Method and device for storing containers having an encapsulated fuel rod or a fuel rod section

Abstract

A method for encapsulating a fuel rod or a fuel rod section in a container includes inserting the fuel rod or fuel rod section into the container. One of the ends of the container is connected to a purging-gas line. The container is dehydrated and purged by use of a purging gas. The ends of the container are connected to a bypass line in such a way that a closed gas circuit is produced and a hot gas is circulated in the gas circuit until the absolute moisture content reaches an end value at which the absolute moisture content no longer rises. The container is disconnected from the gas circuit and subsequently the container is closed in a fluid-tight manner at both ends.

Claims

1. A method for storing containers each having a fuel rod or a fuel rod section encapsulated therein, which comprises the steps of: a) inserting one of the containers into a capsule receptacle having a multiplicity of spacers defining a grid within the capsule receptacle and a suction lance, the capsule receptacle being open at a top side; b) placing a cap onto the open top side of the capsule receptacle, the cap projecting into an interior of the capsule receptacle and having an opening that fluidly connects the suction lance to an extraction line; c) closing the capsule receptacle in a fluid-tight manner by means of a cover placed over the cap, the extraction line guided through the cover; d) extracting water situated in the capsule receptacle by way of the suction lance, the extracting including introducing a scavenging gas and a heating gas into the capsule receptacle through an inlet in the cover and removing the scavenging gas and heating gas through the suction lance and extraction line; e) scavenging the capsule receptacle with the scavenging gas; f) scavenging the capsule receptacle with the heating gas until an absolute moisture content reaches a predefined threshold value; and g) welding the cap to the capsule receptacle and the opening in the cap by means of a welder mounted inside the cover.

2. The method according to claim 1, which further comprises performing the method steps e) and f) one after the other several times in cyclic fashion, wherein the method step e) and subsequently the method step f) are performed in each cycle.

3. A device for a fluid-tight storage of a multiplicity of containers in which a fuel rod or a fuel rod section is encapsulated in each of the containers, the device comprising: a capsule receptacle having a multiplicity of spacers defining a grid within said capsule receptacle, said capsule receptacle having an open top side; a cover for closing said capsule receptacle in a fluid-tight manner; a cap mounted in said cover onto said open top side of said capsule receptacle; a suction lance guided through said cover and through said cap and into said capsule receptacle, said suction lance serving for extracting water situated in said capsule receptacle; said cover having an inlet for introducing a scavenging gas and a heating gas into said capsule receptacle; a relative humidity meter for measuring an absolute moisture content of the heating gas emerging from the device and disposed downstream of said suction lance; and a welder for welding said cap to said capsule receptacle, said welder disposed inside said cover.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a schematic diagrammatic illustration of a device for encapsulating a fuel rod or a fuel rod section according to the invention;

(2) FIG. 2 is a diagram in which a moisture content of a heating gas flowing out of the container or of a capsule receptacle is plotted versus time; and

(3) FIGS. 3-7 are illustrations showing the device according to the invention for a fluid-tight storage of a multiplicity of containers in which the fuel rod or the fuel rod section is encapsulated in each case, during the execution of temporally successive working steps.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a container 2 provided with a fuel rod 20 which has been inserted into a device in which residual water situated in the container 2 is removed from the container 2 and in which the container 2 is closed in gas-tight fashion after the residual water content has been reduced to or below a predefined maximum admissible threshold value. In a preceding working step, the fuel rod 20 shown by dashed lines in FIG. 1 has been inserted into the container 2, onto the ends of which there has been screwed, into an intermediate position, a closure element 10 known for example from European patent EP 1 600 982 B1.

