this. Ammonia and hydrazine were also added to the water to help with the removal of radioactive iodine-131. An investigation by the Hungarian Atomic Energy Agency concluded that the cause of the incident was inadequate cooling of the fuel elements, which were heated due to the radioactive decay of short-lived fission products. These were kept cool by water circulated by a submerged water pump. However the cooling was inadequate, leading to the damage to some elements through a build-up of steam around them, depriving them of most of their cooling. The investigation proposed that the severe damage probably occurred when the lid was released, causing thermal shock to cladding because of the sudden entry of cool water into the system, and explosive steam production. One of the interesting results of the investigation was that the Hungarian Atomic Agency had placed too much trust in the technology and knowledge of the French Framatome Company. The agency did not investigate documentation provided by the company deeply enough, missing a fatal design flaw in the Framatome-designed, produced, and operated cleaning equipment. The discharge of radioactive gases through the stack continued for several days after the incident, although the Hungarian Atomic Energy Agency determined that the radiation levels adjacent to the plant were only about 10% above normal. However, the reactor remained out of service for over a year, finally resuming commercial electricity production in September 2004. The damaged fuel was completely removed by the end of 2006 and in 2014 transported to Russia for final disposal. 2005 incident (INES 1) On 9 April 2005, Unit 1 was shut down for planned maintenance. The defect that occurred during the cooling of the block was classified as INES grade 1 (abnormality), although the power plant originally requested a zero rating. 2009 outage incident (INES 2) A Self Powered Neutron Detector (SPND) was dropped when the wire rope holding it broke during an outage on 4 May 2009. The event was rated as INES 2. All staff were safely evacuated, and no member was exposed to more than the permitted daily radiation dose. 2012 incident (INES 1) On 6 September 2012, scheduled work was done on a gate, but the required written instructions were not completed in time. This is an administrative mismatch was classified as 1 in the International Nuclear Event Scale (INES). Incidents below the International Nuclear Event Scale (INES) Malfunctions (operational events) below