Friday, August 12, 2011

Tepco Adopts Center Cover Recommendation: Sarcophagus

The Center has recommended a permanent sarcophagus for the four reactors that exploded in March.  The Tokyo Electric Power Company (Tepco) has finally decided to construct covers over the reactors.  According to Tepco, the installment of the cover over reactor 1 is a temporary emergency measure until a midterm measure is initiated. The cover is expected to be completed by October.

Tepco should have installed such a covering as soon as possible after the explosions at the reactor buildings. The Center has been making such a recommendation since the explosions occurred. Permanent covers should be constructed as soon as possible.

Reactor 1 with top blown off

The purpose of the cover for the reactor building

Tepco is planning to cover the damaged reactor building with highly airtight material. A cover for a reactor building is installed for the purpose of preventing diffusion of radioactive materials (radioactive materials discharged from the reactor, water vapor from spent fuel pool, rubbles and dust with radioactive materials, etc) and shutting off rain water into the reactor building. If the tent over reactor No. 1 proves successful, similar coverings will be constructed over reactors 2, 3 and 4.

Design Image of Covering

Summary of the structure

The cover has a steel frame structure, where four pillars are built around the reactor building, with beams connecting the four pillars. Roof panels and wall panels are fitted with film materials made of vinyl chloride resin coating and polyester fiber fabric which prevents most diffusion, and these panels cover the whole reactor building.

Dimension of the cover structure is approx. 154 feet (North-South direction) x approx. 137 feet (East-West direction), and approximately 177 feet of height.

The design of the cover for the reactor building confirms the safety of the cover against designed earthquake and wind.

Model of Covering

Large scale units

Steel frame beam (40m), filmed panels for walls (approx. 20m), and filmed panels for the roof (approx. 40m) are assembled into large modules. Large modules will be put together in the site using crawler cranes, with its capable load the largest class in the country (750t). Assembly of large modules will be carried out at Onahama port outside the site, and they will be carried to the site by ship. By this way, we will reduce the work load within the Power Station site and around the reactor building as much as possible.

Measuring / Control Technology

In order to enable remote installment, Tepco will use the latest technology such as systems to control lifted materials from rotating and detach rigging equipment by wireless signals, 3D laser scanning of the turbine building areas, real-time measurement and control of locations of materials in assembly process.

In order to ensure the installment using each of these technologies, Tepco is making tentative assembly at Onahama port. (Tepco)

No comments: