Japan Update: As of 23:58, 6/April, TOKYO

The highly radioactive water is believed to have come from the No. 2 reactor core, where fuel rods have partially melted, and ended up in the pit. The pit is connected to the No. 2 reactor turbine building and an underground trench connected to the building, both of which were found to be filled with highly contaminated water.

To make room to store the highly radioactive water that is hampering the plant’s restoration work, TEPCO continued to dump into the sea massive amounts of low-level contaminated water from inside a nuclear waste disposal facility at the site as well as contaminated groundwater found from around the Nos. 5 and 6 unit buildings.

TEPCO is aiming to dispose of a total of about 10,000 tons of low-level contaminated water into the sea by this weekend, a move which has sparked concern among neighboring countries and strong protests from the domestic fishing industry.

After opening up the disposal facility, which can accommodate 30,000 tons of liquid, some repair work is expected to take place for about a week to ensure that the facility can retain highly radioactive water safely without fear of the stored liquid leaking outside.

The plant’s power grid and most of the emergency diesel generators were knocked out by the magnitude 9.0 earthquake and ensuing tsunami on March 11, resulting in the loss of many of the reactors’ key cooling functions, partial melting of reactor cores and hydrogen explosions.

According to estimates by TEPCO announced Wednesday, 25 percent of the nuclear fuel rods have been damaged at the No. 3 reactor. The company earlier said that 70 percent of the No. 1 reactor’s fuel rods and 30 percent of the No. 2 reactor’s fuel rods have been damaged.

Nishiyama said past hydrogen explosions have likely occurred due to hydrogen accumulation caused by the reaction of melted fuel rods’ zirconium with steam from the coolant water. But now there are concerns that hydrogen may accumulate in the No. 1 reactor under a different process involving radiation-induced decomposition of water into hydrogen and oxygen.

As radioactive substances may be released outside due to the injection of nitrogen through pipes connected to the reactor’s containment vessel, workers are expected to temporarily evacuate when TEPCO starts the process.

The utility has been pouring massive amounts of water into the reactors and their spent nuclear fuel pools as a stopgap measure to cool them down. But the measure is causing ”side effects,” such as the detection of contaminated water in various parts of the nuclear complex and some leakage into the sea.

A seawater sample taken near the No. 2 reactor water intake on Saturday showed a radioactive iodine-131 concentration of 7.5 million times the maximum level permitted under law, or about 300,000 becquerels per cubic centimeter.