Abstract
Flowsheets are presented for the dissolution of Borax IV reactor fuel (6.35% UO/sub 2/)--ThO/sub 2/ pellets encased in 1% nickel--aluminum alloy and bonded with lead). In the preferred method the alurninum is dissolved first in boiling 2 M NaOH--1.78 M NaNO/sub 3/, with a urarium loss of approximately 0.07%. The lead and nickel are then dissolved in boiling 1.5 M HNO/sub 3/, with uranium losses of <0.2%. The oxide core is dissolved in two successive digestions with boiling 13 M HNO/sub 3/--0.04 M NaF--0.1 M Al(NO/sub 3/)) to produce a solution 0.6 M in thoriunn and 0.04 M in uranium. Dissolution of only the aluminum in sodium hydroxide or sodium hydroxide--sodium nitrate solution prior to core dissolution is unattractive since the rate of core dissolution is lowered greatly if lead is present and a product solution containing greater than 0.2 M thorium is unattainable owing to the low solubillty of lead nitrate in nitric acid-- thorium nitrate solutions. Simultaneous dissolution of aluminum and lead in mercury-catalyzed nitric acid appears costly since a mercury concentration of at leset 0.5 M is required to ensure an adequate dissolution rate. The solubility of lead nitrate in nitric acid and nitric acid--thorium nitrate solutions was determined. (auth)
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