Development and implementation of a low-cost ex-situ soil clean-up method for actinide removal at the AWE Aldermaston site, U.K

Agnew, K., Purdie, P., Cundy, A.B., Hopkinson, L., Croudace, I.W. and Warwick, P.E.F.. (2009) Development and implementation of a low-cost ex-situ soil clean-up method for actinide removal at the AWE Aldermaston site, U.K. In Proceedings of the 2009 Waste Management Symposium “Waste Management for the Nuclear Renaissance. Curran Associates for WM Symposia. 17p .

Abstract

This paper details the development (and implementation) of a novel, low-cost electrokinetic soil clean-up method for treatment of Pu-labelled soil wastes at the AWE Aldermaston site, Berkshire, U.K. Nuclear weapons manufacture and maintenance, and related research and development activities, have been carried out at the Aldermaston site for over 50 years, and these historical operations have generated a number of contaminated land legacy issues, including soils which contain above background (although radiologically insignificant) specific activities of Pu. Much of the Pu-labelled soil has been removed (via soil excavation), and is held in containment units on site, prior to remediation / decommissioning. Based on initial small-scale laboratory trials examining the potential for Pu removal and directed migration under a low intensity electrical field, a two year project (funded by the former UK Department of Trade and Industry and AWE PLC) has been implemented, and is reported here, involving a focussed programme of laboratory trials followed by a full-scale field trial to examine the potential of low-cost electrokinetic techniques to reduce the activity of Pu in clay-rich site soils, and reduce site waste disposal costs. Pu (and U) exhibited relatively complex behaviour in the laboratory trials, with Pu forming mobile soluble oxy-anionic species under the high pHs generated by the electrokinetic treatment technique. Clear mobilisation of Pu and U (along with a range of other elements) was however observed, in a range of soil types. The relative efficiency of remobilization was element-dependant, and, in terms of heavy metal contaminants, radionuclides, and the stable analogues of radionuclides known to be problematic at other nuclear sites, was (from most to least mobile) Cl > Zn > Sr > U > Pu > Pb. Both Pu and U showed enhanced mobility when the low-cost soil conditioning agent citric acid was added prior to electrokinetic treatment. Full-scale field trials of the treatment method during summer 2008 involved ex-situ, but on-site, treatment of soil wastes in a lined steel cell, using low-cost materials (e.g. portable 12 V batteries, cast iron electrodes), over a 2 month period. The development and field-scale implementation of the remediation technique on a working nuclear site involved the development of a detailed safe system of work, with standard operating and Quality Assurance procedures, and the involvement and cooperation of a range of on-site and off-site organisations. The implications of: - the laboratory and field trial data; and - the site and regulatory requirements for the implementation of the clean-up process for the application of similar remediation or waste management methods on other nuclear sites are described and evaluated here.

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Contributors

Author: A.B. Cundy

Author: P.E.F.. Warwick

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