After weeks on standby, robots have been called from the sidelines to help inspect reactor buildings at Japan's damaged Fukushima Daiichi nuclear power plant. Tokyo Electric Power Company sent a remote-control robot into the No. 1 and No. 3 nuclear reactor buildings on Sunday and then into the No. 2 reactor the following day. The move comes about one month after the robots arrived in Japan. Their implementation has been delayed by excessive radiation and heat that threatened to prevent the bots from working properly once deployed.

TEPCo decided to take a chance earlier this week, sending a Packbot made by iRobot Corp. in Bedford, Mass., to measure radiation, oxygen and temperature inside the reactors. The Packbot, designed primarily for explosive ordinance disposal, is not radiation hardened but was outfitted with a HazMat sensing kit that can detect gamma radiation, organic compounds and dangerous chemicals. "We'll learn more about the effects of radiation on the robots as time and operations continue, but so far they seem to be working well inside the reactors," says an iRobot spokesman.

Each 10.9-kilogram Packbot rolls along on tracks and is equipped with a three-link arm that can lift up to about 13.6 kilograms, move debris and potentially relocate hazardous materials. In addition to being able to negotiate stairs, the Packbot can travel at up to 9.3 kilometers per hour and climb grades as steep as 60 degrees.

The Packbot ran into trouble in the No. 2 reactor building when its camera fogged up, the result of humidity resulting from cooling water poured on the reactor's fuel rods, The Wall Street Journal reports. Data collected by the robots in the No. 1 and No. 3 reactor buildings indicated that the radiation levels are elevated but not too high for workers to stay for a limited period of time, according to the Journal. This contrasts with a report Monday by the Associated Press that "radiation levels are far too high for repair crews to go inside."

The situation at the Daiichi site remains very serious but there are early signs of recovery in some functions, such as electrical power and instrumentation, according to the International Atomic Energy Agency. TEPCo announced Sunday that it hopes to achieve a "cold shutdown" of the plant within six to nine months. This term describes a condition in which the water cooling the nuclear fuel rods dips below 100 degrees Celsius and the reactors are considered stable.

Image of Packbot courtesy of iRobot