Patent Number: 052763358
Section: summary

FIELD OF INVENTION This invention relates to an improved container and a method of making such a container for storing and transporting highly radioactive material. BACKGROUND OF INVENTION Nuclear reactors generate substantial amounts of radioactive waste material in the form of spent fuel rods which are still highly radioactive. Special containers or casks are needed to transport them to preprocessing plants or for storing them. These casks must act as shields against radioactivity and must be structurally strong and sound as well as inexpensive as possible. Lead is well known to be a good shield against radioactivity but lead is too soft for secure fabrication and fastening. Depleted uranium is better and the shielding material of choice. It is cast into the desired shape and then sandwiched between steel or other structural members to provide the necessary strength and rigidity for the cask. However, castings suffer from voids due to cracks, gas holes, shrink holes and the like, which results in less than the specified thickness of depleted uranium for shielding. In addition, the large castings required are in the range of fifty to sixty thousand pounds while the largest uranium furnaces in current operation have typically no more than a five to six thousand pound capacity. As a result, the casks must be cast in pieces and then securely fastened together in such a way as to not only provide a rigid, unitary container but also so as to provide no clear, unshielded line of sight path through the cask along which radiation could escape. SUMMARY OF INVENTION It is therefore an object of this invention to provide an improved container or cask and a method of making such a cask for storing and transporting highly radioactive material. It is a further object of this invention to provide such an improved cask and method which eliminates voids, cracks, gas holes, shrink holes and the like normally occurring in cast forms. It is a further object of this invention to provide such an improved cask and method which eliminates the need for casting the depleted uranium shield portions. It is a further object of this invention to provide such a cask and method which assures ample uniform thickness of the depleted uranium shield. It is a further object of this invention to provide such a cask and method which enables a single continuous construction for the depleted uranium shield portions. It is a further object of this invention to provide such a cask and method in which the depleted uranium shield can be easily shaped to any desired form. It is a further object of this invention to provide such a cask and method which requires no large capital investment in melting furnaces or casting dies. It is a further object of this invention to provide such a cask and method which permits testing of shielding before final fabrication. It is a further object of this invention to provide such a cask and method which enables effective X-ray or ultrasonic examination of the shielding. It is a further object of this invention to provide such a cask and method which enables dynamic, high-speed X-ray or ultrasonic examination of the shielding. The invention results from the realization that a truly effective cask for storing and transporting highly radioactive materials can be constructed by using depleted uranium in the form of wire, of various cross-sectional shapes, wound to form a continuous shield for the body of the cask and also for the end caps. This invention features a cask body for storing and transporting highly radioactive materials. There is an inner shell and a number of layers of depleted uranium wire wound on the inner shell to create a radioactive shield against emanation of radioactivity from material stored within the inner shell. In a preferred embodiment the inner shell may be cylindrical or polygonal, the wire may be round, rectangular or polygonal, and the the wire may be wound tensilely stressed onto the inner shell for applying a compressive stress on the inner shell. The wire layers may be staggered to minimize overlap of joints from layer to layer and they may be wound circumferentially on the inner shell. The invention also features a cask body for storing and transporting highly radioactive materials, including an inner shell, a number of layers of depleted uranium wire wound on the inner shell to create a radioactive shield against emanation of radioactivity from materials stored within the inner shell, and an outer shell spaced from the inner shell, and covering and protecting the depleted uranium wire. The outer and inner shells may be fixed together to form a single unitary structure, and the outer shell may have the same shape as the inner shell. The invention also features a cask for storage and transport of highly radioactive materials including a cask body having an inner shell and a number of layers of depleted uranium wire wound on the inner shell to create a radioactive shield against emanation of radioactivity from material stored within the inner shell. There are also a base member for capping each end of the body. Each of the base and cover members includes an inner plate and a number of layers of depleted uranium wire wound on the inner plate to create a radioactive shield against emanation of radioactivity from materials stored within the cask. The inner plate may include a depleted uranium plug, and the depleted uranium wire may be wound spirally or circumferentially about the plug. The plug may be tapered to automatically induce a staggering in the joints between the wire from layer to layer. The cover and base members may include outer plates spaced from their inner plates and covering and protecting the depleted uranium wire wound on the inner plates. The invention also features a method of making a cask body for storing highly radioactive materials, including the steps of providing an inner shell having the shape of the storage cavity for the radioactive material to be stored, and winding a plurality of layers of depleted uranium wire on the inner shell to create a radiation shield against emanation of radioactivity from materials stored within the inner shell. In a preferred embodiment, the shell may be cylindrical, polygonal or any other shape, and the wire may be round, rectangular, polygonal or any other shape. The wire may be wound tensilely stressed onto the shell for applying compressive stress on the inner shell, the wire layers may be staggered to minimize overlap of joints from layer to layer, and the wire may be circumferentially wound on the inner shell. The method may include adding an outer shell spaced from the inner for covering and protecting the depleted uranium wire. The outer shell may be joined to the inner shell to form a single unitary structure. The outer shell may have the same shape as the inner shell. The method may also include in a preferred embodiment constructing a base member and a cover member for capping each end of the body by winding for each member a number of layers of depleted uranium wire on an inner plate to create a radioactive shield against emanation of radioactivity from materials stored within the cask. The inner plate may be provided with a depleted uranium plug, and the depleted uranium wire may be spirally or circumferentially wound about the plug. An outer plate may be added to each member spaced from the inner plate for covering and protecting the depleted uranium wire. The plug may be tapered to automatically induce staggering of the joints between the wires from layer to layer.