Showing papers by "Atomic Energy of Canada Limited published in 1995"

Experimental Fretting-Wear Studies of Steam Generator Materials

Abstract: Flow-induced vibration of steam generator tubes results in fretting-wear damage due to impacting and rubbing of the tubes against their supports. This damage can be predicted by computing tube response to flow-induced excitation forces using analytical techniques, and then relating this response to resultant wear damage using experimentally derived wear coefficients. Fretting-wear of steam generator materials has been studied experimentally at Chalk River Laboratories for two decades. Tests are conducted in machines that simulate steam generator environmental conditions and tube-to-support dynamic interactions. Different tube and support materials, tube-to-support clearances, and tube support geometries have been studied. The effect of environmental conditions, such as temperature, oxygen content, pH and chemistry control additive, have been investigated as well. Early studies showed that damage was related to contact force as long as other parameters, such as geometry and motion, were held constant. Later studies have shown that damage is related to a parameter called work-rate, which combines both contact force and sliding distance. Results of short and long-term fretting-wear tests for CANDU steam generator materials at realistic environmental conditions are presented. These results demonstrate that work-rate is an appropriate correlating parameter for impact-sliding interaction.

Interfacial Heat Transfer Between Steam Bubbles and Subcooled Water in Vertical Upward Flow

Abstract: In two-fluid modeling, accurate prediction of the interfacial transport of mass, momentum, and energy is required. Experiments were carried out to obtain a data base for the development of interfacial transport models, or correlations, for subcooled water-steam bubbly flow in vertical conduits. The experimental data of interest included the interfacial area concentration, interfacial condensation heat transfer, and bubble relative velocity. In the present investigation, bubble condensation in subcooled water-steam flow in a vertical annulus at low flow rate and low pressure is investigated experimentally. A high-speed video system (up to 1000 frame/s) was used to visualize two orthogonal views of the flow simultaneously. A digital image processing technique was used to track and measure the velocity and size of the collapsing bubbles. The axial void fraction distribution was also measured by a single beam gamma densitometer.

Ingested soil: bioavailability of sorbed lead, cadmium, cesium, iodine, and mercury

Abstract: Ingestion of soil, inadvertent or otherwise, is an important route of exposure for contaminants that are not geochemically or biologically mobile. There is little known about the bioavailability of these contaminants, especially when the contaminants are sorbed onto native soil particles. We investigated this with in vitro acid-extraction and enzymolysis experiments and with in vivo single and chronic exposure studies with mice (Mus musculus). The only anion studied was 125 I, and soil in the diet had no effect on the carcass 125 I content. The bioavailability of the cations tested decreased in the order of 134 Cs> 203 Hg> 115 Cd= 210 Pb, and the effect of soil in the diet on concentrations in the carcass decreased in the same order. Soil in the diet significantly decreased the bioavailability of 134 Cs, by more than four-fold, whereas the effect on 210 Pb was only 1.1-fold and was not significant. The results of the in vitro digestions ordered theelements in the same way as observed in the in vivo analyses. These results indicate that for contaminants that are not very mobile and are sorbed onto native soil particles, the presence of soil in the diet does not markedly affect bioavailability in the gut

Fragment flow and the multifragmentation phase space.

Abstract: Fragment distributions have been measured for Au+Au collisions at [ital E]/[ital A]=100 and 1000 MeV. A high detection efficiency for fragments was obtained by combining the ALADIN spectrometer and the MSU-Miniball/WU-Miniwall array. At both energies the maximum multiplicity of intermediate mass fragments (IMF) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at [ital E]/[ital A]=100 MeV may be related to a reduction of the density in momentum space which is caused by the collective expansion.

Smooth Termination of Collective Rotational Bands.

Abstract: Rotational cascades observed in neutron-deficient nuclei with $Z\ensuremath{\approx}51$ are described as the first examples of smoothly terminating bands in heavy nuclei, since they show a continuous transition from high collectivity to a noncollective state. Excellent agreement between experiment and calculations in the Nilsson-Strutinsky cranking model is obtained for the ${}_{51}^{109}{\mathrm{Sb}}_{58}$ nucleus.

