Showing papers by "Atomic Energy of Canada Limited published in 1992"

A variable step size LMS algorithm

Abstract: A least-mean-square (LMS) adaptive filter with a variable step size is introduced. The step size increases or decreases as the mean-square error increases or decreases, allowing the adaptive filter to track changes in the system as well as produce a small steady state error. The convergence and steady-state behavior of the algorithm are analyzed. The results reduce to well-known results when specialized to the constant-step-size case. Simulation results are presented to support the analysis and to compare the performance of the algorithm with the usual LMS algorithm and another variable-step-size algorithm. They show that its performance compares favorably with these existing algorithms. >

Production bias due to clustering of point defects in irradiation-induced cascades

Abstract: In the conventional rate-theory treatment of irradiation-induced dimensional changes based on the concept of dislocation bias, it is implicitly assumed that interstitials and vacancies are produced continuously and uniformly in the form of Frenkel pairs. This implies that all produced point defects are free and are available for annihilation at sinks. This approach may not be appropriate, however, for cases where the damage is produced in the form of cascades. In the cascades both vacancies and interstitials are produced in a highly segregated fashion in that the distributions of vacancies and interstitials are separated from each other in space. This spatial segregation is maintained even after the end of the thermal spike phase during which vacancies condense in the central region of the cascades whereas the high concentration of highly mobile interstitials form clusters at a certain distance from the cascade centre. The consideration of interstitial clustering within the cascade region yields ...

Diffusion of Iodide in Compacted Bentonite

Abstract: Diffusion coefficients, D, are critical parameters for predicting migration rates and fluxes of contaminants through dense bentonite-based barrier materials used in many waste containment strategies. Values of D were determined for I- (129I) is a relatively long-lived radionuclide present in high-level nuclear fuel waste, in saturated bentonite using both transient and steady-state techniques. The bentonite was compacted to dry densities, pb, ranging from 0.9 to 1.6 Mg m-3, and saturated with a synthetic groundwater solution having an ionic strength of 0.22. Two different D values were determined: an apparent diffusion coefficient, defined as Do(pi) and an effective diffusion coefficient, defined as Do(pi ne), where Do is the diffusion coefficient in pure bulk solution, the tortuosity factor, and ne the fraction of the porosity of the saturated clay that is available for diffusion. The value of Da decreased from approximately 6 X 10(-10) m2 s-1 at dry density approximately 0.9 Mg m-3 to 1 X 10(-10) ml s-1 at 1.6 Mg m-1. The decrease in Da with increasing dry density is attributed to a decrease in tortuosity factor as dry density increased. The effect dry density on effective diffusion coefficient was even greater: effective diffusion coefficient decreased from approximately 6 X 10(-11) m2 s-1 at dry density approximately 0.9 Mg m-3 to 3 X 10(-12) m2 s-1 at 1.6 Mg m-3. In addition to tortuosity effects, this decrease is ascribed to a decrease in n(e) with increasing dry density. For I-, n(e) is generally less than n (the total solution-filled porosity of the clay) because of factors such as anion exclusion. Within the dry density range examined, the migration time for 129I to move through the barrier material can be increased somewhat by increasing dry density; relative to the long half-life of 129I, however, the increased migration time is not significant. On the other hand, there appears to be a critical dry density value for this clay of approximately 1.4 Mg m-3, beyond which the flux of 129I from the clay can be markedly decreased. This critical value is probably a function or the specific surface area of the clay inasmuch as it influences the magnitude or the anion-exclusion volume. By compacting a bentonitic barrier material to a density greater than the critical value, the potential hazard associated with the long-term disposal of nuclear fuel waste that contains 129I can be decreased.

Thermodynamic calculation and experimental verification of the carbonitride-austenite equilibrium in Ti-Nb microalloyed steels

Abstract: The sublattice-regular solution model has been adapted to describe the thermodynamics of complex carbonitrides. This model has been applied to titanium- and niobium-bearing microalloyed steels for calculation of the mole fraction and composition of the carbonitride precipitates and the residual solute levels in the austenite. Both experimental results and calculations show that titanium nitride predominantly forms at very high temperatures and titanium-niobium carbides go to completion at low temperatures. Quantitative agreement between the experimental measurements and the predictions for carbonitride compositions as a function of temperature is demonstrated.

