Water containing high amounts of radioactive iodine has been spewing directly into the Pacific Ocean from a large crack discovered Saturday in a 6-foot-deep pit at the coastal Fukushima Daiichi Nuclear Power Plant. After an unsuccessful attempt to flood the pit with concrete to stop the leak, workers on Sunday turned to trying to plug the apparent source of the water — an underground shaft thought to lead to the damaged reactor building — by plugging the shaft with a makeshift putty: more than 120 pounds of sawdust, three garbage bags full of shredded newspaper and about 9 pounds of a polymeric powder that officials said absorbs 50 times its volume of water.

Although the stopgap measure did not appear to be succeeding, workers would keep trying to stem the leak, said Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency.

Experts estimate that about 7 tons an hour of radioactive water is escaping the pit. Safety officials have said that the water, which appears to be coming from the damaged No. 2 reactor at Fukushima Daiichi, contains one million Becquerels per liter of iodine 131, or about 10,000 times levels normally found in water at a nuclear facility.