Run the water through an ion exchange process. There are zeolites specific to elements like cesium. Send the spent resin to be mixed with borosilicate glass and melted, then placed in steel casks. Same process used at the West Valley Demonstration Project.
https://en.m.wikipedia.org/wiki/West_Valley_Demonstration_Project
This is the same technology used by the French nuclear industry for decades.
I worked on this project.
The problem is Tritium. thats where the radioactivity in the release water is coming from. As a hydrogen isotope you can’t separate it from sea water.
BUT.
They are releasing a million tons. In the Pacific ocean the dilution will result in 1 part per
660,000,000,000.
This is a (deliberately) “scary topic” propaganda piece. The weights of water are exaggerated by using tons, as if the dilute tritium contaminated water were solid high level waste.
Tritium has a short half life, after 10 years it already had decayed down! If the rest of the water is released “over decades” only a vanishingly small amount of the original will be left.
Tritium is a hydrogen isotope, it can’t be filtered or chemically separated from the ordinary hydrogen in the water. If, for example, 2 tons of tritium were originally in the water, all of these 1.25 “million tons” of frightenly “contaminated tons of water” has now decayed to less than one ton of tritium. Tritium is a weak emitter anyway, the 1.25 million tons of regular water shields the radioactive ones very well. The 250 trillions of regular salt water will shield even better.