Fukushima Nuclear Accident Update Log

IAEA Briefing on Fukushima Nuclear Accident (2 June 2011, 18:30 UTC)

Presentations:
Summary of Reactor Status
Fukushima Radiological Monitoring and Consequences
Fukushima Marine Environment Monitoring
Watch Video

On Thursday, 2 June 2011, the IAEA provided the following information on the status of nuclear safety in Japan:

Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious.

The IAEA receives information from various official sources in Japan through the Japanese national competent authority, the Nuclear and Industrial Safety Agency (NISA). This Update Brief is based on information issued by the IAEA Incident and Emergency Centre up to 16:00 UTC on 31 May 2011.

1. Fukushima Daiichi Nuclear Power Plant Status

Tables 1 - 4 track progress for Units 1 - 4 towards fulfilling the three basic safety functions of the IAEA safety standards: prevention of criticality, removal of decay heat and mitigation of radioactive releases. The tables replace the three-colour table that was used previously. The charts are cross-referenced to the Tokyo Electric Power Company (TEPCO) "Roadmap" plan to bring the nuclear reactors and the spent fuel pools at the Fukushima Daiichi plant to a stable cooling condition and to mitigate radioactive releases.

On 17 May 2011, TEPCO provided a status report against the TEPCO "Roadmap" showing progress since the Roadmap was issued on 17 April 2011. While the basic policy and targets defined in the Roadmap remain, several changes were made to account for new information obtained and progress made to date.

On 13 May TEPCO commenced the preparatory work for the installation of a cover for the reactor building of Unit 1. The reactor building cover will be installed as an emergency measure to prevent the dispersion of radioactive substances until mid- to long term measures, including radiation shielding, are implemented.

TEPCO has reported that information obtained after calibration of the reactor water level gauges of Unit 1 shows that the actual water level in the Unit 1 reactor pressure vessel was lower than was indicated, showing that the fuel was completely uncovered. The results of provisional analysis show that fuel pellets melted and fell to the bottom of reactor pressure vessel at a relatively early stage in the accident.

TEPCO reported that "most part of the fuel is considered to be submerged in the bottom of reactor pressure vessel and some part exposed." TEPCO also reported that leakage of cooling water from the reactor pressure vessel is likely to have occurred. However, TEPCO considers that the actual damage to the reactor pressure vessel is limited, on the basis of the temperatures now being measured around the reactor pressure vessel.

The results of the analysis are provisional; TEPCO will continue to conduct investigations. Similar analyses will be conducted for Units 2 and 3 when radiation levels allow calibration of the instrumentation.

Nitrogen gas is still being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion inside the containment vessel.

In Units 1, 2 and 3 fresh water is being continuously injected both via the feed water system lines and the fire extinguishers lines into the reactor pressure vessel; temperatures and pressures remain stable.

To protect against potential damage as a result of future earthquakes, TEPCO started work on 9 May to install a supporting structure for the floor of the spent fuel pool of Unit 4. TEPCO has formulated the hypothesis that the damage to the Unit 4 building could have been caused by hydrogen generated at Unit 3 that flowed into Unit 4.

Fresh water is being injected as necessary into the spent fuel pools of Units 1 - 4. Water supply from concrete pump trucks is being gradually replaced by the Fuel Pool Cooling and Clean-up system in Units 1 to 3. However, closed loop cooling has not been yet established.

Stagnant water with high levels of radioactivity in the basement of the turbine buildings of Units 1 and 3 is being transferred to the condensers, the radioactive waste treatment facility, the high-temperature incinerator building and temporary storage tanks. Stagnant water in the basement of the turbine building of Unit 6 is being transferred to a temporary tank. Countermeasures against the outflow of water to the sea and to prevent and minimize the dispersion of radionuclides in water have been put in place.

Full-scale spraying of anti-scattering agent is continuing at the site with the use of both conventional and remote controlled equipment.

2. Radiation Monitoring

The daily monitoring of the deposition of caesium and iodine radionuclides for 47 prefectures is continuing. Since 17 May, deposition of I-131 has not been observed. Low levels of Cs-137 deposition were reported in a few prefectures on a few days since 18 May; the reported values range of from 2.2 to 91 Bq/ m2 for Cs-137.

Gamma dose rates values for all 47 prefectures are reported daily by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. On 31 May the gamma dose rate reported for Fukushima prefecture was 1.5 µSv/h. In all other prefectures, reported gamma dose rates were below 0.1 µSv/h; with a general decreasing trend. Meanwhile, the decrease of the gamma dose rate has slowed down, since the short-lived radionuclides have decayed away.

Gamma dose rates reported specifically for the monitoring points in the eastern part of Fukushima prefecture, for distances of more than 30 km from the Fukushima Daiichi plant, showed a general decreasing trend, ranging from 0.1 µSv/h to 17 µSv/h, as reported for 31 May.

On-site measurements at the west gate of the Fukushima Daiichi plant indicate the presence of I-131 and Cs-137 in the air in the close vicinity of the plant (within approximately 1 km). The concentrations in air reported for 29 May were about 3 Bq/m3 for I-131 and about 9 Bq/m3 for Cs-137. The values observed in the previous days show daily fluctuations with an overall decreasing tendency.

