The accumulation of contaminated water and the existence of radioactive debris continue to hamper work to stabilize the reactors at the damaged Fukushima Daiichi nuclear power plant in Japan. Meanwhile, South Korea and China have agreed to greater cooperation with Japan in nuclear safety and disaster management.
|A photo taken on 20 May 2011 shows the interior of Fukushima Daiichi 1's reactor building (Image: Tepco)
On 20 May, two workers at unit 1 of the Fukushima Daiichi plant made their way to the basement of the reactor building to assess flooding there. The workers reported that the water in the basement was some 4.2 metres deep. This was slightly higher than the level measured over a week ago, when plant owner Tokyo Electric Power Company (Tepco) first confirmed the existence of water.
Last week, Tepco reported that following the installation and calibration of two new water level gauges, water level readings suggested that most of the fuel in unit 1 had earlier melted and fallen to the bottom of the reactor vessel, where it has solidified and been kept adequately cooled. The company said that most of this core melt probably occurred within 16 hours after the unit automatically shutdown when the earthquake struck on 11 March. This core melt is suspected to have caused damage to both the reactor pressure vessel and the containment vessel, allowing water to leak out of the reactor.
The increase in the level of the water in the basement of the reactor building suggests that water being pumped into the reactor to keep it cool is indeed leaking through both the reactor vessel and containment vessel.
Tepco continues to empty water from the cabling trench at unit 2 and from the turbine building of unit 3. This water is being pumped to the central waste treatment facility on the plant site. By 20 May, some 7932 tonnes of water had been removed from the trench at unit 2, while 852 tonnes had been pumped from unit 3's turbine building.
Hydrogen explosions in the reactor buildings of both unit 1 and 3 led to radioactive debris being scattered in the areas around the units. The existence of this debris has hampered work to stabilize the reactors, although workers have now been able to enter units 1, 2 and 3 to assess damage. However, radiation levels in the area around the reactor building of unit 1 have fallen by almost half since early April as a result of a large amount of this debris being cleared.
Tepco has now reported that the presence of highly radioactive debris around unit 3. The company said that it had found debris releasing 1000 millisieverts per hour in an area south the unit's reactor building - the highest level of radiation so far discovered in debris on the Fukushima Daiichi site. Tepco said that it will use remote-controlled vehicles to remove the contaminated debris to enable work to bring the reactor to cold shutdown to progress quicker.
|The 'Mega Float' arrives at Fukushima Daiichi (Image: Tepco)
Meanwhile, a huge barge arrived at the plant on the morning of 21 May. The steel barge - measuring some 136 metres long and 46 metres wide - will be used to store up to 10,000 tonnes of contaminated water. Radioactive water will be pumped from the plant to the 'Mega Float' barge, moored at the quay on the site, through pipes. Tepco plans to store mildly contaminated water from the site in temporary storage facilities, such as the barge, so that more highly radioactive water can be contained at the plant and treated accordingly.
During the fourth Korea-Japan-China summit in Tokyo on 21-22 May, the premiers of the three countries agreed to strengthen cooperation in nuclear safety and disaster control management.
The leaders - South Korean president Lee Myung-bak, Japanese prime minister Naoto Kan and Chinese premier Wen Jiabao - adopted a joint statement, agreeing to share information for disaster control and nuclear plant safety management, along with cooperation in achieving sustainable growth through boosting efficiency in the renewable energy sector.
They agreed to set up an early notification system for emergencies, share information and strengthen consultations between them. The three leaders also agreed to cooperate in prompt information sharing and sending support missions when a disaster occurs.
President Lee noted that one of the significant outcomes of the summit lies in the agreement to advance cooperation in nuclear safety and disaster management among the three countries, whose geographic closeness means that a single nuclear safety accident or natural disaster in one country can affect all three.
Kan accompanied Lee and Wen on a visit to the city of Sendai in Miyagi prefecture, which was badly damaged by the earthquake and tsunami that struck on 11 March. They later visited a gymnasium serving as a makeshift shelter in Fukushima for residents evacuated because of the accident at the nearby Fukushima Daiichi plant.
In a move to show that food from the Fukushima area is safe to eat, the premiers were served meals containing meat, vegetables and fruit produced in the region.
Researched and written
by World Nuclear News