ID :
195928
Tue, 07/19/2011 - 19:25
Auther :
Shortlink :
http://m.oananews.org//node/195928
The shortlink copeid
Japan moves on to stage to seek cold shutdown of crippled reactors+
TOKYO, July 19 Kyodo -
Japan said Tuesday it has succeeded in stably cooling the crippled nuclear reactors at the Fukushima Daiichi power plant and reducing the radiation dose around the site, an announcement that would lead restoration efforts to move on to the next stage of seeking a ''cold shutdown'' of the reactors by January.
In an updated road map to contain the four-month-old nuclear crisis, unveiled the same day, the government said it plans to work out by around autumn safety guidelines to maintain the ravaged plant's stability for a long period, while plant operator Tokyo Electric Power Co. will seek to start removing spent nuclear fuel within three years following the stabilization of the reactors.
''We're starting to see a tremendous critical condition heading toward a certain level of settlement,'' Prime Minister Naoto Kan told a parliamentary committee as he welcomed the completion ''almost as scheduled'' of the so-called ''step one'' phase of the utility's restoration road map.
''Some progress has been made earlier than originally scheduled'' in the step one phase,'' Kan also told a meeting of the government's task force on the world's worst nuclear crisis in 25 years.
The government left unchanged the originally set timeline to achieve the ''step two'' phase, which includes the goal of realizing a cold shutdown of the Nos. 1 to 3 reactors, in the latest scenario.
Industry minister Banri Kaieda said the government could lift a directive that requires residents in a zone 20 to 30 kilometers from the plant to be prepared to evacuate or stay indoors in an emergency, before completing the next phase.
The road map also showed that the government will consider lifting a ban on people entering areas within a 20-kilometer radius of the plant towards the end of the step two phase, which is to be implemented in the three to six months following the completion of the first phase.
As for the definition of a state of cold shutdown, the government said that the bottom part of a reactor's pressure vessel should be basically kept at 100 C or below, and that radiation exposure caused by the additional release of radioactive substances should be ''greatly restrained.''
At present, the maximum amount of such substances leaking from the damaged Nos. 1 to 3 reactors is 1 billion becquerels per hour, around one two-millionth of the level at the time of the accident, the utility known as TEPCO said.
Based on the data, the maximum radiation dose amounts to 1.7 millisieverts per year around the plant, and TEPCO is expected to bring the level to below the legal limit of 1 millisievert per year, an official at the government's Nuclear and Industrial Safety Agency said.
TEPCO also said it will try to improve the operational ratio of water decontamination devices from around 70 percent of capacity this month as well as consider creating another system as the current water treatment system can be used for only about a year.
The utility plans to design an underground wall, expected to extend 30 meters deep, to prevent contaminated water from seeping from the reactor and turbine buildings and getting mixed with groundwater, it said.
Restoration efforts have continued since the March 11 magnitude 9.0 earthquake and tsunami hit the six-reactor complex and led the cooling functions of the reactors and spent nuclear fuel pools at the Nos. 1 to 4 units to fail.
One of the key challenges during the past months has been how to deal with the massive amount of highly radioactive water that has accumulated in the reactor turbine buildings and nearby areas as an outcome of an emergency measure to continue injecting water into the reactors to cool the fuel inside.
Nitrogen, an inert gas, is also being injected into the reactors to prevent hydrogen explosions, which could lead to the release of massive amounts of radioactive substances. But basically all the spent fuel tanks of the Nos. 1 to 4 units are already being kept cool.
Japan said Tuesday it has succeeded in stably cooling the crippled nuclear reactors at the Fukushima Daiichi power plant and reducing the radiation dose around the site, an announcement that would lead restoration efforts to move on to the next stage of seeking a ''cold shutdown'' of the reactors by January.
In an updated road map to contain the four-month-old nuclear crisis, unveiled the same day, the government said it plans to work out by around autumn safety guidelines to maintain the ravaged plant's stability for a long period, while plant operator Tokyo Electric Power Co. will seek to start removing spent nuclear fuel within three years following the stabilization of the reactors.
''We're starting to see a tremendous critical condition heading toward a certain level of settlement,'' Prime Minister Naoto Kan told a parliamentary committee as he welcomed the completion ''almost as scheduled'' of the so-called ''step one'' phase of the utility's restoration road map.
''Some progress has been made earlier than originally scheduled'' in the step one phase,'' Kan also told a meeting of the government's task force on the world's worst nuclear crisis in 25 years.
The government left unchanged the originally set timeline to achieve the ''step two'' phase, which includes the goal of realizing a cold shutdown of the Nos. 1 to 3 reactors, in the latest scenario.
Industry minister Banri Kaieda said the government could lift a directive that requires residents in a zone 20 to 30 kilometers from the plant to be prepared to evacuate or stay indoors in an emergency, before completing the next phase.
The road map also showed that the government will consider lifting a ban on people entering areas within a 20-kilometer radius of the plant towards the end of the step two phase, which is to be implemented in the three to six months following the completion of the first phase.
As for the definition of a state of cold shutdown, the government said that the bottom part of a reactor's pressure vessel should be basically kept at 100 C or below, and that radiation exposure caused by the additional release of radioactive substances should be ''greatly restrained.''
At present, the maximum amount of such substances leaking from the damaged Nos. 1 to 3 reactors is 1 billion becquerels per hour, around one two-millionth of the level at the time of the accident, the utility known as TEPCO said.
Based on the data, the maximum radiation dose amounts to 1.7 millisieverts per year around the plant, and TEPCO is expected to bring the level to below the legal limit of 1 millisievert per year, an official at the government's Nuclear and Industrial Safety Agency said.
TEPCO also said it will try to improve the operational ratio of water decontamination devices from around 70 percent of capacity this month as well as consider creating another system as the current water treatment system can be used for only about a year.
The utility plans to design an underground wall, expected to extend 30 meters deep, to prevent contaminated water from seeping from the reactor and turbine buildings and getting mixed with groundwater, it said.
Restoration efforts have continued since the March 11 magnitude 9.0 earthquake and tsunami hit the six-reactor complex and led the cooling functions of the reactors and spent nuclear fuel pools at the Nos. 1 to 4 units to fail.
One of the key challenges during the past months has been how to deal with the massive amount of highly radioactive water that has accumulated in the reactor turbine buildings and nearby areas as an outcome of an emergency measure to continue injecting water into the reactors to cool the fuel inside.
Nitrogen, an inert gas, is also being injected into the reactors to prevent hydrogen explosions, which could lead to the release of massive amounts of radioactive substances. But basically all the spent fuel tanks of the Nos. 1 to 4 units are already being kept cool.
