Showing papers by "Atomic Energy of Canada Limited published in 2001"

Measurement of the rate of ve + d → p + p + e- interactions produced by 8B solar neutrinos at the sudbury neutrino observatory

Abstract: Solar neutrinos from the decay of 8B have been detected at the Sudbury Neutrino Observatory (SNO) via the charged current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to νe, while the ES reaction also has a small sensitivity to νμ and ντ. The flux of νe from 8B decay measured by the CC reaction rate is φCC(ν e )=[1.75±0.07(stat.) −0.11 +0.12 (syst.)×0.05(theor.)]×106cm−2s−1. Assuming no flavor transformation, the flux inferred from the ES reaction rate is φES(ν x )=[2.39±0.34(stat.) −0.14 +0.16 (syst.)]×106cm−2s−1. Comparison of φCC(νe) to the Super-Kamiokande collaboration’s precision value of φES(νx) yields a 3.3σ difference, assuming the systematic uncertainties are normally distributed, providing evidence that there is a nonelectron flavor active neutrino component in the solar flux. The total flux of active 8B neutrinos is thus determined to be (5.44±0.99)×106 cm−2 s−1, in close agreement with the predictions of solar models.

Dosimetry of beta-ray ophthalmic applicators: comparison of different measurement methods

Abstract: An international intercomparison of the dosimetry of three beta particle emitting ophthalmic applicators was performed, which involved measurements with radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets, plastic scintillators, extrapolation ionization chambers, a small fixed-volume ionization chambers, a diode detector and a diamond detector. The sources studied were planar applicators of 90Sr-90Y and 106Ru-106Rh, and a concave applicator of 106Ru-106Rh. Comparisons were made of absolute dosimetry determined at 1 mm from the source surface in water or water-equivalent plastic, and relative dosimetry along and perpendicular to the source axes. The results of the intercomparison indicate that the various methods yield consistent absolute dosimetry results at the level of 10%-14% (one standard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standard deviation) depending on the source and the depth. Crucial to the proper interpretation of the measurement results is an accurate knowledge of the detector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are suggested.

Calculation of beta-ray dose distributions from ophthalmic applicators and comparison with measurements in a model eye.

Abstract: Dose distributions throughout the eye, from three types of beta-ray ophthalmic applicators, were calculated using the EGS4, ACCEPT 3.0, and other Monte Carlo codes. The applicators were those for which doses were measured in a recent international intercomparison [Med. Phys. 28, 1373 (2001)], planar applicators of Ru-106-Rh-106 and Sr-90-Y-90 and a concave Ru-106-Rh-106 applicator. The main purpose was to compare the results of the various codes with average experimental values. For the planar applicators, calculated and measured doses on the source axis agreed within the experimental errors (<10%) to a depth of 7 mm for Ru-106-Rh-106 and 5 mm for Sr-90-Y-90. At greater distances the measured values are larger than those calculated. For the concave Ru-106-Rh-106 applicator, there was poor agreement among available calculations and only those calculated by ACCEPT 3.0 agreed with measured values. In the past, attempts have been made to derive such dose distributions simply, by integrating the appropriate point-source dose function over the source, Here, we investigated the accuracy of this procedure for encapsulated sources, by comparing such results with values calculated by Monte Carlo, An attempt was made to allow for the effects of the silver source window but no corrections were made for scattering from the source backing. In these circumstances, at 6 mm depth, the difference in the results of the two calculations was 14%-18% for a planar Ru-106-Rh-106 applicator and up to 30% for the concave applicator. It becomes worse at greater depths. These errors are probably caused mainly by differences between the spectrum of beta particles transmitted by the silver window and those transmitted by a thickness of water having the same attenuation properties. (C) 2001 American Association of Physicists in Medicine.

The Effects of Bundle Geometry on Heat Exchanger Tube Vibration in Two-Phase Cross Flow

Abstract: Many shell-and-tube heat exchangers operate in two-phase flows. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross flow simulated by air-water mixtures. Normal (30 deg) and rotated (60 deg) triangular, and normal (90 deg) and rotated (45 deg) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1000 kg/(m 2 s) and void fraction from 0 to 100 percent. The effects of tube bundle geometry on vibration excitation mechanisms such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed.

