Irradiation tests of prototype self-powered gamma and neutron detectors

In the framework of the SCK•CEN-CEA Joint Instrumentation Laboratory, we are developing and optimizing a self-powered detector for selective in-core monitoring of the gamma field. Several prototypes with bismuth emitters were developed and tested in a pure gamma field (PAGURE at CEA) and in mixed neutron and gamma fields (OSIRIS at CEA and BR2 at SCK•CEN). MCNP modelling was performed to calculate the gamma and neutron sensitivities. Apart from a few failing prototypes, all detectors showed equilibrium signals proportional to the gamma field with a good long-term stability. A tubular geometry design was finally selected as the most appropriate, coupling a larger sensitivity with better response characteristics. In the same experiment six prototype SPNDs with continuous sheaths were extensively tested: with Co, V and Rh emitters, and with varying geometries. The prompt and delayed response contributions and the signal contributions due to the impact of gamma rays were experimentally determined. The evolution of the signals was continuously followed during the full irradiation period. The signal-to-noise level was observed to be well below 1%. The absolute neutron and gamma responses for all SPNDs are consistent.