Saturday, April 12, 2014

External Hazards at Nuclear Power Plants:

A New Study

I recently learned of a report from the European Commission on external-hazard related events at nuclear power plants.  I will caution that, to date, I have read only the summary of the report, so my observations are based on what is in the summary.  

In light of Fukushima, everyone has been sensitized to the fact that an external event has the potential to trigger a serious accident at a nuclear power plant.  For the Fukushima event, the external events were an earthquake and a tsunami.  However, those who follow event reports at nuclear power plants also know that there are a variety of other ways that the external environment can impact nuclear power plant operations, including severe weather events, floods, and the clogging of intake pipes.  For that reason, a report such as this can help provide some perspective on the kinds of accidents possible.
This report provides some useful pie charts showing the percentages of different kinds of accidents in the data base of the IAEA-OECD/NEA Incident Reporting System (IRS), as well as pie charts for the same types of events for French reactors and for German reactors.

It is interesting to note that the percentages of some of the types of accidents differ significantly.  The reasons for this are not completely clear.  It may be due in part to differences in environment in individual countries that might, for example, make the nuclear plants of one country more or less vulnerable to clogging of intake pipes.

I should note that the report says that it does not address earthquake hazards, as they have already been addressed in other reports.  I also note that the report doesn't separate different types of events within a class of events.  For example, they say they have taken tsunamis into consideration, but there is not a separate category for tsunamis.  Rather, they are considered a type of flooding event.  While this may be reasonable in terms of the similarity of most of the consequences, given the post-Fukushima concerns about tsunamis, it might have been useful to see a more explicit breakout of such events within the flooding category.

A key conclusion of the report is that, for the IRS database, the main external phenomenon affecting nuclear plant operation is extreme weather conditions. The next most frequent phenomena affecting nuclear power plants are water intake fouling (mostly of biological origin) and lightning.  (The most frequent events were different for France.)  The external hazards, in general, had no severe actual impacts on nuclear safety based on the events reported to the IRS database.

The authors also observed that, where events had previously occurred, corrective actions had often been taken, and those corrective actions noticeably reduced the effects of a recurrence of the event.  This reinforces the importance of studying events, such as they have done, and of making sure the lessons learned have been assimilated.  Such studies can also help assure that the money and effort spent on corrective actions go toward changes that will reduce the recurrence of events with the greatest potential consequences.


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