Critical Heat Flux Tests
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Critical Heat Flux (CHF) tests are performed in a full scale, horizontal CANDU fuel channel using directly heated fuel simulations with segmented (end plate) geometry and non-uniform axial and radial power distributions. The fuel simulations are typically equipped with moveable internal thermocouples which can be remotely positioned to monitor dryout over most of the surfaces of the downstream bundle elements. Fuel simulations representing 28-element, 37-element and 43-element CANDU fuel have been successfully tested in flow channels simulating both uncrept and crept pressure tubes.
Boiling Transition (BT) tests are performed in a full-scale vertical BWR fuel channel (up to 10x10 bundle arrays) using directly heated fuel simulators equipped with internal thermocouples (up to 10 per rod) at precise locations to determine critical power. The fuel simulators have non-uniform axial power distributions (cosine, inlet peaked, outlet peaked) and can be powered individually to provide multiple radial peaking patterns. The fuel simulations can be arranged to minimize magnetic forces during testing and reactor grade spacers can be employed.
The power supply has up to 16 megawatts of 12 pulse rectified DC power available with 13 individually controlled power zones which operate up to 330 volts to neutral. The power supplies can be operated together for directly heated fuel simulations or individually with independent control of each for indirectly heated fuel simulators. The power supplies have accurate power metering and are computer controlled to provide preset distributions and programmed power ramps. For the BWR tests with indirectly heated fuel simulators, multiple zones can be controlled on-line to provide unlimited radial peaking patterns and the power supplies can be connected with approximately half of the current flowing in the reverse direction to minimize magnetic forces.
A modern data acquisition system monitors and records the test conditions and provides dryout detection for all of the fuel simulator thermocouples at scanning rates of typically 10 Hz per channel.
