The Identification and Degradation of Isosaccharinic Acid, a Cellulose Degradation Product
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THE IDENTIFICATION AND DEGRADATION OF ISOSACCHARINIC ACID, A CELLULOSE DEGRADATION PRODUCT
B.F. GREENFIELD, G.J. HOLTOM, M.H. HURDUS, N. O'KELLY, N.J. PILKINGTON, A. ROSEVEAR, M.W. SPINDLER AND S.J. WILLIAMS AEA Technology, Harwell, Didcot, Oxfordshire, UK, OX1 1 ORA.
ABSTRACT Nirex is seeking to develop a deep underground repository for the disposal of solid intermediate-level and low-level radioactive wastes (ILW and LLW) in the UK. One possible influence on the behaviour of radionuclides is the formation of water-soluble complexants by the degradation of the solid organic polymers that will be present in the wastes. The degradation products of cellulose have been shown to increase the solubility of plutonium and other radionuclides and to reduce sorption onto near-field and far-field materials. Degradation of cellulose under anaerobic alkaline conditions produces a range of organic acids. In this paper 2-C-(hydroxymethyl)-3-deoxy-D-pentonic acid (isosaccharinic acid, ISA) is identified by High Performance Liquid Chromatography as a significant component of cellulose leachates. A combination of fractionation of cellulose leachates and plutonium solubility determinations shows that ISA is responsible for the majority of the enhancement of plutonium solubility observed in such leachates. Further degradation of ISA by chemical or microbial action may lessen the effect of degraded cellulose leachates. Experimental studies on the chemical degradation of this compound under alkaline conditions suggest that the presence of oxygen is required. Microbial degradation studies show that the plutonium solubility in solutions of ISA is reduced by their exposure to microbial action. INTRODUCTION Nirex is seeking to develop a deep underground repository for the disposal of solid intermediate-level and low-level radioactive wastes (ILW and LLW) in the UK 1. It is currently planned to place packages of conditioned waste in vaults, which will be backfilled with a cementitious grout. After closure of the repository, resaturation of the near field will take place and the wastes will be progressively exposed to highly alkaline, anaerobic porewater. It is necessary to develop an understanding of the important physical and chemical processes that determine the behaviour of radionuclides in this near-field environment and any effects that may influence this behaviour 2 One possible influence is the formation of water-soluble complexants by the degradation of the solid organic polymers that will be present in the wastes. These include cellulosic materials, polyvinylchloride (PVC) and other synthetic materials which will be subjected to chemical, microbiological and radiolytic attack. Work carried out by AEA Technology under the Nirex Safety Assessment Research Programme (NSARP) has shown that the chemical degradation of cellulose under alkaline conditions is of particular interest 3. In terms of its effect on radionuclide behaviour, cellulose is the most important organic material likely to be present in significant concentrations in IL
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