Design of a Liquid Neutron Filter Device at the JSI TRIGA Reactor for Fission Rate Measurements under Simulated High-Temperature Conditions

A novel experimental setup has been developed for improving nuclear data through fission reactor rate measurements using a borated liquid filter. The experimental device involves simulating a temperature shift of the thermal peak in the neutron flux spectrum by varying the boric acid concentration in a specially designed container filled with borated water. Monte Carlo neutron transport simulations were conducted to optimize the filter geometry, evaluate fission chamber response, and determine the most suitable beam port location for implementation at the Jožef Stefan Institute TRIGA Mark II reactor. Among the options, the thermal column beam port was selected for its favorable neutron spectrum and reduced radiation streaming, despite the radial port offering more uniform flux conditions. The device enables measurements using dual fission chamber setup for comparative measurements under similar irradiation conditions, with an additional channel for dosimetry. Results show that the thermal spectrum can be shifted to correspond to an equivalent temperature from 30°C to 100°C. Boron concentration will be precisely controlled via a combination of volumetric analysis and neutron absorption measurements using an external neutron source. Construction of the experimental system is underway, with the first measurements expected in early 2026.