A METHOD AND A PLANT FOR THE TEMPORARY STORAGE OF RADIOACTIVE WASTES

Abstract: A building is provided for the temporary storage of radioac­ tive wastes within the area of the nuclear plant where they are produced, which building comprises one or several para­ lelepipedal 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: A method and a plant for the temporary storage of radioactive wastes The present invention relates to a method and a plant for stowing radioactive wastes into a temporary storage with radiation shielding walls. More speeifically, 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 eoncrete cointainers. Such containers are then ultimately stored in controlled locations such as abandoned caves or mines, disches 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such circumstances the wastes must be stored in shielded and monitored temporary storages from which the drums can be withdrawn and shipped to the ultimate confinement place, when this is made available.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 isotopic mixture of the material filled into the drums. The drawbacks of the prior art techniques for the temporary confinement of wastes are overcome by the present method and equipment. The basic concept of this invention consists of enclosing the wastes within relatively small metal containers such as readily handlable drums and of stowing them 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 other 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 drum 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 wich 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 overturing 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 for transferring the drums in shielded condition from said shielded room to the storage building through unprotected areas; c) a machine similar to that of paragraph a) for picking up the drums from the trailer and lay them at full length; d) 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; e) doubled motors and remote control equipment for all the machines. The novel structural features of the above machinery and the method of using it as set forth in the appended claims are included in the object of the invention. Thir 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 plan view of the storage building, as seen from the level of line I-I of fig. 2; Fig. 2 is a vertical cross-section of the building of the invention along line II-Il of fig. 1; Fig. 3 is a vertical cross-section of the building along line III-III of fig. 1; Fig. 4 is a vertical axial cross-section of the hooking machine for lifting the drums; Fig. 5 is a longitudinal vertical cross-section of the shielded trailer for transferring the drums according to the invention; Fig. 6 is a side view of the drum overturning machine wherein the drum is in vertical attitude; Fig. 7 is a side view of the overturning machine wherein the drum is in horizontal position; Fig. 8 is a side view of the machine for stowing the drums into the tunnel and taking them therefrom; ; Fig. 9 is a partially sectioned view of the lower portion of the machine of fig. 8; Fig. 10 is a partially sectioned view of the upper portion of the machine of fig. 8 as seen along the travelling direction of the machine; Fig. 11 is a top plan view of the upper portion of the machine of fig. 8; Fig. 12 is a side view of the forked slide and guide tails along with the mechanism for controlling the tiltable head of the travelling lift. This is shown while pushing a whole row of drums along a tunnel; Fig. 13 shows the mechanism of fig. 12 in its position when the drum has been laid flat on the tunnel rails; Fig. 14 is a plan view of the guides along which the forked slide travels and of the mechanism for tilting the slide head; Fig. 15 is a cross section af the forked slide along line XV-XV of fig. 14, some parts of the slide being omitted foz clarity. With reference to the drawings, the storage building of the invention is made up of a rectangular reinforced-concrete foundation 2 (fig. 1) on which two identical structures 3 and 5 are based which are symmetrical with respect to a medium corridor or gallery. Only one of the structures will be described for the sake of brevity. It comprises a strong frame including two end walls 7 and 7' and two intermediate walls 11 and 13. All said walls are interconnected at their by a reinforced-concrete slab 15 overlaid on said foundation 2 integral therewith and at their tops by a reinforced-concrete roof 17. Between each of the end walls 7,7' and one of the intermediate walls 11,13 thirtysix structural beamlike elements 19 are stacked in six piles. Element 19 consists of a reinforced-concrete beam with inverted U shape. The ends of the vertical arms of the U fit into respective indentations of which the underlying element is provided along both of its upper corners. In this way a tunnel 20 is defined by each U-shapped beam and the underlying one; the capacity of the tunnel being of 20 drums. Thirty elements 19 are stacked within the space defined between the two intermediate walls 11, 13 whereby the elements within one half of the storage building are one hundred and two and the total for the whole building is twohundred and four. Thus the total capacity of the building is 4080 drums. The vertical and horizontal partitions by which the tunnel are separated from one another have shielding capacity against beta and gamma radiation. The tunnels open at one end thereof into the main gallery 4 and at the other end into a respetive auxiliary gallery 12,12' which is provided along the outer side of both structures. The main gallery 4 end the auxiliary galleries 12, 12' extend upwards and widen to form two steps 416, 418, 418', 416' at their inner sides at the level of the upper surface of roof 17. The purpose of said steps is