They’ve been using sea water to cool the rods, but when the level threatens to overflow the reactor buildings, they’re flushing the water back into the ocean (ref here and here). This is an obvious radioactivity hazard to the environment, so an auxiliary coolant recirculation system is required.

(For simplicity, only one pump cascade is illustrated.)

The small housings contain pumps. A shipping container is used for a sediment trap. When it fills to the top, it can be swapped out and buried at a waste site.

The pump on the right will get a lot of sediment passing through it, and will consequently have a short life. Maybe a filter can be placed in front of it too.

The hose on the right will likely get clogged and have to be swapped. But instead of being buried, perhaps it can be flushed and reused.

The equipment will eventually have to be buried too, as it will become highly radioactive from the sediment, which will have become highly radioactive from association with the fuel rods. Teleoperated robots will be handling a lot of these operations, but in the short-term perhaps the low-tech solution is grappling hooks.

If there’s a significant sediment build-up already, it’s essential to start recirculation and filtering coolant water immediately, even before the coolant pump cascade is in place. Sediment in sea water could potentially erode the casings on the fuel rods, allowing fuel to collect at the base of the cooling pools and reactors. That would raise the possibility of accumulating a critical mass and causing refission even with boron in the coolant.