The Tokyo Electric Power Company (TEPCO) has plugged the outflow of radioactive water from the Fukushima nuclear power plant into the sea using sodium silicate.
Tepco injected sodium silicate into the ground near a seaside pit from where the radiation seepage occurred, reports the Financial Times.
Tepco has pumped 6,000l of the chemical, which is more often used as a wood preservative and an adhesive in car engines, and a hardening agent into the ground near the pit.
However, contamination may continue as water from other smaller leaks continues to reach the sea, according to the firm.
Seawater samples taken immediately outside the plant on 5 April 2011 measured radioactive iodine-131 at 7.5m times the legal limit.