Safety goals and design criteria for small heating reactors

Abstract

Small (10–50 MWth) reactors as decentralized sources of heat are being discussed in many countries. Such reactors are economic only if they can be built near their consumers of energy, and only if they can operate for most of the time unsupervised or unmanned. Existing rules or regulations currently applied to conventional nuclear power plants also apply, in principle, to small reactors. Intuitively, the rather unusual design requirements of unmanned operation and, to a lesser extent also, the siting mandate have to be compensated by an increase in rigour in particular criteria. Such an increase can only be judged subjectively, since neither operational experience nor satisfactory risk assessments for district heating reactors are available at this time. The Swiss Nuclear Safety Inspectorate (HSK) has attempted to lay down some basic safety goals and design criteria, which reflect the need for unmanned operation and the exceptional siting mandate. The goals and criteria so prescribed are not meant to be a firm set of regulations but rather serve as provisional requirements for reactors of this type. Over the last few years three competitive designs for small heating reactors have been proposed by Swiss design teams. These have shown that it is possible to design such reactors which comply with the HSK proposed safety goals and criteria, and still remain economically attractive.