Results 1 - 10 of 317
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[en] The prompt critical Point Kinetical Equations are solved for linear and quadratic temperature feed back for 'Step Input' reactivities in the frame of the Hansen-Fuchs-Model. The influence of the precursor neutrons on energy in the power maximum can be calculated in the first approximation. Comparisons of AIREK-Code calculations and KEWB experiments confirm in the validity of neglecting the precursor neutrons for input reactivities rsub(o) >= 1.2[S]. The analytical considerations are mostly conservative and agree with the KEWB experiments within 30%. Finally, the magnitude and influence of the parameters are described, which govern the 'Step Input' excursions. (orig.)
[de]Es werden die 'punktkinetischen Gleichungen' im Rahmen des Hansen-Fuchs-Modells bei linearer und quadratischer Temperaturrueckkoppelung fuer sprungfoermige Reaktivitaetszufuhr geloest. Die verzoegerten Neutronen koennen bei der analytischen Berechnung der Energie im Leistungsmaximum in erster Naeherung beruecksichtigt werden. Vergleiche mit dem AIREK-Code anhand von Parametern aus dem KEWB-Programm bestaetigen die berechtigte Vernachlaessigung der verzoegerten Neutronen fuer Eingabereaktivitaeten rsub(o) >= 1,2[S]. Die analytischen Nachrechnungen sind meist konservativ und stimmen im allgemeinen bis auf 30% mitden KEWB-Experimenten ueberein. (orig.)
[en] Criticality safety experiments with nuclear fuel solution were initiated in 1995 at the Nuclear Fuel Cycle Safety Engineering Facility (NUCEF) at JAERI. Chemical compositions of fuel solutions used for the experiments were varied in wide range using the fuel treatment system in NUCEF. This system allows to dissolve, dilute, concentrate, purify, and store the fuel solution. Dissolution of UO2 pellet to nitrate solution and preliminary tests to optimize operation conditions of concentrator and extractor (mixer-settler) were carried out
[en] The effects of temperature, heating-time, concentration of HNO3 and γ-ray irradiation on the valence states of iodine in a simulated fuel solution of a medical isotope production reactor (MIPR) were investigated. About 83% of I- was oxidized to IO3- and 10% of I- was oxidized to I2 in uranyl nitrate solution after heating at 70 deg C for 6 hours. Heating and existence of oxidant, U and ionizing radiation accelerate the oxidation process of iodine, and results in most of the iodine being produced in high oxidation states such as in IO3- and IO4-. The results indicate that the production of 131I by MIPR can be carried out by extraction of iodine in high oxidation states from the fuel solution. (author)
[en] Two apparatuses are described for the automatic dilution and evaporation of nuclear fuel solutions. By this means it is possible to carry out the preparation of samples automatically: for example, the transformation of the solution from the nitrate into the chloride form. A measured volume of the solution thus prepared can then be applied automatically for the analytical procedure. (author)
[en] Aqueous nuclear fuels offer a unique set of characteristics for homogeneous reactor nuclear applications. Their advantages include high nuclear stability and inherent safety, high power density, high burn-up, simple preparation and reprocessing, easy fuel handling, high neutron economy, and simple control system leading to simple mechanical designs. The major disadvantages are corrosion, limited uranium concentration, and radiation decomposition of water. Likewise, organic coolants offer certain properties that are conducive for small reactor applications. These include reduced corrosion and activation, and low vapour pressures with good heat-transfer capabilities. Their major disadvantages are decomposition, fouling and flammability. A particular organic coolant, HB-40, has been extensively studied in Canada and was used for nineteen years in the 60-MWt organic-cooled WR-1 reactor at the Whiteshell Nuclear Research Establishment (WNRE) of Atomic Energy of Canada Limited (AECL). Proper attention to design and coolant chemistry in the nineteen years of operation in the WR-1 reactor kept the coolant aspects related to decomposition, fouling and flammability to acceptable levels. For small reactor applications, organic coolants are potentially superior to heavy water in terms of overall cost. The purpose of this thesis work was, through a literature review, to select the most suitable aqueous fuel and materials of construction for two proposed small inherently safe reactors, the QH-1 reactor and the homogeneous SLOWPOKE reactor under design at the Royal Military College of Canada.
