KAERI Underground Research Tunnel, KURT

What is KURT for ?

The high-level radioactive waste generated from the operation of nuclear power plants should be carefully treated and disposed safely. The KAERI Underground Research Tunnel(KURT) is for developing a Korean disposal system for the High-level repository, which will be constructed with public acceptance in the future. KURT will be an major infrastructure for validating the safety and feasibility of the suggested disposal system by various in situ experiments.

Most of the advanced countries operating nuclear power plants have their own underground research laboratories. It is not necessary to use radioactive material in underground research laboratory, because the validation of a disposal system can be indirectly assessed by investigating the groundwater flow and rock mass characteristics. During the licensing process for KURT, The utilization of radioactive material in KURT is prohibited by law.

KURT is located at a mountainous area inside of KAERI territory in Yusung Gu, Deajeon, Korea. KURT has total length of 255m with 180m long access tunnel and two research tunnels of total 75m long. The maximum depth of 90m could be effectively achieved by selecting the tunnel direction to the peak of a mountain. The horseshoe shape tunnel with 6m wide and 6m high is located at good quality granite rock body.
터널모양
Access tunnel
Research module
Horseshoe shape
6m wide x 6m high
Length 180m
Slope -10%
Left module : 30m
Right module : 45m
Slope : 2%
Maximum depth : 90m

※ Site characterization

To investigate the geological characteristics of the site, surface survey, borehole drilling, and various in situ tests had been carried out. From the geophysiacl survey, it was possible to estimate the geological layers and fracture zones around the site. Residual weathered soil layer and silty sand containing rock fragment cover the surface. Under the layers, weathered rock, soft rock, normal rock, and hard rock layers are sequentially distributed. The host rock is granite, which is considered as one of the candidate host rocks of the geological repository for LILW as well as HLW. Andesitic dykes were encountered in several locations. Rock cores from borehole drilling showed that the rock conditions were improving with depth. During the construction, three faults and fracture zones cross the access tunnel. It was planned that the research modules to be located in relatively good conditioned rock for safe operation of the in situ experiments

※ HLW displsal system
High-level waste will be encapsulated in corrosion resistant metal container and disposed in several hundred meters deep underground repository tunnel. The hazardous radionuclies released from the waste will be isolated from biosphere by multi-barrier system consisted of several engineered barriers and natural barrier. Waste container, bentonite buffer, backfill and surrounding rock mass will act as barriers for protecting the release of radionuclides for long time.

Main steps for KURT project

From the long-term research and development for developing a reference HLW disposal system since 1997, the necessity of an underground research tunnel was raised. In Jan. 2003, it was decided to construct an underground research tunnel within KAERI territory for the validation of the reference disposal system by in situ experiments.

Site characterization and detailed design were successfully completed in 2004. In November 2004, KAERI received the construction license from municipal governments(Daejeon city and Yusung Gu) and Ministry of Science and Technology(MOST). The construction was started in Mar. 2005 and completed in Nov. 2006.

Major steps
2003. 1 Project initiation based on the National Nuclear Energy R&D Program
2003 Site characterization
2004 Basic and detailed design
2004.11 Achieved construction license
2005. 3 Start construction
2006.11 Completion of the tunnel
*Total budget : $ 3 million

Review of KURT

KURT is consisted of the access tunnel and research modules in which main in situ experiments will be carried out. To place the research modules below the top of the mountain, and to reduce the length of the access tunnel, the tunnel portal was located under the steep slope at the end of the valley.

The slope of the access tunnel was designed to be -10% in order to achieve the maximum tunnel depth more effectively. The two research modules at left and right sides of the access tunnel are 30m and 45m long, respectively. For natual drainage, +2% slope was adopted at the research modules. Controlled blasting technique was applied in order not to disturb the rock around the tunnel as well as the research facilities nearby the tunnel including Hanaro research reactor

KURT is essential facility for disposal study

The development and implementation of waste disposal projects will be essential for the acceptability of future nuclear power program. The absence of proven disposal technique for the radioactive waste, especially HLW, will act as the "Achilles' hill" of the nuclear industry. It is necessary to develop an adequate disposal system, which has long term safety under the characteristics of Korean geological conditions.

In many advanced countries, including USA, Japan, Canada, Sweden, France, and Finland, disposal concepts with an deep underground repository at several hundred meters were already suggested for the disposal of HLW. In Korea, a long-term R&D program for devleoping an HLW disposal concept was started in 1997 and a Korean reference disposal system will be suggested in near future.

At the radiological safety point of view, there is no technical problem on the geological disposal of HLW. However, an underground research tunnel is essential in order to refine the Korean disposal system based on the validation studies at the research tunnel.

The underground research tunnel will be actively used to produce fundamental data needed for establising national policies related to the management of radioactive waste. The in situ experiments based on the reference disposal system will help enhancing the public acceptance to the performance of multi-barrier disposal system as well as to the overall safety of nuclear energy.

