EP0072356B1

EP0072356B1 - A method and a plant for the temporary storage of radioactive wastes

Info

Publication number: EP0072356B1
Application number: EP82830193A
Authority: EP
Inventors: Mario Marena
Original assignee: Enel SpA
Current assignee: Enel SpA
Priority date: 1981-06-30
Filing date: 1982-06-29
Publication date: 1987-06-10
Also published as: DE3276552D1; IT8148799A0; ATE27745T1; EP0072356A1; IT1142713B

Abstract

A building is provided for the temporary storage of radioactive wastes within the area of the nuclear plant where they are produced, which building comprises one or several paralelepipedal blocks in which a plurality of tunellike compartments are defined by partitions adapted for shielding each compartment from the others and from the environment. A plurality of drums are stowed lain side by side in each compartment. Particularly, two of said buildings blocks are located symmetrically at the sides of a gallery toward which the loading and unloading openings of said compartment are facing. A set of machines such as travelling lift (40) comprising a square section column (42), are provided for transferring the drums from a room of the nuclear plant where they are filled and sealed to the storage building through unprotected areas. Said set includes a machine for loading the drums into said tunnels and unloading them therefrom.

Description

The present invention relates to a plant for storing radioactive wastes into a temporary storage with radiation shielding walls.
More specifically, according to this invention, the wastes are stored within the same area of the nuclear plant from which the wastes derive, until an ultimate confinement is made available.
The wastes to be confined essentially comprise exhausted ion exchange resins, filter media, liquid wastes, etc.
The most modern technique of waste confinement comprises fixing the wastes in a concrete or bitumen mix and sealing them within steel or concrete containers. Such containers are then ultimately stowed in controlled locations such as abandoned caves or mines, ditches or galleries purposedly excavated, etc.
. A problem arises when no controlled storage is available in the same area or even the same nation where the nuclear plant is located.
Under such circumstances the wastes must be stored in shielding and monitored temporary storages from which the drums can be withdrawn and shipped to the ultimate confinement place, when this is made available.
A major problem arises when the wastes are to be handled for such shipment or for their dispersion at the end of their decay period. Such handling is not feasible in practice if the drums are too heavy and cumbersome and if they are not orderly stowed for readily singling out the drum batches according to their age and to the radioactivity dosage at the moment of storing them as determined through the isotropic mixture of the material filled into the drums.
DE-A-29 06 629 by Nukem GmbH discloses a plant for storing radioactive materials, specifically irradiated fuel elements;, which plant comprises a building wherein one or more structures are included with a plurality of metal cylindrical housings in which one or more cylindrical containers are received co-axially with said housings which may be horizontal or slightly sloping; said plant being provided with a device for preventing said drums from rolling out of said tunnels; the fuel containers being centered within each housing by means of longitudinal ribs or pins projecting from the inner surface of the housing walls. No means are disclosed for safely loading the containers into the housings and for withdrawing them therefrom. Furthermore, the storing and withdrawing of said fuel containers in said housings and therefrom according to said document appear obviously very cumbersome and time consuming.
The drawbacks of the prior art technique for the temporary confinement of wastes are overcome by the plant according to claim 1.
According to this invention the wastes are enclosed within relatively small metal containers such as easily to handle drums and are stowed into a chamber whose walls have positive shielding capacities from the waste radiation. According to the invention, the drums are disposed within the chamber in such an order that the different batches and even the different drums can be singled out. However, such a procedure implies the shielding of the drums during the transfer of them from the shielded room, where the drums are filled, to the storage building.
In designing the plant and related machinery, an analysis of the potential accidents is to be made and the proper measures are to be taken for obviating them. For instance, the building structure will be designed for standing a reference earthquake statistically foreseable for the site concerned. Another safety measure comprises the provision of doubled motors to ensure a continuous operation in case of failure of one of the motors.
For realizing the above concept a building is constructed with shielding walls wherein a number of horizontal tunnellike chambers are provided for receiving each a number of drums lying flat crosswise of the tunnel. Each tunnel is shielded from the others and the whole assembly of tunnels is shielded from the outer space. Briefly said building comprises two identical blocks symmetrical with respect to a gallery intervening between them, an array of tunnels being defined in each block. One end of each tunnel opens towards said gallery while the outer end opens towards an auxiliary gallery along the other side of the building. Both openings of each tunnel, after stowing any drum thereinto, are closed by means of a slab slidably fitted in vertical slides at the sides of each vertical row of tunnels. The tunnel floors are slightly sloping whereby the drums are tending to roll towards the tunnel opening facing the gallery. However they are prevented from getting out of the tunnel by a stop mechanism with which each tunnel opening is provided. The drum last stowed is retained within the tunnel by the rising end sections of a pair of rails with which the tunnel floor is provided and, for better security, a checking device is provided at the mouth of the tunnel.
The present invention is substantially aimed to providing a machinery for taking the drums from a conveyor in a shielded room, loading them on a shielded trailer in upright position, transferring the trailer into the storage building, transferring the drums from the trailer to an overturning machine and then on the forks of a lifting and propelling machine, which will be called travelling lift hereinafter, loading them into a tunnel of the storage building and closing the tunnel.
Such operations are to be repeated in part when the drums are to be recovered and transferred somewhere else, or to the ultimate storage site.
The following machines have been developed for carrying out the above operations.

