Patent Number: 051568187
Section: summary

BACKGROUND OF THE INVENTION AND PRIOR ART A wide range of radioactive waste processes are known for the isolation of a variety of low level wastes (LLW) and intermediate level wastes (ILW) by the use of volume reduction, and solidification. The resulting product of these processes, which may be substantially uncontaminated, slightly contaminated, or remain highly contaminated, is then usually packaged in drums or other containers for disposal. Ideally, radioactive waste should be as substantially reduced in volume as is commercially practical due to the excessively high costs of disposal or storage. Typically, this is accomplished by tight packing into containers such as metal drums or the like. Such containers suffer from various disadvantages including the fact that they are usually round and therefore a considerable amount of storage space is lost due to the dead space between the containers. Additionally, such containers are known to bulge or corrode over time. One improved method of reducing the volume of radioactive waste is uniaxial centrifugal casting thereof as is disclosed in U.S. Pat. No. 4,897,221 issued Jan. 30, 1990 to Frank Manchak, Jr. Other uniaxial centrifugal waste casting methods are disclosed in U.S. application Ser. No. 328,020 filed Mar. 23, 1989 by Frank Manchak, Jr., et al, and in U.S. application Ser. No. 384,087 filed as a CIP of Ser. No. 328,020 on Jul. 21, 1989. These applications both disclose the use of reinforcing cages which are used in the casting mold. It is now suspected, although not scientifically proven, that high density packing of radioactive waste not only reduces the volume to be stored, but also that such high density packing also provides greater inherent radiation shielding and reduced radiation leakage as compared to less dense packing. For some radioactive materials, high density packing is also suspected to reduce the radioactive half life, i.e., enhance the rate of radioactive decay. A high density packing process and apparatus is desired so that hazardous radioactive waste can be more densely and rapidly compacted into a radiation shielded dense monolithic form having strength and structural integrity for transport and which can be monitored for radiation compliance and, if necessary, provided with additional radiation barrier material before leaving the centrifugal casting apparatus. As referred to herein, the term "castable radioactive materials" is meant to comprise a hardenable mixture of radioactive waste materials and other waste materials mixed as necessary with one or more hardenable materials such as polyorganic compounds or cementitious materials or the like. As used herein, the terms "monolith", "cast monolith" and "monolithic form" are intended to refer to a solidified casting having one or more layers of radiation encapsulating material on the exterior thereof. Such monoliths may be provided, as taught herein, either by casting the entire monolith including shell layers of impact resistant and radiation shielding materials and the hazardous waste at the jobsite or, in the alternative, by using pre-formed shells and merely casting the waste at the jobsite. In pre-formed shells are used, provision must be made for casting additional radiation barrier material inside of the pre-formed shells if jobsite conditions dictate. SUMMARY OF THE INVENTION In a first embodiment, the present invention provides a method of isolating hazardous radioactive waste for disposal comprising the steps of: a) injecting a flowable charge of heat curable radiation shielding material into a rotatable mold, said charge being of volume calculated to provide a radiation barrier wall of selected minimum thickness on all interior surfaces of said mold; PA0 b) rotating said mold to centrifugally distribute said radiation shielding material on the interior surfaces of said mold; PA0 c) heating the walls of said mold during rotation thereof to cure and solidify said radiation barrier wall; PA0 d) filling the cured radiation barrier wall with castable radioactive waste material while rotating said mold to centrifugally compact and cast said radioactive waste material inside of said barrier wall to form a monolith comprised of said cast waste material and barrier wall; PA0 e) removing said mold from said monolith; PA0 f) detecting the amount of leakage radiation emitted by said monolith; PA0 g) applying additional radiation shielding material to the exterior surface of said monolith if the detected leakage radiation exceeds a predetermined threshold level; and PA0 h) transporting said monolith to a storage area. PA0 a) a bifurcated centrifugal casting mold having at least two separable mold parts and fluid inlet and fluid outlet ports aligned along a first axis, said mold being supported for rotation about said first axis; PA0 b) means for supporting a completed cast monolith in