[en] As a baseline for all CANDU 6 refurbishment project, AECL has retained a manual removal method. However, the higher radiation levels at the Gentilly 2 power plant, and the relative uncertainty of the heat transfer system (HTS) decontamination outcome, has pushed HQ's higher management to finance a feasibility study analyzing a novel approach for the feeder removal. For the last 2 years, Hydro-Quebec has been working on an alternative way to remove feeder in preparation for the refurbishment of its power plant. The process would use Teleoperated Master-Slave Mechanical Arms to remotely perform the entire feeder removal task thus reducing the radiation exposure and increasing the overall safety of the worker. This paper will present an overview of the work executed in this study, putting emphasis on the actual Remote Feeder Removal (RFR) scenario, its principal tasks and the tooling developed to achieve this. This work was executed through a close relationship between the Hydro-Quebec Research Center (IREQ) and Gentilly-2 prerefurbishment project teams. (author)

[en] Is the hydrogen economy of the future just another fish story? Absolutely not! There have been many changes affecting the energy equation over the last 10 years and conditions have changed. In this presentation, we examined the reasons why, in the very near future, hydrogen production and distribution will be increasingly visible on many industries' radar screens. Our presentation provides an overview of the fundamental energy triangle and its myriad opportunities. We will look at the excitement being generated by gasification, GTL, and the expected availability of 'cheap' hydrogen. We will seek to confirm that experimental projects are now behind us. We will demonstrate that we are ready to move rapidly towards the pre-commercial applications that will eventually provide significant savings and other benefits to a wide variety of industries. Beyond our ability to produce and deliver hydrogen, Air Liquide is an enabler of the H₂ economy. We are actively developing the H₂ architecture and infrastructure that will allow many Canadian firms - who have already demonstrated leadership in H₂ technologies - to expand their markets and grow into highly successful organizations. Air Liquide has the strength of 104 years of scientific achievement, technical excellence, and business success. The Air Liquide Group is dedicated to devoting the necessary resources - on both sides of the Atlantic and around the world - to ensure the successful implementation of a number of innovative H₂ projects. Our presentation includes a brief description of some of these projects. We think you will be surprised at their variety and impressed by how these projects are closely related to today's energy issues. We hope to convince you that the hydrogen economy of the future is filled with promise and potential. (author)

[en] Highly resolved radiation-hydrodynamics FCI2 simulations have been performed to model laser experiments on the National Ignition Facility. In these experiments, cylindrical gas-filled hohlraums with gold walls are driven by a 20 ns laser pulse. For the first time, simulations show the appearance of Kelvin-Helmholtz (KH) vortices at the interface between the expanding wall material and the gas fill. In this paper, we determine the mechanisms which generate this instability: the increase of the gas pressure around the expanding gold plasma leads to the aggregation of an over-dense gold layer simultaneously with shear flows. At the surface of this layer, all the conditions are met for a KH instability to grow. Later on, as the interface decelerates, the Rayleigh-Taylor instability also comes into play. A potential scenario for the generation of a mixing zone at the gold-gas interface due to the KH instability is presented. Our estimates of the Reynolds number and the plasma diffusion width at the interface support the possibility of such a mix. The key role of the first nanosecond of the laser pulse in the instability occurrence is also underlined.

[en] The primary coolant circuits of CANDU reactors contain considerable quantities of carbon steel as the material of the feeder pipes and headers that connect the reactor fuel channels to the steam generators. Early in 1996, the CANDU-6 at Point Lepreau confirmed that several of the feeders at the reactor outlet were corroding much faster than anticipated. Subsequent measurements at other reactors revealed accelerated corrosion of outlet feeders at all the CANDU-6s, at Darlington and at Bruce. The CANDU industry reacted to the findings by implementing a program of intensified feeder inspection at operating reactors, development of improved monitoring and inspection tools and research into the controlling mechanisms. The longest-operating CANDU-6s have the most feeder thinning, so much of the utility activity aimed ultimately at plant life assurance is concentrated at Gentilly-2 in Quebec and Point Lepreau in New Brunswick. Already, detailed measurements and thermalhydraulic simulation have indicated that thinning rate is a strong function of coolant flow rate but not steam quality, while on-line monitors are starting to correlate thinning rate directly with reactor operating parameters such as coolant chemistry. Also, laboratory experiments and modelling have linked the mechanism to the phenomenon of flow-assisted corrosion, in which the normally protective magnetite film on the carbon steel dissolves in the rapidly-flowing coolant that is deficient in dissolved iron at the reactor outlet. Results suggest that lowering the magnetite solubility by changing the coolant alkalinity or increasing the protective nature of the oxide with coolant additives should be effective countermeasures in operating reactors. In new reactors, specifying a minimum concentration of chromium in the carbon steel should avoid the problem altogether. (J.P.N.)