Recent advances in the understanding of damage production and its consequences on void swelling, irradiation creep and growth

Abstract: The consequences of displacement damage produced by energetic particles on physical and mechanical properties of metals and alloys have been investigated both experimentally and theoretically for several decades. Over the years, a number of theoretical models have been proposed to rationalize the rate and magnitude of defect accumulation under different irradiation conditions. In recent years, significant advances have been made in understanding the nature of the damage produced in this form of multi-displacement cascades. The new knowledge regarding the intra-cascade recombination and clustering of self-interstitial atoms and vacancies during the cooling-down phase of cascades makes it necessary to re-examine the appropriateness of the available models for describing the accumulation of damage under cascade damage conditions. In this paper, recent advances in the understanding of damage production and its consequences are reviewed. A historic perspective is adopted. A comprehensive analysis of the effects of temperature, dose rate and particle type on multi-phenomena (swelling, creep, growth, microstructure evolution, RED, RIS) is presented to discuss the strength and weakness of various models, as they have evolved with the understanding of the damage processes. It has been shown that the irradiation damage modeling has progressed from the standard rate theory model to the BEK model to the production bias model with an increasing degree of sophistication as increasingly more realistic features of the irradiation damage production process were incorporated. It is shown that the newly proposed production bias model uniquely includes the necessary features of cascade damage production in its treatment of the damage accumulation.

Are multifragment emission probabilities reducible to an elementary binary emission probability

Abstract: Experimental intermediate-mass-fragment multiplicity distributions for the [ital E]/[ital A]=80 and 110 MeV [sup 36]Ar+[sup 197]Au reactions are shown to be binomial at all excitation energies. From these distributions, a single binary event probability [ital p] can be extracted that has a thermal dependence. Thus, it is inferred that multifragmentation is reducible to a combination of nearly independent emission processes. If sequential decay is assumed, the increase of [ital p] with excitation energy implies a contraction of the time scale that is qualitatively consistent with recent fragment-fragment correlation data.

X-ray diffraction studies of oriented lipid bilayers

Abstract: This brief review of the X-ray diffraction technique used to study oriented lipid bilayer systems is primarily intended to demonstrate to the nonspecialist in the lipid field the amount of detailed information that can be obtained simply by visually inspecting the diffraction pattern and making some measurements with a ruler and protractor. The information that can be extracted from X-ray diffraction data is illustrated by selected examples of our most recent work.Key words: X-ray diffraction, oriented multibilayers, electron density profiles, subgel phase, phase problem.

Measurement of Compound Nucleus Space-Time Extent with Two-Neutron Correlation Functions.

Abstract: Two-neutron relative-momentum correlation functions have been measured in the 130 MeV {sup 18}O+{sup 26}Mg reaction. Differences in the longitudinal and transverse correlation functions, observed for the first time for neutrons, allow an independent determination of the spatial extent and the time scale for decay of the {sup 44}Ca compound nucleus. A comparison with theoretical calculations indicates a radius of 4.4{plus_minus}0.3 fm and an average neutron emission time scale of 1100{plus_minus}100 fm/{ital c} for {sup 44}Ca at 100 MeV excitation energy. Correlation functions selected by cuts on the total momentum of the neutron pair give a quantitative characterization of the cooling of a compound nucleus. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Use of semiquantitative reverse transcription-polymerase chain reaction to study gene expression in normal human skin fibroblasts following low dose-rate irradiation.

