Press Conference by the Chief Cabinet Secretary

JAPANESE

CHIEF CABINET SECRETARY EDANO: Let me start by giving you some more information concerning estimation of radiation exposure that have been made using SPEEDI (System for Prediction of Environmental Emergency Dose Information). There were questions about this at the press conference this morning.

At around noon today, I received a report from the Nuclear Safety Commission on estimation of radiation exposure with the SPEEDI system. The details will be released later today by the Nuclear Safety Commission, so please refer to them for more details.

The SPEEDI system estimates the exposure dose of radioactive iodine received by the thyroid gland, based on measurements of radionuclides in the atmosphere and recent climatic conditions. To date, large amounts of data have been obtained, and we have been releasing to the public the results of radiation measurements made at various monitoring locations, including inside the nuclear reactors, in units of μSv. The SPEEDI system is a simulation system. It uses measurements of the levels of radioactive material in the air and the atmosphere to estimate how much radioactive material is coming out of the reactors. Based on these estimates, the system runs simulations to calculate how far the radiation has dispersed and whether the levels represent any risk to human health, taking into account weather conditions and other factors.

We have been giving instructions for this system to be used thoroughly to carry out the estimates, but as I said this morning, unfortunately given the situation in the nuclear power station at the moment it is not possible to measure how much radioactive material is coming out of the reactors at the present time. I think I said then that we had given instructions to try to use the data available to infer the levels of radioactive materials being emitted from the reactors by a process of inverse calculation. To do this, you need to get data for the amount of radioactive materials, more precisely radionuclides, in the atmosphere over an area of land downwind of the site; monitoring to obtain this data was successfully carried out yesterday, and now a report has been issued detailing the results of simulations carried out using this data.

The results of the simulations carried out based on the data show areas where the thyroid gland exposure dose may have been 100mSv or higher, assuming that of a person spends the whole day outdoors. The simulation suggests that even in some areas beyond the 30 kilometer radius of the Fukushima Daiichi Nuclear Power Station, it is possible that radiation exposure doses may have reached levels of 100mSv or more. At the moment, however, the analysis does not suggest that it is necessary for people to evacuate or remain indoors at the present time.

Specialists will continue to monitor radiation levels and carry out more accurate simulations. We will take great care in our response from now to ensure that radiation exposure doses do not reach a level of 100mSv, where there is the possibility of an impact on human health.

Radiation exposure doses are strongly influenced by wind direction. The SPEEDI system carries out simulations based on wind direction and other factors. As a result, it cannot run simulations without measurements of radioactive material in a downwind area. Consequently, if the place you are in now happens to be downwind of the power station, we advise you to keep your windows closed and to remain indoors in an airtight environment as much as possible as a precautionary measure.

That’s all from me for now.