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AbstractThe principle needs of ITER with regard to nuclear analysis can be divided into the broad categories of safety and licensing, plant operation, and decommissioning although there is much overlap and interdependence within these categories.This paper reviews the status of the methods applied to date and recommends the future strategy which ITER should adopt to address the continuing requirements and responsibilities. This is done by consideration of the application of radiation transport codes, the creation of an ITER reference neutronics model, the application of a neutronics results database, and the management tools which will be required. Areas in which new codes and techniques need to be developed will be identified.

Bulk Shield experiment representing a mock-up of the ITER inboard blanket and vacuum vessel was completed in 1997 at the 14 MeV Frascati Neutron Generator (FNG) at ENEA Frascati. The objective of the experiment was to verify the calculational methods and nuclear data files used in the design and shielding calculations for fusion reactor. The benchmark experiment was analysed using the discrete ordinates transport code DORT, and the sensitivity and uncertainty analysis code package SUSD3D developed within the EFF project. Neutron cross-sections taken from FENDL-1 and FENDL-2 evaluations were used in the transport calculation. The results were compared with the measured reaction rates and with those calculated by the Monte Carlo code MCNP4A using FENDL-1. Good agreement between MCNP and DORT results was observed. No significant difference between FENDL-1 and FENDL-2 results was found, FENDL-2 performing slightly better. The transport calculations were combined with the sensitivity and uncertainty analysis whose application has proven to be very useful in order to obtain information on the importance of various nuclear data in the neutron transport, to explain the discrepancies between the calculation and the measurement, or at least to discard some possible reasons for the discrepancy. The sensitivity analysis coupled with the covariance matrices can guide future nuclear data research and development.

Without Abstract:

Absolute activation reaction rate (RR) measurements were carried out in a mock-up of the inboard shield of the International Thermonuclear Experimental Reactor (ITER) reactor at the Frascati neutron generator (FNG). Since the mock-up has a thickness of about 1m, a flux gradient of six orders of magnitude is observed for the high-energy part of the neutron spectrum. This required, for the high threshold reaction (e.g.93Nb(n,2n)92Nb) to be measured, the use of ultra-low background germanium detectors. These detectors allowed activity to be measured, even in the deepest positions of the mock-up, with a total error lower than ± 15%. The measured reaction rates (E) are also compared with the results of the transport calculation (C)performed using the MCNP code and the FENDL-1 library. The C/Eratios for some of the measured quantities are reported. These results show a systematic underestimation of the calculated quantities with respect to the measurements. The underestimation is as high as 30% in the deepest positions.