Routine bi-annual whole body monitoring of a process operator who works in a Hex to urianium dioxide conversion showed a higher than normal burden of uranium in the lungs. Subsequent monitoring has indicated that the worker may have exceeded 50 mSv CEDE. Further monitoring over a period of weeks is still required to enable a final confirmation of the dose. Routine surveillance of uranium air levels in the plant has not revealed any unusual results and no other workers have been affected. A normal internal inquiry has been convened and the Nuclear Installations Inspectorate has been informed as the relevant UK regulatory authority in accordance with the requirements of UK legislation.