The reactor core consists of maximum 85 fuel elements (3.75 cm in diameter and 72.24 cm in length), which are arranged in an annular lattice. Two fuel elements have thermocouples implemented in the fuel element which allow measuring the fuel temperature during reactor operation. At nominal power (250 kW), the center fuel temperature is about 200 °C. Because of the low reactor power level, the burn-up of the fuel is very low. The first core operating for about 50 years was shipped back to the US in November 2012, new fuel was transferred from the US to allow further operation into the next decade.