Budapest  - In a mishap during maintenance work, a device that measured neutron flow fell into the Block 4 reactor at the nuclear power plant in Paks, but no radioactivity was released, plant administrators said Tuesday.

The accident happened on Monday, when the winch cable broke that was to have hauled it out of the reactor interior.

There were no injuries to workers, plant officials said.

Hungarian nuclear energy officials rated the accident at level 2 on the 0-7 International Nuclear and Radiological Event Scale (INES) scale. Seven is the most serious accident.

The plant has had at least three previous incidents. In 2003, radioactive gas was released from damaged fuel rods in a level-3 "serious incident."

In 2006 and July 2008, there were level-1 incidents connected to maintenance mishaps.

The plant is 100 kilometres south of Budapest. (dpa)