Protective Actions

In April, the Government of Japan announced protective actions to reduce the external exposure to the population beyond a distance of 30 km from the Fukushima-Daiichi Nuclear Plant. NISA has reported that the evacuation of the "Planned Evacuation Zones" within Iitate village and Kawamata town commenced on 15 May. Confirmation of completion of the evacuation is awaited.

Food Monitoring and Food Restrictions

Food Monitoring (Reported from 19 to 31 May)

Food monitoring data were reported from 19 to 31 May by the Ministry of Health, Labour and Welfare for a total of 818 samples collected in 18 different prefectures. Most of the monitoring continues to be concentrated in Fukushima prefecture, where 328 out of the 818 samples (over 40%) were collected.

Analytical results for 766 samples (over 93%) of the 818 samples indicated that Cs-134 and Cs-137 or I-131 were either not detected or were below the regulation values set by the Japanese authorities. However, 52 samples were above the regulation values for radioactive caesium and/or iodine.

In Fukushima prefecture, five samples of fishery products collected on 16 and 17 May; one sample of unprocessed tea leaves collected on 17 May; three samples of shiitake mushrooms and nine samples of bamboo shoots collected on 19 May; five samples of seafood collected on 20, 21 and 23 May, and; one sample of Japanese apricot, two samples of shiitake mushrooms and seven samples of bamboo shoots collected on 26 May were above the regulation values for Cs-134/Cs-137. One sample of algae collected on 21 May was also above the regulation values for Cs-134/Cs-137 and I-131.

In Chiba, Gunma, Ibaraki and Tochigi prefectures, eighteen samples of unprocessed raw tea leaves collected on 17, 19, 24 and 26 May were above the regulation values for Cs-134/Cs-137.

Food Restrictions

Consolidated and updated information on food restrictions in Fukushima prefecture were reported on 30 May by the Ministry of Health Labour and Welfare indicating that restrictions on the distribution of bamboo shoots were lifted in the Hirata-Mura area. However, restrictions remain in effect on the distribution of raw unprocessed milk, turnips, bamboo shoots and ostrich fern in specific areas of the prefecture. Restrictions on the distribution and consumption of sand lance fish (the whole prefecture) and specific non-head type (e.g. spinach) and head-type leafy vegetables (e.g. cabbage), flower head brassicas (e.g. broccoli, cauliflower) and shiitake mushrooms (specific areas of the prefecture) also remain in effect.

In Ibaraki prefecture there is a continuing restriction on the distribution of spinach produced in the cities of Kitaibaraki and Takahagi.

3. Marine Monitoring

The marine monitoring programme is carried out both near the discharge areas of the Fukushima Daiichi plant by TEPCO at 22 locations and at off-shore stations by MEXT on 16 stations. The radioactive contamination of the marine environment had occurred by aerial deposition and by continuing discharges and outflow of water with various level of radioactivity from the four damaged reactors at Fukushima Daiichi.

Seawater Monitoring

The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Fukushima Daiichi plant at the screen of Unit 2 have been measured every day since 2 April. Concentrations of Cs-134 and Cs-137 decreased from of more than 100 MBq/L initially to less than 5 kBq/L on 7 May but increased again to levels of around 20 kBq/L at the 16 May and to about 10 kBq/L on the 17 May. Since then the concentrations dropped slowly to less than 2 kBq/L but increased to about 5 kBq/L on 29 May. The levels of I-131 are varying significantly and the activity ratio to radio-caesium is not constant. On 28 and 29 May the concentrations were around 20 kBq/L. The variability of I-131 relatively to the radio-caesium concentrations could be an indication of retention of caesium by the zeolite sandbags in place, which would have almost no effect on iodine or further production of decay products in the reactor.

Monitoring of the marine environment is performed by TEPCO on the near field area and by MEXT at off-shore sampling positions. The monitoring of MEXT includes also measurement of ambient dose rate in air above the sea, analysis of ambient dust above the sea, analysis of surface samples of sea water and analysis of samples of sea water collected at 10 m above the sea bottom and in a mid-layer as well at a few locations for sediments. On most of the offshore stations I-131, Cs-134 and Cs-137 reached levels below the applied detection limit of 10 Bq/L. There will be a further decrease of the concentration during the propagation of contaminated waters in the sea. The activity found in surface sediments at the near shore stations close to the reactors was between 24 and 320 Bq/kg for Cs-137 in the middle of May. The activity in sediments decreases with distance, but is also highly dependent upon the sediment type. The contamination of marine sediments indicates the enrichment of radio-caesium on particulate matter and its removal from the water column into the sea floor.

4. IAEA Activities

The Fact Finding Mission to Japan has now concluded the first part of its work and is on its way back to Vienna. The next part of the work will be to finalize and agree on the report, which will be presented at the Ministerial Conference in June. A preliminary summary is available on the IAEA website.

Presentations:
Summary of Reactor Status: Unit 1, 18 May 2011
Summary of Reactor Status: Unit 2, 18 May 2011
Summary of Reactor Status: Unit 3, 18 May 2011
Summary of Reactor Status: Unit 4, 18 May 2011

On Friday, 20 May 2011, the IAEA provided the following information on the status of nuclear safety in Japan:

1. Fukushima Daiichi Nuclear Power Plant Status

Tables 1 - 4 track progress made for each of Units 1 - 4 towards fulfilling the three basic safety functions of the IAEA safety standards: prevention of criticality, removal of decay heat and mitigation of radioactive releases. The tables replace the three-colour table that was used previously. The charts are cross-referenced to the Tokyo Electric Power Company (TEPCO) "Roadmap" plan to bring the nuclear reactors and the spent fuel pools at the Fukushima Daiichi plant to a stable cooling condition and to mitigate radioactive releases.

