[en] Fuel elements for a nuclear reactor may consist of a bundle of parallel fuel rods with a circular cross-section whose positions will form a grid. In the grid a guide tube for a control rod may have a cross-section covering the cross-sections of several adjacent fuel rods. According to the invention this cross-section comprises circular arcs that agree with the cross-section of covered fuel rods and which are connected by concave arc sections. The invention is intended in particular for high-conversion reactors. (orig./RW)

[en] Fuel assembly for a nuclear reactor having a bundle of fuel rods of circular cross section extending parallel to one another and disposed at positions forming a raster, including a guide tube for a control rod extending parallel to the fuel rods in the bundle and occupying the positions for and having a cross section covering the cross section of a plurality of mutually adjacent fuel rods in the raster the cross section of the guide tube being defined by circular arcs conforming with those of the circular cross section of the adjacent fuel rods covered thereby and being connected by concave arcuate sections

[en] A combined solvent-extraction-atomic-absorption technique, by which extraction is obtained using Aliquat 336-D.I.B.K. and analyses of the organic extract is done on a Pye Unicam PU 9000 atomic-absorption spectrometer, is presently being employed by the Laboratory for the determination of trace amounts of Mo, As and Sb in stream sediments collected during geochemical sampling. The elements of interest were taken into solution with K₂S₂O₇ fusion of 1,0g of the sample, followed by treatment of the fusion cake with 6M HCl. Extraction of Fe(III) was prevented by reduction to the not extractable Fe(II) state with ascorbic acid. Treatment with KI reduced As and Sb from the V state to the III state. Fusion, HCl, ascorbic acid and KI treatment, solvent extraction and aspiration of the organic extract into the atomic-absorption spectrometer was carried out in the same vessel - a Pyrex 50ml centrifuge tube (for the fusion, treatment with HCl, ascorbic acid and KI and the solvent extraction) fitted with a B29 ground-glass cone into which a B29 ground-glass socket was placed; the latter had attached to it a length of narrow-bore Pyrex tube for containing the organic extract for its aspiration into the atomic-absorption spectrometer. Standards for the analysis of unknown samples were prepared by 'spiking' 1,0 g portions of a soil (containing very low amounts of Mo, As and Sb) after K₂S₂O₇ fusion and during the HCl disintegration of the fusion cake, with known amounts of Mo, As and Sb. The accuracy of the method has been assessed by 'spiking' tests (Mo, As and Sb) using a soil sample containing very low amounts of Mo, As and Sb and by the use of geochemical reference materials - Soil SO-5 (Mo, As and Sb) and Soil NIM 77/69 (Mo only). Precision tests were also performed. Accuracies and precisions found were adequate for geochemical prospecting purposes. The method allowed the determination of Mo, As and Sb down to 1,0, 5,0 and 0,5 ppm respectively and was both rapid and relatively inexpensive

No abstract available

[en] In the scope of the analysis of hypothetical accidents in gasbreeders the ejection of a shutdown rod in a 1,000 MW(e)-GCFR is investigated. The shutdown rod generates a reactivity ramp of about 60 /s during the ejection leading to a superprompt critical power excursion. The initiation phase is calculated using a point kinetics code, that represents the core by a fuel rod of mean power with cooling channel. The disassembly phase is calculated using the hydrodynamics code KADIS, a descendent of the ANL-Code VENUS. Mass and energy of molten fuel at the end of disassembly phase is 27,600 kg and 24,000 MJ respectively, corresponding to 0.87 MJ/kg. In form of parameter variations the influence of some initial conditions of the disassembly phase is studied: reactivity ramp, reactivity, power level, and mean fuel temperature. The report contains a representation and discussion of the computational results as well as a description of the applicated models and in the appendix a complete listing of the used data. (orig.)

[en] In order to increase the safety and to improve the cooling process during core meltdown there may be arranged a catching tub from graphite in the reactor vessel below the core as well as a second tub below the pressure vessel itself. The first tub is connected with an interspace below the ceiling of the containment by means of supply and discharge pipes. The second tub, however, may be directly in contact with the gas space of the containment, the air contained in it sewing as coolant. In the first case a liquid metal like Hg, Zn or Pb is provided as coolant. These coolant loops are completed to from a heat exchanger by cooling the containment, especially the region of the ceiling, from outside by means of a spruikling system. (DG)

[en] The object of the invention is to ensure a sufficient removal of heat in the case of an accident involving a core melt of a nuclear reactor - in particular a breeder reactor. A cooled tank to catch the melted core is inside the containment under the reactor core. According to the invention, there is a coolant pipeline from this tank to the containment serving as heat exchanger. The cooling of the containment (of metal) used as heat exchanger is further imporved upon by a series of measures. 12 subclaims. (UWI)

[en] A gas-coolant nuclear breeder reactor is described which includes a core enclosed by a pressure vessel having a bottom beneath the core potentially capable of burning through if the core melts due to excessive operating temperatures. A basin is positioned beneath the core, either outside or inside of the pressure vessel, to intercept the melted core. The heat of the melted core must be dissipated rapidly because the reactor is enclosed by a steel containment vessel which might be unable to resist the internal pressure that would otherwise result from the heat. Therefore, means are provided for conducting a fluid coolant cooling the metal core, in the basin, from the latter to an extended area of the inside of the steel containment vessel which, being of relatively high heat conductivity, conducts the heat from the coolant to the atmosphere outside of the containment vessel. Cooling water may be sprayed on the outside of this containment vessel to assist in the dissipation of the heat. Arrangements are provided for increasing the efficiency of the heat transfer from the melted core to the fluid coolant

[en] One measure to improve fuel utilization in light water reactors is to increase the conversion ratio in a tight, hexagonal PuO₂/UO₂ mixed oxide fuel pin lattice. The PWHCR (pressurized water high converter reactor) is the Siemens/KWU approach towards this kind of tight lattice reactor, with the main characteristics of the actual concept being zirconium-clad fuel rods and an average moderator-to-fuel volume ratio of 1.2. In a recent study, concerning the nuclear core design for the PWHCR, mainly the questions related to the fuel assembly design, the reactivity control system and fuel management strategies have been addressed. Results of the investigations essentially confirmed the concept of the tight lattice PWR to be technically feasible. (author). 5 refs, 8 figs, 4 tabs

[en] The current series of experiments for the investigation of the physics of a light water high conversion reactor (LWHCR) has been in progress at the PROTEUS reactor facility in Switzerland since 1985. Reaction rate ratio and k∞ measured in these thermally driven LWHCR lattice experiments were predicted by several institutes participating in this program. The development of suitable calculational methods and the introduction of new cross-section sets based on the nuclear data files JEF-1 and KEDAK-4 have reduced the differences between calculated and measured k∞ values, but discrepancies between some of the measured reaction rate ratios and calculations are still considerable. It has been shown that deficiencies in nuclear data as well as inaccuracies in the treatment of resonance absorption could be responsible for these discrepancies. (author) 4 figs., 23 refs