratory flow rate method. Based on these results, doses exceeding 500 mGy/a may be common in mammals and birds (i.e. the burrowing owl) living in radon-rich soils. Published risk coefficients for small mammals suggest that about 17 cancers would occur in 1,000 animals at these exposure rates. Although the potential effects from these exposures were not examined in this study, the study raises questions about how the animals may respond physiologically to this largely natural stress.

Control of the morphology and surface properties of nickel ferrite

Abstract: Nickel ferrite powders with particle sizes in the 3–5 μm range have been prepared from coprecipitated nickel–iron oxalate precursors. Firing the nickel–iron oxalate precursor in the range 300–1100°C produced samples of high chemical purity, while introducing significant variations in the distribution of crystallite sizes and surface morphologies. An increase in the powder density from 4.2 to 5.2 g cm-3 and a decrease in the surface area of the nickel ferrite from 120 to 0.2 m2g-1 were effected by increasing the firing temperature to 1100°C.

The Introduction of Microbial Nutrients into A Nuclear Waste Disposal Vault during Excavation and Operation

Abstract: AECL (Atomic Energy of Canada Limited) has developed a concept for permanent geological disposal of used nuclear fuel waste in Canada. This concept would involve disposal of the waste in corrosion-resistant metal containers, surrounded by compacted clay-based buffer and backfill materials, in a vault 500-1000 m deep in granitic rock of the Canadian Shield. Such a vault would not be a sterile environment. Microbial activity would be expected in those areas of a vault where effects of heat, moisture content, and radiation would not exclude microbial life and where sufficient nutrients would be present. Although the granitic rock environment is naturally nutrient-poor, a substantial amount of nutrients could be introduced from residues of explosives used in the excavation of a vault. Using standard rock leaching techniques, measurements of the concentrations of such residues were made in excavated rock, tunnel walls and mine service-water supplies at AECL's Underground Research Laboratory. The effects of these residues on the bacterial population size in groundwater were also determined. Results showed that the largest potential nutrient addition (both N and C) to a vault would result from using untreated broken rock as part of the backfill. Nitrate in the residues could increase groundwater bacterial populations by several orders of magnitude.

A two-phase boundary-layer model for laminar mixed-convection condensation with a noncondensable gas on inclined plates

Abstract: A finite-volume-based numerical model for mixed-convection laminar film condensation from a flowing mixture of a vapor and a heavier noncondensable gas on inclined isothermal flat plates is presented. The full boundary layer equations for the liquid film and the vapor-gas mixtures (including liquid inertia and energy convection terms) are solved implicitly with appropriate liquid-mixture interface conditions. Results were obtained for three mixtures, covering wide ranges of liquid Prandtl number and free-stream gas concentration in the forced-convection, mixed-convection and free-convection flow regimes. The effects of liquid inertia were found to be significant only for low-Prandtl-number fluids and lower gas concentrations. The effects of liquid energy convection were found to be significant only for high-Prandtl-number fluids and to be most significant for mixed-convection condensation.