Accident at the Fukushima Dai-ichi nuclear power stations of TEPCO--outline & lessons learned

Abstract

The severe accident that broke out at Fukushima Dai-ichi nuclear power stations on March 11, 2011, caused seemingly infinite damage to the daily life of residents. Serious and wide-spread contamination of the environment occurred due to radioactive materials discharged from nuclear power stations (NPSs). At the same time, many issues were highlighted concerning countermeasures to severe nuclear accidents. The accident is outlined, and lessons learned are extracted with respect to the safety of NPSs, as well as radiation protection of residents under the emergency involving the accident. The materials of the current paper are those released by governmental agencies, academic societies, interim reports of committees under the government, and others.

Figure 1.

Location of Fukushima Dai-ichi Nuclear Power Stations of TEPCO. The Station faces to Pacific Ocean and is about 200 km from Tokyo.

Figure 2.

Typical bird-eye view of the MARK-I type reactor containment of Units 1 to 4 of Fukushima Dai-ichi Nuclear Power Station. Left figure is taken after modification from the report of March 19, 2011 by the Nuclear Energy Institute of the United States, courtesy of GE corporation.

Figure 3.

Electric power of Emergency Diesel Generators (D/G) and power supply of Power Center (P/C) compared to the tsunamis of about 14 m height. Taken after modification from the original figure provided by TEPCO.

Figure 4.

Core temperature and hydrogen production in Units 1 to 3 (from TEPCO data). Taken from Mainichi Newspaper after modification and permission.

Figure 5.

Exposure to the thyroid estimated with SPEEDI code, released on the end of March 2011. Dose represents an integral one from 6:00 a.m. of March 12 to 0:00 a.m. of March 24. Taken after modification from the former Safety Commission of Japan.

Figure 6.

Contamination by ¹³⁴Cs and ¹³⁷Cs in Fukushima Prefecture measured using an airplane on April 20, 2011. Taken after modification from MEXT’s Website to Enlarge Distribution Maps of Radiation Doses, etc./Digital Japan Web System.

Figure 7.

Typical farmer house contaminated by ¹³⁴Cs and ¹³⁷Cs in IItate-mura of Fukushima Prefecture (on May 19, 2011).

Figure 8.

Dose rate inside the house before and after decontamination around the house. A PHITS simulation indicated dose contribution of about 3∼4 µSv/h after decontamination inside the house due to radiations from cedars.

Figure 9.

Assessment of the safety design for waste storage and an image of storage, of which surface dose on clay cover is <10⁻³ µSv/hr (1/10 of background dose rate) and mobility of Cs in Bentonite is about 0.3 mm per 300 years.