A Japanese official says fuel rods at a troubled nuclear reactor were temporarily exposed.

The exposure happened at Unit 2 of the Fukushima Dai-ichi plant _ the latest reactor to lose its ability to cool down. The other two reactors at the plant are facing a meltdown and authorities are racing to cool them with sea water.

Fukushima government spokesman Masato Abe said Monday that Unit 2's rods were briefly exposed. Sea water is being channeled into the reactor to cover the rods again.

Abe could not confirm if the rods were ever totally exposed.

Their exposure raises the risk of the reactor overheating, which can lead to meltdown.