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The Start-Up Monitoring Module (STUMM) is currently under development as a dedicated calibration and diagnostic system intended for the commissioning stage of IFMIF-DONES. The module will be positioned in proximity to the neutron source, within the irradiation zone used for material testing. Its main purpose is to enable accurate characterization of neutron source parameters and prevailing irradiation conditions.
The STUMM system is designed to incorporate around 240 detectors organized within specialized rigs. Its diagnostic configuration comprises eight Rabbit Systems (RS) for measuring thermal, epithermal, and fast neutron fluxes. Additionally, it includes 66 pairs of Micro-Fission Chambers equipped with U-238 and ionization chambers (amounting to 132 detectors) dedicated to fast neutron flux monitoring. For thermal and epithermal neutron measurements, 36 Micro-Fission Chambers with U-235 or alternatively Self-Powered Neutron Detectors (SPND) are planned. 28 gamma thermometers further complement the system for evaluating nuclear heating, and 44 thermocouples for temperature measurements.
Due to the extreme operating environment—high neutron fluxes and mixed radiation fields—the detectors must ensure strong radiation resistance while avoiding signal saturation. Although largely based on commercial technologies, several components require adaptation to meet IFMIF-DONES conditions.
This work presents studies of the STUMM system response under representative irradiation scenarios. Both active detectors (MFCs, ionization chambers, gamma thermometers) and the Rabbit System, treated as a semi-passive technique, are analyzed. The selection of activation materials and optimization of detector configurations are discussed. The results support validation of the diagnostic concept and reliable neutron source characterization during commissioning.
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