[en] The method designs the manufacture of e.g. rod-shaped fuel element fillings in which fuel particles are suspended within a liquid and solidifiable binder such as graphite powder in pitch. The fuel particles are filled into cavities whose cross-sections correspond to those of the fuel rods. After closing with a covering plate, a piston exerts a force from below on it until its solidification. To follow, the liquid binder is injected through lower openings in the cavities. Due to the lubricity of the binder, the cavities are heated to 150 to 1750C, the packing of particles are homogenized. This procedure is further supported by the constant pressure of the pistons. Excess binder and air can flow out through openings in the covering plate. After cooling and solidification of the binder as well as after removal of the covering plate, the piston thrusts out the formed bodies or fuel rods from the cavities by an upwards movement. (DG/LH)
[de]Das Verfahren sieht die Herstellung von z.B. Brennelementfuellungen in Stabform vor, bei denen Brennstoffteilchen innerhalb eines fluessigen und verfestigungsfaehigen Bindemittels, wie Graphitmehl in Pech, suspendiert werden. Hierzu werden die Brennstoffteilchen in Hohlraeume geschuettet, deren Querschnitte denen der Brennstaebe entsprechen. Nach Verschluss mit einer Abdeckplatte uebt ein Kolben von unten eine Kraft bis zu ihrer Verfestigung auf sie aus. Danach erfolgt eine Einspritzung des fluessigen Bindemittels durch untere Oeffnungen in die Hohlraeume. Aufgrund der Schmierfaehigkeit des Bindemittels, die Hohlraeume werden dabei auf 150 bis 1750C erwaermt, wird die Packung der Teilchen vergleichmaessigt. Unterstuetzt wird dieser Vorgang noch durch den konstanten Druck des Kolbens. Ueberfluessiges Bindemittel und Luft koennen durch Oeffnungen in der Abdeckplatte abstroemen. Nach Abkuehlung und Verfestigung des Bindemittels sowie nach Abnahme der Abdeckplatte stoesst der Kolben die Formlinge bzw. Brennstaebe aus den Hohlraeumen durch eine Aufwaertsbewegung an. (DG)
[en] The specification applies to nuclear grade aqueous plutonium nitrate solutions. Included are solutions prepared from plutonium of different isotopic compositions as is normally produced by in-reactor neutron irradiation of natural or slightly enriched uranium. Excluded is plutonium-238 used for isotopic heat sources. The specification was discontinued in October 1980
[en] With the closure and de-inventory of the Los Alamos Critical Experiments Facility (LACEF) starting in 2004, the United States lost its only remaining solution critical assembly capability. In 2018, Lawrence Livermore National Laboratory (LLNL) commenced work on the feasibility and conceptual design of a solution critical assembly for thermal and epithermal studies (SOCRATES) at LLNL leveraging existing nuclear facilities. Technical requirements for the new facility include creation, characterization, transfer, use, and disposal of a wide variety of actinide solutions leveraging existing capabilities of LLNL's Plutonium Facility. A versatile criticality facility would necessarily need to be situated at the same site of the fuel fabrication facility (e.g., the Pu Facility) as off-site shipment of fissile solution is not permitted in the US. The mission of the solution critical facility would include: (a) studying the criticality characteristics of both 'old' and 'new' actinide wet chemistry processes (nitrates, chlorides, sulfates, fluorides) with varying fuel concentrations; (b) allowing for a variety of geometric configurations; (c) allowing for operations in burst mode, 'free run', and steady state; (d) investigating multiphysics dynamic characteristics of critical solutions; (e) providing a source of neutron and gamma radiation (and shields) for criticality alarm and dosimetry testing; and (f) providing activation and fission products for radiochemistry experiments. This paper will summarize existing assets and future challenges for siting a solution critical facility at LLNL - Livermore site.
[en] A review is given concerning the published knowledge about the chemistry of ruthenium in nitric acid solution with special reference to nitric acid nuclear fuel solutions. Possibilities of the spectroscopic description of the different existing ruthenium complexes are discussed and papers are presented dealing with the estimation of the proportions of the different ruthenium compounds in nuclear fuel solutions. Finally, arguments are derived for the preparation of ruthenium-containing model solutions, which adequately simulate the composition of real nuclear fuel solutions. (author)