FLOOD PROTECTION | SAFETY & SECURITY
leads to further potential threats that must not be ignored, for example deliberate embankment failures that could trigger flooding of coastal areas and nuclear power plants. Given the consequences, as illustrated by the 2011
Fukushima disaster, the devastating effects that tsunamis can have on nuclear power plants represents a turning point in the debate about flood safety. Although the Fukushima Daiichi nuclear power plant already had a flood wall of 4 metres in height, this was raised to 5.7 metres after the Indian Ocean tsunami in 2003. While this is a clear response to the lessons learned from this earlier event the enormous wave heights of the tsunami of 11 March, 2011, saw even this increased protective wall proven to be insufficient. The tsunami wave on this occasion reached a peak height of 14 metres and as high as 10 metres at the site of the nuclear power plant with devastating effects. The external power supply was destroyed and the critical infrastructure of the nuclear power plant, such as the emergency diesels, emergency standby and transformer buildings, were flooded. The subsequent collapse of the internal battery supply meant that the cooling water pumps for the reactors could no longer be supplied with power – a decisive factor in the nuclear disaster that followed. These events revealed the weaknesses of existing safety
precautions against the effects of tsunamis and flooding and underlined the urgency of developing more robust and reliable protection systems. It has become clear that the construction of flood walls alone is not sufficient to cope with the potential risks for nuclear power plants.
A solution-focused approach A multidisciplinary approach and, in the best case, a complementary passive system is needed to increase the safety of these plants and thus prevent similar disasters in the future. For this purpose, it is urgently necessary to identify building openings within a nuclear power plant that are important for safety and to protect them from flooding, regardless of their height. In an emergency diesel building, which is critical infrastructure, for example, this includes the combustion air intake, the diesel exhaust system, the fresh air intake and the exhaust air openings. Furthermore, an important goal in the development of an appropriate flood protection system is to achieve diversity compared to the existing flood protection walls and ensuring functionality of the system independent of the height of the tsunami. A key aspect is the passive operation of the system, both when closing and opening with the system’s independence from an external power supply ensuring a high level of reliability, as it continues to function even in the event of power failures or technical problems. Control of single fault criteria and a multi-redundant design are further important features to consider in the design of a flood protection system. This ensures that the functionality of the system is maintained even if individual components fail. An additional application of the system is the prevention of internal flooding from room to room. This can also prevent possible contamination carry-over. In addition, strict requirements are to be set with regard to earthquake safety in accordance with specific nuclear regulations, such as KTA 2201.4 or KTA 3211.2. The system to be developed should also be able
to withstand various environmental conditions, such as flotsam, muddy water, high and extreme outside temperatures and high exhaust gas temperatures.
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In order to maximise protection against potential debris and other external influences, an associated debris protection system should be developed in addition to the flood protection system. One of the most important functions of debris protection is to protect against floating loads, such as debris like gas/fuel tanks or trees. In addition, debris protection should be designed to minimise the impact of blast pressure waves. For this purpose, reinforced concrete structures are typically used to reduce the effects of pressure waves and protect the various system components. It is also conceivable to extend the structure with explosion pressure flaps. Furthermore, the debris protection should potentially be designed to withstand extreme weather conditions such as severe winds, ice loads and abnormally high outside temperatures. In addition, an earthquake decoupling system should
integrated into the debris protection system to protect the systems from the effects of an earthquake and minimise any potential damage. The debris protection should be anchored using anchor plates and/or in conjunction with the existing building reinforcement to ensure stability. Further plant-specific protective measures can be implemented in the debris protection system to protect nuclear facilities from additional threats. These measures could include additional protection against debris from an aircraft crash, where the design aims to minimise the impact of such an event. Further precautions can be taken to protect nuclear
facilities from damage caused by tornadoes and/ or tornado-induced loads. And, depending on the requirements, debris protection can be further developed to defend against terrorist attacks by reinforcing the structures and implementing object protection grids, for example.
The TsunamiFloodProtection system Based on these core criteria, INNOMECOM AG has developed its TsunamiFloodProtection (TFP) system using a specified qualification plan to ensure its effectiveness and reliability.
Below: The devastating effects that tsunamis can have on nuclear power plants represented a turning point in the debate about flood safety after the 2011 Fukushima disaster
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