Qualification of miniature fission chambers at high temperature in OSU Research Reactor

¹ Instrumentation Sensors and Dosimetry Laboratory, CEA Cadarache, St-Paul-lez-Durance, France
² Idaho National Laboratory, Idaho Falls, ID, USA

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Published online: 6 November 2025

Abstract

With the renewed interest in Sodium Fast Reactors and Advanced Small modular reactors such as Molted Salt ones, there is a need for high temperature (600 °C) neutron instrumentation. In this context, two types of miniatures fission chambers were identified for testing, a CFUE43 dedicated to high temperature conditions and a CF3, the reference fission chamber for in core measurement at CEA. An irradiation was performed at the Ohio State University Research Reactor, in a high temperature irradiation rig that might reach temperatures up to 1200 °C. The rig was installed against the reactor casing, allowing the experimental load to see a maximum neutron flux of about 10¹² n/cm²/s at full power.

During three days, the fission chambers were irradiated at different temperature steps, from 20 °C up to 820 °C. Electronic pulse shape, leakage current and counting mode were monitored in parallel thanks to the libera MONACO 3 measurement system. CFUE 43 cannot be operated in counting or Campbell mode because of the low electromagnetic immunity of its mineral cable. CF3 fission chamber can be operated in counting mode above 600 °C even if its leakage current is high, of the order of 10 µA. Failure of CF3 with temperature was monitored. It can be explained with simple models.