3.13. Subroutine Descriptions and Flowcharts

The subroutines used in the core-channel thermal hydraulics calculations are described below, grouped by the phase of the calculation where they are used.

Steady-state Thermal Hydraulics:

SSTHRM–	Driver for the steady-state calculations:
SSCOOL–	Calculates steady-state coolant, structure, reflector, and gas plenum temperature for each axial node. Also calculates coolant pressure and saturation temperature at each axial node.
SSCLM1–	Calculates steady-state coolant pressures and saturation temperatures for the multiple pin option.
SSHTR–	Calculates steady-state fuel and cladding temperatures in the core and blankets.
SSNULL–	Driver for the steady-state null transient.

Pre-Voiding Transient Temperature Calculations:

TSCL0–	Driver of the pre-voiding thermal hydraulics.
TSHTRN–	Driver for the pre-voiding transient temperature calculations. Calls TSHTN1, TSHTN2, TSHTN3, TSHTN4, TSHTM2, and TSHTM3 as appropriate.
TSHTN1–	Calculates reflector, coolant, and structure temperatures in a reflector zone.
TSHTN2–	Calculates cladding, coolant, structure, and plenum gas temperatures in the gas plenum region.
TSHTN3–	Calculates fuel, cladding, coolant, and structure temperatures in the core and axial blankets.
TSHTN4–	Calculates the axial node size and the coolant density and specific heat for each axial node.
TSHTN5–	Called from TSHTN3 to adjust fuel and cladding temperatures to account for the heat of fusion if melting is occurring.
TSHTM2–	Multiple pin version of TSHTN2.
TSHTM3–	Multiple pin version of TSHTN3.

Fuel and Cladding Temperatures During Boiling:

TSBOIL–	Driver for the boiling module.
TSHTRV–	Calculates fuel and cladding temperatures in the core and axial blankets.

Pre-voiding Coolant Flow Rates and Pressures:

TSCNV1–	Extrapolates coolant temperatures, computes coolant flow rate and pressures. Also tests for start of boiling. Sets variables for coupling with PRIMAR-4. Called by TSCLO every coolant step.
TSCNV2–	Called by TSCNV1 to compute flow-rate coefficients xI1(JC), xI2(JC), xI3(JC), and xI5(JC).
TSCNV3–	Called by TSCLO, only at the end of a heat-transfer step, to get heat-transfer coefficients Herc(JC) and Hsic(JC). Calls TSCNV8 to get liquid heat-transfer coefficients hc(JC).
TSCNV7–	Computes \(\rho_{\text{c}}\), \(\mu_{\text{c}}\) for liquid sodium.
TSCNV8–	Computes liquid heat-transfer coefficient \(h_{\text{c}} \left( \text{JC} \right)\).
TSCLM1–	Multiple pin version of TSCNV1.

Auxiliary Routines:

CFUEL–	Calculates the specific heat of the fuel as a function of temperature. For coding efficiency, one call to CFUEL gives the specific heats for all radial nodes at an axial node, rather than using as separate call to CFUEL for each radial node of each axial node.
CCLAD–	Calculates the specific heat of the cladding as a function of temperature. One call to CCLAD returns the values for all axial nodes in the core and axial blankets.
KFUEL–	Calculates the thermal conductivity of the fuel as a function of temperature. One call to KFUEL provides the values for all radial nodes at an axial node.
KCLAD–	Calculates cladding thermal conductivity as a function of temperature. One call to KCLAD returns the values for all axial nodes in the core and axial blankets.
INTRP–	General interpolation routine that uses linear interpolation from a table to obtain y as a function of x. A single call to INTRP with an array of x’s will return an array of resulting y’s.
SHAPE–	Multiplies the array of axial power shapes by the current time-dependent power to obtain the current power, in watts, at each axial node in a channel.
HBSMPL–	Calculates the bond gap conductance at each axial node if the simple bond gap conductance model is used. Otherwise, DEFORM-4 calculates the bond gap conductance; and HBSMPL is not called.
INVRT3–	Solves a tri-diagonal matrix equation of arbitrary size.

Figure 3.1.2 is a flowchart for subroutine TSCLO, Figure 3.13.1 is a flowchart for subroutine TSHTRN, and Figure 3.13.2 is a flowchart for subroutine TSHTN3. The logic in the other pre-voiding single pin transient heat-transfer routines is very simple and straightforward. Subroutine TSHTRV is similar to TSHTN3, except that TSHTRV does not calculate coolant and structure temperatures. Also, in TSHTRV the axial nodes are completely de-coupled, so the order in which they are treated is immaterial. For simplicity, the axial node loop in TSHTRV always starts at the bottom and works up.

Figure 3.13.1 Flowchart for Subroutine TSHTRN

Figure 3.13.2 Flowchart for Subroutine TSHTN3