Following is an update released by UN atomic watchdog International Atomic Energy Agency (IAEA) on the Japan's Fukushima Daiichi nuclear power plant.
Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious but there are early signs of recovery in some functions, such as electrical power and instrumentation.
Changes to Fukushima Daiichi Plant Status
The transfer of contaminated water from the trench of the Unit 2 Turbine Building to the condenser started on 12th April and continued on 13th April until approximately 660 tonnes were transferred.
To minimize the movement of contaminated water to the open sea, temporary boards to stop water (3 steel plates in total) were installed on 13th April on the ocean-side of the Inlet Bar Screen of Unit 2.
Silt fences have also been installed in the inlet canal and in front of the Inlet Bar Screens of Units 1, 2, 3 and 4. On 11th April, a silt screen was installed at the southern end of the inlet canal. The installation in front of the Inlet Bar Screen of Units 3 and 4 was completed on 13th April and for Units 1 and 2 on 14th April.
As of 14th April, white smoke was still observed coming from Units 2 and 3. White smoke was also observed coming from Unit 4 on the 14th April.
On 13th April, Japan's Nuclear and Industrial Safety Agency (NISA) reported that the Tokyo Electric Power Co. (TEPCO) had begun to install a backup line for providing fresh water to the Reactor Pressure Vessels (RPVs) at Units 1, 2, and 3.
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.
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 has stabilised. The pressure in the RPV is increasing as indicated on one channel of instrumentation. The other channel shows RPV pressure as stable. 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 95oC). In Unit 1, the temperature at the feed water nozzle of the RPV is 197oC and at the bottom of the RPV is 119oC. In Unit 2, the temperature at the feed water nozzle of the RPV is 150oC. In Unit 3 the temperature at the feed water nozzle of the RPV is 91oC and at the bottom of the RPV is 121oC.
On 14th April, a concrete pump truck, with a capacity of 50t/h, began spraying fresh water to the Unit 3 spent fuel pool. In Unit 4, a sample of the water in the spent fuel pool was collected for analysis.
There has been no change in status in Unit 5 and 6 and the Common Spent Fuel Storage Facility.
On 14th April, depositions of both Iodine-131 and Cesium-137 were detected in 1 and 5 prefectures respectively. For both I-131 and Cs-137, the depositions detected were below 20 Bq/m2 at all stations.
Gamma dose rates are measured daily in all 47 prefectures. The values have tended to decrease over time. For Fukushima, on 14th April a dose rate of 2.0 µSv/h was reported. In the Ibaraki prefecture, a gamma dose rate of 0.14 µSv/h was reported. The gamma dose rates in all other prefectures were below 0.1 µSv/h.
Dose rates are also reported specifically for the Eastern part of the Fukushima prefecture, for distances beyond 30 km from Fukushima Daiichi. On 14th April, the values in this area ranged from 0.1 to 21 µSv/h.
In cooperation with local universities, Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT)has set up an additional monitoring programme and measurements of the gamma dose rates are made in 54 cities in 40 prefectures. As of 14th April, the gamma dose rates were below 0.1 µSv/h in 45 cities. In 8 cities, gamma dose rates ranged from 0.13 to 0.17 µSv/h. In Fukushima City, a value of 0.42 µSv/h was observed.
Only in a few prefectures, I-131 or Cs-137 is detectable in drinking water at very low levels. As of 12th April, one restriction for infants related to I-131 (100 Bq/l) is in place in a smallscale water supply in a village of the Fukushima prefecture.
On 14th April, an IAEA Team made measurements at 11 different locations in the Fukushima area at distances ranging from 15 to 39 km, South and Southwest from the Fukushima Daiichi nuclear power plant. At these locations, the dose rates ranged from 0.3 to 2.8 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.16 to 2.5 MBq/ m2. The highest values were observed at distances of less than 23 km from the power plant.
NISA reported on 14th April that among approximately 300 workers at the Fukushima Daiichi plant, 28 have received accumulated doses exceeding 100 mSv in the period related to this emergency. No worker has received a dose above Japan's guidance value of 250 mSv for restricting the exposure of emergency workers.
Analytical results related to food contamination were reported by the Japanese Ministry of Health, Labour and Welfare on 14th April for a total of 50 samples taken from 11th - 14th April.
Analytical results for all of the samples of various vegetables, mushrooms, fruits (strawberry), various meats, seafood and unprocessed raw milk in ten prefectures (Chiba, Fukushima, Gunma, Ibaraki, Kanagawa, Nagano, Niigata, Saitama, Tochigi and Yamagata) indicated that I-131, Cs-134 and/or Cs-137 were either not detected or were below the regulation values set by the Japanese authorities.
On 14th April, the Prime Minister of Japan approved the lifting of restrictions on the distribution of kakina in Tochigi prefecture.
TEPCO is conducting a programme for seawater (surface sampling) at a number of near-shore and off-shore monitoring locations.
On some days, two samples were collected at the same sampling point, a few hours apart and analysed separately.
Until 3rd April a general decreasing trend in radioactivity was observed at the sampling points TEPCO to TEPCO. After the discharge of contaminated water on 4th April, a temporary increase in radioactivity was reported. Since 5th April, a general downward trend in the concentration of radionuclides in sea water for all TEPCO sampling points has been observed.
On 15th April, new data for TEPCO1-4 sampling points have been reported. At all four locations, the concentration of both I-131 and Cs-137 measured on the 12th April was below 2kBq/l.
For TEPCO 5-10 no new data have been reported.