On 17 May 2011, TEPCO provided a status report against the TEPCO "Roadmap". Progress has been made during the last month since the issuing of the Roadmap on 17 April 2011. While the basic policy and targets defined in the Roadmap remain, several changes were made to account for new information obtained and progress made to date.

On 13 May TEPCO commenced the preparatory work for the installation of a cover for the reactor building of Unit 1. The reactor building cover will be installed as an emergency measure to prevent the dispersion of radioactive substances until mid- to long term measures, including radiation shielding, are implemented.

TEPCO has reported that information obtained after calibration of the reactor water level gauges of Unit 1 shows that the actual water level in the Unit 1 reactor pressure vessel was lower than was indicated, showing that the fuel was completely uncovered. The results of provisional analysis show that fuel pellets melted and fell to the bottom of reactor pressure vessel at a relatively early stage in the accident.

TEPCO reported that "most part of the fuel is considered to be submerged in the bottom of reactor pressure vessel and some part exposed." TEPCO also reported that leakage of cooling water from the reactor pressure vessel is likely to have occurred. However, TEPCO considers that the actual damage to the reactor pressure vessel is limited, on the basis of the temperatures now being measured around the reactor pressure vessel.

With regard to the status of the reactor core of Unit 1, TEPCO believes that because the fuel has been being cooled continuously by means of water injection, it is unlikely that the situation could result in a future release of large amounts of radioactive material.

The results of the analysis are provisional; TEPCO will continue to conduct investigations. Similar analyses will be conducted for Units 2 and 3.

Nitrogen gas is still being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion inside the containment vessel.

In Units 1, 2 and 3 fresh water is being continuously injected into the reactor pressure vessel; temperatures and pressures remain stable.

To protect against potential damage as a result of future earthquakes, TEPCO started work on 9 May to install a supporting structure for the floor of the spent fuel pool of Unit 4.

Fresh water is being injected as necessary into the spent fuel pools of Units 1 - 4.

Stagnant water with high levels of radioactivity in the basement of the turbine buildings of Units 1, 2 and 3 is being transferred to the condensers, the radioactive waste treatment facility, the high-temperature incinerator building and temporary storage tanks. Stagnant water in the basement of the turbine building of Unit 6 is being transferred to a temporary tank. Countermeasures against the outflow of water to the sea and to prevent and minimize the dispersion of radionuclides in water have been put in place.

Full-scale spraying of anti-scattering agent is continuing at the site with the use of both conventional and remote controlled equipment.

2. Radiation Monitoring

Deposition in 47 Prefectures

The daily monitoring of the deposition of caesium and iodine radionuclides for 47 prefectures is continuing. Since 12 May negligible deposition has occurred. I-131 was reported in only one prefecture and Cs-137 was reported in three prefectures, with a value of 4.8 Bq/m2 for I-131 and a range of from 4.7 to 10 Bq/m2 for Cs-137.

Gamma Dose Rates in 47 Prefectures

Gamma dose rates are measured daily in all 47 prefectures. The Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan reports values on the basis of data collected from each prefecture. On 18 May the value of gamma dose rate reported for Fukushima prefecture was 1.6 µSv/h. In all other prefectures, reported gamma dose rates were below 0.1 µSv/h, with a general decreasing trend.

Gamma Dose Rates in Areas More Than 30 km from Fukushima Daiichi Plant

Gamma dose rates reported specifically for the monitoring points in the eastern part of Fukushima prefecture, for distances of more than 30 km from the Fukushima Daiichi plant, showed a general decreasing trend, ranging from 0.1 µSv/h to 17 µSv/h, as reported for 17 May.

Maps of gamma dose rates, deposition of Cs-134 and deposition of Cs-137 within the 80 km zone around the Fukushima Daiichi plant were produced by means of aerial gamma ray monitoring by the Nuclear Safety Technology Centre of MEXT and the United States Department of Energy.

The map of the deposition of radiocaesium is presented in Fig. 1. The values represent the sum of Cs-134 and Cs-137. The areas in green show a deposition of these two radionuclides of between 0.6 and 1 MBq/m2. The areas in yellow indicate a deposition of between 1 and 3 MBq/m2. The areas in red indicate a deposition of between 3 and 30 MBq/m2. All are normalized to 29 April 2011.

The map shows that the results obtained are consistent with all previous reported measurements of deposition in soil and of gamma dose rates.

Air Concentrations of Radionuclides On-site at Fukushima Daiichi Plant

On-site measurements at the west gate of the Fukushima Daiichi plant indicate the presence of I-131 and Cs-137 in the air in the close vicinity of the plant (within approximately 1 km). The values observed in the previous days show daily fluctuations with an overall decreasing tendency.

Concentrations of Radionuclides in Drinking Water

As of 10 May, the restriction on the consumption of drinking water relating to I-131 - which had been applied since 1 April as a precautionary measure for one remaining location (the village of Iitate in Fukushima prefecture), and only for infants - was lifted.

