Tepco's plans for water issues

Friday, 1 April 2011

Engineers have plans to deal with contaminated water at the Fukushima Daiichi site, although enacting them will take time. New water storage and treatment facilities are planned for construction.

 

The power plant has been in dire trouble since it was overrun by a 14-metre tsunami on 11 March. This disabled heat removal pumps as well as power supplies, leaving three reactors on site to overheat. Fuel ponds also overheated at these and one other unit.

 

The Fukushima 50+   Tepco have said that some 370 people are at work at the Fukushima Daiichi site, 51 of whom are contractors.   At the fully stabilised Daini site, which remains under emergency status, there are 626 workers, of which 64 are contractors.   So far, 21 workers have received radiation doses of more than 100 millisieverts, while none have reached the level of 200 millisieverts. The regulatory limit for this emergency situation is 250 milliseiverts.

Perhaps unsurprisingly after a tsunami, efforts to get normal systems back into operation have been hampered by contaminated water on site. There are pools of water in the basements of turbine buildings, some of which are significantly contaminated, as well as flooding in trenches that carry cabling and pipework.

 

At the same time, water being discharged from the site to sea has shown radioactivity far beyond regulatory limits. One factor in this is run-off water carrying radionuclides deposited on the ground.

 

Treatment plant

 

To tackle the discharges Tokyo Electric Power Company plans to construct a 6000 tonne water tank as well as a 4000 tonne pond. These will work in conjunction with a 20 tonne per hour treatment facility to handle water from drainage canals around all six reactors at the plant.

 

The tank and pond should be complete around the middle of this month, with the treatment facility following about two weeks later. The set-up should let the company mitigate the discharges to sea by safely storing and sampling the water and only discharging it after treatment.

 

Preparing to pump

 

Pumping is already underway to clear the basement of the turbine buildings using a complicated chain of three different tanks for temporary storage.

 

Water will be pumped from the basements up to condenser units and from there to condensate storage tanks. Finally it will be directed into two separate suppression pool water surge tanks, each shared between units 1 to 4.

 

At unit 1 the company has pumped water from the basement into the condenser but this is now full to its 1600 tonne capacity. Preparations are underway for the later two stages of pumping and Tepco noted that the 1900 tonne condensate tank is already full.

 

Tepco has yet to start pumping at units 2 and 3. It said both the 3000 tonne condensers and 2500 tonne condensate tanks of these units were already full.

 

The end location, the shared suppression pool water surge tanks, each have capacities ot 3400 tonnes. These are 63% and 54% available.
 
Researched and written
by World Nuclear News