Measurement of the thermal and fast neutron flux in a research reactor with a Li and Th loaded optical fibre detector

The spatial dependence of thermal and fast neutron flux was measured axially in the core of a 1 MW research reactor. The measurements were made by a thin optical fibre detector with a neutron sensitive ZnS(Ag) scintillation tip. For thermal neutrons Li-6 was used, whereas for fast neutrons Th-232 was used as neutron converter. The spatial dependence was measured by moving the fibre axially with a uniform speed. The measurement takes a few minutes, compared to up to 10 h with the conventional wire activation method. Comparison with traditional measurements shows a good agreement. (C) 1999 Elsevier Science B.V. All rights reserved.