Evaluation of Niowave's Proposed Solvent Washing Approach

Abstract

Niowave, Inc., is a domestic supplier of medical and industrial isotopes from uranium (U) and radium (Ra). The company has recently entered into a cooperative agreement with the U.S. Department of Energy's National Nuclear Security Administration (NNSA) and plans to deploy a superconducting electron accelerator (LINAC) to fission U for molybdenum-99 ( 99 Mo) production without the need for a nuclear reactor or highly enriched uranium (HEU). NNSA provided funding to the Savannah River National Laboratory (SRNL) to support Niowave in this effort.Niowave will chemically process the irradiated material for recovery and purification of valuable isotopes, beginning with the dissolution of targets in nitric acid (HNO3). A modified Plutonium Uranium Reduction Extraction (PUREX) process will be implemented for the recovery of U. The PUREX process utilizes a tributyl phosphate (TBP) in normal paraffin hydrocarbon (NPH) solvent which, when contacted with the nitric acid feed, extracts actinides into the organic phase. Ionizing radiation and nitric acid cause degradation of both the TBP and NPH. The principal degradation products of TBP are dibutyl phosphate (DBP) and monobutyl phosphate (MBP), which decrease U stripping efficiencies. NPH degradation products include a variety of oxidation and nitration products, which tend to affect phase separation and may retain certain short-lived fission products. A solvent washing process has been proposed to treat the degraded solvent by contacting it with 4 wt% sodium carbonate (Na2CO3) followed by contact with 0.1 M HNO3 to neutralize residual alkalinity. The carbonate wash is effective at removing DBP and MBP but does not remove long chain degradation products derived from the solvent. SRNL evaluated the application of the solvent washing process for Niowave at the proposed solvent:carbonate volume ratio (O:A) of 1:1.14 and with a reduced proportion of carbonate at an O:A ratio of 1:0.5. To do so, solvent was contacted with nitric acid and irradiated to the anticipated single pass radiation dose of 394 gray (Gy) and 10x and 100x the anticipated dose to demonstrate the impact of multiple recycles on the solvent quality. The solvent of all three doses was washed at the proposed O:A ratio and alternate O:A ratio of 1:0.5. The quality of the solvent was evaluated based on recommendations for similar processes at the Savannah River Site including DBP concentration, interfacial tension (IT), and disengagement time. Revision viii