Fukushima Nuclear Accident Update Log
Updates of 18 April 2011
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- 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 Monday, 18 April 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:
1. Current Situation
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.
On 17 April, the Ministry of Economy, Trade and Industry (METI) announced that TEPCO had issued a "Roadmap towards Restoration from the Accident at the Fukushima Daiichi Nuclear Power Station." The roadmap outlines 63 measures to be taken in two steps over a period of six to nine months. TEPCO declared they will "make every effort to enable evacuees to return to their homes and for all citizens to be able to secure a sound life."
Changes to Fukushima Daiichi Nuclear Power Plant Status
The IAEA receives information updates from a variety of official Japanese sources, through the national competent authorities: the Nuclear and Industrial Safety Agency (NISA) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT).
Based on the information received by 18 April 2011, 02:00 UTC the following update related to the reactor units at the Fukushima Daiichi Nuclear Power Plant and related environmental conditions is provided.
As a countermeasure against a possible tsunami, the distribution boards for the pumps injecting water to the reactor pressure vessels of Units 1, 2 and 3 were transferred to higher ground on 15 April. In order to minimize the liberation of radioactive material into the ocean, two sandbags filled with Zeolite were placed between the Inlet Screen Pump Room of Unit 1 and Unit 2. Further, five sandbags filled with Zeolite were placed between the Inlet Screen Pump Room of Unit 2 and Unit 3 on 17 April. The Zeolite material is designed to capture specific radioactive elements. It is intended to sample and analyze the Zeolite material periodically to determine the effectiveness of this procedure.
The removal of debris (amount equivalent to 8 containers) using remote-control heavy machinery continued on 16 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 has stabilised. The pressure in the RPV is stable.
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.
RPV temperatures remain above cold shutdown conditions in all Units, (typically less than 95 °C). In Unit 1 the temperature at the feed water nozzle of the RPV is 180 °C and at the bottom of the RPV is 117 °C. In Unit 2, the temperature at the feed water nozzle of the RPV is 141 °C. In Unit 3 the temperature at the feed water nozzle of the RPV is 91 °C and at the bottom of the RPV is 122 °C.
In accordance with the report of the Nuclear Emergency Response HQs (Prime Minister's Office) from 15 April, thermography temperatures of the Containment Vessel and Spent Fuel Pool in Unit 1 were 33 & deg;C and 36 °C respectively. In Unit 3 the temperatures were 68 °C and 59 °C at the same positions. Also on 15 April, thermography temperature of the Unit 2 reactor building roof was 31 °C
As of 16 April, no white "smoke" was seen to be coming from Unit 1 although white "smoke" was still observed coming from Units 2 and 3. As of 16 April white "smoke" was also visible in Unit 4.
Fresh water injection (around 45 tonnes) to the spent fuel pool was carried out via the spent fuel pool cooling line of Unit 2 and completed by 16 April. Due to the occurrence of an earthquake on 16 April, the motor-driven pump was stopped. The spent fuel pool was confirmed to be filled with water.
In accordance with NISA Release 94, TEPCO took water samples from the spent fuel pool of Unit 4 on 12 April, in order to examine the conditions. The sample was taken by using the arm of the concrete pump vehicle. At the same time, the temperature of water in the spent fuel pool of Unit 4 was measured with a thermistor attached to the arm of the concrete pump vehicle. The activities for I-131, Cs-134 and Cs-137 were 220 Bq/cm3, 88 Bq/cm3 and 93 Bq/cm3 respectively.
There has been no change in the status in Units 5 and 6.
The power supply to the Common Spent Fuel Pool was temporarily interrupted due to a short-circuit on 17 April.
2. Radiation Monitoring
From 15 to 17 April, I-131 was detected in only one prefecture on 15 April; with a reported value of 4.1 Bq/m2. During this period, deposition of Cs-137 was detected in 8 prefectures. The total deposition of Cs-137 in these prefectures on these 3 days ranged from 2.3 Bq/m2 to 66 Bq/m2.
