On Saturday, 9 April 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:
1. Current Situation
Earthquake of 7 April
The IAEA confirms that an earthquake occurred in Japan at 14:32 UTC 7th April. The IAEA International Seismic Safety Centre has rated it as a 7.1 magnitude, revised from an initial 7.4 magnitude. The epicenter of the earthquake was 20 km from the Onagawa nuclear power plant and approximately 120 km from the Fukushima Daiichi and Daini nuclear power plants. With the recovery of external power at the Rokkasho Reprocessing Plant, all sites reported on yesterday have external power.
Changes to Fukushima Daiichi Plant Status
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.
Nitrogen gas is continuing to be 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 8 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 246 °C and at the bottom of the RPV is 119 °C. In Unit 2 the temperature at the feed water nozzle of the RPV is 141 °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 89 °C and at the bottom of the RPV is 110 °C.
The concrete pump vehicle continued to spray fresh water to the spent fuel pool in Unit 3 on 8 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 8th April, low levels of deposition of both iodine-131 and cesium-137 were detected in 10 and 7 prefectures respectively. The values reported for iodine-131 ranged from 1 to 46 becquerel per square metre, for cesium-137 from 5 to 42 becquerel per square metre.
Gamma dose rates are measured daily in all 47 prefectures and the values continue to decrease. For Fukushima, on 8th April a dose rate of 2.3 µSv/h, for the Ibaraki prefecture a gamma dose rate of 0.15 µSv/h were reported. The gamma dose rates reported for the other 45 prefectures were below 0.1µSv/h.
Since the end of March, MEXT has set up an additional monitoring programme in cooperation with local universities. Measurements are made in 26 cities in 13 prefectures. As of 8th April, in 17 cities, the gamma dose rates were below 0.1 µSv/h. In 8 other 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. Typical normal background levels are in the range 0.05 to 0.1 µSv/hr.
The IAEA Team in Fukushima made measurements on the 8th April at 8 different locations at distances of 24 to 42 km, in Northwesterly directions from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 1.6 to 56 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.2 to 5.0 Megabecquerel per square metre. The highest beta-gamma contaminations have been determined at distances of less than 30 km.
Since our written brief of yesterday, data related to food contamination has not been reported. However, on 8th April the Ministry of Health, Labour and Welfare reported that the Emergency Response headquarters had approved the lifting of restrictions on the distribution of unprocessed raw milk in certain locations in Fukushima prefecture (city of Kitakata and the towns of Aizumisato, Bandai, Inawashiro, Michima, Minamiaizu and Simogo) and on the distribution of spinach and kakina in Gunma prefecture.
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 the Map 1
Until 3rd April a general decreasing trend was observed at the sampling points TEPCO 1 to TEPCO 4. After the discharge of contaminated water on 4th April, a temporary increase has been reported.
On 6th April at the near-shore sampling points TEPCO 1, TEPCO 3 and TEPCO 4 a decrease in the concentration of I-131 and Cs-137 have been reported. However, at the sampling point TEPCO 2 an increase in the concentration of I-131 (from about 20 kBq/l on 5th April to about 40 kBq/l) and Cs-137 (from about 15 kBq/l on 5th April to about 25 kBq/l) was observed.
For the six sampling points TEPCO 5 to TEPCO 10 on 6th April levels of I-131 below 0.4 kBq/l and Cs-137 below 0.2 kBq/l were measured.
MEXT Off-shore Monitoring Programme
As reported in the brief of 8th April, MEXT initiated the off-shore monitoring program on 23rd March and subsequently points 9 and 10 were added to the off-shore sampling scheme. On 4th April, MEXT added two further sampling points to the north and west of sampling point 1. These are referred to as points A and B on the map below.
0n 9 April new data have been reported for samples taken on the 5th April. These data were for the sampling points MEXT3 and MEXT5. At MEXT3 there was an increase from about 3 Bq/l on 1st April to about 10 Bq/l on 5th April for I-131. At MEXT5 there was an increase from about 12 Bq/l on 1st April to about 65 Bq/l for I-131and from about 15 Bq/l to about 40 Bq/l for Cs-137 on 5th April.
No new data for the other sampling points have been reported.
3. IAEA Activities
A team of three agency experts in BWR technology continue to meet with TEPCO and NISA officials in Tokyo.