PALLAS has opted for a pool-type reactor. A special variant of this is a tank-in-pool-type reactor. In such a reactor, the water basin provides space for fuel elements and control rods. The fuel elements are responsible for the formation of the neutrons during nuclear fission. The PALLAS-reactor is designed to operate with low-enriched uranium, which means that the amount of uranium-235 (235U) is less than 20 per cent of the total amount of uranium used (mostly 238U).