TEPCO starts to cover unit 1

17 June 2011

Preparations have begun to fit a temporary cloth cover over the damaged Fukushima Daiichi unit 1 reactor to block rain and wind from the contaminated building.

Computer image of planned unit 1 cover
Image sets planned structure in midst of a 3D model of the site based on optical scanning equipment


The structure, made of steel struts holding coated polyester fibre sheets, will measure 54 m high, 46.9 m wide and 42.3 m long. The cover will be assembled from large components by crawler cranes. To further reduce workers' dose rates, it will be built using remote measuring technology and remote fastenings. A detailed three-dimensional model of the site has been created by radar scanners. Installation will be practiced at the Onahama port and using computer models. Site assembly of crawler cranes began on 12 June; construction work is scheduled to begin on 27 July.

Also, Fukushima Daiichi utility TEPCO has submitted a plan for an alternative cooling system of the unit 3 spent fuel pool, along the lines of the successful unit 2 system, which started work on 31 May. Installation work would start on 18 June, and operation is due to begin on 30 June.

An alternative line for water injection of the unit 4 spent fuel pool was installed on 16 June, injecting 75 tons of fresh water with corrosion inhibitor hydrazine.

Tests of the new water treatment system have enabled engineers to estimate tentative decontamination factors of different parts of the system. The system treats contaminated water in four principal stages: oil separation, cesium adsorption, decontamination and desalination. The cesium adsorption system, supplied by Kurion, achieved a decontamination factor of 100,000 on 15 June, an improvement of 100 times compared with tests using low-level contaminated water the previous day. The Areva-supplied decontamination system has a rate of 17,000 for Cs-134 and 18,000 for Cs-137 after low-level contaminated water tests on 15 June. A fault that stopped processing on 16 June has been fixed.

A borehole sample of soil near a waste treatment building, which had been receiving water pumped from the turbine building, has not found any evidence of leaks. The miscellaneous solid waste volume reduction treatment building (a waste incinerator) received 3660 tons of highly-contaminated water from the unit 3 turbine hall building from 17-25 May. Its water level was noticed to be falling; at the same time a trench 10m beneath ground level was noticed to be filling with water. However, results suggest that neither the building nor the trench is leaking. No substantial change in radiation levels has been detected in a nearby sub-drain. A total of eight samples taken at different heights in a borehole excavated to a depth of 3 m below the bottom of the trench have relatively low levels of radiation, and suggest the absence of leaks, TEPCO said.

Finally, TEPCO has written emergency preparedness plans for the Kashiwazaki-Kariwa and Fukushima Daiini sites in the event of a major natural disaster.

The guidelines constitute a kind of preliminary lessons learned from the Fukushima Daiichi emergency.

Although the report had not been immediately translated into English, a summary was available:

-Main control room environment countermeasures include deployment of electric power supply vehicles and establishment of air filtering equipment operational procedures

-To secure communications, a mobile wireless system and satphone system are to be installed in addition to current paging and house telephone systems

-To manage radiation exposure of emergency workers, shielding jackets are to be provided, and a management framework for emergency radiation work has been strengthened

-To prevent hydrogen explosions, tools to cut vent holes in roofs will be deployed; in addition, a reactor building roof vent system and hydrogen detectors will be installed at Kashiwazaki-Kariwa by June 2012

-To enable access after a natural disaster, heavy moving equipment will be deployed to each site.


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