[en] This invention covers a process for supplying fuel to a nuclear reactor core inside a reactor vessel. The core includes a certain number of zones each one of which has a certain number of significantly horizontal layers, each layer comprising a number of individual fuel elements, the fuel elements of the respective layers forming appreciably vertical columns. The fuel elements, at least in the lowest layer, being spent, the process enables the zones to be supplied in sequence. In each zone, unspent fuel elements are withdrawn from the vessel in at least one of the columns but not in all, in order to uncover one or more spent fuel elements which are then removed from the vessel. The unspent fuel elements are moved inside the vessel to other locations (including the previous locations of at least some of the fuel elements previously withdrawn, whether or not spent) in order to uncover one or more other spent fuel elements which are also withdrawn from the vessel. The unspent fuel elements that were withdrawn from the vessel are then moved to other parts of the core and fresh fuel elements are placed in the vessel, at least in the upper layer of fuel elements. This series of operations is repeated in the other zones so as to complete the refuelling of the core

[en] A reusable thermally actuated linkage arrangement includes a first link member having a longitudinal bore therein adapted to receive at least a portion of a second link member therein, the first and second members being sized to effect an interference fit preventing relative movement there-between at a temperature below a predetermined temperature. The link members have different coefficients of thermal expansion so that when the linkage is selectively heated by heating element to a temperature above the predetermined temperature, relative longitudinal and/or rotational movement between the first and second link members is enabled. Two embodiments of a thermally activated linkage are disclosed which find particular application in actuators for a grapple head positioning arm in a nuclear reactor fuel handling mechanism to facilitate back-up safety retraction of the grapple head independently from the primary fuel handling mechanism drive system. (author)

[en] A reusable thermally actuated linkage arrangement includes a first link member having a longitudinal bore therein adapted to receive at least a portion of a second link member therein, the first and second members being sized to effect an interference fit preventing relative movement therebetween at a temperature below a predetermined temperature. The link members have different coefficients of thermal expansion so that when the linkage is selectively heated to a temperature above the predetermined temperature, relative longitudinal and/or rotational movement between the first and second link members is enabled. Two embodiments of a thermally activated linkage are disclosed which find particular application as actuators for a grapple head positioning arm in a nuclear reactor fuel handling mechanism to facilitate back-up safety retraction of the grapple head independently from the primary fuel handling mechanism drive system

[en] The positioning of rod systems described in the present invention has a special application for the mechanisms used to handle fuel in nuclear reactors

[en] An improved process for fuelling a nuclear reactor core is described which makes possible a considerable reduction in the fuelling period compared with previously known processes, and which also makes it possible to use fewer process steps outside the core and a smaller temporary fuel store. (orig./RW)

[en] A method for refueling a nuclear reactor core inside a pressure vessel is described. The method is used with a core which has at least one region comprised of a plurality of layers, each layer being comprised of a plurality of individual fuel elements with the corresponding fuel elements in respective layers forming columns extending transversely of the layers. Unspent fuel elements are first removed from the pressure vessel to expose at least one but not all of the spent fuel elements. The exposed spent fuel elements are then removed and the unspent elements are shuffled within the reactor core without being removed therefrom to expose additional spent fuel elements. These are removed and the shuffling process is repeated until all of the spent fuel elements have been removed. The initially removed unspent elements are then returned to the pressure vessel and placed in the core. New unspent fuel elements are then placed in the pressure vessel to complete the core

[en] The DIII-D tokamak vacuum vessel baking system is used to heat the vessel walls and internal hardware to an average temperature of 350 C to allow rapid conditioning of the vacuum surfaces. The system combines inductive heating and a circulating hot air system to provide rapid heating with temperature uniformity required by stress considerations. In recent years, the time to reach 350 C had increased from 9 hrs to 14 hrs. To understand and remedy this sluggish heating rate, an evaluation of the baking system was recently performed. The evaluation indicated that the mass of additional in-vessel hardware (50% increase in mass) was primarily responsible. This paper reports on this analysis and the results of the addition of an electric air heater and procedural changes that have been implemented. Preliminary results indicate that the time to 350 C has been decreased to 4.5 hours and the temperature uniformity has improved

[en] The DIII-D ohmic heating (OH) coil solenoid consists of two parallel windings of 48 turns cooled by water. Each winding is made up of four parallel conductors. Desired thermal capability of the coil is 80 MJ at a repetition rate of 10 minutes. One of the conductors started leaking water in July 1995. Between July 1995 and December 1997 the coil was operated at a reduced thermal load using one winding. An experiment followed by analysis was undertaken to determine if the OH-coil could be operated at full capacity by relying on conduction heat transfer to the neighboring cooled conductors without actively cooling the leaking segment. The analysis took into consideration the transient energy equations, including the effect of conduction between neighboring conductors. An experiment was performed on the undamaged coil winding to determine the thermal conductance between neighboring conductors. The experiment consisted of passing hot water through cooling channels of two conductors and cold water through the cooling channels of the remaining two conductors of the same winding. The flow rate, inlet and outlet temperatures from each circuit were measured during the transient. From the experimental data and analysis, an average thermal conductance between the conductors was determined to be about 800 W/m²-C. Using the experimentally determined value of the thermal conductance, an analysis was performed on a coil winding consisting of two uncooled conductors and two cooled conductors. Results show that it is possible to operate the full OH-coil to the desired thermal load of 80 MJ per pulse without actively cooling the damaged conductor. During an operational test, the coil was instrumented to measure the outlet water temperature from the conductors before operating it at full current capacity. The coil was operated at 80% energy level and outlet coolant temperatures were compared with analytical results. The comparison between analysis and measured coolant outlet temperatures was within 10%. This gives us sufficient confidence to operate the OH-coil at full capability in the future. It should be noted that the coil can be operated at a capacity of 180 MJ if adequate time is allowed between cycles (∼ 30 minutes) for the coil to cool completely. Forces (I x B) with the repaired conductor limit allowable current. For short pulses (<5 s) this limits the thermal input to less than 180MJ

[en] In order to reduce the occurrence of vacuum leaks and to increase the availability of the DIII vacuum vessel for experimental operation, effort was applied to developing a vacuum-tight brazed feedthrough system for sheathed thermocouples, stainless steel sheathed conductor cables and tubes for cooling fluids. This brazed technique is a replacement for elastomer O ring sealed feedthroughs that have proven vulnerable to leaks caused by thermal cycling, etc. To date, about 200 feedthroughs have been used. Up to 91 were grouped on a single conflat flange mounted in a bulkhead connector configuration which facilitates installation and removal. Investigation was required to select a suitable braze alloy, flux and installation procedure. Braze alloy selection was challenging since the alloy was required to have: (1) Melting temperature in excess of the 250⁰C (482⁰F) bakeout temperature. (2) No high vapor pressure elements. (3) Good wetting properties when used in air with acceptable flux. (4) Good wettability to 300 series stainless steel and Inconel

[en] The principal thrust of the project was to examine a single design in enough depth to gain confidence in the feasibility and desirability of specific design features. However, a valuable spin-off of the project was to develop information of a more generic character to aid in future studies of possibilities for Doublet III. For example, we now feel that Doublet III can be reconfigured with any of a variety of new vacuum vessels, poloidal coil sets, and auxiliary heating systems within three years of project initiation, a period that is short compared to the time scale for developing a completely new facility. In addition, this can be accomplished at a fraction of the cost required to develop a comparable facility