Atomic Energy of Canada Limited

About: Atomic Energy of Canada Limited is a company organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Zirconium alloy & Neutron. The organization has 4845 authors who have published 4826 publications receiving 102951 citations.

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.

Circumstantial evidence for critical behavior in peripheral au + au collisions at 35 mev/nucleon

Abstract: The fragmentation resulting from peripheral Au + Au collisions at an incident energy of {ital E}=35 MeV/nucleon is investigated. A power-law charge distribution, {ital A}{sup {minus}{tau}} with {tau}{approx_equal}2.2, and an intermittency signal are observed for events selected in the region of the Campi scatter plot where {open_quote}{open_quote}critical{close_quote}{close_quote} behavior is expected. {copyright} {ital 1996 The American Physical Society.}

The relationship between gap inventories of stable xenon, 137Cs and 129I in used CANDU fuel

Abstract: Safety assessment of the used fuel disposal concept requires a study of the integrity of used fuel in contact with groundwater. In this context, the initial release of /sup 137/Cs and /sup 129/I from used Canada deuterium uranium fuel segments, exposed to water at 25/sup 0/C, has been studied as a function of fuel irradiation history. Percentages of inventories released after 5 days of leaching are compared to stable xenon fuel-sheath gap inventories. Cesium-137/xenon and /sup 129/I/xenon release ratios average --0.2 for low linear power rating (LLPR) fuel. For high linear power rating fuel, ratios are considerably larger and may approach 1. For LLPR fuel, the ratios become larger when the leaching time is increased. It is proposed that these differences are related to the microstructure of used fuel. The results indicate that the source term for the instantaneous release of isotopes of cesium and iodine should include all of the fuel-sheath gap inventory. Power history data and calculated gas release data can be used to accurately estimate the contribution of the fuel-sheath gap inventory to the source term for radionuclide release.