There are many complex events occurring with some of Japan’s nuclear power plants as a result of the earthquake and tsunami on March 11, 2011. Although the issues are still very much ongoing, it is possible to begin a root cause analysis of the events and issues. In order to clearly show one issue, our analysis within this blog is limited to the issues affecting Fukushima Daiichi Unit 3. This is not to minimize the issues occurring at the other plants and units, but rather to clearly demonstrate the cause-and-effect within one small piece of the overall picture.
The issues surrounding Unit 3 are extremely complex. In events such as these, where many events contribute to the issues, it can be helpful to make a timeline of events. A timeline of the events so far can be seen by clicking “Download PDF” above. A timeline can not only help to clarify the order of contributing events, it can also help create the Cause Map, or visual root cause analysis. To show how the events on the timeline fit into the Cause Map, some of the entries are denoted with numbers, which are matched to the same events on the Cause Map. Notice that in general, because Cause Maps build from right to left with time, earlier entries are found to the right of newer events. For example, the earthquake was the cause of the tsunami, so the earthquake is to the right of the tsunami on the map. Many of the timeline events are causes, but some are also solutions. For example, the venting of the reactor is a solution to the high pressure. (It also becomes a cause on the map.)
A similar analysis could be put together for all of the units affected by the earthquake, tsunami and resulting events. Parts of this cause map could be reused as many of the issues affecting the other plants and units are similar to the analysis shown here. It would also be possible to build a larger Cause Map including all impacts from the earthquake.
The impact to goals needs to be determined prior to building a Cause Map. As a direct result of the events at Unit 3, 7 workers were injured. This is an impact to the worker safety goal. There is the potential for health effects to the population, which is an impact to the public safety goal. The environmental goal was impacted due to the release of radioactivity into the environment. The customer service goal was impacted due to evacuations and rolling blackouts, caused by the loss of electrical production capacity, which is an impact to the production goal. The loss of capacity was caused by catastrophic damage to the plant, which is an impact to the property goal. Additionally, the massive effort to cool the reactor is an impact to the labor goal.
The worker safety and property goals were impacted because of a hydrogen explosion, which was caused by a buildup of pressure in the plant, caused by increasing reactor temperature. Heat continues to be generated by a nuclear reactor, even after it is shutdown, as a natural part of the operating process. In this case, the normal cooling supply was lost when external power lines were knocked down by the tsunami (which was caused by the earthquake). The tsunami also apparently damaged the diesel generators which provided the emergency cooling system. The backup to the emergency cooling supply stopped automatically and was unable to be restarted, for reasons that are as yet unknown.
The outline, timeline and cause map shown on the PDF are extremely simplified. Part of this simplification is due to the fact that as the event is still ongoing and not all information is known, or has been released. Once more information becomes available, it can be added to the analysis, or the analysis can be revised.