In spite of a few reactors built inside rock caverns in the years 1950/70, the nuclear industry refuses to consider underground alternatives to surface plants. The first reactor accident occurred in a Swiss underground plant in 1969, without any health effect, as it was underground. The next one at TMI (USA, 1979) urged Germany to convene a colloquium on underground nuclear plants at Hannover in 1981). Chernobyl (Ukraina, 1986) moved many scientists to demand underground reactors; Fukushima (Japan, 2011) suggested ISRM to entrust prof. Sakurai as chair of an international study commission, the first report of which has been delivered in 2015.
The Fukushima Daiichi nuclear power plant was seriously damaged by the Great East Japan Earthquake (moment magnitude 9.0) which occurred on March 11, 2011. The earthquake generated a giant tsunami with a run-up height of more than 20 m that struck the nuclear power plant (NPP) and was followed by the functional loss of the emergency power supply system due to flooding brought about by the tsunami. This caused the loss of reactor cooling water resulting in a hydrogen explosion of the plant and a core meltdown. As a result, radioactive materials were scattered and a vast area of the region was contaminated with them.
Immediately after, the Japanese government ordered all the 50 reactors in Japan to be shut down. resulting in the shortage of electric power in spite of operation of thermal plants (at higher fuel cost and production of CO2). To overcome such cost and environmental problems, the Japanese government and the companies want to restart the operation of some of the existing NPPs. However, the NPPs must satisfy the new regulations formulated by the Nuclear Regulation Authority (NRA), which was established in September of 2012 on the basis of lessons learned from the Fukushima Daiichi accident, which differ markedly from the old standards. However, it must be difficult to restart the operation, because the new regulatory standards do not guarantee the absolute safety of NPPs, i.e., there is no 100% guarantee for safety even if the NPPs comply with the new standards. This means that we need security for unpredictable accidents. In order to solve this problem, we need a different concept for NPPs from that which has been followed in the past.