Atomic structure holography using thermal neutrons

Abstract: The idea of atomic-resolution holography has its roots in the X-ray work of Bragg1 and in Gabor's electron interference microscope2. Gabor's lensless microscope was not realized in his time, but over the past twelve years there has been a steady increase in the number of reports on atomic-resolution holography. All of this work involves the use of electrons3,4,5,6 or hard X-rays7,8,9,10,11 to produce the hologram. Neutrons are often unique among scattering probes in their interaction with materials: for example, the relative visibility of hydrogen and its isotopes is a great advantage in the study of polymers and biologically relevant materials. Recent work12 proposed that atomic-resolution holography could be achieved with thermal neutrons. Here we use monochromatic thermal neutrons, adopting the inside-source concept of Szoke13, to image planes of oxygen atoms located above and below a single hydrogen atom in the oxide mineral simpsonite14.

Review of the ICRP tritium and 14C internal dosimetry models and their implementation in the Genmod-PC code.

Abstract: Biokinetic models for tritium and 14 C compounds, as described by various ICRP publications, have been incorporated into the Genmod-PC internal dosimetry code. This work reviews the models for tritium and 14 C labeled compounds that the ICRP has formulated over several decades. The ICRP dosimetry prescribed for hydrogen and carbon radionuclides is fundamentally different from that recommended for other elements in that it is based on retention functions for whole body activity instead of compartmental biokinetic models. The ICRP recommends dosimetric methods for tritium and 14 C compounds, ten of which are coded in Genmod-PC as compartmental models, namely, five tritium compounds, e.g., tritiated water, tritium gas, and five 14 C compounds, e.g., carbon dioxide, carbon-labeled methane. The values of the Genmod-PC calculated dose coefficients were compared with the ICRP's values. It is shown how the dose coefficients for intakes of tritium and 14 C compounds are affected by different interpretations of the methods recommended by the ICRP for two of the three classes of vapors and gases. Some aspects of the ICRP models, such as the percent oxidized, would benefit from reconsideration so as to produce tritium and 14 C biokinetics that are less dependent on the radionuclide.

Heavy water production process and apparatus

Abstract: A hybrid BHW-CIRCE process heavy water production system in which most or all of the CECE upper stages of the CIRCE process are replaced with BHW liquid phase catalytic exchange stages. The system allows the CIRCE process to return to a more natural cascade resulting in a more cost effective process.

Influence of gender differences in the carbon pool on dose factors for intakes of tritium and 14C-labeled compounds.

Abstract: The ICRP's biokinetic models for five tritium-labeled and five 14C-labeled compounds (not including radiopharmaceutical compounds and excepting carbon monoxide) incorporate a compartment representing the body carbon pool. Using the ICRP models, as coded into the Genmod-PC internal dosimetry

Kinetics of gaseous iodine uptake onto stainless steel during iodine-assisted corrosion

Abstract: Previous experimental work led to the development of a kinetic model that can be used to quantify iodine sorption behavior on a stainless steel surface The kinetic model, based on the mechanism proposed in earlier work, consists of four chemical reactions The model has reproduced the time-dependent adsorbed iodine concentration data on the coupons observed under various atmospheric conditions and different cycles of loading and purging The iodine adsorption kinetics were then incorporated into a mass transport equation to simulate iodine sorption behavior from a flowing air stream through a length of stainless steel tubing Discussed are the model, the simulation results, and their implications regarding the calibration of iodine transmission through long stainless steel sampling lines used for radiological monitoring of airborne iodine in a reactor containment building following an accident

Apparatus for removing pressure tubes

Abstract: An apparatus and method for removing a pressure tube from a nuclear reactor end fitting. A series of grooves are milled in the inside surface of the pressure tube in the area of the roll fitting by means of an elongated milling tool inserted in the pressure tube. The milling tool has a rotary cutter bit that can be controlled for longitudinal and rotational position and depth of cut from the proximal end of the tool. Once the grooves are milled, the milling tool is withdrawn and replaced with an elongated collapsing tool. The collapsing tool has a pair of jaws that engage the milled grooves and draw the wall of the pressure tube inward thereby releasing it from the end fitting. The use of the present invention avoids the requirement to remove both end fittings to replace a pressure tube.

Uranium and Uranium Compounds

Abstract: An overview of uranium and uranium compounds with an emphasis on their relevance to chemical technology is provided. Uranium and its compounds have many uses both potential and applied, examples include nuclear fuel, radiation shielding, and kinetic energy penetrators. These uses have a substantial economic impact, the aspects of which are provided. Sections are provided which illustrate the occurrence, recovery, and radiochemistry of uranium as well as the properties and preparation of uranium metal. A broad overview of uranium coordination and organometallic compounds is also provided. Drawbacks to the application of uranium and uranium compounds in many processes include the chemical reactivity of the metal and the inherent radioactivity of uranium isotopes. As such, health and safety factors which must be taken into account while working with uranium are discussed.

