A review of the applications of MCNP in neutronics for Fusion Technology at ENEA FRASCATI

In our laboratories there is a group making extensive use of transport codes to calculate the nuclear radiation fields for several kind of applications. These are confined essentially in the frame of Fusion Technology; it is not mean a restriction as many examples will show. Between the used transport codes, the Monte Carlo code MCNP has grown in significance, along the years, due its capability to handle complex geometry models, generally in 3-D, the use of continuous energy nuclear data and the powerful means to treat deep penetration problems, as required in most of the applications. The designers too, as in ITER, suggest explicitly MCNP as reference tool. It has also a solid background in documentation and quality assurance and its development has followed and still today follows strictly the computer and software technology development. These items, too, have contributed to the increase of its significance compared to the other methods and codes. At the moment, about 80% of our computer time is spent for MCNP runs, in our laboratory. An overview is given of the different fields in which MCNP has been used, in the last years: . In the design of the reference Breeding Blanket for the ITER machine. Neutronics has played a key role in the selection of the final design which has the main goal to breed > 0.8, satisfying all the thermal constrains. . In the shielding analyses of ITER respect to the Toroidal Field Coils. The powerful variance reduction techniques have allowed the proper treatment of the deep penetration problem (till 2 meters of materials to cross). Moreover the capability to handle complex geometries has allowed the analyses of the streaming through any single penetration (ports and gaps). . In the analysis of the experiments performed with the Frascati Neutron Generator (FNG) facility. The experimental results obtained in different configurations can be compared with calculated ones to validate the code itself or the nuclear data used. A big amount of work has been published which has involved many laboratories. A general satisfactory agreement has been found with all the main experimental data, (within 20-30% for all nuclear responses at 100 cm of depth). In some cases the electron transport capability of MCNP have been used in these kind of calculations. . In the diagnostic system of the multi-collimator in JET and in ITER. MCNP has been used as calibrating method. Strong source biasing has been required in this case to reach reasonable accuracy. . In the design of IGNITOR machine, for the analysis of nuclear loads and of activation components. . For the Long Term activity (DEMO reactor), the analysis supporting the design of the ITER Test Module (ITM). MCNP has shown satisfactory capabilities to handle these problems. It will be shown also how the latest version MCNP4B with the multiprocessing capability (PVM) together with the available SP2 machine in Frascati (16 processors) has given greater impulse and more power to our analyses capability.