Future Technology for the Seismic Safety of Nuclear Power Facilities

Abstract

Because earthquakes occur frequently in Japan, attention has been given to seismic safety in the design and construction of Japanese nuclear power facilities. A serious accident at the Fukushima Dai-ichi Nuclear Power Plant of the Tokyo Electric Power Company that was caused by the 2011 Great East Japan Earthquake prompted us to review measures to ensure structural safety against future earthquakes and tsunamis. In recent years, progress has been made in investigations and research on the earthquake-resistant design of nuclear power plants. This has contributed to the development of various new technologies based on the new findings. As examples of future technologies for the seismic safety of nuclear power facilities, this chapter describes structure control technologies for nuclear power facilities and technologies to allow for greater diversity in the siting of nuclear power plants.

Appendices

Appendix 12.1: Siting on Quaternary Layer

Figure 12.11 shows an example of a geological structure. The Quaternary layer is composed of the alluvium and diluvium layers. Alluvium is the youngest geological layer formed by sedimentation from 10,000 years ago to date. It is a relatively weak layer that is composed of sand and silt layers, and is spread widely over plain areas of Japan. The diluvium layer is a geological layer that is formed between 1.8 million and 10,000 years ago. Composed of sand and clay layers, it often forms a tightly compacted, rigid ground. For siting on a Quarterly layer, a site covered by sedimentary soft rock, hard cohesive soil or gravel should be chosen.

Fig. 12.11

Example of geological structure

There are many examples of commercial and demonstration reactors built on a Quaternary layer in the world. In the United States, almost half of the nuclear power plants are built on a Quaternary layer. Many similar examples exist in Europe, the Middle East, and South Africa. In Japan, no reactor is built on a Quaternary layer. One of the reasons for this is the need in Japan to ensure safety against a large seismic force.

Appendix 12.2: Underground Siting

By excavating into a hard rock formation, an underground space is created for the installation of major nuclear plant facilities. There are several types depending on underground space geometry (vertical or horizontal type) and construction style (partially underground or completely underground). The most appropriate design and style are chosen while considering site characteristics. If the local rock formation has enough strength and rigidity, a horizontal design is preferred; if not, a vertical design is preferred. If the site exits on steep terrain, full underground construction is preferred; if the site exists on flat or nearly flat ground, partially underground construction is preferred.

Irrespective of these choices in style and construction type, underground siting has the advantage of facilitating the preservation of the original landscape at ground level. In the world, six reactors in total, including research and commercial reactors, have been constructed underground. Five of the six reactors, however, have been disused and decommissioned. Figure 12.12 shows the type of underground siting of nuclear power plants. Figure 12.13 shows an example of the underground nuclear power plant layout.

Fig. 12.12

Classification of underground siting techniques [6]

Fig. 12.13

Example of underground nuclear power plant layout [7]

Appendix 12.3: Offshore Siting

Offshore siting means the construction of a nuclear power plant in a sea area. The nuclear power plant is constructed either on a man-made island built on the seabed or on a floating body. Figure 12.14 shows different types for the offshore siting. There are two types of construction of man-made islands: reclamation and caisson-type man-made island. Figure 12.15 shows the concept of a reclaimed man-made island, whereas Figure 12.16 shows the concept of a floating body.

Fig. 12.14

Different techniques for the offshore siting of nuclear power plants [6]

Fig. 12.15

Concept of offshore siting using a man-made island [6]

Fig. 12.16

Classification of offshore siting using a floating body [8]

Japan has no experience of offshore nuclear power plants. However, abundant experience exists in Japan in the construction and operation of non-nuclear offshore facilities such as fossil-fired power plants on man-made islands and liquefied natural gas terminals on reclaimed grounds in bays. Because offshore facilities in Japan can be subjected to large tsunamis, the feasibility of offshore siting has to be determined after evaluating the risk of tsunamis at the proposed site.