Technical Lessons Learned from the Fukushima-Daichii Accident and Possible Corrective Actions for the Nuclear Industry: An Initial Evaluation

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Rev.: 1
Report Date: July 2011
Appendices: No

Premise

The accident at the Fukushima-Daichii nuclear plant has generated worldwide news and precipitated public concern about the safety of nuclear power in general.  The accident has already caused some governments to re-think their nuclear energy policies, notably including the Japanese and German governments.  There have been calls for cancellation of nuclear construction projects and reassessments of plant license extensions.  This may lead to a global slow-down of the nuclear enterprise, based on the perception that nuclear energy is not safe enough.  However, the lessons to be drawn from the Fukushima accident are different.  

First, the accidnet was a result of the worst earthquake and tsunami in Japan's modern history, an event which has caused the loss of over 20,000 lives and up to $300 billion in damages.  Second, given the extraordinary magnitude of the initiating events (i.e. earthquake was 9.0 vs design 8.2, tsunami wave was 14 m vs design 5.7m), the Fukushima-Daichii plant has performed relatively well in some respects and so far there is no evidence of major human errors in handling the crisis.  It is noted that the containments at Units 1-3 have not massively failed, in spite of the exceptional loads they have been subjet to, i.e. earthquake, tsunami, hydrogen explosions in the reactor buildings, steam discharges from the reactor pressure vessel, exposure to hot seawater, pressure about design limits for days.  The release of radioactivity from the plant has been large (with contributions also from containment venting) and some workers have recieved significant radiation doses (>100 mSv whole-body equivalent), but health risks for them and the general population are expected to be neglibible (see Appendix A).  In fact, no loss of life has occurred or is expected as a result of the accident.  Direct damage and casualties inflicted on Japan by the earthquake and tsunami for exceed any damage caused by the accident at teh nuclear plant.  The Fukushima accident has been rated at the maximum level (Level 7) on the IAEA nuclear event scale, indicating an accident with large release of radioactivity accompanied by "widespread health and environmental effects" like Chernobyl.  However, there are very significant differences between Fukushima and Chernobyl.  Briefly, the amount of the release (~10% of Chernobyl), the presence of the containment structures, the radionuclides released (mostly iodine and cesium isotopes vs. the entire core inventory), the physical form or the releases (mostly aqueous vs. volatile), the favorable currents and winds at the site, and the timing of the release with respect to population evacuation resulted in vastly smaller overall consequences.  Having said this, it is important to analyze the technical lessons that can be learned from Fukushima, so that the safety of nuclear plants in the U.S. and worldwide can be further enhanced and the attractiveness of nucear enery sustained over the long term.  An initial attempt to identify the key lessons from the Fukushima accident is presented here.

Program:     NSP Nuclear Systems Enhanced Performance
Type:     TR 

RPT. No.: 25