a) A machine for lifting the drums in upward position from the delivery conveyor in the shielded room where they are prepared;
b) a machine similar to that of paragraph a) for picking up the drums from the trailer and laying them at full length;
c) a machine (travelling lift) for receiving the drums in horizontal attitude and stowing them into the tunnels and conversely for withdrawing them therefrom at the end of the storage period;
d) doubled motors and remote control equipment for all the machines.

The invention will be better understood from the following description of a preferred embodiment thereof as depicted in the attached drawings.
In the drawings:

Fig. 1 is a vertical axial cross-section of the hooking machine for lifting the drums;
Fig. 2 is a side view of the drum overturning machine wherein the drum is in vertical attitude;
Fig. 3 is a side view of the overturning machine wherein the drum is in horizontal position;
Fig. 4 is a side view of the machine for stowing the drums into the tunnel and taking them therefrom;
Fig. 5 is a partially sectioned view of the lower portion of the machine of Fig. 4;
Fig. 6 is a partially sectioned view of the upper portion of the machine of Fig. 4 as seen along the travelling direction of the machine;
Fig. 7 is a top plan view of the upper portion of the machine of Fig. 4;
Fig. 8 is a side view of the forked slide and guide rails along with the mechanisms for controlling the tiltable head of the travelling lift. This is shown while pushing a whole row of drums along a tunnel;
Fig. 9 shows the mechanism of Fig. 8 in its position when the drum has been laid flat on the tunnel rails;
Fig. 10, 10a is a plan view of the guides along which the forked slide travels, of the mechanism for tilting the slide head and of the drum retaining device;
Fig. 11 is a cross-section of a forked slide along the line XI-XI of Fig. 10, some parts of the slide being omitted for clarity.

With reference to the drawings, the storage building of the invention is made up of a rectangular reinforced- concrete foundation on which two identical structures are based which are symmetrical with respect to a medium corridor or gallery 4.
With reference to Figs. 1-11 the various machines will now be described for transferring the drums from the room where they are prepared and sealed to the storage tunnels.
The Remote Control Drum-Hooking Machine 100 The drums 8 to be handled by machine 100 are cylindrical drums of conventional shape and capacity (about 50 US gall.).
They are provided with two heavy loops 106 with C cross-section at about 1/3 of the drum length and with a solid rim 9 around each end.
Hooking apparatus 100 comprises: a metal sheet cylindrical bell 102 by which the drum to be hooked is partially shrouded in vertical position and in which the hooking mechanism is housed; a mechanism for centering bell 102 on the drum which mechanism comprises four elements which act on four symmetrical points around the upper rim of the drum.
Each of said elements comprises a bell-crank lever 109 pivotally mounted on a first horizontal bulkhead 108 of which bell 102 is provided at mid- height thereof, by means of a spring 107 connected to the end of one arm of lever 109. The end of the other arm has a profile adapted for engaging the inner profile of rim 9.
A vertical electromagnet 110 is mounted at the center of bulkhead 108. A plunger core 112 is vertically movable along the central cavity of electromagnet 110, which core extends downwards from a vertically movable assembly 115. This includes in addition to core 112 a disk 114 on which four links 116 are pivotally mounted which at their other ends are provided each with a slot 116' for connection to the bell by means of a pin 118.
The moving assembly 115 extends beyond disk 114 with a shaft 120 slidably fitted through a bushing 122 engaged with the central hub of a plate 126 attached to a second bulkhead 128' of which bell 108 is provided at the upper section thereof.
A roller 128 rotatably mounted at the end of one arm of a lever 132, pivotally mounted on the body of bell 102, is biassed against link 11'6.
Lever 132 can swing through small angles about its vertical position, the bell body being provided with as many narrow vertical slits 134 as are the levers 132 for letting each lever to pass out of the bell through one of the slits.
The swinging movement of lever 132 is thus dependent on the vertical movement of assembly 115 whose travel upwards is limited by bushing 122, the position of which is adjustable, while the downwards travel of the same assembly is limited by the position of the top surface of the casing 110' in which the electromagnet 110 is enclosed. The longer arm 132' of lever 132 terminates with an inwardly bent hook 132" adapted for engaging the recessed side of the upper hoop 106 of the drum.
The sliding shaft 120 of the movable assembly 115 connects, at its upper end, with a fork 136 through a cross-piece 121 which is mounted on an extension of shaft 120 to rotate about the vertical axis of the hooking machine 100. By means of fork 136 apparatus 100 can be suspended from a monorail hoist (not shown). The mechanisms overlying bulkhead 128' are shrouded by a cylindrical guard 137 around which the electromagnet supply cable 138 is wound.

