Abstract: The method for Pu analysis in large volume water was studied by using a precipitation concentration-ion exchange method. MnO₂ precipitation and Ca-Mg co-precipitation were used in the concentration process. When the volume of water sample was 25 L, the total radiochemical recovery rate of the two precipitation methods can reach about 70%. When the volume of water sample was greater than 50 L, the recovery rate of MnO₂ precipitation decreased significantly. The total radiochemical recovery rate of 100 L water sample by Ca-Mg co-precipitation is 63.5% to 80.2%, the average value is 74.6%±5.9% (n=7), and the minimum detectable limit of ^239+240Pu is 3.1 μBq/L (volume V=100 L, recovery rate Y=74.6%, measurement time t=72 h). The content of ^239+240Pu in an actual fresh water sample was 9.32-15.6 μBq/L, and there was no result which is below detection limit when the sample volume was 100 L.

Key words: large volume water, ^239+240Pu, MnO₂ precipitation, Ca-Mg co-precipitation, ion exchange