Actually, repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. The multi-barrier system typically comprises the natural geological barrier and an engineered barrier system. The most important of all is the Low-Level Radioactive Waste Storage Site, which is located in Longmen, the southeast tip of Lanyu Island, Surrounding by mountains on three directions and facing the sea on one direction. These natural geological barriers are efficient in reducing the influence of the biosphere from radioactive waste.
Aerial photograph of the Low-Level Radioactive Waste Storage Site
Multi-barrier design
The Low-Level Radioactive Waste Storage Site adopts a multi-barrier design, which means the waste is first solidified with cement to form a hard block (the first barrier), and then it is packed in a steel barrel (the second barrier). After arriving at the storage site, it is stored in the concrete trench (the third barrier). The concrete trench in the storage site has an infiltration water collection system (the fourth barrier). After the infiltration water is collected, it is processed by a concentrator until its radioactivity is lower than the instrument's minimum detectable value. Then, the infiltration water can be used again in the site (the fifth barrier).
Earthquake-resistant and tsunami-resistant:
Built on slopes, the Low-Level Radioactive Waste Storage Site is located along the southeast coastline of Lanyu Island. All earthquake-resistant designs of the structures in the Low-Level Radioactive Waste Storage Site are in accordance with relevant provisions of the "Building Structures under Building Technical Regulations".
In June 2009, Taiwan Power Company conducted a "10-year re-evaluation report on the Low-Level Radioactive Waste Storage Site" to re-examine the earthquake-resistant design of each storage trench. The report shows that the peak ground acceleration (PGA) is 0.45g which means facilities, such as storage trenches can withstand earthquakes with magnitudes of 7 or greater according to the “Earthquake Intensity Table by the Central Weather Bureau, Ministry of Transportation and Communications”.
Besides, the coastal area on the east side is built with a 1,300 meter long revetment. It is designed in "gravity type composite section with concrete grouted rock”. The top revetment is 1 meter wide and 12.5 meters above sea level. To prevent the invasion of tsunamis, the elevation of the storage trenches is 11, 14, 16, 22, and 28 meters.
According to the analysis of the tsunami simulation on the Low-Level Radioactive Waste Storage Site, the seawater flooding elevation caused by the tsunami can reach 5.96 meters. It is lower than the lowest elevation of the base where the structure is located (11 meters in elevation), and therefore has no safety impact on the Low-Level Radioactive Waste Storage Site.