Yangyang pumped storage power plant
The Yangyang pumped storage power plant (Yangyang plant) located in Yangyang-gun, Gangwon-do is the biggest energy storage plant in Korea. It has 1000 m of water head-height, the highest in Asia as shown Figure 1. The plant is about 300 km from Daejeon, where the IBS HQ is located. Since August of 2006, it started to produce commercial electricity and can produce up to 250 MW using its four turbines at full capacity.
The main facilities of the power plant such as power generation turbines are located at about 700 m below the surface. In the underground, there are several work tunnels (work adits) around the main facilities as well as the main tunnels. The underground experiment group has been maintained one of those work adits called A6 with a generous agreement of the power company who is running the plant. In July 2013, as soon as the Center for Underground Physics(CUP) was started as one of research centers of the IBS, the construction of another small underground experiment facility in the A5 tunnel was started, reaching completion at the end of 2014.
Y2L-A5 underground facility
In 2003, when the Yangyang power plat was constructed, the Dark Matter Research Center (DMRC) of Seoul National University completed construction of the Y2L-A6 lab site having about 100 m2 area and located at ~700 m depth. In order to directly detect a dark matter candidate, Weakly Interacting Massive Particle (WIMP), in the Y2L they built and operated an experiment with a set of CsI(Tl) detectors. A High Purity Germanium (HPGe) detector system was also constructed and has been operating since.
In the Y2L-A6, it was impossible to expand space further because of topographical constraints. In November 2014, CUP built another underground facility with an area of ~200 m2 in the A5 tunnel, located near the A6 site. This experimental facility is named as Y2L-A5. Right after the Y2L-A5 construction, AMoRE detector (2015), COSINE detector (2016), and a HPGe array (2017) were built subsequently.
The laboratories of Y2L-A6 and A5 are both located at a depth of 700 m. The muon reduction rate, estimated by simulation, is about 10-5 times the surface flux, and the muon flux measured by the COSINE detector at the A5 laboratory is ~4 × 10-3/m2/s. Those numbers are consistent with each other considering that the typical muon rate of ~102/m2/s at the surface. The Y2L-A5 muon rate is also consistent with the measured data at LSC (Laboratorio Subterraneo de Canfranc), one of the world-famous underground facilities. The muon fluxes in different underground laboratories around the world are shown in Figure 2, plotted against the lab depths.
The Y2L-A5 facility consists of two clean rooms and monitoring rooms for each experiment, and several support systems such as a radon-reduction-system, a water-cooling system (PCW), and an electrical room (Figure 3). Also, for the safeties of workers, there are fresh air supply/exhaust system, fire alarm equipment, and a smoke removal system in case of a fire.
Areas of the two clean rooms are 45 m2 and 49 m2 for AMoRE and COSINE experiments respectively. These clean rooms have been maintained as 10,000 class clean rooms with air shower booths and air supplied by dedicated BFUs. In addition, radon free air is supplied to both clean rooms and the air-shower booths from the radon-reduction-system through stainless pipes.
The total electrical power capacity for the Y2L-A5 facility is 180kW which is distributed to each room with 380V and 220V in three phases, and 220 V in single phase. To protect against unplanned outages, an 80 KVA UPS system has been installed to supply all critical powers. The UPS is able to cover power needs for a one-hour outage. Furthermore, for a supply of stable constant voltage, an AVR (Automatic Voltage Regulator) system has been installed.
As mentioned above, the radon-free air system (Figure 4) has been supplying ~120 m3/h of radon-reduced air with about 10,000 of reduction factor. Other significant equipment in the Y2L-A5 includes the Process Cooling Water (PCW) system. In order to cool down the compressors for the AMoRE detector and Radon free air system, 1 ton and 0.5 ton of cooling water is supplied to each per hour.
The ground office with about 80 m2 area is located within 2 km from the entrance of the Yangyang power plant. Three dedicated staff members, including one scientist, monitor and manage the whole facility of the Y2L. When a common emergency occurs, such as a power failure, they not only disseminate information to relevant researchers but also handle the situation themselves if necessary. Especially in case of a serious emergency like a fire, alert systems will automatically notify the Yangyang power plant monitors, the nearest fire station, and the relevant CUP members. However, for certain experiment-wide emergencies, the responsible researchers must respond to the issues.
The AMoRE and COSINE groups dispatch shift workers to Y2L for 24 hours monitoring of their systems to prevent occurrence of unexpected situations. The Y2L is operating based on a systemized management policy that is still being improved, so that measures can be taken immediately.
A part of experiments and facilities in Y2L are going to be moved to a new underground space from 2020, when the new underground laboratory starts operation. Some experiments such as COINE will continue operation in Y2L until 2025.