Abstract Thermochemical heat storage may become a key technology in balancing intermittent renewables by regulating production and demand peaks and in increasing the efficiency of energy systems by reusing waste heat. Nowadays, there is a limited number of commercial products based on this technology, and for larger market penetration an improvement of the technology must be achieved. To advance thermochemical heat storage systems, one has to pay particular attention to studying the processes occurring inside the reactors. For the investigation of the sorption processes with further optimization of the reactor design, a local numerical model of the reactor, carefully validated at the local and global scales, is of significant importance. In the present study, we developed a three dimensional local model of a thermochemical reactor that utilizes ammonia sorption on solid SrCl2. This model simulates the effects of the chemical reaction, heat transfer, and mass transfer separately, and this is its main difference from already existing SrCl2-ammonia models. For the model validation, we used neutron radiography, an alternative to the conventional techniques, i.e., temperature and flowrate measurements. In contrast to these, neutron radiography allows following the state of the reactive bed not for a discrete number of points but via a 2D map. The results of the study demonstrate that the model developed herein is in a good agreement with the detailed neutron radiography data. Since neutron radiography was used as a validation tool for a numerical model for the first time, the procedure of the comparison between the results from our model and neutron radiography was carefully documented. An additional, successful, validation was provided through temperature and flowrate measurements.