Overview on Nuclear Design Problems of Accelerator-based Transmutation Systems with Emphasis on Target Facilities and Their Interfaces with Accelerators

INTRODUCTION Recently, accelerator-based nuclear waste transmutation has been attracted much attention because of remarkable development in accelerator technology. Nevertheless, concepts of tmnsmutation system proposed so far are limited in number and furthermore they are all in the stage of conceptual or pre-conceptual design study. They are also preliminary, and many challenging problems are left to be solved to detail designs and to establish the technical f-ibility of their concepts. In the absence of detailed design studies, it is premature to evaluate quantitatively the pertinent problems and to identify the priority technical issues due to their impacts on the system designs. The purpose of this paper is not to attempt to give a comprehensive surveyor critical review of generic nuclear design problems related to the accelerator-based transmutation systems. It is aimed at providing points to be discussed in this Specialists' Meeting. To illustrate the design considerations of a practical system, a conceptual design of accelerator-based minor actinide transmutation plant(l) made at the Japan Atomic Energy Research Institute (JAER.1) is briefly described as an example of the proposed systems. The 113 plant transmutes about 250 kg of minor actinides by fission and produces 820 W thermal power by using a 1.5 GeV proton beam with a current of 39 mA. Electric power of 246 MW is generated with a conventional stare turbine, and supplies sufikient electricity to power the accelerator. Some problems arising from the design study are presented. Emphasis is placed on the problems related to the nuclear part of the plant design. The scope of this paper also covers such potential problems in other engineering design and in overall system design that may have significant impacts on system nuclear performance. JAERI CONCEPT A conceptual design study was made for a nuclear waste transmutation plant which consists of a high intensity proton accelerator and a sodium-cooled subcritical core with minor actinide alloy fhels and a tungsten target. The plant is designed to bum minor actinides from about 10 units of 3000 MWt LWR and to generate suffkient electricity to supply to its own accelemtor. Schematic diagram of the proposed plant concept is shown in Fig. 1. High current proton beam with the energy of 1.5 GeV is injected into the tungsten target region of the core. Heat genemted in the target and the minor actinide fhels is removed by the forced flow of liquid sodium coolant. The heat is transported through …