September 01, 2011
Tokyo Electric Power Co. has drafted a blueprint for removing fuel from reactors and storage pools at the crippled Fukushima No. 1 nuclear power plant, a task described by experts as unprecedented, daunting and even mind-boggling.
In the draft plan presented at a meeting of the Japan Atomic Energy Commission on Aug. 31, TEPCO said it will fill containment and pressure vessels with water, inspect the condition of the fuel with cameras and then remove the damaged fuel.
The meeting was held in Tokyo’s Kasumigaseki district to study measures to decommission the No. 1 through No. 4 reactors at the Fukushima plant.
However, TEPCO failed to provide a specific time schedule for removing the 1,496 nuclear fuel assemblies from the No. 1, 2 and 3 reactors.
“We are not yet in a position to decide on details (of the plan),” said Kazuhiro Takei, general manager of TEPCO’s Nuclear Fuel Cycle Department.
It could take up to a decade to even start the fuel-removal process.
Fuel melted and accumulated at the bottom of the pressure vessels of the three reactors after cooling functions were lost in the March 11 Great East Japan Earthquake and tsunami.
Experts who attended the meeting described the enormous challenge ahead in dealing with the unprecedented accident, in which meltdowns occurred simultaneously at three reactors.
“We will step into uncharted territory as far as working environment and job requirements are concerned,” one participant said.
“A mind-boggling task lies ahead of us,” said another.
Some experts said the melted fuel could change shape and lead to nuclear fission when it is being removed. They said workers must carefully monitor conditions while removing the fuel.
“We will be required to take a process of trial and error and review work procedures whenever it is necessary,” said Hirofumi Nakamura, a senior official at the Japan Atomic Energy Agency.
In the first step of the draft plan, TEPCO will remove radioactivity inside reactor buildings with robots and remote-control equipment.
Workers will then determine the conditions of the containment vessels and repair the damaged parts to prevent water from leaking to turbine buildings and other places.
In the second step, TEPCO will fill the containment and pressure vessels with water to cool damaged fuel, which is emitting heat, and inspect fuel conditions inside the pressure vessels with cameras. Water shields radioactivity.
The company plans to vacuum out or grab away the fuel with special equipment. There has been no decision yet on how to dispose of the melted fuel.
TEPCO will also begin removing 3,108 nuclear fuel assemblies from storage pools of the No. 1 through No. 4 reactors in about three years because they are not seriously damaged.
Overhead cranes and fuel replacement systems will be installed at storage pools of the No. 1, 3 and 4 reactors because fuel removal equipment was destroyed in the hydrogen explosions at the reactor buildings.
Fuel removed from storage pools will be kept at a common-use pool near the No. 4 reactor building.
Step 2 of the road map for stabilizing the reactors at the Fukushima plant is scheduled to be completed between October and January 2012.
Within three years after Step 2 is completed, containers will be installed to cover the damaged reactor buildings.
TEPCO hopes to begin removing melted fuel in 10 years, according to its earlier estimate based on the Three Mile Island accident in the United States in 1979.
It will take several decades to dismantle and relocate the reactors, according to the estimate.
In the Three Mile Island accident, melted fuel remained inside pressure vessels. At the Fukushima plant, damaged fuel leaked to the outer containment vessels.
It will be extremely difficult to collect damaged fuel scattered in and outside the reactors. It will be no less easy to remove radioactivity and repair damages because various parts of the plant are contaminated with high levels of radioactivity.
(This article was written by Tatsuyuki Kobori and Hidenori Tsuboya.)