Food Monitoring and Food Restrictions (12 - 18 May 2011)

Food Monitoring

From 12 to 18 May, the Ministry of Health, Labour and Welfare reported results of continued monitoring for radioactivity in food. Over this period, results for 503 food samples from fifteen different prefectures were reported. Most of this monitoring continues to be concentrated within Fukushima prefecture (39% of samples reported for 12 - 18 May). The majority of results were below regulation values, but 28 out of these 503 samples (fewer than 6%) were found to have radioactivity levels above the Japanese regulation values for radiocaesium. These samples were collected in three prefectures (Fukushima, Ibaraki and Kanagawa). None of the 503 samples was found to have radioiodine in excess of the regulation values.

In Fukushima prefecture, 175 of the 194 samples (more than 90%) had radiocaesium levels below the regulation values set by the Japanese authorities. However, 19 of the 194 samples (fewer than 10%) exceeded the regulation values for Cs-134/Cs-137. Samples above the regulation values were bamboo shoots (ten samples), shiitake mushrooms (five samples), and four samples of fish (two samples of whitebait, one sample of ayu and one sample of Japanese smelt).

In Kanagawa prefecture, 6 out of 33 samples (18%) were found to exceed the regulation values set by the Japanese authorities for Cs-134/Cs-137, these were six samples of unprocessed tea leaves (an additional ten samples of unprocessed tea leaves were found to have levels below this regulation value).

In Ibaraki prefecture, 3 of the 66 samples (4%) reported were above the regulation values set by the Japanese authorities for Cs-134/Cs-137. These were unprocessed tea leaves (two samples) and parsley (one sample).

Food Restrictions

As of 18 May, the only food restrictions remaining are in Fukushima prefecture and for the cities of Kitaibaraki and Takahagi in Ibaraki prefecture.

In Fukushima prefecture there are restrictions on the distribution and consumption of sand lance fish. In specified areas of Fukushima prefecture there are also restrictions on the distribution of raw unprocessed milk, turnips, bamboo shoots, ostrich ferns and shiitake mushrooms, and restrictions on the distribution and consumption of specific non-head type and head-type vegetables (e.g. spinach and cabbage), flowerhead brassicas (e.g. cauliflower) and shiitake mushrooms.

In Ibaraki prefecture there is a continuing restriction on the distribution of spinach produced in the cities of Kitaibaraki and Takahagi.

3. Marine Monitoring

The marine monitoring programme is carried out both near the discharge areas of the Fukushima Daiichi plant by TEPCO and at off-shore stations by MEXT. The increase in the radioactivity in the marine environment had occurred by aerial deposition and by continuing discharges and outflow of water with high levels of radioactivity from the Daiichi plant.

Seawater Monitoring

The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Fukushima Daiichi plant at the screen of Unit 2 have been measured every day since 2 April. Concentrations of Cs-134 and Cs-137 decreased from initial values of more than 100 MBq/L to less than 5 kBq/L on 7 May, but increased to levels of around 20 kBq/L on 16 May, and to about 10 kBq/L on 17 May. There was a significant increase in levels of I-131 from about 8 to 80 kBq/L from 10 to 11 May, in parallel with the increase for both radiocaesium isotopes. This indicates that there is still some production of fission products. The I-131 levels decreased to about 20 kBq/L on 17 May.

Monitoring of the marine environment is performed by TEPCO in the near field area and by MEXT at off-shore sampling positions. The monitoring of MEXT also includes: measurement of ambient dose rates in air above the sea; analysis of ambient dust above the sea; analysis of surface samples of sea water; and analysis of samples of sea water collected at 10 m above the sea bottom and in a mid-layer, as well as at several locations for sediments. At most of the offshore stations, I-131, Cs-134 and Cs-137 reached levels below the detection limit of 10 Bq/L.

Fig. 1.: Map of deposition of radiocaesium (sum of Cs-134 and Cs-137) for the land area within 80 km of the Fukushima Daiichi plant, as reported by the Japanese authorities (MEXT):

Presentations:
Summary of Reactor Status: Unit 1, 11 May 2011
Summary of Reactor Status: Unit 2, 11 May 2011
Summary of Reactor Status: Unit 3, 11 May 2011

On Friday, 13 May 2011, the IAEA provided the following information on the status of nuclear safety in Japan:

1. Emergency at Fukushima Daiichi Nuclear Power Plant

Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious.

The IAEA receives information from various official sources in Japan through the Japanese national competent authority, the Nuclear and Industrial Safety Agency (NISA). This Update Brief is based on information issued by the IAEA Incident and Emergency Centre up to 17:00 UTC on 11 May 2011.

Fukushima Daiichi Nuclear Power Plant Status

The three attached charts, one for each of the Units 1 - 3, track progress made towards fulfilling the three basic safety functions of the IAEA safety standards: prevention of criticality, removal of decay heat and mitigation of radioactive releases. The chart replaces the three-colour status chart that was used previously. The charts are cross-referenced to the Tokyo Electric Power Company (TEPCO) "Roadmap" plan to bring the nuclear reactors and the spent fuel pools at the Fukushima Daiichi plant to a stable cooling condition and to mitigate radioactive releases.

Nitrogen gas is still being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion inside the containment vessel.

