[en] This paper describes the development of a measurement concept for a clearance of mercury waste from the decommissioning of nuclear facilities. A decontamination of mercury is performed after which large parts of the waste could possibly be released into reuse or conventional mercury disposal. The focus of this work is on the development and validation of a gamma-spectrometric measurement setup that is used for decision-making measurements for a possible clearance procedure. The measurement system is validated by a comparison of experimental measurements with nuclear simulations using Monte Carlo N-Particle^R Transport Code (MCNP^R). The validated MCNP^R simulation model is used to determine the energy-dependent photopeak efficiencies and subsequently the sensitivity of the measurements. Preliminary results of gamma spectrometry in combination with MCNP^R simulations indicate that a clearance of elemental mercury should be possible after decontamination. (authors)