Radioactive water has not been confirmed to have overflowed into the Pacific from seaside underground trenches at the crippled Fukushima Daiichi nuclear power plant, Japan's Nuclear and Industrial Safety Agency said Tuesday.
The levels of water in the trenches, some 55 to 70 meters away from the shore, have been stable and the plant operator, Tokyo Electric Power Co., has taken measures to stop the water from flowing out, such as putting up sandbags and concrete blocks around the shaft, the nuclear regulatory body said.
Among the trenches connected to the Nos. 1-3 reactor buildings, water in the gutter linked to the No. 1 unit is just 10 centimeters below its ground-level hole.
TEPCO said water in the trenches is believed to have come both from the reactor's buildings and tsunami waves, which followed a magnitude 9.0 earthquake that hit northeastern and eastern Japan, including Fukushima Prefecture, on March 11.
Recent readings of radiation have led the utility to suspect the contaminated water originated from the core of the No. 2 reactor, where fuel rods have partially melted, as levels of radiation were very high in a trench and the building housing the generation turbine both near the reactor.
High levels of radiation exceeding 1,000 millisieverts per hour were detected Sunday in water in the trench outside the No. 2 reactor's building.
At a radiation level of 1,000 millisieverts per hour, people could suffer a drop in the count of lymphocytes -- a type of white blood cell -- in just 30 minutes, and half could die within 30 days if they remained in such a condition for four hours.
In the basement of the No. 2 reactor's turbine building, water containing radioactive substances 100,000 times higher than usual for water in a reactor core has been building up.
The nuclear agency said it has ordered TEPCO to strengthen monitoring of the trench water.
On Tuesday, TEPCO continued to pump out radiation-emitting water that has been soaking the basement of the turbine building near the No. 1 reactor to a tank. But such work has yet to start at the Nos. 2-3 reactors' turbine buildings due to difficulties in securing enough space at tanks to move similarly contaminated water.
Hidehiko Nishiyama, a spokesman for the agency, said the temperature of the No. 1 reactor's vessel has been rising to more than 320 C, prompting TEPCO to increase the amount of freshwater injected into the reactor to cool it down.
On Tuesday, workers restored lighting in a control room for the No. 4 unit, the last of the six reactor control rooms to have lighting restored, according to the nuclear agency.
Chief Cabinet Secretary Yukio Edano admitted the difficulties in balancing the two tasks -- the coolant water injection and the removal of leaked radioactive water. The radioactive water leak may be linked to operations to pour massive amounts of water to prevent reactors and spent nuclear fuel pools from overheating.
''We cannot help but put priority on work to stop the nuclear reactors from boiling dry,'' the top government spokesman said. Serious damage to fuel rods from overheating would lead to the emission of enormous amounts of radioactive materials into the air.
Edano also deplored the detection of plutonium in the soil of the Fukushima plant, which was unveiled by TEPCO on Monday, saying the situation is ''very serious'' and suggests ''a certain degree of melting of fuel rods.''
TEPCO has said the confirmed amount of plutonium in the soil does not pose a major risk to human health.
Sakae Muto, vice president of the utility company, said it is ''not easy to examine how far it (the plutonium) has reached.'' Plutonium is more toxic than other radioactive substances such as iodine and cesium and would increase the risk of cancer if absorbed by human bodies.
Prime Minister Naoto Kan, meanwhile, told a parliament session Tuesday that it is ''highly likely'' that the six-reactor Fukushima plant will eventually be decommissioned.
The agency also said high concentrations of radioactive materials such as iodine were detected in seawater near the plant over the weekend, but the concentration has since decreased.