(5) The device contains a first and a second chamber 50, 52 which are arranged spaced apart from one another on a common system axis 53. The first and second chambers 50, 52 are rigidly connected to one another along the system axis 53 by a connecting pipe 100 which is open at both ends. The ends of the connecting pipe 100 form, in the first and second chambers 50, 52, a first and second opening 56, 57 respectively, through which the container 2 that has been inserted into the connecting pipe 100 projects by way of its free ends beyond the connecting pipe 100 into the chambers 50, 52. Between the connecting pipe 100 and the container 2, in the region of the free ends, there are arranged advanceable sealing elements 116 which close a cylindrical gap chamber 119 that is formed between the connecting pipe 100 and container 2, such that the first and second chambers 50, 52, when a container 2 is arranged between them, can be fluidically connected to one another exclusively via the container 2 itself.

(6) In the second chamber 52, the container 2 equipped with the closure element 10 is mounted in a rotationally fixed manner in a receptacle 200 adapted to the closure element 10. Into the first chamber 50 there is inserted a handling tool 202 which engages in torque-locking fashion around the closure element 10 and by which the two closure elements 10 can be screwed to the container 2 into a gas-tight final position.

(7) An inlet line 66 for a scavenging gas G is connected to the first chamber 50, which scavenging gas flows through the container 2 into the second chamber 52 and exits the second chamber via an outlet line 69. The inlet line 66 and outlet line 69 are connected via valves 134 and 136 to a bypass line 118 that runs outside the chambers 50, 52, such that, by closing valves 126 and 130 that are situated in the inlet line 66 and outlet line 69, respectively, for the scavenging gas G, a closed gas circuit is formed whose volume is several times greater than the free volume of the container 2 and is a multiple of the volume, greater than 10 times the volume, in the exemplary embodiment approximately 50 times the volume. In the gas circuit there are arranged a pump 140 and a heating device 142 for circulating and heating, respectively, a heating gas H that is situated in the gas circuit. Also arranged in the gas circuit are measurement devices 150, 152 and 154 by which the temperature, the relative humidity and the pressure, respectively, of the heating gas H flowing into the first chamber 50 and of the heating gas H flowing out of the second chamber 52 can be measured.

(8) The connecting pipe 100 is furthermore surrounded by an outer pipe 202 which is arranged between the chambers 50, 52 and which is connected to a heating circuit 204 in which, likewise, a fluid medium M heated by a heating device 206 is circulated by a pump 208, such that the connecting pipe 100 is thermally insulated with respect to the environment. As an alternative to this, such thermal insulation may also be achieved by the insertion of heat-insulating material or heating elements between the connecting pipe 100 and outlet pipe 202.

(9) The advanceable sealing elements 116 are initially opened, and by injection of scavenging gas G, water is expelled from the processing chambers 50, 52 and the gap chamber 119 via the outlet line 69. Thereafter, the gap chamber 119 is closed by the sealing elements 116, and the water situated in the container 2 between the fuel rod 20 and inner wall of the container 2 is expelled by the scavenging gas G. Thereafter, the valves 126, 130 are closed, and the valves 134 and 136 situated in the bypass line 118 are opened. The heating gas H situated in the bypass line 118 is subsequently circulated continuously in the closed gas circuit. By use of the measurement devices 150, 152 and 154 arranged in each case in the inlet line 66 and in the outlet line 69 in the vicinity of the first and second chambers 50, 52, the temperature, the moisture content and the pressure of the heating gas H flowing in the gas circuit are detected. Using the values for pressure, temperature and relative moisture content measured in the outlet line 69, the absolute water or moisture content in the heating gas H can be determined in kg/m.sup.3, and the development thereof over time recorded.

(10) In the diagram of FIG. 2, ab absolute moisture content X is plotted in curve a versus time t. It can be seen from FIG. 2 that, from a time t.sub.0 from which the heating gas is circulated in the gas circuit, the absolute moisture content X increases continuously until it reaches a constant final value X.sub.max at a plateau. The attainment of the final value X.sub.max indicates that the water situated within the closed gas circuit has completely evaporated. In the event that an open fuel rod or open fuel rod sections is/are situated in the container 2, it is furthermore ensured that the water bound in the nuclear fuel has also completely evaporated.

