TOWARDS THE DECONTAMINATION OF PLUTONIUM CONTAMINATED BRICKS: CREATION OF A CERIUM-BASED SIMULANT CONTAMINATION SYSTEM James Kennedy a,b , Colin Boxall a , Anthony Banford b , Rick Demmer c , Andrew Parker d a Engineering Department, Lancaster University, Gillow Avenue, Lancaster, LA1 4YW, UK b The Centre for Innovative Nuclear Decommissioning (CINDe), NNL, Havelock Road, Workington, CA14 3YQ, UK c Idaho National Laboratory, PO Box 1625 MS 6150, Idaho Falls, ID 83415, USA d The John Tyndall Nuclear Research Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK Email: james.kennedy@nnl.co.uk, c.boxall@lancaster.ac.uk, anthony.w.banford@nnl.co.uk, rick.demmer@inl.gov, aparker11@uclan.ac.uk There is a need for the decontamination of a number of plutonium-contaminated bricks encountered in a legacy BUTEX reprocessing plant on Sellafield site in the UK. Documentary review has indicated that the source of the contamination was a 8 mol dm -3 nitric acid process stream containing 10 mmol dm -3 of Pu in either the (III) or (IV) oxidation state. Here we have sought to emulate the behaviour of Pu(III) by treatment of fired clay brick surfaces with a solution of 10 mmol dm -3 Ce(III) nitrate in 8 mol dm -3 nitric acid. XRD, porosimetry and EDX measurements of the untreated bricks reveal them to be comprised of low porosity silica and aluminosilicate phases with a surface layer of a low-Si content Al-C-N oxide derived from the atmosphere of the kiln in which the bricks were fired. Depth profiling after an initial 6 week acid soak reveals that the acid penetrates <10 mm into the brick. SEM/EDX analysis reveals that acid treatment significantly roughens the brick surface due to dissolution the above described Al-C-N oxide layer. The EDX data also shows that virtually no Ce is retained as tenacious contamination at the brick surface; this may be due to a either a mass action/kinetic effect or taken to indicate that trivalent Ce(III) is less likely to absorb at the crystalline silica/aluminosilicate surface of the brick than its more easily hydrolysable tetravalent equivalent. Preliminary higher-resolution EDX analysis indicates that small quantities of Ce(III) can be detected in pores or cracks on the surface of acid-treated brick samples. This suggests that Ce(III) may be non- tenaciously sequestered into surface defects – and that a simple salt wash may be sufficient to remove it. Based on the above observations, potential decontamination strategies are discussed and future studies outlined. I. INTRODUCTION Radiological decontamination is an essential enterprise that has become more important over the last four decades due to an increased focus on the decommissioning extant nuclear facilities as they reach the end of their design life. The costs and benefits of decontamination need to be balanced against the complete removal and demolition of contaminated areas or facilities. Demolition and removal are often the first options considered in such circumstances as decontamination may be thought of as slow and costly. Decontamination has advantages, including significant waste reduction over demolition. [1] Different contamination scenarios have led to the development of hundreds of decontamination processes. Their selection balances criteria such as cost-effectiveness and waste minimization. Whilst testing on the actual systems where the contamination arises (as "field" radioactive specimens) is appropriate, doing so is often expensive, time-consuming and fraught with risk related to operator exposure. Simulating contamination with non- active contaminant simulants and substitute substrates provides a less expensive, radiologically safer, more controlled and often more informative means of decontamination method selection. Properly implemented, simulant-based studies both require and provide a unique understanding of the system. In a previous study [2] , we have developed a physico-chemical understanding of the factors affecting the decontamination efficiency for the removal of tenacious (americium, cobalt) and non-tenacious (caesium, strontium) contaminants from commonly used mineral-based industrial building materials. These include concrete and granite (in service to the decontamination and clean-up of redundant nuclear facilities) and predominantly urban building materials such as limestone and marble (in service to large scale remediation after a terrorist attack). This work involved the development of representative non-active simulants for Cs, Sr, Am and Co as common radioactive contaminants and an extensive trialling of decontamination techniques on these simulants brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Lancaster E-Prints