Summary of elements

A thermal-hydraulic system to be simulated with the KORSAR computer code is divided into elements. Each element is classified to one of element types adopted in KORSAR [1]. For oriented elements, their orientation is defined (channel inlet/outlet, number of heat conduction surface, etc.).

All elements are numbered, consecutively or not, within their element type.  For distributed elements, the number of their components is selected depending on the problem specification. For each distributed element, consecutive numbering of components from 1 onwards, with no missing numbers, is applied depending on the selected orientation.

The elements make up a nodalization scheme. Connections between the elements of the nodalization scheme are coded in the input file with LAYOUT procedure using valid element representation forms [1].  

Table – Element types in the KORSAR computer code

Element name	Element designation in input file	Purpose of element
Channel	CH	Description of flow in a pipe or fuel assembly with a one-dimensional two-fluid approximation; the Channel element consists of control volumes (or simply volumes) and junctions
Singular channel	SCH	Simulation of critical flow from broken pipes or flow channels assuming equal velocities of liquid and vapor phases
Collector	COL	Simulation of a point (with non-zero volume) of connection to any number of channels or singular channels
Boundary volume	BVOL_T	Setting of boundary conditions for scalar fluid parameters at inlet/outlet of channels or singular channels
Accumulator	ACCUM	Simplified simulation of a closed gas tank partially filled with water of temperature below saturation
Steam-liquid pressure vessel	SLVES	Simplified simulation of pressurizer, steam generator internal space (the secondary circuit),  reactor upper plenum
Free surface tank	TANK	Simulation of a water tank open to atmosphere
Blocked junction	BLJUN	Simulation of dead-end volume condition for channel inlet or outlet
Branch junction	JUNB	Simulation of critical flow at junction between two neighboring channel volumes  assuming equal velocities of liquid and vapor phases
Local loss	LR	Assigning values to coefficients of drag for channel junctions,  channel  inlet and outlet or singular channel
Valve	VAL	Calculation of drag (local loss) coefficients  for valves depending on the stem position; the Valve element connects to channel junction,  channel  inlet/outlet or singular channel
Controller	CONT	Calculation of controlled element (valve stem,  control rod, etc) position, accounting for the lost motion and inertia of the controller’s actuator and in accordance with the defined control law
Mass source	SMASS_T	Setting of the enthalpies and flow rates of phases flowing to or out of channel volumes
Heat conduction structure	HCS	Simulation of the walls of coolant flow pipes, vessels and tanks, fuel rods with specified wall heat transfer boundary conditions assuming constant geometry; a heat conduction structure is transversely divided into layers that have different thermal properties; each layer contains  a number of computational nodes in the transverse direction that are lengthwise divided into volumes
Heat conduction structure power	QHCS_T	Assignment of power levels to heat conduction structures
Moderator	MOD	Calculation of coolant density, void fraction, temperature, and boron reactivity feedbacks for  point neutron kinetics model and calculation of core coolant power
Fuel	FUEL	Calculation of temperature reactivity feedback from weighted average temperature of fuel rods and calculation of power in fuel rods for point neutron kinetics model
Heat transfer boundary condition	BHEAT	Assigning heat transfer surfaces the first-type, second-type, or third-type heat transfer conditions
Coolant power	QFL	Assignment of heat input to or removal from the coolant phases in channel, steam-liquid pressure vessel,and free surface tank elements
Centrifugal pump	CPUMP	Calculation of pump head accounting for impeller inertia, cavitation, and two-phase effects. Flow parameters and head are calculated in the Channel volume to which the pump is connected
Shim rods	SR	Calculation of the amount of reactivity inserted by a group of shim rods depending on the position of rods that is assumed the same for all rods in the group. The reactivity worth of shim rods is calculated in the core element
Core	CORE	Calculation of the reactor core neutron and thermal power.   Neutron power is calculated with a point approximation considering delayed neutrons. Reactivity calculation includes reactivity margin, coolant density and temperature reactivity feedbacks, and worth of control rods. Xenon and samarium poison is ignored.
Radiation heat transfer	RAD	Calculation of radiation heat transfer between the surfaces of heat conduction structures; orientation of the surfaces relative to each other is considered in terms of angular coefficients
Crossflow junction	JN	Making a hydraulic connection of a volume of a channel to a volume of another channel, or to collector, boundary volume, accumulator, steam-liquid pressure vessel, and free surface tank. The hydraulic connection is calculated with a homogeneous approach assuming equal velocities of the liquid and gas phases. The element can be used to model critical break flow.
Turbulent mixing	TM	Simulation of turbulent transfer of energy, momentum, and dissolved boron and noncondensables in a single-phase flow between channel volumes

Reference:

1. KORSARV/3 – User Manual. – NITI, 2019.