Characteristics of the thermal-neutron field in the experimental channel of a pulsed graphite reactor

The current of the sensitive sections of a five-section Compton emission neutron detector, which are placed at different levels in the vertical direction in the central experimental channel of a pulsed graphite reactor, during a regulatable pulse that heats the reactor fuel up to 1400 K was measured. It was established that the shape of the thermal-neutron distribution over the channel height changes during a run: for room-temperature fuel the distribution maximum lies near the center level in the core. As the fuel temperature increases to 550 K and the control rods are extracted, the maximum shifts downwards by approximately 13 cm and with further heating of the fuel up to ∼1400 K; the maximum returns to the center level when the control rods are extracted. 3 figures, 2 tables, 7 references.