THE COLD NEUTRON SOURCE OF GKSS

The Cold Neutron Source (CNS) is operated with hydrogen beyond the cri tical point (p = 13.2 bar and T = 14.2 K) where hydrogen is still gase ous. The operation values of the CNS are T similar to 25 K and p = 15 bar. The supercritical gaseous hydrogen is circulated by a blower (for ced circulation system) at 1 l/s through the moderator chamber and the H-2/He-heat exchanger. However, during reactor operation it was obser ved that the CNS remains under normal operation condition (T < 35 K), even if there is a failure of the H-2-blower. This surprising observat ion is due to the fact, that a stable natural convection is cooling th e CNS during reactor operation. A detailed study confirms the stabilit y of the natural convection. Hence, in the future the CNS will be oper ated not only by forced circulation but also by natural convection.