Analysis of Common Aminopolycarboxylic Acids in Low Level Radioactive Waste

Abstract

The aminopolycarboxylic acids (APCAs), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA), are used throughout the nuclear industry in the decontamination agents used in the decommissioning process, therefore, are often found in radioactive waste. The Low Level Waste Repository (LLWR) impose limits on the acceptance of wastes containing APCAs because, when present in the waste, the ligands have the potential to solubilise and mobilise contaminant species, making them more available for transport to groundwater and ultimately to the bio-sphere. A selective and sensitive methodology to detect and quantify these ligands in a range of complex matrices is advantageous in supporting waste acceptance processes and environmental monitoring at the LLWR. Therefore, a reversed-phase high-performance liquid chromatography (HPLC) procedure has been developed and validated; r2 > 0.999, intra/inter-day relative standard deviation ≤ 10%, recovery = 100 ± 3%, limits of detection (LOD) = 0.31, 0.38 and 4.3 mM for Fe(III)-EDTA, Fe(III)-DTPA and Fe(III)-NTA, respectively. Two peak deconvolution methods (parallel factor analysis and least-squares fitting) were applied to resolve overlapping chromatographic peaks of Fe(III)- and Co(III)-EDTA and the performances compared. Application of the method to leachate from sampling locations around the LLWR site found EDTA in four of the six samples tested (0.4 �M < [EDTA] < 1 �M). A solid-liquid phase extraction technique was optimised for determination of EDTA in samples of incinerated EDTA-contaminated ion-exchange resin (ion-exchange resins derived from operation and maintenance of the nuclear submarine fleet and intended for disposal at the LLWR). No EDTA was detected in incineration residue > LOD concentration (0.32 mg kg-1). The HPLC method was applied to �-irradiated samples of APCA species to quantify the degradation and identify potential radiolysis products. It was found that G(-EDTA) = 2.5 < G(-Fe(III)-EDTA) = 3.2 < G(-Fe(III)-DTPA) = 5.4, and ethylenediaminetriacetic acid is thought to be a significant degradation product formed in the radiolysis of Fe(III)-EDTA.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Francis Livens (Supervisor) & David Mills (Supervisor)