A Thermohydraulic Reactivity Feedback Option for the SORGHUM Code

Abstract

Because coolant-related reactivity feedback may be a significant secondary effect in some reactors and types of analysis, the inclusion of thermohydraulic effects in a general-purpose 3-0 reactor physics code has been considered desirable for some time.

The reactor physics code SORGHUM, used primarily for evaluating control of xenon-dependent spatial flux perturbations, has thus been modified to include a capability for simplified, full-core thermohydraulic reactivity calculations.

Several assumptions were required to keep the increased computational costs within reasonable bounds:

• steady-state flow conditions;
• no two-phase slip;
• thermodynamic properties independent of pressure and temperature;
• flow readjustment with changing channel power determined from an input flow versus power relationship.

The code allows both unidirectional and bi-directional flows and takes into account axial symmetry when input. With the thermohydraulics recalculated at intervals of 10 or more flux iterations, SORGHUM running times appear to be increased about 25% with about 10% increase in memory requirements.