Fukushima cover on its way

Tepco plans to complete the construction of a cover over the stricken Fukushima Daiichi unit 1 by the end of September, according to a progress report submitted to the Japanese nuclear safety agency. Meanwhile, recent analysis suggests most of the fuel in the unit's storage pool is undamaged.

A cover is being installed over the unit 1 reactor building, damaged by a hydrogen explosion on 12 March, as a temporary measure to reduce the release of radioactive materials to the atmosphere as well as to prevent the ingress of rainwater. Preparatory work, such as levelling the ground, began in mid-May. Crawler cranes are to be used in the installation process to minimize the exposure dose of workers and shorten the work period.

According to a report on the construction plan submitted by Tokyo Electric Power Company (Tepco) to the Nuclear and Industrial Safety Agency (NISA) on 24 June, on-site construction work is now underway and is scheduled for completion by the end of September, although the plans include a contingency margin to the end of November.

The cover will be able to accommodate an accumulated snow load of 30 centimetres, wind speeds of up to 25 metres per second, and a horizontal seismic load of 0.2, according to Tepco. 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.
Nuclide analysis of water from the used fuel pool at unit 1 suggests that most of the fuel in the pool is sound, Tepco reports. The analysis of 300 millilitres of water from the pool on 22 June showed higher activity levels than would be expected under normal conditions, but this is assumed to arise from contamination by radioactive materials from rubble, dust and incoming contaminated water.

Trial operations of a system to treat contaminated water at Fukushima are continuing despite an interruption for a caesium absorption unit to be exchanged. According to Tepco, 2489 tonnes of contaminated water had been treated as of 24 June.

(Source : World Nuclear News, edition of 27 June 2011)