The Y2L-A5 facility was planned only for AMoRE R&D experiments (pilot and phase-I) and not for a full-scale experiment (phase-II). Full size detectors for AMoRE Phase-II, a low-mass dark matter search, and dark-photon experiments require much larger spaces than available at the Y2L-A5. As size of a detector increases, it is natural that scale of the experiment space also increases. According to their plans, it is necessary to have about 600 m2, 250 m2, and 200 m2 areas for AMORE phase-II, a low-mass dark matter search, and HPGe experiments respectively. Additional area of 900 m2 or more is required for coming next generation experiments such as searches for dark matter and dark photons, as well as neutrino experiments. In order to secure such a large space, we studied an expansion plan of the Y2L-A5, but it was not approved by the Yangyang power plant. Thus, we started a systematic search for an alternative location.
For more than two years, we explored locations throughout the country to find a suitable site for construction of a new underground lab. In early 2016, we decided to choose an active iron-ore mine. The company, Handeok Iron Ore Co., Ltd., is the only iron-ore mining company in Korea at the moment. The mine is located in Jeongseon-gun, Gangwon-do, in the middle of the main mountain range of Korea (백두대간). A construction plan was established in the middle of the same year. We started the construction from September 2017 after making a complete list of all necessary administrative procedures, negotiated one by one. The construction work is currently in progress as planned.
The new underground facility, called as Yemilab, will have 1000 m thick overburden and 3000 m2 size experimental area. It will house experiments that cannot be carried out in the Y2L with its 200 m2 area and 700 m overburden.
Yemilab construction will utilize favorable access features of the Handeok mine. The site has a 600 m deep vertical shaft referred to as “second shaft” (The “first shaft” is older and only 300m deep). As well, it has a 6 km long transportation tunnel (“ramp way”). Existence of these two access routes was a strong motivation in selecting this site. Especially, the second shaft can provide a quick access to/from the underground. The second shaft is expected to work as primary entrance and exit path to/from the underground lab during both construction and operation. Furthermore, we can make the access tunnel shorter for the same overburden when we start the excavation at the bottom of the shaft. This shaft will be one of the most important elements in the new underground facility. The 6 km long ramp way has a 5 m 5 m cross-section providing an alternative path for transporting large equipment that cannot be moved through the shaft.
Construction of the Yemilab has started in earnest with an agreement with Handeok in December 2016 (the first contract on construction and operation of the Yemilab). The second contract with Handeok for construction of a cage in the second shaft was made in August 2017, with a contract with CM (Construction Management) for the whole Yemilab construction finalized in September 2017. The third contract with Handeok for construction and installation of the cage was made in December 2017, and a contract for the Yemilab’s working design was signed in December 2017 (Figure 1). The working design is completed in the end of May, 2018. The construction of the cage is going to be completed by the end of 2018.
Figure 1: Milestones of the Yemilab construction
The Yemilab construction consists of four independent sub-constructions, construction of the shaft cage, excavation of the tunnel, constructions of underground labs and ground office. The cage is one of the basic facilities for accessing the new underground laboratory. It is going to be installed in the second shaft of the Handeok mine, and is under construction now. The cage parts are custom-made by SIEMAG TECHBERG (SIEMAG), a German mine facility company, delivered at the end of June 2018, and installed in the second shaft. SIEMAG is carrying out the design and supervision of the installation, as well as cage production. The major specifications of the cage are summarized in Table 1. Construction of the cage is completed in October 2018, and currently under two months of commissioning operation. It will be in normal operation mode in early 2019.
Table I-10: Basic data for men-riding cage. ML indicates sea level.
|Shaft dimension||D = 6m, L = 627m|
|Shaft top station||+552 ML|
|Shaft sump||-75 ML|
|Bottom station||-35 ML|
|Hoisting distance||~ 587 m|
|Power supply||440V, 60Hz|
|Maximum payload||1,500 kg|
|Hoisting speed||4 m/s|
|Hoisting hours per day||18|
|Working days per year||300|
The IBS cage will be operated by a dedicated operator for transportations of researchers and research-related hardwares.
The largest part of the Yemilab construction is tunnel construction. This involves excavating about 57,000m3 of tunnel volume including both the ingress tunnel and the experiment tunnels. The access tunnel starts near the bottom of the second vertical shaft, and will have a length of about 800 m. The basement section will begin at the end of the access tunnel. Volume of the experiment area will be about 25,000 m3; depth is expected to slightly exceed 1,000 m on average. The direction and length of the Yemilab tunnel were determined by simulation studies on muon reduction rates based on a topographical map of the area (Figure 2).
The working design of the tunnel was completed by Sam An Engineering Co., Ltd., selected by a public bidding process, with the design period encompasses 5 months from December 2017 to May 2018.
A conceptual diagram of the tunnel structure was ready on March 23, 2018 as shown in Figure 2. The working design for the construction was confirmed through internal and external review procedures.
Figure 2: Yemilab tuunel on a muon flux gradient map. The muon flux gradient is calculated by a simulation with a topography of the Yemi mountain. The access tunnel will go along the most effective direction for muon reduction.
Figure I-39: A layout of Yemilab tunnel.
The new underground space will consist of twenty-six laboratories for eight experiments and ten support rooms. Sixteen labs will be constructed as clean rooms of better than class 10,000. An underground experiment facility with a total area of about 9,000 m2 and a volume of 60,000 m3 is scheduled to be completed in the fall of 2020 with anticipated operation of at least thirty years. After the construction is completed, about two to three months of commissioning operation is planned.
Figure I-40: A design of the Yemilab experiment tunnel.
A roadmap for the construction is shown in Figure 5. Tunnel construction is scheduled to begin by late 2018, and subsequently design orders are being planned for constructions of underground labs and the ground office.