TEPCO has elaborated a measure to fill the primary containment vessel of Unit 1 with water up to a level above the reactor fuel rods. This measure is intended to provide stable cooling of the reactor and reactor pressure vessel. The planned steps are:

  • Reduce radiation levels in the reactor building by installing a filtered air circulation system (completed), remove rubble, decontaminate and install shielding;
  • Recalibrate existing reactor pressure vessel water level and pressure instruments and install additional reactor pressure vessel water level gauges to improve monitoring of conditions inside the reactor pressure vessel;
  • Install primary and secondary closed-loop cooling systems;
  • Flood the containment to provide a water supply for the primary system.

In Units 1, 2 and 3 fresh water is being continuously injected into the reactor pressure vessel; temperatures and pressures remain stable.

To protect against potential damage as a result of future earthquakes, TEPCO started work on 9 May to install a supporting structure for the floor of the spent fuel pool of Unit 4.

Fresh water is being injected as necessary into the spent fuel pools of Units 1 - 4.

Stagnant water with high-level radioactivity in the basement of the turbine buildings of Unit 1, Unit 2 and Unit 3 is being transferred to the condensers, the radioactive waste treatment facility and temporary storage tanks. Stagnant water in the basement of the turbine building of Unit 6 is being transferred to a temporary tank. Countermeasures against the outflow of water to the sea and to prevent and minimize the dispersion of radionuclides in water have been put in place.

Full-scale spraying of anti-scattering agent is continuing at the site with the use of both conventional and remote controlled equipment.

2. Radiation Monitoring

Deposition in 47 Prefectures

The daily monitoring of the deposition of caesium and iodine radionuclides for 47 prefectures is continuing. For the period 5 - 10 May, deposition of I-131 was detected in three prefectures, with values ranging from 1.5 Bq/m2 to 4.5 Bq/m2. Deposition of Cs-137 was detected in eight prefectures in the same period, the values reported ranging from 3 Bq/m2 to 44 Bq/m2. The reported values show that variable but low level deposition of radionuclides was still occurring in some prefectures.

Gamma Dose Rates in 47 Prefectures

Gamma dose rates are measured daily in all 47 prefectures. On 10 May the value of gamma dose rate reported for Fukushima prefecture was 1.7 µSv/h. In all other prefectures, reported gamma dose rates were below 0.1 µSv/h with a general decreasing trend.

Gamma Dose Rates in Areas More Than 30 km from Fukushima Daiichi Plant

Gamma dose rates reported specifically for the monitoring points in the eastern part of Fukushima prefecture, for distances of more than 30 km from the Fukushima Daiichi plant, showed a general decreasing trend, ranging from 0.1 µSv/h to 20.3 µSv/h, as reported for 10 May.

Maps of gamma dose rates, deposition of Cs-134 and deposition of Cs-137 within the 80 km zone around the Fukushima Daiichi plant were produced by means of aerial gamma ray monitoring by the Nuclear Safety Technology Centre of MEXT and the United States Department of Energy (DOE). The maps show that the results obtained are consistent with all previous measurements of deposition in soil and of dose rates.

Air Concentrations of Radionuclides On-site at Fukushima Daiichi Plant

On-site measurements at the west gate of the Fukushima Daiichi plant indicate the presence of I-131 and Cs-137 in the air in the close vicinity of the plant (within approximately 1 km). The concentrations in air reported for 10 May were 4 Bq/m3 for total I-131 and 16 Bq/m3 for total Cs-137. The values observed in the previous days show daily fluctuations with an overall decreasing tendency.

Concentrations of Radionuclides in Drinking Water

As of 10 May, the restriction on the consumption of drinking water relating to I-131 - which had been applied since 1 April as a precautionary measure for one remaining location (the village of Iitate in Fukushima prefecture), and only for infants - was lifted.

Food Monitoring and Food Restrictions

Food Monitoring

The Ministry of Health, Labour and Welfare reported on the radionuclide test results for 4 - 11 May for 436 food samples from 14 different prefectures. The prefectures of Chiba, Fukushima, Gunma, Ibaraki, Miyagi, Niigata and Tochigi accounted for more than 90% of the reported food analysis results, with most food monitoring concentrated in Fukushima prefecture (52% of samples analysed and reported until 11 May). In two prefectures (Fukushima and Kanagawa), 17 out of 436 (3.9%) samples were found to have radioactivity above the Japanese regulation values.

In Fukushima prefecture, levels in 212 (93%) of the 228 samples reported were below the regulation values for I-131 and radioactive caesium. However, 16 of the 228 samples (7%) exceeded the regulation values set by the Japanese authorities for Cs-134/Cs-137, including bamboo shoots (eight samples), shiitake mushrooms (four samples), ostrich fern (two samples), turnip (one sample) and sand lance fish (one sample).

In Kanagawa prefecture, unprocessed tea leaves were the only food that exceeded the regulation values set by the Japanese authorities for Cs-134/Cs-137 (one of thirteen samples, i.e. 7.7%).

Food Restrictions

As of 11 May, the only food restrictions remaining are in Fukushima prefecture and for the cities of Kitaibaraki and Takahagi in Ibaraki prefecture.

