The helium-cooled high-temperature reactor in the Federal Republic of Germany: safety features, integrity concept, outlook for design codes and licensing procedures

Abstract

In the Federal Republic of Germany, the helium-cooled high-temperature reactor (HTR) and the fast breeder reactor are being promoted as advanced nuclear reactor systems. The HTR development based on spherical fuel elements has led to the construction of a 300 MW el prototype reactor, the THTR 300, following favourable experience with the operation of a small experimental reactor, the AVR. The THTR 300 became operational in the mid-eighties. It has exhibited good service behaviour and has confirmed the favourable safety characteristics of the system. At the present time, two HTR concepts are being followed up by German companies, a small HTR (approx. 200 MW th) with a steel pressure vessel and a medium-sized reactor (approx. 550 MW el) with a prestressed concrete pressure vessel for electricity generation. The special safety features of the HTR originate in the core construction of ceramic materials resistant to high temperatures and the low power density of the core. An analysis of the technical safety features shows that the general activity containment concepts developed for light-water reactors (LWR) are not transferable to the HTR. It was necessary to develop technical safety concepts especially for the HTR, and the result is the HTR integrity concept. Technical guidelines and design codes for nuclear plants in the Federal Republic of Germany are tailored to the LWR systems, so that a design code for the HTR had to be formulated. In an extensive research project, the underlying principles for such a design code have been worked out. Licensing procedures have been established for the design, construction and commissioning of the prototype THTR 300 and invaluable experience has been gained. A concept for licensing approval of the HTR module plants, independent of the siting of the modules, is now being investigated.