In 1972, the Atomic Energy Council (AEC) invited scholars and experts from National Tsing Hua University (NTHU), the Institute of Nuclear Energy Research (INER), and Taiwan Power Company (TPC) to review and evaluate radioactive waste storage sites, such as deserted mining pits or tunnels, highland areas, uninhabited islands and offshore islands. The scholars and experts suggested selecting offshore islands for temporary storage and actively promoting research and development of ocean disposal technology, because at that time several countries had already carried out radioactive waste sea dumping. After thorough deliberation, they suggested constructing a low level radioactive waste storage facility at Lanyu Site, near the Longmen area. The following were the merits of the site: (a) isolated topography, located on seashore flat surrounded by mountains on the other three sides with no residents within 5 kilometers, (b) site area over 1 square kilometer, large enough to be worth developing, (c) Low Level Radioactive Waste (LLRW) could be delivered from sources by marine transportation, which is safe and reliable, (d) geographical position would be favorable for future sea dumping of LLRW. By the end of 1975, the Executive Yuan had approved the construction plan.
In August 1978, the Executive Yuan further approved various engineering projects. Stage I of the construction project was started in 1978. With 23 storage trenches, the storage site can store 133,728 drums of LLRW. Lanyu Storage Site has formally received radioactive waste since 1982. When it was established in 1981, Lanyu Storage Site was under the management of the Radwaste Administration (RWA), AEC. In July 1990, TPC took over the management according to the "Radwaste Management Policy" issued by the Executive Yuan, and since then the RWA has changed its position to be a regulatory body.
Safety Design of the Site
Before the site planning began, a drilling survey of geological formations and underground water had been carried out. The layout of storage trenches at the Site was designed according to the topography and the underground water table, so the length of each storage trench differs according to the topography. The height of the trench is 4.5m, 3 m underground and 1.5 m above ground. First, 5 cm of concrete and then 40 cm of reinforced concrete were laid on the bottom of the trench in sequence. The surrounding walls are made of 35 cm-thick reinforced concrete. Three layers of waterproof asphalt belt were laid both on the bottom of the trench, and between the outer wall and the earth. The elastic joint of the trench wall was sealed with 20 cm-long waterproof rubber tape and waterproof gap-filling glue to prevent underground water infiltration. According to the underground water level data, measured monthly in 10 monitoring wells at Lanyu Storage Site, the elevation of the storage trenches’ bottom is over 3 m higher than the highest underground water level. Therefore, there is no danger of underground water infiltration into the storage trenches.
Treatment of Infiltrated Rainwater
To deal with the small amount of rainwater infiltration into the trench, the Site installed an evaporation system in July 1999. The concentrations of both cobalt-60 and cesium-137 in the evaporated distillate are less than 2Bq/l, which is far lower than the discharge limit stipulated by the Safety Standards for Protection against Ionizing Radiation (effluent concentration for cobalt-60 is 269 Bq/l, and that for cesium-137 is 70.2 Bq/l). For added safety, in July 1995 AEC requested TPC to reinforce the sealing of storage trenches and undertake zero trench effluent, and to reuse the small amount of evaporated distillate to repack waste drums.
Waste Storage and Management Program
In 2007, TPC has conducted the management program to inspect the drums if those were good, rusted, deformed, or mal-solidification. Good drums were inspected and cleaned then relocated in the storage trench. Rusted drums were conducted to remove rust then repaint the drums. Deformed drums were conducted to repack in the new galvanized steel container, which enabled to hold 12 drums in one container. Mal-solidified waste was resolidified into the new drum. All drums, after cleaning, recording, and measurement, were relocated into the trench. The trench was also maintained and upgraded to the optimized status before the drum relocation. Each trench after relocation was covered by concrete plates with waterproof sealant. Meanwhile AEC officials had undertaken the safety audit on TPC management program seriously to prevent any safety accident or radiation release during operation. The program was completed in November 2011.
Most LLRW stored at the site were generated from the nuclear power plants, which included filtration residue and spent resin, solidified with cement or asphalt then sealed in 55-gal drums. By February 1996 the site has stored 97,672 drums in total and stopped receiving any radioactive waste since then. Meanwhile AEC had requested TPC to inspect the drum on site to propose a waste storage modification program, and approved such a pilot program proposed by TPC in December 1996. Because of the natural environment of Lanyu Site with high temperature, moisture, and salty ambient atmosphere, many drums stored on site for decades had shown paint scaling or rusted, even few waste in drums presented solification deformation. However the multi-barrier safety design prevented the radiation and contamination releasing into the ambient environment according to the results of environment monitoring.
To ensure the safety of Lanyu Storage Site, the Fuel Cycle and Materials Administration (FCMA), AEC inspects the site every month and audits it once a year. Once defects are found, rectification action must be taken. Due to the long duration of storage, some of the drums used in the early days are corroding. To address this, AEC has ordered the following safety measures:
- Improve the anti-corrosion performance of the waste drums: To increase the service life of the waste drums, AEC has requested all nuclear facilities to use "heat soaked galvanized steel drums" since July 1995.
- Re-examine and repack waste drums:AEC has required TPC to carry out an re-examination and repacking pilot program on corroded waste drums since Dec. 1996. For general re-examination and repacking, TPC has established the Re-examination and Repacking Center and the Waste Drums Retrieval Unit. TPC has completed the re-examination and/or repacking waste drums by November 2011.
Besides ordering TPC to submit the environmental monitoring report according to regulations, AEC has also requested the Radiation Monitoring Center (RMC) of AEC to periodically conduct environmental radiation monitoring in the Lanyu area so as to detect any variations. Direct radiation will be monitored and radioactivity analysis performed on drinking water, seawater, soil, sediment at outfall, beach sand, grass samples, seafood and seaweed. Years of radiation monitoring have shown results that are within the range of natural radiation background variation in Taiwan.
In addition, AEC has conducted a public participation program at the Lanyu environmental radiation monitoring program every year since 2011 so as to relieve the radiation pollution concerns of the Lanyu local people. AEC invited Lanyu residents, local government officials, and Lanyu township representatives to participate in environmental radiation monitoring and sampling at Lanyu. Samples are then analyzed by an independent third party (NTHU) certified by the Taiwan Accreditation Foundation (TAF). Then NTHU sent the monitoring results and analysis report to the Lanyu township office for information disclosure.
All of the monitoring results from 2011 till now have shown that they are far below regulatory criteria and at the level of environmental background radiation. It indicates that the LLW storage site at Lanyu has not resulted in any radiation pollution.
For detail results of environmental radiation monitoring and real-time information, please visit AEC's english website (http://www.aec.gov.tw/english).