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

3. 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
For I=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)
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)
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
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

4. Steady State predictions for UW loop

5. 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.