Operation of the Hooking Machine

Electromagnet 110 is first energized whereby the core 112 is drawn thereinto and link 116 depresses the roller 128 against the force of spring 130. Arm 132' of lever 132 is thus made to swing outward of bell 102, so that the upper rim 9 and the hoop 106 can enter the bell and move past the hooks 132" of lever 132. Bell 102 is then lowered onto the drum until the drum rim 9 engages levers 109 and is centered thereby. The electromagnet is then shut off and spring 130 moves hooks 132" inwardly. The hoisting means is then operated for lifting the apparatus and the drum and the force thereby applied to fork 136, hooks 132" engage hoop 106 and the drum can be lifted along with the hooking apparatus.
The drum can thus be transferred to another location and there laid down. By loosening the pull on fork 136 and energizing the electromagnet 110, the bell can be disengaged from the drum.

Overturning Machine 301 (Figs. 2, 3)

A doubled motor 304 with reducing gear based on foundation 302, is drivingly engaged with sector gear 310 rotatably mounted on a horizontal shaft 312.
On the same shaft 312 a flat rectangular structure 316 is mounted by means of lugs 314, which structure is carried on sector gear 310 and then rotary therewith. Structure 316 on its face opposite to shaft 312 supports a saddle 318 whose profile is adapted for engaging drum 8 at the region thereof between hoops 106.
Two tubular arms 320 are attached to structure 316 which extend perpendicularly thereto from their ends opposite to gear sector 310. A platform 324 is slidably mounted by means of collar 322 on arms 320 for supporting the drum perpendicularly thereto.
Platform 324 is provided at its periphery with two retaining bevelled blocks 326 at diametrical positions which serve as guide for centering the drum.
Platform 324 at its underside has a rack 328 with which sector gear 330 engages which is rotatably mounted on lugs 332' attached to a plate 332 which extends at right angle from structure 316.
Sector gear 330 is rotated by a rod 335 of which one end is connected to the same sector gear by means of pin 331 and the other end is connected to sector gear 310 by means of pin 333. As sector gear 330 rotates, platform 324 is moved according to arrow A of Figs. 2 and 3.
The purpose of the above mechanism is for moving drum 8 to contact saddle 318 before the same is overturned. In fact, due to hoops the drum cannot be directly lowered with its side contacting saddle 318.

d) Machine for Loading and Unloading the Drums into and out of the Tunnel (Figs. 4-11)

