100 tons is roughly 100 cubic metres, or 1 cube of 4.65m. In a year it's a cube of roughly 33.2m each side. Given that the concern seems to be tritium, with a half-life of 12 years, if you want to reduce radiation to about 1/1000th, you'd need 10 halvings, so 120 such cubes. That's a lot, but if you were to build containment basins of "only" 1 depth, it'd be a basin 365 meters each side and 33.2m deep. That's not nothing, but it's likely also excessive.

> They've made progress in reducing the amount (it used to be hundreds of tons daily) but it's still a problem

What exactly is the problem that it is causing?