Experiments on mixing of sodium jets of a different temperature in space above fuel pin heads in fast reactor subassembly of BN-350 and BN-600 types

This paper deals with temperature control of the over-core coolant flow and fluctuation of sodium temperature under steady-state conditions. Local superheating causes deformation in subassembly, blockage of subassembly cross section and in other cases contributes to temperature non-uniformity. Test facility consists of seven model subassemblies with 19 wire wrapped fuel pin simulators within each pin. Only internal subassembly is supplied with electric heat. Subassembly heads are similar in design to that. Measuring unit involving 30 chromel-alumel thermocouples inside of 0.8 mm, stainless steel capillaries are used to measure the temperature field. Unit can move in height from the middle of head (h=0) to 200 mm. Some thermocouples are bent in lateral windows of subassembly head, at the model outlet, at the 'cold' subassembly inlet and in other places. Mean temperatures are measured by the data scanning system