THE ZIRFLEX PROCESS TERMINAL DEVELOPMENT REPORT

The Zirflex Process employs a boiling aqueous solution of ammonium fluoride and ammonium nitrate to dissolve zirconium or Zircaloy. Average unoxidized Zircaloy dissolution rates are from 10 to 15 mils/hr for the optimum charge solution of 5.5M NH/sub 4/F-0.5M NH/sub 4/NO/sub 3/ at a F/Zr mole ratio of 7. Zircaloy, which is oxidized by exposure to high-temperature air or water, dissolves at rates of threeto five-fold less. Cores of uranium, uranium- aluminum, and uranium dioxide are not severely attacked by the Zirflex decladding solutions. Only the soluble uranium enters the waste, with losses varying from 0.3 to 3.0 g/l. The Zirflex waste solution is neutralized to a pH of 10 before storage. This requires approximately 0.07 gallon of 50% caustic per gallon of decladding solution. The neutralized waste consists of nearly 20 vol.% of rapidly settling solids, which are easily slurried under turbulent flow conditions. These solids tend to settle out in streamline flow and therefore agitation is required during temporary storage. Conventional nitric acid core dissolution is generally applicable to Zircaloy-clad uranium and UO/sub 2/ elements since the core material is essentially free from zirconium. The addition of aluminum nitrate to the nitric acid dissolvent at an aluminum/ residual F/sup -/ mole ratio of approximately three is necessary, however, to ixhibit the corrosive action of residual fluoride. Stainless steel can be used as the material of construction for the Zirflex dissolver equipment because of the dissolvent's comparatively mild corrosive action. A corrosicn rate of 11 mils/month was determined using 304L stainless steel exposed to boiling 6M ammonium fluoride. (auth