Implementation of a strategy for managing radioactive scale in the China Clay industry

Abstract

This paper describes the only documented occurrence of radioactive scale in China Clay refining and the advances that have been made in dealing with the problem since it was first discovered in the late 1990s. Extensive characterisation studies have established the mineralogy, crystallography, chemical composition and radionuclide inventory of scale formed at each stage of the refining process. The dominant isotopes present are 226/228Ra, incorporated by co-precipitation in barium sulphate, and members of their decay chains, notably 210Pb and 210Po. Following decontamination trials, a decision was made to adopt ultra high pressure water jetting as the preferred removal method. A state of the art facility has been constructed in Cornwall and has recently entered service. Decontamination gives rise to a slurry comprising scale, associated minerals, corroded metal and large quantities of water. Research to define a suitable immobilisation matrix identified a highly durable cemented product with excellent leach resistance. Full-scale specimens have now been prepared, completing the plant refurbishment cycle. Many of the techniques described in this paper are applicable to other mineral wastes and radioactive contamination problems in complex industrial plant.