The influence of prior deformation on hydride precipitation in zircaloy

Abstract: Precipitation of hydrides has been studied in samples of Zircaloy subjected to prior tensile or compressive deformation before charging with hydrogen. The mean residual stress pattern in the alloys prior to charging was assessed by neutron diffraction techniques and provided a rough guide as to the preferred site of hydride nucleation. Heterogenous hydride nucleation at grain boudaries or twin boundaries was commonly found in samples subjected to 4% prior deformation, while transgranular hydrides were most frequently observed after a prior 1/2% compressive deformation or an annealing. The local stress state at grain boundary facets or twins is thought to be the deciding factor in determining where hydrides nucleate and how hydride stacks form.

C 12 (α,γ ) 16 O cross sections at stellar energies

Abstract: The excitation function of the $^{12}\mathrm{C}$(\ensuremath{\alpha},\ensuremath{\gamma}${)}^{16}$O reaction and the angular distribution of its \ensuremath{\gamma} rays were measured at nine energies ranging from ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.}$=1.37 to 2.98 MeV. These measurements allowed the separation of the E1 and E2 contributions and their extrapolation to the region of astrophysical interest. The analysis of the E1 cross sections with a three-level R-matrix method yields a prediction of ${1}_{\mathrm{\ensuremath{-}}1}^{+6}$ keV b for the S factor at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.}$=0.3 MeV. The contribution of E2 transitions at the same energy is 40\ifmmode\pm\else\textpm\fi{}7 keV b from a cluster-model analysis of the present data.

Interaction between bubbles and fibre optic probes in a bubble column

Abstract: Spherical bulb fibre optic probes, developed and applied for bubble characterization in a bubble column and a slurry bubble column at high temperature, were investigated. The principle of operation of these new optical fibre probes is based on the difference in refractive indices between the gas and the liquid phases. The interaction between the gas bubbles and the fibre optic probes in a bubble column was studied using photographic techniques. The first objective of these experiments was to study the response of the sensors upon contact with gas bubbles of various sizes. The second objective of this study was to establish, under controlled situations, the optical probe bubble detection performance and ability for local quantitative measurements of the bubble rise velocity and the gas hold-up. On a etudie des sondes a fibre optique a bulbe spherique, mises au point et appliquees pour la caracterisation des bulles dans une colonne a bulles et une colonne de suspensions bulleuses a une temperature elevee. Le principe de fonctionnement de ces nouvelles sondes a fibre optique est base sur la difference des indices de refraction entre les phases gazeuse et liquide. On a etudie a I'aide de techniques photographiques I'interaction entre les bulles de gaz et les sondes a fibre optique dans une colonne a bulles. Le premier objectif de ces experiences etait d'etudier la reponse des capteurs au contact avec des bulles de gaz de differentes tailles. Le deuxieme objectif de cette etude etait d'etablir, dans des situations controlees, la performance de detection des bulles de la sonde optique et la possibilite d'effectuer des mesures quantitatives locales de la vitesse de montee des bulles et de la retention de gaz.

Transient free convection and thermal stratification in uniformly-heated partially-filled horizontal cylindrical and spherical vessels

Abstract: An integral approach has been used to analyze the development of the free convection boundary layer on heated concave surfaces, such as those in horizontal cylinders or a sphere. Based on the non-dimensional laminar and turbulent velocity and temperature profiles closed form expressions for the boundary layer thickness, velocity scale as well as the boundary layer commencement after the point of instability are obtained. In addition, the mass flowrate to the thermal stratified region is given.

Differential transmit-receive eddy current probe incorporating bracelets of multi-coil units

Abstract: An eddy current probe for insertion into a tube to be inspected includes a transmitter coil and a pair of sensing coils. The pair of sensing coils have opposite polarity relative to one another and are series connected to provide a differential output. The pair of sensing coils and the transmitter coil are disposed on the surface of the probe. The pair of sensing coils being equally spaced from the transmitter coil and separate from each longitudinally on the probe. Each sensing coil in the pair of sensing coils is thereby angularly displaced from a plane transverse to the probe as measured from the transmitter coil with which a multi-coil unit is formed. Bracelets of coils are formed from plural multi-coil units aligned around the probe to improve sensitivity of the probe. Additional bracelets of coils may be added to the probe, offset rotationally, to improve coverage of the tube. The additional bracelets are longitudinally spaced to prevent interference between transmitter coils of one bracelet and receiver coils of the other bracelet.

