Japan: Fukushima Nuclear Accident Update Log, Updates of 11 April 2011

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IAEA Briefing on Fukushima Nuclear Accident (11 April 2011, 13:00 UTC)


On Monday, 11 April 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:

  1. Current Situation

Earthquake of 7 April

External power has been restored at all sites affected by the 7 April earthquake.

Earthquake of 11 April

The IAEA confirms that an earthquake occurred in Japan at 08:16 UTC, 11 April. The IAEA International Seismic Safety Centre (ISSC) has rated it as a 6.6 magnitude, revised from an initial 7.1 magnitude. The epicenter of the earthquake is 68 km from Daichi, 60 km from Daini, 61 km from Tokai, 173 km from Kashiwazaki-Kariwa and 179 km from Onagawa power plants. The epicenter was in land (37.01 N/ 140.48 E) at a depth of 13.1 km. The IAEA has been in contact with NISA and can confirm the following. Based on a report by TEPCO, NISA confirms at the Fukushima Daiichi nuclear power plant. No changes have been observed on the readings at the on-site radiation monitoring posts. Workers have been evacuated to the seismic evacuation shelter. Off-site power was lost and water injection pumps for Units 1, 2 and 3 stopped. NISA confirmed later that off-site power was restored and water injection resumed 50 minutes after the earthquake.

Changes to Fukushima Daiichi Plant Status

Overall, the situation at the Fukushima Daiichi plant remains very serious but there are early signs of recovery in some functions such as electrical power and instrumentation.

In Units 1, 2 and 3, 60 000 T of contaminated water need to be removed from the turbine buildings and trenches. This water will be transferred to the condensers of each unit and the Radioactive Waste Treatment facility. In addition, temporary storage tanks have been ordered to provide additional capacity for the water and will be located adjacent to the Radioactive Waste Treatment facility. At Unit 1 and 2 water transfer from the condenser to the condensate storage tank was completed on 10 April.

In order to make room for higher contaminated water from the turbine buildings and trenches, 1 343 T of low level contaminated water from Units 5 and 6 sub-drain pit were released to the sea from 4 to 9 April. In addition, 9 070 T of low-level contaminated water was discharged from the Central Radioactive Waste Disposal Facility to the south discharge point.

Nitrogen gas is being injected into the Unit 1 containment vessel to reduce the possibility of hydrogen combustion within the containment vessel. The pressure in this containment vessel is increasing due to the addition of nitrogen.

Since 6 April, TEPCO has been moving debris from Units 1 to 4 to a common storage area on-site using remote controlled heavy equipment.

On 10 April additional anti-scattering agent was sprayed in an area of about 550 m2 on the mountain-side of the Common Spent Fuel Pool to prevent the radioactive materials on the ground from being scattered.

In Unit 1 fresh water is being continuously injected into the RPV through the feed-water line at an indicated flow rate of 6 m3/h using a temporary electric pump with off-site power. In Units 2 and 3 fresh water is being continuously injected through the fire extinguisher lines at an indicated rate of 7 m3/h using temporary electric pumps with off-site power.

In Unit 1 the pressure in the RPV is increasing, as indicated on both channels of instrumentation. In Units 2 and 3 Reactor Pressure Vessel and Drywell pressures remain at atmospheric pressure.

RPV temperatures remain above cold shutdown conditions in all Units, (typically less than 95 °C). In Unit 1 temperature at the feed water nozzle of the RPV is 228 °C and at the bottom of the RPV is 121 °C. In Unit 2 the temperature at the feed water nozzle of the RPV is 149 °C. The temperature at the bottom of the RPV was not reported. In Unit 3 the temperature at the feed water nozzle of the RPV is 92 °C and at the bottom of the RPV is 111 °C.

An additional 60 T of fresh water was injected via the Spent Fuel Cooling System line to the spent fuel pool in Unit 2 by a temporary pump on 10 April.

There has been no change in status in Units 4, 5 and 6.