報告書番号

U44

タイトル（和文）

浮揚式原子力発電所の動揺特性とプラント成立性評価

タイトル（英文）

Dynamic motions of floating nuclear plants(FNP) due to waves and earthquakes and feasibility studies on the FNP

概要 （図表や脚注は「報告書全文」に掲載しております）

需要地に近接した原子力発電所の適地拡大の一方策として，短周期の水平地震動に対して，優れた免震性を有し，水平地震荷重の低減によりプラントの耐震設計を標準化することが可能と考えられる，浮揚式海上立地方式が有力である．まず，経済性の観点から有利である水深25m以下で防波堤等により静穏水域を作り，この水域内に立地する浮揚式原子力発電所の成立性に関わる技術的な課題として，防波堤で囲まれる水域内への波浪や地震による動揺特性，外郭施設の耐震・耐波性を検討した．さらに，プラントの概念設計と外郭施設の概略設計を行い，技術的・経済的側面から検討を加え，浮揚式発電所の成立性の見通しを得た．また，実現に向けての主要な今後の技術課題をまとめた．次に，より一層の立地拡大方策として防波堤を用いない独立式浮体構造について，日本周辺海域の厳しい海象条件の下で，セミサブ型浮体による成立性が高いことを示し今後の検討課題をまとめた．

概要 （英文）

This report has summarized results on feasibility studies on floating nuclear plants (FNP). To extend siting options of the nuclear plants, the FNP is one of the most promising plants next to a siting technology on a man-made island because the FNP is effectively isolated from horizontal earthquake motions and designing plants is expected to be standardized irrelevant to ground conditions. One idea among those on the FNP is that the floating body is moored in a calm basin protected by breakwaters. Technical tasks on dynamic response of the floating body due to waves, wind and earthquakes were investigated using both physical model tests and numerical simulation models. It is required for the breakwaters to reduce a wave height inside the basin to 1.0m. To reduce transmitted waves through the breakwater to a certain limited level under which the FNP’s response to the waves is accepted, conventional rubble mound breakwaters do not function. An additional facilities such as sheet-pile type structure are required at the shallow water region. In deeper water sea, a caisson type breakwater work well to prohibit the transmitted waves. 2-D numerical simulation model was developed to estimate the wave motions in and near the breakwater. Dynamic motion of the FNP in short-crested waves joined to a dolphin-link mooring system was investigated by using numerical simulation and physical model tests with multi-directional wave makers. Wind force acting the power plant was included together with the wave force. It is confirmed that under the design forces a magnitude of the FNP dynamic motion was smaller than the limited one to operate the nuclear plant. Displacement of the mooring system and its force were also smaller than the limited conditions. Because vertical earthquake motions on the FNP are almost the same as the ground motion, pneumatic chambers at the bottom of the barge are installed. It is evaluated by the solution that high frequency vertical acceleration greater than 1Hz on the barge induced by vertical component of an earthquake will be reduced to approximately a quarter of the ground motion. It should be assessed that the stability of seawalls and breakwaters ensuring the safety of backfill against waves and earthquakes. Evaluation of dynamic nonlinear behavior like sliding and settlement is very important in evaluation the seismic stability of seawalls and breakwater, for this purpose, shaking table tests of caisson breakwater were carried out. The dynamic failure mode and effect of water and armored layers on dynamic behavior were investigated. Mainly from technical aspects, the feasibility studies were carried out and economical analysis is also performed. Conceptual design of nuclear power plants was carried out and breakwaters to make a basin were also designed. From these investigations it is concluded that the FNP is feasible. Disclosed was problems for further studies. Another option of floating type of power plant is to site it at open sea without any breakwaters. Dynamic response should be reduced by the floating body itself by enlarging the size. Under a critical wave condition which covers sea surrounding Japan (wave height 18m and wave period 18s), a semi-submerged type of floating structure of which weight is about 800,000 tons is feasible.

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