The makeshift system makes it difficult to contain the radiation leaks, but it is aimed a preventing fuel rods from going into a full meltdown that would release even more radiactivity into the environment.
"We must keep putting water into the reactors to cool to prevent further fuel damage, even though we know that there is a side effect, which is the leakage," Nishiyama said. "We want to get rid of the stagnant water and decontaminate the place so that we can return to our primary task to restore the sustainable cooling capacity as quickly as possible."
To that end, the plant's operator, Tokyo Electric Power Co., said Monday it planned to jettison into the sea about 10,000 tons of water with radiation levels above the legal limit. The move will clear space in a waste storage building to put even more highly contaminated water, TEPCO spokesman Junichi Matsumoto said.
The government decided to allow the step as "an unavoidable emergency measure," Chief Cabinet Secretary Yukio Edano said.
An additional 1,500 tons will be dumped from a trench under the plant's units 5 and 6. That water is threatening to interfere with the workings at those units, whose reactors are under control.
Radioactivity is quickly diluted in the ocean, and Edano said the dump should not affect the safety of seafood in the area.
The crisis has unfolded as Japan deals with the aftermath of twin natural disasters that decimated large swaths of its northeastern coast. Up to 25,000 people are believed to have died in the disaster, and tens of thousands lost their homes. Thousands more were forced to flee a 12-mile (20-kilometer) radius around the plant because of the radiation.
Over the weekend, an 8-inch-long (20-centimeter-long) crack was discovered in a maintenance pit, sending a stream of water into the sea. The area is normally blocked off by a seawall, but a crack was also discovered in that outer barrier Monday.