Fukushima and the consequences: BfS report on the accident's development and causes

Report of BfS as of 8 March 2012 (in German only): "Die Katastrophe im Kernkraftwerk Fukushima nach dem Seebeben vom 11. März 2011: Beschreibung und Bewertung von Ablauf und Ursachen"

One year after the nuclear disaster at Fukushima, the Federal Office for Radiation Protection (BfS) published a report on the development of the accident and its causes.

The basic details of the accident and how it progressed are well known. In terms of what happened within the reactors themselves, however, at the time of reporting the experts were dependent on observations which can be made from outside, the knowledge that comes from experience, and reconstruction models using data acquired by other means. In the estimation of BfS experts, several weak points contributed to Fukushima becoming the worst accident since Chernobyl.

Factors influencing the course of the accident

• The risk of earthquakes - and by extension the risk of a tsunami - was underestimated.
  
  

  Despite the systematic monitoring of seismic activity and a well-documented history of earthquakes stretching back more than a thousand years, seismologists were not prepared for an earthquake on this scale. This is why a tsunami of such proportions was considered impossible. Apparently, the reactors were not adequately designed to withstand internal and external impacts of this magnitude as earthquakes and tsunamis, or other flooding.

• The technical design of the facility, such as an applicable and operational in most emergency situations emergency power supply, showed several weaknesses.
  
  Unit 1 to 4 of the nuclear power plant were insufficiently protected against flooding. The emergency diesel-powered electricity generators, in particular, as well as other key elements of the electricity supply, were installed so low down that they flooded, leading to instant failure.
  The cooling systems for both the reactors and the emergency diesel-powered electricity generators were connected to the same system of saltwater pumps. The destruction of these pumps by the tsunami not only led to the failure of the reactor cooling systems, but also to the failure of the cooling systems for the emergency diesel-powered electricity generators.
  

• The nuclear power plant operators were apparently insufficiently prepared to deal with emergencies.
  
  In the case of the reactors, some of which were nearing the end of their lifecycle, there had been an apparent failure to ensure the consistent retrofitting of building structures and systems technology, with the insufficient rehearsal of emergency drills. Clear instructions to be followed in the event of an emergency were missing.

Nevertheless, in March 2012, it was too early to issue a final assessment on the various stages of the accident, and more especially on its impact on the environment and health. For this reason at the time of reporting, any assessment on the state of the reactors was limited to that, which can be definitely asserted at this time.