said apparatus with the mold parts removed therefrom; PA0 c) powered drive means for rotating said mold and said monolith about said first axis; PA0 d) mold removal means aligned along a second axis substantially perpendicular to said first axis for removing the separate parts of said bifurcated casting mold from a cast monolith while leaving said monolith supported in said apparatus for rotation about said first axis; PA0 e) means for injecting a charge of radiation shielding material into said mold and for filling said mold with castable radioactive waste material; PA0 f) means for heating said mold during rotation of said mold about said first axis; PA0 g) means for detecting radiation emitted by a cast monolith comprised of an external barrier of said radiation shielding material substantially encapsulating cast radioactive waste; and PA0 h) means for applying additional radiation shielding material to said monolith if needed. PA0 a) placing a hardened pre-formed shell of impact resistant radiation shielding material in a rotatable mold; PA0 b) making a preliminary determination of the probable radioactivity of waste material to be cast in said shell; PA0 c) injecting a flowable charge of hardenable radiation shielding material into said shell if the preliminary determination of radioactivity exceeds a threshold value, said charge being of volume calculated to provide said shell with an additional radiation barrier wall of selected minimum thickness on all interior surfaces of said shell; PA0 d) rotating said mold and said shell to centrifugally distribute said additional radiation shielding material on the interior surfaces of said shell; PA0 e) curing said additional radiation shielding material by heating said material during rotation of the mold to harden and solidify said additional radiation shielding material inside said shell; PA0 f) filling the shell with castable radioactive waste material while rotating said mold to centrifugally compact and cast said radioactive waste material inside of said shell to form a monolith comprised of said cast waste material and said shell; PA0 g) removing said mold from said monolith; PA0 h) detecting the amount of leakage radiation emitted by said monolith; PA0 i) applying additional radiation shielding material to the exterior surface of said monolith if the detected leakage radiation exceeds a predetermined threshold level; and PA0 j) transporting said monolith to a storage area. PA0 a) a bifurcated centrifugal casting mold having at least two separable mold parts, said mold being supported for rotation about said first axis; PA0 b) means for supporting a completed cast monolith in said apparatus with the mold parts removed therefrom; PA0 c) powered drive means for rotating said mold and said monolith about said first axis; PA0 d) mold removal means aligned along a second axis substantially perpendicular to said first axis for removing the separate parts of said bifurcated casting mold from a cast monolith while leaving said monolith supported in said apparatus for rotation about said first axis; PA0 e) means for injecting a charge of radiation shielding material into a pre-formed shell placed in said mold and for filling said shell with castable radioactive waste material; and PA0 f) means for heating the interior of said shell during rotation of said mold about said first axis. The present invention further provides, in a first embodiment, an apparatus for isolating hazardous castable radioactive waste for disposal comprising: Preferably, centrifugal casting of the radiation barrier shielding material is accomplished by simultaneously rotating the casting mold about two mutually perpendicular axes so that a particularly dense radiation shielding barrier wall is formed which will contain the radioactive waste material. Separable mold parts are then removed from the cast monolith while still leaving the monolith supported for rotation in the centrifugal casting apparatus. Additional radiation shielding and/or structural integrity are attained, if necessary, by winding a strand of fiber composite material about the formed monolith. In a second embodiment, the invention provides a method of isolating hazardous radioactive waste for disposal comprising the steps of: In the second embodiment, the invention also provides apparatus for isolating hazardous castable radioactive waste for disposal comprising: Further advantages of the preferred embodiments of the methods and apparatus disclosed herein include the fact that costly metal storage drums or steel reinforced concrete drums and the attendant corrosion thereof are eliminated; and that a means for removal of heat generated by radioactive decay and latent chemical reaction in the cast monolith is shown wherein a heat removal pipe, preferably ceramic, may be inserted into the substantially completed cast monolith before final completion of the monolith.