BACKGROUND With the rapid development of nuclear energy in China, a broad spectrum of low level radioactive wastewater (LLRW) has been generated and must be purified prior to discharging to the environment. Reverse osmosis (RO) has been proved an effective technology in the treatment of high boron-containing LLRW in nuclear power plants (NPPs). However, there is always a large amount of salts in the LLRW as background compounds. It is important to understand the influences of salts on the rejection of nuclides and boron. RESULTS CONCLUSION A lab-scale cross-flow membrane filtration unit was used. With the increase of ion concentration, the permeate flux decreased by 15% and 25% for BW30XFR and LE, respectively. Nuclides rejection increased by 2-8% and boron rejection increased by 5-10% when raising salts concentration to 2.5 mmol L-1. Divalent ions such as Mg2+ and SO42- had a stronger impact than monovalent ions such as Na+ and Cl- on nuclides and boron rejection. Increasing ion strength promoted the rejection of trace nuclides and boron, but at the cost of membrane flux loss. The results of dealing with simulated wastewater would give us information to better understand how to treat real radioactive wastewater. (c) 2018 Society of Chemical Industry