Postponing Retrieving Debris

Tokyo Electric Power Company (TEPCO) started the process of retrieving debris, which were made by melted-down fuel rod and other substances, in Fukushima Daiichi Nuclear Power Plant (F1) for the first time since its severe accident in 2011. However, TEPCO stopped its process immediately after starting it, finding a mistake in the process. TEPCO postponed the project for identifying the reason of mistake and will not restart the process until it takes preventive measures.

Soaked in great tsunami produced by the East Japan Great Earthquake in March 11, 2011, F1 lost all of its electric power, causing overheat of fuel rods which were melted down. 880 metric tons of debris still exist on the bottom of unit 1 to 3 of the plant. Having confirmed the situation inside the containment vessels, TEPCO decided to start retrieval this summer.

 

According to the plan of TEPCO, the retrieval would be started from the unit 2, in which  preparation has been relatively progressive, and the scale of retrieval would be gradually enlarged. The company planned to retrieve first debris, which would be lighter than 3 grams, by a device resembled fishing rod and line with length of 22 meters.

 

The device was supposed to be inserted in the containment vessel through a bulb which would separate the inside space full of radiation and the outside. As the staffs prepared to insert five pipes through the bulb, which would guide the device into the vessel, they found that the order of the pipe was not correct. The mistake of the order was already made in July. TEPCO did not double checked the order of those pipes, because reconfirmation of order of the pipe was not on the checking list.

 

Retrieving debris from the containment vessels is the main work for the process of decommissioning F1. Original plan assumed to start the retrieve in 2021. It was postposed three times due to delay of developing robot arms. Since development of the arms have not completed, TEPCO used the device resembling fishing rod. However, the retrieving would be for very small amount of debris at the beginning. It is still unclear how the process will be accelerated.

 

As long as debris are not retrieved and remaining in the site, TEPCO needs to keep them soaked in water to be cool. It produces contaminated water. While TEPCO purifies the water, without retrieving tritium, and stock it in the tanks, there are no more space for building new tanks. It led discharging that processed water into the Pacific Ocean. The discharging invited protest from China and South Korea.

 

It marked one year anniversary on August 24, since TEPCO started the discharging. TEPCO currently is in the eighth period of discharging. Although the government of Japan argues that the discharged water has radiation within international requirement, China uses Japan’s discharge as a diplomatic card in trade. It keeps embargo on Japan’s sea products. Total cost of severe accident in F1 has not determined yet.