Abstract: One way to study the effect of radiation on gene expression is to monitor changes in the levels of specific messenger RNAs. We describe the use of reverse transcription-polymerase chain reaction (RT-PCR) analysis, a faster and more sensitive procedure than the traditional techniques to monitor RNA levels. Using RT-PCR, we confirmed previous results showing increased levels of GADD45 transcripts after high dose-rate X-irradiation in normal human fibroblasts. No differences were observed in the transcript levels of beta-ACTIN, beta-MICROGLOBULIN, Cu-Zn SUPEROXIDE DISMUTASE (SOD-1) and CATALASE. In cells exposed to 3-6 Gy low dose-rate gamma-irradiation we observed increased levels of the GADD45 transcript and lower transcript levels of the genes TOPOISOMERASE II alpha, FACC, CYCLIN A and CYCLIN B. No differences were detected in the transcript levels of beta-ACTIN, beta-MICROGLOBULIN, SOD-1, URACYL-DNA GLYCOSYLASE, CYCLIN C, CYCLIN E, CYCLIN D1, CYCLIN D2, CYCLIN D3, TOPOISOMERASE I and TOPOISOMERASE II beta.

The effect of 210Pb and stable lead on the induction of menta deformities in chironomus tentans larvae and on their growth and survival

Abstract: To determine whether menta deformities in chironomid larvae collected from Port Hope Harbor, Ontario, were the result of exposure to ionizing radiation or to heavy metals in the sediment, Chironomus tentans larvae were exposed in the laboratory to concentrations of {sup 210}Pb and stable lead representative of contaminant levels in the harbor. Exposure to 100, 1,000, and 2,000 Bq {sup 210}Pb g{sup {minus}1} dry sediment had no effect on larval survival, growth, or frequency of deformities. Likewise, exposure to 0.5 and 5.0 mg lead g{sup {minus}1} dry sediment had no effect on the larvae, but exposure to 35.0 mg lead g{sup {minus}1} dry sediment (the maximum levels observed in Port Hope Harbor) resulted in 100% mortality of the larvae. These results indicate that the observed mouthpart deformities in chironomid larvae of Port Hope Harbor are not the result of radiation exposure. They also indicate that heavy metals (lead) may be having an impact on the Port Hope Harbor population. Deformities were observed in all treatments and were confined mainly to the median tooth, with cleft or forked median teeth being the most common deformity. Restriction of the deformities to the median tooth is consistent with an inherited genetic effect, andmore » they consider them to be natural abnormalities. These natural abnormalities must be considered when using chironomid mouthpart deformities as an index of environmental degradation.« less

Low-heat high-performance concrete

Abstract: A Low Heat High Performance Concrete (LHHPC) composition having a very low cement content and high W/CM ratio offers high strengths, low heat of hydration, excellent volumetric stability, low chloride permeability and low pH. To reduce the cement content while maintaining high performance, silica fume and silica flour are used in large quantities. The LHHPC composition can be used for high mass concrete structures and other applications which require low heats of hydration yet offers compressive strength comparable to Standard High Performance Cement (SHPC).

Passive emergency water system for water-cooled nuclear reactors

Abstract: A passive emergency water system for cooling the atmosphere inside containment in a water-cooled nuclear reactor comprises an elevated water reservoir connected to an in-containment heat exchanger. The heat exchanger promotes natural convection of containment atmosphere and heat transfer. Heat from containment atmosphere is transferred to the reservoir by the in-containment heat exchanger via a convective return flowpath. The heat exchanger is preferably an elevated tube bank and the reservoir is preferably external to containment. Baffle walls can be used inside containment to promote circulation of containment atmosphere.

Parameter values to model the soil ingestion pathway.

Abstract: Soil ingestion is an important exposure pathway for contaminants that are not otherwise very mobile in the environment. Health of both humans and animals can be affected. This paper summarizes the literature and recommends models and probabilistic parameter values for risk assessment applications. Models of the pathway require estimates of the amounts of soil ingested, the concentration of contaminants relative to the original soil, and the bioavailability in the gut of the contaminants ingested with soil. Using a lead-contaminated sandbox as an example, the modelling recommendations suggest that a child typically may consume 50 mg d−1 of the sandbox soil, the soil ingested will have a tenfold higher lead concentration than the original soil, and the lead will be as bioavailable as if ingested as inorganic lead in water.

