WO1996004659A1

WO1996004659A1 - Overpacks for drums

Info

Publication number: WO1996004659A1
Application number: PCT/GB1995/001741
Authority: WO
Inventors: Michael Joseph Burton; Alex Young
Original assignee: British Nuclear Fuels Plc
Priority date: 1994-07-29
Filing date: 1995-07-24
Publication date: 1996-02-15
Also published as: GB9415373D0

Abstract

An overpack (40) for a drum (D) containing radioactive material, e.g. uranium trioxide, comprises a lightweight, porous, insulating packing material having a shape adapted to be fitted all around the drum (D) to be packed thereby, the packing material being contained in an outer container (40) which has folds or swages (49) to provide enhanced radial stiffness or strength. One or more plugs (53) may be fitted in the container at one or more of the folds to permit venting to the outside atmosphere of gases inside the container at a predetermined temperature or pressure. The packing material may comprise a hollow body (42) of packing material and a lid (43) of packing material. The body and the lid may have chamfered mating surfaces (58) to minimise loss of heat insulation.

Description

Overpacks for Drums

The present invention relates to overpacks for drums for the containment of radioactive material.

The purpose of the present invention is to provide an overpack for a drum for the containment of radioactive material, eg a powder such as UO3, so that the drum can be handled and transported safely around the world. Such an overpack, and the drum it contains, need to satisfy amongst other things safety standards set by the International Atomic Energy Agency (IAEA) , eg relating to Type 'AF' packages for UO3 powder containment and transport.

According to the present invention there is provided an overpack for a drum containing radioactive material, the overpack comprising a lightweight, porous, insulating packing material having a shape adapted to be fitted all around the drum to be packed thereby, the packing material being contained in an outer container which has folds or swages to provide enhanced radial stiffness or strength. The outer container may be made of steel or other high strength material.

A pressure build up of gases inside the said container may occur gradually over a period of time and especially if the package comprising the overpack is subject to an external fire.

Advantageously, the container may have plugs fitted therein at the said fold(s) to permit venting to the outside atmosphere of gases inside the container. The plugs may be designed to be blown to provide venting at a given pressure and/or temperature.

The packing material may comprise a hollow body of packing material and a lid of packing material. The body and lid may have chamfered mating surfaces so as to minimise loss of insulation at the body/lid interface. The interface may in transverse cross-section extend along a slope, eg at 45°, to the axis of the packing material body. Thus, the lower surface and body mating surface of the lid may have frusto-conical shape whilst the lid mating surface of the body provides an upward sloping ring shape.

The said lightweight packing material may comprise cork. Beneficially, cork is a lightweight porous material which has excellent impact absorption and insulation properties. Additionally, cork chars when it is in contact with a flame and the charring will prevent the drum and its contents from overheating, eg if the drum and overpack were in an environment exposed to a fire.

The overpack according to the present invention allows a drum containing a radioactive material, eg powder, to be transported safely around the world. The overpack affords suitable protection to the drum against drop, fire and heat and also provides a degree of shielding from radiation emitted by the .contents of the drum.

The outer container of the overpack may have a ring at its lower end which protects the base and lower part of the container from damage by impact by suspending it from a floor on which the overpack is standing. The ring may comprise a chimb which is formed by folding the edge of the base of the container around the lower edge of the side wall of the container and welding the two together.

As described in a copending UK Patent Application 9415388.9 (equivalent to a PCT Application of even date) by the present Applicants the overpack according to the present invention may be employed to pack and transport a drum for the sealed storage of radioactive material which has a top portion which comprises a sealable filling neck and a collar provided around the filling neck the collar having an engagement means which allows the drum to be picked up by a lifting means.

The said engagement means may be an inward facing rim or lip on the collar, the underside of which rim or lip provides an annular surface against which a lifting means such as a single, multiple or annular hυok device can engage to provide a lifting action.

