**5. Conclusions and outlook**

These tubes and capsules are then introduced through an opening shown in **Figure 6** into a barium-concrete chamber prepared below the bottom of the dump. Leakage to the ocean will be excluded when the material with highest radioactivity is stored in basin I and basins II and III also have been emptied, provided with a thick concrete layer, and used as dry dump for

**Figure 7.** Standard free energy of formation of metal oxides as a function of temperature.

less-contaminated waste.

98 Environmental Risks

The Fukushima accident (and also the former Three-Mile-Island and Chernobyl catastrophes) has demonstrated that no engineer and manager with wide experiences and deciding power have been on site. In the case of Fukushima, urgent actions for very intense water spraying the fire and the cloud, for suction of the cloud, for manually opening the valve of the passive cooling system and for covering the ground with a thick concrete layer with slope of 2–3° depended on decisions of the owner's headquarters in Tokyo. This was concentrated on the internal problems of the reactors, on political and publicity pressure and anyhow was under enormous stress and was not aware of the consequences for the local population and of the following national and international consequences. The experiences from the Three-Mile-Island accident and the recommendations have been summarized in Ref. [24].

Competent reactor engineers should be educated who learn, besides nuclear technology, about all possible chemical reactions, corrosion and electro-corrosion, properties of the involved materials, failure of materials and components, aero-and hydrodynamics, meteorology, and so on.-.

Another question is about the possibility for emergency interruption of nuclear fission by cadmium-indium alloys inside thin silver tubes and boron carbide/boron nitride/boron oxide composite tubes, whether such tubes can be inserted into Type-II generators until the safe generation III/III+ and IV reactors with a four-fold redundancy of emergency equipment will be developed.

It has become clear that the Fukushima accident could have been prevented if in the planning stage the worst-case scenario would have been considered by the plant owner and by the responsible ministry. Even after the accident caused by the unexpected tsunami, the collateral damages could have been mitigated if a competent foresighted management had timely initiated the described procedures. An international emergency team of top engineers with multidisciplinary and industry experience could assist worldwide in case of heavy nuclear, chemical, fire and other catastrophes.

Anyhow, with the development of the safe generation III and IV reactors the nuclear energy will become more dominating and increasingly replace the fossil energy in view of limited resources, of the CO<sup>2</sup> climate problem and of overall safety concerns. The new high-temperature reactors and fast breeders will have a significantly higher efficiency, consume less fuel and produce less radioactive waste. The renewable wind and solar energy is faced with the electricity storage problem, so that nuclear energy is more and more needed as reliable band energy. Frequently, the storage of radioactive waste is regarded as a problem with concern of the population regarding the site for a deep geological deposit. Recently the concept of a safe deposit the waste in a lonely mountain site has been developed which will be economic and faces less political resistance [25].

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[7] Bryant E. Tsunami, the Underrated Hazard. 2nd ed. Chichester: Springer; 2008. p. 330.

[8] Takahashi S. Design of vertical breakwaters, short course of hydraulic response and vertical walls. In: Proceedings 28th International Conference on Coastal Engineering

[9] Takahashi S, Shimosaki K, Kimura K, Suzuki A. Typical failures of composite breakwaters in Japan. In: Proceedings 27th International Conference on Coastal Engineering.

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The common features of the three nuclear accidents (Three-Mile-Island 1979, Chernobyl 1986 and Fukushima 2011) are the combination of personnel error and mistakes, deficiencies in reactor and safety component design, and component failures. Charles Perrow has formulated the "Normal Accident Theory" that in processes of huge complexity, accidents are due to "unanticipated interaction of multiple failures in a complex system" [26–28]. Thus, for nuclear reactors with their enormous complexity all possible failure combinations should be analyzed and precautions with sufficient redundancy found before the plant is switched on. Of great importance is also multidisciplinary high-level education of reactor engineers and reactor managers and adequate training of operators to reduce accidents and their consequences.

It is hoped that the described experiences will assist in planning future reactors and in reducing collateral damage in case of a future accident which, however, hopefully will not occur.
