another campaign to contain the spread of contaminated sediments in the sea near the power plant, this time coating 180,000 square meters of sea floor with cement. 20 December TEPCO reports that all spent fuel rods have now been safely removed from the storage pool at reactor 4. 2015 10 January TEPCO begins operation of a new reverse-osmosis system to remove strontium from contaminated water. The new system was built to treat 500 to 900 cubic metres of water per day, and reduce the strontium levels in the water by a factor of 100 to 1000. 10 April A robot designed to withstand intense heat and radiation is sent into Reactor 1 to locate the melted fuel. It covers 14 of 18 locations before it stops functioning and has to be abandoned. 5 September The evacuation order is lifted for Naraha Town in Fukushima Prefecture. 10 September The Sendai-1 nuclear reactor resumes commercial operation for the first time since the earthquake in May 2011. This ends almost 2 years with no Japan nuclear power plants in commercial operation since Ohi-1 was halted on 15 September 2013. 26 October After a -year construction project, TEPCO completes a 780 m seaside shielding wall to reduce the amount of contaminated water leaking into the sea. 2016 16 February TEPCO estimates that 749,000 cubic metres of contaminated debris from Fukushima Daiichi will be produced by the year 2027, and releases a plan for incineration and storage of this waste. 2017 3 February TEPCO said the radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant was 530 sieverts per hour, the highest recorded level since the triple core meltdown in March 2011. This is however the first measurement of the radiation level within the reactor area and as such is likely lower than in the initial period after the meltdown. TEPCO also announced that there is a 2-meter hole in a metal grating under the pressure vessel in the reactor's primary containment vessel. 20 June A recent investigation by TEPCO using temperature measurements has determined the probable location of the cores for reactors 1–3. They believe that most of the core debris has breached the pressure vessel and lays at the bottom of the containment vessel for reactors 1 and 3, although some debris seems to be lodged in the control rod drive mechanism for reactor 1.