Patent Number: 042697280
Section: summary

FIELD OF THE INVENTION This invention relates to the storage of spent fuel in repositories in which sulfur is used as the storage medium. More particularly, the invention relates to an improvement in the method for the storage of radioactive wastes in repositories in which the storage medium is liquid sulfur and the repositories are made self-sealing. DESCRIPTION OF THE PRIOR ART In view of the fact that nuclear energy will be increasingly used to supply the world's energy, the nuclear industry is faced with the problem of developing a method for safely disposing of radioactive wastes. It must especially be ensured that the radioactivity from such wastes will not contaminate the environment. Up until a short time ago, storage facilities were expected to hold spent fuel for less than 10 years. However, new policy guidelines require that the fuel may have to be stored for periods of up to 100 years. A number of factors must be taken into consideration in the development of a method for safely storing radioactive wastes for this length of time. For example, the question of storage cost must be considered. In this connection, it will be appreciated that it is always possible to arrange a large number of so-called barriers around the radioactive wastes to be stored. On the other hand, a large number of such barriers will significantly increase the storage costs and, in turn, make the production of nuclear energy less competitive when compared to other sources of energy. The most common storage medium for spent fuel elements has been water. However, water presents problems in that over long periods of time, e.g., up to ten years, it exerts a corrosive effect on the containers and parts of the repositories in contact with the water. This ultimately results in various metallic salts from the repositories and the elements being dissolved in the water. Such salts do possess a level of radioactivity. Consequently, should an accident occur wherein a leak results, the water with the radioactive salts dissolved therein can leak out and is easily absorbed into the ground or evaporates into the atmosphere leaving the radioactive contaminants. Thus, water is not suitable for a long term storage medium. In the past, a variety of methods for storing radioactive materials have been utilized. In U.S. Pat. No. 4,131,564, a process for preparing solid wastes containing radioactive or toxic substances for safe handling, transportation and permanent storage has been described. A similar method is disclosed in U.S. Pat. No. 3,838,061. U.S. Pat. No. 3,824,673 discloses a method for the treatment of irradiated fuel elements, particularly for transporting the fuel elements wherein a molten alloy material is deposited between the fuel rods and the alloy is allowed to solidify. The concept of making containers self-sealing for long-term storage is described in U.S. Pat. No. 3,983,050. In this case, the radioactive material is stored in a container in which powdered cement is added so that any leak will cause hardening of the cement when the storage container is in a moisture-containing environment, such as, open air or a water tank storage. SUMMARY OF THE INVENTION Applicants have discovered that long-term storage requirements which are now considered to be necessary can be met by utilizing, as the storage medium, elemental sulfur. The use of the sulfur avoids the disadvantages of the water previously used and further provides extremely long term storage capability, e.g., up to and even more than 100 years.