Aspekte des Einsatzes von Systemen zur Transmutation radioaktiver Stoffe : Neutronik, Technik, Sicherheitsverhalten

Theoretically, nuclear facilities can be envisaged which transmute toxic nuclear isotopes, typically the spent fuel from PWR's, into isotopes with a considerably lower longsterm toxicity potential. The way to attain that goal is to fission longslived actindes yielding short-lived fission products while specific toxic and very mobile fission products are transmuted by neutron capture. Suitable nuclear facilities can be critical reactors or subcritical systems. The latter are driven by an external neutron source being provided by high energy protons spalling especially heavy atorns within a so-called target (spallation process). In the past most of the work concentrated on the physical aspect i. e. the neutronics of certain favoured systems. The fluid fuel suberitical systems contrived by Los Alamos National Laboratories (ATW) are a good example for that phenomenon. Questions concerning the technical feasibility or the safety of the proposed facilities are only dealt with as an sidesissue. Moreover, the advantages and drawbacks of certain transmutation schemes with their specific interrelation to partitioning has not been sufficiently assessed. The aim of this study is to dose that gap starting with a review of the incentives for transmuting radioactive materials. Special attention is payed to the significance of toxicity potentials and the losses in the fuel cycle. Different nuclear facilities are compared with regard to their potential for incinerating nuclear waste . The neutronics of a typical fluid fuel System is investigated on the basis of the Los Alamos ATW concept. Another recent development, the Integral Fast Reactor, serves as the reference System for a study on differences in the safety behaviour of critical and subcritical systems. As expected, the subcritical system has certainadvantages but is not automatically safer than a similar critical System. lt seems to be more noteworthy that subcritical systerns have a further nuclear degree of freedorn which helps in transmuting actinides as well as fission products. A system using liquid lead as both a coolant and a carrier of the actinides has been contrived and investigated. External cooling loops as well as internal cooling forms seern to be technically feasible. Transmutation with this kind of facilities seems to be promising, since no unsurmountable technical Problems are to be expected