The movement of groundwater is the deciding factor in characterization of geological disposal sites for high level radioactive wastes. As radionuclides leaking from a disposal facility will migrate with groundwater, a small groundwater flow velocity is an advantage in safety assessment. There are many methods for investigating groundwater flow. Central Research Institute of Electric Power Industry (CRIEPI) has focused on developing new techniques to reveal macro- and micro-circulations of groundwater in deep strata. We introduce following four new techniques developed by CRIEPI, after reviewing the tracer techniques for groundwater survey.
(1) New dating method of groundwater
CRIEPI has developed and demonstrated the 3H+3He dating method to survey the flow of groundwater in a large geohydrologic catchment area. This method is based on counting the increase of 3He produced by β-decay of 3H in groundwater. This is available for determining the direction and velocity of groundwater flow from dating data.
(2) Development of a point groundwater flow meter to determine the direction and velocity of groundwater crossing a single hole
CRIEPI has developed a technique that can gauge the velocity and direction of groundwater flow to 10-6cm/s in a single hole, which were difficult to detect by conventional methods.
(3) Development of a cross-hole pressure propagation test method
CRIEPI has developed the cross-hole pressure propagation test method among several holes to make an assessment of groundwater flow in fractured bedrock. This is available for measuring a very small hydraulic conductivity 10-8 to 10-9cm/s.
(4) Development of a multi-functional permeability test device equipped with TV-camera.
CRIEPI has developed a test device that can visually observe the movement of groundwater by a TV-camera in the test duration of low and high pressure water injection as well as in that of spring-water test. This device might be a strong weapon for pearmeability test in fractured bedrock.