for supporting overhead travelling hoists or the like and for providing a walking way for the inspecting personnel. In fact the tunnel openings, upon loading the drums thereinto or taking them out, are to be closed by means of concrete slabs 14 which are handled by said hoists. The floor of tunnels 20 is provided with rails 311 adapted for engaging two hoops 106 of which each drum is provided and it slopes towards the main gallery 4, the slope of rails 311 being about 1%. The rails have a 1% slope in the same direction with respect to the floor whereby the total slope of the rails is about 2%. Rails 311 at their ends near the tunnel opening are bent upwards for retaining the drum last fed into the tunnel as better explained hereinafter. For better safety the opening of the tunnel facing the main gallery is provided with a checking device (figs. 12, 13, 14) which will be described hereinafter. With reference to figs. 4-14 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 1coo. 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 hoops 106 with C eross-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 Dn the drum which means 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 hori zontal bulkhead 108, of which bell 102 is provided at midheight 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 moun ted on the body of bell 102, is biassed against link 116. 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 as sembly 115 whose travel upwards is limited by bushing 122, the position of which is adjus table, 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 movable assembly 115 connects, at its upper end, with a fork 136 through a crosspiece 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 (non 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 levers 132. Bell 102 is then lowered into 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. b) Shielded trailer for transferring the drums through open areas. The shielded trailer 140 of the present invention comprises a four wheel towable vehicle with steerable front wheels 142 and spring supported rear wheels. On the vehicle frame a box or coffer 145 is mounted wherein two drums 8,8 can be housed in vertical tandem position. Coffer 145 is divided in two parts 146, 148 along a horizontal plane at mid height, the two halves being made of a shielding materials, for instalce lead clad steel, and being joined to one another along a shoulder or a groove. c) Overturning machine. (Figs. 6, 7). 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 the l rotary therewith. Structure 312 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 are attached to structure 316 which extend perpendicularly thereto from its side oppositeto the gear sector 310. A platform 324 is slidably mounted by means of collars 322 on arms 320 for supporting the drum perpendicular 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 extend 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 arrows A of figs. 6 and 7. 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 ut of the tunnel (figs. 8-15). A travelling lift 40 is made travel along gallery 4 of the building for transferring the drums, one at a time from the overturning machine to the mouth of the tunnel into which a drum is to be stowed and for pushing it into the tunnel along with the drums therein if any until enough room is gained for locating it beyond the raising end sections 311' of rails 311. Travelling lift 40 is also usable for withdrawing the drums from the tunnels. Travelling lift 40 comprises s square section column 42 mounted on a trolley 74 which travels on a track along the centerline of gallery 4 floor. A plate 45 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 order to serve the tunnels at either side of the gallery 4. Ring gear 46 has a ring 60' fastened thereto which forms the inner race of a ballbearing of which the outer race 6 is fastened to a strong plate 62 extending across 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 respective structure 3 or 5 of the building. A motor 64 (fig. 11) is provided for driving column 42 along gallery 4 through a reducing gear 66, a shaft 62 and pinions 70 which engage 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 springs 78 (see fig. 9). 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 mounted on plate 45 through a sprocket wheel 454 and a chain 452, one end of which is attached to sleeve 70 and the other end to a counterweight 456. Sleeve 70 carries six brackets 74 for supporting two parallel horizontal reciprocally facing guide rails 76 made of C shape (fig. 15). A forked slide 78 is mounted between to move along rails 76 and is provided with four rollers 80 inserted between the flanges of said C shapes and with additional four rollers 77 which roll on the sides of said flanges. Slide 78 in plan view has the shape of of tuning fork with two slender beams 78' extending parallel from a crosspiece 78" and supporting wheels 80. A tiltable head 86 is mounted in front of crosspiece 78" by means of pins 85 and lugs 84 depending from crosspiece 78". Head 86 comprises a first plate 89 in close relation to crosspiece 78" and a second farther plate 88 (fig. 14) 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 engaging the hoops 106 of drum 8 and applying a thrust on the drums 8 without damaging them. A lever arm 202 (figs. 12, 13) 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 crank 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 post 220 is attached to each jaw 218. A single jaw 222 is provided on top of drum 8 which is keyed onto the shaft 334 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 posts 220 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. 12 and 14) 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' extending forwardly from posts 220.