Numerical Modeling of Power Station Steam Condensers - Part 1: Convergence Behavior of a Finite-Volume Model.

Abstract: Computer simulation models of the flow and heat transfer in power station steam condensers have the potential for becoming important design tools These computer models may be used to improve existing designs by identifying ways to improve condenser vacuum and to minimize flow-induced tube vibration To date, such models seem to have experienced convergence problems, or require information to be specified that would not normally be known a priori This article describes components of a finite-volume model that is thought to be typical of those used by several investigators The convergence characteristics of this model are described when it is applied to two problems This model, and its convergence characteristics, provide a baseline against which improvements can be measured The impact of various improvements to this model are reported in a companion article

Electron beam current measuring device

Abstract: An electron linear accelerator for use in industrial material processing, comprises an elongated, resonant, electron accelerator structure defining a linear electron flow path and having an electron injection end and an electron exit end, an electron gun at the injection end for producing and delivering one or more streams of electrons to the electron injection end of the structure during pulses of predetermined length and of predetermined repetition rate, the structure being comprised of a plurality of axially coupled resonant microwave cavities operating in the π/2 mode and including a graded-β capture section at the injection end of the structure for receiving and accelerating electrons in the one or more streams of electrons, a β=1 section exit section at the end of the structure remote from the capture section for discharging accelerated streams of electrons from the structure and an rf coupling section intermediate the capture section and the exit section for coupling rf energy into the structure, an rf system including an rf source for converting electrical power to rf power and a transmission conduit for delivering rf power to the coupling section of the structure, a scan magnet disposed at the exit end of the structure for receiving the electron beam and scanning the beam over a predetermined product area and a controller for controlling the scanning magnet and synchronously energizing the electron gun and the rf source during the pulses.

A Numerical Model for the Corrosion of Copper Nuclear Fuel Waste Containers

Abstract: A model is presented for the prediction of the long-term corrosion behaviour of Cu nuclear fuel waste containers. The model is based on a kinetic description of the processes involved in the uniform corrosion of Cu in a conceptual Canadian disposal vault. The 1-dimensional, multilayer model accounts for mass-transport, electrochemical and chemical processes and predicts the spatial and temporal variations of the concentrations of various dissolved, precipitated and adsorbed species, as well as the time dependence of the corrosion rate and the corrosion potential (ECORR). The variation of [02], [Cu(II)] and ECORR with time can also be used to predict the maximum period over which localized corrosion processes, such as pitting or stress corrosion, may occur. Predictions from the model suggest that 25-mm-thick Cu containers will not fail due to uniform corrosion or pitting in periods ≥106 a.

Overview of current RFSP-code capabilities for CANDU core analysis

Abstract: The Reactor Fuelling Simulation Program (RFSP) is the major computer program in use at Atomic Energy of Canada Limited for the design and analysis of the Canadian deuterium uranium (CANDU) reactor cores. It has seen continuing development in response to growing needs. The major calculational method in RFSP is the solution by finite difference of the neutron diffusion equation in three dimensions and two energy groups. However, a flux-mapping method for reconstructing the core flux distribution is also available. The most important code capabilities are described in this paper.

Modelling the Consumption of Oxygen by Container Corrosion and Reaction with Fe(II)

Abstract: A model is described that predicts the rate of O 2 consumption in a sealed nuclear fuel waste disposal vault as a result of container corrosion, reaction with biotite and the oxidation of organics and other oxidizable impurities in the clay. The most important reactions leading to the consumption of O 2 for Cu containers in a conceptual Canadian disposal vault are container corrosion, the oxidation of dissolved Cu(I) and the oxidation of organics and other impurities in the clay. Consumption of O 2 by the oxidation of dissolved Fe(II) from biotite is significant in backfill materials containing crushed granite and in the rock itself. The O 2 initially trapped in the disposal vault is predicted to be consumed in between 50 and 670 a.