Earthquake Resistance Assessment of Contaminated Water Storage Tank and its Reinforcement Basic Design at Fukushima

Abstract

The core melt accidents at Fukushima Daiichi Units 1-2-3 have occurred due to the tsunami of the Great East Japan Earthquake at March 11, 2011. Now a coolant of approximately 100t is injected into each Reactor Vessel (RPV) in order to cool the fuel debris, and a part of the coolant leaks out from the water. The contaminated water is collected, and it is stored in the contaminated water storage tanks more than approximately 1,000 and the total amounts of coolant exceeds 1,000,000 t. Although the contaminated water is purified by ALPS, it is still in high nuclear pollution density. According to the homepage of Nuclear Regulation Authority (NRA) in Japan, the storage tanks have been placed on the concrete bed without any anchor. Tokyo Electric Company (TEPCO) reported to NRA in 2015 that the design acceleration used for the overturning evaluation of the tanks have 0.3G. At the Fukushima Daiichi Power Station in the Great East Japan Earthquake, the maximum horizontal acceleration was 0.6G, the maximum vertical acceleration was 0.326 G at the time of the Great East Japan Earthquake. Even if an earthquake that is a fraction of this earthquake comes back, there is a possibility that this tank will fall over. The temporary special design guideline is adopted. These tanks have already stored the contaminated water for 6 years. However, it is thought that the more long term countermeasures is necessary for preventing the contaminated water from flowing out into the Pacific Ocean when another great earthquake will attack this area in future. In this paper, we propose a drastic structure to add a foundation without causing ground to the present tank. In the past, the member fastening the steel plate of the upper structure of the tank and the concrete of the lower structure is a foundation bolt, but this time it is a stud welded to the tank side plate. This made it possible to flexibly design and reinforce the foundation itself even after tank installation.