Fukushima Daiichi Accident Information Bulletin No. 4 by the IRSN

CURRENT STATUS OF THE ACCIDENT AND ITS CONSEQUENCES

1.1. The Status of the Fukushima Daiichi Site and Recovery Plan

The state of the three reactors (1, 2 and 3) continues to be a concern. Fresh water is now being used to cool the reactors and pools. Nonetheless, this cooling is still carried out through opencircuit in-vessel water injections and is thus not sustainable. On April 6, TEPCO (Tokyo Electric Power Co.) began injecting nitrogen gas at a low flow rate into the containment vessel of reactor No. 1 to reduce the risk of hydrogen explosion inside the building. The same operation will subsequently be performed in the containment vessels of reactors 2 and 3. These operations will last several days for each reactor and could generate new atmospheric releases. According to TEPCO, the evolution of the pressure inside the containment vessel of reactor No. 1 confirms the presence of a leak in this containment vessel.

TEPCO has moved electrical power supply switchboards to protect them from the impacts of a tsunami.

The presence of contaminated water inside the turbine halls of the three reactors is due to water being poured into the reactors to cool them, and to probable water leaks from the buildings of reactors 2 and 3. Operations to pump this water out are delicate given the large quantities of water to be handled and their high level of contamination.

A crack in the reactor pit adjacent to the turbine hall of reactor 2 has caused a release of highly contaminated water directly into the sea. On April 6, at approximately 6 AM local time, TEPCO successfully stopped the leak by injecting sodium silicate. Some of the contaminated water present in this reactor pit is pumped out and stored in the turbine condenser so as to contain it.

From April 4 to 10, TEPCO intentionally released "slightly contaminated" water into the sea. This mainly concerns 10 000 tonnes of liquid effluents stored in tanks and awaiting treatment and discharge prior to the accident. TEPCO justifies this operation due to the need to free up on-site storage capacity to accommodate the highly contaminated water present in the three damaged reactor buildings. On April 19, after having checked that the storage tanks were leak-tight, TEPCO began transferring the water in the turbine hall of reactor 2 into these tanks.

Measurements taken for several days in seawater near the plant have revealed high contamination of the marine environment, due to the release into the sea of a part of the very highly contaminated water present in the damaged reactors.

Atmospheric releases (steam plumes) are most likely still being generated, but they are slight releases and incomparable to those caused by the containment depressurisation operations carried out during the first week after the accident. In the days that will follow, these releases should not significantly modify the environmental contamination already present.

On April 17 TEPCO presented its recovery plan for the Fukushima nuclear power plant.

The plan has two phases. The first phase, which is to last 3 months, is in the scope of reducing radioactive releases, by developing a reliable method for the cooling of reactors and reactor pools and by ensuring the safety of contaminated water storage. The second phase, which is to last from 3 to 6 months, is in the scope of ensuring the safety of the buildings so as to manage the radioactive releases that were reduced by the end of phase 1, as well as achieving a cold shutdown state for the reactors and reducing the quantity of contaminated water on the site.

The IRSN believes that the actions described in this action plan are credible, but that the timelines provided are only approximate as access remains very limited due to contamination.

1.2. History of dose rate measurements over Tokyo since March 18

The graph below shows the evolution in the ambient dose rate measured by the Teleray radioactive sensor at the French embassy in Tokyo since March 18. Since March 23, no significant concentration of artificial airborne radionuclides has been observed over Tokyo. As a result, only radiation emitted by radioactive deposition contributes to the dose rate measured by the Teleray radiation sensor.
This dose rate has steadily decreased due to the radioactive decay of the short-lived radionuclides present in the deposition. The value of the dose rate (approximately 80 nSv/h) is comparable to that typically measured in a large number of regions and attributable to natural radioactivity.

1.3. Radioactive deposition and contamination in food products from the soil

Radioactive deposits
IRSN does not have enough measurements to estimate the precise magnitude and location of radioactive deposition. However, significant levels of caesium-137 and iodine-131 are observed in the deposits measured in different districts (for example, 28 300 Bq/m2 of caesium and 29 700 Bq/m2 of iodine-131 in the Ibaraki district). Even higher surface deposit levels may be observed in certain areas closer to the accident site, in particular in the Fukushima district.

Results of surface activity measurements for caesium (30-year period of radioactivity, see Appendix 1) are stable over time, implying that there has been no significant additional deposition over the last few days. The deposits of iodine-131 (8-day period of radioactivity, see Appendix 1) decrease, as a result of radioactive decay.

