A hydrogen gas explosion at the No.4 reactor of the Fukushima No. 1 nuclear power plant on March 15 may have helped prevent spent fuel rods from melting down by causing a flow of water into the pool the rods are stored in, according to research by by Tokyo Electric Power Co. It seems that shocks from the explosion damaged a water gate and caused water to flow into the pool from a neighboring part of the facility, TEPCO said. The explosion, which the company assumes was caused by hydrogen gas, was so strong that the outer walls of the reactor building collapsed. At the time of the explosion, the spent fuel rods had been overheating. If that had continued, the company said, the rods might have melted, spewing a far larger quantity of radioactive materials into the air than what actually happened. The nuclear power plant lost its external electricity supply when it was hit by a tsunami following the March 11 earthquake. As a result, injection of coolant water into the pool of the No. 4 reactor also stopped. Currently, TEPCO is injecting water into the pool with a pump originally meant to pour fresh concrete. Although about 70 tons of water is assumed to be evaporating every day from the pool, company officials said even considering evaporation, the water level is not rising as much as expected.