In-situ tracer test in fractured rocks for nuclear waste repository

Due to sustained interest in underground nuclear waste repositories since the 1970s, numerous in-situ tracer tests have been extensively conducted in underground research laboratories or facilities over distances from centimeters to hundreds of meters to determine the key parameters of transport and retention of radioactive nuclides in fractured rocks. The most direct observation results in a tracer test are concentration breakthrough curves, but how to separate the characteristic times of transport and retention based on concentration breakthrough curves alone is still a challenging task. At present, there is a debate concerning how, and to what extent, in-situ tracer tests can be used to evaluate large-scale and long-term transport and retardation behaviors of radioactive nuclides in fractured rocks. To promote the application of in-situ tracer tests to site characterization of subsurface fractured rocks, we first review the in-situ tracer tests conducted in different underground research laboratories or facilities for developing the concept of nuclear waste disposal. Based on the experiences and lessons learned from those in-situ tracer tests, the design and performance procedures of in-situ tracer tests, as well as data interpretation methods, are addressed and discussed to provide the reference and guidance for the future in-situ tracer tests in fractured rocks. Finally, the developments and challenges involved in in-situ tracer tests in fractured rocks are highlighted.