Accident of Fukushima Daiichi Nuclear Power Plant: Sequences, Fission Products Released, Lessons Learned

Abstract

The nuclear accident that occurred at the Fukushima Daiichi Nuclear Power Plant on March 11, 2011 was caused by the extremely massive earthquake and gigantic tsunami, which resulted in a severe accident that extended over multiple reactors simultaneously. In the present chapter the current status of the accident is described in terms of basic information, sequences of the accident, fi ssion products (FP) released, and lessons learned. Although some details of the accident are still not well known, the sequences, causes, and consequences of the accidents have been basically clarifi ed by the efforts of several investigation committees in Japan. The fi ssion products released to the environment were estimated by the severe accident analysis code, MELCOR, from inside the reactor core, and also by the atmospheric dispersion simulations code, SPEEDI, by coupling with environmental monitoring data in the reverse estimation method from outside the plant. The estimated release amount of 131 I is of the order of 120-160 PBq and that of 137 Cs is of the order of 8-15 PBq for both estimations. Lessons learned from the accident identifi ed by the investigation committees cover a wide spectrum of insuffi cient measures, such as for earthquake and tsunami, station blackout, severe accident management, common cause accident at multiple unit site, education and training, chain of command at the accident, disaster prevention, and safety regulation systems. These lessons should be shared all over the world for the higher level of safety assurance of current reactors, and advanced reactors without the need of evacuation in principle should be developed for future.

Estimation of Dose Rate for the Large Japanese Field Mouse (Apodemus speciosus) Distributed in the “Difficult-to-Return Zone” in Fukushima Prefecture

“…Eventually, substantial amounts of radioactive materials were released into the surrounding environment. The total amount of radioactive materials released into the environment was estimated by several organizations such as the Nuclear and Industrial Safety Agency (NISA), the Nuclear Safety Commission (NSC) and Tokyo Electric Power Co. (TEPCO) [2][3][4][5][6]. The estimated values of iodine-131 ( 131 I) ranged between 1.2 and 5.0 × 10 −17 Bq.…”