[en] The proportions of keV ions, incident on a clean silicon surface, which are scattered as doubly or triply charged ions are found to increase with atomic number from C⁺ to Ne⁺. In contrast, the recoil Si²⁺ and Si³⁺ ion yields decrease. A definite collision-energy threshold for the production of each of these multicharged ions is found. All the multicharged recoil silicon ion thresholds are consistent with inner-shell vacancy production at the 3dσ-3pπ level crossing. However, the multicharged scattered ions seem to be produced by a different process. The surface-scattered ion yields may follow the same systematics as x-ray yields, which pass through maxima when the shell energies match

[en] Gentilly-2 NGS is experiencing high radiation fields in the fuelling machine vaults. These high fields make maintenance outages more expensive and their management more complicated. As part of the station refurbishment project, a task group was created to identify the cause of the high fields and make recommendations to prevent their reoccurrence in the second (post-refurbishment) operating cycle. To identify the root cause of the problem, the task group decided to analyse the primary heat transport system (PHTS), the fuel handling system and their inter-relation. Gentilly-2 has had to manage a unique (to CANDU) problem arising from antimony released from the main heat transport pump seals. Antimony deposits on in-core surfaces, becomes activated, and subsequently can be released, especially under oxidizing coolant conditions. It then becomes incorporated into the magnetite deposits on PHTS piping, including the steam generators and inlet feeders. Gentilly-2 has focused a great deal of effort on managing antimony over the last 15 years. As a result of these initiatives, radioantimony fields have been quite effectively managed since 1997, resulting in a decrease in their relative contribution to the total fields. The decrease in radioantimony fields highlighted the significant contribution of ⁶⁰Co cobalt activity; the high levels of both radioantimony and ⁶⁰Co differentiate Gentilly-2 from other CANDU 6 plants. Two types of ⁵⁹Co sources are present in the CANDU PHTS. High surface area materials such as steam generator tubes and feeder pipes contain trace concentrations of ⁵⁹Co as an impurity, which can be released by corrosion. Low surface area materials such as Stellites contain high concentrations of ⁵⁹Co that can be released as either corrosion or wear products. After assessing potential cobalt sources, the task group concluded that PHTS materials were not likely the origin of the high ⁶⁰Co fields. The major PHTS components identified as cobalt sources have the same specifications at Gentilly-2 as at other CANDU 6 plants. Consequently, the task group revisited operating and maintenance practices, going back through station operating history to identify operational practices that could have lead to increased ⁵⁹Co release and/or ⁶⁰Co production. The focus rapidly moved to the fuel handling system, as it had long been suspected, but never proven, that the Stellite ram balls were a major source of ⁵⁹Co; the fuelling machines provide a direct route for the introduction of corrosion or wear products into the reactor core. Data on the gamma fields measured in the fuelling machine D₂O supply room from 1995 to the present were reviewed. Water samples were taken and chemically analysed. The results confirmed the presence of ⁵⁹Co, probably generated by the wear and corrosion of the Stellite ram balls, and also confirmed the presence of antimony in the system. As part of the task group program, γ-spectrometry was performed in the course of a refuelling cycle. The results showed that variations in the general radiation fields observed in the fuelling machine D₂O supply room resulted from variations of the ¹²²Sb and ¹²⁴Sb concentrations in the process water. The presence of ¹²²Sb (t_1/2 3.2 d) suggested that the antimony was recently released from the reactor core. ⁶⁰Co was also detected but the level was constant; ⁵⁹Co from the ram balls is invisible to γ-spectrometry before it is activated to ⁶⁰Co. Remedial actions were implemented in mid-July, 2004. Shortly after, a significant reduction in the radiation fields in the Gentilly-2 fuelling machine ^D2O supply room was confirmed. During an unplanned outage in December 2004, a decrease in fields, in particular those due to ⁶⁰Co and radioantimony, was found at the reactor face. Activity monitoring scheduled for the 2005 annual outage should confirm if the source of the abnormally high fields has finally been identified. This presentation will describe the task force program, the remedial actions taken and the benefits achieved. This work, originally initiated to improve post-refurbishment operations, may bring benefits earlier than expected. (author)

