Computational study of a chromium self-powered detector for neutron flux monitoring in the test blanket module of ITER

Self-powered detectors (SPD) are online detectors for the monitoring of neutron and photon fluxes in nuclear reactors. The simplicity of design and operation of an SPD, its compactness, low-cost, reliability, and durability make it a candidate for active detectors in the European test blanket modules (TBM) of ITER. In this paper, we analyze a chromium emitter based SPD, which is proposed as a fast neutron detector for integration in the European TBMs. We describe a computational technique with Monte-Carlo modeling to predict the response of an SPD in the ITER environment and present the results of a demonstrative study. At first, the neutron and photon flux intensities and their energy spectra are calculated in the TBM through simulations in an MCNP model of ITER. Then, a multi-step multi-particle transport approach is adapted for calculation of the SPD sensitivity to the neutron and the photon spectra. Starting with the information on the composition of the SPD layers, main processes involved in the creation of the detector current are evaluated, corresponding to each of which a partial sensitivity is determined. Finally, a time-profile of the signal and its various components are constructed for one plasma pulse of ITER, with typical duration and fusion power. The range of electric currents achievable with SPDs is obtained, its adequacy for flux monitoring in TBMs is discussed, and finally, some design improvements are suggested.