Vegetables
Data regularly collected in the district of Ibaraki reveal that in less than one month vegetable contamination decreased by a factor of 100 for iodine-131 and by a factor of 10 for caesium-137, showing the combined effect of radioactive decay (for iodine-131) and effects related to the environment (rain, in particular) or plant growth (for iodine and caesium). A decay factor of 10 over a period of 1 month was also observed for caesium in vegetables in Fukushima. However, data available to the IRSN are not sufficient for a detailed analysis of the situation.

New measurements provided by the Japanese ministry of health (MLHW) show that high concentrations of caesium-137 (maximum acceptable level in Japan: 500 Bq/kg) and iodine-131 (maximum acceptable level in Japan: 2000 Bq/kg) are still observed in samples taken since April 9 in food products from the areas around the power plant. For example, contamination measured in spinach in Kitaibaraki (Ibaraki) amounted to 1800 Bq/Kg of iodine-131 and 621 Bq/kg of caesium. In the Fukushima district, iodine-131 and caesium activities remained high on April 11, with 2100 Bq/kg of iodine-131 (in spinach in Fukushima) and 8900 Bq/kg of caesium in broccoli grown outdoors in Otama. However, plants sampled in the districts of Miyagi, Gunma, Saitama and Tochigi over these last three days do not present measurements greater than the maximum levels accepted in Japan.

Mushrooms
Several measurements were taken in mushrooms from the Fukushima district. The latest values are from April 8, 2011. Mushrooms taken from Iidate presented very high iodine-131 and caesium levels—12 000 Bq/kg and 13 000 Bq/kg, respectively.

Milk and meat
In the district of Fukushima, the latest measurements of contamination in milk reveal activities of 27 Bq/L for iodine-131 (the maximum acceptable level for consumption and sale in Japan is 100 Bq/L) and 16 Bq/L for caesium (with a maximum acceptable level of 200 Bq/L in Japan).

Measurements taken in milk from the districts of Miyagi, Gunma, Saitama and Tochigi the last few days reveal no detectable level of contamination.

Measurements taken recently in pork, beef and chicken meat (muscle and liver) in Fukushima reveal no detectable level of contamination.

Tap water
New values obtained on April 14 in Japanese districts reveal maximum levels of 1 Bq/L of iodine-131 and caesium, which is much lower than the consumption norms of 300 Bq/L and 200 Bq/L, respectively.

Conclusion
Measurements available to IRSN do not permit a complete analysis of the situation. However, these measurements show that no increase in deposition and contamination has been observed over thelast few days. On the contrary, surface deposits and contamination in foodstuffs from iodine have greatly decreased over the past month. Food contamination from caesium has also decreased. Nonetheless, measurements have shown that the contamination levels in some food products (vegetables such as spinach and broccoli) grown near the power plant remain above Japan's acceptable limits.

Finally, there is very little data on strontium contamination in the environment. These radionuclides are less volatile than iodine and caesium and, as is supported by the few measurements that exist, it is likely that strontium releases were much smaller than those of iodine and caesium. This assumption is worth confirming through additional measurements.

1.4. Contamination of seawater and marine species in Japan

Radioactive pollution is observed in the sea, at a relatively large distance from the Fukushima Daiichi nuclear power plant. The principle radionuclides regularly measured in the seawater are: iodine-131, caesium-137, caesium-134, caesium-136, tellurium-132/iodine-132. Others have also occasionally been detected, in lower concentrations.

This radioactive pollution has three possible origins: liquid radioactive releases from the site of the accident, atmospheric fallout on the surface of the sea and transport of radioactive pollution by washout of contaminated land.

Seawater
Measurements taken over several days in seawater in the immediate vicinity of the plant (a few hundred metres) have revealed high contamination levels in the marine environment, due to the release into the sea of part of the very highly contaminated water present in the damaged reactors. The impact of these liquid releases has been observed since March 21 near the plant. Concentrations in seawater have reached 63 000 Bq/L of caesium-137 and 180 000 Bq/L of iodine-131.

Concentrations in radionuclides decrease rapidly as distance from the Fukushima Daiichi plant increases. They are approximately 10 times weaker 15 km from the plant and 100 to 500 times weaker 30 km from the plant. At this distance, concentrations vary from 2 Bq/L to 27 Bq/L for caesium-137 and from 3 Bq/L to 57 Bq/L for iodine-131.

Fish and other marine species
The maximum acceptable levels established by Japanese authorities for seafood products since the Fukushima accident are 2000 Bq/kg for iodine-131 and 500 Bq/kg for caesium-137.

The fish exhibiting the highest levels of contamination is the Japanese sand eel or sand lance (Ammodytes personatus). This species is locally and seasonally caught (from January to April).
Other contamination values for seafood products are generally below 100 Bq/kg for iodine-131 and 70 Bq/kg for caesium-134 and caesium-137 together. It can also be noted that radioactive contamination is either not detected or detected at low levels in most fish tested.

