TOKYO — Conditions at a crippled nuclear power plant deteriorated further Tuesday, with a Japanese nuclear safety official saying that the water inside the waste fuel storage pool for a damaged reactor may be boiling.
Hidehiko Nishiyama told reporters that "we cannot deny the possibility of water boiling" in the spent fuel storage pool at the facility.
If the water boils, it could evaporate, exposing the rods. The fuel rods are encased in safety containers meant to prevent them from resuming nuclear reactions, nuclear officials said, downplaying the risk of that happening.
But they acknowledged that there could have been damage to the containers. They also confirmed the walls of the storage pool building were damaged.
A fire, explosions and other damage to the Fukushima Daiichi power plant following a massive earthquake and tsunami on Friday have triggered Japan's worst nuclear crisis since the atomic bombings of Hiroshima and Nagasaki in 1945.
Nishiyama, an official in the economy ministry, which oversees nuclear safety, avoided commenting on the potential risks from rising temperatures caused by a failure in the systems that keep the spent fuel rods cool. He said the plant's operator is considering what to do about the problem.
The Unit 4 reactor at the Fukushima Daiichi power plant caught fire earlier Tuesday and is believed to have caused a release of dangerous levels of radioactivity in the immediate area. Elevated radioactivity readings in surrounding regions were not high enough to pose a health threat, the government said.
Unit 4 was not operating at the time of the tsunami, but its backup power systems failed afterward, preventing cooling systems from working properly. Three reactors already have been wrecked by explosions and nuclear officials confirmed that temperatures in two other reactors that had been shut down for inspections were also rising.
The temperature of the water in the spent fuel storage pool for Unit 4 was 183 degrees Fahrenheit on Monday, when it was last measured. No measurements have been available since then, Nishiyama said.
"We have no information about whether the spent fuel rods are exposed," he said.