Desirably, the drum has a body inside which material is to be stored and, provided beneath the base of the body, a ring or skirt which provides a cylindrical cavity beneath the body. Desirably, the cylindrical cavity has a size such that the collar of an identical drum fits closely inside the ring whereby a plurality of identical drums may be stacked one on top of another to minimise the space in drum storage facility, occupied by such drums. The collar may have an upwardly projecting inwardly sloping surface having the said lip or rim forming a curved surface at its upper end to facilitate fitting the ring or skirt of one drum over the collar of another drum so as to provide stacking of such drums. Although the said ring or skirt is primarily provided for stacking purposes it also provides stiffness and protects the base of the drum against impact damage.

The collar of the drum may have one or more holes to facilitate drainage of water, eg rainwater, which might otherwise collect in the annular space between the collar and neck of the drum.

The filling neck of the drum may have a lip or scroll at its upper end which projects outwardly with reference to the axis of the neck. A cap or lid may be fitted over the mouth of the neck by crimping a skirt on the cap onto the lip or scroll. The cap or lid may for example comprise a circular cap having an annular skirt and the cap may in use be compressed onto the lip and the skirt may be crimped onto the underside of the lip or scroll at a number of equispaced regions around the circumference of the skirt.

The lid or cap of the drum may have regions of different reflectivity to provide a recognisable target for an optical detection system as described in copending UK Patent Application No. 9415300.4 (equivalent to a PCT Application of even date) by the present Applicants.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which

Figure 1 is a cross-sectional side elevation of a drum embodying the present invention.

Figure 2 is a cross-sectional side elevation of a cap suitable for the drum as shown in Figure 1.

Figure 3 is a cross-sectional side elevation of a drum as shown in Figure 1 having another similar drum stacked on top of it.

Figure 4 is a cross-sectional side elevation of a drum as shown in Figure 1 being lifted.

Figure 5 is a cross-sectional side elevation of an outerpack for the drum shown in Figure 1. As shown in Figure 1 a drum 1 is suitable for the safe containment and transport of UO3 powder which may be a recycled product obtained from the reprocessing of spent nuclear fuel. The drum 1 is of generally cylindrical shape with swages 5, 7 to provide added body strength. The body 3 has a base 9 which is concave as viewed from the outside. A ring shaped skirt 11 projects downwardly from the lower end 10 of the outer surface of the body 3 to provide an upturned basin shaped cavity 13 beneath the base 9.

At its upper end the drum 1 has an annular top 15 from which an annular neck 17 projects upwardly. The neck 17 provides a filling mouth 19 shown in brackets in Figure 1 because it is closed by a cap 29 described below. The neck 17 has at its upper end an outwardly projecting overturned or scrolled lip 21. A collar 23 projects upwardly from the periphery of the top 15. The collar has an inwardly sloping portion 23a which terminates at its upper end in an overturned lip 25. A hole 27 is provided in the collar 23 to allow rainwater collecting in the region inside the collar 23 between the neck 17 and the collar 23 to be drained. The top 15 has ridges 15a, 15b and 15c to add strength. The ridge 15c also facilitates attachment, eg by welding of the collar 23 on the top 15.

A cap 29 is employed to seal the filling mouth 19 of the neck 17. The cap 29 is shown before application in Figure 2. The cap 29 comprises a tubular body 31 having a chamfered ring 33 and plate 35 at its lower end. A skirt 37 is formed around the body 31, the skirt 37 being attached to the body 31 by an annular portion 39 of U- shaped cross-section. An elastomer sealing gasket or ring 41 is provided on the inner surface of the portion 39.

In use, the drum 1 is filled with powder, eg U0₃ powder, by an automatic filling machine which delivers the powder through the filling mouth of the neck 17. The cap 29 is then placed loosely on the drum 1, the body 31 being placed in the mouth 19 of the neck 17. The drum 1 and loosely fitted cap 29 are then offered to a capping device (not shown) . This may have a series of jaws evenly spaced around a circular locus around the skirt 37 of the cap 29. The capping device compresses the cap 29 onto the lip and crimps the skirt 37 around the underside of the lip 21 at the positions of the jaws. Figure 1 shows the cap 29 after attachment.