KURT is safe

The main purpose of KURT is to study various geochemical behavior and groundwater flow for simulating the HLW disposal in deep geological condition. It is, therefore, not allowed to use any radioactive waste and radionuclides in KURT.

Instead of that nonradioactive and environment-friendly materials such as NaCl will be used to investigate the migration behavior in deep underground geological condition. In some migration tests, safe radionuclides will be used, but they are not decaying and can be treated as nonradioactive material.

KURT is classified as a general facility, and thus any experiments using radioactive material is illegal. This is formally written in the licence from MOST, Daejeon city, and Yusung district. It is common that the countries possessing underground research laboratories, including USA, Canada, Germany, France, Belgium, and Japan do not use radioactive material in in situ experiments.

KURT will be used for

The main goal of HLW disposal study is to confirm the disposal system developed based on theoretical and laboratory tests will perform as expected in real geological condition in deep rock mass. It is, therefore, required to construct the underground research tunnel in similar geological condition as the HLW repository.

Various in situ experiments such as fluid flow through discontinuities, migration of ion and colloid, and heater test will be carried out for validating the disposal safety of HLW. Long therm safety assessment, geochemical condition, groundwater system, and geological condition will also be performed.

Single Hole Heater Test in Rock
HLW will generate heat when radioactive materials in the waste ar decaying. Because of the decay heat, surrounding rock temperature will increased and that will result in thermal stress, deformation, and mechanical strength change. It will also influence on the groundwater flow pattern and geochemical condition. Such a change for long time will affect on the long term performance of engineered barriers and damage on the repository safety. In the single hole heater test, a 5 kw heater is installed in the heater hole, which has diameter of 11cm. During the heating and cooling phases, overall thermal-hydro-mechanical coupling phenomenon with a consideration of the infleunce of joints and characteristics of excavation damaged zone(EDZ) will be investigated.

THM Behavior of Engineered Barrier System
One of the major part in HLW disposal system is the Engineered Barrier System(EBS), which contacts the waste and receive thermal and mechanical stress from the waste more or less directly. In the THM behavior test a test hole sized 2m diameter and 5m deep will be excavated in the tunnel floor. In the test hole, 1.2m diameter and 2m long cylinder shape electric heater (3kW) will be installed.
The space between the heater and rock will be filled by compacted calcium bentonite blocks with dry density of 1.6kg/m3. The e temperature at the buffer and heater conatct will be controlled to maintain below 95℃. From the test, the temperature distribution, resaturation, and swelling pressre change with the infilteration of groundwater from the rock into the engineered barrier will be investigated.

EDZ Characteristics and Mechanical Stability of Rock
Excavation disturbed zone, in which the physical and chemical properties are changing from the original properties, is developed around a tunnel during or after excavation. The zone influences the mechanical stability and groundwater flow. In the EDZ test, rock mass property and in situ stress change will be measured to determine the characteristics of EDZ. The rock cores collected before and after the excavation will be used to compare the thermal and mechanical property change. Different geophysical tests will be applied to determine the EDZ size. From the study, primary parameters affecting the development of EDZ will be derived and the thermal, hydraulic, and mechanical properties will be determined. These will be used for the computer modelling for evaluating the stability and disposal safety of an underground repository.

Retardation of Solute Migration through Fractured Rock
In the solute migration test, the characteristics of solute retardation by the filling minerals in rock fractures. Small scale fractures or faults on tunnel wall will be chosen for inserting adhesive solution. After test the rock mass containing the fractures or faults will be extracted to investigate the characteristics of migration and pathways and the effect of filling minerals on the solute migration. An in situ test for observing the interaction between the solute and minerals and the colloid filtering phenomenon in the rock factures will be carried out.

Site Investigation Techniques
It is possible to develop QA(Quality Assurance) procedure, which is required for various test using deep boreholes. In the site investigation test, deep geological survey techniques as well as QA procedure for different borehole tests. From the activities, it would be possible to secure various techniques related to deep borehole drilling, rock core survey, rock and groundwater sampling, hydrological testing, borehole logging and alanlysis, long-term monitoring, and etc.

Hydrogeological and Geochemical Baseline Data
It is necessary to provide hydrogeological and geochemical boundary conditions for different in situ experiments in KURT. For that, transition zone to reducing condition, groundwater pressure change with depth, long-term monitoring of groundwater, inflow of groundwater, and major geological structures around the tunnel will be investigated.

URLs in other countries

Many countries generating electricity from nuclear power plants try to improve HLW disposal technique from in situ experiments in underground research laboratories. The results from the experiments are published and contributed to the development in other areas.

KURT developed by KAERI will be used for various purposes including the development of disposal system, which is adequate for Korean geological condition, the development of underground space, and the investigation of geological condition in deep underground. That will contribute on enhancing the level of other related fields.