Recovery of locked-up uranium in slag disc by co-melting in magnesio-thermic reduction

• Published in: Transactions of the Indian Institute of Metals 2008-04, Vol.61 (2-3), p.103-106
• Main Authors: Ladola, Y. S., Chowdhury, S., Sharma, S., Roy, S. B.
• Format: Article
• Language: English
• Subjects: Chemistry and Materials Science; Corrosion and Coatings; Materials Science; Metallic Materials; Tribology
• ISSN: 0972-2815; 0975-1645
• DOI: 10.1007/s12666-008-0023-4

Magnesio-thermic Reduction (MTR) of Uranium tetra Fluoride (UF 4 ) is one of the main industrial methods for producing commercial pure uranium metal in massive form. Nuclear grade natural Uranium (U) metal ingots are produced regularly in UED, BARC following MTR route for fuelling research reactors in BARC. This is a bomb type reaction and is represented by Small excess of magnesium is required to achieve maximum yield. This thermite type reduction is carried out in a closed reaction vessel, popularly known as MTR reactor, lined with magnesium fluoride powder. MTR reactors are made of boiler quality steel. Use of MgF 2 , a reaction by-product, as lining material completely eliminates the chance of foreign element contamination. This lining of MgF 2 not only prevents direct contact of the molten metal and slag with the reaction vessel but also acts as an insulating material immediately after firing and holds the hot molten mass for longer period, thereby facilitating adequate metal-slag separation. This is a batch process and stoichiometric quantity of UF 4 and Mg chips are blended and charged inside the lined reactor. Once the charging is over, the surface is covered with fine MgF 2 powder and sealed by fixing a lid. This sealed reactor is then heated inside an electric furnace at a predefined heating schedule for the reduction to take place. The initiation of reaction is called ‘Firing”. MTR reaction mechanism is a complex one. A large number of side reactions as well as parallel reactions also occur during the conversion of UF 4 to U. This reaction is exothermic and final temperature of the molten product mass i.e. U and MgF 2 goes up to around 1600–1700°C. U settles down at bottom due to large density difference with slag. Good separation is very important for the better yield. Interface of U metal and slag is rich in U content because freshly reduced U metal droplets, which do not get chance to coalesce with the bulk of the metal due to the formation of firm crust at the interface of metal and slag end up getting accumulated at the interface. This interface is removed before subsequent vacuum induction melting and fuel fabrication. This cut interface, which contains entrained metal that could not coalesce with parent metal, some amount of parent metal and quite a good amount of MgF 2 , is called the ‘slag disc’ . It is desirable to recover U locked-up in these slag discs as the recovery of U will not only augment current U inventory but also will reduc