200°C Boron-10 Lined Proportional Counters

Boron-10 lined proportional counters for high temperature use were fabricated and tested. A mixture of Ar and CO 2 was found to be a better ionization gas than that of Ar and N 2 in terms of stability at high temperature. Counters filled with an Ar+CO 2 mixture operated satisfactorily up to 200°C and remained stable over 2 months of operation at 200°C. The change of counter characteristics due to temperature variations and a continuous operation at 200°C were small; it was ascertained that the counters can be operated in such a way that the output count rate exhibits no significant change for a given neutron flux under exposure to temperature changes or a continuous operation at 200°C. The counters are intended to be used for the fuel loading channel of the Nuclear Instrumentation System of "Monju" (Japanese Prototype Fast Breeder Reactor).