Abstract
Due to the mismanagement of nuclear waste as well as heat exchanger degradation for the primary coolant of the one megawatt nuclear research reactor, the fission product 137 Cs has been leaking to the environment ever since 1969. In the past thirty years, the long-lived 137 Cs was accumulated and eventually trapped in the mud of the discharge pond right in front of the waste storage and the reactor facility. The distribution of 137 Cs in mud was measured and contour-mapped to reveal the migration of trace levels of 137 Cs in a period of three decades.