GENERAL RECOMMENDATIONS FOR FRENCH CITIZENS LIVING IN JAPAN

Radioactive releases from the NPP site have caused radiological pollution in part of the national territory, mainly in the districts of Fukushima, Tochigi, Ibaraki and Miyagi. The following recommendations are intended to provide assistance for minimizing potential exposure to radiation caused by these releases and the resulting deposits in the soil. Direct exposure to airborne radioactive releases (external exposure to radiation emitted from the radioactive plume and inhalation of radioactive particles) is essentially over, with radioactive releases now limited in magnitude. At present, the risk of exposure is mainly associated with the consumption of food contaminated by atmospheric fallout. The foodstuffs most prone to this radioactive contamination are leaf vegetables and milk from animals feed on contaminated grass or fodder. In certain areas of the Fukushima district, and beyond the 30 km perimeter around the nuclear site, high levels of radioactive deposition have been identified, with the potential to cause significant external radiation doses in case of extended exposure.

Naturally, these recommendations do not impede the application of measures promulgated by Japanese authorities.


1.5. Food consumption recommendations for all French citizens living in Japan

IRSN recommendations:
- Avoid consuming Japanese sand eel or sand lance.
- Avoid consuming vegetables (spinach, hana wasaki, kakina, komatsuna, lettuce,
chrysanthemum, cabbage, white cabbage, celery, broccoli, bok choy, parsley) and mushrooms
in the districts of Fukushima, Tochigi, Ibaraki, Miyagi and Gunma.
- Avoid giving children fresh milk produced since March 11 in the districts of Fukushima,
Tochigi, Ibaraki, Miyagi and Gunma.
- Make sure that all fresh foods listed above originating from districts where standard threshold
levels for safe consumption have been exceeded (Saitama, Tokyo, Kanagawa, Chiba) are
compliant with applicable Japanese regulations.
- In the absence of information on the origin and radiological quality of fresh foods, consume a
diversified diet, avoiding the repeated consumption of leaf vegetables as much as possible
(spinach, hana wasaki, kakina, komatsuna, lettuce, chrysanthemum, cabbage, white cabbage,
celery, broccoli, bok choy, parsley).

No restrictions are necessary regarding the use of tap water for food preparation and cooking. Products that were hermetically sealed at the time of the accident (canned foods, dry foods, longkeeping milk, bottled spring water) may be consumed without risk.

It is important to note that the occasional consumption of foodstuff with contamination levels slightly exceeding authorized threshold limits does not pose a significant health risk.

1.6. Recommendations for French citizens living in areas most affected by radioactive deposition
In general, French citizens are advised to avoid travelling to the districts of Miyagi, Ibaraki, Tochigi and especially Fukushima for leisure or tourist reasons to prevent undue doses from external radiation caused by radioactive deposition, even if the doses potentially received would be slight in the majority of these districts.

Inversely, due to the slight nature of the doses that would potentially be received, it is no longer justified to avoid travelling to the districts of Miyagi, Ibaraki and Tochigi for professional or important personal reasons, except in applying as a precaution all of the recommendations listed below for French citizens residing in these districts.

Finally, travelling to the northeast section of the Fukushima district is strongly discouraged, within a 40-km distance of the plant in particular, unless absolutely necessary. Should the latter be the case, time spent in this area should be limited to the absolute minimum, strictly applying the recommendations listed below, and only adults should travel to the area.

In any case, it is essential that people follow the instructions regarding the areas from which Japanese authorities have requested the population to keep a distance. These areas include a radius of 20 km around the Fukushima plant, as well as the communities of Katsurao-mura, Namie-machi, Iitate-mura, Kawata-machi and Minamisoma-shi.

French citizens living in the districts of Miyagi, Fukushima, Ibaraki and Tochigi should observe all instructions given by Japanese authorities. In all cases, the IRSN recommends the following:

- Prepare all food for infants and young children using bottled spring water.
- Minimize the consumption of food originating from home gardens.
- Carefully wash all fruits and vegetables.

The IRSN also recommends the application of good hygiene practices at home so as to limit indoor contamination transfers:
- Leave shoes outside, especially during rainy weather.
- Clean floors on a regular basis using a damp cloth.
- Clean air ducts and ventilation systems.
- Vacuum furniture, carpets and rugs (and replace vacuum cleaner bags) on a regular basis.

It is also recommended to wash one’s hands regularly with liquid soap from a dispenser so as to minimize the risk of involuntary contamination by hand-to-mouth contact.