A 5 MW swimming pool research reactor has been in operation at the Hahn-Meitner-Institute in Berlin from 1973 to 1985. In 1985, itwas shutdown for an enlargement of the slow neutron flux by a factor of 1014to several cm−2s−1. This enlargement is achieved by a new fuel arrangement, by adding a Be-reflector and by increasing the reactor power to 10 MW. In addition, a cold source has been installed.