In Fukushima prefecture there are restrictions on the distribution and consumption of sand lance fish. In specified areas of Fukushima prefecture there are also restrictions on the distribution of raw unprocessed milk, turnips, bamboo shoots, ostrich ferns and shiitake mushrooms, and restrictions on the distribution and consumption of specific non-head type and head-type vegetables (e.g. spinach and cabbage), flowerhead brassicas (e.g. cauliflower) and shiitake mushrooms.

In Ibaraki prefecture there is a continuing restriction on the distribution of spinach produced in the cities of Kitaibaraki and Takahagi.

3. Marine Monitoring

The marine monitoring programme is carried out both near the discharge areas of the Fukushima Daiichi plant by TEPCO and at off-shore stations by MEXT. The increase in the radioactivity in the marine environment had occurred by aerial deposition and by discharges and outflow of water with high level radioactivity.

Seawater Monitoring

The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Fukushima Daiichi plant at the screen of Unit 2 have been measured every day since 2 April. Concentrations of Cs-134 and Cs-137 decreased from initial values of more than 100 MBq/L to less than 10 kBq/L on 30 April and have remained constant at this level to the present.

Levels of I-131 on 7 May remained at around 200 Bq/L.

As of 7 May, no relevant changes in the radionuclides concentrations at the other TEPCO sampling positions have been reported.

Monitoring performed by MEXT at off-shore sampling positions consists of:

  • Measurement of ambient dose rate in air above the sea;
  • Analysis of ambient dust above the sea;
  • Analysis of surface samples of seawater;
  • Analysis of samples of seawater collected at 10 m above the sea bottom and in a mid-layer.

On 7 May the data reported only for the sampling points S1, S3 and 9 showed that Cs-137, Cs-134 and I-131 are not detectable.

4. Monitoring Data from IAEA Member States

Over the past ten weeks, the following States have provided the IAEA with monitoring data and/or links to their web sites: Algeria, Austria, Belgium, Bulgaria, Canada, China, Czech Republic, Denmark, Finland, France, Georgia, Germany, Greece, Iceland, Islamic Republic of Iran, Ireland, Italy, Republic of Korea, Latvia, Lithuania, Luxembourg, Malaysia, Mexico, Philippines, Poland, Portugal, Romania, Russian Federation, Singapore, Slovakia, Spain, Sri Lanka, Sweden, Switzerland, Ukraine and United States of America.

Presentations:
Summary of Reactor Status
Fukushima Radiological Monitoring and Consequences
Fukushima Marine Environment Monitoring
Watch Video

On Thursday, 5 May 2011, the IAEA provided the following information on the current status of nuclear safety in Japan:

1. Emergency at Fukushima Daiichi Nuclear Power Plant Since 21 April

Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious.

The IAEA receives information from various official sources in Japan through the Japanese national competent authority, the Nuclear and Industrial Safety Agency (NISA). This Update Brief is based on information received by the IAEA Incident and Emergency Centre up to 17:00 UTC on 3 May 2011.

Fukushima Daiichi Nuclear Power Plant Status

The IAEA has developed new charts for tracking the progress made towards fulfilling the three basic safety functions of the IAEA safety standards: prevention of criticality, removal of decay heat and mitigation of radioactive releases. These new charts, one for each of the reactor units and for the spent fuel pools, will replace the three-colour status chart that has been in use up until now. The charts provide the IAEA with a benchmark for following progress under "Roadmap" plan announced previously by the Tokyo Electric Power Company (TEPCO) to bring the nuclear reactors and the spent fuel pools at the Fukushima Daiichi plant to a stable ccooling condition and to mitigate radioactive releases.

On 27 April TEPCO provided an update of the estimated percentage of core damage for Units 1, 2 and 3: for Unit 1 the core damage was revised from an estimated 70% to 55%; for Unit 2 the core damage was revised from an estimated 30% to 35%; and for Unit 3 the core damage was revised from an estimated 25% to 30%. This reflects a revised assessment since 15 March rather than any recent changes in conditions in the reactor cores.

On 29 April TEPCO checked the status inside the reactor building of Unit 1 using a remotely controlled robot and confirmed that there was no significant leakage of water from the primary containment vessel. Nitrogen gas is still being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion inside the containment vessel.

TEPCO has a plan to fill the primary containment vessel of Unit 1 with water up to a level above the reactor fuel rods. This measure is intended to provide stable cooling of the reactor and reactor pressure vessel. (On 5 May TEPCO submitted a report to NISA on this plan).

In Unit 2 and Unit 3 fresh water is being continuously injected into the reactor pressure vessel and temperatures and pressures remain stable.

Fresh water is being injected as necessary into the spent fuel pools of Units 1 - 4. Radionuclide analysis of a water sample taken from the Unit 4 spent fuel pool on 28 April detected levels of Cs-134 of 49 Bq/cm3; levels of Cs-137 of 55 Bq/cm3; and levels of I-131 of 27 Bq/cm3.

An amount of approximately 70 000 tonnes of stagnant water with high-level radioactivity in the basement of the turbine buildings of Unit 1, Unit 2 and Unit 3 is being transferred to the condensers, the radioactive waste treatment facility and temporary storage tanks. Stagnant water in the basement of the turbine building of Unit 6 is being transferred to a temporary tank. Countermeasures against water outflow to the sea and to prevent and minimize the spread of the radionuclides in water have been put in place.

