[en] This review will not survey the 20 years with all the efforts made in different countries to develop higher density fuel, to perform test irradiations and typical prototype fuel irradiation experiments, post irradiation examinations and actual core conversions. The emphasis is directed to the situation a few years ago when efforts have been rapidly slowing down, and the situation today after having had an international wake up call and comparing these efforts with the primary demand to reduce the proliferation risk worldwide and to have this as an indispensable goal of the international politics. The RERTR program is being back on the stony way. There are some (many?) hopes but many doubts to have the RERTR program a real success. Such a success needs the strong continue support and activities of many governments and especially of the IAEA for years. (author)