Patent Number: 048083372
Section: description

DETAILED DESCRIPTION OF THE DRAWINGS Referring firstly to FIGS. 1 and 2 of the drawings, there is shown a compressible, bellows-type metal canister 1, for use in a hot pressing process for immobilising high level radioactive nuclear waste material in the form of a synthetic rock. The canister typically is generally as described in U.S. Pat. No. 4,645,624. The canister includes a gas filter and discharge arrangement constituting one embodiment of the invention. The canister 1 comprises a base wall 2 and a corrugated bellows like side wall 3 of generally circular cross-section. Concentrically arranged within the corrugated side wall 3 is a cylindrical liner 4. In the centre of the base wall 2 is located a conically-tapered aperture 5 provided with a filter plug shown diagrammatically at 6. Between the corrugated side wall 3 and inner liner 4 of the canister are provided two further, diametrically-opposed apertures 7. All three apertures 5, 7 are connected by an outlet pipe 8 extending diametrically across the base wall 2 and exteriorly of the canister. This outlet pipe 8 is connectable to any suitable waste disposal system, as will be described hereinafter with respect to a preferred embodiment. Referring now to FIGS. 3A and 3B, there are shown two alternative embodiments of filter plug 6 which may be used in association with the central aperture 5 in the base wall 2 of the compressible canister 1. The filter plug 6 in FIG. 3A comprises an inverted castellated cap 9 with which is associated a filter mass 10 made of alumina or titania fibre. This filter material is packed into the conically-tapered aperture 5 and into the gaps between the castellations of the cap 9. The projecting lugs of the castellated cap 9 rest on the upper surface of the base wall 2 around the periphery of the conical aperture 5 and thus compressive forces in the axial direction of the canister are absorbed and ingress of synthetic rock forming components into the filter structure are substantially avoided. The filter plug 6 shown in FIG. 3B differs from that of FIG. 3A only in that it has a filter disc 10' made of Hastalloy in place of the mass of alumina or titania fibre. The filter disc 10' is welded around its periphery as shown at 16 to the conical-aperture 5. Furthermore, in the embodiment of FIG. 3B the outlet duct 8 is formed by the co-operation of a slot in the underside of the base wall 2, the duct being closed on its lower side by co-operation with the uper face of pressure pad 12 resting on a hydraulic ram. The discharge of gases through the outlet duct 8 can be to a gas processing system of the type described below with reference to FIGS. 4A and 4B. The gases will comprise the gas in the interstices of the particulate material in the canister and any volatile components produced from the particulate material during the heating stage. As shown in FIGS. 4A and 4B, the outlet pipe 8 (or outlet duct) is connected to an outlet tube 11. In FIG. 4A, the compressible canister 1 is shown in a free-standing position upon a lower pressure pad 12 of a hydraulic press associated with an induction furnace (not shown) in which the canister is to be heated to a high temperature and then compressed axially. In this arrangement, the outlet tube 11 is L-shaped and has its horizontal limb rotatably but sealingly mounted in a side of the base wall 2; the terminal limb in the illustrated loading position extends upwardly, with its open end free to the atmosphere. In the process, as shown in FIG. 4B, the compressible bellows-type canister 1 is raised by the hydraulic ram to place the upper wall 17 of the canister against a fixed refractory abutment pad 13. The canister is thus positioned so as to be heated in the induction furnace (not shown) which surrounds the canister. However, before heating can commence, the outlet tube 11 is rotated through 180.degree. into a downwardly extending position, such that the terminal limb extends into a manifold arrangement 14 communicating with an exhaust tube 15, which is connected to a low pressure gas filtration system. It is to be noted that the manifold arrangement 14 and associated down pipe 15 are mounted on the lower pressure pad 12, so that they can move in unison with the exhaust tube 11 and canister 1 supported on that pad. Although the high level radioactive nuclear waste incorporated into the synthetic rock materials includes elements volatile at the typical temperatures to which the material is heated (about 1150.degree. C.) it has been fund that little, if any of these components are infact exhausted from the canister; it is thought these volatile components are absorbed into the synthetic rock materials. However, in order to maximize safety aspects it is proposed to collect all gases discharged through the outlet duct 8. The filter structure has a filter material for preventing the ejection of any particulate matter from the canister which might be entrained with the gases. Due to the gae collection system shown in FIGS. 4A and 4B the gaseous stream can be filtered and any radioactive components removed. FIG. 4A shows the loading postion. For transportation the terminal limb 11 of the outlet duct is directed upwardly to prevent damage or catching on any objects. After positioning of the canister 1 on the pressure pad 12, the limb is rotated downwardly to engage in the slotted open end of manifold 14 which together with discharge pipe 15 are fixed to the side of the pressure pad 12. Other configurations for discharge pipe connections could be utilised. Simply, reliable connections are important and one uesful alternative is to provide a V-shaped slot in opposite walls at the end of manifold 14 and to raise the manifold and orientate it so that it engages a side wall of a fixed discharge tube 11 and bridges across a portion of the side wall of the discharge tube having a gas discharge aperture.