Full-scale spraying of anti-scattering agent is continuing at the site with the use of both conventional and remote controlled equipment.

Measures Announced by Government of Japan

The Government of Japan announced the establishment or redesignation of the following zones:

  • A "no entry zone" within 20 km of the Fukushima Daiichi nuclear power plant (as of midnight, Japan local time, on 22 April 2011), with provision for temporary re-entry;
  • "Planned evacuation zones" to be applied to some specific zones outside the 20 km radius from the Fukushima Daiichi plant (from which planned evacuations were expected to be implemented in approximately one month's time from 22 April, so in late May);
  • "Emergency evacuation preparation zones" to be applied to the area within a 20 - 30 km radius from the Fukushima Daiichi plant (except for areas designated as planned evacuation zones), in which preparations should be made so that the residents can take shelter indoors or can evacuate the area by their own means in the event of an emergency.

The designation of "planned evacuation zones" applies to some specific zones outside the 20 km radius from the Fukushima Daiichi plant: "the villages of Katsurao, Namie and Iitate, part of the town of Kawamata, and part of the city of Minamisoma."

The designation of "emergency evacuation preparation zones" applies to the area within a 20 - 30 km radius from the Fukushima Daiichi plant (except for areas designated as planned evacuation zones): "the towns of Hirono and Naraha, the village of Kawauchi, and parts of the cities of Tamura and Minamisoma." In addition, with regard to the areas located within a 20 - 30 km radius from the nuclear power plant, the advisory for sheltering indoors that had been in effect to date was lifted.

With regard to the Fukushima Daini nuclear power plant, the Government of Japan also announced on April 21 that the size of the evacuation zone around the Fukushima Daini plant would be reduced from 10 km to 8 km and the order of evacuation would be lifted from areas farther than 8 km around the plant.

2. Radiation Monitoring (26 April to 3 May 2011)

Deposition in 47 Prefectures

The daily monitoring of the deposition of caesium and iodine radionuclides for 47 prefectures is continuing. For the period 22 April to 2 May, deposition of I-131 was detected in eight prefectures, ranging from 1.8 Bq/m2 to 89 Bq/m2. Deposition of Cs-137 was detected in 13 prefectures in the same period, the values reported ranging from 1.3 Bq/m2 to 92 Bq/m2. The reported values show that variable deposition of radionuclides was still occurring in certain prefectures. The values for deposition are significantly lower than those detected in the first weeks of the emergency and the number of prefectures affected is diminishing.

Gamma Dose Rates in 47 Prefectures

Gamma dose rates are measured daily in all 47 prefectures. The only notable values are those from Fukushima prefecture, where gamma dose rates were 1.8 µSv/h or just under, and Ibaraki prefecture, where gamma dose rates were 0.12 µSv/h or just under. In all other prefectures, reported gamma dose rates were below 0.1 µSv/h, with a general decreasing trend.

Gamma Dose Rates in Areas More Than 30 km from Fukushima Daiichi Plant

Gamma dose rates reported specifically for monitoring points in the eastern part of Fukushima prefecture, for distances of more than 30 km from the Fukushima Daiichi plant, showed a general decreasing trend over the period 26 April to 2 May, ranging from 0.1 µSv/h to 19.7 µSv/h.

Air Concentrations of Radionuclides On-site at Fukushima Daiichi Plant

On-site measurements at the west gate of the Fukushima Daiichi plant indicate the presence of I-131 and Cs-137 in the air in the close vicinity of the plant (within approximately 1 km). The concentrations in air reported for the period 31 March to 1 May ranged from 40 Bq/m3 to 1180 Bq/m3 for total I-131 and 10 Bq/m3 to 270 Bq/m3 for total Cs-137.

Concentrations of Radionuclides in Drinking Water

Since 1 April there has been one remaining restriction on the consumption of drinking water relating to I-131 (with a limit of 100 Bq/L), which is applicable only for the village of Iitate in the Fukushima prefecture and only for infants.

Both I-131 and Cs-137 are still detectable, but in only a few prefectures. According to the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), I-131 was detected in a maximum of six prefectures for the period 22 April to 1 May, with reported values ranging from 0.04 to 0.92 Bq/L; Cs-137 was reported in the same period in up to two prefectures with measured values ranging from 0.05 to 0.41 Bq/L. All these levels are below the limits set by the Japanese authorities for the restriction of water consumption due to the presence of radionuclides. The other samples did not show levels of radionuclides above the detection limit for I-131 and Cs-137.

Radiation Monitoring of Workers and Public

Radiation monitoring of workers and the public is continuing.

On 29 April, NISA reported that as of 27 April, 175 045 people had been monitored for radiation.

On 30 April TEPCO summarized the results of exposure measurements of workers engaged in emergency work whose external exposure exceeded 100 mSv at the end of March 2011. According to the summary, for total internal exposure and external exposure there were: two workers with effective doses of 200-250 mSv; eight workers with effective doses of 150-200 mSv; and 11 workers with effective doses of 100-150 mSv.

"Enforced Plan on Environmental Monitoring"

On 22 April MEXT issued a press release on an Enforced Plan on Environmental Monitoring that has the objectives of obtaining an overview and providing data necessary to support the decision to establish the planned evacuation zones.