After sealing of the drum 1 by the cap 29 the drum 1 may be stored in a stack of drums. Figure 3 illustrates how such a stack is formed. In Figure 3 the drum 1 as shown in Figure 1 has a further identical drum la stacked on top of it. The drum la has a skirt 11a and cavity 13a identical to the skirt 11* and cavity 13 respectively of the drum 1. The skirt 11a of the drum la provides a close fit over the collar 23 of the drum 1, and the base 9 in its region 10a outside its concave region (forming the cavity 13) of the drum la thereby is supported by the drum 1 at the upturned portion of the collar 23 between the sloping portion 23a and rim 25.

Figure 4 illustrates how the drum 1 may be lifted to facilitate automatic handling and stacking. A lifting device 63 comprises a series of lifting arms 65 suspended from a beam 68. The arms" 65 are lowered into the space above the top 15 of the drum 1 between the collar 23 and neck 17. The arms 65 have hands 67 which are located to engage beneath the rim 25. The hands 67 may be pushed inward toward the central axis of the device 63 to clear the rim 25 during lowering of the hands 67 and then pushed outward (eg by spring mechanisms not shown) to engage the rim 25 when beneath the rim 25. Lifting of the drum is then achieved by lifting of the arms 65.

Figure 5 shows an overpack for transport of the drum 1. The drum 1 is shown in phantom outline D. The overpack comprises an outer container 40 containing an inner hollow body 42 of lightweight insulation packing material. The body 42 has a cavity 44 into which the drum 1 is fitted. A cap 43 formed of the same packing material is fitted on top of the body 42. The cap 43 and the body 42 have mating surfaces 58 at an angle of 45 degrees to the axis of the body 42 to minimise heat transfer across the interface between the cap 43 and body 42. The cap 43 is covered by a plate 45 bonded to the cap 43, the plate 45 having a flange 45a which is fixed to the top of the container 40 by bolts 47 provided at various locations around the circumference of the flange 45a.

The overpack shown in Figure 4 protects the drum 1 from heat from external sources. The container 40 has two portions 49 of increased internal diameter primarily to provide radial stiffness and strength. Fusible plugs 53 are provided in the wall of the portions 49. The plugs 53 are designed to be blown at a predetermined gas pressure and/or temperature to allow the built up gas pressure to be released to the outside atmosphere. The container 40 has a ring or chimb 55 at its lower end formed by folding the edge of the base 40a around the lower edge of the side wall 40b of the container 40 and welding the two, so that the ring or chimb 55 has a thickness three times the thickness of the base 40a and side wall 40b. The ring or chimb 55 protects the base 40a and the lower part of the side wall 40b of the container 40 from damage by impact by suspending it from the floor (not shown) .

Claims

1. An overpack for a drum containing radioactive material, the overpack comprising a lightweight, porous, insulating packing material having a shape adapted to be fitted all around the drum to be packed thereby, the packing material being contained in an outer container which has folds or swages to provide enhanced radial stiffness or strength.

2. An overpack as in Claim 1 and wherein one or more plugs are fitted in the said container at one or more of the said folds to permit venting to the outside atmosphere of gases inside the container at a predetermined temperature or pressure.

3. An overpack as in Claim 1, Claim 2 or Claim 3 and wherein the packing mater-ial comprises a hollow body of packing material and a lid of packing material.

5. An overpack as in Claim 4 and wherein the body and the lid have chamfered mating surfaces to minimise loss of heat insulation.

6. An overpack as in Claim 5 and wherein the said mating surfaces extended along a slope at an angle of 45 degrees or approximately 45 degrees to the axis of the said container.

7. An over pack as in any of the preceding claims and wherein the outer container of the overpack has a ring at its lower end to suspend the base of the container from a floor on which it is standing.

8. An overpack as in any one of the preceding claims and which contains a sealed drum in which radioactive material is contained.

9. An overpack as in Claim 8 and wherein the drum contains UO3 powder.