Recent developments in neutronics

The broad approach to fusion presents a number of new changes for neutronics calculations which must cover the analysis of ITER, DEMO, spherical tokamaks and IFMIF. Radiation transport modelling is essential for both the design of these machines and as input to licensing. Recent developments in the field of neutronics are characterised by the need for greater detail, a more rapid production and dissemination of results and the application of new computer technology to address these issues. In recent years Monte-Carlo codes such as MCNP and McBend have been deployed on parallel machines to allow larger more detailed calculations to be carried out. The latest discrete ordinates codes such as Attila can model detailed geometries in 3D. These developments permit more sophisticated representations of the components and the ability to derive their specification directly from CAD designs is being developed. The benefits of these developments are demonstrated in this paper using examples of the design of components for ITER and of IFMIF. An analysis of the RF antenna using Attila was used to assist in the design of shielding in order to minimise the activation behind the port plug; a study of the LIDAR and the polarimeter system was used to aid port integration; and a comparison the efficiency of discrete ordinates codes with Monte-Carlo methods was carried out using calculations of the shielding around the IFMIF target. The use of complementary techniques allows the solution of previously intractable problems related to deep shielding and solution accuracy. These examples also serve to illustrate some of the difficulties and advantages of the use of computer aided design which have implications for the wider design philosophy of ITER. The problem of the dissemination of the results to design engineers and the archiving of results if is being addressed by the development of an integrated results database and QA system. (orig.)