press release, TEPCO reports that levels of caesium-134, caesium-136, caesium-137, and iodine-131 (half-life of ~ 8 days), had spiked since last sampled on 2 March 2011, when these four nuclides were below detection limits. TEPCO's report gives the newly measured concentration (Bq/cm3) of each nuclide as of sampling date, 8 May. Thursday, 12 May TEPCO engineers confirm that a meltdown occurred, with molten fuel having fallen to the bottom of the reactor's containment vessel. The utility says fuel rods of the No. 1 reactor are fully exposed with the water level 1 meter (3.3 feet) below the base of the fuel assembly. The government and TEPCO are described as "consistently appeared to be underestimating the severity of the situation." According to a Japanese press report, there are holes in the base of the pressure vessel, and most of the fuel has likely melted. The nuclear fuel has possibly leaked into the containment vessel, which was damaged by an explosion during the crisis. However, the Nuclear Energy Institute, a nuclear lobbying firm, states that the situation "is in no way alarming. It was anticipated that there was fuel damage in reactors 1, 2 and 3. This is confirmation." Saturday, 14 May A third TEPCO (contractor) employee dies, after falling ill at 06:50, being brought to the plant's medical room unconscious. The likely cause of death is a heart attack. TEPCO says he was exposed to 0.17 millisieverts of radiation on Saturday. Sunday, 15 May A robot sent to the first floor of unit 1 records a radiation level of 2,000 mSv/h. At this level, workers would only be allowed to stay in the area for 8 minutes. In addition, the reactor's containment vessel is leaking large amounts of water into the basement. A TEPCO worker is able to peer into the basement and determines that the 11 m deep basement is approximately half full of water. TEPCO releases a report on the core status of reactor 1, revealing that fuel elements had become exposed above the water just 4 hours after the earthquake and SCRAM, and had fully melted after 16 hours. Wednesday, 18 May Four workers in protective suits and SCBA enter unit 2 for the first time since the 15 March explosion, to check on radiation levels and other conditions inside the building. The workers receive a dose of between 3 and 4 mSv each. Friday, 20 May TEPCO