[en] American experiments of inertial fusion have systematically shown smaller implosion velocities of the capsule than numerical simulations. The gap is between 15 and 20% and it is now usual to reduce the power of the laser in the simulations in order to cope with experimental results. Mechanisms that are considered to explain this gap are: the back-scattering of laser energy, the emergence of hot electrons, or the turbulence inside the laser ignition cavity. This article focuses on the dynamics of the gold wall of the cavity. Simulations have highlighted the instability of the interface between the cavity wall and the gas inside the cavity. These Kelvin-Helmholtz instabilities could explain the deterioration of the X conversion rate. (A.C.)

[en] The SILVA enrichment process relies on the difference in the excitation frequencies of the electron transitions between uranium isotopes ²³⁵U and ²³⁸U. Light emitted by lasers can be tuned exactly to these frequencies, resulting in the selective excitation and ionization of the target isotope, namely isotope ²³⁵U. Subsequently, ions are separated from the ²³⁸U atoms by an electrical field and received on dedicated collectors Pr. In a SILVA plant, laser beams would have to propagate over a long distance in the work-medium, resulting in possible severe temporal and spatial beam distortions. Such effects may drastically reduce the efficiency of the photo-ionization and hence require close attention. Coupled Maxwell-Schroedinger equations describe changes in the material system as well as the temporal and spatial re-shaping of the laser pulses as they propagate through uranium vapour. This system of equations combines Maxwell's wave equation with Schroedinger quantum-mechanical description of field-matter interaction. However, the method suffers from a serious drawback: in the SILVA conditions, it leads to prohibitive computation times. In this context, this article presents an alternative formulation for the induced atomic polarization of an undamped two-level system obviating the need to solve the Schroedinger equation to describe, the propagation of a laser pulse in a near resonant atomic vapor. The method is based on the use of an intensity dependent index of refraction inferred from a quasi-adiabatic approximation. As an example, the final section of the paper discusses the complex time re-shaping undergone by a 5 ns near resonant (frequency shift D = 6 GHz) laser pulse as it propagates through an optically dense medium (N = 4.1013 at/cm³). In this case, the quasi-adiabatic and Schroedinger models are shown to be in fairly good agreement

[en] By means of highly resolved one-dimensional hydrodynamics simulations, we provide an understanding of the burn process in inertial-confinement-fusion baseline targets. The cornerstone of the phenomenology of propagating burn in such laser-driven capsules is shown to be the transition from a slow unsteady reaction-diffusion regime of thermonuclear combustion (some sort of deflagration) to a fast detonative one. Remarkably, detonation initiation follows the slowing down of a shockless supersonic reaction wave driven by energy redeposition from the fusion products themselves. Such a route to detonation is specific to fusion plasmas

[en] We describe an instrument that images the Alcator A tokamak plasma in the soft x-ray energy range with high temporal resolution. Radiation from a cross section of the plasma column is detected by an array of seventeen surface barrier detectors which provides 1 cm poloidal spatial resolution over a 16 cm field of view. The instrument's nominal sensitivity lies in the spectral range from 0.27 to 25 keV; this range includes much of the radiation emitted by the Alcator A plasma, whose core temperature is typically in the 0.6 to 1.1 keV range. The frequency response of the detector-electronics system extends from dc to 170 kHz. We discuss: (1) some design considerations and instrument calibrations, including the instrument's measured response to 0.28, 1.5, 8.0, and 17.5 keV x-rays and its theoretical response to a bremsstrahlung spectrum; (2) the detector-electronics noise levels under various conditions; (3) the instrument's response to an electrically modulated x-ray source; (4) the detector x-ray response as a function of bias voltage and temperature; (5) the detector linearity of response to 1.5 keV x-rays; and (6) the stability of the detector x-ray response despite numerous and prolonged vacuum breaks. Sample data, obtained from Alcator A discharges, are presented