A travelling lift 40 (Fig. 4) is made to travel along gallery 4 of the building fortransferring the drums, one at a time, from the overturning machine 301 to the mouth of the tunnel into which a drum is to be stowed and for pushing it into the tunnel 20 along with the drums therein, if any, until enough room is gained for locating it beyond the raising end sections 311' of raits 311 (Fig. 8). Travelling lift40 is also usable for withdrawing the drums from the tunnels.
Travelling lift 40 comprises a square section 42 (Fig. 5) mounted on a trolley 74 which travels on a track along the centerline of gallery 4 floor. A plate 45 (Fig. 6) is carried on the upper end of column 42 and is attached to a ring gear 46 which engages a pinion 48 of a motor 50. By means of motor 50 column 42 can be rotated about its axis through a 180 deg angle in orderto servethetunnels at either side of the median gallery 4 of the building.
Ring gear 46 has a ring 60' fastened thereto which forms the inner race of a ball bearing of which the outer race 60 is fastened to a strong plate 62 extending across a platform 44.
Platform 44 at each of its four corners is provided with a bracket 52 having a roller 54 mounted at its underside which travels along a bar 57 supported by a series of brackets 58 fastened to structures of the building.
A motor 64 (Fig. 7) is provided for driving column 42 along the median gallery 4 of the building through a reducing gear 66, a shaft 68 and a pinion 70' which engages a rack 72 mounted alongside of bar 57. Column 42 at its lower end is supported on trolley 74 through a thrust bearing 76' and a spring 78 (Fig. 5).
Trolley 74 travels on a rail by means of wheels 83 and is guided by the side rollers 80 with vertical axes which engage the rail at its sides.
A sleeve 70 is slidably mounted on column 42 which is moved vertically along it by a motor 450 (Figs. 6,7) mounted on plate 44through a sprocket wheel 454 and a chain 452, one end of which is attached to sleeve 70 and the other to a counterweight 456.
Sleeve 70 (Fig. 11) carries six brackets 74 for supporting two parallel horizontal reciprocally facing guide rails 76 made of C shape.
A forked slide 78 is mounted between rails 76 to move along them by means of motor 500 and shaft 502 and is provided with four rollers 80 mounted between the flanges of said C shapes and with additional four rollers 77 which roll at the sides of said flanges. Slide 78 in plan view has the shape of a tuning fork (Fig. 10) with two slender beams 78' extending parallel from a crosspiece 78" and supporting rollers 80 (Fig. 11).
A tiltable head 86 (Figs. 8, 9, 10, 10a) is mounted in front of crosspiece 78" by means of pins 85 and lugs 84 depending from crosspiece 78". Head 86 (Fig. 8) comprises a first plate 89 in close relation to crosspiece 78" and a further plate 88 with shock absorbers 92 interposed between the two plates.
On the face of plate 88 opposite to plate 89 four rollers 96 are mounted by means of lugs 94 for engaging the hoops 106 of drum 8 and applying a thrust on the drum 8 without damaging it.
A lever arm 202 (Figs. 8,9) is attached at one end thereof to plate 89 and at its other end to one end of a link 204 which at its other end connects with one arm of a bell-crank lever 206 of which the other arm connects with one end of a rod 210 which at its other end connects with the arm of a crank 212, the latter being actuated by a motor 216 through a - reducing gear 214. Any rotation of motor 216 is thus transmitted to head 86 through the above linkage.
Two lower jaws 218 for grasping drum 8 are attached to plate 89 and an upwardly and then forwardly extending arm 220 is attached to each jaw 218.
A single jaw 222 is provided on top of drum 8 which is keyed onto the shaft 224 of reducing gear 214 but not attached to crank 212. Jaw 222 and crank 212 can be controlled independently from one another by the same reducing gear 214 through a clutch not shown.
The tilting movement of head 86 is requested because the uprising section 311' of rails 311 must be surmounted by drum 8 while loading and unloading it from tunnel 20.
The purpose of arms 220 (Fig. 10) is for cooperating with a swingable frame 226 of which each tunnel is provided at its opening facing gallery 4 for checking the drum row formerly stowed thereinto.
Frame 226 (Figs. 8 and 10a) comprises a front crossbar 226" perpendicular to the tunnel sides and a second crossbar 226' parallel to the former one and two side slant struts 226'" coplanar with said crossbar.
Frame 226 is provided with two arms 230 which extend rearwards towards the tunnel mouth and are pivotally supported on the tunnel sides by means of pins 228. A stop pin 232 at each side of the frame stops the latter at its highest position and another stop pin 232' stops the frame at its lower position suited for propping the drum and preventing the drums already stowed into the tunnel from rolling out.
The swinging movement of frame 226 is controlled by arms 220.