Claims: What is claimed is: 1. A method for the temporary confinement of radioactive wastes in an area next to the nuclear plant where the wastes are produced which method comprises the steps of packing the wastes into metal cylindrical drums, a plurality of said drums being laid flat side by side in a row into each of a plurality of horizontal tunnels with which a parallelepipedal structure is provided, the walls of each tunnel having shielding capacity for preventing any beta and gamma radiation by the waste material therein from reaching either the other tun nel insides or the space which surrounds the structure. 2. A plant for the temporary storage of radioactive wastes in an area next to the nuclear plant where the wastes are produced which plant comprises a plurality of tightly sealable cylindrical metal containers or drums encircled by heavy hoops and by solid rims at both ends, a building made of two identical parallelepipedal structures symmetrical with respect to a median gallery, an array of parallel horizontal through tunnels being defined in each structure adapted for receiving each a plurality of drums laid flat side by side, each tunnel being connectable through either of its ends with a shielded space within said building, the walls of each tunnel having positive capacity of shielding from any beta and gamma radia tion; a set of machines for transferring said drums from a shielded room of the nuclear plant where the wastes are packaged into the drums to said shielded space of said storage building through an unshielded area. 3. A plant as per claim 2 wherein said tunnels have a flat floor which slopes down towards the tunnel opening through which the drums are loaded and unloaded into and out of the tunnel. 4. A plant as per claim 3 wherein the slope of the tunnel floor is 1%. 5. A plant as per claim 4 wherein a track is provided along the tunnel floor adapted for engaging the hoops of which each drum is provided, which track slopes down towards the loading and unloading opening, the slope being 1% with respect to the tunnel floor. 6. A plant as per claim 2 wherein each tunnel of said structure is provided at its loading and unloading opening with a contrivance for retaining the drums within the tunnel which comprises a frame swingably mounted on pivots at the side walls of the tunnel which frame in a first almost horizontal position allows a passage for the drums being loaded into and unloaded out of the tunnel and in an inclined second position it is propped against the last of the drums already stowed, while leaving enough space in the tunnel for an additional drum. 7. A plant as per claim 2 wherein at the sides of each vertical row of tunnel mouths at either side of said structure a vertical guide is provided and as many shielding slabs are provided as the tunnel mouths slidabIe along said guides adapted for closing each tunnel mouth. 8. A plant as per claim 2 wherein the set of machines for transferring said drums from a shielded room of the nuclear plant to the shielded space within said building comprises: a machine adapted for lifting the drums in upward position; a machine adapted for transferring the drums in shielded condition; a machine adapted for overturning the drums; a machine adapted for picking up the drums from said overturning machine, loading them into said tunnels and unloading them therefrom. 9. A plant as per claim 8, wherein said machine for lifting the drums in upright position com prises a vertical cylindrical metal sheet bottomless body on whose inner side surface a set of levers are swingably mounted at constant angular distances around the cylinder axis, one arm of each of said levers being provided at its end with an inwardly bent hook adapted for enga ging the uppermost hook of the drum, the end of the other arm being provided with a cam follower which rolls on a link which is connected by a pin and slot coupling at one end the reof to the upper side of said body and at the other end to a horizontal disk coaxial with said body and attached at its top to a shaft slidably fitted through a first horizontal bulkhead of which said body is provided at its upper section, and connected to the means by which the machine is lifted and at its lower end to a plunger core of an electromagnet mounted on a second horizontal bulkhead of which said body is provided at mid height thereof whe reby the vertical movements of said punger core bring about swinging movements of said le vers. 10. A plant as per claim 8, wherein said machine for trasferring the drums from the nuclear plant to said shielded space within said storage building comprises a trailer which carries a coffer with shielding walls within which two drums can be received in vertical tandem posi tion, said coffer veing horizontally divided in two parts fittable to one another along a shoul der or groove. 11. A plant as per claim 8, wherein said machine for overturning said drums comprises a plat form adapted for receiving a drum in upright position, a flat structure which is provided at its side facing the dritm to be overturned with a saddle 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 fastened to said vertical structure and meshed with the pinion of a motor, a second sector gear meshed with a rack of which the underside of said platform is provided, said second sec tor gear being connected by a link to said first sector gear. 12. A plant as per claim 8, wherein said machine for picking up the drums from said over turning machine, loading them into said tunnel and unloading them therefrom, comprises a column which is suspended from a platform by means of a horizontal thrust ring, said platform being adapted to roll along tracks at either side of said median gallery above the array of loading and unloading mouths of said tunnels, a sleeve slidably mounted on said column and carrying two parallel guide rails on which a forked slide is mounted, a tiltable head being supported by said slide which head is tiltable by a motor through crank and linkage mechanism all mounted on said forked slide and comprises a pair of jaws for en gaging a drum at its underside and four rollers for engaging the hoops of the drum being loaded into the tunnel; said machine comprising further a jaw for engaging the upper side of the drum being loaded, which additional jaw is actuated independently from the underside jaws. 13. A plant as per claim 11, wherein said column is rotatable about its axis through a 180 degrees angle whereby the drums can be loaded into and unloaded from the tunnels of either said symmetrical structures of the building. 14. A plant as per cliams 6 and 12, wherein a vertically and then horizontally extending post is attached on the top of each of said couple of underside jaws adapted for coopera ting with rollers of which said swingable frame is provided for moving it from said second position to said first position. 15. A plant as per claim 12 wherein said crank and linkage mechanism comprises a crank keyed on the shaft of said motor and a rod pivotally connected on one arm of a bell crank pivotally mounted on said slide, the other arm of said bell crank being pivotally mounted on the end of a lever attached to the tiltable head. 16. A plant as per claim 8 wherein said column at its lower end is guided by rollers which enga ge the sides of a rail laid down on the floor of said median gallery. 17. A plant as per claim 8, wherein all the motors by which said machines are actuated are remotelly controllable doubled motors.

Inventors: MARENA, MARIO
Applicants: ENTE NAZIONALE PER L'ENERGIA ELETTRICA - (ENEL)
Application year: 1982
Main classification: G21F9
IPC codes: G21F9