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Prediction of Flow Instabilities in Natural Circulation Mass Flow Rate vs. Power Curve

This study examines the prediction of flow instabilities in the negative slope of the natural circulation mass flow rate versus power curve. The stability code and geometric parameters of the system are analyzed to determine the flow direction and heating conditions. The calculations involve energy and momentum balances, as well as the determination of dimensionless parameters. The study also discusses future work, such as stability predictions for different loop configurations and the neutronics coupling of the heat source.

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Prediction of Flow Instabilities in Natural Circulation Mass Flow Rate vs. Power Curve

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  1. Previous Work • Prediction of flow instabilities in the negative slope of natural circulation mass flow rate versus power curve( Chatoorgoon, 2001)

  2. STABILITY CODE (t = 0) GEOMETRY INITIAL/INLET (t = t+t) • Inputs Geometric Parameters for all components: • Length, Dia, Interfaces • Heating Condition (+1, 0, -1 for heat addition,adiabatic and heat removal) • Direction of flow (+1, 0, -1 for upflow, horizontal flow and downflow) Until (Ptot/ u<) • Sets • Inlet Conditions (i.e. at t=0, sets the enthalpy and pressure at the first node) • Initial Conditions (i.e. at all nodes) • Guess density and inlet velocity UPDATE Update the old properties with the current ones ForI=1, No. of com. J = 2, interface (I) • Performs Energy Balance to Calculate the Enthalpy at New Node Using • Guess density values • Velocity and Pressure at new node as calculated using continuity and momentum equation • Old time step known parameters (i.e. density and velocity, Pressure and enthalpy) • Calculates the Volumetric Heat Generation or Removal for • Heater or Cooler (given constant heat flux or wall temperature ). Heat transfer correlations used: - Dittus-Bolter - Jackson • Performs Momentum Balance to Calculate the Pressure Using • Guess density values • Velocity at new node as calculated using continuity equation • Old time step known parameters (i.e. density and velocity, Pressure) UNTIL (<)  = (new-old) DIMLESS CONTINUTIY THERMPROP • Calculates the Dimensionless Parameters • Reynolds number • Prandtl number • Friction factor • Solves Continuity Equation to Calculate Velocity Using • Guess values of density for all the nodes at new time step • Old time step known parameters (i.e. density and velocity) • State Equation • Calculates improved density as a function of new pressure and enthalpy values. MOMENTUM BOUNDARY ENTHALPY • Assigns the node properties of the first node of new component Update velocity guess based on the pressure drop  =10 If(Ilast comp.) NEWNODEPROP P=(Plast node –Pfirst node) END

  3. Steady State predictions for UW loop

  4. Future Work • Stability predictions for the UW and ANL loop. • Neutronics coupling of the heat source ( using point kinetics model) • Study of instabilities associated with the change in moderation due to neutronics feedback.

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