GB871692A - Process for recovery of nuclear fuel from used fuel elements - Google Patents

Abstract

Spent nuclear fuel elements comprising uranium, plutonium, or thorium, and also containing zirconium, hafnium, or titanium, are immersed in a solution of ammonium fluoride or bifluoride which dissolves at least part of the element. Zirconium alloy cladding may first be removed from a uranium-zirconium core, and then the core material dissolved or disintegrated using a similar solution. The strength of the ammonium fluoride solution may be from 10-50% and it may be used at room temperature up to the boiling point of the solution; the solution may be substantially neutral, having a pH of from 5 to 7. The solution used for removing zirconium cladding may be cooled and concentrated, or solid ammonium fluoride added, to deposit crystals of ammonium fluozirconate which are hydrolysed with ammonia to precipitate zirconium hydrate, convertible by calcination into the oxide; alternatively the entire ammonium fluoride solution may be treated with ammonia to form zirconium hydrate precipitate. The solution of the uraniumzirconium core is filtered to remove insoluble fluorides of fission products and plutonium. On cooling or adding ammonium fluoride to the filtrate, mixed crystals of ammonium fluozirconate and uranium fluoride are obtained and these crystals are slurried with water, the zirconium compound dissolving and the insoluble uranium fluoride being removed; uranium oxide U3O8 is obtained from the fluoride by dissolving in nitric acid, precipitating with ammonia and igniting at 900 DEG C. Plutonium present with the fission product fluorides is recovered by slurrying the precipitate with water and adding a mild oxidising agent and oxalic acid, the plutonium dissolving as oxalate and the other materials remaining insoluble.