Evaluation of Proposed Flowsheet Changes for the Highly Enriched Uranium Blenddown Program

Abstract

At the Savannah River Site, highly enriched uranium (HEU) is dissolved, purified, and blended with natural uranium to make low enriched uranium solutions sufficiently pure for conversion to power reactor fuel. The process to dissolve and purify aluminum-clad HEU fuel at SRS is well-established. However, for the dissolution and recovery of metal scrap, flowsheet changes were proposed. This study evaluates the proposed changes. Specifically, solvent extraction modeling calculations were performed which indicated that one solvent extraction cycle would be sufficient to purify the metal scrap solution by removing boron, which is added as a neutron poison. In addition, stability constants from the literature and Savannah River National Laboratory corrosion studies were documented to demonstrate that boron complexation of fluoride in nitric acid solutions, at the levels anticipated, is sufficient to prevent excessive corrosion in stainless steel vessels. Downstream from the purification process, limitations on the boron concentration in waste evaporators were recommended to prevent formation of boron-containing solids.

Keywords:

• Boron
• corrosion
• fluoride complexation
• solvent extraction
• uranium

ACKNOWLEDGMENT

The authors acknowledge helpful input from Major C. Thompson during this study.

Notes

Decontamination factor or DF = Volumetric feed concentration/volumetric product concentration.

Distribution coefficient or Do/a = Concentration in organic phase/concentration in aqueous phase at equilibrium.

mpy ≡ mils per year.

∗ Note that B solubility is 3–4 g/L in 7–8 M HNO₃ at 25°C.