Abstract
Materials and core components for the next generation power reactors technologies require testing that can be performed in existing research reactors. Such experiments employ devices dedicated to reflect the relevant thermal and neutron parameters simulating conditions present in, for example, but not limited to, HTGR reactors. A novel thermostatic irradiation device named ISHTAR (Irradiation System for High-Temperature Reactors) has been designed and constructed in the MARIA research reactor. Its mission is to enable irradiation of samples in controlled, homogeneous temperature field reaching 1000°C and inert gas atmosphere. The high temperature is achieved by a combination of electric and gamma heating, together with carefully designed thermal insulation. Additionally, samples holder made of graphite with high thermal conductivity enables the temperature homogenization in all directions. Device will be placed inside the Beryllium matrix of MARIA core and cooled with forced circulation of water from the reactor pool loop. This paper presents the outcome of experiments conducted with the rig prototype in external hydraulic mock-up of the MARIA reactor irradiation channel. The results have proved that the desired conditions for irradiation of the samples were achieved and their comparison against computational data has shown the adequacy of the design process. Finally, the loss of flow scenario was tested in protected and unprotected conditions (meaning with and without the safety system based on temperature feedback), proving the operational safety of the ISHTAR design. Experimental results will be used in the future to validate the numerical models (two and three dimensional) of the irradiation rig, providing an improved understanding of free convection and radiation phenomena modeling.
Highlights
MARIA is a channels-in-pool type, water-cooled research reactor
MARIA’s core is highly flexible – fuel channels and beryllium blocks might be freely shuffled between the reactor cycles to meet the requirements of the broad scope of irradiation programmes and experimental studies for each operation cycle
Test of the prototype was performed to measure thermal and hydraulic conditions in the external mock-up of the vertical irradiation channel of the MARIA reactor – coolant flow correlated with the known pressure drop
Summary
MARIA is a channels-in-pool type, water-cooled research reactor It has a nominal power of 30 MWth with a core containing 20+ individually cooled fuel elements located in pressure tubes. MARIA’s core is highly flexible – fuel channels and beryllium (moderator) blocks might be freely shuffled between the reactor cycles to meet the requirements of the broad scope of irradiation programmes and experimental studies for each operation cycle. The initial rig design was carefully optimized to minimize heat flux in axial direction and homogenize the temperature field within the holder filled with materials samples. When the hydraulic conditions were known (and derived from them – heat transfer coefficient), thermal measurements became possible: the temperature at various points inside and outside the rig was measured to map the temperatures and compare them with calculation results of the measurements to prove the adequacy of the design
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