Tokyo Electric Power Company (Tepco) has started assembling a cover over the damaged reactor building of unit 1 at the Fukushima Daiichi nuclear power plant. Meanwhile, an alternative cooling system has now been put into operation at the unit's used fuel pool.
The top section of unit 1's reactor building was wrecked by a hydrogen explosion, the first at the site, on 12 March. With a lightweight construction compared to the thick reinforced concrete of a reactor building, the cover will form a seal around the damaged building to prevent any potential emissions of radioactive material, while protecting the building from the weather.
|Construction starts on covering unit 1's damaged reactor building (Image: Tepco)
Having already conducted a trial assembly of the cover, work to construct a steel frame around the actual reactor building began on 10 August, Tepco said.
The sections of the steel frame will be fitted together remotely without the use of screws and bolts. All the wall panels will have a flameproof coating, and the structure will have a filtered ventilation system capable of handling 10,000 cubic metres per hour through six lines, including two backup lines. The cover structure will also be fitted with internal monitoring cameras, radiation and hydrogen detectors, thermometers and a pipe for water injection. It will be able to handle accumulated snow loads of 30 centimetres and wind speeds of up to 90 kilometres per hour.
According to Tepco's schedule, the cover should be completed in place by the end of September. Similar covers will be designed to fit around the other three damaged reactor buildings.
Fuel pool cooling
Meanwhile, Tepco reported that it has switched from using a water-injection system, where cold water was regularly pumped into the pool and allowed to evaporate on heating, to a circulatory cooling system for the used fuel pool at unit 1. The new system is designed to pump warm water out of the pool, cool it, and then return the water to the pool.
The company said that it began operating the alternative cooling system at 11:22 am on 10 August. The temperature of that fuel pool was previously unknown due to a failure of the instrumentation. However, a reading taken shortly after the alternative cooling system was started indicated that the temperature of the water in the pool was 47.0°C. Another reading taken 24 hours later showed that the temperature had already fallen to 41.5°C.
Tepco has already installed similar alternative cooling systems at the used fuel pools in Fukushima Daiichi units 2, 3 and 4. The temperature of those pools on 11 August was 36.0°C, 33.6°C and 42.0°C, respectively.
Researched and written
by World Nuclear News