Estimation of IFMIF Test Cell Shielding Performance by 3D Calculations (MCNP-TORT)

In order to contribute to establish shielding design criteria, the Bologna group has produced a package of libraries, codes and procedures, for multidimensional shielding IFMIF evaluations: Vitenea-IEF, a new intermediate energy coupled 256-neutron till 150 MeV and 49-gamma-ray till 100 MeV multi-group cross-section library in Ampx format, suitable for Sn radiation transport codes; ANITA-IEAF, a code package able to manage the many reaction channels that open for neutron energies higher than 20 MeV and up to 150 MeV; Libtort, an utility sequence for the production of working libraries for TORT; Proctort, an utility module able to manage the TORT output data file in order to retrieve, process and calculate the various nuclear responses, i.e. neutron and gamma fluxes and dose rates. The 2003 ENEA activity was devoted to the qualification and application of 3D methods, TORT and MCNP-4C2, for the IFMIF dose rate evaluation. The MCMP calculations estimated the dose rates in the Test Cell and its surrounding areas for a “safety conservative geometry”, Concrete ANS, 405 cm, He- 20%, for Beam-on/Start of cycle operational phase, at various detector surfaces in different directions. The total dose rates for the Frontal, Lateral, and Floor directions are less than the recommended one (10µSv/h)(Access/Maintenance room, Test Cell Technology room and Temporally Storage Pits). In order to check the shielding effectiveness, TORT calculations were performed considering various shielding configurations differing in: concrete material composition, He-cooling system treatment and Test Modules location. The Vitenea-IEF library was converted to TORT format via SCALENEA-1 (application of the Bondarenko shielding factor treatment) and GIP module. Two Test Modules locations were considered. The concrete JAERI heavy shows a better shielding performance than the Standard ANS one. The dose rates when the cooling is considered are about 3-4 times higher than when it is not. The presence of the Test Modules inside the Test Cell modifies 2-3 times only the dose rates at the frontal surface. The MCNP-4C2, TORT and 1D SCALENEA-1 dose rate results for the “safety conservative geometry” are in good agreement, within 15% (Frontal direction, 2.55 µSv/h, 2.33 µSv/h and 2.45 µSv/h, respectively). The 1D spherical-thickness-equivalence-approach appears to be a suitable fast method to perform preliminary IFMIF dose rate calculations, useful as an auxiliary tool with 3D methods. The assessment performed with TORT has outlined that important parameters that characterise the shielding design are the concrete composition, its compactness (He-cooling treatment, etc.) and, especially for the Frontal direction, the location-identification of Test Modules inside the Test Cell. As a general conclusion, for shielding estimation and evaluation of all the radiological hazard sources in IFMIF facility, MCNP-4C2 is used as reference code system while TORT for detailed calculations, due to its friendly handling-processing input and output data and its less time consuming, hours instead of days, than Monte Carlo methods.