TEPCO has built and started a new circulation cooling system of the unit 2 spent fuel pool. In the first 24 hours of operation from 31 May to 1 June, it lowered the spent fuel pond temperature by 20 degrees to 48.4°C. Similar cooling systems will be installed at unit 1 and 3 by the end of June, and at unit 4 by middle July.
In the new two-loop system, water leaves the spent fuel pool through the skimmer surge tank, is pumped through valves in the waste treatment building, and to an intermediate heat exchanger in the filter sludge tank room (FSTR) building. There, decay heat passes to a secondary loop which is pumped through an external cooling tower. The cooled spent fuel circuit water returns from the FSTR building, back through different valves in the waste treatment building, and injected directly into the spent fuel pool.
In other news, TEPCO has begun work to set up a filtration system to decontaminate the canal water in front of the Fukushima Daiichi power plant. The canal water, which has received several highly-radioactive water leaks from the plant, was isolated from the sea and the power plant water intakes weeks ago by installing silt fences and sheet piles.
The system, set up between the unit 2 and unit 3 intakes, uses pumps to drive water through a filter and into an adsorption tower. The tower is a 2.3m square cube filled with zeolite, a material that separates out some radioisotopes. Water pumped in to the bottom of the tank sprays upwards through three layers of zeolite before emerging out of the top. Initially, two units will be installed. A test run was scheduled for today.