Well, most likly they do not want dump the materials in to the sea because there are many tons of radioactive material. (more than 100,000 tons)
Also another reason is because radiation makes more radation, It is kind of speads like a viurs.
Right now the workers need to stop the raidation from killing them, since they have to work so close to places spreading radaiton. most radiation is beta raidation which basically a type of electron, beta is like 250 times more stronger than a electron.
To protect their bodies they need a equal charge of energy, to push the radiation away from them, this works because like charges repell each other.
Since they don,t have suits or can make them wihtin a day, they have to make sheilds that have energy charge that will repell beta radiation. So that they can go to work at close ranges.
For most radaiations a charge of 50,000 volts, but a voltage of 12,500 volts will provide protection from most Beta radiations.
I would also say that reactor 3 has just released black smoke, which suggest that a precentage of spent fuel rods have reached a end phase in decay and released Carbon
DwayneD.L.Rabon