(11) Then, with a known free volume of the container 2 and of the fuel rod 20, it is possible from the final value X.sub.max to determine the absolute mass, in grams, of the water vapor situated within the container 2. When the final value X.sub.max has been reached, the valves 134 and 136 are closed. The amount of water still situated within the container 2 is thus known. It would basically be possible for the container 2 to subsequently be closed in gas-tight fashion. It is however preferable for the valves 126 and 130 to be opened again, and for the container 2 to be scavenged again with scavenging gas G. In this way, the water vapor situated in the container 2 and in the fuel rod plenums is expelled, such that the amount of water situated within the container 2 is additionally reduced. Accordingly, the predetermined residual amount can be regarded as an upper value greater than the actual residual amount.

(12) The container 2 may then be welded to the closure elements 10 or subjected to a further treatment as explained below. In the further treatment, the container 2 is removed from the device and placed, by way of a handling tool 220, into a capsule receptacle 222 which is illustrated in FIG. 3 and which is constructed from a cylindrical receiving tube 224 arranged on a frame 226, the frame having a base part 228. The capsule receptacle 222 is provided for receiving a multiplicity of containers 2. For this purpose, a multiplicity of axially spaced-apart spacers 229 in grid form are arranged in the capsule receptacle 222, the containers 2 being guided in the cells of the spacers.

(13) As per FIG. 4, after the capsule receptacle 222 has been filled with the containers 2, there is placed onto the receiving tube 224 a cap 230 which has a central suction lance 232, the latter leading to the base of the capsule receptacle 222 and serving for the extraction of water situated in the capsule receptacle 222. A cover 234 is placed in fluid-tight fashion onto the receiving tube 224, through which cover there leads a suction line 236 which is fluidically connected to the suction lance 232 via an opening 237 situated on the cover 230. Water situated in the capsule receptacle 222 is extracted via the suction line 236, with scavenging gas G being fed in at the same time via an introduction opening 238. Subsequently, heating gas H is supplied via the introduction opening 238 and discharged via the extraction line 236. By contrast to the situation during the drying of the container 2, the heating gas H is not conducted in a closed circuit.

(14) The temperature, relative moisture content and pressure at the outlet are detected by the measurement devices 150, 152 and 154, and from these the present absolute moisture content X is determined, which decreases continuously as the drying process progresses. The profile of the absolute moisture content X with respect to time is illustrated in simplified form by curve b in the diagram of FIG. 2.

(15) The heating gas H is conducted through the capsule receptacle 222 until the absolute moisture content X reaches or falls below a predefined threshold value X.sub.g. The profile of the absolute moisture content X with respect to time is illustrated by curve b in the diagram of FIG. 2. It is ensured in this way that the absolute content of water situated in the interior of the capsule receptacle 222 does not exceed predefined maximum values. In this way, it is possible to make reliable statements as regards whether predefined threshold values are adhered to.

(16) After the drying of the capsule receptacle 222, the cap is, as per FIG. 5, welded to the receiving tube 224 by a welding device 240 which is mounted in the interior of the cover 234 so as to be rotatable about the longitudinal central axis of the receiving tube 224.

(17) In a subsequent step, as per FIG. 6, the opening 237 to the suction lance 232, the opening being situated in the cap 230, is likewise welded by the welding device 240. In the cover 234 there may additionally be arranged ultrasound checking devices by which the weld seams can be checked.

(18) Subsequently, as per FIG. 7, the cover 234 is removed and a transport head 250 is mounted onto the frame 226, which transport head facilitates the transportation of the closed capsule receptacle 222.

(19) Both in the case of the scavenging and drying of the container 2 and in the case of the scavenging and drying of the capsule receptacle 222, these two method steps may be performed several times in cyclic fashion, such that a drying process that has taken place is followed by another scavenging process and subsequently another drying process.