Surface Contamination on Fuel Flasks: Best Practice Advice on Minimising and Measuring Non-Fixed Radioactive Contamination

Abstract

Knowing the levels of non-fixed radioactive contamination on surfaces is important for the safety of personnel and ensuring conformity with the regulations. Best practice will reduce the generation of loose surface radioactivity and enable it to be assessed with reasonable accuracy. This paper summarises experimental work carried out by the Central Electricity Generating Board/Nuclear Electric into the generation of non-fixed contamination, the mechanisms of the swabbing process and how the swab value relates to the, total loose surface radioactivity. It identifies those factors which are, and are not, important in the generation of non-fixed contamination and its measurement. These factors include: paint condition, time in the pond, decontamination vigour, environmental sources, journey time, flask surface location (top/sidelbottom), area wiped, contact pressure, swab – surface contact geometry, soiling, relative humidity prior to swabbing, effect of liquid water during transport but dried off before swabbing, wetness of surface/swab, water chemical composition, effects derived from UV irradiation on paint before contamination, effects of UV and gamma irradiation on paint previously contaminated. Surface soiling (grime and water) are the only significant generators of loose contamination. Swab reproducibility and precision is improved by circumscribing the contact geometry, area wiped and contact pressure. An in situ method of determining total loose radioactivity by multiple swabbing is presented. Best practice advice for minimising and measuring non-fixed contamination is derived.