Prime pagine RA2010FUS:Copia di Layout 1 - ENEA - Fusione

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068 progress report 2010 Figure 3.24 – Picture of the ITER Mock–up assembled at FNG Front casing Front insulation 1st winding 2nd winding Side and rear casing 1st layer SB 1981 1982 Back of SB 2041 2047 CuCrZr Rest of coil Thermal shield IVVS Side and rear insulation VV outer shell VV inner shell 3rd layer FW Manifolds First wall Figure 3.25 – The radial section on the inboard side of the latest ITER Alite model Figure 3.26 – MCNP model (equatorial section (z=0)) 3.5 Neutronics Neutronics shielding experiment on a mock–up of ITER: dose measurement in the magnet coils In the ITER design it is important to minimize the uncertainty in the estimates of the nuclear loads; in particular, the nuclear heating of the TF coils in the inboard leg is the most critical. To this purpose, accurate radiation transport calculations of the shielding is requested. These calculations are very challenging, since the radiation attenuation from the first wall to the TF coils can be many orders of magnitude and, at the same time, accuracy of the order of ±10% or better is required. The calculation must be benchmarked as far as possible against suitable experiments to attain the necessary validation of nuclear data and codes used. To check whether the present design calculations are able to evaluate the shielding properties of the ITER shield at inboard side with sufficient accuracy and reliability, an experiment was realized at the Frascati Neutron Generator (FNG) of ENEA–Frascati. The experiment was commissioned by ITER IO. In this experiment, a mock–up of ITER inboard shield, vacuum vessel and TF coils was replicated and irradiated by 14–MeV neutrons (fig. 3.24). The mock–up also included the borated steel plates presently foreseen by the design as well as some pieces of the actual superconducting cables, which represented the actual experimental region (TF coils). The final mock–up dimensions and materials compositions were based upon the dimensions and materials of the latest version of the Alite Monte Carlo n–Particle (MCNP) model of ITER (fig. 3.25). The resulting nuclear heating in the TF coils was measured by using state–of–the–art experimental techniques (high sensitivity thermoluminescent dosimeters), and compared with calculations performed with the MCNP code and the ITER reference nuclear data library FENDL.–2.1. The experiment also included the measurement of selected reaction rates along the central axis of the mock–up as well as in the coil region. These measured quantities were compared with the results of calculations too. A very detailed model of the experimental set–up was used (fig. 3.26). In this way, the highest level of accuracy was attained in the ratio between the calculated and the experimental quantities (C/E ratio), thus providing fundamental information about the dose absorbed by the superconducting inner coils. For example, for the nuclear heating a slight overestimation is observed within the C/E error (±10%) in the coil region. This accuracy in the C/E ratio was never reached in previous experiments. Moreover, regarding the uncertainty margins in the FENDL–2.1/MCNP–5 prediction, it can be concluded that: • the fast neutron flux is calculated within an uncertainty margin of about ±15% in the ITER shielding blanket and the magnet region. • the thermal neutron flux is calculated within an uncertainty margin of about ±15% in the ITER shielding blanket, vacuum vessel, up to the toroidal field coils.
technology programme (cont’d.) progress report 2010 069 • the nuclear heating is calculated within an uncertainty margin of about ±10% in the spatial region of the ITER shielding blanket and vacuum vessel, and within an uncertainty margin of about ±10% in the region of the toroidal field coil with a total uncertainty on the C/E ratio which is always
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PROGRESS REPORT Euratom-ENEA Associ
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progress report 2010 001 2010 Progr
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progress report 2010 003 038 JET Co
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progress report 2010 005 089 Compac
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008 progress report 2010 Anniversar
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010 progress report 2010 chapter 1
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012 progress report 2010 Table 1.I
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Organization Chart The activities o
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Abbreviation and Acronyms A ac ACCC
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126 progress report 2010 GEM GRS GS
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