Major improvements backfitted into 69-line BWR plants

Very specific rules and regulations for the design, construction, choice of materials and in-service inspections of components of nuclear power plants were adopted in the Federal Republic of Germany from 1978 onward. This led to the replacement of high-tensile, fine-grained structural steel varieties, which were more difficult to process, by less high-tensile, but tougher steel grades easier to use. The new requirements also entailed the replacement of major components because of their materials. In addition, independent emergency core cooling systems and residual heat removal systems were installed. Some of these backfitting measures undoubtedly were necessary, while the usefulness of others remains a matter of dispute. As a consequence of the incident at the Wuergassen Nuclear Power Station, all subsequent safety discussions were led in a highly theoretical manner, especially those about boiling water reactors, the outcome being that often maximum measures were taken in order to increase theoretical plant safety, which did not add to nuclear safety. In the majority of cases, much less extensive backfitting would have been sufficient to reduce the so-called residual risk. Knowledge about the quality status and the burst safety of pipes has been augmented. It is safe to say that the maintainability of plants and, hence, their operational reliability and availability has been optimized as a consequence of improvements in the layout and accessibility of pipes and a reduction in the number of welds. The engineering features of this type of boiling water reactor had rightly been doubted in a few weak spots, but wrongly so in a general way, merely for the existence of those spots. (orig.)