Fukushima Nuclear Accident Update Log
Updates of 10 April 2011
- Story Resources
- In Focus: Fukushima Nuclear Accident
- Fukushima Nuclear Accident: Information Sheet
- Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency
- International Nuclear and Radiological Event Scale (INES)
- IAEA Incident and Emergency Centre (IEC)
- International Seismic Safety Centre (ISSC)
- Response Assistance Network (RANET)
- Japan Nuclear and Industrial Safety Agency (NISA)
→ Summary of Reactor Status
On Sunday, 10 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. The 3 litres of water that were spilled at Onagawa nuclear power plant have been cleaned up.
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 tons 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. In Unit 2 water transfer from the condenser to the condensate storage tank was completed on 9 April.
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.
In Unit 1 fresh water is being continuously injected into the reactor pressure vessel through 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 indicated rates of 7 m3/h and 7 m3/h respectively 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. NISA has indicated that some instruments in the reactor vessel may not be working properly. In Units 2 and 3 Reactor Pressure Vessel and Drywell pressures remain at atmospheric pressure.
RPV temperatures remain above cold shutdown conditions, typically less than 95 °C. In Unit 1 temperature at the feed water nozzle of the RPV is 235 °C and at the bottom of the RPV is 120 °C. In Unit 2 the temperature at the feed water nozzle of the RPV is 145 °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 97 °C and at the bottom of the RPV is 109 °C.
The concrete pump vehicle sprayed fresh water (90 T) to the spent fuel pool in Unit 4 on 9 April.
There has been no change in status in Units 4, 5 and 6 and the Common Spent Fuel Storage Facility.
2. Radiation Monitoring
On 9 April, deposition of both iodine-131 and cesium-137 was detected in 5 and 6 prefectures respectively. The values reported for iodine-131 ranged from 7.8 to 650 becquerel per square metre and for cesium-137 from 3.3 to 370 becquerel per square metre. The highest deposition was reported for both, iodine-131 and cesium-137, in the prefecture of Ibaraki.
Gamma dose rates are measured daily in all 47 prefectures, the values tend to decrease. Dose rates are also reported daily for the Eastern part of the Fukushima prefecture, these values are decreasing as well. As of 9 April, the gamma dose rates, reported for distances of more than 30 km to Fukushima-Daiichi, ranged from 0.2 to 26 μSv/h.
In an additional monitoring programme, set up by MEXT in cooperation with local universities, measurements are made in 27 cities in 14 prefectures. As of 9 April, in 19 cities, the gamma dose rates were below 0.1 μSv/h. In 7 cities, gamma dose rates range from 0.13 to 0.21 μSv/h. In Fukushima City, a value of 0.46 μSv/h was observed. Typical normal background levels are in the range of 0.05 to 0.10 μSv/hr.
As of 7 April, iodine-131 and cesium-137 was detectable in drinking water in a few prefectures at levels far below those that would trigger recommendations for restrictions of drinking water. As of 7 April, one restriction for infants related to I-131 (100 Bq/l) is in place as a precautionary measure in only one village of the Fukushima prefecture.
On 9 April, the IAEA Team made measurements at 8 different locations in the Fukushima area at distances of 32 to 62 km, North and North West from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.4 to 3.7 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 0.19 Megabecquerel per square metre.
3. Marine Monitoring
As reported in the brief of 8th April TEPCO is conducting a programme for seawater (surface sampling) at a number of near-shore and off-shore monitoring locations as illustrated in Map 1.
Map 1: TEPCO Seawater Sampling Locations:
Until 3 April a general decreasing trend was observed at the sampling points TEPCO 1 to TEPCO 4. After the discharge of contaminated water on 4 April, a temporary increase has been reported. On 10 April new data (7 April sampling day) for all TEPCO sampling points have been reported. At the near-shore sampling points TEPCO 1, TEPCO 3 and TEPCO 4 a further decrease with respect to the results for the sampling day 5 April, in the concentration of I-131 and Cs-137 have been reported. At the sampling point TEPCO 2 a further increase in the concentration of I-131 (from about 40 kBq/l on 6 April to about 150 kBq/l) and Cs-137 (from about 25 kBq/l on 6 April to about 65 kBq/l) was observed.
For the six sampling points TEPCO 5 to TEPCO 10 on April 7 the following has been reported: as TEPCO 5, TEPCO 6 and TEPCO 10 a further decrease of the levels of I-131 below 0.2 kBq/l and of Cs-137 below 0.1 kBq/l were measured.
At TEPCO 7 an increase of the level of I-131 has been recorded. At TEPCO 8 and TEPCO 9 an increase in the levels of both I-131 and Cs-137 has been measured. The reading at TEPCO 9 is from about 0.07 kBq/l (6 April) to about 0.37 kBq/l for I-131 and from about 0.05 kBq/l to about 0.21 kBq/l for Cs-137.
MEXT Off-shore Monitoring Programme
As reported in the brief of 8 April MEXT initiated the off-shore monitoring program on 23 March and subsequently points 9 and 10 added to the off-shore sampling scheme. On 4 April, MEXT added two sampling points to the north and west of sampling point 1. These are referred to as points A and B on the map below.
Map 2: MEXT Seawater Sampling Locations:
On 10 April new data have been reported (7 April sampling day) for the sampling points MEXT 6 and MEXT 10. At MEXT 6 sampling point an increase in I-131 (from about 18 Bq/l on 3 April to about 57Bq/l) and Cs-137 (from about 10Bq/l on 3 April to about 20 Bq/l) has been measured. At MEXT 10 the level of I-131 remains about 35 Bq/l as on 3 April; Cs-137 is no longer detectable.
No new data for the other sampling points have been reported at the date of 10 April.
4. IAEA Activities
The team of three Agency experts in BWR technology will conclude their mission on Monday with meetings with NISA, Ministry of Foreign Affairs (MOFA), MEXT, Atomic Energy Commission (AEC) and Nuclear Safety Commission (NSC).
In addition to those reported in previous briefs the following countries have submitted monitoring data and/or links to national websites where data is available: USA, Czech Republic and Latvia.