Claims

1. A plant for the temporary confinement of radioactive wastes contained in cylindrical drums provided with two hoops at about 1/3 of the drum length and with rims at either bottom thereof which drums are supplied to the plant in vertical position which plant comprises two parallele- pipedal building structures identical to each other and symmetrical with respect to a median gallery, each structure being provided with a plurality of tunnels with constant cross-section perpendicular to said gallery and sloping slightly down towards said gallery and arranged in a honeycomb pattern that is in vertical and horizontal rows the walls of each tunnel being effective for shielding beta and gamma radiation, each tunnel being adapted for housing a plurality of drums in horizontal position and being provided with a mouth facing said gallery; said plant being provided with a device for preventing said drums from rolling out of said tunnels, characterized by the fact that said plant is provided:

a) with a machine for lifting said drums in upright position which machine comprises a hollow bottomless cylinder (102) with vertical axis which is provided at midlength with a first horizontal bulkhead (108) and with a second horizontal bulkhead (128') at its upper section; an electromagnet (110) with a vertically movable core being placed at the center of said first bulkhead, a set of levers (132) being swingably mounted at constant angular distances on the inner wall of said cylinder, an arm of each of said levers extending downwards and terminating with a hook for engaging the uppermost hoop (106) of a drum fitted into said cylinder; the mobile core of said magnet being connected, above said second bulkhead, to a lifting means (136) of the cylinder and drum and below the same to the upper arm (132) of each of said set of levers through a disk (114) co-axial with an upper extension of said core, through a link (116) pivotally and slidably attached to the inner surface of cylinder (102) and through a roller (128) rotatably mounted at the end of each upper arm; said second bulkhead working as a upper stop for said disk (114);

b) with a machine (301) for overturning said drums which machine comprises a platform (324) adapted for receiving a drum (8) in upright position, a flat structure which is provided at its side facing the drum to be overturned with a saddle (318) adapted for mating the side surface of the drum between the hoops thereof, two tubular arms perpendicular to said flat structure and fastened thereto, said platform being slidably mounted on said arms, a first sector gear (310) fastened to said vertical structure and meshed with the pinion of a motor, a second sector gear (330) meshed with a rack (328) of which the underside of said platform is provided, said second sector gear being connected by a link to said first sector gear and

c) with a machine (40) for loading and unloading said drums into and out of said tunnels, which machine comprises a vertical column (42) of which the height is at least the same as the array of the walls from which the mouths of said tunnels (20) are facing, which column rests at its bottom on a trolley (74) adapted for running along the center line of said gallery (4) and is suspended from a rotatable platform (44) which runs on rails along both the upper sides (418, 418') of said gallery, above said tunnel mouths; said platform being provided with a motor (450) for lifting and lowering along said column an extensible arm (82) adapted for being directed towards either of said array of tunnels; a vertically tiltable head (86) being carried at one end of said arm which head is tiltable by a motor (216) and is provided with a pair of lower jaws (218) for engaging a drum (8) at its under side and with an additional upper jaw (222) for engaging the upper side of the drum, which is actuated independently of the underside jaws.

2. A plant as claimed in claim 1 characterized by the fact that an arm (220) extends upwardly and forwardly from each of the two lower jaws (218) which arms cooperate through rollers (234) with a swingable frame (226)'with which each tunnel mouth is provided at its opening facing the gallery (4) for checking the row of drums formerly stowed therein; said frame extending rearwards towards the tunnel mouth and being pivotally supported in the tunnel sides by means of pins (228); said frame being provided with a first stop pin (232) at each side of the frame for stopping the latter at its highest position and with a second stop pin (232') for stopping it at its lower position suited for propping the drum and preventing it from rolling out.

3. A plant as claimed in claim 1 wherein said extensible arm (82) comprises two parallel slide guides (76) on which a forked slide (78) is moved by motor (500) through a shaft (502); and wherein a crank and linkage mechanism (202, 204, 206, 210) is provided comprising a crank (212) keyed on the shaft of said motor (216) and a rod (210) which is pivotally connected on one arm of a bell crank lever (206) which is pivotally mounted at a point (206') of said slide, the other arm of said bell crank lever being pivotally mounted on the end of a lever (204) attached to said tiltable head.