Asan Plenum

Nuclear Accident at Fukushima #1 Nuclear Power Station

1.Accident Initiation

Following the earthquake of Magnitude 9.0, a huge tsunami with an estimated height of 15m rushed to the nuclear power station. Among the basic functions to ensure safety, the emergency shutdown was successfully achieved to avoid any nuclear power excursion. The emergency power supply systems were also activated to remove the decay heat. However, a huge tsunami arrived at the site after 50 minutes and lead to the loss of emergency power supply which resulted in hydrogen detonation. The loss of cooling induced core melt and the integrity of containment failed.

2.The messages and comments from Nuclear Salon Fuji-ie

1) Fukushima #1 accident especially to occur from No1 to No3 can be considered as a common cause accident incurred by the tsunami of 15m wave height followed after the earthquake.
2) The accident level of Fukushima has the severity of INES level 7 from the viewpoint of radioisotope discharge. However, Fukushima accident did not result in the radiation hazard like that of Chernobyl.
3) The environmental effects can be followed up through the radiation level changing to follow the half life of Iodine 131. It made also clear that hydrogen detonation did not occur after March 16.
4) Cleanup of the water polluted with radiation takes long time.: Problems inside NPS
5) Soil cleanup has also big concern for school children, farmer etc.: Problems outside NPS
6) The information related to the accident shall be opened to the public as well as to the international community.
7) Accident Management for severe accident shall be improved.
8) Criticality of degraded reactor core: Lessons learned from TMI-2
9) Importance of inherent safety characteristics for decay heat removal?
10) Measurement of reactor plant states: water level, pressure, neutron flux etc in degraded core conditions.