Patent Number: 053486897
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the destruction of alkali metal and alkaline earth metal waste. It particularly relates to a molten salt process for destroying alkali metals such as sodium, potassium, and lithium, and mixtures thereof, present in liquid metal reactor coolants. 2. Description of the Prior Art Alkali and alkaline earth metal waste e.g. radioactive sodium waste from reactor heat transfer media, are hazardous wastes because of the characteristic of reactivity. Before they can be disposed of, this characteristic must be destroyed. A large inventory of such metals, particularly sodium, potassium, lithium and mixtures of these metals are also radioactive. A number of processes for the disposal of these metals such as sodium exists. These include reaction of sodium with water, reaction of sodium with concentrated caustic, reaction with alcohol, burning of sodium in oxygen, calcination with silica, and reactions of sodium with ammonia, hydrogen, halogens and nitrous oxide. However, these present methods for the destruction of the characteristic of reactivity of alkali metals such as sodium have been proven generally unsatisfactory and disadvantageous for various reasons, such as the production of hydrogen, an explosive gas, or oxides, which are highly corrosive. Thus, the provision of a suitable method and the design of facilities to process large quantities of alkali and alkaline earth metal waste, such as sodium, is very challenging. SUMMARY OF THE INVENTION According to the present invention, alkali and alkaline earth metals such as sodium, are reacted with a mixture of carbon dioxide and oxygen (or air) in a molten salt bath, e.g. molten alkali carbonate such as sodium carbonate. The alkali carbonate, e.g. sodium carbonate salt, resulting from the oxidation reaction is not hazardous and merely adds to the volume of salt in the bath. If the feed metal such as sodium is radioactive, most of the radioactivity remains in the molten salt bed. When operated as either a batch or continuous process, there are no reactive off-gas products. The reaction rate and operating temperature are readily controllable and there is essentially no release of radioactive materials from the salt bath. The salt composition of the molten salt bath can be tailored to lower the melting point of the salt. For example, if sodium is converted to sodium carbonate by reaction with oxygen and carbon dioxide, the melting point of the salt will be about 855.degree. C. The reaction can be carried out at much lower temperatures, e.g. within the limits of about 200.degree. C. to about 900.degree. C., provided that the molten salt bed contains salts which result in lower melting mixtures. For example, these salts may include or consist of mixtures of alkali metal halides, e.g. chlorides and alkaline earth halides, e.g. calcium chlorides, and mixtures thereof. The properties of the salt composition may also be tailored by adding sulfate, phosphate or nitrate salts. Some make-up, for example, chloride salt, will be needed to maintain the low melting point. At lower molten salt bath temperatures, the salt vapor pressure and radioactive element carryover will be lower, corrosion will be reduced and metal containment vessels, such as Inconel 600, can be used. As another alternative, if chloride salts are used, chlorine gas or chlorinated hydrocarbons can be sparged through the molten salt bed to convert carbonates to chlorides. OBJECTS OF THE INVENTION It is accordingly one object of the present invention to provide an improved method for the destruction of alkali and alkaline earth metal hazardous waste. Another object is the provision of a relatively simple process for the destruction of such hazardous waste, e.g. sodium, in a molten salt bath to form non-hazardous alkali and alkaline earth metal salts. A particular object is the provision of a method for destruction of alkali and alkaline earth metals, especially sodium, by reaction with a mixture of carbon dioxide and oxygen in a molten carbonate salt bath.