AZ Performance of Steam Reforming Technology in a Long Term Treatment of Waste TBP / Dodecane - 11079

A long term pilot scale experiment with steam reforming treatment technology was conducted for volume and weight reduction of uranium contaminated waste tri-n-butyl phosphate/n-dodecane solvent (TBP/dodecane) which was difficult to incinerate. The technology consists of a steam reforming process and a submerged combustion process. In the first process, TBP/dodecane is vaporized and pyrolyzed with superheated steam in a reducing atmosphere. In the second process, the decomposition gases are completely burned in a submerged combustion reactor. A short term treatment test was carried out before the long term test. The test achieved high mass reduction rate of the waste TBP/dodecane at least 99.3% though severe corrosion of the gasification chamber was observed. This problem was solved by sacrificial anode. After the improvement, the system could be operated safely for 960 hours, the averaged mass reduction rate was 99.6% that was slight higher than the short test one. INTRODUCTION Radioactive organic wastes are generally treated by incineration that can provide high volume reduction rate. However, some kinds of organic wastes such as phosphate esters are difficult to combust because of generation of corrosive compounds and plugging materials. Phosphate esters are widely used as flame retarders and extraction agents in nuclear facilities. Tri-n-butyl phosphate (TBP) is used to extract uranium and plutonium from aqueous solution of spent fuel in reprocessing plants. When spent TBP is incinerated, it is pyrolyzed into hydrocarbons and phosphoric acid [1, 2] and then, phosphoric acid changes into polyphosphoric acids by thermal condensation [3]. The following formulas show pyrolization of TBP (1) and condensation of phosphoric acid (2). (C4H9O)3PO → 3C4H8 + H3PO4 (1) nH3PO4 → HO(HPO3)nH + (n-1)H2O (2) The evaporated polyphosphoric acids stick on the filter and the wall of incinerator and often decrease operating performance. Several alternative TBP treatment technologies have been developed. Acid digestion [4] is a decomposition process of TBP in the mixed solution of nitric acid and concentrated sulfuric acid at 200-250 oC. Strong acids cause corrosion in a decomposition reactor. Pyrolisis [5] is also decomposition process at 400-650 oC adding neutralizer such as calcium hydroxide for prevention of corrosion. This technology provides good corrosion resistance, however, a large amount of secondary waste is generated. Japan Atomic Energy Agency (JAEA) has developed a steam reforming treatment technology for volume and weight reduction of radioactive organic wastes that are difficult to incinerate. Steam reforming is a synthesis reaction of combustible gases such as hydrogen and methane from organic materials with