Tokyo --

A heavily damaged reactor building at the tsunami-stricken Fukushima Dai-ichi nuclear plant has a slight tilt, but the tilt does not pose a risk to the integrity of the building, according to the plant's operator.

The Tokyo Electric Power Co., or Tepco, said in a report Monday to Japanese nuclear regulators that at least two of the walls of the No. 4 reactor building are bulging outward at various points and that the building is tilting. The biggest bulge measured about 1.8 inches about a third of the way up the building, the report said.

The latest findings could add to concerns over the state of the No. 4 reactor building, which houses on its upper floors a cooling pool filled with more than 1,000 spent nuclear fuel rods. Some experts say that the building - ravaged in a hydrogen explosion in the early days of the disaster in March 2011 - is not strong enough to support the fuel pool, especially if another earthquake hits the region.

Damage to the pool or loss of cooling could lead the spent fuel to overheat, releasing large amounts of radiation into the environment, the experts warn. Tepco has said it will start work to remove the spent fuel rods later this year, earlier than initially planned. However, other experts warn against removing fuel rods too hastily, which might pose its own risks.