[tarre]

There are reasons, why not to do that:

1) DF doesn't add up like that at low concentrations. Then it comes down to selectivity of the material. Sodium and cesium have similar chemical characteristics, but CsTreat is very efficient in selecting Cs over Na.

2) Material you are using as filter becomes radioactive waste. You want to keep the volume at minimum.

3) With CsTreat you already reach radioactive Cs levels below measurable limit. There is no reason to try to remove more Cs from that water :)

[pvaldes]

Honest question. Is is being CsTreated since eight years, why we do have radioactive Caesium still accumulating in the coast?

> 2) Material you are using as filter becomes radioactive waste. You want to keep the volume at minimum.

This is very reasonable, but storing sand for 50 years somewhere is technically feasible and maybe even cheaper than storing water. You can put the sand in concrete and obtain a solid block. Then put the package in some kind of coating and bury it in a safe vault. Water instead has the bad habit to leak, run away, and enter in the life chain when bad weather, monsoon or accidents happen. A huge concrete block is also less vulnerable to terrorism than a water tank. Is not so easy to steal a jar of it, for example. Even if you could make a hole in the coating, the product will not just flow out.

[tarre]

>Is is being CsTreated since eight years, why we do have radioactive Caesium still accumulating in the coast?

As far as I know, this is because about 10 PBq of Cs-137 was released during the accident and the released material is transferred by ocean currents. CsTreat is being used for purification of the water, which is pumped into and out the containment to keep core remnants cool. Nowadays the releases are very limited if any.

>This is very reasonable, but storing sand for 50 years somewhere is technically feasible...

You're right. Also CsTreat is solid, rock/sand-like material. It can be stored as mixed into concrete and disposed as low/intermediate-level radioactive waste.

Now you probably want to ask: Why there is huge amounts of radioactive water stored at the plant site? Because of tritium, which is chemically equal to hydrogen and is very expensive to separate from water. Under normal operating licenses of NPPs, you could release such water into environment, but at Fukushima standards are nowadays peculiar.