The International Atomic Energy Agency (IAEA) has published a preliminary
summary of their fact-finding mission to three nuclear power stations affected
by the earthquake and subsequent tsunami. The original document can be found
Some of the key findings include:
- “Hydrogen risks should be subject to detailed evaluation and necessary mitigation systems provided.”
This refers to how it is believed that hydrogen entered Unit 4, which has experienced spent fuel pool heating, but was on shutdown for maintenance at the time of the incident. It is now believed that ductwork shared between Units 3 & 4 provided a pathway for hydrogen generated by Unit 3 to enter Unit 4 and reach dangerous levels. This means that this possibility must be investigated in other plants that share these design aspects, and sytems to vent any buildup of hydrogen must be devised. The hydrogen buildup warrants a careful look at hydrogen venting capabilities for any plants that could suffer from the same design flaw.
- “The tsunami hazard for several sites was underestimated. … Defence in depth, physical separation, diversity and redundancy requirements should be applied for extreme external events, particularly those with common mode implications such as extreme floods.”
Two terms in this point require some explanation. The first, “Defence in depth,” refers to having multiple, redundant, diverse and independent safety systems in place, especially in the case of a single incident that can affect many systems, known as a “common mode” incident. “Common mode” refers to thefact that one incident (such as the tsunami) can disable many safety systems at once. Nuclear power stations will have to be re-analyzed to ensure that, within reason, no single incident or chain of events can disable enough safety systems
to cause a major malfunction.
- The IAEA mission urges the international nuclear community to take advantage of the unique opportunity created by the Fukushima accident to seek to learn and improve worldwide nuclear safety.
The IAEA uses this opportunity to call for the world to learn from the Fukushima incident, in order to improve safety of all other nuclear plants. They see this as a learning opportunity, and there is indeed much information to be acquired by analyzing the situation as it develops.