Gamma dose rates are measured daily in all 47 prefectures. The values tend to decrease over time. For Fukushima, on 18 April a dose rate of 1.9 µSv/h was reported. In the Ibaraki prefecture, a gamma dose rate of 0.13 µSv/h was reported; in all other prefectures, reported gamma dose rates 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 16 April, the values in this area ranged from 0.1 to 25 µSv/h.
In cooperation with local universities, MEXT has set up an additional monitoring programme, for 17 April, measurements of the gamma dose rates were reported for 53 cities in 40 prefectures. In 43 cities, the gamma dose rates were below 0.1 µSv/h. In 9 cities, gamma dose rates ranged from 0.12 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 16 April, one restriction for infants related to I-131 (100 Bq/l) is in place in a small scale water supply in a village of the Fukushima prefecture.
On 15 and 16 April, the IAEA Team made measurements at 44 different locations in the Fukushima area at distances ranging from 20 to 58 km, West from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.6 to 37 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 2.8 Megabecquerel/m2. The highest values were observed at distances of less than 30 km from the power plant.
On 17 April, the IAEA Team made measurements at 17 different locations in the Fukushima area at distances ranging from 20 to 62 km, North and Northwest from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.4 to 3.3 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 0.27 Megabecquerel/m2.
Analytical results related to food contamination were reported by the Japanese Ministry of Health, Labour and Welfare on 15 April (34 samples), 16 April (65 samples) and 17 April (51 samples). These reported analytical results covered a total of 150 samples taken from 13 to 16 April. Analytical results for 146 of the 150 samples for various vegetables, spinach and other leafy vegetables, shitake mushrooms, fruit (strawberries), seafood and unprocessed raw milk in nine prefectures (Chiba, Fukushima, Gunma, Hyogo, Ibaraki, Kanagawa, Niigata, Saitama 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. In Fukushima prefecture, three samples of shitake mushrooms taken on 14 April were above the regulation value set by the Japanese authorities for Cs-134 and Cs-137. One sample of shitake mushrooms taken on 14 April was above the regulation values set by the Japanese authorities for I-131 and/or Cs-134 and Cs-137.
On 16 April, the restriction on the distribution of raw unprocessed milk produced in Fukushima was lifted in 25 areas (Fukushima city, Nihonmatsu city, Date city, Motomiya city, Kunimi town, Otama village, Furudono city, Koriyama city, Sukagawa city, Tamura city (excluding former Toji village area), Miharu town, Ono town, Kagamiishi town, Ishikawa town, Asakawa town, Hirata village, Shirakawa city, Yabuki town, Izumisaki village, Nakajima village, Saigo village, Samekawa village, Hanawa town, Yamatsuri town and Iwaki city).
On 17 April, the restriction on the distribution of Kakina and parsley produced throughout Ibaraki prefecture was lifted. The restriction on the distribution of spinach from Ibaraki prefecture was also lifted with the exception of spinach produced in the cities of Kitaibaraki and Takahagi.
3. Marine Monitoring
TEPCO Monitoring Programme
TEPCO is conducting a programme for seawater (surface sampling) at a number of near-shore and off-shore monitoring locations. Following a directive from NISA, on 16 April TEPCO announced they will increase the number of sea sampling points from 10 to 16. A further four points will be added at 3 km from the coast and two points will be added at 8 km from the coast.
On some days, two samples were collected at the same sampling point, a few hours apart and analysed separately.
Until 3 April a general decreasing trend in radioactivity was observed at the sampling points TEPCO 1 to TEPCO 4. After the discharge of contaminated water on 4 April, a temporary increase in radioactivity has been reported. Again since 5 April, general downward in the concentration of radionuclides in sea water for all TEPCO sampling points has been observed.
On the 18 April no new data for TEPCO sampling points have been reported.
MEXT Off-shore Monitoring Programme
The Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) initiated the off-shore monitoring program on 23 March and subsequently points 9 and 10 were 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. (See Map 2: MEXT Seawater sampling Locations).
The last results reported on 18 April (sampling date 15 April) showed that Cs-137 and I-131 were detected at MEXT 4, 6 and 8. The highest concentrations were recorded at MEXT 4 (below 200Bq/l for Cs-137 and about 160 Bq/l for I-131). At MEXT 6 and 8 sampling locations both C-s-137 and I-131 were reported at levels below about 40 Bq/l.