[en] Strontium activity has been removed from Magnox pond waters by the in-situ precipitation of titanium hydroxide, and subsequent ultrafiltration to remove the strontium-loaded precipitate from the effluent. The titanium hydroxide produced in this way was sub-micron in particle size and had a high adsorption capacity. Strontium decontamination factors in excess of 100 have been achieved after the addition of only 2g/m³ of titanium to the effluent followed by ultrafiltration. Continuous operation of 0.1m² plastic, hollow fibre ultrafiltration modules has been demonstrated. After the addition of 4g/m³ of titanium, effluent was concentrated ten-fold by ultrafiltration and then further concentrated by sedimentation, the supernate being recycled to the ultrafiltration process. The overall process volume reduction factor from effluent to titanium hydroxide sludge was 500 with an overall strontium decontamination factor in excess of 100. Least membrane fouling was observed when using hollow fibres of the largest available diameter and when operating in turbulent flow. It was estimated that a membrane flux of 2m/d could, under appropriate conditions, be maintained for periods of almost 20 days. A flowsheet for the operation of a large ultrafiltration plant is discussed. (author)