Nuclear Accident in Japan March 2011

Abstract

Nuclear Accidents in Japan The Earth’s crust is made up of large plates which move across the planet’s surface, the interaction of these crustal plates causes pressure build up which eventually is released in the Earth crust and as the crust ruptures, seismic waves are created which results in the phenomena known as Earth Quakes. Earthquakes are measured with a seismometer while the intensity of the shaking is measured on the modified Mercalli scale; it is on record that the largest earthquakes are slightly above a magnitude of 9. seismicity or seismic activity of an area refers to the frequency The Japanese archipelago is located on the pacific ring of fire (where a number of the planet’s tectonic plates interact). Hence, the area is prone to earthquakes and volcanic activities with the Japanese landmass being the product of these interactions where it is located at a triple junction where the pacific plate, the Eurasian plate and the diamond shaped Philippine plate are located.The epicentre of Japan’s March 11th earthquake occurred where the pacific plate is sub ducting under the plate beneath northern Honshu with a 9.0 magnitude which lasted almost six minutes. The design of Japanese power plants is meant to withstand specified earthquake intensities evident in ground motion. If they register ground acceleration of a set level, systems will be activated to automatically bring the plant to an immediate safe shutdown. In this case the set scram level was 135 Gal Daiichi and 150 Gal at Daini. Fukushima Daiichi and Daini nuclear power plants were affected by a major tsunami in March 2011. The design basis tsunami height was 5.7 m for Daiichi and 5.2 m for Daini, though the Daiichi plant was built about 10 meters above sea level and Daini 13 meters above. Tsunami heights coming ashore were more than 14 meters for both plants, and the Daiichi turbine halls (contained both the backup diesel generators and much of the electrical switchgear) were under some 5 meters of seawater until levels subsided. This led to the disabling of the power supply of three Fukushima Daiichi reactors, interrupting cooling and hence causing a nuclear accident on 11 March 2011. In the case of Nigeria, earlier seismic findings showed that the country’s location did not fall within the earthquake prone zones. However, recent signs have given seismologists concern following earth tremors along some regions of Nigeria and upon investigation revealed a deep seated pre-Cambrian fracture. In the light of this, there is an urgent need to incorporate seismic criteria in the site investigations for design and construction of major and sensitive structures like Nuclear power plants while adequate study of the crustal and mantle structure beneath Southwestern Nigeria should be carried out by the Nigerian Geoscientists through the Nigerian Geological Survey Agency (NGSA).

Seminar presented by Ethel Iwuala, Muktar kabir, Saiyadi Sulaiman and Oruru Jonathan