To meet these objectives, the plan includes the following:

  • Collection of data on the distribution of radioactive material inside an appropriate area, including the area in the vicinity of the Fukushima Daiichi plant;
  • Preparation for future evaluations of changes in dose rates and accumulated amounts of radioactive substances in all delineated zones around the Fukushima Daiichi plant; and
  • Provision of information on environmental dose rates for the purpose of evaluation of personal radiation doses to local residents.

It was announced that maps will be produced on the basis of the results of environmental monitoring, including maps of dose rates and distributions of radioactivity, estimated accumulated doses and levels of soil surface contamination.

This Enforced Plan on Environmental Monitoring will be conducted in close cooperation between MEXT, Japan Atomic Energy Agency, universities, the Ministry of Defence, the police, prefectural police, Fukushima prefecture, electrical utilities and others, including the United States Department of Energy.

MEXT will compile all the data collected. MEXT and the Nuclear Safety Commission will cooperate with the Ministry of Economy, Trade and Industry (METI) and other organizations, and will establish procedures for standardizations on ranges and methods for the emergency environmental monitoring.

Food Monitoring and Food Restrictions (19 March to 3 May)

Food Monitoring

The Ministry of Health, Labour and Welfare reported that from 19 March to 3 May, 2 461 food samples had been collected from 18 different prefectures. The prefectures of Chiba, Fukushima, Gunma, Ibaraki, Niigata, Saitama and Tochigi accounted for more than 90% of the reported food analysis results, with most food monitoring concentrated in Fukushima prefecture (38% of samples analysed and reported until 3 May). In six prefectures (Chiba, Fukushima, Gunma, Ibaraki, Tochigi, Tokyo), 222 (9%) samples were found to have radioactivity above the Japanese regulation values.

In Fukushima prefecture, levels in over 84% of the 942 samples reported were below the regulation values for I-131 and radioactive caesium. However, 149 of 942 samples (16%) exceeded the regulation values, including vegetables (107 samples), shiitake mushrooms (19 samples), unprocessed raw milk (18 samples) and sand lance fish (five samples).

In Ibaraki prefecture, 89% of the 442 samples reported were below the regulation values. However, 47 of the 442 samples (11%) exceeded the regulation values, including vegetables (37 samples), unprocessed raw milk (five samples) and sand lance fish (five samples).

In four other prefectures, vegetables were the only foods that exceeded the regulation values (11 samples in Chiba, three samples in Gunma, 11 samples in Tochigi and one sample in Tokyo).

Food Restrictions

Restrictions on the distribution and/or consumption of milk and specific types of vegetables have been in place in five prefectures (Chiba, Fukushima, Gunma, Ibaraki and Tochigi) since they were first imposed on 21 March. As of 3 May, the only restrictions remaining are in Fukushima prefecture and for the cities of Kitaibaraki and Takahagi in Ibaraki prefecture.

Specifically, in Ibaraki prefecture there is a continuing restriction on the distribution of spinach produced in the cities of Kitaibaraki and Takahagi. In Fukushima prefecture there are restrictions on the distribution of turnips and on the distribution and consumption of sand lance fish and certain non-head type leafy vegetables (e.g. spinach). In specified areas of Fukushima prefecture there are also restrictions on the distribution of raw unprocessed milk and restrictions on the distribution and consumption of specific head-type vegetables (e.g. cabbage), flowerhead brassicas (e.g. cauliflower) and shiitake mushrooms.

3. Marine Monitoring

The marine monitoring programme is carried out both near the discharge areas of the Fukushima Daiichi plant by TEPCO and at off-shore stations by MEXT. The increase in the radioactivity in the marine environment had occurred by aerial deposition and by discharges and outflow of contaminated water with a high radioactivity level.

Seawater Monitoring

The activity concentrations of I-131, Cs-134 and Cs-137 in seawater close to the Daiichi plant at the screen of Unit 2 were measured every day from 2 April to 2 May. The concentrations fell by several orders of magnitude from initial values of more than 100 MBq/L at the beginning of April to less than 10 kBq/L for Cs-134 and Cs-137 on 30 April, with a continuing decreasing trend over time. The sandbags containing zeolite absorbers for absorbing caesium, which were placed at several locations between Unit 2 and Unit 4 to reduce concentrations of Cs-134 and Cs-137, do seem to have effected the observed reduction in the levels of caesium radionuclides. However, levels of I-131 remained at around 100 kBq/L from 26 April to 30 April; on 2 May they had increased to around 200 Bq/L at this sampling position.

The concentrations of the relevant radionuclides at the other TEPCO sampling positions show a general decreasing trend up to 4 May with some fluctuations.

Monitoring performed by MEXT at off-shore sampling positions consists of:

  • Measurement of ambient dose rate in air above the sea;
  • Analysis of ambient dust above the sea;
  • Analysis of surface samples of seawater;
  • Analysis of samples of seawater collected at 10 m above the sea bottom and in a mid-layer.

The analysis for almost all sampling positions has shown a general decreasing trend in concentrations of the relevant radionuclides over time. Samples were taken at stations 1 - 10 every four days after 2 April. Activity concentrations at MEXT sampling points 30 km off-shore are significantly lower than those at TEPCO sampling points 15 km off-shore due to further dilution. None of the activity concentrations of I-131 and Cs-137 in surface samples taken from points 1, 3, 5, 7, 9 and S

Last update: 17 November 2014