Passive shutdown cooling system for nuclear reactors

Abstract: A nuclear reactor system including a heat transport path around which a coolant is pumped by main circulation pumps to transport heat from the reactor core to a steam generator. A further decay heat removal path is connected in parallel with the steam generator and main pumps and has a heat exchange component located at an elevation such that a natural convection flow will occur in the decay heat removal path when the main pumps are shutdown. Means are provided to mainain a small flow in the decay heat removal path during normal operation of the main pump. That small flow is in the intended direction of the natural convection circulation flow and maintains a temperature difference within the decay heat removal path that provides a buoyancy force to immediately start a natural circulation flow if the main pumps are shutdown. The main pumps are to be shutdown, as is the reactor, on loss of the steam generator as a heat sink. Then the natural convection flow in the decay heat removal path ensures that the heat exchange component is immediately available as an alternate heat sink. The small flow, during operation, can be provided by an additional pump in the decay heat removal path or by bleeding a small flow from an appropriate position in this path.

Hydrodynamic behaviour of a horizontal pulsed solvent extraction column. part 1: Flow characterization, throughput capacity and holdup

Abstract: A horizontal pulsed solvent extraction column (HPC) has great potential in replacing vertical pulsed columns (VPC) in the separation of heavy elements in the nuclear industry. Published work examining the performance of the HPC suggests that the mass transfer efficiency for this column is comparable to the VPC, but information on the hydrodynamic characteristics of the HPC is sparse. This paper describes the flow characteristics of the HPC and presents experimental results and correlations for flooding conditions and holdup of the dispersed phase. Correlations obtained for the HPC for these hydrodynamic parameters are compared to published results for the VPC. La colonne pulsee horizontale (HPC) servant a l'extraction de solvants montre un fort potentiel pour remplacer les colonnes pulsees verticales (VPC) dans la separation des elements lourds dans l'industrie nucleaire. Les travaux publies examinant la performance de la colonne horizontale suggerent que l'efficacite du transfert du matiere pour cette colonne est comparable a celle de la colonne verticale, mais les donnees sur les caracteristiques de la HPC sont rares. On decrit dans cet article les caracteristiques d'ecoulement de la HPC et on presente des resultats experimentaux et des correlations pour des conditions d'engorgement et la retention de la phase dispersee. Les corre'lations obtenues pour la colonne horizontale pour ces parametres hydrodynamiques sont comparees aux resultats publies pour la colonne verticale.

Release Kinetics of Volatile Fission Products Under Severe Accident Conditions

Abstract: An analytical model has been developed to describe the kinetic release behavior of the volatile fission product species (e.g., cesium) from uranium dioxide fuel. This treatment is based on the anal...

Catalytic Gas Sensors

Abstract: Many types of gas sensors employ a catalyst to improve their performance. However, the discussion in this chapter is focused on sensor systems combining a catalyst with a thermal probe that detects the heat released during the oxidation of a combustible gas on the catalyst surface. The roles of the catalyst, the thermal probe and filters for improving poison protection and selectivity are all considered, and available choices for these components are noted. Technical problems and limitations associated with matching the elements to obtain a functional, reliable “thermalcatalytic” sensor system are also reviewed.

Measured stopping powers of 16O and 19F ions in thin elemental films

Abstract: Absolute stopping values for 200–2000 keV ions of 16 O and 19 F were measured in targets of Be, C, Al, Si, Ni, Ti, Ag and Au by the thin-film transmission method. The results with estimated uncertainties of 5% are compared with semiempirical tabulations and measurements by others. The effective charge ratios of 16 O and 19 F ions to hydrogen were again found to be a complex function of ion energy and the stopping medium.

Void nucleation in constrained silver interlayers

Abstract: The process of void nucleation during fracture in thin brazed Ag interlayers has been investigated. Tensile tests were performed on interlayers of five thicknesses. The tensile strength increased rapidly with the ratio of interlayer diameter to thickness(D/T) for the thick interlayers(D/T < approximately 40) while the rate decreased significantly in the thin interlayers. All specimens fractured in the Ag interlayer along a plane near, and parallel to, the steel interface. The fracture surfaces showed silicon oxide inclusions at the bottom of many of the dimples. A series of finite element models were constructed to determine the general stress state in the interlayers and to determine the development of local stresses around inclusions in the interlayer. The finite ele- ment calculations indicated that the distribution of triaxial tension radially across the interlayer varied withD/T. Triaxial stresses, at failure, up to 10 times the uniaxial yield stress of the Ag were predicted from the model. The local stresses around a rigid inclusion in the interlayer developed more quickly, with applied stress, in the thicker interlayers as a result of the increased plastic deformation. The development of local stresses also increased with the proximity of the inclusion to the steel interface. By assuming a critical stress criterion for void nucleation at an inclusion interface, the finite element model was able to predict the experimentally observed nonlinear relationship between the interlayer failure stress andD/T.

