New critical experiments in the framework of an IAEA Coordinated Research Program on `Validation of Safety Related Reactor Physics Calculations for Low-Enriched HTR's' are planned at the PSI PROTEUS facility. The experiments are designed to supplement the experimental data base and reduce the design and licensing uncertainties for small- and medium-sized helium-cooled reactors using low-enriched uranium (LEU) and graphite high temperature fuel. The main objectives of the new experiments are to provide first-of-a-kind high quality experimental data on: (1) the criticality of sample, easy to interpret, single core region LEU HTR systems for several moderator-to-fuel ratios and several lattice geometries; (2) the changes in reactivity, neutron balance components and control rod effectiveness caused by water ingress into this type of reactor; and (3) the effects of the boron and/or hafnium absorbers that are used to modify the reactivity and the power distributions in typical HTR systems. Work on the design and licensing of the modified PROTEUS critical facility is now in progress with the HTR experiments scheduled to begin early in 1991