Incidence of High Nitrogen in Sintered Uranium Dioxide: A Case Study

Nitrogen content, above the specified limit of 75 μg(gU)-1, was encountered in sintered uranium dioxide in the course of its manufacture. The cause was traced to the sintering process, wherein carbon, a degradation product of the die wall or admixed lubricant, was retained in the compact as a result of inadvertent reversal of gas flow in the sintering furnace. In the presence of carbon, the uranium dioxide reacted with nitrogen from the furnace atmosphere to form nitride. The compacts with high nitrogen were also those with low sintered density, arising from low green density. The low green density was due to filling problems of an inhomogeneous powder. The experiments carried out establish the causes of high nitrogen to be the carbon residue from lubricant when the UO2 is sintered in a cracked ammonia atmosphere.

[1]  Keon-Sik Kim,et al.  Sintering of mixed UO2 and U3O8 powder compacts , 2000 .

[2]  M. Eral,et al.  Preparation and characterization of uranyl oxalate powders , 1999 .

[3]  K. Ramachandran,et al.  Uranium dioxide powder preparation, pressing, and sintering for optimum yield , 1999 .

[4]  P. Balakrishna,et al.  Agglomerate-free fine ceramic UO2 powders , 1999 .

[5]  M. Eral,et al.  Investigation of production conditions and powder properties of AUC , 1996 .

[6]  R. Freer,et al.  The effect of binder additions on the green and sintered properties of MnZn ferrite ceramics , 1995 .

[7]  Chou Kan-Sen,et al.  Precipitation studies of ammonium uranyl carbonate from UO2F2 solutions , 1989 .

[8]  P. A. Haas.  A Comparison of Processes for the Conversion of Uranyl Nitrate into Ceramic-Grade UO 2 , 1988 .

[9]  H. Elbel,et al.  Dependence of the UO2-PuO2 pellet structure on fabrication parameters , 1988 .

[10]  H. Tagawa,et al.  Formation of uranium mononitride by the reaction of uranium dioxide with carbon in ammonia and a mixture of hydrogen and nitrogen: II. Reaction rates , 1979 .

[11]  J. Woolfrey.  The preparation of UO2 powder: Effect of ammonium uranate properties , 1978 .

[12]  H. Tagawa,et al.  Formation of uranium mononitride by the reaction of uranium dioxide with carbon in ammonia and a mixture of hydrogen and nitrogen— I synthesis of high purity UN , 1977 .

[13]  J. Janov,et al.  The influence of precipitation conditions on the properties of ammonium diuranate and uranium dioxide powders , 1972 .

[14]  L. C. Watson,et al.  PREPARATION OF URANIUM DIOXIDE FOR USE IN CERAMIC FUELS. PART I. BATCH PRECIPITATION OF AMMONIUM DIURANATE , 1958 .