All materials from shut-down nuclear facilities must be measured and classified for radioactivity content prior to being stored in a radioactive waste repository, or sent to landfill.  The regulators in different European countries have established strict limits based on both activity and different radionuclides, which is the reason why a free release measurement facility must be spectrometric and very sensitive.

The Free Release Measurement Facility, which is being validated in MetroDECOMII,  was installed in CIEMAT, Madrid in the beginning of 2019. This facility is made with specialised very low activity concrete bricks which provide a low-level background shielding for the measurements, and it contains four mechanically coolled  HPGe detectors for gamma-ray detection, four plastic scintillators for pre-selection of wastes, and three neutron detectors. The total weight of the facility is over 70 tons. This facility is transportable and can be dismounted and mounted at another location within two weeks.

The facility calibration is based on validated Monte Carlo calculations using MCNP and PENELOPE codes, and measurement efficiencies can be calculated for an almost unlimited number of measured waste materials. Monte Carlo models have been validated using traceable reference materials (steel balls and tubes, gravel, clay balls) and point-like radionuclide standards produced and certified by European metrology institutes.