Decontamination of Stainless Steel

Abstract: This paper discusses thermal desorption spectroscopy which was investigated as a means of measuring the tritium content and the nature of tritiated adsorbed species on stainless steel surfaces. Thermal desorption spectroscopy has been used to determine the effect of a helium glow discharge on a tritiated, 316 SS, surface. HTO proved to be the main desorption species. Glow discharge cleaning has been observed to reduce the amount of sorbed tritium by a factor of {ge}250.

Axial mixing and mass transfer in a vibrating perforated plate extraction column

Abstract: The axial mixing and countercurrent mass transfer characteristics of a 5 cm diameter extraction column agitated by vibrating perforated Teflon plates have been investigated. The dispersed phase was an organic liquid (usually kerosene) and the continuous phase was water. Axial mixing was measured in both phases using pulse tracer techniques; in the continuous phase the axial mixing was estimated to have a significant effect on mass transfer, but axial mixing in the dispersed phase had a negligible effect. Mass transfer was measured for several different solutes; n-butyric acid, benzoic acid and phenol. The overall heights of a transfer unit (cont. phase) were in the order of 10-20 cm for the organic-acids but higher for transfer of phenol from very dilute solutions. The characteristics of the vibrating plate column have been compared with those of other types of extractor and suggestions are made for further development. On a etudie les caracteristiques du melange axial et du transfert de matiere a contre-courant d'une colonne d'extraction de 5 cm de diametre agitee par des plateaux de Teflon perfores vibrants. La phase dispersee est un liquide organique (generalement du kerosene) et la phase continue de l'eau. Le melange axial a ete mesure dans les deux phases par des techniques de tracage pulse; dans la phase continue, on a trouve que le melange axial avait un effet significant sur le transfert de matiere, tandis que dans la phase dispersee, l'effet est negligeable. Le transfert de matiere a ete mesure pour differents solutes: acide n-butyrique, acide benzoique et phenol. Les hauteurs globales de l'unite de transfert (phase continue) sont comprises entre 10 et 20 cm pour les acides organiques mais elles sont plus elevees pour le transfert du phenol a partir de solutions tres diluees. Les caracteristiques de la colonne a plateaux vibrants sont compares a cells d'autres types d'extracteurs et des suggestions sont apportees pour de nouveaux developpements.

Environmental Monitoring of Tritium in Air with Passive Diffusion Samplersa

Abstract: A field trial in which outdoor air was sampled with an active reference sampler and several passive HTO-in-air samplers simultaneously was carried out at Chalk River Laboratories. Both passive and active samplers were changed on an approximately monthly schedule from 1990 September 2 to 1991 April 18. Average temperatures for the sampling intervals ranged from −8.6°C to +15.5°C and HTO-in-air concentrations measured by the active sampler were typically 10 Bq/m3. A total of 129 passive HTO-in-air sampler measurements were made during the seven sampling intervals. The passive samplers used for the field trial were of the type described by Stephenson,1 prepared with either tritium-free water or a solution of 50% tritium-free water and 50% ethylene glycol. As expected, the samplers prepared with the water-glycol solution performed more consistently than the samplers prepared with water only. Good agreement between passive and active sampler measurements was observed throughout the field trial. Passive...

Performance of wear-resistant iron base hardfacing alloys in valves operating under prototypical pressurized water reactor conditions☆

Abstract: Stroke cycling tests are being conducted on gate valves with iron base hardfacing materials under simulated pressurized water reactor (PWR) conditions to find an alternative to the cobalt-based Stellites. The first phase of the program under PWR conditions where the valves were opened and closed 2000 times over a period of about 1 year has recently been completed. The candidate alloys were EB 5183, EVERIT 50, NOREM 01 and NOREM 04. One valve with Stellite 6 trim served as a standard. Prior to testing, a base-line inaugural inspection was performed. At approximately 3 month intervals and 500 stroke cycles the performance of the alloys was monitored by non-destructive examination, profilometry and leak testing. Also, corrosion coupons were used to monitor metal loss from corrosion alone. The test results show all the candidate alloys performed better than Stellite 6. One valve with EB 5183 and a valve with NOREM 04 did not show any hot leakage as a result of stroke cycling.