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Hot-Channel Stability of Supercritical Water-Cooled Reactors - II: Effect of Water Rod Heating and Comparison with BWR Stability

Jiyun Zhao, Pradip Saha, Mujid S. Kazimi

Nuclear Technology / Volume 158 / Number 2 / May 2007 / Pages 174-190

Technical Paper / Nuclear Reactor Thermal Hydraulics

The single hot-channel thermal-hydraulic stability model is expanded to investigate the effects of heat transport from fuel rods and to water rods on supercritical water-cooled reactor (SCWR) stability. Furthermore, the stability margin of the SCWR is compared with that of a typical boiling water reactor (BWR) by conducting a sensitivity study on operating conditions.

The fuel thermal-dynamic effect is studied by coupling a lumped-parameter fuel model with the three-region coolant thermal-hydraulics model. It is found that the fuel heat capacity would dampen the oscillations in the coolant channel and therefore increase the stability of the system. Also, heating of the water rods, which could be allowed in the core, would improve single-channel stability.

The stability sensitivity to power and flow rate conditions is analyzed for the U.S. reference SCWR design and compared with a typical BWR. The SCWR is found to be more sensitive to power and flow rate changes than the typical BWR. The water rod heating cannot significantly improve this sensitivity feature of the SCWR stability. The traditional stability measure of oscillation amplitude decay ratio does not capture the extent to which a stability margin exists in a particular design of the SCWR. The robustness of stability should be ascertained by examining accommodation of the potential variation and/or uncertainty about the nominal conditions.

 
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