Dose to lung from inhaled tritiated particles.

Abstract: Tritiated particulate materials are of potential hazard in fission, fusion, and other tritium handling facilities. The absorbed fractions (fraction of energy emitted that is absorbed by the target region) are calculated for tritiated particles deposited in the alveolar-interstitial (AI) region of the respiratory tract. The energy absorbed by radiologically sensitive tissue irradiated by tritiated particles, in regions of the lung other than in the AI region, is negligible. The ICRP Publication 71 assumes the absorbed fraction is unity for tritium deposited in the AI region. We employed Monte Carlo methods in a model to evaluate the energy deposition in the wall of the alveolar sac from particles of tritiated beryllium, tritiated graphite, titanium tritide, tritiated iron hydroxide and zirconium tritide. For the five materials examined, the absorbed fraction in alveolar tissue ranged from 0.31 to 0.61 for particles of 1 microm physical diameter and 0.07 to 0.21 for 5 microm diameter particles. The dose to alveolar tissue, for an acute inhalation of tritiated particles by an adult male worker, was calculated based on the ICRP 66 lung model and the particle dissolution model of Mercer (1967). For particles of 5 microm activity median aerodynamic diameter (AMAD), the committed equivalent dose to alveolar tissue, calculated for the five materials, ranged from 32-42%, respectively, of the committed equivalent dose derived assuming the absorbed fractions were unity.

Bend Angle Effect on B2 and C2 Stress Indices for Piping Elbows

Abstract: B 2 and C 2 stress indices are used for calculation of stress terms corresponding to moment loading in evaluation of nuclear piping components. The formulas given in the ASME Boiler & Pressure Vessel Code for calculating these indices for elbows and curved pipes are independent of the bend angle. The objective of this investigation was to study the effect of the bend angle on the values of B 2 and C 2 . For this purpose, elbows with sizes ranging from 2.5 to 20 in. have been studied. The values of B 2 and C 2 have been calculated by detailed analysis using finite element models. Each elbow size has been analyzed for various bend angles (e.g., 15, 30,... 90 deg and above). The results of this study show that the values of B 2 and C 2 based on the ASME Code formulas are conservative and more so if the bend angle is less than 90 deg. The values of B 2 and C 2 decrease as the bend angle is decreased. The reduction in the values is very significant for smaller bend angles. Simple relations have been established to express the dependence of B 2 and C 2 on the bend angle. Based on these results, a modified form of ASME Code formulas is proposed to account for the bend angle effect.

Correlations of chaotic eigenfunctions: a semiclassical analysis

Abstract: We derive a semiclassical expression for an energy-smoothed autocorrelation function defined on a group of eigenstates of the Schr¨ odinger equation. The system we consider is an energy-conserved Hamiltonian system possessing time-invariant symmetry. The energy-smoothed autocorrelation function is expressed as a sum of three terms. The first one is analogous to Berry’s conjecture, which is a Bessel function of the zeroth order. The second and the third terms are trace formulae made from special trajectories. The second term is found to be direction dependent in the case of spacing averaging, which agrees qualitatively with previous numerical observations in high-lying eigenstates of a chaotic billiard.

Stochastic flow and transport simulations of a three-dimensional tracer test in moderately fractured plutonic rock

Abstract: Properties of fractured crystalline rock, especially hydraulic permeability and porosity, can be highly variable spatially. Since it is not possible to completely characterize the subsurface rock properties in every detail, it is customary in performance assessment or safety assessment of geological disposal of used nuclear fuel wastes to resort to stochastic methods to simulate the spatial variability.

Checkerboard shear volume reduction system

Abstract: A method and apparatus for reducing the volume of a cylindrical tube for disposal by crushing flat and then shearing into small coupons. Shearing is accomplished by opposed dies having a checkerboard grid of cutting edges. The resulting coupons are preferably substantially square in shape. The invention is particularly useful for reducing the storage volume of irradiated radioactive pressure tubes from a nuclear reactor.

Correlations of chaotic eigenfunctions: a semiclassical analysis

Abstract: We derive a semiclassical expression for an energy smoothed autocorrelation function defined on a group of eigenstates of the Schrodinger equation. The system we considered is an energy-conserved Hamiltonian system possessing time-invariant symmetry. The energy smoothed autocorrelation function is expressed as a sum of three terms. The first one is analogous to Berry's conjecture, which is a Bessel function of the zeroth order. The second and the third terms are trace formulae made from special trajectories. The second term is found to be direction dependent in the case of spacing averaging, which agrees qualitatively with previous numerical observations in high-lying eigenstates of a chaotic billiard.